Regulation Information Heat Stress §1910.120(g)(5)(x) Wearing PPE puts any worker at considerable risk of developing heat stress. This can result in health effects ranging from transient heat fatigue to serious illness or death. Heat stress is caused by a number of interacting factors, including environmental conditions, clothing, workload, and the individual characteristics of the worker. Because heat stress is probably one of the most common (and potentially serious) illnesses at hazardous waste sites, regular monitoring and other preventive precautions are vital. Individuals vary in their susceptibility to heat stress. Factors that may predispose someone to heat stress include: • Lack of physical fitness. • Lack of acclimatization. • Age. • Dehydration. • Obesity. • Alcohol and drug use. • Infection. • Sunburn. • Diarrhea. • Chronic disease. Reduced work tolerance and the increased risk of excessive heat stress is directly influenced by the amount and type of PPE worn. PPE adds weight and bulk, severely reduces the body's access to normal heat exchange mechanisms (evaporation, convection, and radiation), and increases energy expenditure. Therefore, when selecting PPE, each item's benefit should be carefully evaluated in relation to its potential for increasing the risk of heat stress. Once PPE is selected, the safe duration of work/rest periods should be determined based on the: • Anticipated work rate. • Ambient temperature and other environmental factors. • Type of protective ensemble. • Individual worker characteristics and fitness. Monitoring Because the incidence of heat stress depends on a variety of factors, all workers, even those not wearing protective equipment, should be monitored. • For workers wearing permeable clothing (e.g., standard cotton or synthetic work clothes), follow recommendations for monitoring requirements and suggested work/rest schedules in the current American Conference of Governmental Industrial Hygienists' (ACGIH) Threshold Limit Values for Heat Stress. If the actual clothing worn differs from the ACGIH standard ensemble in insulation value and/or wind and vapor permeability, change the monitoring requirements and work/rest schedules accordingly. • For workers wearing semi-permeable or impermeable encapsulating ensembles, the ACGIH standard cannot be used. For these situations, workers should be monitored when the temperature in the work area is above 70°F (21°C). To monitor the worker, measure: • Heart rate. Count the radial pulse during a 30–second period as early as possible in the rest period. If the heart rate exceeds 110 beats per minute at the beginning of the rest period, shorten the next work cycle by one–third and keep the rest period the same. If the heart rate still exceeds 110 beats per minute at the next rest period, shorten the following work cycle by one–third. • Oral temperature. Use a clinical thermometer (3 minutes under the tongue) or similar device to measure the oral temperature at the end of the work period (before drinking). If oral temperature exceeds 99.6°F (37.6°C), shorten the next work cycle by one–third without changing the rest period. If oral temperature still exceeds 99.6°F (37.6°C) at the beginning of the next rest period, shorten the following work cycle by one–third. Do not permit a worker to wear a semi-permeable or impermeable garment when his/her oral temperature exceeds 100.6°F (38.1°C). • Body water loss, if possible. Measure weight on a scale accurate to "0.25 lb at the beginning and end of each work day to see if enough fluids are being taken to prevent dehydration. Weights should be taken while the employee wears similar clothing or, ideally, is nude. The body water loss should not exceed 1.5 percent total body weight loss in a work day. Initially the frequency of physiological monitoring depends on the air temperature adjusted for solar radiation and the level of physical work . The length of the work cycle will be governed by the frequency of the required physiological monitoring. Prevention Proper training and preventive measures will help avert serious illness and loss of work productivity. Preventing heat stress is particularly important because once someone suffers from heat stroke or heat exhaustion, that person may be predisposed to additional heat injuries. To avoid heat stress, management should take the following steps: • Adjust work schedules: • Modify work/rest schedules according to monitoring requirements. • Mandate work slowdowns as needed. • Rotate personnel: alternate job functions to minimize overstress or overexertion at one task. • Add additional personnel to work teams. • Perform work during cooler hours of the day if possible or at night if adequate lighting can be provided. • Provide shelter (air–conditioned, if possible) or shaded areas to protect personnel during rest periods. • Maintain workers' body fluids at normal levels. This is necessary to ensure that the cardiovascular system functions adequately. Daily fluid intake must approximately equal the amount of water lost in sweat, i.e., 8 fluid ounces (0.23 liters) of water must be ingested for approximately every 8 ounces (0.23 kg) of weight lost. The normal thirst mechanism is not sensitive enough to ensure that enough water will be drunk to replace lost sweat. When heavy sweating occurs, encourage the worker to drink more. The following strategies may be useful: • Maintain water temperature at 50° to 60°F (10° to 15.6°C). • Provide small disposable cups that hold about 4 ounces (0.1 liter). • Have workers drink 16 ounces (0.5 liters) of fluid (preferably water or dilute drinks) before beginning work. • Urge workers to drink a cup or two every 15 to 20 minutes, or at each monitoring break. A total of 1 to 1.6 gallons (4 to 6 liters) of fluid per day are recommended, but more may be necessary to maintain body weight. • Weigh workers before and after work to determine if fluid replacement is adequate. • Encourage workers to maintain an optimal level of physical fitness: • Where indicated, acclimatize workers to site work conditions: temperature, protective clothing, and workload (see "Level of Acclimatization" at the end of this section). • Urge workers to maintain normal weight levels. Table 11 Suggested Frequency of Physiological Monitoring for Fit and Acclimatized Workers a Adjusted Temperature bNormal Work Ensemble cImpermeable Ensemble 90°F (32.2°C) or aboveAfter each 45 minutes of workAfter each 15 minutes of work 87.5°–90°F (30.8°–32.2°C)After each 60 minutes of workAfter each 30 minutes of work 82.5°–87.5°F (28.1°–30.8°C)After each 90 minutes of workAfter each 60 minutes of work 77.5°–82.5°F (25.3°–28.1°C)After each 120 minutes of workAfter each 90 minutes of work 72.5°–77.5°F (22.5°–25.3°C)After each 150 minutes of workAfter each 120 minutes of work a For work levels of 250 kilocalories/hour. b Calculate the adjusted air temperature (ta adj) by using this equation: ta adj °F = ta °F + (13 x % sunshine). Measure air temperature (ta) with a standard mercury–in–glass thermometer, with the bulb shielded from radiant heat. Estimate percent sunshine by judging what percent time the sun is not covered by clouds that are thick enough to produce a shadow. (100 percent sunshine = no cloud cover and a sharp, distinct shadow; 0 percent sunshine = no shadows.) c A normal work ensemble consists of cotton coveralls or other cotton clothing with long sleeves and pants. • Provide cooling devices to aid natural body heat exchange during prolonged work or severe heat exposure. Cooling devices include: • Field showers or hose–down areas to reduce body temperature and/or to cool off protective clothing. • Cooling jackets, vests, or suits. • Train workers to recognize and treat heat stress. As part of training, identify the signs and symptoms of heat stress. Other Factors PPE decreases worker performance as compared to an unequipped individual. The magnitude of this effect varies considerably, depending on both the individual and the PPE ensemble used. This section discusses the demonstrated physiological responses to PPE, the individual human characteristics that play a factor in these responses, and some of the precautionary and training measures that need to be taken to avoid PPE–induced injury. The physiological factors that may affect worker ability to function using PPE include: • Physical condition. • Level of acclimatization. • Age. • Gender. • Weight. Heat rash may result from continuous exposure to heat or humid air. Heat cramps are caused by heavy sweating with inadequate electrolyte replacement. Signs and symptoms include: · muscle spasms, and · pain in the hands, feet, and abdomen. Heat exhaustion occurs from increased stress on various body organs including inadequate blood circulation due to cardiovascular insufficiency or dehydration. Signs and symptoms include: • pale, cool, moist skin • heavy sweating • dizziness • nausea • fainting Heat stroke is the most serious form of heat stress. Temperature regulation fails and the body temperature rises to critical levels. Immediate action must be taken to cool the body before serious injury and death occur. Competent medical help must be obtained. Signs and symptoms are: • red, hot, usually dry skin • lack of or reduced perspiration • nausea • dizziness and confusion • strong, rapid pulse • coma Physical Condition Physical fitness is a major factor influencing a person's ability to perform work under heat stress. The more fit someone is, the more work they can safely perform. At a given level of work, a fit person, relative to an unfit person, will have: • Less physiological strain. • A lower heart rate. • A lower body temperature, which indicates less retained body heat (a rise in internal temperature precipitates heat injury). • A more efficient sweating mechanism. • Slightly lower oxygen consumption. • Slightly lower carbon dioxide production. Level of Acclimatization The degree to which a worker's body has physiologically adjusted or acclimatized to working under hot conditions affects his or her ability to do work. Acclimatized individuals generally have lower heart rates and body temperatures than unacclimatized individuals, and sweat sooner and more profusely. This enables them to maintain lower skin and body temperatures at a given level of environmental heat and work loads than unacclimatized workers. Sweat composition also becomes more dilute with acclimatization, which reduces salt loss. Acclimatization can occur after just a few days of exposure to a hot environment. NIOSH recommends a progressive 6–day acclimatization period for the unacclimatized worker before allowing him/her to do full work on a hot job. Under this regimen, the first day of work onsite is begun using only 50 percent of the anticipated workload and exposure time, and 10 percent is added each day through day 6. With fit or trained individuals, the acclimatization period may be shortened 2 or 3 days. However, workers can lose acclimatization in a matter of days, and work regimens should be adjusted to account for this. When enclosed in an impermeable suit, fit acclimatized individuals sweat more profusely than unfit or unacclimatized individuals and may therefore actually face a greater danger of heat exhaustion due to rapid dehydration. This can be prevented by consuming adequate quantities of water. See previous section on "Prevention" for additional information. Age Generally, maximum work capacity declines with increasing age, but this is not always the case. Active, well–conditioned seniors often have performance capabilities equal to or greater than young sedentary individuals. However, there is some evidence, indicated by lower sweat rates and higher body core temperatures, that older individuals are less effective in compensating for a given level of environmental heat and work loads. At moderate thermal loads, however, the physiological responses of "young" and "old" are similar and performance is not affected. Age should not be the sole criterion for judging whether or not an individual should be subjected to moderate heat stress. Fitness level is a more important factor. Gender The literature indicates that females tolerate heat stress at least as well as their male counterparts. Generally, a female's work capacity averages 10 to 30 percent less than that of a male. The primary reasons for this are the greater oxygen–carrying capacity and the stronger heart in the male. However, a similar situation exists as with aging: not all males have greater work capacities than all females. Weight The ability of a body to dissipate heat depends on the ratio of its surface area to its mass (surface area/weight). Heat loss (dissipation) is a function of surface area and heat production is dependent on mass. Therefore, heat balance is described by the ratio of the two. Since overweight individuals (those with a low ratio) produce more heat per unit of surface area than thin individuals (those with a high ratio), overweight individuals should be given special consideration in heat stress situations. However, when wearing impermeable clothing, the weight of an individual is not a critical factor in determining the ability to dissipate excess heat. Copyright © 2008 J. J. Keller & Associates, Inc. All rights reserved.