Heat Stress 101 (Part 3)
Welcome to part three of our series on “Heat stress”. So far we have discussed what heat stress is, the various conditions resulting from heat stress, and what to look for if you’ve been in the sun too long. In this article I want to talk about prevention, as well as what to do if someone is suffering from a heat related illness. The more you know, the better prepared you will be to help yourself and others.
We know that sunlight contains ultraviolet (UV) radiation, which can cause premature aging of the skin, wrinkles, cataracts, and skin cancer. The amount of damage from UV exposure depends on the strength of the light, the length of exposure, and whether the skin is protected. There are no safe UV rays or safe suntans.
Keeping yourself protected
- If working or exercising OUTDOORS, wear loose fitting, light colored porous clothing which allows free air circulation over the body. Wear a well-ventilated broad brimmed hat
- If working or exercising INDOORS, wear as little clothing as possible. Use fans to circulate the air quickly, open windows and doors to reduce humidity and to provide air circulation and room ventilation.
- Work or exercise in the early morning and evening hours in whatever shade is available. Work moderately over long periods, rather than intensely for short periods.
- Drink cool, electrolyte replacement fluids in moderate amounts frequently before, during and after the heat stress.
- Check body feelings often, and immediately discontinue exercise and get out of the heat if you feel dizzy, faint or nauseated, unreasonably irritable or panicky, sweat so heavily that it falls in drops rapidly from your face or body, or if you become aware of a rapid, pounding heartbeat.
- If you are working with a group, check those around you frequently for the early signs and symptoms of heat stress. Get anyone who complains of feeling hot, appears disoriented, has a flushed face covered with sweat, appears irritable or seems either to stagger or be physically unstable to a shaded, cool and well ventilated area.
If a Person Collapses During Heat Stress:
Take them to a well-ventilated and shaded area, and lay them on the ground or floor. Either remove or loosen their clothing and fan the body surface. DO NOT force the person to drink liquids. Most likely recovery will occur spontaneously and quickly if the skin is moist and cool. When the person has regained consciousness, determine if they were injured when fainting occurred. The person should be watched closely and allowed to rest for at least an hour in a cool environment before being left alone. No one who collapses during a heat exposure should be allowed to become heat exposed again for at least 24 hours, unless approved by a physician.
The 5 most effective ways to reduce heat stress
If the person either does not recover consciousness within 2 minutes, or if their skin is hot and dry, flood the skin and clothing surfaces with cool (not cold) water, fan the body surface vigorously, and SEEK EMERGENCY MEDICAL HELP IMMEDIATELY.
- Fan Ventilation
- Air Cooling
Heat reduction can also be achieved by using power assists and tools that reduce the physical demands placed on a worker. However, for this approach to be successful, the metabolic effort required for the worker to use or operate these devices must be less than the effort required without them. Another method is to reduce the effort necessary to operate power assists. The worker should be allowed to take frequent rest breaks in a cooler environment.
The human body can adapt to heat exposure to some extent. This physiological adaptation is called acclimatization. After a period of acclimatization, the same activity will produce fewer cardiovascular demands. The worker will sweat more efficiently (causing better evaporative cooling), and thus will more easily be able to maintain normal body temperatures.
A properly designed and applied acclimatization program decreases the risk of heat-related illnesses. Such a program basically involves exposing employees to work in a hot environment for progressively longer periods. NIOSH (1986) says that, for workers who have had previous experience in jobs where heat levels are high enough to produce heat stress, the regimen should be 50% exposure on day one, 60% on day two, 80% on day three, and 100% on day four. For new workers who will be similarly exposed, the regimen should be 20% on day one, with a 20% increase in exposure each additional day
Hydration Fluid Replacement
* Cool (50°-60°F) water or any cool liquid (except alcoholic beverages) should be made available to workers to encourage them to drink small amounts frequently, e.g., one cup every 20 minutes. Ample supplies of liquids should be placed close to the work area. Although some commercial replacement drinks contain salt, this is not necessary for acclimatized individuals because most people add enough salt to their summer diets.
- Every worker who works in extraordinary conditions that increase the risk of heat stress should be personally monitored. These conditions include wearing semipermeable or impermeable clothing when the temperature exceeds 21°C (69.8°F), working at extreme metabolic loads (greater than 500 kcal/hour), etc.
- Personal monitoring can be done by checking the heart rate, recovery heart rate, oral temperature, or extent of body water loss.
- To check the heart rate, count the radial pulse for 30 seconds at the beginning of the rest period. If the heart rate exceeds 110 beats per minute, shorten the next work period by one third and maintain the same rest period.
- The recovery heart rate can be checked by comparing the pulse rate taken at 30 seconds, with the pulse rate taken at 2.5 minutes after the rest break starts.
- Oral temperature can be checked with a clinical thermometer after work but before the employee drinks water. If the oral temperature taken under the tongue exceeds 37.6°C, shorten the next work cycle by one third.
- Body water loss can be measured by weighing the worker on a scale at the beginning and end of each work day. The worker’s weight loss should not exceed 1.5% of total body weight in a work day. If a weight loss exceeding this amount is observed, fluid intake should increase.
Other Ways of Controlling Heat Stress
- Reduce the physical demands of work, e.g., excessive lifting or digging with heavy objects;
- Provide recovery areas, e.g., air-conditioned enclosures and rooms;
- Use shifts, e.g., early morning, cool part of the day, or night work;
- Use intermittent rest periods with water breaks;
- Use relief workers;
- Use worker pacing; and
- Assign extra workers and limit worker occupancy, or the number of workers present, especially in confined or enclosed spaces.
Develop a heat stress training program, and incorporate into health and safety plans at least the following components:
- Knowledge of the hazards of heat stress;
- Recognition of predisposing factors, danger signs, and symptoms;
- Awareness of first-aid procedures for, and the potential health effects of, heat stroke;
- Employee responsibilities in avoiding heat stress;
- Dangers of using drugs, including therapeutic ones, and alcohol in hot work environments;
- Use of protective clothing and equipment; and
- Purpose and coverage of environmental and medical surveillance programs and the advantages of worker participation in such programs.
What Personal Protective Equipment is effective in minimizing heat stress?
- Reflective clothing, which can vary from aprons and jackets to suits that completely enclose the worker from neck to feet, can reduce the radiant heat reaching the worker. However, since most reflective clothing does not allow air exchange through the garment, the reduction of radiant heat must more than offset the corresponding loss in evaporative cooling. For this reason, reflective clothing should be worn as loosely as possible. In situations where radiant heat is high, auxiliary cooling systems can be used under the reflective clothing.
- Auxiliary body cooling ice vests, though heavy, may accommodate as many as 72 ice packets, which are usually filled with water. Carbon dioxide (dry ice) can also be used as a coolant. The cooling offered by ice packets lasts only 2 to 4 hours at moderate to heavy heat loads, and frequent replacement is necessary. However, ice vests do not tether the worker and thus permit maximum mobility. Cooling with ice is also relatively inexpensive.
- Wetted clothing such as terry cloth coveralls or two-piece, whole-body cotton suits are another simple and inexpensive personal cooling technique. It is effective when reflective or other impermeable protective clothing is worn. This approach to auxiliary cooling can be quite effective under conditions of high temperature, good air flow, and low humidity.
- Water-cooled garments range from a hood, which cools only the head, to vests and “long johns,” which offer partial or complete body cooling. Use of this equipment requires a battery-driven circulating pump, liquid-ice coolant, and a container. Although this system has the advantage of allowing wearer mobility, the weight of the components limits the amount of ice that can be carried and thus reduces the effective use time. The heat transfer rate in liquid cooling systems may limit their use to low-activity jobs; even in such jobs, their service time is only about 20 minutes per pound of cooling ice. To keep outside heat from melting the ice, an outer insulating jacket should be an integral part of these systems.
- Circulating air is the most highly effective, as well as the most complicated, personal cooling system. By directing compressed air around the body from a supplied air system, both evaporative and convective cooling are improved. The greatest advantage occurs when circulating air is used with impermeable garments or double cotton overalls. One type, used when respiratory protection is also necessary, forces exhaust air from a supplied-air hood (“bubble hood”) around the neck and down inside an impermeable suit. The air then escapes through openings in the suit. Air can also be supplied directly to the suit without using a hood in three ways: by a single inlet, by a distribution tree, or by a perforated vest. In addition, a vortex tube can reduce the temperature of circulating air. The cooled air from this tube can be introduced either under the clothing or into a bubble hood. The use of a vortex tube separates the air stream into a hot and cold stream; these tubes also can be used to supply heat in cold climates. Circulating air, however, is noisy and requires a constant source of compressed air supplied through an attached air hose. This system tethers the worker and limits his or her mobility. Additionally, since the worker feels comfortable, he or she may not realize that it is important to drink liquids frequently.
What to Do for Heat-Related Illness
- Call 911 (or local emergency number) at once.
While waiting for help to arrive:
- Move the worker to a cool, shaded area.
- Loosen or remove heavy clothing.
- Provide cool drinking water.
- Fan and mist the person with water.
This concludes our series on heat stress and related illnesses, I hope that you had time to go over all three articles. Summer is here for most of us and we need to be careful as we go obout our days working or playing in the heat of the summer sun. The sun can do real damage if you’re not careful. Be safe out there.
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