As a fire burns, it moves in all directions and grows very fast. Dangerous gases and dark smoke accumulate and, unlike the movie versions of fires, it is impossible for firefighters to see and search for trapped victims in such an environment. In fact, the super-heated gases and toxic smoke are usually the cause of fatalities when people become trapped inside of a burning building. Breaking windows and cutting holes in the roof is called ventilation and there are many reasons why firefighters do this. It slows the fire’s growth; it helps get rid of the dark smoke that makes it hard for firefighters to see where they are going and it helps the firefighters fight the fire more quickly, improving the ability to save lives and property. Another reason for venting the roof is to stop the horizontal spread of fire throughout a building and direct the heat and flames in a vertical fashion. Firefighters can then get ahead of the fire on a roof, cut holes above the fire and stop the spread of the fire to minimize damage.