How Are Forest Fires Put Out?

Ever seen this before? It’s fertilizer. Judging by its color you probably guessed
it wasn’t just water. It’s a long-term fire retardant that’s
actually a combo of water, fertilizer, and small amounts of other stuff that color it
and help it stick together as it falls. And it’s not being dropped directly on the
fire, it’s being dropped just outside of it. Just one of a few tactics used to stop a destructive
blaze. Wildfires are caused by your typical combustion
reaction, which requires some kind of spark, a fuel, and oxygen. A spark can come from something in nature
like a bolt of lighting, but more likely it’ll come from…us. Over the last couple decades humans have been
responsible for starting over 80% of wildfires with things like tossed cigarettes, or some
more bizarre things like the spark from a hammer hitting a metal stake to plug up a
wasp nest. Even though fires are a natural part of our
ecosystem, when those fires happen on hot, windy days they can pose a real threat to
people and the environment. A massive forest provides a whole lotta fuel,
so unless we want our National Parks to become heaps of ash, there are some blazes that we
need to shut down as quickly as they start. Dumping crazy amounts of water on a forest
fire is one pretty effective approach. Water does a couple big things. First, water interferes with that combustion
reaction because as it vaporizes it creates a layer of water vapor that separates the
fire’s fuel from the atmospheric oxygen it needs to keep going. Second, the water cools the fuel, which slows
and ultimately extinguishes the reaction. During a forest fire, firefighters work quickly
to put out anything ablaze, including embers, which can fly around and spread the fire. They spray water from the ground and sky,
refilling tanks at nearby water sources like lakes, rivers, or even your family’s pool. At the same time crews are creating a fire
break, which is exactly what it sounds like — a break between the fire and its fuel. But dumping water and cutting down forest
often isn’t enough. So, here’s where that bright red stuff comes
in. It’s a long-term fire retardant, which means
it can be sprayed on an area and, unless it gets washed away by a rainstorm, it will stick
around for months. It’s made of 85% water, 10% fertilizer,
and 5% other stuff like clay and gum thickeners that help keep it together so it makes it
to the ground from the plane. And that bright red? That’s from iron oxide, which gives things
a red tint, or from the dyes like you’d find in food. The color usually fades quickly and is only
there to help firefighters see where the long-term retardant has been dropped and what areas
still need to be covered. The key is the fertilizer, which is made of
di- and mono- ammonium phosphate. Unlike water it doesn’t extinguish a fire–it
keeps it from ever starting. It reacts with the cellulose in trees and
other plant-based fuels when nearby flames cause the air to really heat up. This reaction produces carbon, in the form
of ash, and water vapor. That vapor then helps cool the fuel around
it so that it’s less likely to catch fire, slowing the spread of the fire until it burns
out. So, we wanted to see it with our own eyes. We went to the Department of Fire Protection
Engineering at the University of Maryland to see this long-term fire retardant in action. And it worked really well! You can see here that our retardant-soaked
pine needles to the left of the screen never caught fire but the untreated ones were burnt
to a crisp. So this retardant helps keep fire from spreading,
but how about shutting down a raging fire? That’s where, in addition to water, foams
and gels are so useful. Foams are surfactants–they lower the surface
tension of water so that it can penetrate, say, a burning piece of wood. If you’re interested in learning more about
surfactants, check out our video on shaving cream. But back to wildfires–foams are dropped out
of planes onto a blaze, or sprayed from the ground. Although they only stick around for about
30 minutes they keep water from evaporating as quickly as it normally would in such a
hot environment. Keeping water around longer increases the
likelihood of a fire going out. Gels are made up of super absorbent polymers,
like those you’d find in a baby’s diaper. They aren’t used all that often because
they can be kind of a pain to store and separate if they aren’t at the right temperature. Their big selling point is that they can go
on a vertical surface, like the wood roof of a home, and stick to it, unlike foams or
water which drip off. The polymers in the gel can soak up a ton
of water, keeping whatever it’s stuck to well hydrated. In a hot environment, like is the case for
wildfires, the gel will really only stick around for a couple hours. And because they don’t last all that long,
water, foams and gels should mostly be used to put out a fire, not to prevent it. This means that, if you’re trying to protect
your home from flames your best bet is to clear any flammable materials around it so
that the area is less likely to ignite, and maybe lay out some of that fertilizer-based
retardant. If you’re applying foams and gels to your
home when a massive wildfire is only a couple hours out then you’re putting your life
and the lives of first responders at risk. Using these US Forest Service-approved wildfire-fighting
chemicals doesn’t come without questions about what they could be doing to the environment
and…to us. Researchers haven’t found concern when it
comes to humans or their pets, but–when it comes to marine life–studies are ongoing,
and that’s because nutrients like nitrogen and phosphorus, which are found in long-term
fertilizers, can cause things like algal blooms, which are notoriously deadly for aquatic critters. It’s important to note that the US Forest
Service is trying to prevent against this happening by putting strict guidelines in
place. Right now, long-term fertilizer-based retardants
can’t be dropped within 300 feet of open waterways like lakes, creeks, and streams. Continuing to research ways to make these
products even safer is important, but for now they’re probably the least harmful option
we have. Melted fridges, smoldering lead-painted buildings
with asbestos in the walls, electrical wiring and plastic pipes burnt to a crisp–when these
things burn there are some seriously dangerous chemicals released. With global warming it’s looking like these
massive blazes will become all too common. So, if you find yourself in the woods with
a box full of fireworks, please don’t…wait why are you in the woods with fireworks? We’d like to thank Phos-Check for the flame
retardant, foam, and gel so we could do these cool demos. And Michael Gollner and the Department of
Fire Protection Engineering at the University of Maryland for not only letting us take over
their lab but for helping us light things on fire and safely put them out. If you’re craving more firey footage, check
out our past video on How Matches Work. See you next week!

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