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Heat Stress Prevention Working in Hot Weather - Heat Stress Awareness & Prevention Guidelines Working, playing or exercising in the hot, muggy days of summer brings the risk of experiencing heat-related disorders ranging from minor irritation of a heat rash to serious conditions such as fainting, heat exhaustion or heat stroke. This guideline was prepared to provide information and precautions for anyone working in hot conditions and especially for those working outdoors. Review this information to learn about the causes of heat stress; symptoms of heat-related disorders; first aid or emergency medical attention, and most importantly - prevention measures. (Refer to Table #1 on page 6) What is Heat Stress? “Heat stress” refers to the overall heat burden to a person from all environmental sources (hot equipment or processes, sunlight), physical activities performed and clothing worn. All these factors must be taken into consideration when assessing the risk of heat stress. Mild or moderate heat stress may cause discomfort, but is not harmful to health. However, the risk of heat-related disorders increases as the heat stress increases and these can reach levels that are dangerous to health. WHO’S AT RISK? Anyone! Even the young and fit can be affected by heat stress. Those generally at highest risk of suffering a heat-related disorder are those who: Work outdoors or in close proximity to significant heat sources such as furnaces, ovens or hot asphalt. Perform strenuous work as this contributes to the body’s overall heat burden. Don’t self-pace or take regular breaks in cooler areas (e.g. shady or air-conditioned areas). Don’t consume enough water. Are susceptible because of a medical condition. Don’t recognize or ignore symptoms of heat stress. What Contributes to Heat Stress? Temperature As the air temperature increases, your body must work harder to keep cool. Relative Humidity While the ambient air temperature is an important factor, the relative humidity generally plays a more significant role in the risk of heat stress. The reason for this is sweat does not evaporate as easily at higher relative humidity levels and this reduces the body’s ability to cool itself. Page 1 of 7 Heat Stress Prevention Metabolic Heat Load (from physical effort) Exercising, playing or performing physical activities generates body heat. So, the harder you work the more body heat you generate. This metabolic heat adds to the overall heat stress burden and the body must work harder to keep cool. Work categories can be grouped into light, moderate or heavy based on the amount of energy used. Radiant Heat Sources Radiant heat refers to heat [energy] emitted from hot sources such as ovens, furnaces or other hot processes, or from the sun if you are outside. Clothing Lightweight summer clothing typically consists of pants and a shirt. Additional clothing or body coverings, hard hats, helmets or sports equipment for example, add to the overall heat load. Individual or Medical Factors Some personal medical conditions, low salt diets, medications and individual levels of fitness may affect how you are able to cope with heat. Consult with your physician if you are concerned about working in the heat. How Does The Body Cope with Heat? The body has mechanisms that help maintain a safe and relatively steady internal temperature of 37°C: Sweating (cooling effect of evaporation) Increasing blood flow to the extremities Increasing breathing rate. Acclimatization-getting used to hot conditions Sweating and Dehydration Sweating combined with inadequate fluid replacement is the biggest culprit when it comes to suffering serious, adverse health effects. Sweating can lead to dehydration and subsequent complications. At high humidity levels [muggy weather], sweat does not evaporate well and the body’s ability to cool itself is reduced. This increases the risk of overheating and becoming dehydrated. Acclimatization Acclimatization refers to a gradual adaptation of an individual to tolerate heat stress. Acclimatization is a slow, complicated process and only occurs after physical activity under heat stress conditions. The longer you work hard in the heat, the better your body becomes at adjusting to the heat. A person will not be fully acclimatized to a sudden higher level such as during a heat wave. In Ontario, hot spells seldom last long enough to allow acclimatization and summers are not hot enough for workers doing light work (sitting, standing, light arm work) to be considered acclimatized. This is important because you must be careful to avoid intensely working or exercising if it suddenly becomes very hot and/or humid.1 If you are not used to working in the heat then you should take a week or two to get “acclimatized” or used to the heat. 1 Exposure to workplace heat sources may permit acclimatization. Page 2 of 7 Heat Stress Prevention There are a few ways to become acclimatized: If you are experienced on the job, limit your time in hot working conditions to 50 per cent of the shift on the first day, 60 per cent of the shift on the second day, and 80 per cent of the shift on the third day. You should work a full shift the fourth day. If you are not experienced on the job (ex. new employee) you should start off spending 20 per cent of the time in hot working conditions on the first day and increase your time by 20 per cent each subsequent day. You should be able to work a full shift on the fifth day. Another option is to gradually increase the physical demands of the job over a week or two instead of progressively increasing the exposure times. CAUTION! It may take longer for you to acclimatize if you have health problems or are not in good physical condition. Acclimatization can be reduced or lost quickly as your level of acclimatization begins to diminish when the work under heat stress conditions stops. A noticeable loss occurs if you are away from work for four days or more. HEAT STRESS PREVENTION - COPING WITH HEAT AND HOT WEATHER Here are some tips to help you cope with hot, humid weather and protect yourself from heat stress: Take time to get used to working in the heat (see section on acclimatization) Wear light coloured and lightweight clothing. Keep hydrated by drinking plenty of cool fluids (preferably water). Drink at least one cup every 20 minutes - even if you aren’t thirsty! Take rest breaks in cool or shady areas. Schedule work for cooler periods of the day (early morning or evening). Avoid working in peak temperatures if possible. Adjust your work pace according to the environmental conditions and your abilities. Reduce the amount of physical effort required to perform strenuous tasks. Watch for signs of heat stress in co-workers. Seek medical attention if you feel dizzy or light headed. Contact your supervisor if you have concerns regarding working in the heat Never ignore signs of heat stress! Page 3 of 7 Heat Stress Prevention Humidex Rating and Heat Stress Prevention Guidelines for Hot Weather Humidex Rating Environment Canada’s “Humidex” rating is a widely used subjective rating of how hot the temperature “feels” based on combinations of temperature and relative humidity (refer to Table #2 on page 7 for determining humidex levels). It is commonly reported in the media to provide heat stress awareness and warnings for the general population2 based on various degrees of comfort/discomfort. Humidex ranges and the corresponding degrees of comfort are summarized in the following table. Table #3 Humidex and Comfort Levels Humidex Degree of Comfort 20 – 29 No discomfort 30 – 39 Some discomfort 40 – 45 Great discomfort; avoid exertion 46 and over Dangerous; possible heat stroke Humidex Based Response Plan The Occupational Health Clinic for Ontario Workers (OHCOW) developed a simplified approach for managing heat stress in the workplace by correlating recognized heat stress exposure guidelines3 with humidex. This heat response plan involves simultaneously measuring temperature and relative humidity (see note #3 below) and recommends appropriate rest periods and responses for various humidex levels. The humidex based response plan is summarized in the table below. Table #4 Summary Humidex Based Response Plan Humidex 1 (Moderate Unacclimatized work Action & Heavy Acclimatized work) 45+ Only medically supervised work 42-44 Work with 45 min/hr relief 40-41 Work with 30 min/hr relief 38-39 Work with 15min/hr relief 34-37 Warn for symptoms & extra water 30-33 Alert for symptoms & extra water 25-29 Water as needed *Humidex 45+: heat stress should be managed as per ACGIH TLVs Humidex 2 (Moderate Acclimatized & Light Unacclimatized work) 50+* 47-49* 45-46* 43-44 40-42 36-39 32-35 Refer to OHCOW’s full Heat Stress Response Plan document. Notes: (1) The ideal heat stress prevention plan allows workers to regulate their own pace of work, rest breaks and fluid intake by “listening to their bodies” without the need for measurements. (2) Use of the Humidex Response Plan may require adjustments for clothing or radiant heat sources and/or may not be appropriate to use at all. Contact the Occupational Health and Safety Office if you have any questions or require more information regarding heat stress in the workplace. (3) Humidex is not measured directly, it is determined from charts using temperature and relative humidity. Also, media reports of Humidex refer to the general outdoor conditions that may not be representative of your particular location. So, it’s important to take site-specific temperature and relative humidity measurements to determine the Humidex. Measurements must be taken in the shade. 2 3 People of all ages [e.g. young and elderly] ACGIH WBGT TLVs Page 4 of 7 Heat Stress Prevention Recommended weather/environmental triggers for implementing hot weather plans include: • Humidex (local or site specific) reaching or exceeding 35 • Environment Canada humidex advisory (air temperature exceeding 30ºC and humidex exceeding 40) • • Environment Canada weather reports Heat waves (three or more days of temperatures of 32ºC or more); and/or • Ontario Ministry of the Environment smog alert. Click here to view the Ministry of Labour's Heat Stress Guideline Click here to view CCOHS Information on Humidex and Heat Stress Click here to view Environment Canada's Information on Heat and Humidity Please contact the Occupational Health and Safety Department at extension 2225 if you have any questions regarding working in the heat. Remember to always… Think Safe! Work Safely! Occupational Health & Safety Office May 2015 Page 5 of 7 Heat Stress Prevention Table #1 HEAT STRESS SYMPTOMS, TREATMENT AND PREVENTION4 Cause Symptoms Heat Rash Hot humid environment; plugged sweat glands. Heat Cramps Heavy sweating from strenuous physical activity drains a person's body of fluids and salt, which cannot be replaced just by drinking water. Cramps occur from salt imbalance resulting from failure to replace salt loss from heavy sweating. Fainting Fluid loss and inadequate water intake and standing still, resulting in decreased blood flow to brain. Usually occurs in unacclimatized persons. Heat Exhaustion Fluid loss and inadequate salt and water intake causes a person's body's cooling system to start to break down. Heat Stroke If a person’s body has used up all its water and salt reserves, it will stop sweating. This can cause body temperature to rise. Heat stroke may develop suddenly or may follow from heat exhaustion. Red bumpy rash with severe itching. Painful cramps commonly in the most worked muscles (arms, legs or stomach) which occur suddenly at work or later at home. Heat cramps are serious because they can be a warning of other more dangerous heat-induced illnesses. Sudden fainting after at least two hours of work; cool moist skin; weak pulse. Heavy sweating; cool moist skin; body temperature over 38°C; weak pulse; normal or low blood pressure; person is tired and weak, and has nausea and vomiting; is very thirsty; or is panting or breathing rapidly; vision may be blurred. High body temperature (over 41 C) and any one of the following: the person is weak, confused, upset or acting strangely; has hot, dry, red skin; a fast pulse; headache or dizziness. In later stages, a person may pass out and have convulsions. Treatment Change into dry clothes often and avoid hot environments. Rinse skin with cool water. Move to a cool area; loosen clothing, gently massage and stretch affected muscles and drink cool salted water (1/4-1/2 tsp. salt in 1 litre of water) or balanced commercial fluid electrolyte replacement beverage. If the cramps are severe or don't go away after salt and fluid replacement, seek medical aid. Salt tablets are not recommended. Wash regularly to keep skin clean and dry. Reduce activity levels and/or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke. GET MEDICAL ATTENTION. Assess need for CPR. Move to a cool area; loosen clothing; make person lie down; and if the person is conscious, offer sips of cool water. Fainting may also be due to other illnesses. Reduce activity levels and/or heat exposure. Drink fluids regularly. Move around and avoid standing in one place for too long. Workers should check on each other to help spot the symptoms that often precede heat stroke. GET MEDICAL ATTENTION. This condition can lead to heat stroke, which can kill. Move the person to a cool shaded area; loosen or remove excess clothing; provide cool water to drink; fan and spray with cool water. Do not leave affected person alone. Reduce activity levels and/or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke. CALL AMBULANCE. This condition can kill a person quickly. Remove excess clothing; fan and spray the person with cool water; offer sips of cool water if the person is conscious. Reduce activity levels and/or heat exposure. Drink fluids regularly. Workers should check on each other to help spot the symptoms that often precede heat stroke. Never ignore signs of heat stress! 4 Prevention Ministry of Labour Heat Stress Health and Safety Guidelines, May 2013 Page 6 of 7 Heat Stress Prevention Table #2 Determining Humidex Rating and Comfort Ranges 21 °C 100% 29 95% 29 90% 28 85% 27 80% 27 75% 26 70% 26 65% 24 60% 24 55% 23 50% 23 45% 22 22 °C 31 29 29 28 28 27 26 26 24 24 23 23 23 °C 33 32 32 31 30 29 28 27 27 26 25 24 23 24 °C 35 34 33 33 32 31 30 29 28 28 27 26 26 25 25 °C 37 36 35 34 33 33 32 31 30 29 28 27 27 26 26 °C 39 38 37 36 35 34 33 32 31 31 29 28 28 27 27 °C 41 40 39 38 37 36 35 34 33 32 31 30 29 28 28 28 °C 43 42 41 41 39 38 37 36 35 34 33 32 31 29 28 29 °C 46 45 44 43 42 41 39 38 37 36 34 33 32 31 30 30 °C 48 47 46 44 43 42 41 40 38 37 36 35 34 33 31 31 31 °C 50 49 48 46 45 44 43 41 40 39 38 36 35 34 33 31 32 °C 52 51 50 49 47 46 45 43 42 41 39 38 37 36 34 33 33 °C 55 54 52 51 50 48 47 46 44 43 42 40 38 37 36 34 34 °C 58 57 55 53 52 51 49 48 47 45 43 42 41 39 37 36 58 57 56 54 52 51 49 48 47 45 43 42 41 38 37 58 57 56 54 53 51 50 48 47 45 43 42 40 38 58 57 55 53 51 50 49 47 45 43 42 40 57 56 54 52 51 49 47 46 43 42 40 56 54 53 51 49 47 45 43 41 57 54 52 51 49 47 44 43 56 54 52 50 48 46 44 56 54 52 50 48 46 56 54 51 49 47 35 °C 36 °C 37 °C 38 °C 39 °C 40 °C 41 °C 42 °C 43 °C Humidex Degree of Comfort 20 – 29 No discomfort 30 – 39 Some discomfort 40 – 45 Great discomfort; avoid exertion 46 and over Dangerous; possible heat stroke Page 7 of 7 40% 35% 30% 25% 20%