Human Need of Air
Fresh air is required for respiration and for transport of heat and vapor emitted from the human body.
Respiration
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 37 oC.
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 19 oC and 34 oC.
| Dry bulb temperature (oC) | 10 | 14 | 18 | 22 | 26 | 30 | 34 |
|---|---|---|---|---|---|---|---|
| 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 |
