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Heat Index

Equivalent heat index vs. air temperature and relative humidity - in degrees Fahrenheit and Celsius.

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The heat index can be used to indicate how an average person will perceive temperature and humidity and the human body ability to cool it self.

Heat Index in degrees Fahrenheit

The heat index in degrees Fahrenheit can be calculated as

t_HI = -42.379 + 2.04901523 t + 10.14333127 φ

- 0.22475541 t φ - 0.00683783 t² - 0.05481717 φ²

+ 0.00122874 t²φ + 0.00085282 t φ² - 0.00000199 (T φ)² (1)

where

t_HI = heat index (^oF)

t = air temperature (^oF) (t > 57^oF)

φ = relative humidity (%)

Apparent Temperature Heat Stress Index (^oF)
Relative Humidity (% RH)	Temperature (^oF)
Relative Humidity (% RH)	80	85	90	95	100	105	110	115	120	125	130	135	140
0	78	82	87	91¹⁾	94	97	100	103	105	107	108	110	110
5	78	82	86	90	94	98	102	106	110	114	117	121
10	78	82	86	90²⁾	95	100	105	110	116	121	128
15	78	82	86	91	96	102	108	115	122	130
20	79	82	86	91	97	104	112	121	130	140
25	79	82	87	93	100	108	117	127	138
30	79	83	88	94	102	112	122	134	148
35	80	84	89	96	106	116	129	143
40	80	84	91	99	109	121	136	152
45	80	85	92	102	114	127	143
50	81	86	95	105³⁾	118	134	152
55	81	88	97	109	124	141
60	82	89	100	113	129	149
65	82	91	103	118	136
70	83	93	106	123	143
75	84	95	109	128⁴⁾
80	84	97	113	134
85	85	99	117
90	86	102	122
95	86	104
100	87	107

T(^oC) = 5/9[T(^oF) - 32]

Sunstroke and heat exhaustion:

¹⁾ Caution - Fatigue is possible with prolonged exposure and/or physical activity

²⁾ Extreme Caution - Sunstroke, heat cramps and heat exhaustion are possible with prolonged exposure and/or physical activity

³⁾ Danger - Sunstroke, heat cramps and heat exhaustion are likely. Heat stroke is possible with prolonged exposure and/or physical activity

⁴⁾ Extreme Danger - Heatstroke/sunstroke is highly likely with continued exposure

Heat Index in degrees Celsius

Heat index in degrees Celsius:

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Related Topics

Physiology - Human physiology, air quality and comfort temperatures, activity and metabolic rates, health effects of carbon monoxide and more.
Air Conditioning - Air Conditioning systems - heating, cooling and dehumidification of indoor air for thermal comfort.

Related Documents

Carbon Dioxide Concentration - Comfort Levels - CO₂ acceptance and comfort level.
Clothing, Activity and Human Metabolism - Human metabolism at low and high activity with different levels of clothing.
Cooling Load - Latent and Sensible Heat - Latent and sensible cooling loads to consider when designing HVAC systems.
Discomfort Index - Comfort vs. dry bulb, wet bulb and dew point temperature.
Heat Discomfort Zones - Maximum work load vs. temperature and relative humidity.
Heat Index vs. Humidity - The influence of humidity on the apparent temperature and the heat index.
Human Body - Specific Heat - Specific heat of the human body - compared to substances like protein and wood.
Human Heat Gain - Heat gain from persons in air conditioned spaces - in btu/hr.
Met - Metabolic Rate - Metabiolic Rate - Met - is used as a measuring unit for human body heat or power production.
Metabolic Heat Gain from Persons - Human metabolic heat gain in air conditioned rooms.
Predicted Mean Vote Index (PMV) - PMV index predicts mean comfort response of a larger group of people.
Room Sensible Heat Factor - RSHF - Room Sensible Heat Factor - RSHF - is defined as the sensible heat load divided by the total heat load in a room
Sensible Heat Ratio - SHR - The ratio Sensible Heat (or Cooling) Load to the Total Heat (or Cooling) Load.
Wet Bulb Globe Temperature (WBGT) - The Wet Bulb Globe Temperature can be used to measure the general Heat-Stress index.

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