Enter Leak Inputs
Example Data Table
These rows are illustrative examples for layout, review, and training. They help teams compare how pressure, hole size, and ventilation change the result.
| Case | Gas | P1 (bar abs) | P2 (bar abs) | Temp (°C) | Hole (mm) | Cd | Duration (min) | Enclosure (m³) | Vent (m³/min) | Approx. mass flow (kg/s) | Approx. total volume (m³) |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Natural Gas | 6.0 | 1.013 | 20 | 2.0 | 0.82 | 10 | 75 | 0.10 | 0.0027 | 2.38 |
| 2 | Propane | 8.0 | 1.013 | 25 | 3.0 | 0.80 | 5 | 40 | 0.00 | 0.0170 | 1.86 |
| 3 | Hydrogen | 12.0 | 1.013 | 15 | 1.5 | 0.85 | 8 | 60 | 0.20 | 0.0009 | 5.83 |
Formula Used
This calculator models gas discharge through a round opening. It checks whether the pressure ratio has reached the critical level for choked flow.
1) Hole area
A = π × (d / 2)²
2) Source gas density
ρ = P / (R × T)
3) Choked flow mass rate
ṁ = Cd × A × P1 × √(k / (R × T)) × (2 / (k + 1))^((k + 1) / (2 × (k - 1)))
4) Subcritical flow mass rate
ṁ = Cd × A × P1 × √[(2k / (R × T × (k - 1))) × ((P2/P1)^(2/k) - (P2/P1)^((k + 1)/k))]
5) Released quantity
Total mass = ṁ × time and Total standard volume = (ṁ / ρstd) × time
6) Simple enclosure screening
Concentration % = max(Total gas volume - ventilation removal, 0) / enclosure volume × 100
This method is appropriate for quick screening. Detailed safety design should also consider real geometry, two-phase effects, pipe friction, release direction, ignition sources, and validated hazard software.
How to Use This Calculator
- Select the leaking gas from the list.
- Enter upstream and downstream absolute pressures.
- Enter gas temperature, hole diameter, and discharge coefficient.
- Set the release duration for the event you want to study.
- Add enclosure volume and ventilation rate for a concentration screening check.
- Press Calculate Leak Rate to show results above the form.
- Review the graph, compare mass and volume release, then export CSV or PDF if needed.
Frequently Asked Questions
1) Why does the calculator ask for absolute pressure?
Gas density and critical flow equations require absolute pressure. If you enter gauge values directly, the pressure ratio and mass flow estimate can be badly distorted.
2) What is choked flow?
Choked flow happens when the downstream pressure falls below a critical ratio. At that point, the leak rate no longer increases just by lowering downstream pressure.
3) What does the discharge coefficient represent?
It adjusts the ideal equation for real losses caused by edge shape, turbulence, and opening quality. Sharper, rougher leaks usually reduce the ideal theoretical flow.
4) Is the concentration result suitable for code compliance?
No. It is a quick enclosure screening estimate only. Compliance reviews should include actual room shape, mechanical ventilation behavior, detector placement, and approved engineering methods.
5) Can I use this for nitrogen or compressed air leaks?
Yes. The release-rate equations still work, but flammability outputs such as percent of LEL are unavailable because those gases are not flammable in normal conditions.
6) What temperature should I enter?
Use the expected gas temperature at the leak source. If you do not know it, use a realistic operating temperature from equipment data or site records.
7) Why does a small hole still give a large hazard value?
High pressure, long duration, and weak ventilation can let even a modest opening release enough gas to accumulate quickly inside a confined construction space.
8) Can this replace a full hazard study?
No. Use it for early planning, toolbox talks, and quick comparisons. High-risk work still needs a formal assessment, controls, permits, and qualified review.