Character mistake: In the first call to a working structure fire Severide proceeded to head towards the basement from the middle level by walking down stairs but falls through. His first mistake was not checking the stairs with the halligan as any firefighter is taught, to check if they are sturdy. And last but definitely not least no firefighter should ever walk down stairs, especially wooden framed ones if they are on fire.
No Such Thing as Bad Luck - S7-E18
Character mistake: At the formal awards ceremony for Cruz the Police officers and Cruz are in dress uniform with their covers on. Serveride joins them on stage in uniform without his cover on and salutes Cruz. Serveride should have known to have on his cover for the ceremony. (00:58:00)
Answer: Internet sources give many reasons why firefighters do this, but in regards to your question, it's probably because opening walls and ceilings creates better ventilation which allows heat and smoke to escape, giving firefighters better visibility and lowering the temperature.
raywest ★