Preventing Heat-Related Illnesses
How to Reduce Heat Burden from PPE and Other Factors
Editor’s note: The mention of specific companies, products, or services in this article does not constitute endorsement by AIHA or The Synergist.
Heat stress is a critical topic in worker safety, and for good reason. Unabated exposure to extreme heat during work can result in several occupational illnesses and, if not treated properly, even death. With the summer months upon us, now is a good time to review the risks, causes, policies, procedures, mitigation strategies, and training related to heat-related illnesses (HRIs). HEAT-RELATED ILLNESSES Heat stress on the body can result in symptoms of varying severity. It is important to be familiar with the different types of HRIs from least severe to most severe as well as the primary signs and symptoms, the primary cause of illness, and tips for prevention (see Table 1). The primary causes of heat stress in the work force include high air temperatures; high humidity; radiant heat sources, such as sun exposure, especially between 11 a.m. and 3 p.m. on hot days; lack of airflow, as when working in hot, poorly ventilated, or confined areas; direct physical contact with a hot object; strenuous physical activities; lack of hydration; and lack of acclimatization. Personal risk factors include obesity, diabetes, high blood pressure, heart disease, alcohol use, and illicit drug use. Compared to younger workers, those aged 65 years and older are more prone to heat stress and may not adjust as well to sudden changes in temperature. Older workers are more likely to have chronic medical conditions and use medications that affect how the body responds to sunlight or heat. Additionally, some prescription and over-the-counter (OTC) medicines may increase the risk for HRIs. It is important to familiarize yourself with medications that can increase sun sensitivity. Resources such as GoodRx and the California Department of Industrial Relations are great places to start. Important medications to consider include antibiotics, antidepressants, antifungal agents, antimalarial medications, acne medications, some diabetes medications, diuretics, some heart medications such as beta blockers, stimulants, and certain medicines used to treat autoimmune conditions and cancers. Some topical drugs can trigger photodermatitis or photoallergy, which may not appear for a few days. Common signs include itching, rash, redness, and swelling of sun-exposed skin. In individuals with darker skin tones, both kinds of reaction may cause hyperpigmentation. Popular OTC medications can also contribute to severe sunburn. OTC medications including ibuprofen, naproxen, many antihistamines, and supplements such as St. John’s wort can increase sun sensitivity and the risk of sunburn. PPE AND HEAT-RELATED ILLNESSES Personal protective equipment can present a variety of challenges related to heat illness. According to NIOSH, PPE can have the following effects on heat stress risks: • The clothing and gear used for PPE is often not made of breathable materials. As explained in a paper that appeared in Professional Safety, simply adding a shirt and pants will reduce heat loss by 40 percent. • PPE can keep heat and moisture inside and cause the worker’s body temperature to rise. • PPE can reduce the body’s normal abilities to get rid of heat—for example, through sweating. • The weight of some PPE can increase the physical effort needed to do a job, which can cause a worker to get hot faster. • Wearing personal protective clothing or PPE, especially in hot and humid conditions, can cause significant physiological stresses on workers and can lead to discomfort, fatigue, cognitive impairment, reduced manual performance, and HRIs, according to a 2006 paper in Industrial Health. Since the beginning of the COVID-19 pandemic, an increasing number of workers have been regularly wearing face coverings or filtering facepiece respirators (FFRs). While cloth face coverings can add to the user’s heat stress, respirators present a greater burden than the breathable fabric of most face coverings. Users of FFRs and air-purifying negative-pressure respirators can experience increased physiological demand, which can contribute to an increased risk of heat stress.
Table 1. Types of Heat-Related Illnesses
Tap or click on the table to open a larger version in your browser.
Another category of PPE that can have a significant impact on heat stress includes protective clothing made of fabrics that retain body heat. As NIOSH explains on its website, the more encapsulating the PPE that workers must wear, the greater their risk of experiencing heat stress and physiological strain. These fabrics do not breathe much and can add to the heat burden on the user. Basic items, such as waterproof aprons, surgical gowns, surgical caps, respirators, face shields, boots, and gloves, can also increase risks of HRIs. These items can reduce the body’s ability to get rid of heat by sweating. They may make the body hotter by holding in excess moisture, and their weight can lead to a worker getting hot faster. Other PPE, such as welding chaps and welding jackets, also increase the potential for heat stress.
The contributions of gloves and hardhats to heat stress are not commonly recognized, but they can increase the body’s heat load by reducing its ability to dissipate heat efficiently. A 2009 American Society of Petroleum Engineers (ASPE) study found that workers wearing a blue hardhat experienced greater heat stress and evaporated 60 percent more water than those wearing a white hardhat. Impervious gloves can also contribute to worker heat stress and skin dermatitis if the interior of the gloves gets too moist.
REGULATORY REQUIREMENTS AND CONSENSUS STANDARDS While OSHA does not have a standard for heat exposure, the agency has initiated a rulemaking process and launched a National Emphasis Program to address concerns with heat illness in the workplace. From an enforcement perspective, federal OSHA relies on the General Duty Clause of the Occupational Safety and Health Act to address heat illness. The agency can also apply the PPE standard’s requirement for employers to perform a PPE hazard assessment. Other relevant OSHA standards include those that require potable water in the workplace and training in first aid.
Even without a standard for heat illness, OSHA has issued several letters of interpretation (LOI) that discuss an employer’s duty to evaluate and address potential heat stress hazards when selecting and requiring PPE in the workplace. These LOI can be found on the agency’s website.
Some states with approved OSHA plans have enacted heat illness-related standards or are in the process of doing so: • In California, employers must provide training, water, shade, and planning. The requirements begin when temperatures reach 80 F. • The Minnesota standard applies to indoor workplaces. • The Washington standard applies to outdoor workplace exposures. • Maryland’s Occupational Safety and Health (MOSH) regulation is currently in draft form and is going through the public review and comment process.
Organizations that provide voluntary guidance for heat include ACGIH. The ACGIH heat stress guidance, which is based on wet bulb globe temperature (WBGT), allows for adjustments depending on the type of clothing worn, considers the demands of the work being performed, and further refines the Threshold Limit Value (TLV) for thermal stress and the OSHA action levels according to the type of work activity. All details about this guidance are outlined in the ACGIH book of TLVs and biological exposure indices. The ACGIH approach can be effective when considering the impact of extra layers of PPE and clothing.
NIOSH has also published a recommended standard for occupational heat stress to help employers prevent or greatly reduce the risk of adverse health effects.
STRATEGIES TO REDUCE HEAT STRESS Employers have several options for lessening the risks of heat exposure:
Develop a formal heat stress prevention program. A formal program will lay the groundwork for managers and supervisors who are managing heat exposures. Both OSHA and NIOSH have identified the basics of a heat stress management program. The plan should require employee training at all levels, including education on the different types of heat illnesses, their signs and symptoms, steps to minimize the risk of heat illness, and how to treat it.
Use engineering controls when possible. Engineering controls, such as the use of cooling air, are always preferred over other methods to mitigate potential hazards. However, engineering controls can be costly and sometimes impossible to implement due to job location, duration, or schedule.
Encourage acclimatization. Employers should be aware of the importance of acclimatizing workers to the hot environment and include acclimatization as part of their written heat stress prevention procedures. For a new employee entering this type of environment, NIOSH recommends no more than a 20 percent exposure on day one and an increase of no more than 20 percent on each additional day. For workers who have worked in this environment in the past, NIOSH recommends the acclimatization regimen should be no more than a 50 percent exposure on day one, 60 percent on day two, 80 percent on day three, and 100 percent on day four. Note that acclimatization will also be impacted by each worker’s physical condition and total heat stress exposure. As previously discussed, heat stress can be increased by the use of PPE.
Use protective clothing and equipment to reduce HRI risk. Where possible, light-colored, loose-fitting cotton clothing should be used. The lighter colors help reflect some of the sun, and the loose fit allows for maximum airflow and breathability to help cool the skin.
The more encapsu­lating the PPE that workers must wear, the greater their risk of experiencing heat stress and physiological strain.
While traditional PPE can contribute to heat illness risks, some new options can actually reduce these risks. Such clothing may have reflective properties or use cotton or other breathable fabrics. Cooling undergarments, vests, and shirts are available, some of which work mechanically and require batteries to promote airflow. These systems sometimes include a device for cooling hardhats or other headgear. Other cooling systems work passively and require the insertion of ice packs into vests. Towels dipped in water and draped around workers’ necks can also promote cooling.
PPE is critical to worker safety. If traditional PPE—that is, PPE made from non-breathable fabrics—is the only option, cooling devices can help promote its continued use. A powered air-purifying respirator (PAPR) can also provide some level of cooling by delivering air across the user’s head and face.
All these systems have limitations. Some require the employee to be tethered to either a water-cooled line or an air system. The ice packs add weight and will melt after a few hours. It is also essential to select a system that works best with the PPE demands of the job. Before adopting these systems, try the other strategies in this section first.
Structure work shifts accordingly. Work schedules should be structured to limit exposure during peak heating times. Where possible, projects should be planned for the cooler months of the year. Work breaks should be scheduled at set intervals to be sure employees are getting enough water, rest, and shade. The break areas should be designed to promote cooling and shade by providing cover, fans, misters, or even air conditioning.
Provide shade for breaks. Taking time to rest and finding shade are two essential steps for workers. The frequency of breaks needs to increase as the risk of heat stress rises. The conditions of the break area can also affect the length of the required break. For example, a cooler, more shaded area may allow for shorter breaks.
Encourage hydration. NIOSH provides guidance that workers should be encouraged to drink at least one cup (8 ounces) of water every 20 minutes while working in the heat, whether they are thirsty or not. Drinks with alcohol, sugar, or caffeine should be avoided. NIOSH also notes that for jobs with prolonged sweating lasting several hours, electrolyte-containing beverages such as sports drinks are recommended. Water alone cannot replace the electrolytes that are lost while sweating.
Monitor job conditions and employee exposures. The conditions at the job site need to be monitored and heat illness prevention measures adjusted accordingly. The OSHA-NIOSH Heat Safety Tool App can help monitor the heat index and other heat illness prevention details for your location. Other heat stress monitoring devices can be used to obtain direct readings of temperature, humidity, or WBGT.
Even when steps are taken to prevent it, heat illness can still occur, so staff must be trained to recognize the signs and symptoms and how to properly provide first aid.
Embrace new technologies. Current methods for heat exposure assessments, such as heat stress surveys and microclimate measurements, are available but have several limitations. For example, data gathered on outdoor thermal stress often does not include physiological and behavioral parameters. But several new wearable technologies are available that can monitor physiological changes. Such technologies include but are not limited to: • temperature monitoring systems that can also indirectly measure core temperature by a probe attached on an employee’s forehead • shirts with integrated technology that monitors heartrate, air temperature, and humidity to accurately assess core body temperature (a rise in core body temperature is an important indicator of heat illnesses and a key factor in heatstroke) • wrist-mounted devices that monitor environmental and physiological responses, including air temperature, humidity, heart rate, breathing rate, oxygen saturation, maximum rate of oxygen, skin temperature, and humidity • headgear equipped with heat sensors that monitor in-hardhat temperature • wireless ingestible thermometers that provide an immediate and objective measure of core temperature
THE BASICS OF PREVENTION Heat stress is not a new problem, and OEHS professionals will continue to manage this risk as long as workers have tasks to perform in hot environments. While the requirements of heat illness prevention standards may change and technologies help reduce risks, the basic steps in preventing heat illness—including acclimatization, water, rest, and shade—will remain critical.
JEFF L. BEHAR, CIH, CSP, spent the last 25 years as a principal safety engineer for the NASA Jet Propulsion Laboratory in Pasadena, California.
PAUL E. ALLEN, CIH, CSP, ARM, CRIS, AOEE, is the product consulting director, industrial hygiene, commercial risk control with CNA Insurance in Chicago, Illinois.
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Disclaimer: The information, examples, and suggestions presented in this material have been developed from sources believed to be reliable, but they should not be construed as legal or other professional advice. CNA accepts no responsibility for the accuracy or completeness of this material and recommends the consultation with competent legal counsel and/or other professional advisors before applying this material in any particular factual situations. This material is for illustrative purposes and is not intended to constitute a contract. In addition, this material is not intended to establish any standards of care, to serve as legal advice appropriate for any particular factual situations, or to provide an acknowledgement that any given factual situation is covered under any CNA insurance policy. Any references to non-CNA websites are provided solely for convenience, and CNA disclaims any responsibility with respect thereto.
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American Society of Petroleum Engineers: “A Study of Heat Related Factors Caused by Color Selection of Hard Hats and FRC Garments in Outdoor Work Environments,” SPE Annual Technical Conference and Exhibition (presentation by Michael Davis et al, October 2009).
California Department of Industrial Relations: “§3395. Heat Illness Prevention in Outdoor Places of Employment.”
California Department of Industrial Relations: “What Causes Heat Illness?
CDC: “Warning Signs and Symptoms of Heat-Related Illnesses.”
GoodRx: “These Medications Can Make You More Sensitive to the Sun” (July 2020).
Industrial Health: "Protective Clothing in Hot Environments" (2006).
Johns Hopkins Medicine: “Heat-Related Illnesses (Heat Cramps, Heat Exhaustion, Heat Stroke).”
Keller & Heckman: “OSHA Turns Up the Heat on Heat Illness” (October 2021).
Minnesota Legislature: “Minnesota Administrative Rule: 5205.0110 Indoor Ventilation and Temperature in Places of Employment.”
NIOSH: “Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments.”
NIOSH: “Limiting Heat Burden While Wearing PPE.”
NIOSH Science Blog: “Heat Stress Imposed by PPE Worn in Hot and Humid Environments” (August 2020).
OSHA: “Heat.”
Professional Safety: “Chemical Protective Clothing and Heat Stress” (December 1984).
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The Synergist: “It’s the Heat—And the Humidity: Critical Factors for Heat Stress Assessment and Prevention” (April 2020).
WebMD: “Understanding Heat-Related Illness—Symptoms” (July 2021).