HYGIENE AS SCIENCE. MICROCLIMATE. PLACE AND VALUE OF HYGIENE IN THE SYSTEM OF MEDICAL SCIENCES AND
PRACTICAL ACTIVITY OF DOCTORS. METHODS OF HYGIENICAL
RESEARCHES. ORGANIZATION OF EDUCATIONAL-RESEARCH WORK
OF STUDENTS. STRUCTURE OF SES, SANITARY LEGISLATION.
A METHOD OF DETERMINATION AND HYGIENICAL ESTIMATION OF TEMPERATURE,
HUMIDITY, RATE OF MOVEMENT OF AIR, THEIR INFLUENCE ON A HEAT EXCHANGE. A
HYGIENICAL ESTIMATION OF THE COMPLEX INFLUENCING OF PARAMETERS OF MICROCLIMATE ON
THE HEAT EXCHANGE OF MAN (KATATHERMOMETER, EQUIVALENTLY EFFECTIVE, RESULTING
TEMPERATURES).
1. HYGIENE AS SCIENSE
Health -
is defined as a state of
complete physical, mental and social
well-being and not merely absence
of disease or infirmity.
Health is the functional
and/or metabolic efficiency of an organism, at any moment in time, at both the
cellular and global levels. All individual organisms, from the simplest to the
most complex, vary between optimum health and zero health (dead).
Perfect health is an abstraction, which may not
be attainable but is essential for an individual or a family or a group
or a community's strivings. Optimum Health is the highest level of health
attainable by an individual in his/her ecological settings. Positive health
means striving for preservation and improvement of health. Negative health
means scientific efforts for prevention and cure of diseases. To promote and
maintain a state of positive health an individual needs the following
prerequisites:
·Supply of fresh air and sunlight
· Safe and potable water supply
· Balanced diet
· Healthful shelter
·Adequate clothing hygienic
environmental sanitation
·Protection from communicable and
other avoidable afflictions
·Complete sense of protection and
security both socially and economically
·A congenial social and cultural
atmosphere.
· In addition
an individual should have a regulated way of life with proper rest and
relaxation and good and simple habits.
All these factors help to maintain a normal
balance of body and mind, which is must for positive health. The study of all
these factors constitutes a branch of medicine designated as preventive and
social medicine. Any imbalance or deviation in the above factors is likely to
cause a state of illness, when curative aspect of medicine comes into picture.
Hygiene
- is a basic preventive science in
medicine. It generalizes all dates of theoretical and clinical disciplines in
the field of prophylaxis, integrates knowledge’s about complex influence of an
environment for health of the man, work out principles and systems of
preventive measures.
The word Hygiene is derived from the Greek word (Hygeia) Hygieia —
the goddess of
health.
In
Greek
mythology, Hygieia (Roman
equivalent: Salus) was a daughter of Asclepius.
She was the goddess of health, cleanliness and sanitation (and later: the
moon), and played an important part in her father's cult (see also: asklepieion). While her father was more directly
associated with healing, she was associated with the prevention of sickness and
the continuation of good health.
Hygiene
is defined as the science and art of preserving and improving health. Hygiene
deals both with an individual and a community as a whole. Personal Hygiene is
the term used for improvement of hygiene of an individual or a person. Social
Hygiene is usually the term used for dealing with problems of sex especially
for control of venereal diseases. Similarly other terms like mess hygiene, milk
hygiene, hygiene of feeding, hygiene of clothes, hygiene of infant feeding etc., are self-explanatory
Hygiene
and Good Habits are commonly
understood as preventing infection through cleanliness.
In broader call, scientific terms hygiene is the maintenance of health and
healthy living. Hygiene ranges from personal hygiene, through domestic up to occupational hygiene and public health;
and involves healthy diet, cleanliness, and mental health.
PREVENTIVE MEDICINE
“Prevention is better than cure” is an old
saying. Preventive medicine deals with the measures to protect the individuals
from the diseases, and to keep them in a state of positive health. For this we
have to ensure all the above-mentioned prerequisites required for the
maintenance of positive health. The environments must be hygienic, with supply
of fresh air, safe potable water and balanced diet. This aspect of preventive
medicine started gaining more importance from 18th century onwards
with the discovery of various vaccines and sera for the protection against
various diseases like small pox, cholera, plague, whooping cough, tetanus,
tuberculosis, poliomyelitis etc
Ecology is
constituted by the total environment of man. The environment of modern man is
partly natural and partly man-made. It consists of physical, mental and social
factors, which are dynamic and interacting both within themselves and with the
life process in the internal environment of men. The important physical
factors are air, water, food, buildings, their contents and multiple devices
produced by man to adjust the physical environment around him. The important
biological factors are pathogens, other microorganisms as well as living
beings, vectors, plants, etc., which have implications on health and disease.
The important social factors are customs, beliefs, laws, peculiarities and
modes of living of human beings with their implications on health and disease.
What
is pollution.htm
Environmental Sanitation
The word Sanitation
- is derived from the Latin word Sanitas which means a state of health.
Environmental Sanitation means the control of all those factors in man's
surroundings, which cause or may cause adverse effects on his health. The
sanitarian directs his efforts towards hygiene of water and food supply,
hygienic disposal of human wastes, hygiene of housing and control of vectors
and rodents etc.
The following definition now is accepted: «Hygiene
is a science, which investigates regularities of influence of the
environment on the organism of
the man and
public health with the purpose
of the substantiation
of the hygienic
norms, sanitarian rules and measures,
realization of which will ensure
optimum conditions for vital activity,
improving of health and preventing
of diseases ».
The principal topics of
the subject are:
· Hygiene of atmospheric
air
· Water supply hygiene
· Hygiene of nutrition
· Occupational hygiene
· Radiological hygiene
· Hygiene of children and teenagers
· Hospital hygiene
· Hygiene of extraordinary
situation
· Tropical hygiene
Hygiene is a science of
preserving and promoting the health of both the individual and the community.
It has many aspects:
Ø
personal hygiene (proper living habits, cleanliness of body and
clothing, healthful diet, a balanced regimen of rest and exercise);
Ø
domestic hygiene (sanitary
preparation of food, cleanliness, and ventilation of the home);
Ø
public hygiene (supervision of water and food supply, containment
of communicable disease, disposal of garbage and sewage, control of air and
water pollution);
Ø
industrial hygiene (measures that
minimize occupational disease and accident);
Ø mental hygiene (recognition of mental and emotional factors in healthful living) and so
on.
2. THE AIM AND TASKS OF
HYGIENE
Basic aim of hygiene
Preservation
and improving the health of the man is a basic aim of hygiene.
In
this occasion the English scientist E.Parce has told,
that the hygiene has a great and generous purpose: «...To make development of
the man most perfect, life most intense, wasting least fast, and death most
remote».
The tasks of a hygienic science:
1. Study of the natural and
anthropogenesis factors of the environment and social conditions which influence
on health of the man.
2. Study regularities of
influence the factors and conditions of an environment on an organism of the
man or population.
3. Scientific substantiation
and working out of the hygienic norms, rules and measures, which help use
maximum positively influencing on an organism of the man the factors of an
environment and elimination or restriction up to safe levels unfavourable
operating ones.
4. Introduction in practice of
public health services and national economy developed hygienic recommendations,
rules and norms check of their effectiveness and perfecting.
5. Prediction of the sanitarian situation
for the nearest and remote perspective in view of plans of development of the
national economy. Definition of appropriate hygienic
problems, which implying from prognostic situation and scientific working out
these problems.
3. BASIC METHODS OF HYGIENIC RESEARCHES
During the development the hygiene used many
methods of study an environment and its influence on the health of the population.
Methods
of hygiene
1. Methods of
environment studying.
2. Methods of
studying of environmental influence on human organism and health
1. Methods of environment studying
Methods of sanitary examination with further sanitary
description
Speaking
about methods of the research the exterior factors, first of all it is
necessary point at method sanitarian description, which for a long time being
almost only. It did not lost the value and now.
Specific
hygienic method is method of sanitary examination and describing which
is used for studying the environment.
Sanitary examination and describing is carried
out according to special programs (schemes), which contain questions. Answers
to these questions characterize the object, which is being examined
hygienically. As a rule it is usually supplemented by laboratory analyses
(chemical, physical, microbiological and other), which allows characterizing
environment from the qualitative side.
Instrumental and laboratory methods With the help of physical methods we can study microclimatic
conditions, electrical conditions of air, all aspects of radiant energy,
mechanical and electromagnetic oscillation, carry out the spectroscopic
analysis and much other.
By chemical methods we can
determine peculiarities of a natural structure of all elements of an
environment, the quantitative and qualitative indexes of it contamination,
enable to make conclusion about sanitarian troubles of the investigated object.
The biological methods, first of all
bacteriological researches, for example, definition of a credit of the Esherichia colli, have much value
for conclusion about epidemiological safety of the potable water.
Methods of Studying of Environmental Influence on Human
Organism and Health
1. Methods of experimental investigation
A study response of an organism
on various exterior actions plays the major
role for development of modern hygiene. The experiment on the warm-blooded
animals now is leading for
all its areas.
So, toxico-hygienic researches
are compulsory for evaluation of toxicity of
poisonous substances, which uses in
industry and agriculture. Not less widely there
are uses in municipal hygiene
for analysis of industrial wastewater,
in hygiene of foods — for
the definition of harmful impurities,
and in other
areas of hygiene. The skilful
realisation of these researches allows receiving dates for development
of the appropriate
hygienic norms, methods of early
diagnostics of professional diseases and for evaluation
of effectiveness preventive measures.
2. Methods of natural observation
Much value is represented by clinical observations of the people,
which are exposed of the defined exterior factors. In particular, defined value
has working out materials of periodic medical examinations of working harmful
trades. Comparing these observations with dates of the research of an
industrial medium, it is possible form a correct estimate of the recommended
hygienic norms.
Also, in hygiene is widely
applied the method of a sanitary - statistical analysis, with the help
of which may form a true notion about positive and negative influence on health
of the population: it physical development, morbidity, mortality, average life
expectancy etc.
There
are widely used different kinds of hygienic experiments:
1 Experiment
with simulation of natural conditions. They are used for examining and predicting processes which are going on
in the surrounding world (for example, for examining, the influence of chemical
admixtures on the processes of self-clearing of water in reservoirs).
2. Laboratory
experiment on animals. It helps to
study influence of factors of environment on the organism which meets the goal
to substantiate hygienic norms. In the process of this experiment the following
methods are used: physiological, biochemical, immunological,
histological, microscopic, radiobiological, genetic
and others.
3. Chamber
experiment on people. It is used
to study the influence of some factors on the human organism and determine the
norms. This method is used to study such factors as microclimate, illumination,
noise, neural-psychic strain, etc.
”Natural experiment” which helps to study influence of factors of
environment on the human health in real conditions of the life For example,
studying health of people (especially children) who live at different distance
from enterprises throwing out into the atmosphere toxic gaseous substances.
Natural experiment allows to check-up hygienic norms
which were determined in the experiment on animals.
The
health of individuals is studied by way of medical examinations with the usage
of anthropometric, clinical, physiological, biochemical, immunobiological, roentgenological
and other methods of examinations. Their participation in labour and other
types of activity must be taking into account.
The
health of a certain group of people or of all population of the populated area
(region, republic, etc.) is studied with the help of sanitary - statistic
method. There are different criteria which characterize physical development,
demographical peculiarities (birth-rate, death-rate, average life span and
others), morbidity and pathology of studied group.
Epidemiological
method is close to sanitary - statistic method. It is used for studying of
spreading of this or that disease (hypertension, coronary disease, diabetes,
ulcerous disease, etc.). They are studied during certain period (during. a
year, month), on the certain territory (different regions of the city,
republic), among different groups of population (which differ one from another
by age, gender, occupation, conditions of water and food supply, conditions of
life and others). Analysis of these data is used for determining of causes and
conditions which favor the development of disease,
for liquidation of disease as regional pathology, for planning prophylactic
measures.
Methods of mathematical
statistics and modelling are widely used.
Hygienic standardization:
Environmental
standards are definite ranges of environmental factors, which are optimal, or
the least dangerous for human life and health. In Ukraine basic objects of hygienic
standardization are:
§
MAC – maximum admissible
concentration (for chemical admixtures, dust and other hazards)
§
MAL – maximum admissible
level (for physical factors)
§
LD – dose limit (for
ionizing radiation)
§
Optimum and admissible parameters of microclimate, lighting, solar radiation, atmospheric pressure and
other natural environmental factors.
§
Optimum and admissible daily requirements in food and water.
Let's study the methodical
scheme of hygienic norms of substantiation using, the example of MAC for some
toxic substance. The first stage is stud physical and chemical
properties of the substance, elaboration of methods of quantitative
determination of this substance in different subjects, determination of its
regimen of action on the human (duration, interruption, changes of intensity),
ways of getting into the organism, study migration in different elements of the
surrounding, mathematical prediction of duration of existence in different
surroundings.
The second
stage is study direct influence on the organism. It is
started from 'sharp' experiments the main goal of which is getting initial toxicometric data about the substance (determination of LD50,
or LC50 threshold of strong action (LIMac)
and other. With the knowledge of physical and chemical properties of t he substance, its initial toxicological characteristics
and approximate level of MAC can be calculated. The third stage -
is conduction of 'subsharp' experiment during l-2
months for determination of cumulating coefficient and the most vulnerable
physiologic systems and organs specification of mechanisms of action and
metabolism.
The fourth
(basic) stage is carrying out chronic experiment which lasts
4-6 months in the case of modeling of working
conditions, 8-12 - communal conditions, 24-36 - in study processes of aging or
induction of tumours.
During the experiment integral parameters are
studied. They reflect condition of animals, degree of strain of regulative
systems, functions and structure of organs which take part in processes of
metabolism (activity of enzymes), influence of functional loadings.
Numbers of MACs of toxic chemical substances in
the Ukraine are various: for the air of working: zone - more than 800, water-
700, atmosphere air- 200, food-stuffs - more than 200, soil - more than 30.
Basic objects, which
are under the hygienic norms setting, can be divided into two groups.
The first group contains factors of anthropogenous origin,
which are unfavorable for human being, and are not
necessary for the normal life activity (dust, noise, vibration, ionizing
radiation, etc.). MAC, MAL and LD are those parameters, which are set for this
group of factors.
The second group contains factors of natural surrounding which are
necessary (in certain amount) for normal life activity (food-stuffs, solar
radiation, microclimatic factors and others). For this group the following
parameters must be set: optimum, minimum and maximum admissible parameters.
In those cases when factors influence on the human
not only directly (physiologically) but also indirectly (through the environment)
all types of possible influence must be examined at hygienic norms
setting. For example setting of hygienic norms for toxic substance in the water
of natural reservoirs determination of maximum concentrations must be based on
worsening of organoleptic properties of the water (organoleptic sign), toxic
influence (sanitary - toxicological sign) and disturbance of processes of
self-clearing of reservoirs (general sanitary sign). In this case MAC are set
according that harmful parameter which is characterized by the lowest level of
concentration Such parameter is called limiting.
THE
METHOD OF DETERMINATION AND HYGIENIC ESTIMATION OF AIR TEMPERATURE AND
ATMOSPHERIC PRESSURE
Air
temperature is a measure of how hot or cold the air is. It is the most commonly
measured weather parameter. More specifically, temperature describes the
kinetic energy, or energy of motion, of the gases that make up air. As gas
molecules move more quickly, air temperature increases.
Why
is Air Temperature Important?
Air temperature affects the growth and reproduction of plants and
animals, with warmer temperatures promoting biological growth. Air temperature
also affects nearly all other weather parameters. For instance, air temperature
affects:
- the rate
of evaporation
- relative humidity
- wind speed
and direction
- precipitation
patterns and types, such as whether it will rain, snow, or sleet.
How is
Air Temperature measured?
Temperature
is usually expressed in degrees Fahrenheit or Celsius. 0 degrees Celcius is equal to 32 degrees Fahrenheit. Room temperature
is typically considered 25 degrees Celcius, which is
equal to 77 degrees Fahrenheit.
A
more scientific way to describe temperature is in the standard international
unit Kelvin. 0 degrees Kelvin is called absolute zero. It is the coldest
temperature possible, and is the point at which all molecular motion stops. It
is approximately equal to -273 degrees Celcius and
-460 degrees Fahrenheit.
TEMPERATURE
SCALES
Temperature is a physical quantity that is a measure of
hotness and coldness on a numerical scale. It
is a measure of the local thermal energy of matter or radiation; it is measured by a thermometer, which may becalibrated
in any of various temperature scales,
Celsius, Fahrenheit, Kelvin, etc., etc.
Much
of the world uses the Celsius scale
(°C) for most temperature measurements. It has the same incremental scaling as
the Kelvin scale
used by scientists, but fixes its null point, at0°C = 273.15K,
approximately the freezing point of water (at one atmosphere of pressure).[note 1] The
United States uses the Fahrenheit scale
for common purposes, a scale on which water freezes at 32 °F and boils at
212 °F (at one atmosphere of pressure).
For
practical purposes of scientific temperature measurement, the International System
of Units (SI) defines a scale and unit for the
thermodynamic temperature by using the easily reproducible temperature of the triple point of
water as a second reference point. The reason for this choice is that, unlike
the freezing and boiling point temperatures, the temperature at the triple
point is independent of pressure (since the triple point is a fixed point on a
two-dimensional plot of pressure vs. temperature). For historical reasons, the
triple point temperature of water is fixed at 273.16 units of the measurement
increment, which has been named the kelvin in honor of the Scottish physicist
who first defined the scale. The unit symbol of the kelvin is K.
Absolute
zero is defined as a temperature of precisely 0 kelvins,
which is equal to −273.15 °C or −459.67 °F.
One
of the earliest temperature scales was devised by the German physicist Gabriel Daniel Fahrenheit. According
to this scale, at standard atmospheric pressure, the freezing point (and
melting point of ice) is 32° F, and the boiling point is 212° F. The centigrade, or Celsius scale,
invented by the Swedish astronomer Anders Celsius, and used throughout most of
the world, assigns a value of 0° C to the freezing point and 100° C to the
boiling point.
http://www.ux1.eiu.edu/~cfadd/1360/19Temp/Absolute.html
In
scientific work, the absolute or Kelvin
scale, invented by the British mathematician and physicist William
Thomson, 1st Baron Kelvin, is used. In this scale, absolute zero is at -273.16°
C, which is zero K, and the degree intervals are identical to those measured on
the Celsius scale. The corresponding “absolute
Fahrenheit” or Rankine scale, devised by the
British engineer and physicist William J. M. Rankine,
places absolute zero at -459.69° F, which is 0° R, and the freezing point at
491.69° R. A more consistent scientific temperature scale, based on the Kelvin
scale, was adopted in 1933.
An
absolute temperature scale invented in the 1800's by William Thompson, Lord
Kelvin. It places the zero point of the scale at absolute zero,
the temperature which scientists believe is the lowest possible. All molecular
motion would stop there. A Kelvin degree is the same size as a Celsius degree,
so the two scales simply have a constant offset.
Temperature.
An
instrument called thermometer ascertains this.
Generally mercury or
alcohol is used in the thermometers. Mercury is used in thermometers meant for recording high temperatures on account of its uniformity in expansion at different
temperatures, easy visibility, high boiling point and low vapor pressure. Alcohol is used in thermometers for recording low temperatures, because it does not freeze even at low temperatures. Several
kinds of thermometers are used
These are:
(1)Standard
or Dry Bulb Thermometer. It is an ordinary
thermometer.
(2)Maximum
Thermometer. It is used for registering the highest temperature attained in the day or any other period. The thermometer
is laid in a horizontal
position. In the stem of the thermometer, part
of the mercury column is separated by air. When the temperature rises the mercury expands and pushes this broken column forward.
But this column does
not recede when the temperature falls and the main
mercury column contracts. The reading taken indicates the maximum temperature attained during the day.
(3)
The Minimum Thermometer. It is used for recording the lowest
temperature during the night or during the early hours of morning. A small glass index is enclosed in the spirit, which fills the bulb and a part of the stem. When setting the instrument, the index is first brought to the top of the column of the spirit and the instrument is placed in a horizontal position. When the temperature rises, the spirit expands and flows past the index, but when the temperature falls, the spirit contracts and carries the index along with it. The lowest temperature is thus registered. The instrument can be readjusted by tilting.
(4) Six's Maximum and Minimum Thermometer. It is a combination of maximum and minimum thermometers and gives a double reading. It is however, not a very accurate instrument and is therefore no more being used now
in Indian Meteorological
observatories.
Methods
of temperature measure
On
value of temperature regime on the room measure do in difference place on a
vertical.
First measure of temperature is done on 10 cm from the
floor and characterizes air on foot level.
Second measure do on 1,5 meter from the
floor – in respiration zone of man.
Third
place is on 50 cm from ceiling and characterizes convection in
the room. In hospital the second place is situated on level of bad. Measuring
of temperature in horizontal line is done in three points: from external angle
to internal angle on 20 cm. Change of temperature in time is measured by
thermograph. It’s done in three places on 1,5 cm from the floor.
Thermometer
It
is instrument used to measure temperature. The invention of the thermometer is attributed
to Galileo, although the sealed thermometer did not come into existence until
about 1650. The modern alcohol and mercury thermometers were invented by the
German physicist Gabriel Fahrenheit, who also proposed the first widely adopted
temperature scale, named after him.
Types
of thermometers
•Wide
variety of devices are employed as thermometers. The
primary requirement is that one easily measured property, such as the length of
the mercury column, should change markedly and predictably with changes in
temperature.
•Electrical
resistance of conductors and semiconductors increases with an increase in temperature. For thermistor of given
composition, the measurement of specific temperature will induce specific
resistance. This resistance can be measured by galvanometer and becomes measure
of the temperature. With proper circuitry, the current reading can be converted
to a direct digital display of the temperature.
Very
accurate temperature measurements can be made with thermocouples in which small voltage difference (measured in
millivolts) arises when two wires of dissimilar metals are joined to form a
loop, and the two junctions have different temperatures.
•Optical
pyrometer is used to measure
temperatures of solid objects at temperatures above 700° C (about 1300° F)
where most other thermometers would melt. At such high temperatures, solid
objects make so-called glow color phenomenon. The color at which hot objects
glow changes from dull red through yellow to nearly white at about 1300° C
(about 2400° F). The pyrometer contains a light bulb type of filament
controlled by a rheostat (dimmer switch) that is calibrated so that the colors
at which the filament glows corresponding to specific temperatures.
•Another
temperature-measuring device, used mainly in thermostats, relies on the differential thermal expansion between
two strips or disks made of different metals and either joined at the ends or
bonded together.
Special
types of thermometers
Thermometers
may also be designed to register the maximum or minimum temperature attained.
•Maximum
thermometers.A mercury-in-glass clinical thermometer, for example, is maximum-reading
instrument in which trap in the capillary tube between the bulb and the bottom
of the capillary permits the mercury to expand with increasing temperature, but
prevents it from flowing back unless it is forced back by vigorous shaking.
•Minimum
thermometers. Inside capillary tube is alcohol with glass
pin. When temperature increase ethanol moves pin. When temperature decrease
ethanol paces pin for a minimal temperature.
Thermograph.
•Thermograph
consists of vertical pen, bimetallic laminas and clack mechanism. Perceiving
part of instrument is bimetallic laminas, which change it curvature by change
of temperature. By means system of levers which passes changing curvature of
bimetallic laminas by righting pen and we have graphical illustration of
temperatures on paper of clack mechanism.
Table
of Equivalent Temperatures by Celsius and Fahrenheit scales
C
= (F - 32) х 100/180;
F
= (C х 180/100) + 32.
Measuring
Maximum and Minimum temperature
If
possible it is best to record the daily maximum and minimum temperature as well
as that which you record at a specific moment in time when you make your
observations. You can simply use your normal thermometer. With this you need to
record temperatures at about 14:00 where the daily maximum usually occurs, or
very early morning when the temperature is similar to the overnight minimum.
These are good times to take your am/pm measurements.
Studying
the temperature condition of the indoor air
The
temperature is measured in 6 or
more points to fully characterize the temperature conditions of premises.
Thermometers
(mercurial, alcohol, electric or psychrometer dry
thermometers) are placed onto
support racks at three points 0.2 meter high above the floor, at
three points 1.5 meters high (points t2, t4, t6 and t1, t3, t5 respectively)
and at 20 cm from the wall along the diagonal section of the laboratory
according to the diagram:
The
thermometer data are fixed after 10 minutes of the exposition at the point of
measurement.
The
air temperature parameters in premises are calculated using following formulas:
а)
the average temperature in the
premises:
а)
taver.= ,
b) the
vertical variation of the air temperature:
D
c) the
horizontal variation of the air temperature:
D
Diagrams
and calculations are written down into the protocol, the hygienic assessment is made. It is necessary to consider the
following data: the optimal
air temperature must be from +18 to +21оС in residential
and class-room premises, wards for somatic patients, the vertical temperature
variation must be no more than 1.5-2.0оС, horizontal - no more than 2.0-3.0оС. The
daily temperature variations are determined using the thermogram, prepared in
laboratory using the thermograph. The daily temperature variation must be no
more than 6оС.
The
allowable and optimal standards of the temperature, presented in the table 1 are the hygienic assessment
criteria for residential and public premises.
Table
1
The
temperature standards for residential, public and administrative premises
Comment:
* the allowable temperature is no more than 28оС for public and
administrative premises, which are permanently inhabited, for regions with the estimated outdoor air
temperature of 25оС and above – no more than 33оС.
** the allowable temperature is 14оС
for
public and administrative premises where the inhabitants are wearing their
street clothes.
The
standards were established for people that are continuously staying in the
premises for 2 hours or more.
The
temperature standards for the workplace air of industrial areas are set in the
State Standard #12.1.005-88 “General
sanitary and hygienic requirements to the workplace air”, depending on the season (cold, warm) and work category (easy, moderate and hard).
The
optimal temperature standards for the cold season are set from 21 to 24оС during the physically easy work and from 16 to 19оС during the physically hard
work. These temperature ranges correspond to 22-25оС and
18-22оС during the warm season. The allowable maximum
temperature is no more than 30оС
for the warm season, the allowable minimum temperature for the cold
season is 13оС.
Thermoregulation is
the ability of an organism to keep its body
temperature within certain boundaries, even when the
surrounding temperature is very different.
This process is one aspect
of homeostasis:
a dynamic state of stability between
an animal's internal environment and its external environment (the study of
such processes in zoology has been
called ecophysiology or physiological
ecology). If the body is
unable to maintain a normal
temperature and it increases significantly
above normal, a condition known as hyperthermia occurs. For
humans, this occurs when the
body is exposed
to constant temperatures of approximately 55
°C (131 °F), and any prolonged
exposure (longer than a few hours)
at this temperature
and up to
around 75
°C (167 °F) death is almost inevitable. Humans may also
experience lethal hyperthermia when the wet
bulb temperature is sustained above 35 °C (95 °F) for six
hours. The
opposite condition, when body temperature
decreases below normal levels, is known as hypothermia.
The
radiant temperature and the wall temperature determination
The
spherical thermometers are used for the radiant temperature determination in
premises, wall thermometers – for the wall temperature determination (see fig. 6.1 а, b)
The
spherical thermometer consists of the thermometer located inside the hollow
sphere 10-15 cm in diameter
and covered with porous polyurethane foam layer. This material has similar
coefficients of the infrared radiation adsorption as the human skin.
The
radiant temperature is also determined at 0.2 and 1.5 meters above the floor.
The
device has the considerable inertia (up to 15 min.), that is why the thermometer
data must be taken no earlier than after that time.
The
spherical thermometer data at the height of 0.2 and 1.5 m must not vary by more
that 3оС in
comfortable microclimate conditions.
Fig. 6.1. Thermometers for the radiant
temperature determination
a – the section of the spherical
black thermometer
(1
– 15 cm diameter sphere
covered with dull black paint; 2
– thermometer with the
reservoir at the center of the sphere)
b – Wall thermometer with the flat turbinal reservoir
(1
– thermometer; 2 – base cover (foam-rubber); 3 –sticky
tape)
The
values of the radiant temperature below are recommended for different premises (see table 2).
Table
2
Standard
values of radiant temperature for different premises
Special
thermometers with the flat turbinal reservoir are used for the wall temperature
determination. These thermometers are attached to the wall with special putty (wax with colophony addition) or alabaster. The wall temperature is also determined
at 0.2 and 1.5 meters above the floor. In some cases it is necessary to
determine the temperature of coldest parts of the wall.
The
high levels of infrared irradiation in especially hot manufacture areas are
measured using actinometers (solar radiation
instrument) and are expressed in mcal/(сm2×min).
Water
vapor
The
person during all life is exposed to water vapor. Its quantity in air
permanently changes: it decreases or increases. When in air a lot of water
vapor is stored, the conditions for evaporation of moisture are worse. In air
such quantity of water vapor can be stored, that it resilience equals
resilience of liquid that evaporates, - and then the evaporation ceases.
The
evaporation depends on temperature of air, the above last, the implements
evaporation fan-in harder. There fore evaporation as
though goes after temperature of air; temperature of air - is increased the
evaporation is increased also; temperature of air is lowered, the evaporation
is lowered also.
Air
humidity
Humidity is moisture content of the atmosphere. The
atmosphere always contains some moisture in water vapor;
the maximum amount depends on the temperature. The amount of vapor that will saturate the air increases with temperature
rise. At 4.4° C (40° F), 454
kg (1000 lb) of moist air contain maximum 2 kg of
water vapor; at 37.8° C (100° F), the same amount of
moist air contains maximum 18 kg of water vapor. When
the atmosphere is saturated with water, the level of discomfort is high because
the evaporation of perspiration, with its attendant cooling effect, is
impossible.
Humidity is specified in several different ways.
The weight of water vapor contained in a volume of
air is known as the absolute humidity and is expressed in grams of water vapor per
cubic meter.Relative
humidity, given in weather forecasts, is the ratio between the actual content
of the air vapor and the content of the air vapor at the
same temperature saturated with water vapor.
The
maximum damp is measured by that quantity of a water pair in grammas, which one saturates completely 1m3 of air at given
temperature
The
relative humidity is an attitude of absolute humidity to maximum at given
temperature, expresses in percentage, that is:
R=A
/ F х 100,
Where
R - relative humidity;
•A-
absolute humidity;
•F
- maxime humidity.
The
relative humidity interests us because its characterize saturation of air by a pair, its
dryness. For example, if we speak, that relative humidity 60 %, from this
number it is visible, that 40 % of a moisture does not
suffice to saturation of air, that is, it has a capability to receive a
moisture. At relative humidity 80 % we could say, that in this case elasticity
of a pair in atmosphere is higher, at her the liquid evaporates worse. At 90 %
- it is even worse.
Knowing absolute humidity it is possible to
definite dew point, that is that temperature, at which one the absolute
humidity becomes maximum and the air humidity will begin to be condensate and
to precipitate by the way of drops of water. Let's consider such example. What
the temperature this damp will begin to saturate air? It also means to find dew
point.
The
air humidity can be described as deficit of saturation. The deficit of
saturation is a difference between maximum and absolute humidity at same
temperature. Together with it there is also concept a physiological deficit of
saturation. It - difference between maximum damp at the temperature of bodies
of the person 36,5 degree and absolute humidity of
air.
The
most commonly used measure of humidity is relative humidity.
Relative humidity can be simply defined as the amount of water in the air
relative to the saturation amount the air can hold at a given temperature
multiplied by 100. Air with a relative humidity of 50% contains a half of the
water vapor it could hold at a particular temperature.
Figure
-1 illustrates the concept of relative
humidity.
The
following illustration describes how relative humidity changes in a parcel of
air with an increase in air temperature. At 10° Celsius, a parcel of dry air
weighing one kilogram can hold a maximum of 7.76 grams of water vapor
Physiological
relative humidity
Hygiene
uses also concept of physiological relative humidity. It is attitude of
absolute humidity at given temperature of air to maximum at 36,5 degree, expressed in percentage. Physiological relative
humidity characterizes capability of air to accept damp that evaporates at body
temperature. It enables more precisely to evaluate effect of moist air.
Air
humidity can be described as deficit of saturation. The deficit of saturation
is difference between maximum and absolute humidity at same temperature.
There
is also a concept of physiological deficit of saturation. It is difference
between maximum damp at body temperature person 36,5
degree and absolute humidity of air. The physiological deficit of saturation
lets us define how many grams of water the person can spend by evaporation in
given conditions.
Air
humidity is very relevant hygienic
factor because it influences thermo exchange of the person. At low temperatures
in moist air the feeling of cold is stronger than in dry air at the same
temperature.
It
is by outcome that the moist air has large heat conductivity and thermal
capacity. From the same reason in wet clothes it is much more
cold: pores of tissues charged with moisture, and its well carries out
heat.
Human
body permanently loses moisture either by water vapor or by liquid water. It is
established that in quiet condition at room temperature the person loses by
skin approximately 20% of moisture, mild - 15 %, remaining part - urine and
feces. Therefore, in these conditions approximately 35% of water is lost by
evaporation and 65% - in liquid with feces and urine. By activity and heat of
air – in the contrary: 60% of water is lost by evaporation from skin and mild
and much less by urine and feces.
Normal
relative air humidity in dwelling apartments is 30-60%. A great range of normal
air humidity is explained fluctuations by the fact ,
that its influence on the organism depends on a number of conditions. In peace
when the air temperature is 16-200С with a light air motion the
optimum humidity will be 40 - 60%. During physical work when the air
temperature is above 200С or below 150С air humidity must
not be more than 30-40%, and when the temperature above 25 0С
desirable to bring relative humidity down to 20%.
Air
humidity determination methods
Humidity
is determined by psychrometes and hygrometers. Hygrographs
determine humidity fluctuations for a day or a week. Absolute air humidity is
determined by psychrometes (from greek psychros - cold).Psychrometes are of August and Assman
types.
August
psychrometer consists
of two
identical mercury thermometers fixed on a support. By temperature difference on
dry and humid thermometers we can define absolute air humidity with a help of
table or formula.
Assman psychrometer consists of
dry and humid thermometer situating in metal casing that protects from
radiation temperature. There is a ventilator in the upper part of the device.
Ventilator is wound up and during 5 minutes in summer (15 minutes in winter)
registers a temperature difference.
Relative
humidity is measured by hygrometer.
It consists of metal frame in the middle of which a fair defatted woman’s hair
is lightened. When humidity is low the hair becomes shorter, when it is high it
becomes longer.
Instruments
to Measure Humidity
A
whirling psychrometer is a type of hygrometer which can be whirled around like a
football rattle to take readings. You can directly read off the percentage
relative humidity. It is a good idea to wrap it in a damp cloth for a while and
then set the dial to read 100 %. Like paper, human hair stretches when moist
and shrinks when dry. Humidity recorders use this principle, and you can make a
simple hygrometer using this method.
http://www.piercecollege.com/offices/weather/psychrometer.html
The
Psychrometer measures the wet and dry bulb temperature and under natural
evaporation conditions the state of a given mass of air can be described by its
temperature and vapor pressure. If water is allowed to evaporate in an isolated
mass of unsaturated air , it latent heat content increases and its sensible
heat content decreases. The process will stop when the air becomes saturated at
the wet bulb temperature ( Tw). The change in latent heat must equal the change
in sensible heat. http://weather.nmsu.edu/Teaching_Material/soil698/psych.html
A
pair of thermometer placed parallel inside the screen with a bare bulb on the
right indicating the air temperature and is called dry bulb thermometer.
Another thermometer on the left whose blackened globe is covered with a
moistened muslin wick is called wet bulb thermometer. Since they are usually
using in a pair, therefore, we normally call them psychrometer.
The
absolute humidity is calculated using the Regnault
formula:
А
= f – a · (t
- t1) ·
B,
where, А – the
air absolute humidity at the current temperature in Hg mm;
f – maximum pressure of water vapour
at the wet thermometer’s temperature (see the table of saturated water vapours,
table 3);
а – psychrometric coefficient is 0.0011 for enclosed spaces;
t – temperature of the dry thermometer;
t1 – temperature of the wet thermometer;
В – barometric pressure during the
humidity determination, Hg mm.
The
relative humidity is calculated using the following formula:
P
= ,
where, Р –the value of relative humidity to be found, %;
А – absolute humidity, Hg mm;
F – maximum pressure of
water vapour at the dry thermometer temperature, Hg
mm (see the table of
saturated water vapours, table 3).
Table
3
Maximum
pressure of the air water vapour of premises
Psychrometric tables for
the August psychrometer are used for the relative
humidity (RH) determination (if the air velocity is 0.2 m/sec.). The value of RH is found at the
point of the dry and wet thermometers data intersection, table 4.
The
psychrometer operation is based on the fact that the
rate of the water evaporation from the surface of dampened psychrometer’s reservoir is proportional to the air dryness. The drier the air – the lower is
the wet thermometer’s result in comparison to the dry thermometer due to the
latent evaporation.
Determination
of the air humidity using the Assmann aspiration psychrometer
The
significant disadvantage
of August psychrometer is its dependence on
the air velocity. The air
velocity influences the evaporation intensity and the device’s wet thermometer
cooling.
This
disadvantage has been eliminated in Assmann psychrometer due to the usage of the ventilator (see fig. 6.2-b). The ventilator produces the constant air
movement at the 4 m/sec speed near thermometers’ reservoirs. As a result data
does not depend on the air velocity either inside or outside of the premises.
Furthermore, thermometers;’
reservoirs of this psychrometer are protected with
reflecting cylinders around psychrometer’s reservoirs
from the radiant heat.
The
cambric of Assmann aspiration psychrometer
wet thermometer is dampened using the pipette, the spring of the aspiration devise is set or the psychrometer with electrical ventilator is plugged in.
After these procedures the psychrometer is hung up
onto the support at the determination point. The data of wet and dry thermometers
are taken 8-10 minutes later.
The
absolute air humidity is calculated using the Sprung
formula:
,
where: А – absolute
air humidity in Hg mm;
t – maximum pressure of water vapour
at the wet thermometer temperature (see the table of saturated water vapours,
table 3);
0.5 – constant psychometric coefficient;
t – temperature of the dry thermometer;
t1 – temperature of the wet thermometer;
В – barometric pressure at the determination moment in Hg mm.
Relative
humidity is determined using the following formula:
,
where: Р –the
value of relative humidity to be found, %;
А – absolute humidity, Hg mm;
F – maximum humidity at the dry thermometer temperature, Hg mm (see table 3).
Relative
humidity is determined using the psychrometric tables for
aspiration psychrometers. The value of the relative humidity is
found at the intersection point of the dry and wet thermometer data (see table 5).
Hair
or membrane hygrometers are used for the determination of the relative humidity
of the air. These devices measure the relative humidity directly. The
hygrometer operation is based on the facts, that the degreased hair lengthens,
and the membrane/diaphragm weakens when it’s damp, and vice-versa when they are
dry (see fig. 6.2-c).
Table
5
The
relative humidity standards for residential, public and administrative premises
(abstract from Building Norms and Rules 2.04.05-86)
Note:* Allowable humidity is 75% for regions
with the estimated outdoor air relative humidity more than 75%.
Standards
are set for people who continuously stay in premises for more than 2 hours.
Humidity deficit (the difference between the maximum and absolute air
humidity) is determined using the table of saturated water vapours. The absolute air
humidity, calculated using Regnault or Sprung
formulas is subtracted from the value of maximum air humidity according to the
dry psychrometer’s thermometer.
Physiological
humidity deficit (the difference between the maximum air humidity at 36,5оС body temperature and absolute air humidity) is determined using the same table of saturated water
vapours (see table 3).
Dew
point (temperature when
the absolute air humidity is maximum) is determined
using the same table of saturated water vapours (see table 3) in reverse
direction. The temperature when the absolute air humidity is equivalent to the maximum, is found
using the value of absolute humidity.
The
scheme shows, that the rise of temperature provokes the maximum humidity
increase in geometric progression,
the absolute humidity – in arithmetical progression. When the air temperature rises, the
relative humidity is decreases. As
a result the amount of water in the air (absolute humidity) is
essentially lower in cold seasons than in summer, but is closely related to saturation (maximum humidity). That is why the relative humidity is
high in cold seasons and low in summer usually.
The
daily temperature, the air humidity and the atmospheric pressure variation are
determined using the thermograph, hygrograph and barograph respectively
WHAT
IS DRY AIR?
There
are two ways in which dry air is referenced to in meteorology. Both of these ways are
explained below:
1.
One
definition of dry air is a theoretical sample of air that has no water vapor. When looking at tables in meteorology textbooks you
will notice that for the composition of gases in the atmosphere there will
often be a table that shows the abundance of each major gas within dry air.
This is done since water vapor is a variable gas
(ranging from a trace to around 4%). The amount of water vapor
in the air depends on the dewpoint of
the air. When water vapor is ignored what is left is
a fairly fixed percentage of the percent by volume or
percent by mass of Oxygen, Nitrogen and Argon.
However, air in the atmosphere will not be perfectly dry since even in very
cold air there will still be a trace of water vapor.
2.
Another definition of dry air is air that has
a low relative humidity.
When the relative humidity drops below about 40% the air feels dry to skin. If
very low relative humidities persist it can make the
skin dry, lips chapped and can put more static in the air. In the winter when
air with a low dewpoint from outside is heated and
brought inside the air will decrease in relative humidity. To add moisture to
the air some people will buy humidifiers. Although this air is referred to as
dry air it is not perfectly dry. In some cases air will be referred to as dry
even when the outside relative humidity is high but the dewpoint
is low. This is because even if the air has a high relative humidity of 90%
outside, once that air is brought inside and heated the relative humidity will
decrease significantly. In situations in which the dewpoints
are low outside (less than around 32 F) that air will often be referred to as
dry by weather forecasters especially if the skies are clear.
The
role of earth surface type in appearing of winds
Wind
is air in motion. It is caused by horizontal variations in air pressure. The
greater the difference in air pressure between any two places at the same
altitude, the stronger the wind will be. The wind direction is the direction
from which the wind is blowing. A north wind blows from the north and a south
wind blows from the south. The prevailing wind is the wind direction most often
observed during a given time period. Wind speed is the rate at which the air
moves past a stationary object.
Measuring
of wind speed
Plenty
of instruments can measure wind.
•Wind
vane measures wind direction. Most
wind vanes consist of a long arrow with a tail that moves freely on a vertical
shaft. The arrow points into the wind and gives the wind direction.
•
•
•Anemometers measure wind speed. Most anemometers
consist of three or more cups that spin horizontally on a vertical post. The
rate at which the cups rotate is related to the speed of the wind. The cup of
anemometer has measuring borders from 1 to 50 m/sec, the wing one – from 0,5 to
15 m/sec.
•Cathathermometer
– alcohol thermometer with cylindrical or globular reservoir and a capillary
tube, dilated upwards, can measure air motion speed from 1,5 to 2 m/sec.
Anemometer -
•A
cup anemometer has metal cups which
rotate in the wind.
•A
swinging-arm anemometer records the
force of the wind against a single ball or plate. With a ventimeter
wind blows into a hole at the bottom of a tube and raises a plate up it.
•A
Dwyer wind meter similarly uses a
ball. You can easily make a simple anemometer.
Usage of "wind rose" in preventive
sanitary control for settlements, industrial enterprises, resting-places
building.
The
direction of a wind is determined by that part of horizont
from where it blows. A direction and force of wind is taken into account for
need of construction and planning of cities. As the direction of a wind is
constantly changed, therefore it is necessary to know, what winds dominate in
this district. For this purpose all directions of winds on stretch of season or
year are taken into account. On this data they create the schedule named
"rose of winds". Thus, "rose of winds" represents a
graphical image of recurrence of winds.
Wind
scale
Classification
of Wind Speed
Wind
speed can be given according to the Beaufort Scale
mainly used to report weather at sea, "a force 9 gale" for example.
On land, various indicators such as the movement of smoke or branches,
enable the wind speed to be estimated with reasonable accuracy.
•Force
1: 3 km/h (2 mph) smoke drifts
•Force
2: 9 km/h (5 mph) leaves rustle
•Force
3: 15 km/h (10 mph) flags flutter
•Force
4: 25 km/h (15 mph) small branches move
•Force
5: 35 km/h (21 mph) small trees sway
•Force
6: 45 km/h (28 mph) large branches move
•Force
7: 56 km/h (35 mph) whole trees sway
•Force
8: 68 km/h (43 mph) twigs break
•Force
9: 81 km/h (50 mph) branches break
•Force
10: 94 km/h (59 mph) trees blow down
•Force
11: 110 km/h (69 mph) serious damage
•Force
12: 118 km/h (74 mph) hurricane damage
Wind
Projects and Activities
There are lots of projects related
to wind speed and direction. You can build a lot of the instruments yourself
(look at things to do). Investigate why the wind does what it does!
In
enclosed spaces the running speed of air is determined in meters for one
second. The more air in a location varies, it is purer and health. But to admit
of high speeds of motion of air in a location it is impossible, as flows of
cold air, which one acts in a location, can derivate draughts. Is established, that the draught can call in the person or
offensive feels or sometimes catarrhal diseases. The feel of a draught
is at a running speed of air of 0,5m/sec and above.
•Therefore
at cooling locations it is undesirable to make motion of air with speed of
0,5m/sec and more, specially
in a cold season.
•The
motion of air near to temperature and damp it influences heat output by an
organism and, means, on thermo exchange of the person.
•Let's
consider such example. Let's allow, that temperature of air high, or is little
bit lower from temperature of a human body. The relative humidity is high also.
Under such circumstances heat output by a body of the person becomes difficult,
as also temperature of air high. Close up to temperature of a human body. The
stay of the person in such conditions conducts to an overheating.
Atmospheric
pressure
http://www.physicalgeography.net/fundamentals/7d.html
What
is Pressure?
Air
or atmospheric pressure, is the force exerted on the Earth, by the weight of
the air above. That depends on how high the column of air is, so the higher the
surface, the less the pressure. That is why you set your barometer to the
height of your house or school above sea-level to get correct readings. Air
pressure basically refers to the volume of air in a particular environment,
with greater volumes creating higher pressures. On the earth's surface, for
example, it is known as "atmospheric pressure" and refers to the
weight of the earth's atmosphere pressing down on everything. Changes in
pressure can impact the temperature, weather patterns, and cause physiological
problems for people and animals. This pressure can even impact the performance
of a basketball or similarly inflated object.
Atmospheric
Pressure
On the earth, the average air pressure at sea
level is 1.03 kilograms per square centimeter
(kg/cm2) or 14.7 pounds per square inch (psi); this is commonly measured in
bars, in which atmospheric pressure is about 1 bar. This means that hundreds of
pounds of pressure are pressing on everyone from all sides, at all times. Humans and other animals are able to survive
this pressure because their bodies evolved on the surface where it is
natural. If the pressure increases or
decreases, it can result in discomfort or even death.
Changes
in Pressure and Weather
Atmospheric
pressure varies slightly over the earth's surface, and variations in pressure
are responsible for various types of weather.
Low pressure systems are associated with storms, tornadoes, and hurricanes. Sometimes the air pressure at sea level can
drop as low as 870 millibars, which is about 85% of
average air pressure. This only happens
during the most severe storms. Pressure
variations on the earth's surface cause wind: as high pressure air moves toward
low pressure areas, creating gusts.
Various
Pressures at Different Altitudes
On
the top of Mt. Everest, the tallest mountain on earth, the air pressure is just
about a third of what it is at sea level. Humans at high altitudes often
experience discomfort, such as ear popping, due to differences in their
internal and external pressures. At 16 kilometers (km) or almost 10 miles above the surface,
slightly higher than the cruising altitude of a typical jet liner, pressure is
only 1/10th what it is at sea level.
Because low air pressure can be very unpleasant for humans, due to low
oxygen content, all areas of aircraft that contain passengers are artificially
pressurized. In the event of a rupture in an airplane's fuselage, unsecured
items may be "sucked" out of the craft as the high pressure air
within it rushes out into the low pressure environment outside.
Higher
Altitudes and Outer Space
At
31 km or about
19 miles above the earth's surface, in the stratosphere, the air pressure is
only 1/100th what it is at sea level.
From this level on, the atmosphere quickly deteriorates into
nothingness. Above 100 km or just over
62 miles above the surface, the international definition for outer space, the
pressure approaches zero and nearly becomes a vacuum. Humans cannot exist
unprotected in such a low-pressure environment.
Why
is it Important?
Different
pressure regimes have different types of weather associated with them.
Barometer
readings are plotted on a pressure chart. Points on a map that have the same
air pressure are connected by lines known as isobars. By studying the patterns
shown by isobars, forecasters can make predictions about how the weather will
develop. We can identify "troughs" of low pressure and
"ridges" of high pressure.
Barometer
http://www.stuffintheair.com/barometermakes.html
Types
of barometers
Mercury
siphon barometer
consists of long vertical tube.Instrument contains
mercury. We get the result after summation of hailing mercury tube in long and
short knee.
Mercury-cupping
barometer consists of vertical glass tube which has mercury
solder in upper part and open in lower part. Lower part is put into cup with
mercury.
Metal
barometer aneroid. Main
part of this barometer is metal reservoir with cavity. When pressure changes,
change volume and forms of reservoir with mercury.
http://www.bom.gov.au/info/aneroid/aneroid
Barograph.
Point of instruments connects with metallic aneroid.
The recording barometer may be day and week periodical. To establish of the
periodicals it is necessary to open the device’s case, to take down from the
drum’s axis for the tape and on it’s
lower part to see on what period well calculated clock mechanism. 747
Millimeter of a mercury column x 4/3 = 963 mB.This
quantity we put on the tape instead of the beginning record time.
There
is a scheme of an estimation of air behind damp: air name dry, when a water
pair in this there are less than 55 %, slightly dry – at 56 up to 70 %, by
slightly wet - from 71 up to 85 %, hardly wet - have more 86 % and saturated -
100 %.
The
business in that in miscellaneous terrains prevalence a direction of winds
happens miscellaneous. What the dominating direction of winds means? This is a
direction, which one often repeats during one year or season.
On
meteorological stations permanently registry can be defined a cosines speed of
their motion and directions a direction of winds on 4-8 or 16 rhombs. E -
Eastern wind, that is wind, that winds from east. W- Western wind; N - Northern
wind; S – Southern, NE - Northern – Eastern. At a sanitarian estimation of the projects of settlements the
availability on the schedule of a wind rose enables fast and simplly to orient and to evaluate a regularity of
accommodation miscellaneous regions, objects. For example, the regularity of
mutual accommodation of industrial firm, which one will flare air of habitation
point.
The
formation of gas bubbles in the organism during ascent is called decompression
sickness, known also as “the bends”.
Symptoms They
occur 5 minutes to 1 hour after the ascent, sometimes after 2-4 hours. Symptoms
range cough, itching, reddened skin or pains in the joints to serious
respiratory, cardiac and mental damage (such as rapid pulse and heart beat, shortness of breath, pains in the chest and stomach,
paralysis of limbs)
Treatment The
only remedy to do away with decompression sickness is the chamber for
recompression. The diver is exposed to the same pressure (at which he was
before the beginning of bubbles’ formation), necessary to dissolve the bubbles.
Afterwards, the pressure decreases on stages to avoid decompression sickness.
HOW
DOES AIR PRESSURE AFFECT THE BODY?
Air
pressure is the force that is exerted on you by air molecules; the weight of
tiny air particles. Atmospheric pressure is a measure of the force exerted by
the atmosphere, so therefore at any point on the earth’s surface, there is a
quantity of air sitting above your body. If that quantity of air is greater,
there will be more pressure on the body; and if it is less, there will be less
pressure on the body. This is traditionally measured in pounds per square inch
(PSI). 1 PSI is the force of one pound applied to an area of one square inch.
At
high altitudes the quantity of air is less, and the density of air is also
less. As such, there is less air pressure and as a result, less oxygen in a given
volume of air. To demonstrate this, If a person dives below the surface of
water in scuba diving, their body has to contend with both the air exerting
pressure on the surface of the water, and the water above that exerting further
pressure, hence, the deeper you dive, the more pressure there is.
At
sea level, we say atmospheric pressure is 1 atmosphere (this is equal to 14.7
psi). This arbitrary measurement provides a reference point from which we can
determine air pressure at varying altitudes or depths.
For
every 10 metres deep which you go in water, the pressure increases by 1
atmosphere. For example -at 10 metres it is 2 atmospheres; at 40 metres it is 5
atmospheres).
Partial
Pressure Gradients
Partial
pressure gradients follow Henry’s law. Henry's law states that at a constant
temperature, the amount of a given gas dissolved in a given type and volume of
liquid is directly proportional to the partial pressure of that gas in
equilibrium with that liquid. In terms of atmospheric pressure, because a large
percentage of the body is water, as the pressure increases (i.e. as a scuba
diver goes deeper) more gas will dissolve in the blood and body tissues. As
long as the person remains at the same pressure, the gas will remain in
solution.
The
air we breathe is a mixture of gases. Nitrogen is the most abundant gas,
and nitrogen molecules (N2) make up about 78% of our atmosphere. Oxygen
molecules (O2) molecules make up about 21% of the air we breathe, water
molecules 0.5%, and carbon dioxide 0.04%. Each of these gases contributes to
the total pressure in the atmosphere proportional to its relative abundance.
Partial pressure of a gas = the pressure exerted by that one gas (e.g. oxygen)
in a gas mixture (e.g. air).
The
partial pressure of oxygen is much higher in alveoli than in capillaries. That
is, there is a steep partial pressure gradient for oxygen. This partial
pressure gradient causes oxygen to diffuse rapidly from alveoli to capillaries.
A similarly steep gradient affects the diffusion of oxygen from capillaries to
body tissues. The partial pressures shown in the table below are
important in determining the movement of oxygen and carbon dioxide between the
atmosphere and lungs, the lungs and blood, and the blood and body cells. When a
mixture of gases diffuses across a permeable membrane, each gas diffuses from
an area of greater partial pressure to an area of lower partial pressure (the
gas moves down its concentration gradient). Each gas in a mixture of gases
exerts its own pressure as if all other gases were not present.
ALTITUDES
At
altitude the air pressure decreases, so in the same volume of air, there is less molecules present (for example oxygen molecules).
People often say the air is “thinner” at altitude, and the result is that you
will need to breathe faster and deeper to get the same amount of oxygen, and your
heart will pump more blood to increase the supply of oxygen to the brain and
muscles.
Physical
performance is affected at altitudes over 500 feet (1524 metres) the higher the
altitude, the more impaired the physical performance of the body. Physical or
work performance is related to oxygen consumption, which decreases at high
altitudes, due to less oxygen in a given volume of air.
Endurance
capacity is commonly measured by a reduction of 3-3.5% in maximal oxygen
consumption for every 1000 feet ascended above 5000 feet. At a height of around
25,000 feet, performance and oxygen consumption can be reduced by up to 60%.
If
a person remains at high altitudes for long periods, they begin to acclimatise.
At 9000 feet it can take 7-10 days to acclimatise. At higher altitudes it can
take longer. A minority of people will never acclimatise. With acclimatisation,
a person’s performance at higher altitudes will approach normal levels but
never quite reach their norm.
In
contrast, for explosive athletic events, such as 100m sprint and long jump,
reduced atmospheric pressure results in less atmospheric resistance, so the
athlete’s performance is improved.
EFFECTS OF CHANGES IN PRESSURE
The
skin which covers the human body will adjust to changes in pressure; however
body cavities such as ears, sinuses & lungs, do not automatically adjust to
such changes.
Therefore,
this is the reason that changes in air pressure can have the effect of causing
a popping in the ears. This can occurs when flying in a plane or driving up
into the mountains; anything where the atmospheric pressure is raised. In
general, the air in body cavities is normally an equal pressure to the air
outside of the body. However, if atmospheric pressure changes fast, or if there
is any blockage between the outside of the body and the internal cavities
-"equalising" of pressure might not occur properly.
A
tangible example of how you may have experienced this is when you take a drink
bottle on a flight. If you open an empty plastic bottle while you are in the
air, then tightly close it, when you land, you will find the increase in air
pressure has caused the air in the bottle to compress, as if it has been sucked
out with a vacuum, and the bottle has collapsed inwards.
When
scuba diving, as the pressure increases the air spaces in a diver’s body and
equipment will compress. As the pressure decreases, the air spaces will expand.
The amount of compression follows Boyle’s law, which describes how the volume
of gas varies, depending on the surrounding pressure.
Boyle’s
law is: PV = c (where P= pressure, V = volume of
a gas, c = a constant)
This shows that when you multiply the surrounding pressure of a gas, by the
volume of the gas, you will always have the same number. So if the amount of
pressure is increased, the volume of gas must decrease, and vice versa.
The
implications of Boyle’s law for scuba diving are that as a diver descends, the air spaces in their ears, masks and lungs are
decreased, creating a negative pressure and a vacuum like effect. To avoid
injury, the diver will need to equalise the pressure in the air spaces with the
surrounding pressure (see below for more information). While they are diving,
care must be taken to continue breathing – if a diver holds their breath and
ascends to an area where less pressure is exerted, the air trapped in the lungs
will expand and can stretch the lungs and can lead to injury. When ascending,
the air in the diver’s ears and lungs will expand, creating a positive
pressure. These air spaces can become overfull, so the diver will need to
equalise, and breath out any excess air. Failure to do
so can cause the eardrum and lungs to burst. The buoyancy compensator (BCD)
will also expand due to decreased pressure, so the diver will need to release
air from the BCD to control their ascent. On the ascent, consideration also
needs to be taken for the affect of Boyle’s law on
nitrogen gas in the diver’s body. This is explained in more depth later on in
this lesson.
How
does the human organism lose a heat?
Major
part of heat loses through the skin and mucous, other part goes on heating of
food, water and breathes air. Through the skin loses main heat mass: for after
one authors - 85-90%, after other - even 95%, so, only 4-6% loses on heating of
food, breathe air and waters.
http://www.expeditionsamoyeds.org/Hypothermia.html
Because
of that interestingly will learn how the heat is lost by skin. Appear, that skin loses a heat by three ways:
•by
radiation,
•taking and
•on evaporation of
sweat moisture.
For
data of Rubner, we can say, that man attached to
light work in room conditions
•loses
by radiation about 40%,
•taking
- about 30% and
•by evaporation - about 20% of heat.
These
ciphers are directed for orientation, and really they consider vacillate dependency on conditions.
HEAT
TRANSFER,
in physics, process by
which energy in the form of heat is exchanged between bodies or parts of the
same body at different temperatures. Heat is generally transferred by
convection, radiation, or conduction. Although these three processes can occur
simultaneously, it is not unusual for one mechanism to overshadow the other
two. Heat, for example, is transferred by conduction through the brick wall of
a house, the surfaces of high-speed aircraft are heated by convection, and the
earth receives heat from the sun by radiation.
Heat
Transfer Heat can be transferred by three processes: conduction, convection,
and radiation. Conduction is the transfer of heat along a solid object; it is
this process that makes the handle of a poker hot, even if only the tip is in
the fireplace. Convection transfers heat through the exchange of hot and cold
molecules; this is the process through which water in a kettle becomes
uniformly hot even though only the bottom of the kettle contacts the flame.
Radiation is the transfer of heat via electromagnetic (usually infrared)
radiation; this is the principal mechanism through which a fireplace warms a
room.© Microsoft Corporation. All Rights
Reserved.
CONDUCTION
This
is the only method of heat transfer in opaque solids. If the temperature at one
end of a metal rod is raised by heating, heat is conducted to the colder end,
but the exact mechanism of heat conduction in solids is not entirely
understood. It is believed, however, to be partially due to the motion of free
electrons in the solid matter, which transport energy if a temperature
difference is applied. This theory helps to explain why good electrical
conductors also tend to be good heat conductors (see Conductor, Electrical).
Although the phenomenon of heat conduction had been observed for centuries, it
was not until 1882 that the French mathematician Jean Baptiste Joseph Fourier gave
it precise mathematical expression in what is now regarded as Fourier's law of
heat conduction. This physical law states that the rate at which heat is
conducted through a body per unit cross-sectional area is proportional to the
negative of the temperature gradient existing in the body.
The
proportionality factor is called the thermal conductivity of the material.
Materials such as gold, silver, and copper have high thermal conductivities and
conduct heat readily, but materials such as glass and asbestos have values of
thermal conductivity hundreds and thousands of times smaller, conduct heat
poorly, and are referred to as insulators (see Insulation). In engineering
applications it is frequently necessary to establish the rate at which heat
will be conducted through a solid if a known temperature difference exists
across the solid. Sophisticated mathematical techniques are required to
establish this, especially if the process varies with time, the phenomenon
being known as transient-heat conduction. With the aid of analog and digital
computers, these problems are now being solved for bodies of complex geometry.
CONVECTION
Conduction
occurs not only within a body but also between two bodies if they are brought
into contact, and if one of the substances is a liquid or a gas, then fluid
motion will almost certainly occur. This process of conduction between a solid
surface and a moving liquid or gas is called convection. The motion of the
fluid may be natural or forced. If a liquid or gas is heated, its mass per unit
volume generally decreases. If the liquid or gas is in a gravitational field,
the hotter, lighter fluid rises while the colder, heavier fluid sinks. This
kind of motion, due solely to nonuniformity of fluid
temperature in the presence of a gravitational field, is called natural
convection. Forced convection is achieved by subjecting the fluid to a pressure
gradient and thereby forcing motion to occur according to the law of fluid
mechanics.
If,
for example, water in a pan is heated from below, the liquid closest to the
bottom expands and its density decreases; the hot water as a result rises to
the top and some of the cooler fluid descends toward the bottom, thus setting
up a circulatory motion. Similarly, in a vertical gas-filled chamber, such as
the air space between two window panes in a double-glazed, or Thermopane, window, the air near the cold outer pane will
move down and the air near the inner, warmer pane will rise, leading to a
circulatory motion.
The
heating of a room by a radiator depends less on radiation than on natural
convection currents, the hot air rising upward along the wall and cooler air
coming back to the radiator from the side of the bottom. Because of the
tendencies of hot air to rise and of cool air to sink, radiators should be
placed near the floor and air-conditioning outlets near the ceiling for maximum
efficiency. Natural convection is also responsible for the rising of the hot
water and steam in natural-convection boilers (see Boiler) and for the draft in
a chimney. Convection also determines the movement of large air masses above
the earth, the action of the winds, rainfall, ocean currents, and the transfer
of heat from the interior of the sun to its surface.
RADIATION
Wilhelm
Wien German physicist Wilhelm Wien won the 1911 Nobel Prize in physics. His
discoveries in the field of radiation, including the laws that govern heat
radiation, laid the foundation for the development of the quantum theory.© The Nobel Foundation
This process is fundamentally different from
both conduction and convection in that the substances exchanging heat need not
be in contact with each other. They can, in fact, be separated by a vacuum.
Radiation is a term generally applied to all kinds of electromagnetic-wave
phenomena. Some radiation phenomena can be described in terms of wave theory
(see Wave Motion), and others can be explained in terms of quantum theory.
Neither theory, however, completely explains all experimental observations. The
German-born American physicist Albert Einstein conclusively demonstrated (1905)
the quantized behavior of radiant energy in his classical photoelectric
experiments. Before Einstein's experiments the quantized nature of radiant
energy had been postulated, and the German physicist Max Planck used quantum
theory and the mathematical formalism of statistical mechanics to derive (1900)
a fundamental law of radiation (see Statistics). The mathematical expression of
this law, called Planck's distribution, relates the intensity or strength of
radiant energy emitted by a body to the temperature of the body and the
wavelength of radiation. This is the maximum amount of radiant energy that can
be emitted by a body at a particular temperature. Only an ideal body (blackbody,)
emits such radiation according to Planck's law. Real bodies emit at a somewhat
reduced intensity. The contribution of all frequencies to the radiant energy
emitted by a body is called the emissive power of the body, the amount of
energy emitted by a unit surface area of a body per unit of time. As can be
shown from Planck's law, the emissive power of a surface is proportional to the
fourth power of the absolute temperature. The proportionality factor is called
the Stefan-Boltzmann constant after two Austrian physicists, Joseph Stefan and
Ludwig Boltzmann, who, in 1879 and 1884, respectively, discovered the fourth
power relationship for the emissive power. According to Planck's law, all
substances emit radiant energy merely by virtue of having a positive absolute
temperature. The higher the temperature, the greater the amount of energy
emitted. In addition to emitting, all substances are capable of absorbing
radiation. Thus, although an ice cube is continuously emitting radiant energy,
it will melt if an incandescent lamp is focused on it because it will be
absorbing a greater amount of heat than it is emitting.
Opaque
surfaces can absorb or reflect incident radiation. Generally, dull, rough
surfaces absorb more heat than bright, polished surfaces, and bright surfaces
reflect more radiant energy than dull surfaces. In addition, good absorbers are
also good emitters; good reflectors, or poor absorbers, are poor emitters.
Thus, cooking utensils generally have dull bottoms for good absorption and
polished sides for minimum emission to maximize the net heat transfer into the
contents of the pot. Some substances, such as gases and glass, are capable of
transmitting large amounts of radiation. It is experimentally observed that the
absorbing, reflecting, and transmitting properties of a substance depend upon
the wavelength of the incident radiation. Glass, for example, transmits large
amounts of short wavelength (ultraviolet) radiation, but is a poor transmitter
of long wavelength (infrared) radiation. A consequence of Planck's distribution
is that the wavelength at which the maximum amount of radiant energy is emitted
by a body decreases as the temperature increases. Wien's displacement law, named
after the German physicist Wilhelm Wien, is a mathematical expression of this
observation and states that the wavelength of maximum energy, expressed in
micrometers (millionths of a meter), multiplied by the Kelvin temperature of
the body is equal to a constant, 2878. Most of the energy radiated by the sun,
therefore, is characterized by small wavelengths. This fact, together with the
transmitting properties of glass mentioned above, explains the greenhouse
effect. Radiant energy from the sun is transmitted through the glass and enters
the greenhouse. The energy emitted by the contents of the greenhouse, however,
which emit primarily at infrared wavelengths, is not transmitted out through
the glass. Thus, although the air temperature outside the greenhouse may be
low, the temperature inside the greenhouse will be much higher because there is
a sizable net heat transfer into it.
In
addition to heat transfer processes that result in raising or lowering
temperatures of the participating bodies, heat transfer can also produce phase
changes such as the melting of ice or the boiling of water. In engineering,
heat transfer processes are usually designed to take advantage of these
phenomena. In the case of space capsules reentering the atmosphere of the earth
at very high speed, a heat shield that melts in a prescribed manner by the
process called ablation is provided to prevent overheating of the interior of
the capsule. Essentially, the frictional heating produced by the atmosphere is
used to melt the heat shield and not to raise the temperature of the capsule
(see Friction).
What
is the heat losing way by radiation?
From
physics we know, that any more heated body radiates more heat, than less
heated. So, even not colliding with it, it gives to it its heat, while the temperatures
of both bodies will not complete with each other.
•Man
in room conditions is usually circled by objects with more low temperature,
than his body, that is why takes place heat losing by radiation.
•Also
heat is lost by installation. In this case a heat is lost by two ways - conduction and convection.
•Conduction is a heat transition on the strength of
contiguity of objects, and also air parts from more heated to less heated. Convection is a heat transmission on the strength of
mediators - air, steam, liquid, the fractions of which, heating attached to contact
with more warm body, bear off heat and return it attached to contiguity with
more cold objects. On the strength of temperature difference in intermediate
environment, for example, in air, the convectional streams are generated.
•The
third way of heat losing is evaporation
of moisture.
A
human skin is always covered by sweat, water of which evaporates. For this
process it is necessary expenditure of warm /secretive evaporation temperature
/.
http://ppo.tamuk.edu/ehs/Heat_Stress/heatstress.htm
Microclimate –
it is meteorological
conditions in work zone, which characterized by complexes of factors that act
on organism of peoples it is temperature, humidity and rate movement of air,
and also radiation temperature and warm radiation. Temperature of air is
favorable factors which influence on heat exchange. Radioactive temperature –
it is the temperature that surround people of superficiality or intensive sun
or another radiation.
Microclimate
is a thermal status of the limited space. It results from combined action of
air temperature, radiation heat, air humidity and air movement velocity.
Microclimate defines heat state of an organism. Microclimate is influenced by
latitude, topography, human activities and vegetation as well as other factors.
Sometimes they mean microclimate as variations of the climate within a given
area, usually influenced by hills, hollows, structures or proximity to bodies
of water. The warmth and humidity of the air in close proximity to a plant or
heat/moisture source may differ significantly from the general climate of the
premise.
Air
treatment/air cooling differs from ventilation because it reduces the temperature
of the air by removing heat (and sometimes humidity) from the air. Air
conditioning is a method of air cooling, but it is expensive to install and
operate. An alternative to air conditioning is the use of chillers to circulate
cool water through heat exchangers over which air from the ventilation system
is then passed; chillers are more efficient in cooler climates or in dry
climates where evaporative cooling can be used.
Local
air cooling can be effective in reducing air temperature in specific areas. Two
methods have been used successfully in industrial settings. One type, cool
rooms, can be used to enclose a specific workplace or to offer a recovery area
near hot jobs. The second type is a portable blower with built-in air chiller.
The main advantage of a blower, aside from portability, is minimal set-up time.
Another
way to reduce heat stress is to increase the air flow or convection using fans,
etc. in the work area (as long as the air temperature is less than the worker's
skin temperature). Changes in air speed can help workers stay cooler by
increasing both the convective heat exchange (the exchange between the skin
surface and the surrounding air) and the rate of evaporation. Because this
method does not actually cool the air, any increases in air speed must impact
the worker directly to be effective.
If
the dry bulb temperature is higher than 35°C (95°F), the hot air passing over
the skin can actually make the worker hotter. When the temperature is more than
35°C and the air is dry, evaporative cooling may be improved by air movement,
although this improvement will be offset by the convective heat.
When
the temperature exceeds 35°C and the relative humidity is 100%, air movement
will make the worker hotter. Increases in air speed have no effect on the body
temperature of workers wearing vapor-barrier clothing. Heat conduction methods
include insulating the hot surface that generates the heat and changing the
surface itself. Simple engineering controls, such as shields, can be used to
reduce radiant heat, i.e. heat coming from hot surfaces within the worker's
line of sight. Surfaces that exceed 35°C (95°F) are sources of infrared
radiation that can add to the worker's heat load. Flat black surfaces absorb
heat more than smooth, polished ones.
Having cooler surfaces surrounding the worker assists in cooling
because the worker's body radiates heat toward them. With some sources
of radiation, such as heating pipes, it is possible to use both insulation and
surface modifications to achieve a substantial reduction in radiant heat.
Instead
of reducing radiation from the source, shielding can be used to interrupt the
path between the source and the worker. Polished surfaces make the best
barriers, although special glass or metal mesh surfaces can be used if
visibility is a problem.
Shields
should be located so that they do not interfere with air flow, unless they are
also being used to reduce convective heating. The reflective surface of the
shield should be kept clean to maintain its effectiveness.
HVAC
(heating-ventilation-air conditioning) system defines indoor microclimate.
A
microclimate maintenance system (general HVAC system) created in several rooms
gives a possibility to use an economic decision, the idea of which consists in
use of one outdoor unit and several indoor units (from two to four). It is
explained by the fact that in adjacent room’s air-conditioners have to carry out
similar functions of cooling or heating.
This
makes it possible to use one outdoor unit for work with indoor units which
carry out cooling, for example. As a result such a system has lower operating
costs and lower power consumption and at the same time allows you to carry out
air-conditioning in one or several rooms, where indoor units are installed.
HEAT
BALANCE
Fundamentals
of heat transfer Humans are homeothermic, which means
they must maintain body temperature within a narrow range in varying
environmental conditions. The normal deep body temperature (core body
temperature) at rest is between 36-37.5 oC, although
extremes in excess of 40 oC have been recorded in
athletes and workers exposed to very severe environmental conditions. These
temperatures are at the upper limit of human physiological tolerance, however
they illustrate that people do get exposed to such conditions during their work
practice. The variation of resting core body temperatures also demonstrates the
individual diversity that may exist in a working population. This variation
means that people may have different tolerances to working in the heat. Some
people cannot tolerate mild increases in core body temperature whereas others,
as illustrated, can continue to work at much higher temperatures. The factors
that may account for this variation among workers are still, however, poorly
understood.
Thermal
homeostasis is maintained by achieving a balance between the various avenues of
heat gain and heat loss from the body. There are two recognised
sources of heat load;
a) Environmental, which may be positive or negative, that
is, there may be a heat gain or a heat loss from the body.
b) Metabolic, which is generated by muscular activity.
ENVIRONMENTAL
FACTORS AFFECTING THERMOREGULATION
The
principal methods of heat exchange between the body and the external
environment are: convection, conduction, radiation and
evaporation.
Convection
The
rate of convective exchange between the skin of a person and the ambient air in
close proximity to the skin, is dictated by the
difference in temperature between the air and the skin temperature together
with the rate of air movement over the skin.
When
the air temperature is greater than the skin temperature, there will be a gain
in body heat from the surrounding air, conversely when the skin is warmer than
the air temperature there will be a loss of heat from the body. Because warm
air rises (less dense than cool air) the warm air will rise from the body and
cool air will come in to take its place. This process is then repeated. The
process is called convection.
Radiation
The
surface of the human body constantly emits heat in the form of electromagnetic
waves. Simultaneously, all other dense objects are radiating heat. The rate of
emission is determined by the absolute temperature of the radiating surface.
Thus if the surface of the body is warmer than the average of the various
surfaces in the environment, net heat is lost, the rate being directly
dependent on the temperature difference. This form of heat transfer does not
require molecular contact with the warmer object. The sun is a powerful
radiator, and exposure to it greatly decreases heat loss by radiation. When the
temperature of the objects in the environment exceeds skin temperature, radiant
heat energy is absorbed from the environment. Under these conditions the only
avenue for heat loss is by evaporative cooling.
Conduction
The
difference between heat loss by conduction and radiation is that with
conduction the body must be in contact with the object. In such circumstances
the heat moves down its thermal gradient from the warmer to the cooler object,
the heat energy being transferred from molecule to molecule. The warmer
molecule slows down after it has lost some of its heat and the cooler molecules
move faster having gained heat. The temperature transfer continues until
eventually the temperature of the two objects equalises.
The rate of the heat transfer through conduction depends on the difference in
temperature between the two objects and the thermal conductivity of the two
objects.
Evaporation
When
water evaporates from the surface of the skin, the heat required to transform
it from a liquid to a gas is dissipated from the skin, this acts to cool the
body. Evaporative heat loss occurs from the respiratory tract lining as well as
from the skin. There is a constant gradual loss of water from the skin that is
not related to sweat glands. The skin is not fully waterproof and so some water
is lost out through pores in skin, and lost by evaporation. This loss is not
subject to physiological control and is termed insensible perspiration.
Sweating is an active process requiring energy and controlled by the
sympathetic nervous system. The rate at which this process proceeds can be
controlled and therefore the amount of heat loss can be controlled.
Radiation
and convection are insufficient to prevent warming up of the body during heavy
manual work or at high surrounding temperatures. Under these circumstances heat
loss is aided by evaporation of water. At environmental temperatures above
about 36 oC, heat is lost exclusively by evaporation.
At higher temperatures heat is taken up by the body from the environment by
radiation, conduction and convection.
Sweating
then becomes profuse in order to maintain the balance between heat uptake and
heat loss by evaporation. In order to be effective, sweat must be evaporated
from the skin. If sweat merely drips from the surface of the skin or is wiped
away, no heat will be lost.
Thermal
equilibrium of the body is maintained by balancing the relationship
M
± C ± K ± R - E ± S = O
Where
M = metabolic heat (always positive).
C = convective heat exchange.
K = conductance heat exchange through surfaces
in direct contact with
the skin.
R = radiative heat
exchange between skin or clothing surroundings.
E = evaporation of water from the skin surface
and respiratory tract .
S = heat storage (heat balance exists when S
is zero).
METABOLIC
FACTORS AFFECTING THERMOREGULATION
In
addition to heat exchange between the body and the environment, internal heat
is produced by metabolic processes. Although digestion and other body processes
contribute slightly, by far the greatest influence is the heat generated during
external work. Body heat is gained directly from the reactions of energy
metabolism. When muscles become active, their heat contribution can be
tremendous. For example, at rest, the rate of body heat production is
relatively low; the resting oxygen consumption is approximately 250 mL/min
corresponding to a rate of heat production of 70W. During work, the rate of
oxygen consumption can increase eightfold, and the rate of heat production is
correspondingly increased. There are four work components which can affect
metabolic heat load: work rate, work nature, work pattern and posture.
Work
rate
Muscular
work is mechanically a very inefficient process. The major muscles such as the
upper or lower limb muscles can only achieve 20-25% mechanical work efficiency.
A substantial proportion of the rest of the energy is generated as heat. There
is therefore a direct relationship between work rate and metabolic heat
production.
Work
nature
Much
of work is a mixture of dynamic and static components. As the proportion of
static work (meaning no movement) increases, the muscles become even less
efficient with the result that more energy is produced as heat. The nature of
the work can therefore influence the metabolic heat load.
Work
pattern
The role that scheduling plays in modern work can also influence
the heat load. Set timing of breaks at work may mean that the worker
cannot stop and cool down. This may effect thermoregulatory efficiency and
therefore work tolerance. On the other hand, self paced
work may allow the worker to operate more safely in conditions of thermal
stress.
Posture
The
effect of poor posture when working may place an additional burden or loading
on muscles. This will result in additional heat generation by the muscles as a
consequence of mechanical disadvantage.
THE
INFLUENCE OF CLOTHING ON THERMAL LOAD
Heat
exchange is relatively easy to analyse in the basic model, that is the exchange between human skin and the micro-climate
created by a layer of ambient air.
However,
when layers or even a layer of clothing is used heat exchange becomes far more
complex. The space between the skin and the outermost garment becomes a very
complicated micro-climate consisting of air and fabric layers changing depth
with each body movement. The insulative
characteristics of this environment are given by the behaviour
of the air trapped between the skin and clothing. This means that any factor
that alters the thickness of the air layers and so the insulative
properties will lead to a decrease or increase in heat loss from the body. The
difficulty of understanding the effect of heat balance is enhanced when the behaviour of the air and air exchange between the clothing
layers and the environment is considered. The size, shape, and number of pores
in the garment influence air exchange and movement and therefore the insulative properties of the clothing. These factors in
turn influence the ability of the person wearing the clothing to lose heat
generated by muscular activity. A change of clothing insulation is the easiest
and the quickest method of thermal adaptation, although there are practical or
cultural limits to this form of physical thermoregulation. There are cases,
however, where humans may adjust their metabolism rather than clothing
insulation, as has been shown by in a North American elderly population. If the
heat generated by these factors is not lost, then a rise in core body
temperature and heat illness will result.
The
subject of thermal comfort is complex and beyond the confines of this work,
however, it is relevant to persons working in hot environments. The importance
of protecting the skin from harmful ultra-violet radiation and against non thermal hazards in the workplace is becoming
increasingly important. Because workers should wear clothing to protect
themselves from these hazards, the thermal properties required of clothing to maximise cooling is an important consideration. There have
been a number of reviews on this subject.
HUMAN
THERMOREGULATION
It
was previously stated that as ambient temperature increases, the effectiveness
of heat loss by radiation, conduction and convection decreases. When ambient
temperature exceeds body temperature, heat is actually gained by these
mechanisms of thermal transfer. In such environments, or when conduction,
convection and radiation are inadequate to dissipate substantial metabolic heat
loads, the only means for heat dissipation is by sweat evaporation. The rate of
sweating increases directly with the ambient temperature.
The
total amount of sweat evaporated from the skin depends on three factors:
1)
The surface exposed to the environment.
2)
The temperature and humidity of the ambient air.
3)
The convective air currents around the body.
Relative
humidity is by far the most important factor determining the effectiveness of
evaporative heat loss. When humidity is high the ambient vapour
pressure approaches that of moist skin and evaporation is greatly reduced. Thus
this avenue for heat loss is essentially closed, even though large quantities
of sweat are produced.
This
form of sweating represents a useless water loss that can lead to dehydration
and overheating. As long as the humidity is low, relatively high environmental
temperatures can be tolerated. For this reason, hot, dry desert climates are more
comfortable than cooler but more humid tropical climates.
Most
studies on human thermoregulation have been performed in climate chambers as
opposed to the outdoor natural environment where most physical activity takes
place.
The
thermal environment under outdoor conditions may include significant radiant
heat gain, especially on sunny days. For humans, the colour
of skin and clothing is of importance for the reflection and absorption of
solar radiation, with darker colours having greater
absorptive heat gain. It has also been reported by that the radiant heat gain
from sun, direct and indirect, is between 160-230W per hour. It has also being
shown that the heat load gained from direct sunshine is significant, for this
reason predictions of heart rate and sweating rate based on climate chamber
experiments will 6give too low values for outdoor exercise in the sun. Although
solar radiation is only moderate in heat balance, the addition of this extra
heat stress, even in temperate climates, may be critical for near maximal
exercise performance, or for unacclimatised,
physically untrained workers where thermoregulation and cardiovascular
stability become important for physical performance and endurance.
Sunstroke
is more accurately called heatstroke since it is not necessary to be exposed to
the sun for this condition to develop. It is a less common but far more serious
condition than heat exhaustion since it carries a 20-percent mortality rate.
The most important feature of heatstroke is the extremely high body temperature
(105°F [41°C] or higher) that accompanies it. In heatstroke, the victim has a
breakdown of his sweating mechanism and is unable to eliminate excessive body
heat. When the body temperature rises too high, the
brain, kidneys, and liver may be permanently damaged. Sometimes the victim may
have preliminary symptoms, such as headache, nausea, dizziness, or weakness.
Breathing is deep and rapid at first; later, it is shallow and almost absent.
Usually the victim is flushed, very dry, and very hot. His pupils are
constricted (pinpointed) and the pulse is fast and strong. See figure for a
comparison of these symptoms with those of heat exhaustion.
TREATMENT. When providing first aid for heatstroke, keep in
mind that this is a true life and death emergency. The longer the victim
remains overheated, the more likely he is to suffer irreversible body damage or death. The main objective of first
aid is to get the body temperature down as quickly as possible.
Figure
Symptoms of heatstroke and heat exhaustion.
Move
the victim to the coolest possible place, and remove as much clothing as
possible. Body heat can be reduced quickly by immersing the victim in a
cold-water bath. When a cold-water bath is not possible, give the victim a
sponge bath by applying wet, cold towels to the whole body. Exposing the victim
to a fan or air conditioner also promotes body cooling. When cold packs are
available, place them under his arms, around his neck at his ankles, and in his
groin. When the victim is conscious, give him cool water to drink Do NOT give
him hot drinks or stimulants.
Because
of the seriousness of heatstroke, it is important to get the victim to a
medical facility as soon as possible. Cooling measures must be continued during
transportation.
COLD
WEATHER INJURIES
When
the body is subjected to severely cold temperatures, blood vessels constrict
and body heat is gradually lost. As the body temperature drops, tissues are
easily damaged or destroyed.
All
cold injuries are similar, varying only in degree of tissue injury. The extent
of injury depends on such factors as wind speep,
temperature, type and duration of exposure, and humidity. Tissue freezing is
accelerated by wind, humidity, or a combination of the two. Injury caused by
cold, dry air is less than that caused by cold, moist air, or exposure to cold
air while you are wearing wet clothing. Fatigue, smoking, drugs, alcoholic
beverages, emotional stress, dehydration, and the presence of other injuries
intensify the harmful effects of cold.
You should also
know that in cold weather,
wounds bleed easily because the low temperatures
keep the blood from clotting
and increased bleeding, of course,
increases the likelihood of shock.
Also, wounds that are open
to the cold
weather freeze quickly. The body
loses heat in the areas
around the injury, as blood
soaks the skin around the
wound, and clothing is usually
torn. Therefore, early first-aid treatment becomes even more important
during periods of low temperatures.
GENERAL COOLING (HYPOTHERMIA)
General
cooling of the entire body is caused by continued exposure to low or rapidly
dropping temperatures, cold moisture, snow, or ice. Those persons exposed to
low temperatures for extended periods may suffer ill effects, even if they are
well protected by clothing, because cold affects the body system slowly, almost
without notice. As the body temperature drops, there are several stages of
progressive discomfort and disability. The first symptom is shivering, which is
an attempt by the body to generate heat. This is followed by a feeling of
listlessness, drowsiness, and confusion. Unconsciousness may follow quickly.
You will have already noted signs of shock. As the temperature drops even
lower, the extremities (arms and legs) freeze. Finally, death
results.
TREATMENT.
Hypothermia
is a MEDICAL EMERGENCY. THE VICTIM NEEDS HEAT. Rewarm the victim as soon as
possible. It may be necessary, however, to treat other injuries before the
victim can be moved to a warmer place. Severe bleeding must be controlled and
fractures splinted over clothing before the victim is moved.
When
the victim is inside a warm place and is conscious, the most effective method
of warming him is immersion in a tub of warm water (100°F to 105°F [38°C to
41°C]) or warm to the elbow-never hot). When a tub is not available, apply
external heat to both sides of the victim, using covered hot-water bottles or,
if necessary, any sort of improvised heating pads. Do not place artificial heat
next to bare skin. When immersion is used, only the body, not the limbs, should
be immersed. Immersion of the arms and legs causes cold blood to flow from them
to the body core, causing further detrimental cooling of the core. Dry the
victim thoroughly when water is used to rewarm him. The most frequently
recommended field treatment is "buddy warming." Since the victim is
unable to generate body heat, merely placing him under a blanket or in a
sleeping bag is not sufficient. For best results, the nude victim should be
placed in a sleeping bag with two volunteers stripped to their shorts to
provide body-to-body heat transfer. This technique can be used by untrained
personnel in a tent in the field and WILL SAVE LIVES!!!
When
the victim is conscious, give him warm liquids to drink, Hot
tea with lots of sugar is particularly good. No alcoholic beverages, please.
As soon as
possible, transfer the victim to
a medical facility, keeping him warm
in route. Be alert for
signs of respiratory failure and cardiac arrest
during transfer
Heat-Related
Illnesses - Symptoms: You will experience cramps,
dizziness, weakness, nausea, pale skin, you will be flushed, your
skill will be moist and cool, or ashen. You will also experience a rapid but
weak pulse. Possible Condition: If the victim is
experiencing cramps get them to a cool area, give them cool water to drink; and
massage and stretch affected muscles. If the victim is experiencing heat
exhaustion then move them to a cool place as well; make sure to loosen the
clothing so its not touching
their skin. Then apply wet towels directly to the skin, fan victims body; give
cool water to drink. For heat stroke, follow the same steps for heat
exhaustion. Make sure to make them rest on their side; absolutely do not let
the victim to continue their normal activities for rest of the day and then
have them re-evaluate them the next day before allowing to return to any
physical activities.
Hypothermia
- Symptoms: The victim will have a glassy stare, they will shiver, and experience numbness. They also
may become unconscious. Possible Condition: The victims entire body’s temperature will loss heat and drop
below safe temp levels. Course of Action: First and
foremost remove any wet clothing from the victims
body and get them dry ASAP. You will want to gradually warm the victim by
adding layers gradually. Once they have reached a safe temp put them in warm,
dry clothing and have them move to a warm, dry place. Once you have moved them
to a warm environment give them warm liquids but make sure they do not contain
any alcohol or caffeine. Usually most people think of tea but make sure its a non
caffeinated tea. The reason i keep saying gradually is cause you do not want to warm the victim to quickly or
submerse them in a warm bath because it could cause heart problems.
Frostbite
- Symptoms: The part of the body that is frostbitten
will have a loss of sensation. The skin will appear waxy. It will also be cold
and white, yellow, blue or flushed. Possible Condition: Parts
of your body have been exposed to extremely low temperatures for an extended
period of time. Course of Action: Remove any
accessories from the area that has been exposed and is frostbitten. Immediately
soak the affected area in a warm bath (make sure the water is no more then 105 degrees F) until color
and warmth returns. Dress frostbitten area with sterile dressings and bandages.
If your hands and feet are frostbitten place the gauze between the toes and
fingers. A tip to help warm up the hands is to place them under your armpits;
and if possible place your frostbitten feet on another persons stomach. It is very important to remember
absolutely DO NOT RUB FROSTBITTEN SKIN.
REFERENCES:
Principal:
1.
Hygiene
and human ecology. Manual for the students of higher medical institutions/ Under the general editorship of V.G. Bardov.
– K., 2009. – PP. 14-34,
71-106.
2.
Datsenko I.I., Gabovich R.D
.Preventive medicine. - K.: Health, 2004, pp. 14-74.
3.
Lecture
on hygiene.
additional:
1.
Kozak D.V., Sopel O.N., Lototska O.V. General Hygiene and Ecology. – Ternopil: TSMU, 2008. – 248 p.
2.
Dacenko I.I., Denisuk O.B., Doloshickiy S.L. General hygiene: Manual for practical studies. -Lviv:
Svit, 2001. - P. 6-23.
3.
A
hand book of Preventive and Social Medicine. – Yash
Pal Bedi / Sixteenth Edition, 2003 – p.
26-36, 92-97.
