Work out confined space ventilation instantly with clear inputs, formula shown and shareable results.
Confined space ventilation has two stages. Pre-entry purge replaces the atmosphere several times over, conventionally at least seven air changes, before anyone enters. During work continuous forced ventilation maintains a high air change rate, commonly twenty per hour, to dilute any contaminant generated by the work itself.
Working airflow
CFM = volume ft³ x target ACH / 60
Purge time
Minutes = volume ft³ x purge air changes / blower CFM
Preliminary estimate only. Confined space entry requires a permit, continuous atmospheric monitoring, an attendant and a rescue plan under the applicable regulations.
CFM = volume ft³ x target ACH / 60. Confined space ventilation has two stages.
Blowing in generally gives better mixing and is the usual choice, but where a heavier-than-air contaminant collects at the bottom, extraction from the low point with fresh air supplied at the top works better.
This calculator takes 4 inputs: Space volume, Target air changes per hour during work, Air changes for pre-entry purge, Blower capacity. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.