OSHA Heat Stress Requirements

9 Steps to Heat Stress Prevention

Date First Published on SafetySmart Compliance: August 4th, 2014
Topics: Heat & Cold Stress |

heat stress

An average of 30 workers die on the job each year as a result of heat stroke.

The problem with heat stress is that it’s invisible and sneaks up on its victims. It’s also kind of invisible in the sense that OSHA doesn’t have a heat stress standard. But heat stress is still very much on OSHA’s enforcement radar. Here’s a look at the liability risks posed by heat stress and the 9 practical measures necessary to manage them.


OSHA Requirements for Heat Stress

The OSHA General Duty Clause (GDC), Sec. 5(a)(1) of the Occupational Safety and Health Act, requires employers to protect workers from other “recognized hazards” not addressed in a specific standard. “This includes heat-related hazards that are likely to cause death or serious bodily harm,” OSHA states on its “Water. Rest. Shade.” heat stress website.

Example: After receiving a workers’ complaint, OSHA cites an Ohio steel and iron castings manufacturer plant for heat stress violations under the GDC. The plant brought in fans and radiant heat shields but temperatures were still an unacceptable 95° F [Duriron Co. v. Secretary of Labor, 750 F.2d 28 (6th Cir. 1984)].

Click here to find out how OSHA inspectors determine if an employer provides adequate heat stress protection.

Who’s at Risk of Heat Stress & OSHA Liability

High risk indoor operations include:

  • Foundries;
  • Glass, brick, ceramics, rubber and chemical plants;
  • Mining;
  • Smelting;
  • Electrical utilities (especially in boiler rooms);
  •  Steam tunnels;
  • Bakeries, confectioneries, food canneries and commercial kitchens; and
  • Laundries.

High risk outdoor operations include:

  • Construction;
  • Refining;
  • Asbestos removal; and
  • Hazardous waste sites.


There are 9 basic steps to take to protect workers from heat stress:

Step 1: Conduct a Heat Stress Hazard Assessment

Risk factors you need to consider in heat stress hazard assessment, include (Click here for a Heat Stress Hazard Assessment Checklist):

  • Temperature: Consider not just ambient temperature as shown by the thermometer but how the air actually feels to the worker. Rule of thumb: If temperatures exceed 85° F, you have a problem.
  • Humidity: Humidity can come not just from humid outdoor air but also from steam generated by indoor equipment. Rule of thumb: If relative humidity exceeds 85%, you have a problem.
  • Heat Radiation: Sources of heat radiation that heighten the danger of heat illness include direct sunlight and other nearby generators of light or heat, e.g., fire welding and hot surfaces.
  • Air Movement: Stagnant air tends to be hotter; but circulating air that’s already hot, e.g., air near steam pipes, can also heighten heat stress risks.
  • Workload: Strenuous work like carrying heavy objects long distances intensify heat stress dangers.
  • Workers’ Physical Condition: Consider the age, weight, fitness and acclimitazation, i.e., whether they’re used to working in hot conditions.
  • Clothing: Thick clothing and heavy equipment like respirators and face hoods aggravate heat stress risks; lighter clothing of natural fibers alleviate them.

Click here to find out the methods OSHA inspectors use to assess heat stress hazards at workplaces.

Step 2: Acclimatize Your Workers

The human body is capable of adapting to heat exposure to some extent via a process called acclimatization. Essentially, the body learns to sweat more efficiently and maintain normal body temperatures.

Accordingly, an OSHA Directive lists acclimatization as a measure employers should consider to protect workers from heat stress.  According to the Directive, a properly designed and applied acclimatization program involves exposing employees to work in a hot environment for progressively longer periods. NIOSH (1986) recommendations for workers with experience in jobs where heat levels are high enough to produce heat stress:











For new workers similarly exposed, the recommended regimen is 20% on Day 1, with a 20% increase in exposure each additional day.

Step 3: Ensure Sources of Cool Drinking Water

Make ample supplies of cool (50° to 60°F) water, Gatorade or other cool liquid (except alcoholic beverages) available to workers in or near the work area. Encourage workers to drink small amounts frequently, e.g., one cup every 20 minutes.

Step 4: Implement Appropriate Engineering Controls

The Directive lists 7 general types of engineering controls that employers should consider using to reduce heat stress dangers in hot work environments:

  1. General ventilation to dilute hot air with cooler air (generally from the outside) which can include permanently installed ventilation systems for large areas or entire buildings and/or portable or local exhaust systems for smaller areas.
  2. Air treatment/air cooling which doesn’t just ventilate but reduces air temperature by removing heat and in some cases humidity.
  3. Air conditioning which cools the air but is expensive to install and operate. Using chillers to circulate cool water through heat exchangers over which air from the ventilation system is then passed may be a more cost-effective alternative, the Directive acknowledges.
  4. Local air cooling to reduce air temperature in specific areas. Two common methods: i. cool rooms that enclose a workplace or provide a recovery area near hot jobs; and, ii. portable blowers with built-in air chillers.
  5. Convection, or use of fans to increase air flow (where air temperature is less than the workers’ skin temperature). Changes in air speed help workers stay cooler by increasing both the convective heat exchange (the exchange between the skin surface and the surrounding air) and the rate of evaporation. Because this method doesn’t actually cool the air, any increases in air speed must impact the worker directly to be effective.
  6.  Heat conduction methods like insulating the hot surface that generates the heat and changing the surface itself.
  7. Simple engineering controls used to reduce radiant heat, i.e. heat coming from hot surfaces within the worker’s line of sight, which can include shields that are located so as not to interfere with air flow (unless they’re also used to reduce convective heating). In addition, some sources of radiation, such as heating pipes, can be cut substantially via use of both insulation and surface modifications.

Step 5: Provide Appropriate Heat Stress Training

According to NIOSH (1986), a proper heat stress training program should include:

  • Knowledge of heat stress hazards;
  •  Recognition of predisposing factors, danger signs and symptoms;
  • Awareness of first-aid procedures for, and the potential health effects of, heat stroke;
  • Employee responsibilities in avoiding heat stress;
  • Dangers of using drugs, including therapeutic ones, and alcohol in hot work environments;
  • Use of protective clothing and equipment; and
  • Purpose and coverage of any environmental and medical surveillance programs and why workers should participate in them.

(Click here to get heat stress training materials you can use at your workplace; there’s also a lot of good free training stuff on the OSHA website)

Step 6: Monitor Exposed Workers

According to the OSHA Directive, “every worker who works in extraordinary conditions that increase the risk of heat stress should be personally monitored.” Methods:

  • Checking heart rate by counting the radial pulse for 30 seconds at the start of the rest period and shortening the next work period by 1/3 (with the same rest period) of any worker whose heart rate exceeds 110 beats per minute.
  • Checking recovery heart rate, i.e., heart rate measured at a fixed, reference period over one minute after activity stops, by comparing pulse rate taken at 30 seconds (P1) with pulse rate taken at 2.5 minutes (P3) after the rest break starts.
  • Checking worker’s body temperature orally with a clinical thermometer after work stops and before the worker drinks water and shortening the next work cycle by 1/3 if oral temperature taken under the tongue is over 99.68° F (37.6°C).
  • Measuring body water loss by weighing the worker on a scale at the beginning and end of each work day to ensure weight loss doesn’t exceed 1.5% of total body weight in the work day.

Step 7: Implement Other Work & Administrative Controls

As with other hazards, heat stress dangers can be managed by implementing controls affecting how the work is actually done. Examples:

  • Establishing safe work procedures for doing jobs in extreme heat; (Click here for Model Safe Work Procedures for Hot Weather Work);
  • Scheduling practices, e.g.,  carrying out hot outside jobs during the coolest part of the day or doing inside routine maintenance and repairs of hot areas in the winter;
  • Taking steps to cut the physical demands of work, e.g., use of lifting tools so workers don’t have to manually carry heavy objects;
  •  Providing cool temperature recovery areas, such as air-conditioned enclosures and rooms;
  • Giving records ample periods of intermittent rest and water breaks; and
  • Having fresh workers relieve workers after they’ve been in the heat for a certain period.

Step 8: Make Workers Use Appropriate Clothing

Ensure that workers who work in extreme heat dress appropriately including light weight, loose fitting clothing made of natural fibers like cotton. Workers exposed to sunlight should also wear light colors, sunglasses and protective skin lotions and creams. Reflective clothing keeps the skin from absorbing radiant heat but reduces the body’s evaporative cooling by blocking air exchange through the garment and, accordingly, should be worn as loosely as possible.

Step 9: Make Workers Use Appropriate Personal Protective Equipment

PPE for work in extreme heat can include:

  • Ice vests that can keep the body cool for 2 to 4 hours;
  • Wetted clothing like terry cloth coveralls that are especially effective in cooling the body when worn underneath reflective and other impermeable protective clothing.
  • Water cooled garments like hoods that cool the head and/or vests and long johns that cover more of the body.
  • Clothing and equipment that circulate air from a supplied air system around the body.

Implementation Strategy: Create a Heat Stress Plan

One of the most effective ways to implement all these measures is to incorporate them into a Heat Stress Plan. There’s no such thing as a one-size-fits-all plan. Details of your own plans will vary according to your industry, facility type, work process, etc. But the Model Plan in the TOOLS section of the SafetySmart Compliance Center lays out the fundamental elements a basic plan should include and can be adapted for your own workplace; there’s also a Short Version of a Model Plan if you’re in the market for something a little simpler.