Why do firefighters break windows?

After rescue, the second goal in firefighting is to limit property damage. Relieving smoke and heat are key to achieving this goal. Breaking windows is quick, usually effective, and replacing window glass is relatively inexpensive. Ideally, ventilation in this manner is coordinated with the movement of hoselines to attack the fire. Sometimes this type of ventilation is done selectively to encourage the fire to move in a particular direction, usually away from people believed to be trapped in the building or away from important building contents.