Two-in, two-out

In firefighting, the policy of two-in, two-out refers to United States Occupational Safety and Health Administration policy 29 CFR 1910.134(g)(4)(i) that mandates that firefighters never go into a dangerous situation in a fire or rescue incident alone, and that there be two firefighters outside the hazard area to initiate a rescue of the firefighters inside, should they become in trouble, during the initial stages of the incident where only one crew is operating in the hazard area. Once a second crew is assigned or operating in the hazard area, the incident is no longer considered in the initial stages and a dedicated firefighter assist and search team or rapid intervention crew is required.

There should always be (at least) two firefighters together when they enter a location that is considered a hazard area that is considered "Immediately Dangerous to Life or Health" (IDLH), i.e., the interior of the structure fire. Firefighters operating in the hazard area must operate in a buddy system and maintain voice or visual contact with one another at all times. This assists in assuring accountability within the team. They must operate together as a team the entire time they are in the hazard area. At no time, under any circumstances are they permitted to separate from one another. If one firefighter has to exit the hazard area, for any reason, such as their air supply getting low, they must both exit.

OSHA requires that one of the two firefighters outside must be dedicated to accounting for the two firefighters inside, and, if necessary, initiate a fire fighter rescue. The other firefighter is permitted to take on other roles, such as incident commander in charge of the emergency incident, safety officer or equipment/pump operator. However, the second firefighter outside cannot be assigned tasks that are critical to the safety and health of any other employee working at the incident.

These rules also apply to all training with live fires inside structures, and are even more important when inexperienced trainees are inside.

Emergency rescue activities can be performed prior to assembling an entire team, without violating this section of the regulations, under 29 CFR 1910.134(g), Note 2. Responders may still be limited by local safety procedures, by command, and by the exercise of reasonable prudence under the circumstances.

The National Fire Protection Association (NFPA) defines the policy that refers to a safety system to protect firefighters, known as rapid intervention crew (RIC) or firefighter assist and search team (FAST), where two or more firefighters enter a building and at least two more remain outside, near the entrance, fully equipped and ready to help in case of emergency. Firefighters enter a building in teams to extinguish the fire and/or make a rescue. When a team enters an IDLH atmosphere (the "two-in"), two more firefighters (the "two-out") stand by at the entrance in full personal protective equipment (to include bunker gear and self-contained breathing apparatus), and ready with rescue tools, in order to rapidly enter the building if the team inside becomes endangered. By some interpretations, the rule requires at least two more firefighters to remain outside, even when the standby team has gone in to find and rescue the first team. However, the rule specifically exempts an emergency rescue with fewer personnel on hand (i.e., no additional "two-out" required if they go in to find the "two-in"), although the increased risk to all four should be obvious if further backup is not on-scene.

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