Back to Basics is a weekly feature that highlights important but possibly overlooked information that any EHS professional should know. This week, we examine how to protect employees from summer heat hazards.
Even as workplace heat hazards continue unabated, the regulation of worker heat injuries and illnesses continues to evolve:
- 2025 is the first summer under Maryland’s new heat stress standard.
- It’s the first full summer under California’s indoor heat illness prevention standard.
- The federal Occupational Safety and Health Administration (OSHA) is holding a series of virtual hearings this summer on the proposed federal heat illness prevention standard.
- New Mexico just concluded a public comment period on its proposed heat injury and illness prevention rule.
If you have employees who work outdoors or in hot indoor environments (such as commercial bakeries or un-air-conditioned warehouses), you should take steps to prevent heat illness, especially during periods of excessive heat. Heat stress controls include providing access to rest, shade, and ample drinking water. Also, consider adopting California’s requirement of at least 1 quart of cool drinking water per worker per hour for outdoor workers.
Effective heat illness prevention programs also include acclimatization schedules for new or returning workers and emergency response procedures in case one of your workers develops heatstroke or another heat-related injury or illness.
Having a written program and providing worker and supervisor training will help ensure your policies and procedures get implemented on the job.
Evolving regulatory picture
Several states, including California, Maryland, Nevada, Oregon, and Washington, have heat illness prevention standards. Minnesota has a standard for cold and hot working environments.
Last year, California established a Heat Illness Prevention in Indoor Places of Employment standard. The state rule applies to most indoor workplaces, such as manufacturing facilities, restaurants, and warehouses.
In indoor workplaces where the temperature reaches 82° F, employers must take steps to protect workers from heat illness. Employer requirements under the state standard include providing water, cooldown areas, rest, and training.
Additional requirements for high-heat workplaces that apply when the temperature reaches 87° include cooling work areas, implementing work-rest schedules, and providing personal heat-protective equipment. Where workers wear clothing that restricts heat regulation or work in high-radiant-heat areas, further requirements apply.
The California Division of Occupational Safety and Health (Cal/OSHA) compiled an employer assistance guide comparing the new indoor rule with the state’s outdoor rule. Employers with both indoor and outdoor workplaces may be covered by both regulations.
Last September, the Maryland Occupational Safety and Health (MOSH) published a heat stress standard.
The Maryland standard contains requirements for a heat stress prevention and management program, heat acclimatization, shade, and drinking water and procedures for managing high-heat working conditions, emergency response, and training. Maryland also requires employers in the state to monitor the heat index.
The Maryland standards apply to both indoor and outdoor work environments. Acclimatization requirements involve gradually increasing heat exposure times over a 5- to 14-day period, with a maximum 20% increase in exposure time each day. Both new employees and those returning from a work absence must undergo a period of acclimatization.
This spring, the New Mexico Occupational Health and Safety Bureau (OHSB), a division of the New Mexico Environment Department (NMED), accepted public comments on a proposed heat illness and injury prevention rule. The public comment period closed May 30.
New Mexico’s proposed rule would require employers in the state to establish, implement, and maintain prevention programs. Requirements of the rule would apply to both indoor and outdoor workplaces and would require employers to provide fluids, regular rest breaks, and cooling areas.
The proposed New Mexico rule would also require acclimatization periods of gradually increasing heat exposures, enabling workers to adapt to high-heat work environments, as well as requirements for emergency medical care, recordkeeping, and worker and supervisor training.
Last year, OSHA issued a proposed heat injury and illness prevention standard, which contains requirements for water, shade, paid breaks, heat acclimatization, and training.
The rule’s requirements would be triggered by a National Weather Service heat index of 80° F or a Wet Bulb Globe Temperature (WBGT) equal to the National Institute for Occupational Safety and Health’s (NIOSH) recommended alert limit (RAL). Additional high-heat requirements would be triggered by a heat index of 90° F or a WBGT equal to NIOSH’s recommended exposure limit (REL).
The public comment period on the proposed rule closed on January 14, but OSHA is holding a series of virtual public hearings this summer on the rulemaking. OSHA and the Department of Labor have made no other announcements about the status of the rulemaking.
Your heat stress prevention program
Under the Occupational Safety and Health Act, you must provide your employees with a workplace free of known safety and health hazards, which include heat-related hazards. You can find employer assistance on OSHA’s website for addressing heat-related hazards. Resources for creating a heat illness prevention plan include:
- Planning to protect workers before heat hazards are present;
- Understanding heat hazards in your workplace and calculating heat stress;
- How to protect new workers;
- Getting guidance on engineering controls, work practices, and personal protective equipment (PPE) for heat hazards; and
- The keys to prevention, which are water, rest, and shade.
Heat-related illnesses include heat cramps, heat exhaustion, heat rash, heatstroke, and rhabdomyolysis, the rapid breakdown, rupture, and death of muscle.
Factors contributing to occupational heat stress include environmental factors like air temperature, humidity, and sunlight; the workload or level of physical activity; clothing and protective gear that inhibit the body’s ability to lose excess heat; and individual risk factors.
OSHA recommends using a WBGT monitor to measure workplace environmental heat. WBGT devices contain three different thermometers: a dry bulb thermometer to measure the ambient air temperature, a natural wet bulb thermometer to measure the potential for evaporative cooling, and a black globe thermometer to measure radiant heat. A WBGT device accounts for four major environmental heat factors: temperature, humidity, radiant heat, and wind.
The heat index doesn’t measure worksite heat as accurately as the WBGT, and you shouldn’t rely on the heat index alone for an accurate hazard assessment.
Resources for controlling heat-related hazards include workplace recommendations from NIOSH, such as:
- Limiting workers’ time in the heat and/or increasing recovery time spent in a cool area.
- Reducing the metabolic (physically difficult) demands of the job.
- Using tools or equipment designed to minimize manual strain.
- Increasing the number of workers per task.
- Training supervisors and workers on heat stress.
- Using a buddy system, whereby workers observe each other for signs of heat-related illnesses.
- Requiring workers to conduct self-monitoring and creating a work group (workers, a qualified healthcare provider, and a safety manager) to make decisions on self-monitoring options and standard operating procedures.
- Providing adequate amounts of cool, potable water near the work area and encouraging workers to drink often. Water should be easy to access on a worksite and provided in sufficient quantities for the duration of work.
- Using a heat alert program whenever the weather service forecasts a heat wave.
- Instituting a heat acclimatization plan and encouraging increased physical fitness.
- Proper hydration, including cool, potable water for short work periods and additional fluids that contain electrolytes for those working 2 hours or more in hot conditions.
- Encouraging workers to drink at least 1 cup (8 ounces) of water every 20 minutes while working in the heat and not just when they’re thirsty.
Those working long shifts in the heat lose salt and other electrolytes when they sweat. The loss of electrolytes can cause muscle cramps and other health problems. Water alone can’t replace electrolytes, so you should provide electrolyte-containing beverages like sports drinks on longer work shifts that last more than 2 hours.
Workers also need rest when working in the heat. The length and frequency of rest breaks should increase as heat hazards rise.
Breaks should last long enough for workers to recover from the heat. The need for rest is affected by factors that include heat and workers’ physical activity levels. Skipping breaks isn’t safe in hot conditions.
Workers need to take breaks in shade, which can include shady areas, air-conditioned vehicles, a nearby building or tent, or an area with fans and misting devices. Indoor workers exposed to heat sources like ovens or furnaces should be allowed to rest in a cool, air-conditioned area away from heat sources.
Worker training in your heat illness prevention program should cover the following topics:
- Recognizing the signs and symptoms of heat-related illnesses and administering first aid;
- The causes of heat-related illnesses and steps to take to reduce heat stress risks, such as drinking enough water and monitoring the color and amount of urine output;
- An understanding of the added heat load caused by exertion, clothing, and PPE;
- The effects of other factors like drugs, alcohol, and obesity on tolerance to occupational heat stress;
- The importance of immediately reporting to a supervisor any symptoms or signs of heat-related illness in yourself or in coworkers; and
- Procedures for responding to symptoms of possible heat-related illness and for contacting emergency medical services.
Supervisor training should also cover how to implement appropriate acclimatization; procedures to follow when a worker has symptoms of heat-related illness, including emergency response procedures; monitoring weather reports and responding to hot weather advisories; and monitoring and encouraging adequate fluid intake and rest breaks.
Acclimatization involves gradually increasing workers’ time in hot conditions over 7 to 14 days. An acclimatization schedule for a new worker should start with no more than 20% of the usual duration of work in the heat on the first day and no more than a 20% increase on each additional day.
For experienced workers returning from a vacation or another absence, the schedule should be:
- No more than 50% of the usual duration of work in the heat on day 1
- No more than 60% of the usual duration of work in the heat on day 2
- No more than 80% of the usual duration of work in the heat on day 3
- No more than 100% of the usual duration of work in the heat on day 4
An effective heat illness and injury prevention program begins as a written program covering acclimatization, training, worker monitoring, emergency response procedures and first aid, and the provision of water, rest, and shade.