NEAR-COLLAPSE AT THE FIRE STATION
Much has been written about structural collapse and roof failures. Certainly, knowledge of construction is very important, as firefighters are faced with potential collapse every time they respond to an alarm. But what happens when the roof system at the fire station fails and the ceiling begins falling under normal conditions?
The Farmington Hills (MI) Fire Department was faced with such a situation when members discovered that the truss assembly of the roof was failing and the roof was caving in. The Farmington Hills fire headquarters is a 13-year-old structure of ordinary construction. There is nothing unusual within the building. The roof assembly consists of engineered wood trusses with plywood decking and shingles.
We discovered the problem while we were inspecting the building, looking for items to be included in the annual budget request. Initial concerns centered around some cracks in the masonry walls. We contacted the city building official to assist with the inspection. The cracks were deemed insignificant. We also showed the building official the second floor layin ceiling assembly, which was sagging. We were planning on making repairs and asked the building official his opinion as to the best way to do so. We removed some ceiling tiles to perform an inspection and discovered a broken truss member. The break was significant in that it was completely through the bottom cord and was not located at a connector. We examined other parts of the ceiling and found additional breaks. We halted the inspection and consulted a structural engineer. After his investigation, he condemned the second story, declaring it unsafe, and ordered immediate temporary shoring.
Once the shoring was installed, the entire ceiling assembly was removed for inspection. Inspection found that 29 out of 31 trusses had broken completely through in at least one place and that many had broken in three or four places. The breaks occurred on the top and bottom cords and web members. Further examination of the trusses determined that a fire retardant used on the wood caused the rapid deterioration of the trusses. A heavy snowfall immediately prior to the discovery was suspected of providing the proverbial “straw that broke the camel’s back.” While the roof assembly did not completely collapse, the structural engineers performing the inspection believed that it was just a matter of time before either another snowfall or wind would have caused a collapse. Further examination found the same conditions on the roof system above the apparatus bay. Emergency repairs were authorized, and the entire roof assembly was replaced.
LESSONS LEARNED
In retrospect, we believe that two lessons can be learned from our experience. The first applies to building ownership. Never underestimate the importance of inspecting your facilities completely at least once a year. If fire retardant-treated trusses were used (particularly in the late 1970s), be aware of the potential problems (see sidebar). Excessive heat and moisture tend to accelerate the deterioration of wood trusses treated with certain fire retardants. Adequate ventilation can help prevent problems.
The second lesson applies to firefighting and its hazards. A fire in a building that contains fire retardanttreated trusses causes the roof assembly to fail much earlier and presents a danger to the people below and on the roof. If there had been a fire in our structure, firefighters would have been in immediate danger and more than likely would have been unaware of the imminent dangers.
Our concern is that other buildings constructed with the same materials may pose the same danger. We have educated our firefighters to increase their awareness and look for the signs of deterioration. Indicators inside the building are sagging or uneven drop ceilings. This information must be gathered during inspections or preincident surveys, as firefighters in smoky conditions would be unable to recognize these problems. From the exterior, the problem can be recognized by a severe sag in the roof In our case, there was a difference of almost one foot between the gable end and the center of the roof. Firefighters must recognize that severe sagging, regardless of the type of building construction, makes the roof unsafe under fire conditions.
The Farmington Hills Fire Department was extremely fortunate to discover this problem before a disaster occurred. Our hopes are that the increased awareness will motivate our firefighters to be more observant and more safety conscious when operating on the fireground. Our misfortune reemphasizes the hidden dangers to which firefighters can be exposed during seemingly “routine” operations. ■
