(Photos by Brian Clark/bclark@modbee.com)

On January 1, 2010, Modesto Fire Department responded to a residential structure fire that was started in the garage from the residents using a candle to provide light while filling a gasoline generator. The resulting fire engulfed the garage and prompted the decision to have the truck company perform vertical ventilation OPS on the roof in concert with engine companies dealing with extinguishing the fire.

RIC Team In Place Two truck company firefighters fell through the roof while performing ventilation operations. The good news here is that a RIC team was set up and in place. When the mayday was issued, the two firefighters were immediately located, removed and turned over to EMS on the scene. This was a text book operation for bread and butter residential structure fires with contingencies in place, should something go wrong.

Fuel Loading: We all know about fuel loading right? Lot's of fuel in the garage (e.g. cardboard boxes, books, newspapers, car, lawn mower, edger, gas cans, hazmat, you know, common stuff...) means that you will have a lot of heat generated, which of course lends itself toward accelerating the intensity of the fire and the eventual structural failure and collapse of the roof.

Truss Construction and Gusset Plates: Couple this with the common use of gusset plates that are used for Truss Construction where you have a piece of metal with pointed spikes punches through the metal connecting pieces of wood to create a truss.

This is great for companies mass producing homes today but not great for us considering that there is not much purchase for the gusset plate to attach itself to the wood. Remember when we actually used nails to build homes? This is a big enough issue that even the CDC has issued a warning for firefighters. Please take the time to review this.

NIOSH Publication No. 2005-132:
Preventing Injuries and Deaths of F...


What prompted me to create this post was the following quotes from the Modesto Bee newspaper:

““There was a catastrophic failure on the roof and the two firefighters fell through,” Patino said. “Upon collapse, the mayday was reported. The intervention crew was pressed into service and within a couple of minutes, they had both firefighters out.”

Patino said the intensity of the heat caused the roof to collapse significantly sooner than usual, adding that he was told by crew member that he had never seen a roof fail in that short amount of time.”


The CDC / NIOSH report specifically warns and lists three scenarios that can occur in which fire fighters suffer fatalities and injuries while operating at fires involving truss roof and floor systems:


1. While fire fighters are operating above a burning roof or floor truss , they may fall into a fire as the sheathing or the truss system collapses below them.

2. While fire fighters are operating below the roof or floor inside a building with burning truss floor or roof structures , the trusses may collapse onto them.

3. While fire fighters are operating outside a building with burning trusses , the floor or roof trusses may collapse and cause a secondary wall collapse.


Fire Engineering wrote an exceptional article on the subject that gets into much more of the process of why things collapse and the times associated depending upon how things are constructed and the specific materials. This chart gives a good general idea as to how long you have before structural collapse can occur...


Key Question: My question for the more experienced engine company and truck folks out there is how do you approach residential structure fires where the garage is fully involved?

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Out here on the West Coast the majority of our residential structure fires are with lightweight trusses and has been for the last twenty plus years. The experience of these firefighters is with lightweight trusses. Collapse of this nature is not typical.
Early collapse of lightweight trusses with fire in the truss void is indeed typical. The firefighters in question might not have seen it before, but it happens so frequently that there are entire books and web sites on the topic.

If you get lucky for 20 years, then have a bad outcome once when the bad outcome not only is predictable but happens all over the country, it's not just bad luck when the predictable bad outcome occurs.

Here are a few sources:

NIOSH

Firehouse.com

NIST

Firefighterclosecalls

PennWell Publications

Firefighter Near Miss Reporting System

FireRescue 1

The Kitchen Table - Tactical Renaissance - Christopher Naum

My point is that you can't let what happened at the last fire lull you to sleep. You need to treat EVERY lightweight truss as if it's going to collapse as soon as fire enters the truss void. If some of them hold up a little longer, that's great, but we are not entitled to expect it.

Here in SC, we have a saying that you can't judge the next hurricane by past hurricane performance, and hurricane performance is pretty predictable.

Lightweight wood truss performance is predictable when they are exposed to fire - they're going to collapse.

We need to anticipate the collapse and modify our old-school dimensional timber-frame tactics accordingly, or we'll continue to be "surprised" by the sudden collapses of lightweight trusses that have been exposed to fire.

Adding the weight of firefighters and our equipment doesn't do anything to make the burned trusses stronger, either.

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