Work Rest Cycle In Heat Calculator

Work out work rest cycle in heat instantly with clear inputs, formula shown and shareable results.

About Work Rest Cycle In Heat Calculator

Threshold limit values for heat set a WBGT ceiling for continuous work that falls as metabolic rate rises and is lower for unacclimatised workers. Above that ceiling the permissible work fraction falls, and the standard response is a work rest cycle within each hour, taken in a cooler recovery area so the body sheds accumulated heat.

Formulas

Continuous work ceiling

Ceiling WBGT falls about 1.5 °C for every 100 W above 300 W metabolic rate, and is 2 °C lower for unacclimatised workers

Work fraction

Fraction falls approximately 25 percent per °C of WBGT above the ceiling

Worked example

With the default values below, Work Rest Cycle In Heat Calculator returns Work minutes per hour of 60. Change any input above and every figure here is recalculated in your browser.

Inputs used

Wet bulb globe temperatureaccepts 15–45 °C: 30 °C
Metabolic rateaccepts 100–600 W: 300 W
Worker statusone of Acclimatised, Unacclimatised: Acclimatised

Results

Work minutes per hour: 60 min
Rest minutes per hour: 0 min
Permissible work fraction: 100.0% %
Risk category: Continuous work permissible

Step by step

1Values used
2Continuous work ceiling
3Work fraction
4Work minutes per hour= 60 min
5Rest minutes per hour= 0 min
6Permissible work fraction= 100.0 %
7Risk category= Continuous work permissible

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Work rest scheduling in heat must follow the applicable heat stress standard and be supervised by a competent person with physiological monitoring where appropriate.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Work rest scheduling in heat must follow the applicable heat stress standard and be supervised by a competent person with physiological monitoring where appropriate.

Frequently Asked Questions

How is the Work Rest Cycle In Heat figure worked out?

Ceiling WBGT falls about 1.5 °C for every 100 W above 300 W metabolic rate, and is 2 °C lower for unacclimatised workers. Threshold limit values for heat set a WBGT ceiling for continuous work that falls as metabolic rate rises and is lower for unacclimatised workers.

Does rest have to be out of the heat?

Yes, ideally. Resting in the same conditions allows only limited recovery, so the rest fraction has to be much larger. A shaded, ventilated or air conditioned recovery area is the effective control.

What values do I need to enter?

This calculator takes 3 inputs: Wet bulb globe temperature, Metabolic rate, Worker status. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.