Collapsing Wall Near Miss
A masonry wall collapsed outwardly on a firefighter during suppression operations following the collapse of the structure’s roof systems.
South Bend Firefighters were called to the reported fire at the store at Lincoln Way Foods Store at 736 Lincoln Way West just after 07:00 hours on Friday August 8, 2008. When companies arrived, according to Fire Chief Howard Buchanon, smoke was already coming out of the roof, and efforts to get into the building were stalled by thick clouds of smoke.
By 8 a.m., crews had been told to back away from the building, Buchanon said, as the fire had grown dangerous and there was fear of collapse. One 25-year-old firefighter, was hurt when part of a brick wall collapsed outward, striking him on the head. The injured firefighter was said to have had a minor concussion, but was revived quickly. Chief Buchanon said he and another firefighter, who also sustained injuries, were taken to Memorial Hospital with minor injuries.
Chief Buchanon said the size of the fire forced crews to take a defensive position, mainly working to keep the fire contained. By the time crews were able to bring the fire under control, the building's roof and three of its walls had collapsed. The two story building housed a former grocery store up to 1980 and was once a part of the Oliver Plow Company dating back to the early 1900’s. The blaze took over four hours to control.
The building appears to have been Type III ordinary construction, with published reports indicating it was built in the early 1900’s. The outer walls apparently were constructed of masonry construction and consisted on masonry units and brick construction as evidenced by the news video.
The following useful information on masonry construction is excerpted from a number of news letters and publications of Chief Vinny Dunn, (ret) FDNY. Please refer to his exceptional book entitled; Collapse of burning buildings: A guide to Fireground Safety as well as other text books on related subject areas.
Masonry Wall Collapse
There are three ways in which a masonry exterior building wall may collapse. The wall may fall straight out in a monolithic piece at a 90-degree angle, in a manner similar to a falling tree; the wall may crumble straight down in a so-called "curtain" fall collapse; or the wall may collapse in an inward / outward fashion, with the top falling inward and the bottom outward.
This is the most common type of masonry wall failure which occurs at fires. The wall falls straight out and the top of the collapsing wall strikes the ground, a distance equal to the height of the failing section measured from the base of the wall. A fifty-foot section of wall collapsing in a 90-degreeangle fall will cover at least fifty feet of ground with brick. Bricks and steel linters may bounce or roll out even farther. One example of how a multistory brick exterior wall can collapse at a fire in this manner is as follows: A fire spreading uncontrolled throughout a brick-and-joist structure causes the interior collapse of all floors. The pile of compressed rubble created by the fallen interior exerts an outward or lateral force against the inside of one of the still-standing brick enclosing walls. As the wall experiences this lateral force, a vertical crack or separation appears at a corner, starting at the top and progressing downward. The wall begins to lean outward at the top, separating from the other enclosing walls, and falls straight out at a 90-degree angle.
A free-standing wall of a burning structure can also become unstable and fall outward during extremely cold weather. If the inside surface of the masonry Wall is heated by the fire while the outside surface remains cold, unequal expansion of the masonry will occur; the heated inside of the wall will expand and the outside contract, causing the wall to lean outward and possibly to fall. Large accumulations of ice forming on the outside of a wall can cause it to become unstable and fall, regardless of the temperature of the inside surface. The force of a large-caliber stream of water can also be a destabilizing factor capable of causing a masonry wall to collapse. Directed from one side of a fire building against the inside of a freestanding wall, a high-pressure aerial stream can be powerful enough to cause the wall to collapse outward on to firefighters operating on the outer side of the building.
Masonry walls often separate from the other enclosing walls at corners where they intersect. If there is no brick bonding of the intersecting walls by either overlapping brick bonding or metal reinforcing rods, the wall may split apart at this point. Vertical cracks allowing walls to separate and fall at a 90-degree angle may also be the result either of structural movement caused by uneven settling of the foundation prior to the fire or of a combination of window openings and cracked spandrel walls over each window.
In this type of collapse, the exterior masonry wall drops like a falling curtain cut loose at the top. The wall crumbles and falls straight down, with brick and mortar forming a pile on the ground near the base of the wall. The collapse of the brick veneer, brick cavity, or masonry-backed stonewall often occurs in a curtain-fall manner. If the metal ties holding a brick veneer wall to plywood backing are destroyed by fire, or if mortar bonding between an exterior finished stonewall and a masonry backing wall is washed away by hose streams, large sections of brick or stone veneer may fall off the building's exterior. Firefighters entering, leaving, or operating near the doorways beneath the curtain-fall collapse may be killed or seriously injured by falling brick.
Another situation of potential curtain-fall collapse occurs when fire has collapsed the interior of a multi-story brick-and-joist structure and the remaining free-standing walls have many window openings with brick arches serving as linters. If one of the masonry walls starts to fall and the brick arches spanning the tops of the wall openings crumble and fall apart, the wall will fall downward rather than straight out.
When a masonry wall becomes unstable and begins to lean inward, it does not always mean that the wall will fall inward. Firefighters operating ground streams must still maintain a safe distance between themselves and the unstable wall, for when a section of the broken wall falls inward, the lower portion of the wall may kick outward, or the upper portion may initially fall inward but then slide down and outward into the street, bottom first. Known as an inward/outward collapse, this type can be caused by a force directed against the inside surface of the collapsing wall. An explosion or the outward impact caused by the collapse of a roof or several floors in a pancake fashion, the upper floors, falling on top of the lower ones can cause an inward/outward collapse of several enclosing walls simultaneously.
An example of an inward/outward collapse is a masonry wall failure caused by the collapse of a bowstring timber truss roof. When the design of the timber truss includes hip rafters sloping down from the front and rear bowstrings, one end of the hip rafters is tied into the outermost truss section and the other end into the masonry-enclosing wall. If the bowstring trusses are weakened by fire and the roof fails, the load of the falling roof is transferred from the truss supports to the front and rear masonry walls. In some instances, the load transmitted to the masonry wall through the hip rafters cracks the front wall and collapses it in an inward/outward manner. The top section falls inward and the bottom section outward, into the street. The extent of the area in front of the fallen structure, covered with tons of brick and steel linters, depends upon the amount of internal force transmitted against the inside of the enclosing wall by the failing roof.
A secondary collapse of the front masonry wall following a bowstring truss roof collapse is extremely dangerous. Firefighters anticipating a roof collapse may be caught off guard and be struck or buried by the secondary front or rear wall collapse. When planning for a bowstring timber truss roof collapse, firefighters should also consider a front or rear wall collapse. In such cases one-story enclosing walls have been driven out into the street for a distance equal to the height of the one-story wall.
A fire officer can never predict the way in which a wall will collapse, so when he establishes a safe distance between the unstable wall and the firefighters in his command, he must expect the worst: a 90-degree-angle wall collapse with chunks of bricks and steel linters thrown out farther than the falling wall. As a general rule, the so-called "collapse zone"-the area adjacent to an unstable wall that firefighters should not be allowed to enter-is a distance equal to the height of the wall.
NIOSH Recommendation: Fire departments should ensure that officers and fire fighters at a structure fire continuously analyze the building to identify collapse potential.
Discussion: The threat of a partial or complete collapse is always a possibility at structure fires. It is important that the IC, officers, and fire fighter sevaluate factors that may suggest potential collapse. Factors that may signal potential collapse include but not limited to; bulging or cracked masonry walls, heavy loads and weakened structural members. Load imposition and load resistance can be visualized by identifying any structural element that is carrying something it should not, and whether the key elements are being attacked by fire (e.g., HVAC units, signs, heavy stock, overhangs, open-spans, unsupported loads, or a reinforced facade).Examples of weak links include trusses (floors/roofs), structural connections, and any overloading when buildings are being used for occupancies for which they were never intended.
A collapse sequence should be visualized using available information. This will assist in assessing if walls will fall inward or outward, if the building can withstand a partial collapse, or if a failure of the roof would lead to a catastrophic collapse.
NIOSH Recommendation: Fire departments should ensure that a collapse zone is established and clearly identified at structure fires involving buildings susceptible to collapse.
Discussion: If structural integrity is questionable, a collapse zone needs to be established. Fire fighters and officers must recognize and know the dangers of operating underneath or near a parapet wall. As a free-standing masonry wall, a parapet has little if any lateral stability and presents an extreme collapse hazard. Collapse may be caused by the failure of
the roof structure pulling the wall in or pushing it out. Also, an external load such as a sign or electric service reacting on a wall weakened by fire conditions may cause the collapse of a parapet. The collapse zone should be equal to the height of the building plus an additional allowance for debris scatter and at a minimum should be equal to 1½-times the height of the building. For example, if the wall were 20 feet high, the collapse zone would be established at least 30 feet away from the wall.
NIOSH Recommendation: Fire departments should ensure that pre-emergency planning is
completed for mercantile and business occupancies.
Discussion: Pre-emergency planning, preplanning, and pre-incident planning are all terms that mean essentially the same thing. By first identifying target hazards (occupancies that present high risk to life safety and property) within a department’s jurisdiction, the fire department can prioritize and begin to establish pre-emergency plans for those target hazards. Pre-emergency planning enhances effective and safer operations and helps save lives and protect property. Pre-emergency planning can help in identifying: the age of the structure; structural integrity; type of roof structure and supports; type of interior support structures, and type of building materials. The fire department can assign the first due companies to complete the pre-emergency survey, allowing personnel to become familiar with the property.
Dunn V . Collapse of burning buildings: a guide to fireground safety. Saddle Brook, NJ: Fire Engineering Books & Videos.
NIOSH . Preventing injuries and deaths of fire fighters due to structural collapse. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS