By
Bob BourgeoisBob is a former District Fire Chief (FF 40 yrs), former LLC owner (public safety case studies), BSME Columbia Univ
With input from
Joe MaloneyJoe is a former District Fire Chief (FF 32 yrs, 19 as District Chief), 1st draft 12Jul21 Latest rev 26Dec24 Feedback/Qs roomfiresetc@gmail.com
Fig. 2-1 Porch fires need fast water
Firefighters put out heavy fire in open porches by wetting the burning fuel surfaces—painting them with water. Since nearly all of those surfaces are easy to paint, these fuel-controlled fires do not need big GPM—even with big flames.
What porch fires do need is speed. Threats to people, exposures, and the structure are best met by a fast exterior attack. Choose your default line for speed and mobility, but also consider how good it will be when working among vehicles, fences, junk etc.
Don’t overthink things. Stacked porches are best hit from the lowest floor up, but plenty have been knocked from the top down. The best nozzle pattern is probably a narrow cone, but straight streams work fine. Attacking from the flank is often a good idea, but not critical.
A sloppy knockdown in 15 seconds is much better than a textbook job that takes 60 seconds. Don’t run (physically or mentally), but act.
Threats to outside FFs include fuel stored on the porch (gas can, propane tank etc), weakened porch structure, and the big distraction of big fire. Take advantage of distance and shielding opportunities. Stay off the damaged porches. Step back mentally and look around.
When the exterior fire has been knocked down, take four seconds to wash the porch ceiling, soffit, or anywhere else the fire could enter a cockloft, trussloft, or attic.
Etc
Fig. 2-2 Rear porches. How fast can you get water here?
Top floor occupants are likely to be the most threatened. Top floor operations are likely to be the most risky.
Porch fires often block building exits. Quick water is the main remedy but you should also adjust your search plan.
Doors and windows are an easy avenue of spread to the interior. Try to keep them intact until knockdown, but expect problems.
Be careful about venting elsewhere in the building while the exterior fire is still heavy. You don’t want to create a flow that sucks fire into the building.
Interior floor joists next to an intense porch fire can suffer surprising amounts of damage. Don’t trust floors near the porches until you’ve checked them by opening the ceiling below.
Assume that the cockloft or attic is involved—even if the thermal imager doesn't show it yet.
Get post-fire pix of the spot where the fire did or didn't enter the cockloft or attic. Use them in the review.
Questions
Fig. 2-3 Front porch on single-family dwelling. Fast knockdown could save occupants above. Maybe deck gun for speed and reach?
Why is it better to attack stacked porches from the bottom up?
When you wet high surfaces, any fire below them will work to dry them out and reignite them. When you wet low surfaces, they stay wet and you can work your way up.
How can we calculate the GPM required to knock down a porch fire?
I don’t know, and it might be a moot point. You’re flowing enough water if you can reach all the fuel surfaces and if each surface stays wet for a few seconds. You will almost certainly need more GPM to get the reach than you will need to knock the fire.
Are there any situations that require extra GPM?
Sort of. Asphalt shingles require more water than other common fuel surfaces. If a roof or other area seems stubborn, you can put more water on each square foot by slowing down your sweep speed. Be systematic about making progress across that surface.
Fight the fire in front of you—not the theoretical one that you think you understand.
