Humidity refers to the amount of water vapor that is present in the air. Relative humidity is humidity expressed as a percentage of the maximum amount of water the air can hold (saturation) at the same temperature. Average relative humidity is taken over a period of time and it is the common measure of humidity. Humidity is dependent on the prevailing ambient temperature. Ambient temperature and humidity affect the working conditions in an environment. When the ambient temperature is 24 oC and relative humidity is 100%, we feel like it is 27 oC. Humans are most comfortable at a relative humidity of about 45%. The human body attempts to maintain steady temperature that is between 36 oC and 37 oC at all times.
In hot weather, sweat is generated by the body and this cools the body as the sweat is evaporated. As relative humidity increases, sweat does not evaporate as quickly as needed. Sweat evaporation ceases completely when the relative humidity reaches about 90% (CCOHS, 2017).
Heat Rashes: These are tiny red spots on the skin. Heat rashes may trigger a prickling sensation causing discomfort to the worker. The red spots are the result of inflammation due to poor thermal regulation or inadequate evaporation of sweat leading to plugging of the sweat glands.
Heat Exhaustion: Symptoms of heat exhaustion include weakness, dizziness, nausea, headache, diarrhea, muscle cramps and excessive sweating. It is caused by excessive loss of water and salt from the body when working in hot weather.
Exertional Heat Stroke: This is heat stroke in which the body temperature rises due to strenuous work in hot weather. Sweating is usually present. Heat stroke is the most serious type of heat illness. A good sign of heat stroke is when the body temperature rises above 41 oC.
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