Today, we will tackle a crucial topic as we head into those hotter months – exposure to heat. Whether working outdoors, enjoying summer fun, or simply trying to stay cool, understanding how to manage heat exposure is crucial for your health and safety.
This post will discuss the essentials of staying safe when temperatures rise. We’ll discuss the risks associated with excessive heat, how to recognize the signs of heat-related illnesses, and practical steps to protect yourself and others. Staying informed and prepared can make all the difference in enjoying the summer without any heat-related mishaps.
What You’ll Learn
- Understanding Heat Risks: Gain insights into the potential dangers of heat exposure and how it can impact your health.
- Recognizing Heat-Related Illnesses: Learn how to identify the symptoms of heat-related conditions such as heat exhaustion and heatstroke.
- Practical Heat Safety Tips: Discover effective strategies to stay cool and safe during high temperatures, including hydration tips and protective measures.
Introduction
The human body must maintain a constant internal environment, even when external conditions alter. This equilibrium is called homeostasis. Homeostatic balance occurs when receptors monitor the environment and respond to these changes to balance the body’s internal workings within a small window or range.
However, the body has only a limited capacity to adjust to extremes of temperature and humidity. An imposed heat stress from the environment will strain the body. This typically produces physiological reactions such as increased skin temperature, sweat production, heart rate, and core temperature. Low levels of heat stress cause discomfort because the body must adjust to cope with the extra heat load, while higher levels can lead to serious health problems.
The Effects of Exposure to Excessive Heat
When the body is unable to regulate core body temperature at an optimal level adequately, heat illness may result. Working in a hot environment puts the body (and the cardiovascular system) in a difficult situation.
Ultimately, the body must ensure working muscles have an adequate blood supply, but it must also redistribute blood to the skin to facilitate heat exchange through conduction. To do this, a disproportionate amount of blood is shunted to the skin for heat exchange. The consequence of this routing of blood is a reduction in the volume of blood returning to the heart, thereby decreasing the amount of blood pumped per heartbeat (stroke volume).
In hot conditions, vasodilation first increases heat loss, which increases blood flow and raises skin temperature. If this is insufficient, body temperature will rise further, and sweating increases heat loss by evaporation. Repeated exposure to heat leads to modified responses in the sweating mechanism and cardiovascular system. This is known as heat acclimatization.
Excessive fluid loss can occur over a work shift when the environment is hot and humid (the air is saturated with water vapor). This is due mainly to evaporative heat loss achieved by sweating and inadequate hydration. Depending upon the severity of fluid loss, the total blood volume can decrease so much that stroke volume is reduced.
The significant effects of exposure to heat stress are prickly heat rash, heat cramps, heat edema, heat syncope, heat exhaustion, heatstroke, and hyperpyrexia.
Physiological Monitoring of Exposure to Heat
Heat stress can be assessed by measuring its effect on the human body using physiological monitoring (Tustin et al., 2018). This involves testing individual workers rather than the environment in which they are working. The advantages of this type of exposure include:
- The ability to track an individual’s response to heat
- Avoid generalizations about fitness, acclimatization, and hydration that are assumed with environmental monitoring.
Direct measurements of heart rate, core body temperature, skin temperature, and sweat loss are the most efficient and accurate methods of evaluating whether a worker is at risk of a heat-related illness.
Environmental Monitoring of Exposure to Heat
The least intrusive way to monitor a worker’s exposure to excessive heat is to measure the environment. Environmental factors influencing heat exchange include the air temperature, humidity, airflow, and surrounding surface temperature. Therefore, the four fundamental parameters that need to be considered are:
- Air temperature (wet bulb and dry bulb)
- Relative humidity (the partial pressure of water vapor in the air expressed as a percentage of saturation vapor pressure, which varies with temperature)
- Mean radiant temperature (the average temperature emitted from a radiant heat source)
- Air velocity (the air velocity is related to evaporative and convective methods of heat loss).
Heat Stress Indices
A heat stress index is a single number that integrates the effects of fundamental parameters in any thermal environment. It aims to correlate the number with the thermal strain experienced by an exposed person. At this point, it is essential to distinguish between two terms: heat stress and heat strain. Heat stress describes the total heat load on the body from all sources. Heat strain relates to the physiological response to the imposed stress.
Heat stress indices aim to accurately predict workers’ physiological state during exposure. This, in turn, will allow assessment of the permissible exposure duration and rest breaks. Even though the development of an index has continued for a century, it has proved difficult to derive a single-figure heat stress index that is both an accurate indicator of risk and universally applicable.
More than a dozen heat stress indices are probably available to study the relationship between heat stress and heat strain. The main indexes that can be used to manage the risk of heat stress are the:
- Effective Temperature (ET) or Corrected Effective Temperature (CET)
- Predicted 4-hour Sweat Rate (P4SR)
- Wet Bulb Globe Temperature (WBGT)
- Heat Index (HI)
- Required Sweat Rate.
While WBGT is the long-accepted index representing the environmental contributions to heat stress (Tustin et al., 2018; Falahati et al., 2012), the Heat Index is also a commonly reported index and is used for heat stress guidance (Garzon-Villalba et al., 2019).
Controls for Heat Exposure
Minimizing exposure to heat is best achieved using an integrated approach based on the hierarchy of control (Chirico & Magnavita, 2019). Where heat is identified as a risk, a policy should be drawn and procedures developed to incorporate issues such as:
- Defining the nature and magnitude of hot work and any regulatory requirements for compliance
- Methods of evaluating exposure to heat
- Pre-employment medicals and fit-for-work testing
- Acclimatization
- Clothing and personal protective equipment
- Diet, fluid replacement, and hydration
- Engineering controls, including ventilation and cooling systems
- Training for personnel exposed to hot conditions.
Summary
Exposure to heat typically results in the body compensating for any temperature gains to maintain homeostasis. However, where this is impossible, a resulting heat strain may occur. Risks associated with exposure to heat can be managed through either physiological or environmental monitoring.
Environmental indices such as WBGT, ET, P4SR, HI, and required sweat rate can be used for exposure to heat.
Helpful Resources
- Heat Exposure and Human Health in the Context of Climate Change, by Yuming Guo and Shanshan Li
- Human Health and Physical Activity during Heat Exposure, by Yuri Hosokawa
Bibliography
Chirico, F., & Magnavita, N. (2019). The significant role of health surveillance in the occupational heat stress assessment. International Journal of Biometeorology, 63, 193-194. https://link.springer.com/article/10.1007/s00484-018-1651-y
Falahati, M., Alimohammadi, I., & Zokaei, M. (2012). Evaluating the reliability of WBGT and P4SR by comparison to core body temperature. Iran Occupational Health, 9(3), 22-31. https://www.researchgate.net/publication/286272413_Evaluating_the_reliability_of_WBGT_and_P4SR_by_comparison_to_core_body_temperature
Garzon-Villalba, X., Ashley, C., & Bernard, T. (2019). Benchmarking Heat Index as an occupational exposure limit for heat stress. Journal of Occupational and Environmental Hygiene, 16(8), 557-563. https://pubmed.ncbi.nlm.nih.gov/31233385/
Notley, S., Flouris, A., & Kenny, G. (2018, September). On the use of wearable physiological monitors to assess heat strain during occupational heat stress. Applied Physiology, Nutrition, and Metabolism, 43(9). https://cdnsciencepub.com/doi/abs/10.1139/apnm-2018-0173
Tustin, A., Lamson, G., Jacklitsch, B., Thomas, R., Arbury, S., Cannon, D., Gonzales, R., & Hodgson, M. (2018, July 6). Evaluation of Occupational Exposure Limits for Heat Stress in Outdoor Workers — United States, 2011–2016. Morbidity and Mortality Weekly Report, 67(26), 733-737. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6048976/
