Manufacture and use of chloroprene monomer.

There are only six manufacturers of chloroprene (CD) located outside of the former Communist Bloc countries. Five of these manufacture chloroprene from butadiene via a two step process consisting of chlorination and subsequent dehydrochlorination. The sixth dimerizes acetylene and then hydrochlorinates the dimer to produce CD. Both the acetylene and butadiene-based manufacturing processes are conducted within sealed systems. Therefore, the only potential exposure during manufacture is sampling for product quality, strainer/filter changing and accidental leaks or spills. All six manufacturers produce CD only for the production of polymer. Manufacturers convert CD into polychloroprene polymer (PCP) via emulsion polymerization. A solution of CD and other ingredients is mixed with an aqueous caustic solution to produce an emulsion. Free radicals initiate polymerization and free radical scavengers are added to stop the reaction at the desired conversion. After unreacted monomer is removed, PCP can be sold as a latex (colloid) or isolated and dried to produce solid product. The PCP manufacturing process is also designed to be a closed system. However, the extreme reactivity of CD and the inherent stickiness of PCP polymer, makes it necessary to 'open' the process to remove polymer. This results in potential for operator exposure, in addition to the items mentioned for CD manufacture. With the use of appropriate engineering controls, work practices and personal protective equipment for activities with exposure potential, actual workplace exposures are controlled below the occupational exposure limits (2-10 ppm). The solid PCP products, which comprise approximately 92% of the total amount of polymer manufactured, contain <1 ppm CD. Most PCP latexes contain <0.1% residual CD. So, the potential for CD industrial exposure is limited to CD and PCP manufacture.

Occupational exposure to butadiene, isoprene and chloroprene.

Workers are exposed to butadiene, isoprene and chloroprene in the manufacture of these monomers and in their use in the production of various elastomers. These include styrene butadiene rubber, polybutadiene, polyisoprene, butyl rubber and neoprene. Monomer production and extraction are done in typical closed chemical process units where low background levels of the monomers are the result of minor leaks in valves and pumps. Occasionally, higher levels occur as a result of planned or unplanned events that cause releases. Polymer production is also a closed process, but the occasional clogging of pipes and equipment with polymer requiring maintenance operations where some release is likely occurs much more often than for monomer production. For this reason, exposure levels are generally higher on polymer production units. Polymer finishing is essentially an open process, but almost all monomer should have been stripped from the polymer before finishing. Where small amounts of solvents or monomers remain in the polymer and are volatilized in finishing, they are captured by vapor control systems. As a result, exposures in finishing are typically low. Measured levels of exposure in recent years are presented. In general, modern levels of exposure are well below OSHA, ACGIH and other applicable limits. Few measurements were made prior to the 1970s, but epidemiological estimates made by modeling suggest that levels could have been quite high in the 1940s and 1950s. In these years, manual reactor cleaning was common, and pumps often leaked.