09 May 2020
What is the styrene?
Source: By Sreenivas Janyala: The Indian Express
The gas that leaked from a chemical factory on the outskirts of Visakhapatnam on 7 May 2020, leaving at least 11 dead and sending hundreds to hospital, is called styrene. A look at its structure, the kind of industries that use it, and the kind of health hazards experts associate it with:
Styrene is an organic compound with the formula C8H8. It is a derivative of benzene (C6H6). It is stored in factories as a liquid, but evaporates easily, and has to be kept at temperatures under 20°C. Also known as ethenylbenzene, vinylbenzene, and phenylethene, Styrene is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concentrations have a less pleasant odor.
Styrene is the main raw material for synthesis of polystyrene, or (C8H8)n. Polystyrene, in turn, is a versatile plastic that is used to make parts of various appliances such as refrigerators or micro-ovens; automotive parts; and parts of electronics such as computers; and also to manufacture disposable cups and in food packaging. Styrene is also used as an intermediate to produce copolymers — which are polymers derived from one or more species of monomers such as styrene.
Exposure to styrene gas affects the central nervous system, said Dr K Vijay Kumar, Head of the Department of Respiratory Medicine, Andhra Medical College. “Breathlessness, respiratory problems, irritation in eyes, indigestion, nausea, transient loss of consciousness, unsteady gait, giddiness are caused by exposure to it. In this incident, people were exposed to the gas for a short duration, so there may not be any long-term effects,” Dr Kumar said.
However, in people suffering from respiratory illness such as asthma, and those who have chronic obstructive pulmonary diseases, these conditions may get exaggerated, Dr Kumar said. “Those suffering from diabetes or hypertension may have anxiety disorders.”
It is the mucous membrane that is mainly affected by exposure to styrene gas. In Visakhapatnam, the styrene gas leak caused acute breathlessness among many people, a few of whom asphyxiated to death.
Experts say that if people are exposed to the gas for a long period, there is a chance of their developing leukaemia and headaches. Studies on the effects on health due to occupational exposure to styrene have, however, been inconclusive.
As per the United States Environmental Protection Agency, tests involving acute exposure of rats and mice have shown styrene to have low to moderate toxicity by inhalation and oral exposure. Animal studies have reported effects on the entral nervous system, liver, kidney, and eye and nasal irritation from inhalation exposure to styrene. Liver, blood, kidney, and stomach effects have been observed in animals following chronic oral exposure.
Styrene gas leaked from a storage tank of LG Chem Polymers. The factory was established in 1961, originally as Hindustan Polymers, to manufacture polystyrene. It was merged with McDowell & Co of the UB Group in 1978, then taken over in 1997 by South Korea-based LG Chem, which renamed it LG Polymers. The factory manufacures general-purpose polystyrene and high-impact polystyrene, expandable polystyrene, and engineering plastics compounds. It is located at RRV Puram in Gopalapatnam, 15 km from Visakhapatnam city.
A company official said 1,800 tonnes of styrene was stored in a tank of capacity 2,400 tonnes. The gas leaked from this tank when officials were preparing to reopen the factory that was shut for 44 days due to the lockdown. About half the gas leaked before it was contained.
As explained, styrene has to be stored in gas tanks under 20°C to keep it stable. The temperature has to be continuously monitored, and any exposure to light or heat may result in polymerisation. A team of 15 engineers and officials remained on duty at the factory throughout the lockdown period to monitor it. If temperature rises, inhibitors have to be added to keep the styrene stable. At LG Chem, an inhibitor tank is attached to the styrene storage tank but it failed to stabilise it in time. As a safety measure, the styrene tanks are never filled to capacity.
As the styrene was stagnant for 44 days, officials said, it was possible that some gas accumulated at the ceiling of the storage tank and its temperature rose beyond the specified 20°C, and the styrene started vaporising and escaped. This is called auto-polymerisation. However, the exact cause is still being ascertained. The company has not explained how the storage tank ruptured and the gas escaped.