Continuity mistake: At the hospital, when Cruz talks to Herrmann while he still has the oxygen mask on, Herrmann's hand keeps switching between clutching the mask on his face and resting at his side. (00:38:45)
Where the Collapse Started - S4-E22
Visible crew/equipment: After the paramedic locates the injured firefighter, the shot cuts to the outside and the camera operator's shoulder can be seen in the lower left of the shot.
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 ★