Saturday, June 11, 2016

Lessons From Fort McMurray on Fire Pathways

The Fort McMurray fire of last month, which has burned nearly 600,000 hectares and is still only 70 percent contained, qualifies as a major urban disaster, but it also has a hopeful side. We saw that a ferocious fire doesn’t mean your whole city has to burn down. About two thirds of Fort McMurray was spared. Some of that was a matter of luck, but much of it had to do with the way the fire got from the forest to the burnable part of a structure. Some structures burned down because there was a simple pathway for the fire to follow. The downtown remains largely intact, partly because the commercial buildings had nothing on the exterior that a fire could get hold of.

With that in mind, take a look at this picture of a detail of my house. The forest near my house is plenty damp this year, but wherever there is a forest there will someday be a fire. There is a problem in the picture and a very obvious clue to what the problem is.

What most people will notice first is the missing ornamental shutter. Some might also complain that the shutters are too long for the window. Even purely decorative shutters ought to match the length of the window they are decorating. The excessive length of the shutter is, in fact, an important detail.

The missing shutter, though, is the clue, not the problem. I took this photo after taking down one of the two shutters. Well, okay, it practically fell down just by looking at it.

Underneath the stucco, the exterior wall you’re looking at is masonry. It won’t burn by itself. However, the ornamental shutters are vinyl. Once the vinyl starts burning, it can produce a very hot vertical flame, more than hot enough to jump the one-inch gap and ignite the eaves and roof above. But how would the shutters catch fire?

There, as some readers may already know, is the crux of the problem. The bush below the shutters is growing right up against the outside wall of the house. That’s a bad landscaping design for a number of reasons, but especially when you look at the scenario of a drought-induced forest fire. After a few weeks with no rain, a bush, even if still green, can dry out enough that it takes only one fly-away ember from a forest fire or similar source to ignite it. Then, if the bush is right up against the house as this one is, the situation has gone from the already serious problem of having a fire in the neighborhood to the much more serious problem of having a fire licking the exterior wall of the house.

The bush is too risky all by itself, but having the decorative shutters there to carry the fire to the roof makes matters worse. If the video I’ve seen from Fort McMurray is any indication, this specific fire pathway would result in the entire house burning down in a matter of minutes. By contrast, in the same scenario but without the bush and the decorative shutters, there is a chance that the house might not catch fire at all. In Fort McMurray, similar details sometimes separated the house that burned from the house next door that didn’t.

The time to address problems like this is not when a drought has already taken hold and there is a warning of a fire risk. That’s because the power tools routinely involved in this kind of work themselves present a slight risk of creating a spark and a fire. Rather, the right time is when doing routine maintenance and groundskeeping — in other words, a normal summer Saturday.

For me the day was today. It took me maybe a hour this morning to cut away this particular fire pathway, and the work might have gone faster if I hadn’t paused to write this account of it. I’ll leave it as an exercise for another day to make the outcome look prettier. Even including that step, though, it’s a small price to pay to reduce the risk of losing an entire house in a future fire event.

Looking at my house this way has made me question whether it really makes sense to have a roof of shingles that are ultimately a form of paper. That’s a question I may look at again when it is time to replace the roof. Large-scale fire events are expected to be more frequent in the future, so we may have to get used to looking at cities and buildings in terms of their flammable materials, the way fire experts are already trained to do.