Air Change For Contaminant Control Calculator

Work out air change for contaminant control instantly with clear inputs, formula shown and shareable results.

About Air Change For Contaminant Control Calculator

Dilution ventilation airflow is the contaminant generation rate divided by the acceptable concentration, multiplied by a mixing factor because real rooms never mix perfectly. K ranges from about 1.5 for good mixing with the source far from workers, to 10 for poor mixing with the source in the breathing zone.

Formula

Dilution airflow

Q = G x K / C

G: Generation rate, mg/min
C: Target concentration, mg/m³
K: Mixing factor 1.5 to 10

Worked example

With the default values below, Air Change For Contaminant Control Calculator returns Dilution airflow required of 30.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Contaminant generation rateminimum 0.01 mg/min: 50 mg/min
Target airborne concentrationminimum 0.001 mg/m³: 5 mg/m³
Mixing factor Kaccepts 1–10: 3
Room volumeminimum 0.1 m³: 200 m³

Results

Dilution airflow required: 30.00 m³/min
Airflow in cubic feet per minute: 1,059 CFM
Air changes per hour required: 9.00 ACH
Airflow assuming perfect mixing: 10.00 m³/min

Step by step

1Values used
2Dilution airflow
3Dilution airflow required= 30.00 m³/min
4Airflow in cubic feet per minute= 1,059 CFM
5Air changes per hour required= 9.00 ACH
6Airflow assuming perfect mixing= 10.00 m³/min

Assumptions and limits

The result is derived only from the 4 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 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Preliminary estimate only. Ventilation for contaminant control must be designed by a qualified engineer or occupational hygienist to a recognised industrial ventilation standard.

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

Preliminary estimate only. Ventilation for contaminant control must be designed by a qualified engineer or occupational hygienist to a recognised industrial ventilation standard.

Frequently Asked Questions

How is the Air Change For Contaminant Control figure worked out?

Q = G x K / C. Dilution ventilation airflow is the contaminant generation rate divided by the acceptable concentration, multiplied by a mixing factor because real rooms never mix perfectly.

When is dilution ventilation the wrong choice?

For highly toxic materials, high generation rates, or where the source is close to the worker. In those cases local exhaust at the source is the only reliable control.

What values do I need to enter?

This calculator takes 4 inputs: Contaminant generation rate, Target airborne concentration, Mixing factor K, Room volume. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.