Heat stress and its impacts on occupational health and performance

Workplace heat stress is a well-known occupational health hazard, and climate change characterized by the increased frequency and intensity of extreme heat events has made risks more severe and widespread. Heat stress is prevalent in numerous industrial and commercial occupational settings, either outdoors or indoors. Operations that involve high environmental heat, physically demanding activities or impermeable protective clothing have a high potential for incurring heat stress among exposed workers. Workplaces with such conditions may include firefighting, iron and steel manufacturing, mining, glass factories and food canneries. Outdoor tasks performed in hot weather and under direct exposure to sunlight, such as construction, agriculture, oil and gas well operations, and outdoor horticulture and cleaning, are also likely to induce heat stress to employees. This editorial paper highlights the current progress and needs for research on heat stress and of its impacts on occupational health and performance. Heat stress causes physiological and psychological discomforts, deteriorates performance and productivity, increases incident rates and even threatens survival. Increased thermoregulatory, cardiovascular and perceptual strains on the body promote confusion, irritability and other emotional stress, which may cause workers to become distracted from tasks or ignore safety procedures. Understanding the effects of heat stress and implementing appropriate intervention strategies to relieve the harmful impacts of heat stress has been the focus of a significant amount of research. Studies of this nature require a multi-disciplinary approach involving physiology, management and technology. The effects of heat stress can be described by physiological and psychological responses. Management of heat stress utilizes a set of framework, principles, processes and measures to prevent injuries, accidents and other adverse consequences. Technology in terms of techniques, tools, systems and machineries has been adopted as an effective means to protect workers from the hazardous effects of heat stress. Heat stress could be a result from a combination of factors, including environmental conditions, metabolic heat and thermal effects of clothing ensemble. Heat strain is the physiological response of a person in dissipating heat stress. The international standard, ISO 9886:2004 specifies measurements of body core temperature, heart rate, skin temperature and loss of body mass through sweating for evaluation of body heat strain. The upper limits of these physiological parameters have been prescribed by some regulatory organizations for monitoring of workers’ safety in heat stress occupational environments. So far a number of devices such as Ingestible Core Body Thermometer Pill and Polar Heart Rate Monitor have been used for measurement and monitoring of these physiological parameters. However, application of these devices is limited and inconvenient because they are costly and may disturb workers’ normal activities. The physiological strain experienced by a person can be estimated by the heat stress factors and is evaluated by a single index. A heat stress index is a single value that integrates the effects of the six basic parameters (i.e. ambient temperature, relative humidity, radiant temperature, air velocity, metabolic rate and clothing properties) in any human thermal environment such that its value could vary with the thermal strain experienced by an individual. Measurement of wet bulb globe temperature is by far the most widely used and accepted empirical index for managing occupational heat stress; and is recommended as a heat stress standard. The heat stress standard is calculated using the recordings of wet bulb temperature, globe temperature and dry bulb temperature. However, wet bulb globe temperature measurements are insensitive to the cooling effect due to wind velocity and are incapable of measuring the effect of workers’ metabolic rates.