Oxygen Depletion Calculator for Inert Gas Releases
Estimate the oxygen concentration in a room after an inert gas such as nitrogen, argon or CO₂ is released, either as a sudden release of a known volume or as a continuous leak against room ventilation.
- O₂ = 20.9 × V ÷ (V + Vgas) = 18.17 %
- Assumes the gas mixes fully and displaced air leaves the room
Oxygen Depletion Formulas
Continuous: O₂(∞) = 20.9 × Qair ÷ (Qair + Qgas)
O₂(t) = O₂(∞) + [20.9 − O₂(∞)] × e−(Qair + Qgas)t ÷ V
V is the room volume, Vgas the released inert gas volume at room conditions (1 L of liquid nitrogen gives about 0.68 m³ of gas), Qair the fresh air ventilation rate and Qgas the leak rate. The room is assumed perfectly mixed; in reality heavy gases like argon and CO₂ collect low, so local oxygen can be much lower.
Worked example
Releasing 15 m³ of nitrogen into a 100 m³ room lowers oxygen to about 18.2 %, which is oxygen deficient. A 10 m³/h leak against 200 m³/h of ventilation settles at about 19.9 %.
Frequently Asked Questions
What oxygen level is dangerous?
Normal air has 20.9 %. Many standards treat below 19.5 % as oxygen deficient; below about 18 % effects become serious, and very low levels can cause sudden collapse.
Why is a well mixed model not enough?
Heavy gases settle in pits and low areas and light gases rise, so local concentrations differ from the room average.
How much gas does liquid nitrogen give?
About 680 to 700 litres of gas per litre of liquid at room conditions.
Learn more on the blog
Hazardous area classification zones
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
Read Full Article