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Humindex

Humindex

This calculator calculates Humindex, index used by Canadian meteorologists to describe how hot the weather feels to the average person, by combining the effect of heat and humidity.
Timur2016-07-02 07:42:25
These calculators calculate Humindex, index used by Canadian meteorologists to describe how hot the weather feels to the average person, by combining the effect of heat and humidity. Humidex value is basically an equivalent or apparent temperature (one that human body would feel). It's a standard for Canada, but variations are used around the world. Humidex differs from the heat index used in the United States in being derived from the dew point rather than the relative humidity.

The current formula for determining the humidex was developed by J. M. Masterton and F. A. Richardson of Canada's Atmospheric Environment Service in 1979.

Formula:

\text{Humidex} = \text{Air temperature}\ +\ 0.5555 \times (6.11 \times e^{5417.7530 \times \left(\frac{1}{273.16} - \frac{1}{\text{dewpoint in kelvins}}\right)} - 10)

Here, the dewpoint temperature should be given in Kelvin, the magic number 5417.7530 is a rounded constant based on the molecular weight of water, latent heat of vaporization, and the universal gas constant.

This calculator below uses this formula to calculate humindex by air temperature and dew point.

Humindex using temperature and dew pointCreative Commons Attribution/Share-Alike License 3.0 (Unported)
 Humindex:
 Meaning:
Recommendations: 


Also, there is another formula which relates humindex to temperature and relative humidity, which value easier to get than dew point value.

\text{Humidex} = \text{Air temperature}\ + \frac{5}{9} \times (6.112*10^{7.5 \times \frac{T}{237.7+T}} \times \frac{H}{100} - 10)

This calculator below uses this formula to calculate humindex by air temperature and relative humidity.

Humindex using temperature and relative humidityCreative Commons Attribution/Share-Alike License 3.0 (Unported)
 Humindex:
 Meaning:
Recommendations: 


How to interpret humindex?

According to Environment and Climate Change Canada - Spring and Summer Weather Hazards humindex has the following meanings:

  • 20 - 29: No discomfort
  • 30 - 39: Some discomfort
  • 40 - 45: Great discomfort; avoid exertion
  • 46 and over: Dangerous; possible heat stroke

Also, Canadian Centre for Occupational Health and Safety gives the following recommendations based in humindex reading for "Humindex 1 - Moderate physical work, unacclimatized worker, OR Heavy physical work, acclimatized worker":

  • below 25: None
  • 25-29: Supply water to workers on an "as needed" basis
  • 30-33: Post Heat Stress Alert notice. Encourage workers to drink extra water. Start recording hourly temperature and relative humidity.
  • 34-37: Post Heat Stess Warning notice. Notify workers that they need to drink extra water. Ensure workers are trained to recognize symptoms.
  • 38-39: Work with 15 minutes relief per hour can continue. Provide adequate cool (10-15C) water. At least 1 cup (240 mL) of water every 20 minutes. Workers with symptoms should seek medical attention.
  • 40-41: Work with 30 minutes relief per hour can continue. Provide adequate cool (10-15C) water. At least 1 cup (240 mL) of water every 20 minutes. Workers with symptoms should seek medical attention.
  • 42-44: If feasible, work with 45 minutes relief per hour can continue. Provide adequate cool (10-15C) water. At least 1 cup (240 mL) of water every 20 minutes. Workers with symptoms should seek medical attention.
  • above 45: Only medically supervised work can continue.

Source: Humidex Rating and Work




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