Industrial firefighting is hard, dangerous work. Exposure to fumes, chemicals and burns put firefighters at risk. Extreme heat at fires and high temperatures during strenuous physical activity also pose risk.
Heat stress occurs when an accumulation of heat inside the body outpaces its ability to dissipate heat.
This heat stress can occur from accumulated heat either made internally by the human body's physiological processes, especially the work by muscles, or absorbed externally in an environment like those working in the summer sun or in a blazing fire. As heat accumulates, the body must work to dissipate and help maintain thermoregulation. As the environment introduces more heat stress to the body, it becomes unable to dissipate at a sufficient rate to maintain a safe internal temperature.
Many medical conditions known as heat-related injuries can occur if the level of heat stress on an individual is sufficient. Heat-related injuries span a spectrum from nominal to severe.
At the lower end of severity are heat rashes and heat cramps. These are early manifestations of too much heat stress on the body. Without proper intervention, heat exhaustion can proceed to heat stroke, which can damage the brain and other vital organs, and even cause death.
WHAT CAUSES HEAT-RELATED INJURIES?
The major contributing factors to heat stress are the environment, the worker, and the work. Understanding these three factors can help.
A heat-related injury occurs when the body’s normal mechanisms cannot regulate its internal temperature. Typically, at high temperatures, the body's primary effort to cool itself occurs through the evaporation of sweat. Under certain conditions, however, this cooling system becomes less effective. When surrounding air has high humidity levels, sweat cannot evaporate as quickly, preventing the body from releasing heat. Without proper fluid intake, excessive fluid loss and electrolyte imbalance may lead to dehydration. In these cases, a person’s body temperature rises rapidly.
Additional factors also limit the body’s ability to regulate temperature. These factors include: age, obesity, fever, dehydration, heart disease, poor circulation and drug or alcohol use.
HOW TO CALCULATE HEAT LEVELS
Understanding the environment of a work area lays the backdrop for understanding how to prevent and mitigate heat stress. Take heat measurements at the work site or as close to the work site as possible. For jobs where workers move between different zones or locations, take heat measurements at each individual area and during each period of working in constant heat levels. Generate worker task zone heat profiles to understand variations and set threshold limits.
The best approach in determining environmental heat is to use the Wet Bulb Globe Thermometer (WBGT) method. The U.S. Army was one of the earliest users of WBGT. The method is widely accepted to provide the most accurate estimation of heat by considering five different variables in its equation:
- Wind speed
- Sun angle
- Cloud cover (solar radiation)
You can use methods such as Corrected Effective Temperature (CET), or Wet Globe Temperature (WGT) to convert them to an approximation of WBGT. You can find a detailed dive on WBGT at Korey Stringer Institute.
With WBGT, commanding officers, safety managers and industrial hygienists can manage workloads and help optimize performance in high-temperature environments.
Let’s look at how the type of work increases the risk of heat injuries and the effort needed to reduce the impact.
As a workload becomes more challenging, the body recruits more muscles to perform. The higher the workload (intensity and duration), the more the body generates heat. Muscle groups transfer body heat via the conductive heat exchange between the working muscles and blood to the core, resulting in an increased body temperature. In short, the more rigorous the work and the longer it lasts, the more core temperature will increase.
Understanding what type of work is being achieved helps determine a safe zone to complete it in. There are a few methods for evaluating work type for individuals working in hot environments.
Here are two common formulas for determining workload based on environmental heat:
- NIOSH has a handy guide to help and urges employers to limit worker exposures to combinations of metabolic and environmental heat greater than the applicable Recommended Alert Limits (RALs) and Recommended Exposure Limits (RELs)
- OSHA has a similar method used to determine the metabolic work rate, which is then used to determine the Threshold Limit Value (TLV) or Action Limit (AL)
The American Conference of Governmental Industrial Hygienists (ACGIH) prescribes screening criteria for TLV and Action Limit for Heat Stress tables but recommends using physiological monitoring in advanced workload scenarios.
HOW HOT IS MY TEAM GETTING?
That’s a great question for firefighter safety. Let’s look at how to measure the heat generated by firefighters to help with heat-related illness prevention.
As firefighters perform activities, their muscles generate heat. We call this metabolic heat. Finding the metabolic heat of an individual occurs in two ways, through direct and indirect calorimetry. Both must be performed in a laboratory setting. Fortunately, the National Institute for Occupational Safety and Health (NIOSH) recommends an alternative to gauge how your team is doing: physiological monitoring (e.g., equipping sensors for heart rate, core body temperature, and body water loss, etc.).
With recent advances in remote physiological monitoring, the right balance between accuracy and practicality is being found.
6 TYPES OF HEAT STRESS
Heat-related illnesses can vary in severity. It’s important to understand the possible progress of an injury and intervene at the earliest level. An increase in a body temperature of two degrees Fahrenheit can affect mental functions. A five-degree Fahrenheit increase can cause serious illness or death. For workers in hot environments or during hot weather, a heat injury may be an underlying cause for other types of injuries like heart attacks, falls and equipment accidents.
Heat rash is a milder form of a heat-related injury and occurs in hot humid environments. It occurs when sweat ducts become blocked from profuse sweating. It can occur at any age but is most prevalent in children.
Heat rash often appears as a cluster of small red pimples or blisters. The skin irritation can be itchy. It typically occurs on the neck and upper chest, in the groin, under the breasts, and in the elbow creases.
Heat Cramps: Often associated with heavy perspiration, most notably during strenuous activities heat cramps are the body's response when sweat depletes needed internal salt and moisture levels. As the body loses these electrolytes, it can lead to painful muscle cramps, often following exercise. Heat cramps may also be a symptom of heat exhaustion. Heat cramps most often present in the abdomen, arms, or legs following strenuous activity. If the affected person has heart problems or is on a low-sodium diet, seek medical attention for heat cramps.
Heat Syncope (fainting): Heat syncope is a fainting episode that occurs when your body, to cool itself, causes blood vessels to dilate so much that it reduces blood flow to the brain. When a person rapidly rises from prone or sitting positions, a fainting spell can occur. It typically occurs when individuals are not acclimatized to the heat. Dehydration and lack of acclimatization can be contributory factors to heat syncope.Signs of heat syncope include dizziness or lightheadedness and fainting because of prolonged exposure to heat, dehydration, or orthostatic hypotension.
Heat Exhaustion: Heat exhaustion is the body's response to an excessive loss of water and salt in sweat because of engaging in physical activity (work or exercising) in a hot environment. The body temperature may be normal or mildly elevated, but not above 104 F (40 C). It often occurs in individuals who unaccustomed to working or exercising in the heat. Signs of heat exhaustion: nausea and vomiting, headache, muscle cramps, weakness, and profuse sweating.
Heat Stroke: The most severe form of heat-related injury, heat stroke, can lead to death or permanent disability. Heat stroke occurs when the body’s temperature rises rapidly over 104 Fahrenheit (F). With such a quick rise, temperatures at this level can quickly damage the brain and other vital organs. The extent of injury depends on the duration of exposure to excessive heat and the peak temperature attained. We sometimes refer to heat stroke as sunstroke.
Signs of heat stroke include: high body temperature (above 104 F), skin that is red or hot, either moist or dry skin (sweating may have stopped), rapid heart rate, difficulty breathing, headache, dizziness, loss of coordination, nausea and vomiting, confusion and restlessness, seizures, and unconsciousness/coma.
HEAT STRESS PREVENTION
A vigorous heat-related illness prevention program is a multi-pronged approach that minimizes the impact on your team’s exposure to heat-related illnesses and injury.
The OSHA Technical Manual Section III: Chapter 4 helps highlight what a successful heat-related illness prevention program could look like. It has four main pillars:
- Acclimatization Program: A great program begins with preparation. For firefighters working in hot work zones, a heat acclimatization program is a must. Heat acclimatization occurs over a period somewhere between 7-14 days with a methodical, incremental approach where environment and exposures are sufficiently stressful to invoke profuse sweating and elevated body temperatures but not to a point of heat exhaustion. Generally, a slower, more methodical approach will achieve the best results in a workforce.
- Medical Monitoring Program: Strong heat-related illness prevention programs can factor in a worker's individual medical needs as well as interpret the aggregate needs of an organizational workforce at scale. A properly set up medical monitoring program seeks to evaluate workers before, during and after risk exposures and look for ways to mitigate any unnecessary impact on the physiology of an individual.Properly equipped programs provide accurate measurement for monitoring the health of a workforce (core temperature, hydration, pulse, blood pressure, etc.). This information drives conversation around what is or is not working in a program and how to support the workforce.
- Training Program: Just like many safety topics, awareness and action are key to maximizing effects. Providing team members with a clear understanding of preparedness for hot work ensures adequate knowledge and shows leadership's buy-in to safety.Typical training sessions should include topics such as how to spot symptoms other members, understanding proper hydration, and understanding what other factors can contribute to heat stress. Adequate training reserved for management staff on proper weather reports, how to use adjusted temperatures (heat index, humidex or WBGT) to decide. The OSHA Heat Illness Prevention Training Guide outlines an approach to training. It provides flexibility to deliver training in either one 45-minute training session or three 15-minute sections to cover: Health effects of heat, how to respond to symptoms, and preventing heat illness.
- Heat Warning System: A heat warning system (HWS), heat health warning system (HHWS) or heat alert program (HAP) is an action plan set in place to help notify a group of individuals, whether at the community, organization, or worksite level of an impending heat wave and to begin to help to minimize the risks associated with it. There is increasing evidence that heat warning systems are effective in reducing mortality and even morbidity rates during a heat wave.
Include thoughtfully implemented plans ranging from short-term warnings, advisories, cooling shelters and “buddy” checks to longer-term plans such as improving building and living environments into an effective heat warning system. An effective heat warning system has these components:
- Weather forecasts such as those from the National Weather Service
- A system for determining how weather patterns may impact a range of health outcomes
- A spectrum of thresholds and actions
- A mechanism for alerting the areas impacted, whether those areas are widespread or targeted.
Zack Braun is cofounder and CEO at FireHUD Inc where he has led the commercialization efforts of their flagship product, the BioTrac Platform. The team focuses on creating reliable, rugged, and easy-to-use safety solutions for firefighter, military, and industrial applications. FireHUD received five distinct SBIRs from the National Science Foundation and the United States Department of Defense totaling nearly $2M in funding. Braun is on the Forbes 30 under 30 list and recognized by many safety organizations for his work with FireHUD. He is a graduate of the Georgia Institute of Technology in Atlanta, Georgia, where he lives with his two dogs. He looks forward to getting married this summer and continuing to advance the safety of firefighters, military members, and industrial workers in the ever-growing field of Connected Worker Safety.