Document yrJQBBy70a9KGYMYwZXRvbZ64

^v^CCL j news features w VCM-Exposure Standards. i Too Tough Too Soon? R&S 004468 After virtually ignoring Industry's findings on cancer risk for a dec ade, the U. S. government is now calling for zero-detectable am bient levels of vinyl chloride monomer (VCM) in plants that make or use It At hearings this week, some clashes are expected as industry tells why it thinks the timetable should be extended. Hearings begin tomorrow--June 25th--in' Washington on just what level of exposure to vinyl chloride monomer (VCM) can be tolerated by workers without seriously endan gering their health. Once again, and ironically in this instance, a clash be tween government agencies and in dustry seems inevitable. The Occupational Safety and Health Administration (OSHA) pro poses to set a standard for employee exposure at "zero." as determined by a sampling and analytical method capable of detecting vinyl chloride in concentrations of 1 ppm (with an ac curacy of 0.5 ppm). OK, But . . .--VCM manufac- DEVICE measures VCM exposure by drawing air through sorbent tube. 110 turers are not basically opposed to reducing exposure levels as much as possible--for example, B. F. Good rich Chemical Co. (the U. S.'s largest vinyl chloride producer) now oper ates at levels of about 15 ppm in its polymer plant, and even lower in its monomer facility. What bothers manufacturers is having to achieve, in a telescoped time-period "no de tectable level of exposure." As a Goodrich spokesman ex plains. "The situation we're facing with vinyl chloride exposure levels is not dissimilar to the zero pollution legislation for controlling water pol lution--the final last percentage points are achievable only at enor mously high costs." The irony of this particular situ ation is that producers of vinyl chlo ride voluntarily alerted the govern ment of the chemical's involvement in several deaths from liver cancer (angiosarcoma). In fact, over 13 years ago Dow Chemical Co. reported that longterm VCM exposures of animals to 100 ppm VCM for 4`A to 6 mo. (at the equivalent of "normal working hours") resulted in slight liver dam age. At that time, Dow recom mended that exposure levels be re duced to 50 ppm, though the government's maximum allowable concentration was 500 ppm. The Dow recommendation was not ac cepted by the American Conference of Governmental Industrial Hygien ists (ACGIH). In 1962, on the basis of work done at Yale University, ACGIH concluded that 500 ppm offered an adequate safety margin for human exposure to VCM. and published 500 ppm as the recom mended standard. That same level was also accepted by OSHA as a na tional standard in 1971. However, beginning in the mid1960s. the Manufacturing Chemists Assn, funded an investigation of the possible health dangers involved in VCM manufacture. In mid-1972. MCA established technical liaison with European researchers who were also investigating the safe-exposure limits of VCM. One decision by MCA arising from this agreement was to initiate an epidemiological study of VCM/PVC (polyvinyl chloride) workers in the U. S. And in early 1973, MCA signed a contract with Industrial Bio-Test Laboratories, Inc., (Northbrook. III.). In late June 1973, MCA requested a meeting with the National Institute for Occupational Safety .and HealtET this was an-anged for July 17, 1973. A summary of the-published toxicity data on vinyl chloride, and other pertinent information, was presented to NIOSH at that time. A physician representing the European research ers reported at the meeting on stud ies in Europe in which tumors were observed in rats at exposure levels as low as 250 ppm. Six months later, in January 1974, B. F. Goodrich Chemical Co. in formed NIOSH that the deaths of several of its employees from angio sarcoma might have been occupa tionally related. In the succeeding months, similar reports were made to NIOSH of possibly job-related liver angiosarcoma by Union Car bide Corp.. Goodyear Tire & Rub ber Co. and Firestone Plastics Co. In early April. OSHA acted and is sued an Emergency Temporary Standard that reduced exposure lev els from 500 ppm to 50 ppm. with the understanding that this new stan dard was to be in effect only until October while the whole question of VCM exposure safety levels was ex plored more closely. Timetable Too Fast?--Despite what seems to be a long history of self-investigation and concern by the vinyl chloride industry, this week's scheduled hearings in Washington, are expected to spark some clashes. The industry' is deeply concerned about the possible economic impact JUNE 24,1974/CHEMICAL ENGINEERING Photo: Anatola J, Slpln Co. NEWS FEATURES. . . R&S 004469 of a "no detectable level" being es tablished immediately. In an effort to assess what the costs might be. the Soc. of the Plastics Indusuy, which is expected to partici pate in the hearings, has hired Ar thur D. Little. Inc., the Cambridge, Mass., consulting firm, to prepare an economic impact survey. Even the unions concur that eco nomic hardships for workers could result from the proposed standard. However, as Anthony Mazzocchi, legislative director of the Oil. Chem ical and Atomic Workers Union (which represents about 1,200 VCM/PVC workers) notes, "The men at Niagara Falls {where Good year has a plant] are caught. They're in a dilemma. What's their option? Work and eat today so they can die 20 years from now?" (Goodrich says the morale of its workers is goodmen are still applying for jobs on its vinyl chloride line.) What's Being Done--Simply stated, there are two major areas of concern in a VCM plant--ambient air containing vinyl chloride mono mer particles, and the need to peri odically enter the reactor vessels for cleaning. Research has indicated that the workers'who clean the polymer ization reactors by scraping arc ex posed to VCM concentrations of 600 to 1,000 ppm at hand level. One monitoring device being looked at with interest is a personal sampling pump, manufactured by Anatole J. Sipin Co. (Although areamonitoring instruments have the ad vantage of immediate detection, they may not measure exact working con ditions.) The Sipin device contin uously draws an air sample from a worker's breathing zone through a sorbent tube over an 8-hr working an April of the organic materials breathed by a worker. The personal sample pump was looked at with in terest by some Cincinnati-based NIOSH personnel at a meeting on monitoring for VCM, held in Hous ton. As for reactor cleaning, GAF Corp. has developed a system whereby a solvent, trademarked M-Pyrol (n-methyl-2-pyrrolidone), is pumped through the heating unit and sprayed into the reactor to be cleaned. When about one-quarter full, the reactor is shut off and the 112 solvent recirculated. The heavy spray of hot solvent absorbs the vinyl chlo ride monomer and, at the same time, dissolves the PVC residue. Although PVC itself is considered an.unusually inert material, residual monomer can be entrapped within the pores of the polymer. Up to now, the industry has not made it a prac tice to strip the residual monomer from the polymer. However, work is now underway to develop the re quired technology. Experts say that the residual monomer could be dropped by dilution with compound ing agents and by the mixing action during such compounding. Goodrich, for one. is already ex ploring possible approaches to re moving the residual monomer, and plans to set up a pilot operation soon.--JMN New Catalyst Lowers Polypropylene Costs Belgium's Solvay has a new cata lyst that It claims can cut up to 20% off the capital cost of a poly propylene polymerization plant. For 20 years, the U.S.'s Hercules and Italy's Montecatini have been battling over patent rights on cata lysts used to make polypropylene. But that contest may now be aca demic: Hercules has just purchased a license from Solvay, and other big polypropylene producers are likely to follow suit. What Solvay has apparently done is develop a catalyst that is 4-5 times more active than previous choices and yields a product with only 15-20 ppm of titanium catalyst residue. Thus, the expensive alcohol washing and purification steps that have been required to lower the titanium con tent below 100 ppm are not required. The Old Way--The standard poly propylene catalyst now on the mar ket uses trichlorinated titanium in the form of hexagonal or cubic crys tals. These form tiny nodules or balls that are ball milled to obtain a larger surface for exposure to the mono mer. The problem is that relatively large quantities of the catalyst often find their way into the polymer, harming the polymer's thermal and other physical characteristics. Also, the ball-milling process damages the surface of the catalyst crystals, which in turn affects the shape of the poly mer particles. Researchers have tried to over come the titanium problem by in creasing the catalyst surface area, thus cutting down the amount of cat alyst required and thus the amount of carryover. One approach has been the use of porous nodules, but the problem has been that the percent of useless (atactic) polymer has risen from about 6% to 10%, thus negating the benefit of the increased activity. Solvay's Way--The porous nodule approach was also chosen by Solvay. but with its version the atactic waste is only 4-5%. Solvay's catalyst takes the form of tiny dense spheres that are 20-40 mi crons dia.; monomer seeps inside, breaking them into smaller frag ments that finally measure only about 60 X and are composed of 3-4 crystals each. The surface area thus achieved is up to 200 mVg. vs. only about 4-5 m'^/g conventionally. To make the new catalyst, says the company, a standard trichlorinated titanium product is reduced in an organo-aluminum solution, then a complexing agent is added followed by a dose of quadrichlorated tita nium--the very product that usually leads to atactic polymer. Solvay is building an industrialscale plant to produce the new cata lyst. and is soon to start construction of a 50,000-ton/yr polypropylene plant due onstream by the end of 1975; expansion is planned up to an eventual 100,000 tons/yr. And Her cules has plans for a 100,000-ton/yr polypropylene plant in Belgium. JUNE 24,1974/CHEMICAL ENGINEERING