When there is a wildfire the news often reports when there is a drop in temperature noting that this helps the firefighters.
What is the mechanism(s) by which a drop of a few degrees in temperature helps the firefighters?
Because fighting fires is hot work, and firefighters are in danger of overheating (heat stroke, etc.) while on the job. The cooler the ambient temperature, the harder and longer they can work before needing a break.
I find it hard to believe that there is not something more to it than the health, safety and comfort of the firefighters. Were that all there were to it should the news stories not report on the ambient temperatures around urban industrial fires too? The ambient temperature must somehow have a significant affect on the fuel or something.
I don’t know that a couple of degrees would help much - but fire takes heat+fuel+oxygen. If you lower the ambient temperature, it’s going to slow the rate of spread. It also would slow the rate at which potential fuel dries out, I guess - but I don’t know how much of temperature would be needed to make either affect significant.
Fire spreads through three mechanisms.
The cooler the ambient temperature the reduced chance/rate the adjacent fuel will catch fire, especially from flying embers
No. Wildland fire fighters can take as many breaks as they want. Fluid intake is plentiful. Heat stroke is practically unheard of in wildland fire fighting. However, heat exhaustion is not. Then again, the training and physical requirements, combined with safety standards makes such problems minimal. If air temperature is dangerously high (combined with low humidities), you don’t fight fire aggressively. Much of the time under those conditions you let it burn. Given the dilemma of saving resources or saving lives and the policy is no resource (timber, buildings, etc.) is worth a human life.
Lower temperatures increase the relative humidity. Increased RH increases the fuel moisture and lowers a fire’s sustainability. Of course, vegetation, topography, short-term and long-term fuel moisture indices, among other factors must all be taken into account. In my experience the most aggressive wildland fire fighting occurs in the early morning to take advantage of lower winds and higher RH numbers. As the the day progresses, air temperatures rise, the RH drops, winds pick up and fuel moisture levels drop. That’s why wildland fire dangers get worse in the mid- to late afternoons and early evenings. Yeah, prolonged heat waves just make it all happen faster.
I’ve been on fires that at 6 am were smouldering, barely creeping a foot an hour. By 3 pm they were infernos moving at tens to hundreds of feet a minute. I’ve also been on fires in November with snow on the ground and moving faster than you can run.
Duckster, you’re a wildland firefighter, it sounds like?
If so, you and your collegues are awesome. Thank you. In 2007 we had a big nasty fire that got way, way, way too close for comfort (days after I moved here, 'twas interesting) and a whole bunch of kickass firefighters came in and saved our collective asses.
Seriously. Awesome. I know fire has its place but there’s plenty of mostly-uninhabited Idaho that can burn all it needs to, just not right here!
My first wildland fire was in 1981. Was a line firefighter in the 1980s in Idaho, Wyoming, Oregon, California, and one winter fire in Virginia. Gone in the 1990s. In the 2000s I moved into incident command, having served on Type I teams and area command teams. In 2007 I was in Idaho with an area command team overseeing the southern Idaho Fires. Lately, mostly home base support. I keep my Red Card up to date. Now I’m adding COOP to the resume.
What many do not realize is wildland fire fighting has changed quite a bit in 30 plus years. Caring for fire fighters has gone way up, all to protect everyone. And women. So many women at all levels, even on the line. Women smokejumpers and rappelers, too. And make no mistake, just as tough as the men.
What hasn’t changed are the ages. Really brave kids, from 18 on up. Lots in their 20s. And many do it as a summer job.