Part 214 min

2.4 Lowering the heat: controls, clothing and sun

Water, rest and shade keep a worker in the fight. They do not lower the heat. Controls do — and they follow the same hierarchy as every other hazard: change the environment first, then change how and when the work is done, and only then rely on what a person wears. This chapter walks the hierarchy for heat, from engineering controls through scheduling to clothing and cooling PPE, and finishes with the exposure that outdoor crews take all day without noticing: the sun itself.

1 Engineering controls: making the environment cooler

OSHA's Heat Stress Guide opens its control section with the blunt version: the best way to prevent heat illness is to make the work environment cooler. The published options split by pathway.

Engineering controls for heat, by pathway
Control	Acts on	Where it fits
Air conditioning, or increased ventilation with cooler outside air	Convection, evaporation	Indoor workplaces
Reflective shields and barriers; insulating hot surfaces	Radiation	Foundries, boilers, ovens, steam lines
Sealing steam leaks, keeping floors dry, de-humidification	Evaporation (lowers water vapor pressure)	Plants, laundries, kitchens
Fans to increase air speed over the worker	Convection, evaporation	Only while air is cooler than skin
Shade over the work, not only over the break	Radiation	Outdoor work

The fan line carries a warning in both sources. OSHA's guidance says fans improve heat exchange between the skin surface and the air unless the air temperature is higher than skin temperature — above that, a fan is a convection oven. OSHA's proposed rule turns the same physics into a duty: at ambient temperatures above 102 °F, an employer providing fans would have to evaluate whether fan use is harmful, considering humidity, and discontinue it if it is.

On the job: in a workplace where high ambient temperatures are normal — foundries, steel mills — OSHA's guidance is to seek professional consultation to evaluate the extent of heat exposure and recommend prevention. That is an industrial hygiene assessment, and it is a reasonable thing for a crew to ask for.

2 Administrative controls: changing the work and the clock

When you cannot cool the place, you change the exposure. The published measures are unglamorous and they work.

1
Reschedule. Monitor weather reports daily and move high-heat jobs to cooler times of day; schedule routine maintenance and repair projects for the cooler seasons of the year.
2
Reduce the physical demands. Cut excessive lifting, climbing and digging where you can; spread work over more people; use relief workers or extra crew on long, demanding jobs.
3
Change the work/rest cycle. If heavy tasks cannot be avoided, increase the amount of rest time and schedule frequent rest periods with water breaks in shaded or air-conditioned recovery areas.
4
Acclimatize new and returning workers on the schedules from Chapter 1.3 — the single most effective administrative control there is.
5
Watch. Set up a buddy system if possible; if not, check routinely, several times an hour, that workers are using water and shade and are not showing symptoms.

Note the last one: OSHA's guidance says several times an hour, not once a shift. A supervisor who "keeps an eye out" is not running an observation program.

3 Clothing and cooling PPE

Clothing sits last in the hierarchy for a reason: it does not change the environment, and it can make things worse. The published guidance runs in both directions.

What helps. Reflective clothing such as safety vests, worn as loosely as possible, can minimize heat illness. Water-dampened cotton whole-body suits are described as an inexpensive and effective personal cooling technique. Cooling vests with pockets holding cold packs are comfortable and effective. More complex water-cooled suits exist, but may require a battery-driven circulating pump and liquid coolant — real equipment with real maintenance.

What hurts. Heavy personal protective clothing and equipment is on the InfoSheet's risk factor list. Anything vapor-impermeable — chemical coveralls, rain gear, encapsulating suits — closes the evaporation pathway completely. OSHA's proposed rule would require an employer whose employees wear vapor-impermeable clothing to evaluate the resulting heat stress hazards, implement policies based on reputable sources, and document that evaluation in the written plan.

The proposal would also require that where cooling PPE is provided, its cooling properties be maintained at all times during use. A cooling vest whose packs have been warm since 10 a.m. is a heavy vest.

Common mistake: letting PPE for one hazard create another. Adding a Tyvek suit for a dust exposure without changing the work/rest cycle trades a lung hazard for a heat hazard. The right move is to plan both at once, in the same document.

4 The indoor heat problem

Heat is not only an outdoor hazard, and indoor heat has no forecast at all. Bakeries, foundries, laundries, kitchens, warehouses under a metal roof, plant floors next to a furnace — all of them can run above outdoor conditions all year.

OSHA's proposed rule handles indoor work with its own paragraph. At identified indoor work areas the employer would have to provide one of: increased air movement, such as fans or comparable natural ventilation, with de-humidification if appropriate; an air-conditioned work area; or, where there are radiant heat sources, other measures that effectively reduce exposure to radiant heat, such as shielding, barriers or isolating the heat sources. Indoor break areas would have to be air-conditioned or have increased air movement and, if appropriate, de-humidification. And warning signs would be required at indoor work areas whose ambient temperature regularly exceeds 120 °F.

For indoor heat, WBGT is usually the honest metric: it is the one that captures the furnace, and the indoor equation (0.7 T_nwb + 0.3 T_g) is built for exactly that case.

5 The exposure nobody measures: sun and UV

Outdoor crews take a second exposure all day that has nothing to do with temperature. OSHA has stated in a letter of interpretation that there are no OSHA-mandated employee exposure limits to ultraviolet radiation — neither 1910.97 (non-ionizing radiation) nor 1910.1096 (ionizing radiation) covers UV light. There is no meter on the wall and no PEL.

There is a public forecast. EPA and the National Weather Service publish a daily UV Index: 1-2 low, 3-7 protection needed, 8 and above extra protection needed. EPA's sun safety guidance is that UV is strongest between 10 a.m. and 4 p.m., that a shadow shorter than you means high UV and a shadow taller than you means lower UV, and that sunscreen should be SPF 15 or higher, broad spectrum, applied about 15 minutes before going out and reapplied every two hours — including on cloudy days and after sweating.

On PPE, OSHA's 1998 interpretation puts the order plainly: employers are to use effective forms of protection such as wide-brim hats and long-sleeve clothing, and in situations where the only effective means of protection is sunscreen, then it too may be used. Shade and clothing first; sunscreen where nothing else works. The printable version of all of this for a tailgate meeting is the sun and UV toolbox talk.

10 a.m. - 4 p.m.

Shadow shorter = high UV

Sleeves and brim first

SPF 15+, every 2 hours

6 Putting the hierarchy on one job

Take a roofing crew tearing off and re-covering a flat roof in August. The heat index says 92 °F; the crew is in full sun on a black membrane; the work is heavy; two of them started Monday.

Engineering: you cannot air-condition a roof, but you can put up a canopy over the staging area and stage material in the shade so the walk to the water is short and cool. Administrative: start at 5:30 a.m. and finish the hot exposure by early afternoon; rotate the tear-off between crews; put the two new people on the acclimatization schedule with the shaded staging work; run a named buddy system. Hydration: coolers on the roof, not on the ground, with cool water and individual cups. PPE: light, loose, long sleeves and a brim; cooling vests if the employer provides them, with packs swapped at each break. UV: sunscreen at the water station so reapplying happens where drinking happens.

None of that is exotic, and all of it is in the published guidance. What makes it happen is that somebody wrote it down the night before, which is where Part 4 of this course ends.

Key takeaways

Cool the environment first: air conditioning, ventilation, shielding radiant sources, insulating hot surfaces, sealing steam leaks.
Fans help only while the air is cooler than skin; OSHA's proposal would require evaluating fan use above an ambient 102 °F.
Administrative controls are rescheduling, reducing physical demands, longer rest, acclimatization and observation several times an hour.
Reflective and cooling clothing helps; vapor-impermeable clothing closes the evaporation pathway and would require a documented evaluation under the proposed rule.
Indoor heat has no forecast: the proposal would require air movement, air conditioning or radiant shielding, and warning signs above 120 °F.
There is no OSHA UV exposure limit — use the EPA UV Index, shade and clothing first, sunscreen where nothing else protects.

Free educational content — not OSHA-authorized training, no certificate or card issued. Follow your employer's program and the standards cited.