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Human Need of Air

Fresh air is required for respiration and for transport of heat and vapor emitted from the human body.

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An adult at rest breathes 15 - 18 respiration per minute - exchanging 0.5 liter - approximately 0.5 m3/h. With harder work the rate is 3 to 6 times more (1.5 - 3 m3/h).

The average composition of exhaled air is

  • Oxygen 16.5%
  • Carbon dioxide 4.0%
  • Nitrogen and Argon 79.5%

The quantity of carbon dioxide exhaled in 24 hrs is about 1 kg.

Equilibrium of Heat

Heat is generated within the human body by the combustion of food. The heat is lost from the body by

  • Conduction and convection - about 25%
  • Radiation - about 43%
  • Evaporation and moisture - about 30%
  • Exhaled air - about 2%

Evaporation prevails at high ambient temperatures. Conduction and convection prevails at low ambient temperatures. Heat is liberated in a rate maintaining the internal body temperature at 37oC.

Heat loss from human body

The total heat loss from an adult at normal activity is approximately 118 W (2 Met) in at room with temperatures between 19oC and 34oC.

Dry bulb temperature
Sensible heat (W) 135 112 100 95 84 59 29
Latent heat (W) 22 22 22 24 34 59 90
Total heat (W) 157 134 122 118 118 118 119
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Related Topics


Human physiology, air quality and comfort temperatures, activity and metabolic rates, health effects of carbon monoxide and more.

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Exposure limits for various air contaminants.

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Ammonia and health symptoms - smell and threat to life.

Body Weight vs. Body Height

Typical ideal body weight versus height.

Carbon Dioxide Concentration - Comfort Levels

CO2 acceptance and comfort level.

Carbon Dioxide Concentration in Rooms Occupied with People

Carbon dioxide concentration in a room may indicate air quality and ventilation system efficiency.

Carbon Monoxide and Health Effects

Exposure to Carbon Monoxide - CO and health effects.

Emissions from the Human Body

Gaseous polutants emissions from human bodies.

Human Body - Specific Heat

Specific heat of the human body - compared to substances like protein and wood.

Human Body Composition

Composition of the human body.

Human Heat Gain

Heat gain from persons in air conditioned spaces - in btu/hr.

Humans - Required Rest Time

Relaxation rest time vs. working time and activity.

Life Expectancy

Age and life expectancy for men and women.

Met - Metabolic Rate

Metabiolic Rate - Met - is used as a measuring unit for human body heat or power production.

Outdoor Makeup Air

Acceptable indoor air quality and required make up air.

pH in Human Biological Material

pH in human materials like blood, salvia and more.

Physiology - Activity and Metabolic Rate

Heat production from the human body vs. activity.

Recommended Relative Humidity

Recommended relative humidity level.

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