EngineerHub.orgWhat this simulator does
The model converts spilled cryogenic liquid to warm gas, introduces that inert gas into an effective room mixing volume over a finite release period, and solves the oxygen balance while outdoor air ventilation continues. Use the mixing-zone fraction to screen a low-level accumulation zone rather than assuming perfect room-wide mixing.
Inputs
Results
The oxygen balance is solved numerically in a constant-volume, perfectly mixed control volume:
Here V is the effective mixing volume, C is room oxygen fraction, Qᵥ is outdoor-air ventilation, Cₐ is supply-air oxygen fraction, and Qg is inert gas generation. An equal mixed-gas outflow maintains constant room pressure and volume. Liquid-to-gas conversion uses liquid density, molar mass, and the ideal-gas law at the selected room temperature and pressure.
The release rate is constant during the entered boil-off duration and zero afterward. The model does not calculate heat transfer into the pool; the boil-off duration is an engineering input.
Transient oxygen concentration
Orange: predicted oxygen concentration. Dashed line: selected alarm setpoint. The OSHA oxygen-deficient threshold is 19.5 vol% at ordinary workplace conditions; local requirements may differ.
Interpreting the result
| O₂ concentration | Screening interpretation |
|---|---|
| ≥ 20.0% | Near normal atmosphere, subject to measurement uncertainty. |
| 19.5–20.0% | Reduced margin; investigate ventilation and release assumptions. |
| < 19.5% | Oxygen-deficient under OSHA respiratory-protection criteria. |
| < 16% | Severe impairment can occur; treat as a critical emergency condition. |
Do not enter or attempt rescue in a suspected oxygen-deficient area without a site-specific emergency plan, atmospheric monitoring, and properly trained responders.
Model limitations
- Cold nitrogen and argon vapour can collect near floors, pits, drains, and trenches. A one-zone model may underpredict local depletion.
- Jets, door opening, thermal plumes, obstacles, and ventilation short-circuiting are not resolved.
- Pressure relief and exhaust are assumed adequate to maintain constant room volume.
- Liquid oxygen is excluded because it creates oxygen-enrichment and fire hazards rather than depletion.
- Carbon dioxide is excluded because toxicity and phase behaviour require additional criteria beyond oxygen displacement.
Technical basis and safety references
The 19.5 vol% alarm reference follows OSHA’s definition of an oxygen-deficient atmosphere. EIGA guidance emphasizes that inert gases can create oxygen-deficiency hazards and that adequate ventilation and oxygen monitoring may be required. Cryogenic release volume is estimated from conservation of mass and ideal-gas expansion at the user-selected ambient conditions.
Reference data used in the model: approximate normal-boiling-point liquid densities: LN₂ 808 kg/m³, LAr 1,395 kg/m³, and LHe 125 kg/m³. These values are suitable for screening calculations, not custody transfer or detailed vessel design.