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CDC Releases Study on Workplace Heat Risks

Thursday, August 9, 2018

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The Centers for Disease Control and Prevention recently took on research to find out if heat exposure limits recommended by its own National Institute for Occupational Safety and Health, as well as the American Conference of Governmental Industrial Hygienists, were sufficient to protect workers.

© iStock.com / Double_Vision

The Centers for Disease Controls and Prevention recently took on research to find out if heat exposure limits recommended by its own National Institute for Occupational Safety and Health, as well as the American Conference of Governmental Industrial Hygienists, were sufficient to protect workers.

It found that some of the heat index guidance given by the Occupational Safety and Health Administration might not be sufficient.

The Study

Exposure limits specify the maximum combination of environmental heat (measured by wet bulb globe temperature, which looks at air temperature, relative humidity, wind speed and radiation/sunlight) and metabolic heat (workload) to which workers are exposed. However, the CDC noted, that heat index is often used when WBGT is unavailable for a job site.

Limits are lower for workers who are unacclimatized to the heat, those who wear clothing or equipment that inhibits heat dissipation and those who have predisposing risk factors.

To determine whether these limits are effective in protecting workers, the CDC retrospectively reviewed 25 outdoor occupational heat-related illnesses—14 fatal, 11 nonfatal—investigated by OSHA from 2011 to 2016.

For each incident, researchers assessed personal risk factors and estimated WBGT, workload and acclimazation status.

WBGT at the time of each incident was estimated using a validated heat and mass transfer model and heat index was computed via a standard algorithm. In cases in which the worker’s clothing likely impaired heat dissipation, clothing adjustment factors were added to the estimated WBGT.

Total heat stress was then compared with the applicable NIOSH exposure limit. The sensitivity of the exposure limits was defined as the percentage of cases where heat stress met or exceeded the applicable limit.

The Findings

Research found that heat stress exceeded exposure limits in all 14 fatalities and in eight of the 11 nonfatal illnesses, and the analysis suggests that when WBGT is unavailable, a heat index screening threshold of 85 degrees Fahrenheit could identify potentially hazardous levels of workplace environment heat, which is where the discrepancy with OSHA guidelines comes in.

© iStock.com / daizuoxin

Exposure limits specify the maximum combination of environmental heat (measured by wet bulb globe temperature, which looks at air temperature, relative humidity, wind speed and radiation/sunlight) and metabolic heat (workload) to which workers are exposed. However, the CDC noted, that heat index is often used when WBGT is unavailable for a job site.

OSHA recommends using the heat index to protect workers and separates temperatures into four categories: less than 91 degrees Fahrenheit is a lower level risk that should be met with basic heat and safety training; 91 to 103 degrees is a moderate risk and at that time employers should implement precautions and heighten awareness; 103 to 115 degrees is high risk and additional precautions to protect workers should be taken; and greater than 115 degrees is considered a very high to extreme risk and should trigger “even more aggressive protective measures.”

“Although OSHA does not have an enforceable permissible exposure limit for heat stress, OSHA guidance states that a heat index of [less than 91 degrees Fahrenheit] is associated with ‘lower’ risk of heat-related illness unless other factors (e.g., direct sun, little air movement, strenuous workload or nonbreathable clothing) are present,” the report states.

“However, six of 14 deaths in this report occurred when the heat index was [less than 91 degrees]. Additional evidence supports the possibility of serious illness when the Heat Index is [less than 91 degrees].”

The CDC recommends the following:

  • Employers should measure heat stress throughout the workday by using WBGT and take actions to prevent exposure limits from being exceeded;
  • When WBGT is unavailable, a heat index threshold of 85 degrees Fahrenheit should be used to screen for hazardous workplace environmental heat; and
  • A comprehensive heat-related illness prevention program should 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, engineering and administrative controls to reduce heat stress, medical surveillance and provision of fluids and shady areas for rest breaks.

   

Tagged categories: Fatalities; Health and safety; NIOSH; OSHA; Research; Safety

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