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2. Product Information and Characteristics

2.1. General Description and Hazardous Properties

Styrene (C6H5-CH=CH2, CAS RN:100-42-5; EC No.: 202-851-5, EEC Annex I Index No.: 601-026-00-0), also known as ethenyl benzene, phenyl ethylene, phenyl ethene, vinyl benzene, cinnamene or styrene monomer, under ambient conditions is a colourless clear liquid with a distinctive sweetish aromatic odour. It is miscible with most organic solvents in any ratio and is a good solvent for synthetic rubber, polystyrene and other high molecular weight polymers. From the environmental impact point of view, it is only slightly soluble in water (approx. 300 ppm at ambient conditions) and consequently the acute hazard of spilled styrene will be very limited for most aquatic species. However styrene may cause tainting (unpleasant taste) in food from aquatic organisms exposed to low environmental concentrations. According to the Standard European Behaviour Classification (Bonn Agreement) styrene is classified as a “floater evaporator”.

Figure 1: Chemical Structure of Styrene
Figure 1: Chemical Structure of Styrene

Styrene is a monocyclic alkenyl aromatic compound with a molecular weight of 104. Being rather volatile and having a flash point of 32 oC, styrene is classified as a flammable substance, which in use may form flammable/explosive vapour-air mixtures. Despite its high boiling point, styrene will eventually end up in the air. For other typical parameters, the reader is referred to Table 1 ( 2.2): Typical Physical Properties of Styrene.

Short-term exposure to styrene in humans results in respiratory effects, such as throat irritation and lung constriction, irritation to the eyes, and neurological effects such as dizziness (see Section 3 “Health Aspects” for more details). To date styrene is classified in the EU as harmful by inhalation, irritating to the eyes and to the skin (see Section 3 “Health Aspects” for more details).

Very low concentrations of styrene vapour will react with bromine and with chlorine in sunlight to form an extremely potent lachrymatory agent.

The characteristic unpleasant odour and the low odour threshold (0.1 ppm; 0.43 mg/m3) allow styrene to be readily detected in the workplace at levels below the occupational exposure standards.

Styrene will polymerise when contaminated by oxidising agents and most halides. The polymerisation reaction is exothermic and if contained may become violent. If the heat is not removed, the bulk styrene temperature may rise to a level at which polymerisation is self-sustaining and very rapid, evolving the release of large quantities of heat together with volumetric expansion. The most commonly used polymerization inhibitor is tertiary butyl catechol (4-tert-butylcatechol (TBC) or p-tert-butyl catechol; CAS RN 98-29-3; EC No.: 202-653-9). TBC is classified acc. to EC Directive 67/548/EEC, but some suppliers assign a classification as irritant or even corrosive. TBC may cause sensitization by skin contact, is toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment. More details on the inhibition mechanism and polymerisation reaction are highlighted in Section 2.4 and Appendix 2.

Styrene can accumulate static charges; hence special attention should be paid to take precautionary measures against static discharge (spark hazard) (refer to Appendices 3, 4, 5 and 6 for more details).

The carbon:hydrogen ratio of styrene is almost 1:1 resulting in considerable amounts of carbon oxides (CO2, CO) and free carbon to evolve when burned. Burning styrene can generate large quantities of thick black smoke (refer to Section 7.3.2 for more details).

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