What is the phrase used to describe how many fully-equipped firefighters must be on scene, before two may enter a structure?

The phrase "two in, two out" refers to the safety standard that requires a team of at least four firefighters to be present on scene before two can enter a structure. This guideline ensures that while two firefighters are inside working to combat the fire or perform rescues, there are at least two firefighters outside who are ready to respond if needed. This practice is crucial for ensuring the safety of firefighters, as it allows for immediate assistance in case of an emergency, such as when a firefighter becomes trapped or injured inside the structure. The presence of a backup team also gives the entry team the ability to safely evacuate if conditions deteriorate. This two-in, two-out rule is a fundamental principle in firefighting operations, emphasizing the importance of teamwork and safety in hazardous environments.