Ammonium nitrate: what is the chemical blamed for
blast in Lebanese capital?
The deadly explosion in Beirut has been blamed on
thousands of tonnes of the chemical used in fertilisers and explosives
‘We’re cursed’: shock and despair in Beirut as explosion
devastates city
Helen
Sullivan and Tom Phillips
Wed 5 Aug
2020 02.59 BSTLast modified on Wed 5 Aug 2020 07.30 BST
The likely
cause of the huge blast in Beirut on Tuesday appears to have been the highly
reactive chemical ammonium nitrate.
Lebanon’s
prime minister, Hassan Diab, said 2,700 tonnes of ammonium nitrate exploded
after lying unsecured in a warehouse for six years, tallying with reports that
a ship carrying a similar quantity of the chemical had unloaded its cargo at
the port in 2013. It remains unclear what caused the chemical to ignite.
Ammonium
nitrate is a common industrial chemical used mainly for fertiliser because it
is a good source of nitrogen for plants. It is also one of the main components
in mining explosives.
It is not
explosive on its own, rather it is an oxidiser, drawing oxygen to a fire – and
therefore making it much more intense, according to Gabriel da Silva, a senior
lecturer in chemical engineering at the University of Melbourne.
However, da
Silva said, it ignites only under the right circumstances, and these are
difficult to achieve. “You need extreme circumstances to set off an explosion,”
he said.
While
ammonium nitrate can in fact put out a fire, if the chemical itself is
contaminated, for example with oil, it becomes highly explosive. “I think
that’s what’s happened here,” said da Silva.
While the
chemicals in the air should dissipate fairly quickly, lingering pollutants can
cause problems later, for example if they acidify rain.
“If you
look at the smoke that came from the blast it’s this kind of blood red colour.
That’s because of the nitrogen oxide air pollutants in it,” he said.
If the
2,700-tonne figure is accurate, that would make the ammonium nitrate explosion
larger than the 1947 Texas City Disaster, when a consignment of 2,300 tonnes of
ammonium nitrate exploded, killing nearly 500 people. The blast created a
4.5-metre (15ft) tidal wave.
The images
coming out of Beirut are also horribly reminiscent of the destruction inflicted
on the Chinese city of Tianjin by a 2015 warehouse disaster that killed more
than 170 people and left hundreds injured.
On the
night of 12 August a series of cataclysmic detonations rocked an area of
warehouses where large quantities of hazardous chemicals, also including sodium
cyanide and potassium nitrate, were being stored, in some cases illegally.
Chinese
authorities later claimed the first explosion had been triggered when the
summer heat caused a highly flammable compound called nitrocellulose to
spontaneously ignite. Nearby stores of ammonium nitrate then caught fire and
exploded in the major port city, which lies 110km (70 miles) south-east of the
capital Beijing.
Firefighters
who rushed to the scene reportedly attempted to extinguish the initial blaze
with water – only to inadvertently exacerbate the situation because of the
presence of hazardous flammable chemicals. The majority of those killed were
firefighters, including at least one teenager.
Such was
the force of the Tianjin explosions that they registered as small earthquakes.
Then, as
now, witnesses filmed apocalyptic, almost surreal footage showing the scale of
the inferno.
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