Planning work in extreme heat
On Thursday a heat wave is forecast for Monday to Wednesday. Tuesday is the second-floor slab pour on a public works depot, rebar crews work on the open deck all week, and two labourers start on Monday.
Plan hot days before they arrive, in writing: who measures the heat at the work; how hours, water, shade and rest change as it rises; how new and returning workers build up; and who watches for symptoms. The Canadian Centre for Occupational Health and Safety (CCOHS) recommends a buddy system because people are less likely to notice their own symptoms. US federal OSHA reports that almost half of heat-related deaths happen on a worker's first day on the job or first day back after an extended absence.
- Write the plan with your safety lead, following your jurisdiction's rules and assessing workload, clothing, radiant heat and acclimatization.
- Measure at the work, not from the forecast, and name who takes readings and how often.
- Tie readings to actions suitable for this task. The OHCOW humidex response plan published by CCOHS assumes moderate work by unacclimatized workers; its relief table does not establish safe breaks for heavy work, extra heat or restrictive clothing. Have the safety lead set rest and stopping triggers.
- Move the heaviest work to the cool hours: early morning or late afternoon.
- Put cool water, shade and rest near the work. CCOHS advises water at 10 to 15 °C and drinking every 15 to 20 minutes, thirsty or not.
- Build up exposure gradually. For new workers, OSHA recommends 20% of usual heat exposure on day one, then 20% more each day. Plan returning workers' exposure with the safety lead.
- Pair workers and name a watcher. Dizziness, headache, nausea or heavy sweating call for shade, cooling and medical aid; stay with the person. Confusion or unconsciousness calls for 911 and immediate cooling while help is coming.
Common mistakes
- Using the weather forecast instead of readings at the work.
- Applying a moderate-work humidex table to heavy work without an assessment.
- Letting a new worker match an experienced worker's heat exposure.
Checklist
Before the heat arrives
- Plan written to the rules where you work
- Who takes readings at the work
- An action for each reading
- Heavy work in the cool hours
- Water and shade near the work
- New workers built up; buddies paired
Check your understanding
The rebar crew offers to skip its relief breaks and finish tying the next pour by noon. Why hold it to the plan?
