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subject le echo >e radar mrse of collision m 2 to nultane:t) gives n course ;ar that nite and bly the lowever, zone of ny with tributed istic of :xcessive jrrupted .se with datively atly rethat the can be to two ad work ts). in from ed when s small, uli were 30 min 1 hand),' 'ere not ing the %-35%. results, ) at the uence of tributed ti triad. is by no led mamost as .onstant i makes t in the istances idi lions highly tli will ; where : action Vinyl, polyvinyl chloride it must be expected that vigilance will decline fairly soon. PREVENTIVE MEASURES The decline of vigilance may thus be caused by fatigue (due to overwork, an over-long working day, a working environment not adapted to physiological needs, or lack of training on the part of the worker); or, and this is a more frequent cause, by monotony of work. The following are methods of countering this decline: (a) anticipating fatigue by all possible means; (b) ensuring that the intervals between stimuli are not excessively long and that the stimuli attain a minimum level; (c) not giving a worker tasks which are too simple or devoid of interest; (d) stimulating motivation; () ensuring that the work is not carried out in an arid environment; (/) leaving the worker a free choice as to his rhythm of work. MACWORTH, N. H. (1950). Researches on the measurement of human performance. Special Report Series No. 268. Medical Research Council, London. DEESE, J. (1955). Some problems in the theory of vigilance. Psychological Review, 62, 359. BROADBENT, D. E. (1957). The vigilant man and the active man. Symposium on Vigilance. The advancement of science, 339. BAKER, C. H. (1963). Further towards a theory of vigilance. In: BUCKNER', D. N.; McGRATH, J.J. Vigilance. A Symposium. McGraw-Hill, New York, San Francisco, Toronto, London. SCHMIDTKE, H.; MICKO, H. G (1964). Unlersuchungen Uber die Reaktionsieit bei Dauerbeobachlung. Westdeutscher Verlag, KOIn, Opladen. SCHMIDTKE, H. (1965). Die ErmOdung. Huber, Bern, Stuttgart. MOODY, J. A.; DUGGAR, B. C. (1966). .Alertness manage ment in industry. American Industrial Hygiene Association Journal, 27, 17. SCHMIDTKE, H. Germany {Fed. Rep.). Vinyl, polyvinyl chloride Dahm Vinyl ehloride (CH>:CHC1) CHLOROETRYLENB m.p. 160 *C b.p. 13.9 *C v.pr. 760 mmHg (13.8 *C) v.d. 2.15 f.p. -78 *C (open cup) slightly soluble in water; soluble in ethyl alcohol; very soluble in ethyl ether flammable limits 4-21.7% TLV ACG1H (ceiling) 500 ppm, 1 300 mg/m1 MAC USSR 30 mg/m1 a colourless gas with a mild, sweetish odour. The monomer, vinylchloride, can be produced by adding hydrogen chloride to acetylene (CH;CH + HC1 -CH:CHC1) which is passed over a catalyst of activated charcoal impregnated with 10% mercuric chloride, or by the dehydrochlorination of 1,2 dichloroethane.. It is used mainly as an intermediate in the manufacture of plastics, as a refrigerant and in organic syntheses. HAZARDS AND THEIR PREVENTION The inhalation of a 2.5% concentration of vinyl chloride may cause dizziness, disorientation, a burning sensation in the soles of the feet, followed by a headache, lasting about 30 min. These symptoms will disappear after removal from the exposure. The symptoms of workers exposed to concentrations ranging from 0.04 to 1.1 mg/1 included headaches, neurotic disturbances, disturbances such as hyperhidrosis, dermatographia, light anaemia and possibly leucopenia. Sometimes paraesthesia was determined in the distal parts of limbs, occasional whitening of the palms of the hands, and a decrease of surface sensitivity. Although the gas does not possess adequate warning properties, such as odour or irritant action, dizziness and disorientation should be considered as warnings of excessive atmospheric contamination. Extremely high concentrations will generally cause almost immediate helplessness and unconsciousness. During the mixing of gases for the production of vinyl chloride, the environment may be contaminated by metallic mercury, which is reduced from the mercuric chloride in the catalyst and deposited on the walls of the reactor. Sufficient ventilation is important during the production of vinyl chloride. Workers entering the reactors must comply with appropriate protective regulations. Polyvinyl ehloride H HH H H pvc sp.gr. 1.41 MAC USSR (dust) 6 mg/m1 -- G--G-- C-- G--O-- I II I I h a h ci h a while thermoplastic sub stance with good mechanical and electrical properties and a high resistance to chemicals. It can withstand temperatures of of 65-80 *C very well, but if heated to approximately 160 "C, it disintegrates with the release of hydrogen chloride. The properties of PVC can be altered according to the additives used and the desired molecular weighL Production. PVC is produced by the polymerisation of vinyl chloride in the presence of initiators such as 0.1-0.5% benzoyl peroxide. Polymerisation is carried out continuously or intermittently in rotating autoclaves. The properties of commercial PVC products can be modified by the addition of stabilisers, plasticisers, filling agents and pigments, as well as by copolymerisation with other monomers. Uses. If rolled into sheets, the plasticised PVC may be used as imitation leather or as a floor covering. It may also be moulded into electric insulators, water pipes, handies and various consumer goods. Further chlorination of PVC in a tetrachloroethane medium forms a product which is precipitated by the addition of an equal volume of methyl alcohol. After drying, a powder is obtained which is used in the manufacture of films or synthetic fibres. After immersion in acetone and carbon disulphide, it may be spun and used as a textile yam. HAZARDS AND THEIR PREVENTION PVC is odourless and hygienically faultless. During polymerisation, however, an explosion hazard may exist and inhalation of vinyl chloride may also be a health hazard. Dust could be a problem for employees filling sacks with the dried polymer. Dioctylphtbalate, the most important plasticiser, may escape into the air of the workroom in which the PVC is processed. This appears as a fog which consists of particles smaller than 5 pm. The dioctylphthalate content in the air of a PVC processing plant, measured at the point where the material left the machine, was 5.fe mg/m1 where the PVC was plasticised with up to 20% phthalate and 0.24 mg/m1 in the case of rigid PVC to which only up to 1.5% phthalate was .added. An exposure to phthalate concentrations of approximately 5 mg/m1 caused an 1467 BFG36097 t$668^Z Vlnylldene, polyvinylidene chloride irritation ot the upper respiratory passages, while an exposure to approximately 40 mg/m at an air temperature of 30 *C, caused considerable irritation of the upper respiratory tract, of the conjunctivae and lacrimation. The formation of acne (chloracne) on the face and forearms of workers handling PVC products, has been reported; this was caused by the chloronaphthalene used as a mould release compound. Two cases of skin damage have been reported among persons working with PVC. From the results of skin tests it was assumed that complex toxic and allergenic mechanisms may be responsible for this. Thus, the emulsifier, with its strong degreasing properties, or the solvents may cause not only an irritation of the skin, but further sensitisation to PVC which is generally not considered to be a sensitiser. Acro-osteolysis and disorders resembling Raynaud's phenomenon have been reported in workers employed on PVC polymerisation. Spinning entails exposure to acetone and carbon disulphide possibly leading to nervous and digestive disorders and an irritation of the mucous membranes. Owing to the explosive hazard during polymerisa tion, the tanks should be guarded by wire netting. It is also advisable to install remote controls and to provide an alarm system in the plant to detect any leakage ot vinyl chloride into the workroom air. The employees filling sacks with the dried polymer should wear respiratory protective equipment. SONNECK, H. J. (1962). Benifsbedingte HauUchadcn dutch Polyvinytchlorid. Berufsdermatosen, 10, 38. WALLS, W. L. (1964). Vinyl chloridt expiation. NFPA S7-13. National Fire Protection Association, Boston, Massachusetts. ZDRA2IL, J.; PlCHA, F. (1965). Estery kyseliny flalove v ovzduii pH zpracovini polyvinylchloridu. Pracovni Ukafslvl, 17, 257. SUCIU, I.; DREJMAN, I.; VALASKAI, M. (1967). Elude des maladies dues au chlorure de vinyle. Mcdicina del Lavoro, 58,261. CORNISH, H. H.; ABAR, E. L. (1969). Toxicity of pyrolysis products of vinyl plastics. Archives of Environ mental Health, 19, 15. VIOLA, P. L. (1970). Pathology of vinyl chloride. Medieina del Lavoro, 61, 174. ROUBAL. J. Czechoslovakia. Vinylidene, polyvinvlidene chloride Daht, Dubz Vlnylldene chloride (CH,:CCI,) l, 1-D1CH LOROETHYLEKE sp.gr. 1.22 m. p. -122.1 *C b.p. 32 *C v.pr. 591 mmHg (25 *C) v.d. 3.3 f.p. 15 *C (open cup) explosive limits 7-16% MAC USSR 50 mg/m-* a colourless liquid with a chloroform-like odour. It is prepared by the chlorination of ethane, or by additional chlorination of vinyl chloride, followed by thermal dehydrochlorination. CHiiCHCl + a, -+ CHsClCHCls -* CH,:CC1, + HC1 Its main use is as a chemical intermediate in the production ot vinylidene polymer plastics. HAZARDS AND THEIR PREVENTION It pure vinylidene chloride is kept between -40 *C and +25 *C in the presence of air or oxygen, a violently explosive peroxide compound of undertermined struc ture is formed, which can detonate from slight mecha nical stimuli or from heat. The vapours are moderately irritating to the eyes and exposures to high concentrations may cause effects similar to drunkenness, which may progress to uncon sciousness. The liquid is an irritant to the skin which may be in part due to the phenolic inhibitor, added to prevent uncontrolled polymerisation and explosion. White mice died after exposure to concentrations of 5-10 mg/1. A concentration of 8 mg/1 caused irritation of the mucosa and death from respiratory failure within 24 h. In rabbits, an exposure of 0.2 to 2 mg/1 slowed down the conditioned reflexes within 40 min. Chronic exposures to concentrations from 0.5-2 mg/I for 3 h daily, for 4 months, did not show any clear effects, but post mortem changes included bronchitis, slight dystrophic changes in the liver, swelling of the epithelium of the convoluted renal tubules, and an increase in spleen follicles. If the ear was immersed in liquid vinylidine chloride for 1 min, an inflammation resulted. Owing to its explosive nature, this compound must not be bandied or stored in the presence of oxygen or air. Treatment. Removal from exposure of high vapour concentrations will usually ensure complete recovery from the anaesthetic effect. Spilled liquid should be washed off the skin and contaminated clothing removed immediately and thoroughly cleaned before re-use. Polyvinylidene chloride H a H Cl H Cl a white thermoplastic substance which it tasteless, odourless, and non-toxic. LLLLU HMa HINCI H ICl It is made by the poly merisation of vinylidine chloride with peroxides or other free-radical catalysts. Suspen sion, emulsion and solution processes are used. The high temperature of softening (110-200 *C) and the relatively low temperature of disintegration (above 225 *C) make processing difficult. By copolymerisation with a compound such as vinyl chloride (usually 10 %), the chemical properties can be improved and the temperature ot processing lowered. Polyvinylidene chloride and its copolymers are made into boards, packagingfllm, pipes and mouldings. In an emulsion it is used for impregnation as a paint for paper, fabric, leather, etc. Since fabrics produced from polyvinylidene synthetic fibres are extremely strong and chemically stable, they are also used in the production ot upholstery or as filtration materials in chemical industries. ROUBAL, J. Czechoslovakia. Vinyls, polyvinyls Dubj Vinyls are chemical intermediates and are used primarily as monomers in the manufacture of plastics. Many of them can be prepared by the. addition of the appropriate compound to acetylene. Examples of vinyl monomers include vinyl chloride, vinyl fluoride, vinyl acetate, vinyl ethers and vinyl esters. Polymers are high molecular-weight products formed by poly merisation which can be defined as a process involving the combination of similar monomers to produce another compound containing the same elements in the same proportions, but with a higher molecular weight and different physical characteristics. Vinyl and polyvinyl ehloride See separate article. Vlnylldene and polyvinylidene chloride See separate article. 1468 2489: BFG36098