Recommended heat exposure standards are effective in protecting most workers from serious illness and death, according to new data from the Centers for Disease Control and Prevention.

In a study published this week in CDC’s Morbidity and Mortality Weekly Report, researchers reviewed 25 outdoor work-related incidents associated with heat exposure — 14 fatal cases and 11 that were nonfatal — that had previously been investigated by the Occupational Safety and Health Administration between 2011 and 2016. The point of the study was to evaluate recommended occupational exposure limits for heat stress from CDC’s National Institute for Occupational Safety and Health — the standards had been tested in experimental settings, but not in outdoor workplaces.

The NIOSH limits, which align with guidelines from the American Conference of Governmental Industrial Hygienists, include a maximum combination of environmental heat, which is measured by wet bulb globe temperature, and metabolic heat, or body temperature. (Wet bulb globe temperature is based on four factors — air temperature, relative humidity, wind speed and radiation — and is considered the recommended workplace environmental heat metric.)

Researchers found that heat stress exceeded exposure limits in all 14 deaths studied and in eight of the 11 nonfatal heat-related illnesses. Further examination found that when wet bulb globe temperature isn’t available, a heat index threshold of 85 degrees Fahrenheit is likely an effective way to know when occupational heat has reached dangerous levels.

The study noted that among workers wearing a single layer of normal clothing, four of the nine nonfatal heat illnesses and four of the 12 fatalities occurred when the heat index was between 85 and 90 degrees. The heat index was less than 91 degrees in 12 of the 25 cases, including six of the deaths.

“In this analysis, the exposure limits had 100 percent sensitivity for identifying fatal levels of heat stress in outdoor industries,” the study stated. “This result suggests that the recommended limits are sufficiently protective of most workers.”

Researchers went on to recommend to employers: “The comprehensive heat-related illness prevention program should also include an acclimatization schedule for newly hired workers and unacclimatized long-term workers (e.g., during early-season heat waves), training for workers and supervisors about symptom recognition and first aid (e.g., aggressive cooling of presumed heat stroke victims before medical professionals arrive), engineering and administrative controls to reduce heat stress, medical surveillance, and provision of fluids and shady areas for rest breaks.”

OSHA doesn’t currently have a standard that covers people working in hot environments, though it does have a general duty to protect workers from dangerous conditions, including heat, while a number of states have adopted their own heat protections for workers. In 2015, according to data released last year from the Bureau of Labor Statistics, environmental heat led to 37 work-related deaths and more than 2,830 nonfatal occupational injuries and illnesses that required time off work.

For more on NIOSH’s heat recommendations, visit www.cdc.gov/niosh/topics/heatstress/default.html. For a copy of the new CDC study, visit www.cdc.gov/mmwr.