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.
“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.
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.
standards are definite ranges of environmental factors, which are optimal, or
the least dangerous for human life and health. In
§ 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 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
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.
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.
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.
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
(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.
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.
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.
•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.
•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.
•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.
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.
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:
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 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 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 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.
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 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.
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 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.
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
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.
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%.
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.
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.
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.
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.
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.
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).
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.
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.
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.
•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.
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 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.
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.
•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.
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.
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.
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.
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.
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.
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.
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
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.
At high altitudes (1500m and above), there is still approximately 21% of oxygen in the air, but due to the low atmospheric pressure (B < A), the partial pressure of oxygen is reduced. Due to the pressure gradient, significantly more energy is also required for the lungs to take in oxygen. Hence, to adapt to the difficulty of obtaining and lack of oxygen, the body will increase the mass of red blood cells and hemoglobin in the blood, as well as reduce muscle metabolism to enable a more efficient use of oxygen. This effect is able to last for up to 2 weeks after returning to lower altitudes giving altitude trained athletes a competitive advantage.
When the atmospheric pressure drops, tissues expand. The expansion of tissues in and surrounding joints aggravates the nerves, causing pain. Thus, patients living in geographical locations with a higher atmospheric pressure tend to experience a greater severity of osteoarthritis (pain in the joints due to expansion of tissues).
Drops in atmospheric pressure also have an impact on headaches, particularly sinus headaches. When atmospheric pressure drops (such as in an ascending airplane or before a storm), gases in the sinuses and ears are at a higher pressure than those of the surrounding air. The air pressure tries to equalize, causing pain in the face and ears. Those that suffer from chronic sinusitis or have a cold have the most issues, as the air becomes trapped in the sinuses and is unable to equalize.
Increases in atmospheric pressure (such as in a descending airplane) results in a condition called “ear popping” where air particles rushes into the ears to balance out the pressure inside and outside of the ears. This may result in pain for some people.
Other health effects of high pressures such as that during diving could be found at Effects of Hydrostatic Pressure on the human bodympression Sickness
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
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.
•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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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!!!
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.