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Measuring Oxygen
Measuring Oxygen (Deficiency and Enrichment)
Oxygen Sensors
Composition of fresh air
- 78.1 % Nitrogen
- 20.9 % Oxygen
- 0.9 % Argon
- 0.1 % All other gases
- Water vapor
- CO2
- Other trace gases
Oxygen Deficiency
- Most widely accepted definition: Air is oxygen deficient whenever concentration is less than 19.5%
Partial Pressure O2 vs. % Vol at Varying Altitudes
| Height | Atm. Pressure | PO2 | Con. | ||
| feet | meters | mmHg | mmHg | kPa | %Vol |
| 16,000 | 4,810 | 421.8 | 88.4 | 11.8 | 20.9 |
| 10,000 | 3,050 | 529.7 | 111.0 | 14.8 | 20.9 |
| 5,000 | 1,525 | 636.1 | 133.3 | 17.8 | 20.9 |
| 3,000 | 915 | 683.3 | 143.3 | 19.1 | 20.9 |
| 1,000 | 305 | 733.6 | 153.7 | 20.5 | 20.9 |
| 0 | 0 | 760.0 | 159.2 | 21.2 | 20.9 |
19.5% O2 at sea level = 18 kPa
Oxygen Deficiency
- Occurrence associated with:
- Confined spaces
- Unventilated cellars
- Sewers
- Wells
- Mines
- Ship holds
- Tanks
- Enclosures containing inert atmospheres
Causes of Oxygen Deficiency
- Displacement
- Microbial action
- Oxidation
- Combustion
- Absorption
Oxygen displacement in a fully enclosed vessel
- For every 5% total volume displaced, O2 concentration drops by about 1%
- If 5% of the fresh air in a closed vessel is displaced by methane, the O2 concentration would be about 19.9%
- The atmosphere would be fully explosive while the O2 concentration would still be above the normal alarm setting!
Oxygen displacement in an open topped confined space
Symptoms of Oxygen Deficiency
| 20.9 % | Oxygen content in fresh air |
| 19.5 % - 12 % | Impaired judgment, increased pulse and respiration, fatigue, loss of coordination |
| 12 % - 10 % | Disturbed respiration, poor circulation, worsening fatigue and loss of critical faculties, symptoms within seconds to minutes |
| 10 % - 6 % | Nausea, vomiting, inability to move, loss of consciousness, and death |
| 6 % - 0 % | Convulsions, gasping respiration, cessation of breathing, cardiac arrest, symptoms immediate, death within minutes |