Asphyxiation Calculation

The risk of asphyxiation, a condition of insufficient supply of oxygen to the body, can be assessed by using several factors to calculate the resulting oxygen concentration.


Effects of Oxygen Deprivation

The effects of low oxygen concentration are a factor of both the oxygen concentration of the space and the length of exposure. Only small changes are noted by individuals exposed to low concentrations of oxygen, but loss of consciousness can occur without warning.


% O2 Concentration Effect
19 - 21% No Hazard.
16 - 19% Increased breathing rates, accelerated heartbeat, and impaired thinking or coordination may occur at any form of exertion.
10 - 16% Increased breathing rates and accelerated heartbeat, decreased mental effectiveness, visual acuity, and muscular coordination may occur even at rest.
  6 - 10% Nausea, vomiting, lethargic movements, loss of consciousness may occur.
< 6% Prolonged exposure will result in death.

An asphyxiation calculator has has been prepared to help determine oxygen levels and asphyxiation hazards as defined by health and safety professionals. The inputs will determine oxygen levels for a given asphyxiation scenario. Any type of asphyxiant gas can be applied by specifying the volume of the asphyxiant gas either in an uncompressed state [cubic foot], or in a liquefied state [liter, gallon] and providing its gas expansion ratio (from liquefied to ambient) under Asphyxiant Type selecting Specify.



Example: Laboratory

The example laboratory suite consists of one large open space. One 120 liter tank filled with liquid Nitrogen is used to fill smaller dewars, the largest of which is 35 liters (9.25 gal). Oxygen concentration of air is 21 %. The room specifications are:


 Room Volume: Square Footage x Height of Ceiling  6000 FT3
 Net Room Volume (Including Laboratory Equipment)  90 %
 Mechanical Ventilation Rate (Based On Empty Room)  1000 CFM
 Or Air Changes Per Hour (Based On Empty Room Volume)  10

Exposure Scenario A: Spillage of 35 Liter Dewar with Mechanical Ventilation

Results:

  • Estimated Oxygen Concentration Immediately After 35 Liter (9.25 Gal) Spill = 17.7 %
  • Time Until Oxygen Level Returns to 19 % = 3 Minutes (Apply Additional Safety Factor of 2)

Exposure Scenario B: Spillage of 35 L Dewar with Natural Ventilation (1 Air Change/Hour).

Results:

  • Estimated Oxygen Concentration Immediately After 35 Liter (9.25 Gal) Spill = 17.7 %
  • Time Until Oxygen Level Returns to 19 % = 27 Minutes (Apply Additional Safety Factor of 2)

Exposure Scenario C: Catastrophic Event Spilling 80 Liters of the 120 Liter Gas Tank with Mechanical Ventilation

Results:

  • Estimated Oxygen Concentration Immediately After 80 Liter (21 Gal) Spill = 13.4 %
  • Time Until Oxygen Level Returns to 19 % = 7 Minutes (Apply Additional Safety Factor of 2)

Disclaimer: This worksheet is general in calculating asphyxiation hazards and is used for illustration purposes only. No warranties are expressed or implied. Klausbruckner & Associates is not liable for any direct, indirect, special, incidental or consequential damages arising out of the use of this worksheet.




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