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About Work/Rest Schedules

Rather than being exposed to heat for extended periods of time during the course of a job, workers should, wherever possible, be permitted to distribute the workload evenly over the day and incorporate work/rest cycles. Work/rest cycles give the body an opportunity to get rid of excess heat, slow down the production of internal body heat, slow down the heart rate, and provide greater blood flow to the skin.

For the best protection from heat-related illness, workers should spend the rest periods of the cycle in a cool place, for example in a lightly air conditioned room, trailer or vehicle, or if one is not available, then in full shade.

Rest periods do not necessarily mean that the workers are on break; these can be productive times. During the rest periods, workers may continue to perform mild or light work, such as completing paperwork, sorting small parts, attending a meeting, or receiving training (e.g., instructions for upcoming work, or a tailgate safety talk).

Have a knowledgeable person at the worksite that is well-informed about heat-related illness and able to modify work activities and the work/rest schedule as needed. When evaluating an appropriate work/rest schedule:

• Shorten work periods and increase rest periods:
  
  
• As temperature rises
• As humidity increases
• When sun gets stronger
• When there is no air movement
• When protective clothing or gear is worn
• For heavier work
  
  
• Assign new and un-acclimatized workers lighter work and longer rest periods. Monitor these workers more closely.

The figures and tables below are examples of general guidelines for setting work/rest schedules. When possible, more frequent shorter periods of exposure to heat are better than fewer longer exposures. This means that the work/rest schedules are often based on 1-hour cycles and might call for a rest period of 15 minutes every hour during hot weather, but 45 minutes per hour when temperature and humidity are extreme. Individual requirements may vary greatly. The work/rest schedules in these tables do not guarantee protection against heat-related illness and should not be used as a substitute for good judgment or experience. The tables generally apply to healthy, acclimatized adults under the age of 40.

Setting appropriate work rest schedules is critical for protecting workers during outdoor work. Often it requires the assistance of a trained safety and health profession. In addition to the methods provided as examples below, OSHA provides free and confidential advice to services small and medium-sized businesses in all states across the country. Contact OSHA’s On-site Consultation Program for assistance in developing your heat-related illness preventions plan and work/rest schedules that are appropriate for your worksite. For more information or for additional compliance assistance contact OSHA at 1-800-321-OSHA (6742).

Methods for Developing Work/Rest Schedules

Figure 1 is the US Army Work/Rest/Water Consumption table used for setting work/rest schedules during field operations. The hydration and work/rest schedule assume an average sized, heat acclimated soldier wearing battle dress uniforms (BDU). Factors such as lack of acclimitization, poor fitness, and cumulative inadequate hydration and may increase the risk of heat-related illness and should be taken into account when using the schedules in Figure 1. This is one method for determining work/rest schedules using an alternate to the Heat Index called the Wet-Bulb Globe Temperature (WBGT). The WBGT is obtained using specialized equipment (a wet-bulb globe temperature meter, also known as a WBGT meter). The meter provides a heat reading based in part on factors similar to those NOAA uses to determine the heat index, but the WBGT reading also considers solar load (radiant heat, from sunshine) as well as how quickly moisture evaporates. WBGT meters are readily available from commercial sources of environmental monitoring and technical instruments. Several hand-held models cost less than $200 (in 2011).

Table 1 presents an approach for setting work/rest schedules for workers wearing normal clothing drawn from the US EPA/OSHA joint publication, A Guide to Heat Stress in Agriculture. Tables 1 and 2 use an adjusted temperature calculation to approximate the Wet Bulb Globe Temperature (WBGT). These tables are for use where instruments which measure WBGT are unavailable. Some of the work/rest times in Table 1 for hot/dry conditions may be conservative, due to approximation of WBGT. While Tables 1 and 2 allow 13° for the full heating effect of the sun, the effect of solar heat can be greater under some conditions. Table 1 is based in part on there being perceptible air movement. Where there is little or no air movement, Table 1 is not appropriate.

Other resources with approaches and tips for setting work/rest periods include:

• OSHA’s Technical Manual Table III: 4-2 offers a simple chart showing several example WBGT meter readings and the appropriate work/rest schedules for light, moderate or heavy work.
  
  
• The American Conference of Governmental Industrial Hygienists (ACGIH) describes a detailed method of determining work/rest schedules based on numerous factors including WBGT meter readings. The schedule can be adjusted for work demands and clothing type. This work/rest schedule method is published as: Heat Stress and Strain, in TLVs and BEIs, American Conference of Industrial Hygienists, Cincinnati, OH.

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