“Everybody complains about the weather, but nobody does anything about it.”  — Charles Dudley Warner

A few weeks ago, we were treated to the sight of icicles hanging from NFL Coach Andy Reid’s moustache during the Chiefs-Dolphins playoff game in Kansas City. That gut punch of arctic air to the Midwest overwhelmed us. Here, our heating system couldn’t keep up with the cold and temperatures in the office dropped to less than 55°F. They stayed there for over a week. Most of us ended up working from home.

Every year at about this time, after a severe cold snap, attention turns to keeping workers safe by keeping them warm. In a few months, we’ll forget all about extremely cold temperatures and turn our attention to heat stress and other hazards associated with hot weather.

And so it will go.

The question comes up about how cold is too cold for working without protection, and how hot is too hot for working without preventative measures.

Extreme Temperatures

Both heat stress and cold stress can be fatal. In the winter, we worry about frostbite, trench foot, hypothermia, and chilblains. In the summer, we worry about heat rash, heat cramps, heat syncope, heat exhaustion, and heat stroke. It is easy to find a list of symptoms associated with cold stress and heat stress. On the other hand, it is very difficult to find temperature limits, either high or low, for the workplace.

In its Cold Stress Guide, OSHA acknowledges that “OSHA does not have a specific standard that covers working in cold environments.” Likewise, in TWI Bulletin No. 12 (OSHA 4185-07 2022), OSHA states that “currently, OSHA does not have a specific standard addressing heat-related hazards.”

However, OSHA is quick to point to the general duty clause, which requires employers to provide workers with employment and a place of employment which are free from recognized hazards which are causing or are likely to cause death or serious physical harm. Among those recognized hazards are heat stress and cold stress.

While OSHA has not established limits, it has made it clear the objectives of any limits are to prevent the core body temperature from exceeding 38 C (100.4°F) or from going below 36 C (96.8°F). Unfortunately, there is no practical way to insert a rectal thermometer into each worker to keep track of this. So, standards would be helpful, even if OSHA hasn’t published any.

Heat Stress

There are a couple of standards that OSHA and other regulatory agencies have identified as relevant. For heat stress, OSHA refers to the National Weather Service’s Heat Index (HI), and to the American Conference of Government Industrial Hygienist’s (ACGIH’s) temperature threshold limit values (TLVs), which are based on Wet Bulb Globe Temperature (WBGT). The WBGT takes into account air temperature, humidity, windspeed, cloud cover, and sun angle, and is considered a better indicator than heat index, which is based on air temperature and humidity only.

The ACGIH TLV for WBGT depends on workload, the ratio of work to rest time, and clothing. At the most extreme conditions, the WBGT below which no special provisions are required is 24 C (75°F) (before adjusting for how heavy the work clothing is). On the other hand, under very light conditions, the WBGT above which special provisions are required may be as high 32.5 C (90.5°F).

OSHA has found that HI is more familiar to many, and has established these hazard levels:

  • Caution when HI is less than 26.7 C (80°F)
  • Warning when HI is between 26.7 C (80°F) and 32.2 C (95°F)
  • Danger when HI is higher than 32.2 C (95°F)

However, for purposes of enforcement, OSHA inspectors cite for the failure to have a heat stress prevention program in place on any day that the National Weather Service (NWS) announces a heat advisory or heat warning for the local area.

The conditions for a heat advisory or heat warning vary across the company. In St. Louis, the NWS issues a heat advisory when the HI is expected to be around 40.6 C (105°F) or if the HI will be in the range of 37.8 to 40 C (100 to 104°F) for at least four consecutive days. The conditions in St. Louis for a heat warning is an HI of 43.3 (110°F) for two days, or an HI above 40.6 C (105°F) for four consecutive days.

Cold Stress

OSHA and other regulatory agencies also turn to the ACGIH TLV guidelines for cold temperature limits. The ACGIH TLV guidelines are based on air temperature and the NWS’s Wind Chill Index. The NWS bases the Wind Chill Index on air temperature and wind speed.

A good compilation of the ACGIH TLV guidelines can be found in Chapter 7 of the U.S.EPA’s Emergency Responder Health and Safety Manual, specifically in Appendix I. Down to 16 C (60.8°F), there are no special requirements. Below 16 C (60.8°F), workers must wear gloves suited for cold temperatures, and below 4 C (39.2°F), additional safeguards are required, e.g. auxiliary heat. There are several lower benchmark temperatures and wind chill indices that have more restrictive requirements.

What About Work in an Office Environment?

Citing ASHRAE Standard 55, the Canadian Standards Association advises in CSA Z412:17 (R2023) that the optimum temperature in an office during the summer is 24.5 C (76.1°F), with an acceptable range of 23 to 26 C (73.4 to 78.8°F). Likewise, it advises that the optimum temperature in an office during the winter is 22 C (71.6°F), with an acceptable range of 20 to 23.5 C (68 to 74.3°F). As you might imagine, OSHA is silent on the subject.

Working Indoors without HVAC

There are a lot of reasons that workers may be indoors without HVAC. Warehouses and indoor production areas are often designed without HVAC. Even when there is HVAC, external conditions can render them inadequate. So what temperature range is safe for workers? For physical work, we can count on 16 to 27 C (61 to 81°F) to be safe without any special protection to be in place. Beyond those temperatures, hot or cold, we need to be alert to the potential for extreme temperature stress and work accordingly.

In the office, standards say we need to be in the range of 20 to 26 C (68 to 79°F), although I expect that most office workers would find even that range too wide. Regardless, 13 C (55.4°F) was too cold for working in the office. I’m glad we elected to work from home.

As for football? OSHA doesn’t regulate it. But regardless, professional football has preventative measures in place to protect their workers, er, players, from temperature extremes.


  • Mike Schmidt

    With a career in the CPI that began in 1977 with Union Carbide, Mike was profoundly impacted by the 1984 tragedy in Bhopal and has been working on process safety ever since.