Working in excessive heat can cause illness, whether outdoors (this summer again brought record-breaking heat to parts of North America), or indoors where equipment, combustion or other factors raise ambient working temperatures. Occupational safety and health agencies have slowly been expanding explicit requirements that employers protect their workers against heat stress. Most recently, the Maryland Department of Occupational Safety and Health (MOSH) adopted Heat Stress Standards effective September 30, 2024 (COMAR 09.12.32).
What situations do the new standards cover?
A body must shed excess heat to maintain a stable internal temperature when ambient temperatures are high. This is accomplished mainly by circulating blood to the skin, and by sweating. These mechanisms become less effective when the air temperature is close to or warmer than normal body temperature, and/or when high humidity deters effective evaporation. Even when they do work, the body tends to heat up, and fluids and salts lost by sweating will have to be replaced. Thresholds and interpretations vary across different governmental and professional standards.
Maryland’s new standards apply when employees are exposed to a heat index of 80 degrees Fahrenheit (oF) or higher, when working indoors or outdoors. However, the following situations are excluded:
- Emergency operations and essential services that involve protecting life or property;
- Incidental exposures when an employee is not required to perform work activities for more than 15 consecutive minutes per hour; or
- Buildings, structures, and vehicles that have a mechanical ventilation system or fan that maintains the heat index below 80 oF.
The standards define “heat index” as “a measure of how hot it feels when relative humidity is taken into account along with the actual air temperature, which can be extrapolated from temperature and relative humidity using the National Weather Service [NWS] Heat Index Calculator.”
What must employers do to prevent and manage heat-related illness?
In workplaces where employee heat exposures meet the standards above, the employer must do the following:
- Monitor workplace heat index – employers must monitor the heat index throughout each work shift, using one of the following:
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- Direct measurement of heat and humidity – this is required where employees work in buildings and structures that do not have mechanical ventilation systems
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- Use local weather reported by NWS or another recognized source to determine the heat index
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- Use the National Institute for Occupational Safety and Health (NIOSH) Heat Safety Tool application to determine the heat index
- Prepare a written Heat-related Illness Prevention and Management Plan with the following
- “How sufficient amounts of drinking water will be provided;
- How employees will be provided sufficient opportunities and encouragement to stay hydrated by drinking water;
- How to recognize the symptoms of heat-related illness, including heat exhaustion and heat stroke;
- How to respond to suspected heat-related illness, including heat exhaustion and heat stroke;
- How employees will be provided with sufficient time and space to rest in shaded or cool, climate-controlled areas to cool off;
- How the employer will implement rest break schedules as necessary;
- How the employer will consider environmental conditions, workload, required clothing, personal protective equipment, and alternative cooling and control measures when determining rest break schedules;
- How employees will be encouraged to take rest breaks as needed to prevent heat-related illness;
- How employees will be trained on the hazards of heat exposure and the necessary steps to prevent heat-related illness;
- The use and maintenance of alternative cooling and control measures used to manage heat;
- Procedures for heat acclimatization [see below];
- Procedures for high-heat conditions [see below]; and
- The emergency response plan [see below].”
- Acclimatization
- Provide acclimatization of employees exposed to workplace heat for up to 14 days, for new employees and those returning after 7 or more consecutive days of absence
- Monitor employees for heat-related illness during their acclimatization period (via phone/radio, a buddy system, or other effective method)
- Prepare a written acclimatization schedule with specified information
- Shade
- Unless “demonstrably infeasible or unsafe” provide shade to workers in outside hot areas, and outside, open, and exposed to air on at least three sides; prevent contributing heat sources from reducing effectiveness; sized for the number of employees utilizing the shaded area; arranged in a configuration that allows employees to sit in normal posture; and accommodate the removal and storage of personal protective equipment (PPE) during use
- Can cool with indoor mechanical ventilation system if adequate; or other alternative with benefits equivalent to shade
- Drinking water – provide at least 32 ounces of drinking water per hour per worker, at no cost to employees (may be provided at start of shift, or during shift)
- High-heat procedures – when the heat index reaches or exceeds 90 oF, including at least the following:
- Work and rest schedules to protect employees from heat-related illness, considering environmental conditions, activities, and clothing/PPE; and
- Rest periods, including either minimum rest period of 10 minutes for every 2 hours worked in heat index 90 - 100 Ff and minimum rest period of 15 minutes for every hour worked in heat index above 100 oF; or rest period as provided for in NIOSH recommendations; or alternative procedures at least as effective.
- Monitoring of exposed employees for signs of heat-related illness (via phone/radio, a buddy system, or other effective method)
- Emergency response – as specified, including onsite response and accessing offsite resources
- Training – for new and returning employees, including specified heat issues and the employer’s plan and procedures (and meeting required record requirements).
The written plan must be available and accessible to employees, and to MOSH upon request.
Now what?
These requirements are now effective in Maryland. Non-Maryland employers should at least consider them as guidelines for use in evaluating protections against heat; other jurisdictions are adopting or considering similar requirements (notably California, which I wrote about HERE https://blog.stpub.com/california-adds-heat-protection-rules-for-indoor-workplaces ), and the US federal Occupational Safety and Health Administration (OSHA) has proposed a standard that would apply to indoor and outdoor workplaces in OSHA-regulated parts of the country (which I wrote about HERE https://blog.stpub.com/osha-proposes-workplace-heat-protection-standard ; the future of that proposal under the incoming Trump administration is uncertain).
Self-Assessment Checklist
Do any of my organization's workers work in indoor situations where ambient heat may create a hazard of heat illness (e.g., enclosed spaces, work in manufacturing or other processes involving hot materials or equipment, and/or in confining and heat-retaining clothing and equipment)?
If so, does the organization provide appropriate:
- Training (tailored to the workplace source(s) of heat hazards, preventive measures, and responses to heat illness?
- Water?
- Shade or other appropriate ways for workers to cool down?
- Planning and procedures?
Does the organization include assessment of heat hazards in the design and construction of new facilities, and in structuring of work activities?
Where Can I Go For More Information?
- MOSH
- OSHA
- National Weather Service
About the Author
Jon Elliott is President of Touchstone Environmental and has been a major contributor to STP’s product range for over 30 years.
Mr. Elliott has a diverse educational background. In addition to his Juris Doctor (University of California, Boalt Hall School of Law, 1981), he holds a Master of Public Policy (Goldman School of Public Policy [GSPP], UC Berkeley, 1980), and a Bachelor of Science in Mechanical Engineering (Princeton University, 1977).
Mr. Elliott is active in professional and community organizations. In addition, he is a past chairman of the Board of Directors of the GSPP Alumni Association, and past member of the Executive Committee of the State Bar of California's Environmental Law Section (including past chair of its Legislative Committee).
You may contact Mr. Elliott directly at: tei@ix.netcom.com