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Trainer’s Corner: The dangers of the front wall

Trainer’s Corner is dedicated to giving you the tools to make good judgment calls on the fire ground. “Good judgment comes from experience. Experience comes from bad judgment.” (Author unknown) Unfortunately, in our profession, bad judgment can result in devastating and sometimes fatal results.

February 25, 2009
By Ed Brouwer

Topics
train1 
Protective or decorative
canopies or cornices are
hazards to firefighters.
 
train2 

Trainer’s Corner is dedicated to giving you the tools to make good judgment calls on the fire ground. “Good judgment comes from experience. Experience comes from bad judgment.” (Author unknown) Unfortunately, in our profession, bad judgment can result in devastating and sometimes fatal results. 

When it comes to the topic for this month’s column, front-wall collapse, I admit that I have no experience at all. All but one year of my fire service has been in rural departments. Yet the need to address this safety concern is paramount. Although there are a number of deadly fixtures on the front walls of burning buildings that have collapsed and killed firefighters, there is little printed material available.

In order to do justice to this topic I enlisted the help of my friend Vincent Dunn, specifically his 2005 training newsletter Front Wall Collapse.

Other than Dunn’s newsletter, Firefighting Strategies and Tactics by James Angel et al. (2000 Delmar Thomson Learning) has the most pertinent information.

With permission from Dunn, we’ve reproduced the key points from his newsletter. If you have Internet access feel free to go to his website, www.vincentdunn.com,  for a downloadable copy of the complete newsletter.

Incident commanders, although careful to size up each incident with consideration given to firefighter safety, too often miss the obvious – the front wall. The deadly fixtures on the front wall I referred to earlier are a parapet, marquee, canopy or a cornice. Any one of these fixtures on the front wall of a burning building should be monitored continuously for any sign of failure.

A parapet, according to the Delmar’s Firefighter’s Handbook 2nd Edition, (now out of print)  is “the extension of a wall past the top of the roof.”

Parapets (typically masonry) are free standing and are used to give the building a finished look. Business owners use parapets to hide roof equipment, hang signs and support utility connections.

Dunn, in his newsletter, describes a marquee, canopy and a cornice as follows:

  • A marquee is a large metal structure attached over the entrance to a theatre or store. A marquee extends from the front wall out to the street and is used to display signs.
  • A canopy is a cloth, wood or metal covering over a building entrance designed to protect people from the weather.
  • A cornice is a horizontal ornamental construction along the entire front wall of a building, usually near the top.

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Additional items on a front wall make it more prone to collapse and pose. According to firefighting training materials, incident commanders too often miss the obvious – the front wall.


 

Now that we have an idea of what these fixtures look like and what purpose they serve let’s discover how fire and collapse can cause them to become deadly.

Consider a marquee; very few understand that as water streams are being applied to a burning building, water from those streams can enter into the hollow portion of the marquee. Normally there are drain holes within these fixtures but during a fire these can become clogged. If that were to occur the hollow would fill with water and collapse due to excess weight. In turn, if the marquee collapses it can pull the parapet wall down with it, crushing firefighters below. 

Perhaps you’ve seen the photo often used by training officers of seven or eight firefighters standing on top of a small porch roof or canopy? It begs the question, “What were they thinking?”

Speaking of canopies, the IC should not order hoses to be stretched or ladders to be placed on top of a canopy roof. Firefighters have been killed (outside the building) operating hoselines beneath a canopy that collapses. The area beneath a canopy should be considered inside the collapse danger zone.

Dunn reminds us that one of the greatest tragedies in the history of fire fighting was caused by a canopy collapse. It occurred in a burning meat packing plant in Chicago in 1910. During the fire, a brick wall and a canopy attached to it collapsed. Twenty-one Chicago firefighters were crushed to death beneath the crumpled metal canopy and bricks.

According to Front Wall Collapse, parapet walls are free standing. A freestanding wall is considered by engineers to be the least stable of three basic types of wall (free standing, nonbearing and bearing wall) because it has fewer connections to a structure. The more connections a wall has to the structure, the more stable the wall.

 Front-wall strategies 
  Four strategies Vincent Dunn suggests an IC use to safeguard firefighters when the front wall of a burning building appears about to collapse.
• Use the reach of the hose stream. Firefighters should use the 50-foot reach of a hose stream.
• A collapse zone can be established by the IC. A collapse zone is the distance equal to the height of the wall in danger of collapse.
• Flank the front wall. Firefighters operating hose streams can be positioned in front of adjoining buildings and their hose streams can be directed on the burning building from a flanking position. The stream may not be as effective but the fire-
fighters will be away
from the front of the
building wall in danger
of collapsing.
• Corner safe areas can be established around the burning building. If the front wall and all the other walls of a burning building collapse outward simultaneously (which is very unlikely) there would be four corner areas on the fire ground where fewer bricks would land. These are the so-called four corner areas. Probability of survival is greatest in the four corner safe areas. When there is danger of collapse a safety strategy used by an IC is to position firefighting apparatus inside the four corner safe areas.

Dunn further explains it this way: “A parapet wall built over a one- or two-storey commercial building with large display windows beneath it is a collapse-prone structure because the parapet walls are often supported by steel beams. A steel beam spans the large windows and supports the parapet wall above. If, during a fire, the steel beam designed to support a parapet is heated to 590 C and starts to expand, warp, twist or sag, it can collapse the parapet wall off its foundation.” A small shock during a fire, the impact of a master stream or an aerial ladder can cause a parapet wall collapse.

“Ironically,” Dunn says, “a parapet wall often supports a marquee, canopy or cornice. This is an unstable structure supporting an unstable structure.” Dunn reported some additional details regarding marquees. “A marquee beam goes through a parapet wall and is connected to a roof or floor beams behind the facade. The marquee may also be connected to the parapet by steel cables.”

If a marquee collapses during a fire, it can pull the facade wall down with it.

Dunn continues: “A marquee is a cantilever beam supported only at one end. This is considered by engineers to be the least stable of the three basic beam designs: a cantilever beam [supported at one end]; a simple support beam [supported at both ends]; and a continuous support beam [supported at both ends and the centre].“A canopy is more of a collapse danger than a marquee, Dunn says.

Similar to a marquee a canopy is a cantilever beam, but where a marquee is one large continuous beam, a canopy is made up of non-continuous beams. These multiple beams are held together by cables or bolts.  Because these continuous beams are only supported at one end, if any one part fails, it can trigger a complete canopy collapse.

According to Front Wall Collapse, the most dangerous type of canopy is a metal or woodshed suspended over a truck-loading area. These corrugated tin or wood canopies are designed to provide protection for workers and products from the weather. In older parts of some towns, skylights, originally designed to provide light on the platform below, are sometimes tarred over. These would certainly collapse if stepped on should a firefighter mistake it for a scuttle cover. 

Some canopies have a system of tracks and rails suspended from the underside. “Heavy products unloaded from trucks or railroad cars are attached to the rail system and pushed inside the building,” Dunn says. The IC should be aware that the weight of these rail systems heightens collapse danger.

Another cantilever structure on the front wall is a cornice. The important difference with the cornice is that a cornice can burn and spread fire.

Dunn says. “A cornice may be constructed of wood or combustible plastic and it may have a wood framework inside, and/or wood shingles outside.”

The IC should understand that flames blowing out of a window below a cornice will spread to the cornice. Flames may then spread along the underside of the cornice or inside its framework to another exposure.

A cornice destroyed by fire can collapse off the facade. Firefighters operating at one end of a building can be crushed under a falling cornice that starts to collapse at the opposite end.

Special thanks to everyone who helped us out with this topic. I was reminded of Joe Cocker singing, “With a little help from my friends.” With that in mind I am going to ask for your help. If you would be interested in networking with me as a resource for Trainer’s Corner please e-mail me your contact info.


Ed Brouwer is the chief instructor for Canwest Fire in Osoyoos, B.C., and the training officer for West Boundary Highway Rescue. The 20-year veteran of the fire service is also a fire warden with the B.C. Ministry of Forests, a wildland interface fire suppression instructor/evaluator and a fire-service chaplain. Contact Ed at ed@thefire.ca


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