There is an old saying that if you play with fire, eventually you will get burned. The same can be said for certain chemicals. Of course, I don’t mean “play” in the literal sense. What I mean is that when chemicals are produced, especially on a large scale, as many are, accidents can happen. However, risk can be minimized by adhering to good manufacturing practice and proper handling and storage of chemicals. Unfortunately, human error, negligence and greed can take a toll.
Recently, eight workers died from inhalation of methyl formate vapours when the chemical was mishandled at a plant in China. Exactly what happened isn’t clear, but it is likely that proper procedures were not being followed when a shipment was being transferred for further processing. Methyl formate is a volatile liquid that when inhaled eventually breaks down to yield formic acid and methanol with the latter being further metabolized to formic acid. Toxicity is two-fold. Methyl formate inhibits the enzyme cytochrome oxidase that is critical to cells’ use of oxygen. Without oxygen, they die. Then there is the problem of formic acid causing acidosis with all sorts of negative effects on body chemistry.
Methyl formate is an important industrial chemical produced on a large scale by the reaction of methanol with carbon monoxide. It is the starting material for the synthesis a host of other compounds, and because of its volatility also finds use as a blowing agent in the production of polyurethane foam insulation. It is a suitable alternative to ozone-depleting Freons. Methyl formate is commonly produced and handled without a problem, at least as long as human error doesn’t enter the picture, as it likely did in the case of the Chinese accident.
Compared with the tragic events in the Chinese port city of Tianjin in 1965, the methyl formate accident was a minor one. Tianjin was rocked by a series of explosions that flattened a large warehouse, destroyed hundreds of cars in an adjacent lot, caused extensive damage to neighbouring apartment blocks, injured some 800 people and resulted in the death of 173, mostly firefighters and policemen. It all began when stocks of nitrocellulose, a common ingredient in various lacquers including nail polish, caught fire in the August heat. The flames ignited a stock of ammonium nitrate fertilizer stored nearby, resulting in a sequence of thunderous blasts.
Any story involving nitrocellulose peaks my interest because I frequently use “flash paper” in my presentations. This is tissue paper that has been treated with a mix of nitric and sulphuric acids to convert the paper’s cellulose into nitrocellulose, an extremely flammable substance. In this reaction, nitro groups become attached to the cellulose and serve as an internal source of oxygen, speeding up the combustion process.
An engaging story, probably apocryphal, describes the discovery of nitrocellulose by Swiss chemistry professor Christian Schonbein, who while carrying out experiments in his kitchen, spilled a mixture of nitric and sulphuric acids on the floor. He quickly grabbed his wife’s cotton apron to wipe up the mess and then proceeded to hang it in front of the fireplace to dry. The professor was shocked to see the apron go up in flames and essentially vanish without producing any smoke! Cotton is essentially cellulose, and Schonbein had unwittingly nitrated it to yield nitrocellulose. This came to be known as “guncotton” since on combustion it produces a large volume of gases that can be used to propel bullets.
Due to its flammability, nitrocellulose is stored dampened with water and alcohol. The containers in Tianjin were improperly stored, exposed to the summer heat that allowed the nitrocellulose to dry out and ignite. A large supply of ammonium nitrate fertilizer was illegally stored nearby, and when heated by the flames, began to decompose to yield a gaseous mix of carbon monoxide, carbon dioxide, nitrogen and water vapour. The rapid expansion of these gases created the explosion. To make the situation even worse, drums of solid sodium cyanide were also stored at the facility in an illegal fashion. When sodium cyanide with water, it can release highly toxic hydrogen cyanide gas which may have accounted for some of the deaths.
Chinese investigators concluded that “safety management procedures were inept” and assigned various degrees of blame to 74 government officials, some for “taking bribes and abusing power.” The head of the company that managed the storage facility was sentenced to death, later commuted to a life sentence.
The Tianjin ammonium nitrate explosion was not the most devastating such event. That dubious “honour” goes to the 1947 explosion of ammonium nitrate aboard a cargo ship in Texas City, Texas, in 1947, killing close to 600 people. Then there was the explosion in Beirut in 2020 that took some 220 lives and injured more than 5000 people when ammonium nitrate in a port warehouse exploded sending a huge orange fireball into the sky flowed by a shockwave. The orange colour is due to nitrogen dioxide that forms when nitric oxide reacts with oxygen. The nitric oxide originally forms from oxygen and nitrogen released by ammonium nitrate decomposition.
Not all ammonium nitrate explosions are accidental. The 1995 Oklahoma City blast that killed 168 people in a federal office building was orchestrated by Timothy McVeigh, an anti-government terrorist. So, is ammonium nitrate a “good” or a “bad” chemical? Of course, it is neither. When used as a fertilizer, it made possible the green revolution, enabling the feeding of millions of people. When callously, illegally stored, or when used as a weapon by terrorists, it has resulted in many deaths. But ammonium nitrate, or methyl formate, do not make decisions about how they are produced, stored or used. People make these decisions. And people are..well…people.