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Heat Stress - MOSH

image of man outside in a hard hat leaning on a piece of equipment taking a rest break

Overview

Heat-related illness has been acknowledged as a workplace hazard for many years. Understanding heat stress can help maintain safety when working in hot conditions. Workers exposed to extreme heat or hot environments face risks of heat stress, leading to various occupational illnesses and injuries such as heat stroke, exhaustion, cramps, and rashes. Heat also heightens the risk of accidents due to sweaty palms, fogged safety glasses, and dizziness, while burns can result from contact with hot surfaces or steam. Those particularly vulnerable to heat stress include outdoor laborers and workers in occupations like firefighting, baking, farming, construction, mining, boiler operation, and manufacturing. Workers over 65, overweight individuals, those with heart disease or high blood pressure, and those on medications sensitive to heat are at greater risk. Preventing heat stress is vital. Employers should train workers on recognizing, preventing, and managing heat stress to safeguard their health and safety.

Maryland's heat stress standard, COMAR 09.12.32 went into effect September 30, 2024. The standard applies to all workplaces where the heat index is 80° F or higher.

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MOSH Heat Stress Regulation and Guidance Documents New

Heat Stress Standard: Summary of Key Maryland Requirements

Maryland Occupational Safety and Health (MOSH) Heat Stress Standards apply to both indoor and outdoor workplaces where there is employee exposure to a heat index at or above 80 degrees Fahrenheit. This document is intended to provide guidance on the Maryland Heat Stress Standards. Employers should refer to COMAR 09.12.32 for full requirements of the standards.

Heat Index Monitoring:

The heat index is to be monitored through direct measurements, local weather data, or the NIOSH Heat Safety Tool application.

Heat-Related Illness Prevention and Management Plan:

A written plan must be developed, implemented, and maintained. The plan should be available and accessible to employees and MOSH upon request.

Acclimatization:

Employees who are newly exposed to heat or are returning from 7 or more days of absence are to be provided with acclimatization for a period of up to 14 days. During the acclimatization period, employees are to be closely monitored through regular observation and/or communication. An acclimatization schedule is to be put in writing.

Shade:

Shaded areas are to be provided for employee rest periods. If a shaded area is demonstrably infeasible or unsafe alternative cooling and control methods must be implemented. Cooling with an indoor mechanical ventilation system may be used as an alternative.

Drinking Water:

Suitably cool drinking water must be provided to employees at no cost and located as close to the work area as practicable. Each employee should have at least 32 ounces of water per hour available to them.

High Heat Procedures:

When the heat index reaches or exceeds 90°F high heat procedures shall be implemented. This includes employee rest periods or alternative cooling and control measures, and mandatory employee monitoring. Rest periods should follow the table below or NIOSH recommendations.

Heat Index

Rest period

Above 90°F and below 100°F

Minimum of 10 minutes every 2 hours

Above 100°F

Minimum of 15 minutes every hour

Employers shall implement an emergency response plan.  This plan shall include procedures for communication, response, monitoring and care, emergency contact, and transport.

Training:

Employees and supervisors shall be provided prior to initial heat exposure. Retraining is to be conducted annually, and immediately following an incident at the worksite involving a suspected or confirmed heat-related illness. The training must be presented in a manner employees can understand. Training records shall be maintained for one year and provided to MOSH upon request.

Tips for Preventing Heat Illness

  • Stay hydrated by drinking 1 cup of cool water every 20 minutes, even if not feeling thirsty.
  • Opt for drinks with electrolytes for longer durations, avoiding energy drinks and alcohol.
  • Take breaks in shaded or cool areas to allow the body to recover.
  • Dress appropriately for the heat with a hat and light-colored, loose-fitting, breathable clothing.
  • Replace a damp or soiled face covering and check on others verbally.
  • Acknowledge individual differences in heat tolerance and understand personal risk factors.
  • Familiarize yourself with engineering controls, work practices, and personal protective equipment to mitigate heat-related risks.

Working in Outdoor and Indoor Heat Environments

Many outdoor fatalities, ranging from 50% to 70%, occur within the initial days of working in warm or hot environments due to the body's need to gradually acclimatize to heat. This process, known as heat acclimatization, is crucial as lack of it significantly increases the risk of fatal outcomes. Occupational risk factors for heat illness include heavy physical activity, warm environments, lack of acclimatization, and clothing that retains body heat. Heat exposure can pose hazards indoors or outdoors, year-round, under suitable conditions, not just during heat waves. Employers must also fulfill their responsibility to safeguard workers' safety and health and implement strategies voluntarily to ensure safe and productive workplaces.

Below are examples of industries in which workers have experienced heat-related illnesses.

(Courtesy OSHA)
Outdoors Indoors
Agriculture Bakeries, kitchens, and laundries (sources with indoor heat-generating appliances)
Construction – especially, road, roofing, and other outdoor work Electrical utilities (particularly boiler rooms)
Construction – roofing work Fire Service
Landscaping Iron and steel mills and foundries
Mail and package delivery Manufacturing with hot local heat sources, like furnaces (e.g., paper products or concrete)
Oil and gas well operations Warehousing

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Symptoms and Causes of Heat Illness

As indicated by its name, heat illness conditions arise due to heat exposure, where excessive heat raises the body's core temperature. Prolonged exposure to abnormal levels of heat and humidity, without sufficient relief or fluid intake, can trigger a range of heat-related illnesses. Sweating becomes ineffective in cooling the body. Heat illness can range from mild to life-threatening, including several different conditions. Heat-related illnesses can impact employees' job performance and elevate their likelihood of experiencing accidents.

The most common heat illness is categorized as either mild or severe.

Heat Rash - Occurs when excessive perspiration becomes trapped beneath the skin, obstructing sweat glands.

Heat Cramps - Muscle cramps can develop when intense sweating causes the loss of electrolytes and fluids, typically during exercise in hot conditions.

Heat Exhaustion - This condition can occur following prolonged exposure to high temperatures without adequate fluid intake.

Heat Stroke - Results from a rapid rise in core body temperature due to elevated heat and humidity. Most serious heat-related illness.

Heat Standards from Other OSHA State Plans for Reference and Resources