heat stress Acclimatization
Sample Acclimatization Schedule
NIOSH Acclimatization Recommendations
for New Workers
1st day 20% usual work duration
2nd day 40% usual work duration
3rd day 60% usual work duration
4th day 80% usual work duration
5th day 100% usual work duration
NIOSH Acclimatization Recommendations
for Workers with Previous Experience
*
with
the Same Job
1st day 50% usual work duration
2nd day 60% usual work duration
3rd day 80% usual work duration
4th day 100% usual work duration
*Workers returning from an absence
• Managers should have a formal acclimatization plan for
employees working in the heat. Starting new employees at
full intensity is not safe.
• Adjustments to the acclimatization schedule may be
needed depending on the worksite’s situation and on
individual factors.
• Most workers should be able to safely handle a full
workload after 4 days of gradual increase, even though
they will usually not be fully acclimatized yet. Most
people will continue to see benecial improvements in
heat tolerance for up to 2 weeks after exposure starts.
• Sudden shifts in work intensity or sudden increases in
environmental temperature can increase the risk for heat
illness even for acclimatized workers.
Case Study: Hazards of Not Acclimatizing Workers
A 41-year-old construction worker was sawing boards in 93 °F
heat. At 5 p.m., the worker collapsed in the parking lot. He was
found by another employee. His body temperature was recorded
at 108 °F when he was admitted to the hospital. He died the next
day. At the time of the incident, the employee had been working
for the company for one day. The company had no formal heat
stress policy or acclimatization plan.
Lessons Learned
• Heat casualties often occur with new or less experienced
employees.
• Deaths from heat stress often occur during the rst few days
on the job.
• Employers should have heat stress policies, and should implement acclimatization plans.
Photo by ©Thinkstock
DEPARTMENT OF HEALTH AND HUMAN SERVICES
Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health
DHHS (NIOSH) Publication No. 2017-124