Move heat controls upstream into the work plan.

Two checks on one work package. The planning pressure score screens the package from the inputs a project engineer can influence before release. The shift check then takes WBGT hour by hour and compares it with the NIOSH limit for the task, the clothing, and the crew. Both are planning aids. Measured WBGT on site governs the day.

Heat index iA screening proxy for air temperature and humidity (the public heat index). The occupational standard for field decisions is measured WBGT with the ACGIH/NIOSH work-rest tables. This planner prioritizes controls at the work-packaging stage; it does not replace WBGT monitoring or site safety rules.96 F Shift length 8 hr Crew size (monitoring span) iCrew size does not change an individual worker's heat strain, so it does not feed the exposure score. It sizes the observation load: more workers need more eyes to catch early symptoms.12

Task intensity iApproximate ACGIH metabolic categories. Light: light assembly, monitoring. Medium: sustained walking, moderate lifting, hand-tool work. Heavy: shoveling, manual material handling, sustained overhead work.

Radiant exposure

PPE burden iRequired PPE can add heat strain by trapping heat or limiting evaporation, even when the hazard control is necessary.

Acclimatization iNew, returning, or mixed crews need more conservative planning because heat tolerance builds over repeated exposure.

Shift check iThe hour-by-hour check runs on WBGT, the occupational heat measure, and not on the heat index above. Take WBGT from a site meter, the National Weather Service forecast, or the OSHA outdoor WBGT calculator. Enter the value at shift start and the peak for the day. The hours between follow a smooth daily curve, and the afternoon is taken to cool at two thirds of the rate the morning warmed, which is the cautious side. Hours before the entered start are held at the start value.

Shift start 7:00 WBGT at shift start 76 F Peak WBGT 88 F Hour of peak 15:00

WBGT comes from iA meter on site, or WBGT worked out from measured weather, is usually within about 2 F. A forecast misses by more. An assessment of next-day WBGT forecasts (Clark and Konrad, 2020) found a typical miss near 2 F and much larger misses on some days, so the forecast setting plans for 4 F either side.

Clothing iThe NIOSH clothing adjustment, added to WBGT before the limit is applied: work clothes and cloth coveralls 0, SMS coveralls 0.5 C, polyolefin coveralls 1 C, double-layer cloth 3 C, limited-use vapor-barrier coveralls 11 C. This is separate from the PPE burden above, which feeds the planning pressure score.

Read the note

65 pressure

Planning pressure

Controlled high exposure

The work can proceed only with planned recovery, shade access, and supervisor-visible exposure checks.

30 / 15 work/rest start point

Hourly field review

Resequence first lever

4 of 8 hours over the NIOSH limit

300 of 480 work minutes inside the limit

4:00 adds 150 min earlier start

Shift check against the NIOSH limit iThe limit is the NIOSH recommended exposure limit for an acclimatized crew and the recommended alert limit for a new or mixed crew, from the equations in NIOSH publication 2016-106. NIOSH prints the limits as equations and as curves, and the two differ slightly. This check uses the equations. Task intensity is taken at the top of its NIOSH workload band: light 233 W, medium 349 W, heavy 465 W. Work minutes come from the hourly time-weighted metabolic rate, with rest at 116 W in the same heat, stepped down to 60, 45, 30, 15, or 0.

Effective WBGT, with 4 F either sideNIOSH limits

Work minutes inside the limit, by hour

No WBGT reading yet? The OSHA outdoor WBGT calculator estimates it from weather data.

Control package

Exposure drivers

Foundations

This planning screen draws on established heat-stress practice:

ACGIH TLV: Heat Stress & Strain: WBGT-based occupational exposure limits and work/rest
NIOSH Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments (2016-106): the limit equations, workload bands, and clothing adjustment factors behind the shift check
OSHA Heat NEP: National Emphasis Program on outdoor and indoor heat hazards
NWS Heat Index: caution-to-danger categories (basis for the 103°F floor)

Planning support only. This does not replace OSHA requirements, a heat illness prevention plan, medical judgment, or site-specific safety authority. The shift check applies NIOSH recommended limits, which are guidance for healthy workers and not regulation, and it assumes rest is taken in the same heat.