When is hot too hot?

Keeping workers safe as summer heat approaches requires dedication

Warmer weather is returning to most of the U.S., and for the roofing industry, that means the beginning of the busy season and the all-too-familiar hazards of working in extreme heat. Not only is roofing work physically demanding but it also is performed outdoors in direct sunlight where employees are exposed to excessive heat and environmental conditions that can lead to heat-related illnesses. Yet some roofing professionals underestimate the importance of understandingnand preventing heat-related illnesses.

The likelihood of a roofing worker experiencing a heat-related illness is greater than you may think. The Center for Construction Research and Training’s 2019 study, “Heat-related deaths among construction workers in the United States,” found construction workers experienced about one-third of all heat-related fatalities among all fatal occupational injuries and the trades at highest risk were roofing workers, cement masons, construction helpers and brick masons.


So when is hot too hot? The short answer is: It depends. Part of the issue’s complexity is the term “heat stress,” which people often use generically. The National Institutes for Occupational Safety and Health says heat stress is a combination of several factors, including a worker’s heat exposure from physical activity, environmental factors, and his or her clothing and personal protective equipment. These factors create an increased amount of heat stored by the body, which NIOSH refers to as the net heat load.

NIOSH says the body responds to heat stress by working harder to lose heat through sweating and increased heart rate to maintain a normal core body temperature (about 98.6 F). This physiological response is referred to as heat strain.

The body’s ability to maintain a normal core body temperature is influenced by several factors, including:

  • Air temperature
  • Humidity
  • Radiant heat (such as working in direct sunlight)
  • Skin temperature
  • The speed and temperature of air moving over the body
  • Hydration
  • Clothing
  • Fitness level
  • Age
  • Preexisting health conditions

Heat stress and the accompanying heat strain can increase the risk for heat-related illnesses.

Heat stress that leads to illness can come in several forms, including heat rash, fainting, heat cramps, heat exhaustion and heatstroke. Heat exhaustion quickly can progress to heatstroke, a life-threatening condition requiring immediate emergency medical response.

Heatstroke can develop after a prolonged period of exposure to a hot, humid environment during a period of a few days, which may or may not involve physical activity. Heatstroke also can develop after heavy exertion. Someone experiencing heatstroke may sweat and have moist skin or skin that is dry and hot. This is important to understand when training workers about the signs and symptoms of heat-related illnesses. Heat-stroke caused by exertion and nonexertion can be life-threatening and require immediate response, including rapid cooling and calling 911.


Preventing heat-related illnesses begins with understanding heat stress and the risk factors. How can you effectively address the hazards of heat stress in your workplace? Start with implementing a heat stress management plan that includes water, rest, shade plus training. Training should highlight the key elements of hydration, shaded rest breaks, acclimatization and an emergency response plan.


Ensuring proper hydration and rehydration after exertion at work and at home are essential steps to preventing heat-related illnesses. Dehydration from working in the heat can be compounded by activities while not at work, and dehydration is the primary cause of heat exhaustion.

Hydration is critical to replacing lost fluids and electrolytes. NIOSH says adequate water consumption (8 ounces every 15 minutes) with regular meals is sufficient to maintain water and electrolyte balance. Workers should not overconsume caffeinated beverages and sugary sports drinks, which are not hydrating.

Rest breaks

Periodic shaded rest breaks during times of high heat are an important part of your heat stress management program. Shaded rest breaks, staggered work hours and earlier start times can help prevent heat-related illnesses.


Heat exposure that may be too hot for one person may not be problematic for another based on personal risk factors and can be difficult to assess on an individual basis. When determining how well a worker has been acclimatized to heat, the answer to what is too hot becomes even more variable. Often, heat stress develops when workers have not worked in heat for a period of time and are not properly acclimatized.

Steve Rowlinson, professor emeritus at the University of Hong Kong, Hong Kong, notes workers who are able to acclimatize to high-heat environments are less likely to suffer from heat stress and heat-related illnesses. He also says acclimatization improves the body’s ability to have a “more efficient heat dissipation system” and “reserve sodium in sweat,” thereby resulting in a worker being more tolerant to heat stress.

Acclimatization takes place gradually over a period of days by a worker increasing the amount of time spent working in a high-heat environment. The Occupational Safety and Health Administration and NIOSH have different recommendations for the amount of days necessary for acclimatization; however, the consensus appears to be between three and seven days.


Preparedness is critically important regardless of the nature of an emergency, and being prepared to respond can be challenging in the industry because job locations and personnel regularly change. Making sure employees are familiar with the location of emergency care is an integral part of a project’s emergency action plan. Training should include recognition of signs, symptoms and risks of heat-related illnesses; prevention; and the buddy system, which assigns each person a partner to look after and report any concerns.

As part of an emergency response plan, your crews will need, at a minimum, materials on-site to facilitate rapid cooling until emergency responders arrive. Rapid cooling is critical during a heat emergency and must be applied quickly when heatstroke is suspected.

Margaret C. Morrissey, author of the 2021 article, “Heat Safety in the Workplace: Modified Delphi Consensus to Establish Strategies and Resources to Protect the US Workers,” highlights the need for rapid cooling such as the TACO method, or tarp-assisted cooling, and notes full-body immersion in water cooler than 62 F is the preferred and most effective method to quickly lower core body temperature. This significantly can improve health outcomes during a heat emergency.

Through pre-job planning and preparedness, this can be achieved on a roof by covering a tarp with ice water or cool water and then wrapping or rolling it around the affected worker’s body until emergency responders arrive. Morrissey also says evaporation using mist and fans is the second most effective method for rapid cooling; ice packs applied to the groin, armpits and neck are less effective but can be used to cool a worker suffering from heatstroke.

In addition to these prevention measures, of equal importance is engaging workers in safety and health programs and practices that instill a sense of ownership and encourage workers to lead and drive safety efforts in the workplace daily.

NRCA provides several resources that can help you train workers about heat safety, and OSHA and NIOSH have developed the OSHA-NIOSH Heat Safety Tool App, a useful resource for planning outdoor work. The app features real-time heat index and hourly forecasts with corresponding risk levels from minimal to extreme risk levels specific to a user’s location. The app also provides information about the signs and symptoms of heat-related illnesses as well as procedures to follow during a heat-related emergency.

In addition, OSHA continues to expand its resources and guidance on its website, osha.gov, to help employers prevent heat-related illnesses.

How is heat measured?

Ambient air temperature is the temperature of the surrounding environment.

Heat index is the measurement of how hot it feels when relative humidity is factored in with ambient air temperature. However, there are limitations with a heat index measurement because it fails to consider other factors beyond ambient air temperature and humidity, such as solar load, stagnate air and clothing.

A different tool, the wet bulb globe temperature, factors in wind, solar load and other weather parameters in addition to ambient air temperature and humidity. According to the National Weather Service, this method is “a particularly effective indicator of heat stress for active populations such as outdoor workers and athletes.” NRCA recommends OSHA adopt a similar approach focused on geographic regions with any regulation addressing heat injury and illness in the construction industry.


To further protect workers, the federal government has introduced plans to promulgate a new OSHA standard for heat.

On Sept. 20, 2021, the Biden administration announced initiatives at OSHA and other agencies to enhance workplace safety, specifically workers exposed to high heat. The administration’s list of OSHA initiatives included developing a workplace heat standard to apply to all industries and address outdoor and indoor heat. Additionally, the administration stated implementation of a new enforcement initiative regarding heat-related hazards would parallel an OSHA rulemaking process to prioritize heat-related inspections, both programmed and unprogrammed, on days when the heat index exceeds 80 F.

On Oct. 27, 2021, OSHA published its Advanced Notice of Proposed Rulemaking for Heat Injury and Illness Prevention in Outdoor and Indoor Work Settings. The document asked 114 questions seeking input about numerous aspects of heat illness prevention, such as how OSHA state-plan states have chosen different triggers for respective regulatory activity.

For example, California’s trigger is 80 F ambient air temperature; Oregon’s trigger is an 80 F heat index; Washington’s trigger is 89 F ambient air temperature (though it could be lower if workers are wearing heavy clothing); and Minnesota’s trigger is between 77 F and 86 F wet bulb globe temperature based on workload. Notice there are three heat measures being used: ambient air temperature, heat index and wet bulb globe temperature.

NRCA submitted comments to OSHA regarding the Advanced Notice of Proposed Rulemaking, as well as signed onto comments submitted by the Construction Industry Safety Coalition, which comprises construction trade associations. NRCA’s comments expressed NRCA’s belief that any regulatory measures to address heat hazards must address the construction industry while considering the unique and dynamic nature of its workplaces and workforce. NRCA noted the multiple tools OSHA can adopt for employers to assess the risk of heat stress and implement protective measures for employees and highlighted the limitations of using heat index and ambient air temperature as measurements to trigger protection measures.

NRCA further commented that “protective measures within a proposed standard must be practical in their approach so employers are not overwhelmed and/or overburdened by the requirements. Failing to recognize the need for a practical and useful approach in the construction industry will have the all-too-often effect of noncompliance in the smaller employer settings.”

OSHA also is working to launch a formal National Emphasis Program before summer that will target heat hazard cases in high-risk industries.

In addition, OSHA formed a heat work group within the National Advisory Committee on Occupational Safety and Health to engage stakeholders and inform ongoing efforts to develop guidance and a regulatory standard. The work group consists of three members of the full National Advisory Committee on Occupational Safety and Health who represent the public sector, labor and management, as well as members from different workplace sectors and industries.

OSHA has tasked the work group with reviewing all stakeholder comments submitted to OSHA under the Advanced Notice of Proposed Rulemaking and developing key recommendations for potential elements for a proposed heat injury and illness rulemaking.

In addition to the regulatory activity at the federal level, heat stress prevention and management is getting attention in other places. In late 2020, the American National Standards Institute’s A10 Committee for Construction and Demolition Operations began the development process for a new consensus standard, ANSI/ASSP A10.50, addressing heat stress management. The standard would identify industry best practices and establish minimum requirements for preventing heat-related injuries and managing heat stress hazards and exposures for workers involved in construction and demolition. NRCA is actively involved in the A10.50 standard development subgroup.

NRCA offerings

NRCA offers the following resources, some in Spanish, to help keep your workers safe in high-heat environments:

  • The NRCA Safety Manual
  • NRCA’s Toolbox Talks
  • Pocket Guide to Safety
  • Targeted Safety and Health
  • Training Series on Heat Stress

All are available at shop.nrca.net.


NRCA continues to strive to better understand and prevent heat-related illnesses. Through The Roofing Alliance, a study is currently underway to examine heat stress conditions among roofing workers. The study is being conducted through Florida Gulf Coast University’s U.A. Whitaker School of Engineering, Fort Myers. The study will address multiple aspects, including but not limited to an investigation into roofing worker response to working in hot environments.

Ultimately, roofing companies regardless of size should take steps to address and prevent heat stress for their workers. NRCA will continue to stay engaged with all regulatory rulemaking and consensus standard development related to heat stress while providing updates as the efforts progress.

I encourage all employers to review their current heat stress management programs or begin to develop new programs to address and prevent heat-related illnesses. NRCA provides members with resources and training in English and Spanish to help ensure the safety and health of their workers.

CHERYL M. AMBROSE, CHST, OHST, is an NRCA director of enterprise risk management.


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