- In April 1995, a truck bomb ripped apart a building
in downtown Oklahoma City.
In August 2015, a series of explosions shook
the port of Tianjin and northern China.
And in August 2020, a warehouse fire set off
a blast in Beirut so powerful
that neighboring countries could feel it.
These were all caused by the compound ammonium nitrate,
which over the last century has been involved
in at least 30 disasters and terrorist attacks.
But what is ammonium nitrate?
Well, it's used in all kinds of things
from making antibiotics to instant cold packs.
And it's a key ingredient in fertilizer.
You might be wondering,
Why are we using something that has
the potential to be so deadly to grow food?
(music chime)
I like to think of ammonium nitrate as
a Jekyll and Hyde chemical.
When it's stored properly,
it's the mild mannered Dr. Jekyll.
Plants love it
because it supplies them with nitrogen
which they need to grow.
And although our atmosphere is mostly nitrogen,
plants can't actually use it in that form,
but they can use it in the form of nitrate.
Under the wrong conditions,
ammonium nitrate can turn into
Dr. Jekyll's evil alter ego,
Mr. Hyde.
- [MAN] Window
- [BOY] Are you serious?
- [MAN] Yeah. (explosion)
So what makes this normally harmless compound turn deadly?
First, you need a lot of it.
There's this thing called critical diameter,
which is essentially the amount of a compound
you would need for it to detonate.
Ammonium nitrate is critical diameter is huge,
about 100 times bigger than TNTs.
- And it's quite inert by itself.
But sometimes if there's a fire
quite near the ammonium nitrate,
and ammonium nitrate is in a huge pile,
ammonium nitrate can catch on fire.
- Once ammonium nitrate reaches 210 degrees Celsius,
it starts to melt,
quickly producing a bunch of gases,
mainly nitrous oxide,
water vapor and nitrogen gas.
If those gases can't escape,
temperatures go up
and the reaction gets faster and faster.
Now this on its own could lead to an explosion.
In the case of a Beirut,
6 million pounds of ammonium nitrate
had been improperly stored in a warehouse,
sitting around and soaking up moisture
for nearly seven years.
- And particularly though nitrate has been a bit wet,
it becomes very hard like cement,
it's not fluffy powder anymore
- So out of fire,
and that hardened ammonium nitrate starts
to heat up and melts.
- And then the pressure starts to increase
where the gases can't escape.
- The burn rate or the speed at which ammonium nitrate
is burning starts to pick up.
When the burn rate is
slower than the speed of sound,
that's deflagration,
but when it becomes faster than the speed of sound,
that causes a shockwave through
the ammonium nitrate which detonates it.
But ammonium nitrate doesn't
need to be in a compressed form to create a disaster.
At the port of Tianjin,
1.7 million pounds of ammonium nitrate was being stored in
a warehouse near a place where nitrocellulose
was also being stored.
Unlike ammonium nitrate,
nitrocellulose is highly flammable.
The nitrocellulose caught fire,
spreading to the stored ammonium nitrate,
causing it to detonate.
Tianjin and Beirut were some of
the deadliest accidental ammonium nitrate disasters over
the last century.
But terrorists have also weaponized the chemical.
Like in the 1995 Oklahoma City bombing,
where terrorist detonated a truck
loaded with 5,000 pounds of ammonium nitrate fertilizer,
killing 168 people.
When I see a large explosion on the news,
my first instinct is to ask,
"Was that an accident?
Or was it planned?"
- If its a terrorist attack,
you wouldn't have a fire,
it will happen very quickly.
You wouldn't have time for people to video it,
it'll be done
within minutes.
Because what they're doing,
they have the explosive,
they will detonate it,
cause a blast do the utmost damage they can
and that's it.
- Because of its prevalence and terrorist attacks,
Some countries have outlawed ammonium nitrate.
In one instance in 2011,
the US Army detonated about 2,000 pounds
of ammonium nitrate fertilizer
that it collected in Afghanistan.
It was done very far away from homes
or people so the resulting shockwave
wouldn't cause damage or injury.
Sometimes the shockwave is more deadly
than the explosion itself.
- A shockwave is compressing
the air going through the atmosphere,
and at the tip of the shockwave,
the temperatures are three to 4,000 degrees centigrade
and the speed of the shockwave is supersonic.
So as a shock waves going through the atmosphere as it hits
windows of course it shatters them because
it pushes them out.
As it hits people,
it'll break our bones
because they're brittle,
but the rest of it will go through
but it'll burn us because it's very hot.
It'll flip over cars,
it will flip over ships.
It'll break anything brittle.
it will shatter anything brittle as
it goes through the atmosphere.
- So if you find yourself in a place
where you see a massive fire burning,
get as far away from it as possible
and away from any windows because
you don't know what's burning.
So if it detonates,
the shockwave that follows could be devastating.
Yes, all of this is scary.
But Dr. Akhavan made it clear that
we should not be freaked out about ammonium nitrate.
- Because people worry now,
so they shouldn't be worried about ammonium nitrate.
It is safe to use.
Its nothing more.
It's not classed as an explosive.
So very rarely does it go up.
It's only when it's old,
and there's a fire next door
and also stored in huge quantities.
Otherwise it's fine.
- So having a bag of ammonium nitrate fertilizer
in your garage is not cause for concern.
So keep on using it,
your tomatoes will probably thank you.
Happy gardening.
(upbeat outro music)