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Rule of 20%

1 OSHA and HazCom article tagged "Rule of 20%" — practical, CFR-cited guidance verified against primary sources.

Worker Acclimatization to Heat: OSHA's 7-14 Day Protocol & the 'First Day' Risk

New and returning workers face the highest heat-illness risk on day one. OSHA's guidance ramps them up over their first one to two weeks with the Rule of 20 percent. The schedule, the data behind it, and what the proposed rule would add.

Jun 25, 2026

8 min read

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