Monitor Thermal Stress EO 007.02 Monitor Thermal Stress

References Traveller’s Health, 4th Edition CF General Safety Manual, Volume 2, Ch 39 CCOHS - Working in Hot Environments, 2nd Edition DAOD 5021-2 Heat Stress (CFAO 34-47) CF H Svcs Gp PG 4440-10 Heat Stress CF Heat Stress Pamphlet

Effects of Climatic Extremes Humans are very adaptable provided they are properly prepared: -equipment -acclimatized -proper, effective PPE and clothing

Environmental Conditions Temperature Wind Speed Moisture Radiation .the weather conditions you encounter can be defined by four factors: temperature, humidity, wind-speed, and amount of solar radiation.

Environmental Conditions Temperature: The termoneutral zone for an adult, that is the temperature at which an adult at rest lying on a hammock in the shade wearing scanty clothing, neither gains nor loses heat, is 28°C. Humans regulate their body temperature very accurately, and even minor variations in temperature of vital body organs cause a person to feel unwell. Serious variations may results in death.

Environmental Conditions Temperature above 28°C, or any form of exertion at a temperature near to this value, mean that the body must actively lose heat to maintain a normal core temperature. At temperatures below this value, a resting adult will cool unless clothed or taking exercise. The lower the temperature, the more protection an individual needs. However, temperature by itself is a poor guide to environmental control

Environmental Conditions Wind speed in the heat is acceptable as it evaporates sweat and keeps a person cooler. Wind chill in the cold is the opposite and cools too fast. Wind chill factors

Environmental Conditions Moisture: Water has appro 30 times the thermal conductivity of air and moist air conducts heat much more rapidly than dry air. Humid environments are less comfortable than dry conditions. Humid winter vs dry winter.

Environmental Conditions Radiation: Obvious difference in temp from direct sunlight and shaded temp. Less obvious in high altitude where the atmosphere has less chance to attenuate the sunlight. These are all factors in the WBGT heat index used to determine work rest cycles. There is always a difference between measured temperature in shade and sunlight. Radiant heat warms, but can also burn exposed skin.

Climatic Types Four Main Types: Hot and Dry Hot and Wet Cold and Dry Cold and Wet The combination of these four factors enables us to describe four extreme climates.

Climatic Types Hot and Dry Deserts have low humidity, little rain, scanty vegetation, cloudless skies intense sunshine, and winds that vary from light breezes to violent storms.

Hot and Dry At night, clear skies allow rapid heat loss to space by radiation and convection, so there can be heavy dews and occasional frost.

Climatic Types Hot and Wet Abundant moisture, frequent cloud cover, and shade from tree canopy combine to maintain the temperature at a fairly constant level throughout the year with little variation between day and night.

Climatic Types Cold and Dry In polar areas shade temperature rarely, if ever, rises above freezing. Much of the land is covered with snow and ice. If the skies are clear there will be brilliant summer sunshine and a lot of radiant heat.

Climatic Types Cold and Wet Temperate Climates – North America, Western Europe etc. Air Temps between 15 °C and -2 °C are comfortable when dry, but can be hazardous when combined with wind. (Winnipeg for example.)

Body Temp and Control Homeostasis: Maintain a body’s core temp at 37°C (+/ -) 0.5°C Core temp can fall when heat loss is greater than heat generation Controlled by heat production and heat transfer methods A 1.5 C difference can disturb natural functions in the body, organs etc. Comfort Zone: For most people when the Air Temperature ranges from 18 - 22oC and the RH is about 45%. Under these circumstances heat production inside the body equals the heat loss from the body and the internal body temperature is kept around 37oC.

Body Temp and Control Heat Production generated through metabolism Examples of heat production - exercise, involuntary shivering Heat Transfer:

Body Temp and Control Heat Transfer from hot to cool body to environment and vice versa 4 main methods radiation, conduction, convection and evaporation

Body Temp and Control Radiation all objects radiate heat in the form of electromagnetic waves. Can be seen with infrared cameras. In the outside environment (cold) we will radiate heat and cool down.

Body Temp and Control Conduction transfer of heat by direct contact ie touching metal objects in the winter. Metals and water conduct heat away rapidly.

Body Temp and Control Convection transport of heat by motion of warmed gases and liquids. Clothing will help reduce the effects of convection on the body.

Body Temp and Control Evaporation if the skin surface is wet, the evaporation of water will cool the skin (sweating). If body temp high, sweat good. If cold, this is bad and it may cool down too rapidly. modified by: activity, shelter, clothing and technological aids

Occupational Exposure to Cold Single most important aspect of life-threatening hypothermia is the fall in the deep core temperature of the body Deep core temperature should not fall below 36oC Pain in the extremities may be the first early warning of danger to cold stress Fatal exposure to cold among workers have almost always resulted from accidental exposures involving failure to escape from low environmental air temperatures or from immersion in low temperature water. The single most important aspect of life-threatening hypothermia is the fall in the deep core temperature of the body. Workers should be protected from exposure to cold so that the deep core temperature does not fall below 36 o C (96.8 o F); lower body temperatures will very likely result in reduced mental alertness, reduction in rational decision making, or loss of consciousness with the threat of fatal consequences. Pain in the extremities may be the first early warning of danger to cold stress. During exposure to cold, maximum severe shivering develops when the body temperature has fallen to 35 o C (95 o F). This must be taken as a sign of danger to the workers and exposure to cold should be immediately terminated for any workers when severe shivering becomes evident. Since prolonged exposure to cold air or to immersion in cold water, at temperatures well above freezing, can lead to dangerous hypothermia, whole body protection must be provided.

Occupational Exposure to Cold Evaluation and Control Includes protection/prevention against exposed skin and total body cooling for dry and wet conditions Regulations and recommendations are based on outdoor environmental factors ( ie temperatures and wind chill) For exposed skin, continuous exposure should not be permitted when the air speed and temperature results in an equivalent chill temperature of -32 o C (-25.6 o F). Superficial or deep local tissue freezing will occur only at temperatures below -1 o C (-30.2 o F) regardless of wind speed. At air temperatures of 2 o C (35.6 o F) or less, it is imperative that workers who become immersed in water or whose clothing becomes wet be immediately provided a change of clothing and be treated for hypothermia. Special protection of the hands is required to maintain manual dexterity for the prevention of accidents: If fine work is to be performed with bare hands for more than 10-20 minutes in an environment below 16oC special provisions should be established for keeping the workers’ hands warm. If the air temperature falls below 16oC (for sedentary, 4oC for light, - 7oC for moderate work, and fine manual dexterity if not required, then gloves should be used by the workers. To prevent contact frostbite, the workers should wear anti-contact gloves. c. When cold surfaces below -7oC (are within reach, a warning should be given to each worker to prevent inadvertent contact by bare skin. d. If the air temperature is -17.5oC or less, the hands should be protected. Provisions for additional total body protection are required if work is performed in an environment or below 4oC. The workers should wear cold protective clothing appropriate for the level of cold and physical activity: a. Wind, draft or artificial ventilating equipment should be reduced by shielding the work area or by wearing an easily removable windbreak garment. b. If the clothing on the worker may become wet on the job site, the outer layer of the clothing in use may be of a type impermeable to water and/or easily changed. c. If exposed areas of the body cannot be protected sufficiently, protective items should be supplied in heated versions. d. If the available clothing does not give adequate protective to prevent hypothermia or frostbite, work should be modified or suspended until adequate clothing is made available or until weather conditions improve.

Occupational Exposure o Cold Work-Warming Regimen Below 7oC shelters should be available and encouraged to use frequently especially with signs of frostbite/frostnip Warm, sweet drinks to help prevent dehydration and cooling Buddy system, periodic breaks and warming, clothing, and observation Dehydration, or the loss of body fluids, occurs insidiously in the cold injury due to a significant change in blood flow to the extremities. Warm sweet drinks and soups should be provided at the work site to provide caloric intake and fluid volume. The intake of coffee should be limited because of the diuretic and circulatory effects. If work is performed continuously in the cold at an equivalent chill temperature (ECT) or below -7oC, heated warming shelters (tents, cabins, rest rooms, etc.) should be made available nearby. The workers should be encouraged to use these shelters at regular intervals, the frequency depending on the severity of the environmental exposure. The onset of heavy shivering, minor frostbite (frostnip), the feeling of excessive fatigue, drowsiness, irritability, or euphoria are indications for immediate return to the shelter. When entering the heated shelter, the outer layer of clothing should be removed and the remainder of the clothing loosened to permit sweat evaporation or a change of dry work clothing provided. A change of dry work clothing should be provided as necessary to prevent workers from returning to work with wet clothing. For work practices at or below -12oC, the following should apply: a. The worker should be under constant protective observation (buddy system or supervision). b. The work rate should not be so high as to cause heavy sweating that will result in wet clothing; if heavy work must be done, rest periods should be taken in heated shelters and opportunity for changing into dry clothing should be provided. c. New employees should not be required to work fulltime in the cold during the first days of employment until they become accustomed to the working conditions and required protective clothing. d. The weight and bulkiness of clothing should be included in estimating the required work performance and weights to be lifted by the worker. e. The work should be arranges in such a way that sitting still or standing still for long periods is minimized. Unprotected metal chair seats should not be used. The worker should be protected from drafts to the greatest extent possible. f. The workers should be instructed in safety and health procedures. The training program should include as a minimum instruction in: i. Proper rewarming procedures and appropriate first aid treatment. ii. Proper clothing practices. iii. Proper eating and drinking habits. iv. Recognition of impending frostbite. v. Recognition of signs and symptoms of impending hypothermia or excessive cooling of the body even when shivering does not occur. vi. Safe work practices.

Occupational Exposure to Cold Workplace Recommendations Special caution required when dealing with the cold and: -vibration -toxic substances ☠ -snow and ice (eyes) -predisposed personnel -wind chill Special design requirements for refrigerator rooms include the following: a. In refrigerator rooms, the air velocity should be minimized as much as possible and should not exceed 1 meter/sec (200 fpm) at the job site. This can be achieved by properly designed air distribution systems. b. Special wind protective clothing should be provided based upon existing air velocities to which workers are exposed. Special caution should be exercised when working with toxic substances and when workers are exposed to vibration. Cold exposure may require reduced exposure limits. Eye protection of workers employed out-of-doors in a snow and/or ice-covered terrain should be supplied. Special safety goggles to protect against ultraviolet light and glare (which can produce temporary conjunctivitis and/or temporary loss of vision) and blowing ice crystals should be required when there is an expanse of snow coverage causing a potential eye exposure hazard. Workplace monitoring is required as follows: a. Suitable thermometry should be arranged at any workplace where the environmental temperature is below 16oC so that overall compliance with the requirements of the TLV can be maintained. b Whenever the air temperature at a workplace falls below -1oC the dry bulb temperature should be measured and recorded at least every 4 hours. c. In indoor workplaces, the wind speed should also be recorded at least every 4 hours whenever the rate of air movement exceeds 2 meters per second (5 mph). d. In outdoor work situations, the wind speed should be measured and recorded together with the air temperature whenever the air temperature is below -1oC. e. The equivalent chill temperature should be obtained from Table 2 in all cases where air movement measurements are required; it should be recorded with the other data whenever the equivalent chill temperature is below -7oC (19.4oF). Employees should be excluded from work in cold at -1oC or below if they are suffering from diseases or taking medications which interferes with normal body temperature regulation or reduces tolerance to work in cold environments. Workers who are routinely exposed to temperatures below -24oC with wind speeds less than five miles per hour, or air temperatures below -18oC with wind speeds above five miles per hour, should be medically certified as suitable for such exposures. Trauma sustained in freezing or subzero conditions requires special attention because an injured worker is predisposed to cold injury. Special provisions should be made to prevent hypothermia and freeing of damages tissues in addition to providing for first aid treatment.

Occupational Exposure to Cold Progressive clinical presentation of hypothermia: General Safety Program Chapter 39 page 39C-7 Appendix A Table 1 Have student take a look at Table 1 and explain it

Occupational Exposure to Cold Cooling power of wind on exposed flesh expressed as equivalent temperature: General Safety Program Chapter 39 page 39C-8 Appendix B Table 2 Have student take a look at Table 2 and explain it

Occupational Exposure to Cold TLV’s work / warm-up schedule for four hour work shift General Safety Program Chapter 39 page 39C-9 Appendix C Table 3 Have student take a look at Table 3 and explain it

Effects of Extreme Cold operational needs require some employees to work outdoors in conditions of extreme cold. it is important to know how to prevent these effects from occurring, and how to deal with the effects before medical help can be reached.

Effects of Extreme Cold Frostbite: Destruction of body tissues, usually in the face, hands or feet, by freezing Circulation of blood in the tissue is slowed, then stopped The skin appears a waxy white and becomes numb Can lead to destruction of tissue and loss of fingers or toes

Effects of Extreme Cold Hypothermia: Lowering of body temperature due to the prolonged exposure to cold Heat is lost from the body faster than it can be generated by metabolic activity Gradual deterioration of body function leading eventually to loss of consciousness and death

Effects of Extreme Cold Trench foot: Local cooling of the feet Usually in cold, damp or even wet conditions, and can occur under conditions less cold than those producing frostbite

Effects of Extreme Cold Clothing – most important factor is LAYERS!! maintain layers of warm air around the body be worn in a number of layers, so that one or more items of clothing can be discarded when doing heavy work outer layer should be wind-proof

Effects of Extreme Cold Clothing —gloves should also be in layers, again with a wind-proof outer layer. Mitts are warmest, but a pair of gloves should be carried for more exacting work "Mukluk" type footwear is best for the feet, provided that they will not get wet protection of the head is essential as this is where most heat loss occurs. Face masks may also be needed.

Effects of Extreme Cold Keeping dry wet clothing will conduct heat away from the body sweating should be avoided by wearing only enough layers of clothing when working hard, and by opening clothing at the neck dry socks should be put on each morning snow must be brushed off all clothing before it is put on

Effects of Extreme Cold Avoid the wind- Build windbreaks or arrange to work on the lee side of buildings or trees HEAT LOSS The body loses heat in several different ways: 1. Direct contact with cold water (greatest heat loss); 25-30 times more heat when in contact with cold wet objects than under dry conditions; 2. Contact with cold air. The rate of loss depends on the air speed and the temperature difference between the skin and the surrounding air; 3. Cold food and drink; (minimal) 4. During breathing (inhaling cold air & evaporation of water from lungs).

Effects of Extreme Cold Frostbite prevention: Use buddy system, check each other Hold his/her bare hand over the affected area to warm it up Fingers can be warmed by placing the hands close to the body, preferably under the armpits If feet are frozen, the person should not walk, take the person to warm place, see a doctor

Effects of Extreme Cold Hypothermia treatment: Slow re-warming Person should be protected from further heat loss by wrapping in blankets and moving to a medical treatment centre Unconscious patients to be handled very gently Hot water bottles or other warming devices, should not be more than comfortably warm and not be applied directly to skin

Occupational Exposure to Heat Introduction -Based on TLV’s where workers can be exposed without adverse effects -Acclimatized, fully clothed, and with proper water and salt intake -WBGT used to monitor The heat stress Threshold Limit Values (TLVs), refer to heat stress conditions under which it is believed that nearly all workers may be repeatedly exposed without adverse health effects. These TLVs are based on the assumption that nearly all acclimatized, fully clothed (e.g., lightweight pants and shirt) workers with adequate water and salt intake should be able to function effectively under the given working conditions without exceeding a deep body temperature of 38oC. Where there is a requirement to protect against other harmful substances in the work environment and additional personal protective clothing and equipment must be worn, a correction to the Wet Bulb Globe Temperature (WBGT) TLV values must be applied. Since measurement of deep body temperature is impractical for monitoring the workers’ heat load, the measurement of environmental factors is required which most nearly correlate with deep body temperature and other physiological responses to heat. At the present time, the WBGT Index is the simplest and most suitable technique to measure the environmental factors. Assessment of Heat stress Two kinds of factors must be taken into consideration when heat stress is being assessed: Situational factors Situational factors are numerous and include: type of clothing worn, degree of physical exertion required, efficiency of sweating mechanism, degree of acclimatization, psychological stress created by the danger, availability of fluids for drinking, and any additional stresses such as noise and vibration, the state of health, fatigue, and motivation. Many of these factors do not lend themselves to precise measurement and the estimation of their significance depends on experience and individual judgment. Environmental Factors The thermal effects of an environment can be assessed by measurements of air temperature, relative humidity, air movement, and radiant heat. The interaction of these factors can be correlated with comfort, discomfort and operational effectiveness

Occupational Exposure to Heat Adverse Health Effects Heat related illnesses such as heat cramps, heat exhaustion and heat stroke HEAT STROKE most serious Pregnant workers more at risk Adverse Health Effects: The most serious of heat-induced illnesses is heat stroke because of its potential to be life-threatening or result in irreversible damage. Other heat induces illnesses include heat exhaustion which in its most serious form leads to prostation and can cause serious injuries as well. Heat cramps, while debilitating, are easily reversible if properly and promptly treated. Heat disorders due to excessive heat exposure include electrolyte imbalance, dehydration, skin rashes, heat edema, and loss of physical and mental work capacity. If during the first trimester of pregnancy, a female worker’s core temperature exceeds 39 o C (102.2 o F) for extended periods, there is an increased risk of malformation to the unborn fetus. Additionally, core temperatures above 38 o C (100.4 o F) may be associated with temporary infertility in both females and males.

Work-Rest Cycle also known as workload measurements based on heat from the body combined with environmental heat TLV’s assume the workplace temperature is similar to the rest place based on an 8hr/day, 5 day/workweek light, medium and heavy loads Heat produced by the body and the environmental heat together determine the total heat load. Therefore, if work is to be performed under hot environmental conditions, the workload category of each job should be established and the heat exposure limit pertinent to the workload evaluated against the applicable standard in order to protect the worker exposure beyond the permissible limit. The TLVs are based on the assumption that the WBGT value of the resting place is the same or very close to that of the workplace. Where the WBGT of the work area is different from that of the rest area, a time-weighted average value should be used for both environmental and metabolic heat. The TLVs for continuous work are applicable where there is a work-rest regimen of a 5- day work week and an 8-hour work day with a short morning and afternoon break (approximately 15 minutes) and a longer break (approximately 30 minutes). Higher exposure values are permitted if additional resting time is allowed. All breaks, including unscheduled pauses and administrative or operational waiting periods during work, may be counted as rest time when additional rest allowance must be given because of high environmental temperatures.

Work-Rest Cycle General Safety Program Chapter 39 page 39B-2 Table 1 Have student take a look at Table 1 and explain it

Metabolic Rates General Safety Program Chapter 39 page 39B-11 Table 8 Have student take a look at Table 8 and explain it

Acclimatization Clothing: light summer clothing as customarily worn by workers when working under hot environmental conditions. if special clothing is required for performing a particular job and this clothing is heavier or it impedes sweat evaporation or has higher insulation value, the worker’s heat tolerance is reduced

Acclimatization Acclimatization and Fitness: TLVs are valid for acclimated workers who are physically fit extra caution must be employed when unacclimatized or physically unfit workers must be exposed to heat stress conditions.

Acclimatization Heat Acclimatization heat acclimatization is acquired only gradually, being fully achieved over up to three weeks of continued physical activity under heat stress conditions similar to those anticipated for future work

Water/Salt Supplementation Drinking water should be available and close enough to the work area 150 ml every 15-20 mins and cool 10-15oC Advised to use extra salt in food or water “sport drinks” not actually mentioned During the hot season or when the worker is exposed to artificially generated heat, drinking water should be made available to the workers in such a way that they are stimulated to frequently drink small amounts, i.e., one cup every 15-20 minutes (about 150 ml or 1/4 pint). The water should be kept reasonably cool, 10 o C to 15 o C (50 o F to 60 o F) and should be placed close to the workplace so that the worker can reach it without abandoning the work area. The workers should be encouraged to salt their food well during the hot season and particularly during hot spells. If the workers are unacclimatized, salted drinking water should be made available in a concentration of 0.1 % (1 g salt to 1.0 liter or 1 level tablespoon of salt to 15 quarts of water). The added salt should be completely dissolved before the water is distributed, and the water should be kept reasonably cool.

Prevention Profuse and prolonged sweating should be eliminated for long-term routine tasks Can produce dehydration and loss of body electrolytes May lead to heat exhaustion or muscle cramps Can also disturb normal cardiovascular functions

Prevention Heat stress management must always be the prevention of heat stroke, which is life-threatening and the most serious of the heat-induced disabilities Victim’s skin is hot and dry, sweating has ceased, and the body temperature may be 40 deg C or higher Immediate emergency care is needed

Heat Stress Policy DAOD 5021-2 Heat Stress Policy The WBGT Index has been selected by the CF Advisory Group as the one instrument to be used in describing physiological environments for the CF, and it shall be employed to express environmental heat stress. Policy Direction The WBGT Index has been selected by the CF Advisory Group as the one instrument to be used in describing physiological environments for the CF, and it shall be employed to express environmental heat stress. Loss of operational efficiency, both mental and physical, occurs under certain definable degrees of heat stress. Personnel have an increased resistance to heat injury when their water and salt balances are maintained, and when they are in proper physical condition. Where personnel are provided with adequate water and a normal diet with conservative addition of salt, the use of salt tablets is seldom required to maintain a salt balance, even in hot climates, except on occasion when extreme and prolonged physical exertion is necessary.

Responsibility Table Responsibilities (Where heat stress is suspected) a. D Med Svcs will develop documentation and training pertaining to the recognition, prevention and treatment of heat stress. b. Any member/supervisory staff will adopt preventive measures to minimize the risk of heat stress when conducting physical activities in a hot environment.

Responsibility Table Every CF or DND employee will take the following action when heat stress is suspected: remove the victim from activity, administer F/A, asses the condition or have it assessed by competent personnel, and take action to avoid further complication.

Responsibility Table The Unit PMed Tech will be responsible for measuring the WBGT Index and reporting the results to the Base Surgeon when reading levels exceed a value of 27°C. The Base/Wing/Fleet Surgeon shall report the results to the CO of the Unit and advise him of its effect on personnel, so that preventive measures may be implemented

WBGT Use Heat Stress Guidelines: Recognition and Prevention pamphlet

Control Measures Engineering Controls -most effective Administrative Controls Personal Protection

Control Measures Engineering controls include: Reducing Metabolic Heat Production (heat produced by the body): minimize the need for heavy physical work and the resulting build up of body heat. Reducing the Radiant Heat Emission from Hot Surfaces: Covering hot surfaces with sheets of low emissivity material such as aluminum or paint that reduces the amount of heat radiated from this hot surface into the workplace.

Control Measures Insulating Hot Surfaces: Insulation reduces the heat exchange between the source of heat and the work environment. Shielding: Shields stop radiated heat from reaching work stations.

Control Measures Ventilation and Air Conditioning: Ventilation, localized air conditioning, and cooled observation booths are commonly used to provide cool work stations. Cooled observation booths allow workers to cool down after brief periods of intense heat exposure while still allowing them to monitor equipment. Reducing the Humidity: Air conditioning, dehumidification, and elimination of open hot water baths, drains, and leaky steam valves help reduce humidity.

Control Measures Admin Controls include: Acclimatization, work-rest cycles, water/salt, education, and first aid

Control Measures Personal Protection Ordinary clothing provides some protection from heat radiated by surrounding hot surfaces. Specially designed heat-protective clothing is available for working in extremely hot conditions. In hot and humid workplaces, light clothing allows maximum skin exposure and efficient body cooling by sweat evaporation.

Control Measures Workers who move back and forth between very hot, dry indoor environments and cold winter outdoor environments find that long underwear moderates the extremes in temperatures. Eye protection which absorbs radiation is needed when the work involves very hot objects, such as molten metals and hot ovens.

Control Measures Work that requires the wearing of impermeable clothing presents an added heat burden as the clothing reduces the body's ability to dissipate heat. Under such circumstances, it is often necessary to reduce the exposure limit values of WBGT to levels below those appropriate for workers wearing light clothing.

WBGT Standards General Guidelines: A WBGT Index reading of 27°C has been designated as the maximum figure for a normal working and living environment to which personnel should be exposed General guidelines A WBGT Index reading of 27°C has been designated as the maximum figure for a normal working and living environment to which personnel should be exposed. This figure shall be used as a design criterion for military vehicles, other operational environments and personnel accommodation. When this figure is exceeded, discretion must be used in the planning of heavy exercise for unseasoned personnel. Consideration must be given to possible performance decrements in personnel engaged in more sedentary but critical tasks (flying, air traffic control, etc.).

WBGT Standards Readings above 27C The higher the temperature, the higher the humidity, the greater the physical activity and/or the more critical the task then the shorter the safe exposure time. WBGT readings above 27C guidelines On some occasions members will be exposed to more severe conditions and a WBGT Index reading higher than 27°C. This will be associated with increasing discomfort and decrease in performance. In this regard, time is a factor. Humans can, depending on the activity, tolerate high environmental temperatures without significant adverse effects if the exposure time is kept brief. The higher the temperature, the higher the humidity, the greater the physical activity and/or the more critical the task then the shorter the safe exposure time.

WBGT Standards WBGT Index reading 27°C - 29.5°C These are marginal conditions for conducting moderate to severe physical activities or critical tasks. There must be alertness in non-acclimatized personnel.

WBGT Standards WBGT Index reading 29.5°C - 31°C Heat stress can be expected in personnel conducting moderate to severe physical activities or critical tasks. These activities should be curtailed as required; particularly for non-acclimatized personnel

WBGT Standards WBGT Index reading over 31°C Moderate to severe physical activities or critical tasks should be suspended. Other activities should be curtailed as required.

WBGT Standards when the WBGT Index reading is above 29.5C, every effort should be made to reduce the adverse effects of excessive heat on personnel engaged in moderate to severe physical work or critical tasks (by reducing the time on duty, increasing rest periods, etc.). In addition, medical advice should be requested when potential heat stress situation exists in any operational activity.

Conclusion Thermal stress is a common problem, as the extremes of both hot and cold can be dangerous Keep in mind that a change in the body’s core temperature will impair performance greatly Conclusion Heat stress is a common problem, as are the problems presented by a very cold environment. Evaluation of heat stress in a work environment is not simple. Considerably more is involved than simply taking a number of air-temperature measurements and making decisions on the basis of this information. One question that has to be asked is whether the temperature is merely causing discomfort or whether the continued exposure will cause the body temperature to either fall below or rise above safe limits. Keep in mind that a change in temp greater than 5°C from the core temp will impair performance greatly.

Questions?