In a recent Brotherhood Instructors, LLC. lecture we discussed parapet walls and their hazards to firefighters. Here is a little more explanation along with some photos to illustrate the point. Parapet walls were typically brick or block construction but have changed over the years to incorporate other construction materials as well. Regardless of construction type parapet walls are dangerous to UNKNOWING firefighters. A little time spent researching and learning about parapet wall construction and past parapet wall collapses will make you a KNOWING firefighter and these construction features will be of little danger to you. There are multiple methods of parapet wall construction, below are a few examples.
This photo is of a vacant/abandoned building in the Bronx, NY. Part of the parapet has already collapsed which gives us a nice view of the construction features that are normally concealed by the parapet. Towards the left side of the photo you can see the structural brick walls which continue up past the roof to create the parapet. To the right we can see the block construction with the metal I beam on top. The I beam spans the front of the store where the roll down gate and main entrance are located. Also visible are the “fire cut” roof rafters. The angled end of the rafters allows them to pull out of their pocket in the wall without acting as a lever and causing a collapse of the wall. This feature is sometimes effective and sometimes not. It is much less effective if the exterior wall has been tied back to the rafters at all. Another visible feature is the inverted or rain roof. These roofs are usually constructed of a 2×4″ frame which is held up by 2×4″ risers. The roof is slightly pitched to allow for drainage. The space between the ceiling and the roof is known as the “cock loft” and depending on the length of the inverted roof risers can be of considerable size.
This photo is of the other side of the building in the previous picture. You can again see the block wall extending past the roof to create the parapet and the inverted roof. Take notice of where the roof surface meets the parapet. This area, if not flashed or waterproofed properly can be a source of leaks. The water leaking into the building over time can freeze, causing expansion and weakening the structure. It should also be noted that metal expands when exposed to heat. This meta I beam, if exposed to fire, could very easily expand and push the masonry walls out of plum and cause a collapse.
This photo is of a newer style parapet wall. This building is of masonry and metal construction. The parapet wall has been added to make the building look much larger than it actually is. I believe this parapet wall to be metal framed with metal paneling over top. This parapet is significantly lighter than the masonry parapets per square foot but is still plenty heavy enough to kill members operating below it if it was to fall.
The following pictures show signs that are either on top of or attached to the front of parapet walls. Loads such as these need to be counterbalanced on the other side of the parapet for stability. The most common counterbalance method is to tie the parapet or the load back to the roof rafters. The tiebacks are lag screwed into the roof rafters. Deterioration from weather or fire can cause these tiebacks to become loose at their attachment points. When the tiebacks fail the parapet will either fail immediately or be extremely unstable until it does fail. Firefighters on the roof are in an ideal position to examine these building features and determine their stability. If there is any doubt about the stability do not be shy about notifying the incident commander and any members operating below.
Parapets can also collapse due to actions taken by firefighters. Parapets have been known to collapse after being hit with the stream of a master stream device or being bumped by an aerial ladder or tower ladder bucket. A general rule for defensive operations at a one story taxpayer (store) fire is to keep everyone off of the sidewalk. This beginning benchmark for a collapse zone is easy to identify and if done consistently will become second nature.
Quite a few firefighters have been seriously hurt or killed by parapet wall collapses. Spending a little time learning about them may save your life or the lives of your brothers. Construction is one of the most important topics for firefighters to be well versed in. Any time spent on building constriction training or familiarization is time well spent. If nothing else, google Francis Brannigan and Vincent Dunn and read everything they wrote.
Here are a few links for additional information:
Front Wall Collapse by Vinny Dunn. An excellent look at front wall construction features and hazards.
Basic Brick Construction by Quikrete. An illustrated look at brick construction features.
Video of San Francisco firefighters being crushed by a parapet wall collapse… hard to watch.
Video of a newer style parapet wall collapse. No injuries due to proper collapse zone setup for a defensive operation.
Video of a collapse in Marlborough, MA.