Confined-Space Pre-Entry Ventilation (OSHA 1910.146)
L x W x H volume, contaminant-driven target ACH (combustible / O2-deficient / H2S / CO / general), minutes-to-purge and steady-state ACH, plus the 1910.146(d)(5) 4-gas-meter reminder. Companion to the v3 confined-space-purge tile.
Formula and source
V = L * W * H (or operator-supplied volume). minutes_to_purge = V * N / Q. steady_ACH = Q * 60 / V. Default N (target air-changes) keyed to contaminant class: combustible-gas / oxygen-deficient / general = 7; H2S / CO = 10.
OSHA 29 CFR 1910.146 (Permit-Required Confined Spaces); NIOSH 80-106 (Working in Confined Spaces).
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