VHP Aeration Time Calculator
Estimate how long it takes to bring hydrogen peroxide vapour down to a target concentration, from the volume, the starting concentration and the air removing it. The ideal curve is a lower bound; the method notes explain why real aeration is longer.
Engineering estimate only. Confirm by testing and validation for your equipment and load.
How the calculation works
If the space is well mixed and nothing releases peroxide back into the air, the concentration falls exponentially. Each air change removes the same fraction of what is left, so the time depends on the ratio of starting to target concentration, not the difference:
Q in m³/h, V in m³, η = fraction removed per pass through the catalyst, k = effective air changes per hour
Going from 400 ppm to 1 ppm is a factor of 400, which takes about 6 effective air changes (ln 400 ≈ 6.0). Halving the target to 0.5 ppm adds only one more air change's worth of time — but only in the ideal case.
Why real aeration takes longer
- Off-gassing. Gloves, gaskets, plastics, filters and any cellulose absorb peroxide during the gassing phase and release it slowly. Near the end of aeration this release, not the air change rate, sets the pace.
- Imperfect mixing. Corners, the space behind equipment and the inside of cabinets clear more slowly than the open room.
- Condensation. Any micro-condensate must evaporate before the concentration can fall.
- Sensors. Low-range sensors respond slowly, and the reading at one point does not represent the whole space.
The dashed line on the chart shows the same space with half the ideal removal rate, to illustrate how sensitive the result is. Your validated aeration time comes from measured data during cycle development, at the slowest location, with the real load.
More detail: VHP aeration and residual H₂O₂, material compatibility, and for filling isolators hydrogen peroxide uptake into product.
Common questions
How long does VHP aeration take?
In an ideal, well-mixed space it takes about ln(C0/Ctarget) effective air changes — roughly 6 air changes from 400 ppm to 1 ppm. Real spaces take longer because materials release absorbed peroxide, so the validated time comes from measurements.
Does a catalytic converter speed up aeration?
Yes. Air recirculated through a catalytic converter has most of its hydrogen peroxide broken down to water and oxygen, so it adds to the effective air change rate without needing more fresh air.
Why does aeration slow down near the end?
Because the air concentration is then low enough that peroxide released from absorbent materials dominates. That release does not speed up with more airflow as much as dilution does.
What target concentration should I use?
1 ppm is a common re-entry limit based on occupational exposure limits. For aseptic filling of sensitive products the start condition is often lower and should come from a product uptake study.
More tools: Isolator leak rate calculator · VHP equipment selector
Send your numbers to an engineer
Use the button under the result to fill this form, or describe your space and equipment. An engineer reviews it and replies.