Ever seen this before?
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,
实际上是一种结合 包括水 肥料
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
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 that 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.
如从湖泊 河流 甚至是你家的泳池
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 that it makes 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.
从而使水易渗入 比如 一块燃木
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.
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,
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!
Ever seen this before?