Enter Inputs
Example Data Table
| Project | Gas | Volume (m3) | Initial | Target | Purity | Safety | Leakage | Std Gas (Nm3) | Mass (kg) |
|---|---|---|---|---|---|---|---|---|---|
| Tunnel Cross-Passage | CO2 | 150 | 0 ppm | 5000 ppm | 99.5% | 1.10 | 5% | ≈ 0.30 | ≈ 0.55 |
| Tank Void Space | N2 | 40 | 0% | 2% | 99.9% | 1.15 | 8% | ≈ 0.94 | ≈ 1.16 |
| Service Gallery | Ar | 75 | 0 ppm | 12000 ppm | 99.9% | 1.20 | 10% | ≈ 0.12 | ≈ 0.21 |
Formula Used
- Concentration change (fraction): Δ = (Ctarget − Cinitial)/10^6 for ppm, or Δ = (Ctarget − Cinitial)/100 for percent.
- Injected gas volume (ambient): Vgas = Vspace × Δ ÷ Purity × Safety × (1 + Leakage).
- Standard volume conversion: Vstd = Vgas × (Pamb/Pstd) × (Tstd/Tamb), using Pstd=101.325 kPa and Tstd=273.15 K.
- Moles (ideal gas law): n = (Pamb×Vgas)/(R×Tamb), with R=8.314.
- Mass required: m = n × M, where M is molar mass of the selected gas.
- Flow guidance: Flowstd = Vstd/Time (shown as L/min and m3/h).
How to Use This Calculator
- Measure or estimate the enclosure volume, then choose its unit.
- Select the gas and set your concentration unit (ppm or percent).
- Enter initial and target concentrations from your method statement.
- Apply gas purity, safety factor, and a leakage allowance for realism.
- Enter ambient temperature and pressure for accurate conversions.
- Optionally add dosing duration and cylinder capacity for planning.
- Press Calculate Dosage to display results above the form.
- Use Download CSV or Download PDF for records.
Confined Space Gas Dosing Planning
Gas dosing work often supports commissioning, inerting, odor control, or controlled atmospheres around temporary enclosures. Start by defining boundaries, sealing quality, and ventilation status. Measure free air volume, not gross geometry. Include dead zones, voids, and equipment displacement. A 3% volume error can shift required gas by the same proportion, before safety factors are applied. Cross-check volume with drawings and a quick smoke test before opening cylinders on site.
Concentration Targets and Measurement Alignment
Targets are commonly specified in ppm or percent by volume. The calculator converts the concentration difference into a fraction, then scales by space volume. Align inputs with your monitoring method: direct-reading meters may report ppm, while some method statements specify percent. Record initial readings, stabilization time, and sampling locations. If initial concentration is nonzero, only the required increment is dosed.
Purity, Leakage, and Safety Margins
Cylinder labels list purity, but site delivery lines, regulators, and mixing can introduce losses. The purity factor corrects for inert content, while leakage allowance covers imperfect seals and pressure equalization. A safety factor provides a controlled buffer for mixing uncertainty and operational variability. Keep factors defensible: note assumptions, inspection results, and any temporary openings during dosing.
Temperature and Pressure Effects on Volume
Gas volume is reported at ambient conditions and also converted to standard volume (Nm3) for consistent planning. On warm days, the same mass occupies more volume; at higher pressure, it occupies less. Using ambient temperature and pressure improves conversion accuracy, supports cylinder sizing, and makes daily comparisons meaningful across shifts. Where barometric changes are significant, update pressure inputs.
Flow Rate and Cylinder Logistics
Entering a dosing duration produces a standard flow guidance in L/min and m3/h. This helps match regulators, manifolds, and hose diameters to avoid freeze-off and unstable dosing. Cylinder count is estimated from usable standard volume per cylinder, supporting procurement and staging. Always verify final concentration with calibrated instruments, document readings, and attach exported CSV or PDF to permits and handover records.
FAQs
1) What is “standard volume” in this calculator?
Standard volume (Nm3) normalizes gas quantity to 0°C and 101.325 kPa. It helps compare cylinder supplies and flow plans across different ambient temperatures and pressures.
2) Should I use ppm or percent for targets?
Use the unit stated in your method statement or gas monitor. Ppm suits low concentrations, while percent suits larger targets. Ensure both initial and target values use the same unit.
3) How do I choose a leakage allowance?
Base it on enclosure sealing quality, door frequency, and duct penetrations. For well-sealed temporary enclosures, 2–5% is typical; poorly sealed spaces may need higher allowances and stronger verification.
4) Does purity significantly change the required amount?
Yes. Lower purity means less active gas per cylinder, so the injected volume increases. Use supplier documentation and consider line purging where purity is critical.
5) Why does the mass result matter if I dose by volume?
Mass supports procurement, transport planning, and safety documentation. It also helps validate whether a cylinder’s contents are sufficient when standard volume ratings are unavailable.
6) Can this replace gas safety procedures?
No. It supports planning only. Always follow confined-space controls, permits, ventilation lockouts, rescue plans, and continuous monitoring with calibrated instruments before entry or handover.