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!