STYRENE - The Culprit of Visakhapatnam Chemical Gas Leak
Today's morning news brought a piece of distressing news for us, a gas leak of styrene occurred at LG Polymers, Visakhapatnam which spreads to nearby villages over a radius of three kilometers creating widespread panic in the nearby areas. The recent news reported a death toll of nearly 10 people in addition to the thousands that got affected in nearby villages like Venkatapuram, Gopalapatnam, Padmapuram, B.C. Colony, and Kamparapalem.
The company was originally Hindusthan Polymers, which was launched in 1961. It was taken over by LG, a famous South Korean electronics giant, in 1997 and renamed to LG Polymers India Pvt Ltd.
Styrene, also known as Ethenylbenzene, Phenylethylene, Vinylbenzene, Cinnamene, etc, has a Molecular Weight of 104.15 g/mol and is insoluble in water while also being less dense than water. It is highly soluble in organic solvents such as Acetone, CCl4, Benzene, Ether, n-Heptane, and Ethanol. It is a liquid at ambient temperature highly volatile and highly inflammable and gets polymerized easily in the presence of free radicals, oxygen, or heat and thus special care is necessary for its storage. Stabilized styrene monomer appears as a clear colorless to dark liquid with an aromatic odor. Vapors heavier than air and irritating to the eyes and mucous membranes
Polymerization can take place in storage as well as under more controlled conditions. Styrene polymerizes slowly at normal ambient temperatures but very rapidly at elevated temperatures. Styrene polymerization is initiated by heat, lack of inhibitor and dissolved oxygen, and contact with peroxides and other free-radical initiators, ionic initiators, and redox initiators. The polymerization process is exothermic, evolving heat which if not dissipated rapidly enough, the temperature of the monomer will rise, increasing the rate of polymerization and further evolution of heat The temperature may rise to the point where the reaction becomes very rapid and self-sustaining (a runaway polymerization). Normally temperatures above 65°C (149°F) are needed to initiate runaway polymerizations.
During a runaway polymerization, the temperature will reach and exceed the boiling point of styrene. The vapor may erupt violently from the tank vents or, if the vents are plugged or too small, it can create enough pressure to rupture the tank. As the liquid polymerizes and becomes more viscous, vapor bubbles may become trapped, expanding the liquid and causing spills or rupture of the tank.
Polymerization during storage may be prevented by close attention to monomer temperature, inhibitor level, polymer content, and oxygen content. TBC (4-tert-butylcatechol) is customarily added to styrene to prevent polymer formation and oxidative degradation during shipment and subsequent storage. Inhibitors prevent polymerization in two ways. (1) They can react with the free radical which initiates the polymerization reaction and growing chain. (2) They can act as an antioxidant and prevent polymerization by reacting with oxidation products in the monomer. It should be noted that sufficient oxygen must be present for inhibition. In the absence of oxygen, polymerization will proceed as if no inhibitor were present. Thus the presence of oxygen is necessary for styrene but air present in the free space of tanks causes the polymerization of styrene was the inhibitor (TBC) is absent. Thus ordinarily the bulk styrene is flushed with air once in a week and the free space in the tank is filled with inert nitrogen to reduce vaporization. The tank is also cooled regularly with water; however special care is taken not to mix water with styrene since any impurities present initiate polymerization reactions. If the TBC concentrations fall to a dangerously low level, polymerization has begun, resulted in unpredictable situations depending on environmental condition especially the temperature. The dangers of fire and explosion are real because styrene can form explosive mixtures in the air at room temperatures. Precautions should be taken to assure that no ignition of vapors can occur, especially where elevated temperatures are involved.
The most important products obtained by the polymerization of styrene are polystyrene (PS), rubber-modified high impact polystyrene (HIPS), styrene-butadiene latex (SBL), styrene-acrylonitrile copolymer (SAN), acrylonitrile-butadienestyrene/terpolymer (ABS), and styrene-butadiene copolymer (SBR, synthetic rubber). Other important uses of styrene are in styrene-polyester resins, latexes, and styrenated oils and alkyls.
Polystyrene is primarily used in packaging, disposables, and low-cost consumer products, and the polystyrene beads (EPS) are used in the food and beverage packaging, insulation and cushion packaging. Improved grades of resins are used in higher performance applications, such as home electronics and appliances. ABS and SAN have many uses in the consumer durables market. Styrene-based polyesters have lifetimes of over thirty years in both indoor and outdoor applications. Thermoplastic elastomers are directly replacing natural and traditional synthetic rubbers in many established applications. Other applications include carpet backing (SB Latex), production of tires (SB Rubber), and castings for textiles and paper.
If pure, styrene has a sweet balsamic, almost floral characteristic odor, but usually contains aldehydes that have a typical penetrating smell, sharp, sweet, and unpleasant. Contact may cause irritate skin, eyes, and mucous membranes, chronic (long-term) exposure to styrene in humans results in effects on the central nervous system (CNS), such as headache, fatigue, weakness, and depression, CSN dysfunction, hearing loss, and peripheral neuropathy. Styrene is not a poisonous gas like that played havoc in Bhopal gas tragedy; however, the gas could cause severe harm when inhaled in large quantities, posing a threat to those who reside closest to the plant. Human studies are inconclusive on the reproductive and developmental effects of styrene; several studies did not report an increase in developmental effects in women who worked in the plastics industry, while an increased frequency of spontaneous abortions and decreased frequency of births were reported in another study. Several epidemiologic studies suggest there may be an association between styrene exposure and an increased risk of leukemia and lymphoma. However, the evidence is inconclusive due to confounding factors.
The suggestive first aids for the chemical contacts for the eyes are prompt washing (irrigate) with large amounts of water, occasionally lifting the lower and upper lids. If irritation, pain, swelling, lacrimation, eye tissue is frozen or photophobia persists, get medical attention as soon as possible. For skin contact, dust it off immediately and then flush the contaminated skin with water (washing with soap and water is more advisable since styrene is insoluble in water). If this chemical or liquids containing this chemical penetrate the clothing, promptly remove the clothing and flush the skin with water. If a person breathes large amounts of this chemical, move the exposed person to fresh air at once. If breathing has stopped, perform artificial respiration. Keep the affected person warm and at rest. When breathing is difficult, properly trained personnel may assist the affected person by administering 100% oxygen. Keep the affected person warm and at rest.
For information regarding security measures in storing styrene Click Here
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