Check heat safety limits and warning levels.
Occupational heat guidance is expressed as a work-rest cycle within each hour, tightening as heat index and workload rise. Rest grows with the amount by which the heat index exceeds the 27 C caution threshold and with work intensity, eases for acclimatised workers, and increases where there is no shade to recover in. Fluid replacement scales the same way, since sweat rate rises with both heat and effort.
Work-rest cycle in heat
Rest minutes per hour = (heat index - 27) x 3.2 x intensity factor, x0.8 if acclimatised, x1.2 without shade, capped at 50; work minutes = 60 - rest
Heat stress management is regulated in many jurisdictions and individual risk varies with health, medication and fitness. These figures are general guidance — follow official heat standards, your employer's heat illness prevention plan and medical advice.
Guidance ranges from a short break each hour in caution conditions to 45 minutes of rest per hour in danger conditions with heavy work. Rest should be taken in shade or a cooled area.
Roughly 250 ml every 15-20 minutes during heavy work in high heat, around a litre an hour. Drinking to thirst alone tends to under-replace during sustained effort.
Substantially. Over one to two weeks of graduated exposure, sweat rate and plasma volume adapt and heat strain at the same workload falls markedly.