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A wall of a burning building can collapse in one of three ways: a 90-degree-angle collapse, an inward-outward collapse or a curtain-fall collapse. The 90-degree-angle masonry wall collapse is the most dangerous because it creates the largest outward collapse danger zone. In this case, the wall falls outward from the building a greater distance than it would in either an inward-outward collapse or a curtain-fall collapse.
A wall that collapses at a 90-degree angle will fall straight outward, in a manner similar to a falling tree cut by a woodsman. It will cover the ground below with deadly bricks and timber for a distance at least equal to the height of the falling wall section. If a 25-foot-high wall collapses at a 90-degree angle, it would fall straight outward for 25 feet. No one within 25 feet of the building would survive; all would be buried beneath the collapsed wall.
Whenever there is a danger of wall collapse, plan for the worst – a 90-degree-angle collapse. Establish a collapse danger zone equal to the height of the wall, or even 1½ or twice the height of the wall, depending on your size-up. Withdraw all firefighters from the burning building for a required distance called the “vertical” or “outward collapse” danger zone.
After the vertical or outward collapse danger area is determined, the incident commander must also estimate how much of the wall’s horizontal area may collapse. This area is the “horizontal” collapse danger zone. For example, consider a 25-foot-high wall with a parapet extending over a row of stores, 100 feet long with a 10-foot-long bulge in the parapet at the center. In this case, the horizontal collapse danger zone may be a horizontal area 10 feet directly in front of the bulge or the entire length of the wall. The incident commander’s size-up must determine whether the masonry wall is tied together by steel reinforcement rods; in that case, failure of the small, 10-foot portion could pull down the entire wall. To be safe, a horizontal collapse zone should be considered the entire wall instead of just the unstable portion.
When a collapse danger zone is established, a fire officer must trade off the advantage of close-up hose stream penetration, through an open door or window of a burning building, for the greater advantage of the safety of firefighters operating in the bucket of an aerial platform. This practice conforms to the priorities of firefighting decision making: life safety first, including firefighters, and fire containment second.
The reach of a hose stream can be used as a safety measure. It lets firefighters move away from a dangerous wall and still discharge water on the fire. The typical reach of a handheld hose stream is 50 feet; that of a master stream is up to 100 feet. By using this distance as a safety device, a 50-foot hose stream could let firefighters operate 25 feet outside a collapse danger zone. The officer could withdraw firefighters 25 feet from a dangerous wall and still discharge water into a burning building from a distance of 25 feet. In this instance, by increasing fireground safety, maximum hose stream penetration is sacrificed; however, another hose stream could be positioned at another side or at the rear of the burning building to regain fire stream penetration. Such a fireground strategy increases fireground safety.
When there is no danger of wall collapse, the most effective use of an aerial stream from a ladder, aerial platform or snorkel takes place from close to the building through a window, door or other opening. Even when battling a fire in a one-story building, an aerial platform may be used at a low angle, close to the building. When large, plate-glass windows have been removed by flames or by firefighters for ventilation purposes, there is a large open area and, most importantly, there is no danger of wall collapse, a powerful stream from an aerial platform at a low angle can sometimes sweep the open space and quickly extinguish a large fire. However, when there is danger of wall collapse or where interior partitions or stock subdivide a row of small stores, it is less effective ,but safer to operate the stream from above. This strategy increases safety of firefighters operating in the basket or at the tip of the aerial.