The recent Ohio train derailment and subsequent fire that released vinyl chloride into the environment has been a terrifying experience for the nearby population. The accident rekindles memories of the 1979 train accident in Mississauga, Ontario, when over 200,000 people had to be evacuated after a wheel bearing overheated and caused a propane tanker to burst into flames. The fear was that a car close to the fire and loaded with liquid chlorine would overheat, vapourize the chlorine and cause an explosion. Chlorine is extremely toxic, a property first made use of during the World War I by the Germans in an attack against the Allies at Ypres in Belgium. Chlorine gas is heavier than air and spreads along the ground with lethal effects on all living things. Luckily, at Mississauga, firefighters were able to cool down the chlorine car, prevent an explosion and a potential disaster.
The accident in Ohio had a similar cause, overheating of a wheel bearing that caused a derailment and fire. Like in Mississauga, an evacuation was ordered, but here the major worry was about the release of vinyl chloride gas carried in five cars. Vinyl chloride is not nearly as toxic as chlorine, but inhaling it still represents a risk. Another concern is that with heat, vinyl chloride can be converted into phosgene, a highly toxic gas, although experiments have shown that this reaction does not occur to a great extent. Another decomposition product is hydrogen chloride, also a toxic gas. There is also the theoretical possibility of burning vinyl chloride forming dioxins which are known carcinogens. So far, no dioxins have been detected.
Some of the derailed cars also released ethylene glycol monobutyl ether, ethylhexyl acrylate, isobutylene and butyl acrylate, all of which can cause lung irritation, nausea and dizziness. Most of these leaked out of the cars without vapourizing and ended up in the Ohio river causing some damage to wildlife.
Why was vinyl chloride being transported in such high volumes? It is the starting material for the synthesis of polyvinyl chloride (PVC), the third most widely-produced plastic in the world after polyethylene and polypropylene. The conversion of vinyl chloride into PVC was first patented in 1913 by German chemist Friedrich Klatte who accidentally discovered that exposure of the chemical to sunlight resulted in its polymerization. However, the PVC that Klatte produced was too brittle to be of any use and it remained a chemical curiosity until the 1920s when Waldo Semon was hired by the BF Goodrich company to try to find a substitute for natural rubber which was in short supply. Semon discovered that mixing PVC with various chemicals, particularly phthalates, eliminated the brittleness and converted PVC into a useful flexible material.
It wasn鈥檛 long before items such as vinyl car roofs, records, shower curtains, toys, water pipes, rain gear, blood bags, wire insulation and medical tubing made of PVC hit the market. Then as early as 1938, reports about the toxicity of vinyl chloride began to appear. Workers in the PVC manufacturing industry reported dizziness and confusion when exposed to vinyl chloride vapours. And then in 1949, liver damage was reported in 15 of 48 workers exposed to vinyl chloride in Russia. By 1971, the type of liver damage in workers had been clearly identified and the news was not good. Vinyl chloride caused angiosarcoma of the liver, a rare but extremely dangerous form of liver cancer. The industry began to implement measures to curb worker exposure to vinyl chloride, but there is still controversy over the time frame involved. Some industry documents show that companies were aware of the vinyl chloride risk before it became a matter of public record and were slow in responding to the danger because limiting worker exposure could interfere with production.
Finally, in 1974, the U.S. government declared angiosarcoma of the liver to be an occupational disease after six cases were diagnosed among vinyl chloride workers at the B. F. Goodrich Chemical Company plant in Louisville, Kentucky. This forced the industry to adopt stricter controls over the amount of vinyl chloride that workers could inhale. At the time, vinyl chloride was also being used as a propellant in spray cans and this application was banned. Today, the maximum vinyl chloride allowed in workroom air is 1 ppm and the industry has come up with equipment that complies with this.
The known carcinogenicity of vinyl chloride obviously raises the question of the increased risk of cancer in people who may have been exposed to it in Ohio. The link with cancer has only been noted in long-term occupational exposure and it is unlikely that a single exposure, even at higher levels than allowed in industrial facilities, would trigger cancer. Short-term inhalation of vinyl chloride can certainly cause breathing problems, dizziness and even loss of consciousness, but luckily, thanks to the quick evacuation of the area surrounding the accident, no serious health problems have been reported.
Given the immense amounts of chemicals being produced and transported around the world, the total avoidance of accidents is impossible. But learning from an accident is certainly possible. The Mississauga accident resulted in the recommendation to install heat detectors around the wheel carriage in trains, but it seems the Ohio disaster train was not equipped with these. Neither was it equipped with electronically controlled pneumatic brakes, a safety measure that the railway industry lobbied against vigorously when Congress proposed a law to have them installed on trains because of the costs involved. As Winston Churchill said, those who fail to learn from history are doomed to repeat it.
