Heat Stress

Heat stress is one of the most common (and potentially serious) illnesses that can affect many workers at indoor and outdoor job sites. As a result of heat stress, several mild to severe physical reactions can occur such as fatigue, anxiety, irritability, decreased concentration, and decreased dexterity and movement. If left untreated, heat stress ultimately can result in death. Heat-related illnesses are a leading cause of death from natural weather or environmental events. According to the American Public Health Association (APHA), an average of 658 people died per year in the U.S. from 1999 to 2009 due to exposure to excessive natural heat.

Although the Occupational Safety and Health Administration (OSHA) currently does not have standards specific to heat-related illnesses, courts have interpreted OSHA's general duty clause to mean that an employer has a legal obligation to provide a workplace free of conditions or activities that either the employer or industry recognizes as hazardous and that cause, or are likely to cause, death or serious physical harm to employees when there is a feasible method to abate the hazard. This includes heat-related hazards that are likely to cause death or serious bodily harm.

When hazards related to heat are present or expected to be present at a job site, employers should plan ahead to protect workers. Employers should create a written plan to prevent heat-related illness. A job safety analysis (JSA) is a great hazard assessment that can be beneficial to mitigating heat stress. Heat conditions can change rapidly and management commitment to adjusting heat stress controls is critical to prevent heat illness. An individual at the job site should be responsible for monitoring conditions and implementing the employer's heat plan throughout the workday. This individual can be anyone with the proper training, which includes knowing how to

  • identify and control heat hazards;
  • recognize early symptoms of heat stress;
  • administer first aid for heat-related illnesses; and
  • activate emergency medical services quickly when needed.

The Personal Protective Equipment (PPE) standard at 29 Code of Federal Regulations (CFR) 1910.132(d) requires every employer in general industry to conduct a hazard assessment to determine the appropriate PPE to be used to protect workers from the hazards identified in the assessment. The National Institute for Occupational Safety and Health (NIOSH) has published criteria for a recommended standard for occupational heat stress. The NIOSH document “Criteria for a Recommended Standard – Occupational Exposure to Heat and Hot Environments” (NIOSH Publication Number 2016-106, February 2016) includes recommendations for employers about how to prevent heat-related illnesses.

Heat Stress Ailments and First Aid

The various degrees of heat-related illnesses (in order of less severe to most severe) and the appropriate first aid measures to take are summarized as follows:

  1. Heat Fainting - Occurs when an individual is in a standing position, caused when the return of blood to the heart is not sufficient and the brain suffers from a temporary shortage of blood supply. Lying flat helps to restore the normal blood circulation. The individual should be moved to a cooler area.
  2. Heat Rash - Also known as prickly heat, is skin irritation caused by sweat that does not evaporate from the skin, and is the most common problem in hot work environments. Symptoms include the appearance of tiny red bumps or blisters on the skin, often on the upper chest, neck, and folds of skin. Try to work in a cooler, less humid environment when possible, and keep the affected area dry (can apply mild drying lotions).
  3. Heat Cramps - Caused by profuse perspiration with an inadequate fluid intake and chemical replacement (especially salts). Symptoms are muscle spasms and pain in the extremities and abdomen, and can occur during or after work hours. To treat heat cramps, rest and drink plenty of water and electrolyte supplements, such as sports drinks cut with water. A few hours should lapse before the worker returns to strenuous work. If the cramps do not abate, have worker seek medical attention.
  4. Heat Exhaustion - Is the body's response to loss of water and salt from heavy sweating, and is caused by increased stress on various organs trying to meet increased demands to cool the body. Symptoms are fast heart rate, headaches, nausea or vomiting, shallow breathing, profuse sweating, weakness, thirst, irritability, dizziness or light-headedness, lethargy, and pale, cool, moist, clammy skin. Treatment methods include:
    • Have worker sit or lie down in a cool, shady area.
    • If available, have a fan blow on worker to help cool down.
    • Give worker plenty of water or other cool beverages to drink.
    • Cool worker with cold compresses/ice packs.
    • If signs or symptoms worsen or do not improve within 60 minutes, take worker to a medical clinic or emergency room for medical evaluation or treatment.
    • Worker should not return to work that day.
  5. Heat Stroke Is the most serious form of heat-related illness and can result in death, if left untreated. Occurs when the body becomes unable to regulate its core temperature, sweating stops, and the body can no longer rid itself of excess heat. Symptoms include lack of perspiration, very high body temperature, confusion, seizures, fainting, strong rapid pulse, and red, hot, dry skin. Immediately get medical help by calling 911! Cooling must immediately occur to prevent serious injury and/or death. While waiting for help:
    • Place worker in shady, cool area.
    • Loosen clothing, remove outer clothing.
    • Fan air on worker; cold packs in armpits.
    • Wet worker with cool water; apply ice packs, cool compresses, or ice if available.
    • Provide fluids (preferably water) as soon as possible.
    • Stay with worker until help arrives.

Heat Index

Outdoor workers who are exposed to hot and humid conditions are at risk of heat-related illness. The risk of heat-related illness to outdoor workers becomes greater as the weather gets hotter and more humid. This situation is particularly serious when hot weather arrives suddenly early in the season, before workers have had a chance to adapt to warm weather. For people working outdoors in hot weather, both air temperature and humidity affect how hot they feel. The U.S. National Oceanographic and Atmospheric Administration (NOAA) developed the heat index system, which combines both air temperature and relative humidity into a single value that indicates the apparent temperature in degrees Fahrenheit, or how hot the weather will feel. The higher the heat index, the hotter the weather will feel, and the greater the risk that outdoor workers will experience heat-related illness. The heat index is a better measure than air temperature alone for estimating the risk to workers from environmental heat sources. NOAA’s heat index table followed by a table showing the protective measures to be undertaken based on the heat index are as follows:

Heat Index Risk Level Protective Measures
Less than 91°F Lower (Caution) Basic heat safety and planning
91°F to 103°F Moderate Implement precautions and heighten awareness
103°F to 115°F High Additional precautions to protect workers
Greater than 115°F Very High to Extreme Triggers even more aggressive protective measures

Other factors should be taken into consideration when using the heat index, even if the heat index value is lower.

  • Working in direct sunlight - adds up to 15 degrees to the calculated heat index number.
  • Conducting prolonged or strenuous work.
  • Wearing heavy protective clothing or impermeable suits.

Evaluation and Monitoring

Before initiation of the work tasks, site conditions as well as the staff preparedness should be assessed by properly-trained personnel. Physical factors such as the type of work, level of physical activity and duration, and clothing color, weight and breathability should be evaluated before starting a work task. For outdoor work, the heat index table should be used to derive the anticipated maximum heat index number based on the forecast high temperature and humidity for the workday. Modifications should be made before task initiation to ensure that these factors do not exacerbate possible heat issues.

Once the work has begun, monitoring the vital signs of workers is vital to the prevention of heat stress. It is important to identify heat stress symptoms before they become serious. The following monitoring systems should be used when working under heat stress conditions:

  • Fluid Intake - When wearing impermeable clothing, it is possible to have a sweat rate as high as 3.5 liters/hour. These lost fluids must be replaced intermittently throughout the day.
    • Water is highly recommended, but workers are encouraged to drink any hydrating beverage of their choice, such as fruit juices or electrolyte replacement drinks cut with water (recommended 3:1 ratio for either). Alcoholic and caffeinated beverages and beverages with a high sugar content are not recommended as they provide little to no bodily rehydration. Whatever drink is chosen for consumption, it should be served cooled to between 50 and 60 degrees Fahrenheit (oF).
    • Fluid intake should begin before the work shift starts and after the morning weight is recorded. This provides for body water that will be lost in the first work period.
    • For each one-half pound lost, 8 ounces of replacement fluids should be consumed.
    • One and one-half percent body water loss is acceptable, if it is replaced before the following morning.
  • Temperature - The deep core body temperature is most representative of actual body temperature. During field conditions, an oral temperature can be established for each individual from data collected over a two-week period, then used as a standard in monitoring for heat stress for the respective individual.
  • Heart Rate - The heart rate is probably the best indicator of overall body stress. The pulse, in addition to reflecting aerobic exercise, becomes more rapid as the body tries to cool itself. A maximum heart rate should be established for each worker.

Prevention and Controls

Tailgate Safety Meetings at job sites where protective gear is being worn are an important element of heat stress prevention. Fluid replacement and rest periods are the most effective means of alleviating heat stress. The following preventative measures should be taken into consideration when working during times or in areas of high air temperature:

  • Monitoring for heat stress.
  • Acclimatization of workers.
  • Establishment of work and rest regimes. Consider frequent breaks and reasonably short work periods with intermittent rest periods. The accessible rest areas should be cooler than the work areas.
  • Pacing of tasks to help alleviate heat stress.
  • Performance of heavy tasks in cooler areas or at cooler times (early morning or later in evening).
  • Provide employees with access to shaded areas that are either open to the air or provide the employees with ventilation or cooling.
  • Rotation of personnel on jobs performed in high temperature areas.
  • Implement a buddy system when Level B or C PPE is required.
  • Use of ice vests.
  • Maintenance of shower sprinkler on the site.
  • Provide cool drinking water and sports drinks, if possible, to replace electrolytes.
  • Eating salty foods during rest regimes.

Workers need to have a written job safety analysis to prevent heat-related illness. A JSA worksheet will help workers identify the hazards within a jobsite and then determine what controls and safety procedures need to be implemented. JSABuilder.com is a fantastic on-line job safety analysis app to assist in preparing your Job Safety Analysis or Activity Hazard Analysis. Set up a free trial account today and follow us on Twitter @JSABuilder, where we Tweet about Health and Safety, provide Safety tips, and updates on current Health and Safety topics.