Heat Acclimatization Schedules
Most heat-related deaths at work happen in a worker’s first few days on the job, or during the first hot days of the year. The body needs one to two weeks of gradually increasing heat exposure to adjust. Acclimatization is one of the most effective ways to prevent heat illness.
- Construction
- General Industry
- Agriculture
- California
- Maryland
- Nevada
- Oregon
- Washington
What acclimatization does
- You start sweating sooner and sweat more, so you cool better.
- Sweat contains less salt.
- Heart rate and body temperature stay lower during the same work.
NIOSH schedules
| Worker | Day 1 | After that |
|---|---|---|
| New to the job or the heat | No more than 20% of the usual time in heat | Increase by no more than 20% each day |
| Experienced, returning | 50% | 60% on day 2, 80% on day 3, 100% on day 4 |
“Time in heat” can be managed by shorter shifts in the heat, more breaks in shade or air conditioning, or lighter work at first.
Who needs it
- New hires and temp workers, even if they’re from a hot climate
- Workers back after a week or more away (vacation, illness, injury)
- Everyone during the first heat wave of the season
- Workers moving from cool to hot jobs, such as indoor to roof work
- Anyone wearing heavy PPE or chemical suits
Tolerance fades fast
Acclimatization begins to fade after several days away from the heat and can be largely lost after a week or two. Don’t assume an experienced worker is still adapted after time off.
Supervisor actions
- Write the acclimatization plan into the heat illness prevention program.
- Pair new workers with a buddy and check on them often.
- Schedule the heaviest work early in the day.
- Provide cool water close to the work and encourage drinking about a cup every 15 to 20 minutes.
- Watch for early symptoms and act quickly. See Heat Illness.
State rules: California, Washington, Oregon, Maryland, Nevada and other states have heat rules, and several require close observation or acclimatization of new workers. See State Heat Rules.
Standards & references
Last updated: