Calculator
Heat stress guide for Australian conditions
1) Why heat stress matters
Across Australia, summer heatwaves can push outdoor temperatures beyond 40°C, and radiant heat from sunlit ground, metal, and concrete can make exposure feel even hotter. High heat load reduces physical and mental performance, raises accident risk, and can quickly progress from cramps and exhaustion to heat stroke. Indoor work can also be risky near ovens, roofs, and poorly ventilated sheds.
2) Inputs and indices used by this tool
This calculator uses air temperature, relative humidity, wind, and sun exposure to estimate Wet Bulb Globe Temperature (WBGT) and Heat Index. WBGT is popular for work and sport planning because it combines humidity, radiant heat, and air movement. Heat Index focuses on temperature and humidity. If you have a heat stress meter, switch to measured mode and enter globe and natural wet-bulb values.
3) Sun and radiant heat can change everything
Direct sun adds thermal load even when the shade temperature seems manageable. As a practical rule of thumb, afternoon sun can add up to about 8°C to how conditions feel. Shade structures, reflective barriers, and task rotation reduce radiant exposure and should be considered alongside rest breaks.
4) Typical Heat Index communication bands
Many heat index charts group risk as: Caution (~27–32°C), Extreme Caution (~32–39°C), Danger (~39–51°C), and Extreme Danger (≥52°C). Use these bands to communicate conditions quickly, then rely on WBGT, workload, and worker symptoms for on-the-ground decisions.
5) WBGT and workload adjustments
Heavier workloads generate more internal heat, so the safe continuous-work WBGT is lower. This tool lets you select workload and add a clothing adjustment when PPE traps heat. If your workplace uses a specific heat protocol, edit the risk cutoffs so results align with your internal thresholds.
6) Work/rest cycles and hydration targets
When adjusted WBGT rises above your threshold, schedule extra rest each hour and move breaks into cool, ventilated areas. Frequent small drinks are easier to sustain than large infrequent ones; for hot work, 250 mL every 15–20 minutes equals roughly 0.75–1.0 L per hour, depending on sweat rate and conditions. During long sweaty shifts, consider electrolytes.
7) Red flags and immediate actions
Stop work and cool the person if you see confusion, collapse, severe headache, vomiting, or very hot skin. Move to shade, loosen clothing, apply cool water and fan airflow, and call for urgent medical help if symptoms are severe or not improving quickly. Early action saves lives.
FAQs
1) Should I use WBGT or Heat Index?
Use WBGT for work planning because it accounts for humidity, radiant heat, and wind. Use Heat Index as a quick “feels like” check. If you have measured Tnwb and Tg, measured WBGT is best.
2) What if I don’t know solar radiation?
Choose a sun exposure profile. “Shade/overcast” uses a lower solar estimate, while “Full sun” assumes strong radiation. If you have a site sensor or forecast value, switch to custom and enter it.
3) How do I pick the clothing adjustment?
Add a small positive value when PPE reduces sweat evaporation or traps heat. Start with 0.5–2.0°C for heavier ensembles and refine using your organisation’s guidance, worker feedback, and any measured WBGT comparisons.
4) What rest break does the calculator recommend?
It estimates minutes of rest per hour once adjusted WBGT exceeds the continuous-work threshold for the selected workload. Treat it as planning guidance, then apply site rules, supervision judgement, and worker symptoms.
5) How much water should workers drink?
Drink regularly, not just when thirsty. A common hot-work approach is about 250 mL every 15–20 minutes (≈0.75–1.0 L/hour). Increase if sweating heavily, but avoid overdrinking plain water without electrolytes during prolonged sweating.
6) Does acclimatisation change the numbers?
Acclimatisation improves tolerance and sweat efficiency over 1–2 weeks, lowering risk at the same WBGT. The calculator flags non-acclimatised workers so you can add more rest, reduce workload, and monitor closely early in the shift.
7) When should I seek urgent medical help?
Seek urgent help if there is confusion, fainting, seizures, very hot skin, or symptoms worsening despite rest and cooling. Heat stroke is an emergency—cool rapidly, call emergency services, and do not delay transport.