HEAT AND DISCOMFORT INDEX

This page shows two of the most interesting tables (Humidex Index and Thom's Index) useful to evaluate how current temperature and relative humidity can affect the sultriness or discomfort sensation and cause health danger in the population.

During summer season, or in very hot periods anyway, the human organism makes use of perspiration to maintain its temperature within proper physiological limits. The sweat, which is most made of water, evaporates (endothermal phenomenum) taking away heat so as to have a cooling effect on the skin. An high humidity level in the surrounding environment may obstruct this process limiting the evaporation. The human body so can't eliminate the excessive heat (compared to its own physiological limits) receiving a sensation of an higher temperature.

Obviously all the formulas used to calculate the discomfort indexes produce theoretic average data which may be highly influenced by a lot of human and environmental factors such as: height, weight and sex of the individual, clothes used, presence of shade or wind, carried out activity, etc.

For graphical reasons in the tables you can find combinations of temperature (degrees Celsius) and relative humidity which can't really occur as they exceed the ability of our atmosphere to hold water vapour (e.g. temperature 38 C° and 90% relative humidity)

HEAT AND DISCOMFORT INDEX

HUMIDEX INDEX OF APPARENT TEMPERATURE ( degree C )

Up to 29 C°	No discomfort
From 30 to 34 C°	Slight discomfort sensation
From 35 to 39 C°	Strong discomfort. Caution: limit the heaviest physical activities
From 40 to 45 C°	Strong indisposition sensation. Danger: avoid efforts
From 46 to 53 C°	Serious danger: stop all physical activities
Over 54 C°	Death danger: imminent heatstroke

THOM'S DISCOMFORT INDEX

Up to 21	No discomfort
From 21 to 24	Less than half population feels discomfort
From 25 to 27	More than half population feels discomfort
From 28 to 29	Most population feels discomfort and deterioration of psychophysical conditions
From 30 to 32	The whole population feels an heavy discomfort
Over 32	Sanitary emergency due to the the very strong discomfort which may cause heatstrokes