Heat Stress Management Pavel C ASTU UK CB 050 Vojenská chemie, toxikologie ochrana před vysoce toxickými látkami Přírodovědecká fakulta Masarykovi university Brno Jaro 2011 Heat Exhaustion Degrees Celcius Body temperature Body temperature must be maintained within very narrow limits for optimum physical and mental performance. The man has to maintain thermal balanced exchanges with outside environment, permitting him to maintain his body temperature on non-dangerous level. The man's core body temperature can not exceeds 38,5°C, and the difference between core temperature and skin temperature cannot be less than 1 °C to have correct thermal exchange. Metabolic Heat The body produces heat due to metabolic process. The overall man's metabolic rate consists of basal metabolic rate plus work metabolic rate depend on his current activity. The body produces more heat during work than rest. At body rest it is lowest with a value of about 115 Watt with the standard man sitting or about 160 Watt when standing. Thus total thermal metabolic rate has to be kept in balance with environment not to exceed optimal core body temperature. Thermal balance Thermal balance of a man is influenced biochemical process of basal metabolic rate plus work metabolic rate, evaporation of sweat, and heat energy transfer by radiation, conduction, convection and sun radiation Heat Energy Transfer i represents nature way of cooli | wet surfaces. Liquids during their evaporation consume heat energy resulting in cooling surface or environment. Sun Radiation represents transmitting of heat energy by infrared radiation and its absorption on surface, resulting increasing temperature of a subject. Direct sun radiation is eliminating by covers or shade. Conduction represents transmission of heat energy through a substance from a region of higher temperature to a region of lower temperature. Region/objects have to be physically in direct contact. Convection represents transfer/exchange of heat energy a solid surface in gas or liquid media by upward movement of the heated and less dense medium. Radiation represents emission of energy as electromagnetic waves Heat Stress Environment Normally, the body cool itself be evaporation of sweat and radiation of heat at the skin's surface. The combination to solar and non-solar radiant energy or enclosed areas with high temperature and high humidity, metabolic heat production, and the used of impermeable (which prevents evaporative cooling) as well air permeable protective clothing place an individual/responder at high risk for heat injury. Adding layers over the standard cloth of workers increase the risk of heat stress even in moderate environmental temperatures and work intensity 39 — 38,5 B 38 37,5 37 36,5 Time-pattern of Rectal Temperature Standard Man v=1.0 m/s 30% r.h. A 20°C 280W A 30°C 280W A 40°C 280W -O- 20°C 350W -O- 30°C 350W 40°C 350W O 20°C 450W O 30°C 450W ♦ 40°C 450W 10 20 30 40 50 60 70 80 90 100 110 120 Time in [min] Factors to Predispose Heat Stress ■ Lack of physical fitness ■ Obesity ■ Dehydration ■ Lack of acclimatization ■ Age ■ Sunburn ■ Diarrhea ■ Infection ■ Chronic disease ■ Alcohol, tobacco and drug use Heat Stress Symptoms Heat Rash results from continuous exposure to heat or humid air Heat Cramps are caused by heavy sweating with inadequate fluid intake Warning signs vary but may include the following: ■ Muscle spasm ■ Pain in the hands, feet, and abdomen Heat Stress Symptoms Heat Exhaustion is a milder form of heat-related illness ■ Heavy sweating ■ Paleness ■ Muscle Cramps ■ Tiredness ■ Weakness ■ Dizziness ■ Headache ■ Nausea or vomiting ■ Fainting ■ Skin: may be cool and moist ■ Pulse rate: fast and weak ■ Breathing: fast and shallow Heat Stress Symptoms Heat Stroke is the most serious heat-related illness. Body temperatures rise to 41 °C or higher within 10 to 15 minutes. Heat stroke can cause death or permanent disability if emergency treatment is not provided ■ An extremely high body temperature above 39,5°C ■ Red, hot, and dry skin (no sweating) ■ Throbbing headache ■ Lack of perspiration ■ Nausea ■ Dizziness and confusion ■ Rapid, strong pulse ■ Coma First Aid to Heat Illness Get the person to a shady area and if possible, seek an air-conditioned environment Drink cool, nonalcoholic, non-caffeinated beverages (avoid extremely cold liquids because they can cause cramps) Get medical assistance as soon as possible First Aid to Heat Illness ■ Cool the person rapidly, using whatever methods you can. For example: ■ Immerse the person in a tub of cool water; ■ Place the person in a cool shower or spray the person with cool water from a garden hose; ■ Sponge the person with cool water; ■ Wrap the person in a cool, wet sheet and fan him vigorously (if the humidity is low) First Aid to Heat Illness Monitor body temperature and continue cooling efforts until the body temperature drops to 38,5°-39°C Monitor heart pulse rate and blood pressure Rest and do not engage in strenuous activities Factors with Using PPE PPE restricts heat loss mechanisms because of its high insulation and low permeability to water vapor. In addition, physical work tasks require more effort when individuals wear protective clothing because of added weight, and restricted movement PPE restricts vision and hand operation capabilities This results in more body heat to be dissipated than normal and body temperature tends to rise quickly Hand operation capabilities Hand operation capabilities Factors with Using PPE ■ Encapsulated suits increase the heat strain associated with most environments and work rates by creating a microenvironment of small volume around worker's body. ■ The impermeability to vapor of the suit crates high local humidity, restricting evaporative cooling and conductive/convection cooling. ■ In effects, the suit creates an environment (tropical conditions) at the body surface hotter and wetter under almost any circumstances than the environment outside the suite. Factors with Using PPE The amount and type of personal protective equipment worn is directly related to reduce work tolerance and the risk of heat stress. Protective clothing and equipment add weight and bulk, and diminish or prevent liquid and vapor exchange is resulting into: Severely reduce the body's normal heat exchange mechanism by evaporation, convection, and radiation. Increases energy expenditure by about 1.2 percent for every kilogram of added weight. A bulky suit can increase by 2 to 4 times the energy ordinarily needed to perform task. Recommendation Therefore, when selecting protective equipment, carefully evaluate each item's health benefit against its potential for increasing heat stress risk. Once protective equipment is selected, determine the length of the work period based on: Work rate Ambient temperature Sun radiation and other environmental factors Type of protective ensemble Individual worker characteristics Work Intensity Factors Work Intensity Work Activity Metabolic Rate[W] \ /o r\ / 1 inh+ Sitting, Laying, Standing, Driving Truck Light Observing, Walking Hard Surface 3.6 km/h, load 0-30kg 175-325 Moderate Walking Reconnaissance, Fitness Exercise Walking Hard Surface 5.6 km/h, 20kg load 325-400 Heavy Pick and Shovel, Decontamination 400-500 Very Heavy Carry casualty on stretches Walking Hard Surface 5.6 km/h, 30kg load 500 and above work-rest" Regime of cycles "work-rest" has to carefully planed and executed. Recommended work-rest schedule should be for example, 10-15 minutes of work and Note that continuous work under these conditions may lead to heat casualties after 49 minutes, see Graph #1. 39 -i Time-pattern of Rectal Temperature in regime Work & Rest v=1,0 m/s T=40°C 30%r.h. O ^ 38,5 E 3 38 2 CD Q. £ 37,5 o <><><><><><> 0,5 : I 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 o very Light Work -*- Light Work Ambient Temperature [°C] — — Moderate Work —a— Heavy Work Monitoring to Prevent Heat Stress Because the occurrence of heat stress depends on a variety of factors, all workers, even those not wearing protective equipment, should be monitored For worker wearing semi-permeable or impermeable encapsulating ensembles, monitor when ambient temperature is above 21 °C. It may be also necessary to monitor at lower temperatures if humidity is high Frequency of Physical Monitoring Temperature Semi-permeable Suit Impermeable Suit 32 or above °C After 45 minutes After 15 minutes 31-32 60 30 28-31 90 60 25-28 120 90 22-25 150 120 Monitoring to Prevent Heat Stress To monitor individual it is recommended to measure: Heart Rate Oral or Ear temperature Skin temperature Body Weight Heart Rate Count the radial pulse during a 30-second period immediately following the end of a work period. If the heart rate exceeds 140 beats per minute at the end of a work period and 100 beats per minute at the end of a rest period, shorten the next work cycle by 1/3rd or lengthen the rest period. If the heart rate still exceeds 140 beats per minute at the end of the next work cycle, shorten the following work cycle by 1/3rd or lengthen the rest period by 1/3rd 150 n TIME-pattern of HEART PULSE in Climatic Chamber at 25°Celsia 10 15 20 25 30 35 40 45 50 55 60 65 Time [min'_ — SP ■ -PM —OF Oral or Ear Temperature Use a clinical thermometer 3 minutes under the tongue or ear infrared thermometer for reading core temperature within few seconds. If oral/ear temperature exceeds 37,5 °C, shorten the next work cycle by 1/3rd or lengthen the rest period by 1/3rd. If oral/ear temperature still exceeds 37,5 °C, shorten the following work cycle by 1/3rd or lengthen the rest period by 1/3rd. Do not permit a worker to wear a semipermeable or impermeable protective suit when his oral/ear temperature exceeds 38-38.5 °C. Ear Temperature Ear Thermometer 0 standard man 39 38.5 38-°"DISCOMFORT 37.5 37.0- 36.5 2 Work = 150 Tnin = 50% 120 ISO 180 TIME in nin 210 240 270 300 Figure 12 : Time-pattern of rectal temperature-Ensemble E1 Body Weight It is recommended if possible measure body weight at the beginning and end of each work day to see enough fluids are being taken to prevent hydration. Do not allow more than a 1.5 % body weight loss a working day. Measures to Prevent Heat Stress ■ Proper training and preventative measures will help avert serious illness and loss of work capability. ■ Preventing heat stress is particularly important because once someone suffers from heat stroke or heat exhaustion, that individual is predisposed to additional heat injuries. ■ To avoid heat stress, management should take the following steps: ■ Moderating the heat strain associated with an encapsulating ensemble is accomplished in the following ways: Work Schedule Modify work/rest schedules according to monitoring requirements - generally, for every hour of work, and allow 30 minutes rest. Work-rest cycles to permit cooling and rehydration, and examination. Mandate work slowdowns as needed. Rotate personnel: alternate job functions to minimize overstress or overexertion at one task. Perform work during cooler hours of the day if possible Monitoring of Temperature and Wind Provide Shaded Area for Responders Drinking regime A worker in impermeable suit performing a moderately intense task at an adjusted temperature exceeding +27-30°C could lose as much as 1 liter per hour working according the work/rest schedule or 2 liter per hour if working continuously. This should represent deficiency water of 7-8 liter per 8 hours. More water may be required depending on the ambient temperature and humidity. The individuals working in hot environment will excrete also significant amount of salt during sweating. Drinking regime When heavy sweating occurs, encourage the worker to drink more. Use following strategies: Maintain water temperature at 10-17 °C. Include also drinks enriched with minerals/salts to adjust electrolyte balance in body. Provide small disposable cups that hold about 0.2 liter (2 del) of water. Have workers drink 2-4 cups (0.4-0.5 liter) of fluid-preferable water or diluted drinks, before beginning work. Urge workers to drink 1 or 2 cups every 15 to 20 minutes, or at each monitoring break. Weight workers before and after work to determine if fluid replacement is adequate. Physical Fitness Provide an aerobic and/or other exercise program Acclimatize workers to site work conditions: temperature, protective equipment, and workload Urge workers to maintain normal weight levels. Discourage smoking and drugs consumption during off hours. Training Train workers to recognize and treat heat stress. As part of regular acclimatization and PPE performance training, identify also the symptoms of heat stress, and providing heat illness first aid Microclimate Cooling Provide cooling devices to aid natural body ventilation during prolonged work or severe heat exposure. Reduce body temperature by increasing the temperature gradient across the suit: shielding individual from radiant heat source, cooling the work space or, in dry environments, wetting the surface of the suit with field showers or hose sprayers. Loose fitting cotton or integrated fabric underwear and/or clothing to help absorb moisture and protect skin from direct contact with heat-absorbing protective clothing. Microclimate Cooling Microclimate cooling systems in which an air or liquid cooled vest/jackets, suits worn under or above PPE removes heat away from skin. Another principle is based on forced ventilation of body space under PPE, when cleaned ambient air helps evaporate sweat from skin and reduce humidity inside of protective suit. Forced evaporation of sweat provides natural cooling effect. Wet Cooling Coverall Provide Cooling Shower Cooling Vest Cooling Underwear Ventilation Suit Ventilation Suit Cooling Filtration-Ventilated Unit Maximum Work Times in IPE [Permeable Suit with Protective Mask] 600 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Ambient Temperature [°C] Very Light Work Light Work Moderate Work Heavy Work Maximum Work Times Working in IPE [Permeable Suit and Protetive Mask] 60 50 40 30 20 10 A_6_ -4- _ 0 —i 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Ambient Temperature [°C] o Moderate Work Heavy Work Maximum Work Times Working in IPE [Impermeable Suit and Protetive Mask] 250 200 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 Ambient Temperature [°C] o Mode rate Work Medical Surveillance Medical surveillance is the systematic collection, analysis, and dissemination of disease data on groups of workers. It is designated to detect early signs of work-related illness. A hazardous material work site medical program should provide the following surveillance: Periodical medical examination (with follow-up examinations, when appropriate), and Termination examination Medical Testing Program pcastulik@yaahoo.co.uk