Employees working in hot environments experience an increase in perspiration and heart rate, and their blood circulation is closer to the skin's surface to help lower their core body temperature(1). To overcome the physiological changes in their employees, progressive companies are developing a heat healthy program that includes acclimating their workers to the higher temperatures, making them aware of working conditions and encouraging them to get into good physical condition. There are several means of improving conditions to help your workers overcome the stresses of heat.
1) Engineering controlsVentilationincludes the use of fans to help dilute the hot air. Greater airflow also helps to increase evaporative cooling of perspiration due to convective cooling (which works as long as the air temperature is less than the worker's skin temperature). When it's not feasible to cool or ventilate large work areas, local, portable ventilation units, some with built-in air chillers, can be used.
Air treatments include cooling the air, air conditioning, removing humidity in the work area or the use of chillers and heat exchangers.
Shielding includes insulating the heat-producing equipment or enclosing it and allowing the heat to vent directly to the outdoors. Another type of shielding is to have employees work in an enclosed, separately cooled space.
2) Administrative controlsModifying the employees' workload for one to two weeks as the hot environment sets in allows them to build up an acceptance of their newly changed working conditions. A typical acclimatization schedule begins by limiting the employee's occupational heat exposure to:
- one-third of the workday during the first and second days;
- one-half of the workday during the third and fourth days; and
- two-thirds of the workday during the fifth and sixth days(2).
Regardless of what type of training and acclimatization schedule a company implements, some employees may be heat-intolerant - unable to adapt to working in hot environments. An intolerant person does not show the normal decrease in heart rate after acclimatization. Employees that may be prone not to acclimatize are those with cardiovascular disease or who have had heat stroke(2).
Moreover, employees who are unfit or out of shape could take more than 50 percent longer to become acclimated than a worker in good physical condition.
3) Work schedulesWork/rest regimens are based on the Wet Bulb Globe Temperature (WBGT) Index. OSHA's Technical Manual presents the regimens as a starting point (see Table 1).
Employee training should also be part of this program and should include:
- changes in work schedules to allow for acclimatization;
- understanding the effects of heat;
- hazards of heat stress;
- need for physical conditioning;
- recognizing the signs and symptoms of heat emergencies;
- first-aid procedures;
- dangers with using drugs and alcohol (including prescription drugs); and
- using personal protective equipment.
4) Fluid replacementPreventing heat stress not only includes the acclimatization regime but also fluid replacement. Employees may not feel they are thirsty, but in hot environments they lose weight as they perspire.
Rutgers Cooperative Extension Service, in conjunction with NIOSH, recommends replacing the four to eight quarts of sweat that are lost while working in hot environments with one-half to one cup of cool water every 20 minutes of the workday. The water should be about 55 degrees F(1).
By concentrating on these four practices, you will write a prescription for a heat-safe workforce.
References(1) Zhao, W. and Ann L. Kersting. Preventing Heat Stress in Agriculture. Fact Sheet FS747, Rutgers Cooperative Extension Service and the National Ag Safety Database.
(2) Sawka, M. N. Human Adaptations to Exercise - Heat Stress. The Journal of Physiology, (1999) 521P, pp. 23S.
(3) OSHA Technical Manual, Section III, Chapter 4: Heat Stress.