Today's city skylines are impressive, but the multi-story buildings that comprise them present an enormous challenge to emergency responders. Upper floors are generally inaccessible to fire crews arriving in the "hook-and-ladder" vehicles conventionally used to douse flames. Considering the number of building occupants and the quantity of valuable contents, rescue plans that involve climbing up and down stairs aren't a viable option. The best way to defeat fire in these buildings is to quickly and reliably prevent its spread.

Fire protection engineering is the application of science and engineering principles to the protection of people and property from destructive fire. The most effective means that fire protection engineers have to prevent a potentially lethal and destructive multi-story blaze from developing is the modern version of a technology that has been around for nearly 150 years: a fire sprinkler system.

Until the 1940s, sprinklers were installed almost exclusively for the protection of commercial warehouses and factories. But as fire and building officials began comparing the safety records of buildings with and without sprinklers, sprinkler systems eventually became mandatory safety equipment in most public buildings, including hospitals, schools, and hotels.

Upon detecting a fire, fire sprinkler systems immediately activate to control the fire's spread. These systems are reliable because they are simple. Fire sprinklers have no moving parts. A connector is placed every few feet along a water supply pipe to allow water to flow out. The fire sprinkler acts as a plug to hold the water in until it is needed. When heat from a fire reaches the sprinkler, a built-in heat-sensitive trigger — usually a glass tube filled with liquid or a solder link — ruptures, releasing the water. Because fire sprinklers are heat-activated, only those sprinklers closest to a fire activate.

The vast majority of fires in buildings with sprinklers are controlled by just one or two sprinklers that release water at a rate of about 25 gallons per minute. That's nothing compared with the hundreds or thousands of gallons per minute that firefighters spray to extinguish a fire. The greatest testament to the effectiveness of fire sprinklers is that there have never been multiple deaths from a fire in a building with a proper sprinkler system. Nevertheless, only 40% of high-rise buildings and less than 2% of homes have fire sprinkler systems.

Research and analyze fire safety strategies in public and private buildings in this NOVA classroom activity.

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