“Heat stress” is a term to describe the total heat load imposed on the body by a combination of factors: the type of work being done, the surrounding air temperature and humidity, exposure to sunlight, air movement, and the clothes being worn. If the heat load is too great, the body’s core temperature rises, causing a variety of heat stress disorders ranging from an irritating heat rash to a life- threatening heat stroke.
"Heat stress" is a term to describe the total heat load imposed on the body by a combination of factors: the type of work being done, the surrounding air temperature and humidity, exposure to sunlight, air movement, and the clothes being worn. If the heat load is too great, the body's core temperature rises, causing a variety of heat stress disorders ranging from an irritating heat rash to a life- threatening heat stroke.
In order for the human body to function normally, it needs to maintain a core temperature within the acceptable range of 1oC (1.8oF) above the normal temperature of 37oC (98.6oF). As the body produces heat during work, it cools itself by increasing the blood flow to the skin to move heat out of the body. If this is not enough to cool the body, the sweat glands increase the flow of perspiration to the surface of the skin. As the sweat evaporates, the skin is cooled. This process becomes difficult when the surrounding humidity level is high. As people overheat, their physical and mental condition begins to deteriorate.
Heat stress disorders affect us in different ways depending on their severity. Mild cases of heat stress cause fatigue, irritability, thirst, or heat rash. As the level of heat stress increases, heat cramps develop as a result of heavy exertion, dehydration, and the loss of body salts. Fainting, heat exhaustion (pale and clammy skin, weakness, dizziness, and nausea) and heat stroke (hot and dry skin, increased heart and breathing rate, and confusion) are the three most severe effects of heat stress. Each can be life-threatening and requires immediate medical attention.
Heat stress is a safety hazard as well as a health hazard. In hot workplaces, heavy tasks become exhausting, people become easily distracted, their patience is shorter, they are less alert, more irritable, and mental and physical tasks requiring skill become much more difficult to perform safely.
There are a number of ways silviculture employers can reduce the risk of heat stress on the job. The first line of defence is to provide engineering controls such as cool rest areas for outdoor workers, ventilation and air conditioning systems in mills as well as insulating or shielding heat sources from nearby workers. Administrative controls and work practices could include rescheduling hot work for cooler times of the day, reducing workers' exposure time to the heat, allowing workers adequate time to get accustomed to hotter environments, providing cool drinking water, and ensuring that frequent rest breaks are taken.
It's important to drink plenty of cool water while working in the heat. If the water lost through sweating is not replaced, it will result in dehydration and a reduction in the volume of circulating blood in your body. Personal apparel and special protective equipment are also a very important control measure. Wearing light-coloured clothing and hat will reflect radiant heat away from your body.
Loose-fitting clothing should be worn when humidity levels are high. And under extreme conditions, air and water-cooled garments or ice-packet vests should be considered.
The Ontario Ministry of Labour recommends that workplaces develop a hot weather plan to control heat stress hazards. A hot weather plan should establish environmental "triggers" that put the plan into effect. These triggers could include a Humidex reading of 35oCor more, A Humidex advisory from Environment Canada, and heat waves consisting of three or more days of temperatures of 32 1/4 Cor more. Employers should have hot weather plans in place between May 1st and September 30th of each year.
The Ministry of Labour has developed a health and safety guideline on heat stress. You can access the guideline by visiting www.labour. gov.on.ca and typing "heat stress" in the search box.
The Ontario Forestry Safe Workplace Association (OFSWA) has created SafePlanting.com, a comprehensive online health and safety training program for treeplanters. For more information or to order the program for your workers, visit www.safeplanting.com or contact OFSWA at 705-474-7233 ext. 267.
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