General
two-in, two-out
What does two-in, two-out mean?
The minimum staffing rule for interior structural firefighting: any two members who go inside an IDLH atmosphere must have at least two more outside, in full PPE on air, ready to drag them out if it goes wrong. Exception is a known life rescue.
"We held at the door until the second engine arrived — couldn't make entry without two-in, two-out covered."
Origin
US OSHA respiratory-protection rule (29 CFR 1910.134(g)(4)), adopted into fire-service practice in the late 1990s. Interior firefighting at an IDLH atmosphere requires a minimum of four trained, equipped personnel — two working, two standing by as rapid-intervention.
Frequently asked questions
What does two-in, two-out mean?
It's the OSHA rule that two firefighters go inside an IDLH fire while two are staged outside, ready to rescue them.
Why does the two-in, two-out rule exist?
It ensures a backup team is always ready outside to rescue the crew working inside a dangerous fire.
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