As many as 100 people were killed and nearly 4,000 injured in two huge explosions that rocked downtown Beirut, the Lebanese Red Cross said on Wednesday.
The blasts took place on Tuesday evening (around 6.10 p.m. local time), shaking buildings all over the city while also causing severe damage and casualties, Xinhua reported.
President Michel Aoun said that 2,750 tonnes of ammonium nitrate, used in fertilizers and bombs, had been stored for six years at the port without safety measures. He said that was "unacceptable".
A common chemical ingredient of agricultural fertilizers, the nitrogen-rich compound is also the main component of the explosive composition known as Ammonium Nitrate Fuel Oil (ANFO). It is also the main component in many types of mining explosives, where it’s mixed with fuel oil and detonated by an explosive charge.
What is this chemical, how and where is it used or misused, what hazards does it present, and what are the rules and regulations about its use in India?
In its pure form, ammonium nitrate (NH4NO3) is a white, crystalline chemical which is soluble in water. Produced as small porous pellets, or “prills”, it’s one of the world’s most widely used fertilizers. It is the main ingredient in the manufacture of commercial explosives used in mining and construction.
In India, The Ammonium Nitrate Rules, 2012, under The Explosives Act, 1884, define ammonium nitrate as the “compound with formula NH4NO3 including any mixture or compound having more than 45 percent ammonium nitrate by weight including emulsions, suspensions, melts or gels but excluding emulsion or slurry explosives and non-explosive emulsion matrix and fertilizers from which the ammonium nitrate cannot be separated”.
Ammonium nitrate as an explosive
Pure ammonium nitrate is not an explosive on its own. It is classified as an oxidizer (Grade 5.1) under the United Nations classification of dangerous goods. If mixed with ingredients like fuel or some other contaminants, or because of some other external factors, it can be very explosive.
However, for combinations to explode, triggers like detonators are required. Many Improvised Explosive Devices (IEDs) used by terrorists around the world have ANFO as the main explosive, triggered by primary explosives like RDX or TNT. In the majority of terror attacks in India, including those in Pulwama, Varanasi, Malegaon, Pune, Delhi, Hyderabad, and Mumbai, ammonium nitrate has been used along with initiator explosives like RDX.
Stored ammonium nitrate is a major fire hazard
Large quantities of stored ammonium nitrate are regarded as a major fire hazard, with multiple reported cases across the world. The explosion of large storage can happen primarily in two ways.
One is by some type of detonation or initiation because the storage comes in contact with the explosive mixture. Second, the blast can result due to a fire that starts in the ammonium nitrate store because of the heat generated due to the oxidation process at a large scale. The second one seems to be the primary likely cause of the incident at Beirut port. There are several documented examples of deadly ammonium nitrate fire and explosion incidents in the past, some with large numbers of fatalities like in China in 2015 and in Texas in 1947.
What could have caused the explosion?
Ammonium nitrate does not burn on its own.
Instead, it acts as a source of oxygen that can accelerate the combustion (burning) of other materials.
For combustion to occur, oxygen must be present. Ammonium nitrate prills provide a much more concentrated supply of oxygen than the air around us. This is why it is effective in mining explosives, where it’s mixed with oil and other fuels.
At high enough temperatures, however, ammonium nitrate can violently decompose on its own. This process creates gases including nitrogen oxides and water vapor. It is this rapid release of gases that causes an explosion.
Ammonium nitrate decomposition can be set off if an explosion occurs where it’s stored if there is an intense fire nearby.
While we don’t know for sure what caused the explosion in Beirut, footage of the incident indicates it may have been set off by a fire – visible in a section of the city’s port area before the explosion happened.
It’s relatively difficult for a fire to trigger an ammonium nitrate explosion. The fire would need to be sustained and confined within the same area as the ammonium nitrate prills.
Also, the prills themselves are not fuel for the fire, so they would need to be contaminated with, or packaged in some other combustible material.
Residents’ health at risk
In Beirut, it has been reported 2,700 tonnes of ammonium nitrate was stored in a warehouse for six years without proper safety controls.
This will almost certainly have contributed to the tragic circumstances that resulted in a commonplace industrial fire causing such a devastating explosion.
An ammonium nitrate explosion produces massive amounts of nitrogen oxides. Nitrogen dioxide (NO₂) is a red, bad-smelling gas. Images from Beirut reveal a distinct reddish color to the plume of gases from the blast.
Nitrogen oxides are commonly present in urban air pollution and can irritate the respiratory system. Elevated levels of these pollutants are particularly concerning for people with respiratory conditions.
The fumes in Beirut will present a health risk to residents until they naturally dissipate, which could take several days depending on the local weather.
Regulations in India about ammonium nitrate
Because it is used as an ingredient for the production of industrial explosives, anesthetic gases, fertilizers, cold packs, and has a strong possibility of misuse, ammonium nitrate is highly regulated in India, at least in the letter.
The manufacture, conversion, bagging, import, export, transport, possession for sale, or use of ammonium nitrate is covered under The Ammonium Nitrate Rules, 2012. The rules also make storage of ammonium nitrate in large quantities in populated areas illegal in India.
For the manufacture of ammonium nitrate, an Industrial license is required under the Industrial Development and Regulation Act, 1951. A license under the Ammonium Nitrate Rules, 2012 is also required for any activity related to ammonium nitrate.