Example data table
| Scenario | Inputs | Output (O₂ %) | Output (ppmv) |
|---|---|---|---|
| Partial pressures | Total 101.325 kPa, O₂ 21.278 kPa | 20.990% | 209,900 |
| Molar flows | O₂ 0.21, N₂ 0.78, CO₂ 0.01 mol/s | 21.000% | 210,000 |
| Continuous purge | V 10 m³, Q 2 m³/min, t 10 min, inlet 0% | 2.827% | 28,270 |
Formula used
Oxygen percent: %O₂ = 100·y
ppmv: ppmv = 10⁶·y
Works when flows represent molar amounts at the same basis.
Volume changes: N = Q·t / V
mg/m³ = (n/V)·MW·1000
How to use this calculator
- Select a calculation mode that matches your measurements.
- Enter inputs in the responsive fields; keep units consistent.
- Enable mg/m³ conversion if you have temperature and pressure.
- Press Calculate to display results above the form.
- Use Download CSV or Download PDF to save the run.
Measurement context and units
Engineering oxygen concentration is commonly reported as percent by volume, mole fraction y, or ppmv. This calculator outputs all three and can optionally estimate mg/m³ using the ideal gas relationship at a specified temperature and pressure. It is suitable for air, inerting, and combustion-support assessments in ducts, vessels, and confined spaces during reviews.
Partial pressure workflow
For gas mixtures at known total pressure, Dalton’s law gives y = P_O2 / P_total. At 101.325 kPa, dry air near 20.9% oxygen corresponds to about 21.3 kPa O2 partial pressure. Converting bar, atm, or psi to kPa preserves the ratio and reduces input mistakes.
Component flow workflow
When gases are blended through metered streams, composition follows y = ṅ_O2 / Σṅ_i. Enter O2, N2, CO2, Ar, and H2O molar flows in a single unit basis. For 0.30 mol/s O2 and 1.20 mol/s N2, y = 0.20, giving 20.0% and 200,000 ppmv. Equal-basis volumetric flows can approximate y if temperature and pressure match.
Purging and dilution dynamics
For vessel purging with constant volume and perfect mixing, oxygen follows C(t) = C_in + (C0 − C_in)e^(−Qt/V). The dimensionless factor N = Qt/V represents volume changes. Example: V = 10 m³, Q = 2 m³/min, t = 10 min gives N = 2 and reduces 20.9% to about 2.83% with inert inlet. The Plotly curve displays concentration versus time for the selected settings.
Interpreting results for operations
Typical workspace guidance flags oxygen-deficient atmospheres below 19.5% and oxygen-enriched conditions above 23.5%, where fire risk increases. The risk band summary supports alignment with permits and monitoring plans. For process data, ppmv is often preferred: 20.9% equals 209,000 ppmv, while 1.0% equals 10,000 ppmv.
Data integrity and reporting
Accuracy depends on absolute pressures, calibrated flow meters, and a realistic mixing assumption. When mg/m³ is enabled, the calculator uses n/V = yP/(RT). At 25°C and 101.325 kPa, 20.9% oxygen is roughly 273,000 mg/m³. Use CSV export for traceable runs and the PDF report for shift logs. Recalculate after changes in ventilation, purge rate, or supply composition.
FAQs
Which mode should I choose?
Use partial pressure when you know total pressure and O2 partial pressure. Use flows when you have metered component streams. Use purge when oxygen changes over time in a vessel or room due to ventilation or inerting.
Why does ppmv match percent by volume?
For dilute gases, ppmv is the volume fraction times one million. The calculator uses ppmv = y×10^6 and percent = 100×y, so 20.9% becomes 209,000 ppmv.
What does the risk band mean?
The band is a quick screen against common operational thresholds: below 19.5% is oxygen-deficient, above 23.5% is oxygen-enriched. Always follow your site procedure and confirm with calibrated gas testing.
How accurate is the purge curve?
It assumes perfect mixing, constant volume, and equal exhaust flow. Stratification, dead zones, and short-circuiting can slow removal. Treat the curve as a planning estimate and validate with measurements.
When should I enable mg/m³?
Enable it when you need mass concentration for ventilation calculations or reporting. Enter realistic gas temperature and absolute pressure; the conversion uses the ideal gas law and oxygen molecular weight.
Can I use volumetric flows in the flow mode?
Yes, if all streams are at the same temperature and pressure, volumetric flow ratios equal molar flow ratios. If conditions differ, convert to molar basis or use measured composition instead.