Oxygen Deficiency Risk Calculator

Work out oxygen deficiency risk instantly with clear inputs, formula shown and shareable results.

About Oxygen Deficiency Risk Calculator

Any gas released into a confined space displaces air and dilutes oxygen in proportion to the volume added: predicted oxygen is measured oxygen times space volume over the total volume after release. Below 19.5 percent entry is prohibited without supplied air, and below 16 percent judgement is impaired before the victim recognises the problem.

Formulas

Dilution

Predicted O2 = measured O2 x volume / (volume + inert gas released)

Restoration

Fresh air required = volume x (20.9 - predicted) / predicted

Worked example

With the default values below, Oxygen Deficiency Risk Calculator returns Oxygen after inert gas release of 17.925%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Measured oxygenaccepts 0–25 %: 19 %
Space volumeminimum 0.1 m³: 50 m³
Inert gas released into the spaceminimum 0 m³: 3 m³

Results

Oxygen after inert gas release: 17.925% %
Deficit against normal air: 1.90% %
Risk category: Oxygen deficient — entry prohibited without supplied air
Fresh air needed to restore 20.9 percent: 8.30 m³

Step by step

1Values used
2Dilution
3Restoration
4Oxygen after inert gas release= 17.925 %
5Deficit against normal air= 1.90 %
6Risk category= Oxygen deficient — entry prohibited without supplied air
7Fresh air needed to restore 20.9 percent= 8.30 m³

Assumptions and limits

The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Confined space entry requires a permit system, calibrated continuous gas monitoring, forced ventilation and trained rescue arrangements.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Preliminary estimate only. Confined space entry requires a permit system, calibrated continuous gas monitoring, forced ventilation and trained rescue arrangements.

Frequently Asked Questions

How is the Oxygen Deficiency Risk figure worked out?

Predicted O2 = measured O2 x volume / (volume + inert gas released). Any gas released into a confined space displaces air and dilutes oxygen in proportion to the volume added: predicted oxygen is measured oxygen times space volume over the total volume after release.

Why is oxygen deficiency so insidious?

There is no smell or irritation, and the first symptom is impaired judgement, so the victim does not recognise the danger. It remains the leading cause of confined space fatalities.

What values do I need to enter?

This calculator takes 3 inputs: Measured oxygen, Space volume, Inert gas released into the space. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.