Rubber Production

RUBBER PRODUCTION. Rubber is a technical product obtained by special processing of rubber with sulfur. Besides rubber, which is the main raw material, and sulfur, the following are used: 1) reclaim, a product from processing old rubber products; 2) vulcanization accelerators—inorganic (lead compounds) and organic—thiuram (tetramethyl-thiuram-disulfite), which proved to be a strong poison in animal experiments, diphenyl-guanidine, a convulsant poison (animal experiments), mercaptax, which has a bitter taste. Liquid accelerators, products of condensation of aniline and its derivatives with a series of aldehydes (oleic, acetic, etc.), are used less frequently; 3) active fillers: gas black, zinc oxide, kaolin, etc.; 4) pigments: antimony sulfide, vermilion, ultramarine, chromium oxide, etc.; 5) inert ingredients: chalk, barite, infusorial earth, lithopone, etc.; 6) softeners: factis, resins, rosin, various oils, etc. Main productions: a) footwear or galosh production, b) tire production (auto and bicycle tires and tubes), c) industrial equipment, d) asbestos production, and e) auxiliary productions (cord, reclaim, black, etc.). As of January 1, 1933, 56,902 workers and employees were employed in the rubber industry. The factories are concentrated in Moscow, Leningrad, and Yaroslavl. Main facilities in Moscow: the 'Krasny Bogatyr' factory, footwear production—9,108 workers; 'Kauchuk', industrial equipment—4,056 workers; in Leningrad—the group of 'Krasny Treugolnik' factories: footwear factory—19,758 workers; tire factory—4,465 workers; industrial equipment factory—6,242 workers; asbestos factory—1,438 workers, etc.; in Yaroslavl—the Rubber-Asbestos Combine, in its start-up period, a world giant built according to the latest technical specifications, including a tire factory (the largest in Europe), an asbestos factory, a reclaim factory, a cord factory, a winding factory, a sole factory, etc. There is also a small factory for seamless products—the 'Krasny Rezinshchik' in Kiev (621 workers). The production processes for almost all products proceed according to the following scheme: a) preliminary processing and weighing of rubber, sulfur, and other ingredients of the rubber mixture, b) mixing rubber with sulfur and other ingredients, c) preparation of parts, d) cementing or molding of the product, e) varnishing (only for some products), f) vulcanization, i.e., processing of products for a certain time at a temperature of 135-140°, as a result of which the interaction of rubber with sulfur occurs; this method is called hot vulcanization. Cold vulcanization (immersion of products in a solution of sulfur monochloride in gasoline or carbon disulfide) is also used, but due to its toxicity and fire hazard, this method has not been widely adopted in the Soviet rubber industry in recent years, g) finishing operations: removal of products from the mold, sorting, rejection, etc.—Preliminary processing of the components of the rubber mixture. In workshops for washing and drying rubber, which has the shape of cakes or bales weighing up to 100 kg, it is crushed into small pieces, which are steamed in vats with water at 50-60°, washed on fluted, and then smooth rolls, dried, and then weighed into separate portions according to the assignment. Rubber crushing is done by cutting it on special cutting machines—'guillotine', where the knife acts hydraulically, on band disc knives, with hand saws and by tearing and cutting by hand.--Sanitary features: 1) unfavorable meteorological conditions during rubber washing (temperature 24-25° with relative humidity 40-50%) and during its drying (temperature 30-35° with relative humidity 35-40%) and poor lighting; 2) significant physical stress, 3) contact of workers' hands with cold (washing rolls) and hot water (steaming rubber) and frequent wetting of feet, and 4) forced standing position with forward tilt of the body and danger of injury when hands get between rolls during washing and from cutting tools when cutting rubber. In chalk workshops, crushing, drying, sifting, and weighing of the components of the rubber mixture are carried out. In the largest quantities, chalk, kaolin, black, sulfur, lime, etc. are processed. Until last year, lead litharge, lead white were used in large quantities, which are now generally not used. The production processes are not mechanized and not sealed, as a result of which large amounts of dust, mostly indifferent, enter the air of the work premises. Dustiness ranges from 15-16 mg/m³ (neutral zone) to 100 mg/m³ near dust-generating units; most often dustiness is around 35-50 mg/m³. Near drying boilers, temperature is elevated (25-30° with relative humidity 30-50%). Sifters work on their feet with almost continuous movement and carrying of significant weights. For weighers, dustiness is 5-6 mg/m³; carrying of weights and contamination with dust is also less. The main occupational hazards of weighers are: 1) close contact and inhalation in small amounts (0.1-0.2 mg/m³) of dust from organic accelerators and 2) visual strain during weighing. Faktis—a frequently used ingredient of the rubber mixture—a rubber-like substance obtained by the interaction of vegetable oils (rapeseed, linseed) and sulfur. It is manufactured either in special premises or in varnish workshops. Oil is loaded mechanically or manually by buckets into a steam-heated boiler, and with constant stirring, it is boiled down at a temperature of 120-130°. During this process, gases are released from the oil, containing acrolein (detected in amounts up to 0.05 mg/l). To the boiled-down oil, sulfur is added in a ratio of 1:5; at this time, 'faktis gases' are abundantly released, in which hydrogen sulfide was detected (according to Uspensky's data at the 'Kauchuk' factory in 1925/26 from 0.01 to 0.18 mg/l). Fine faktis dust causes irritation of the skin. The temperature in the workshops is somewhat elevated. Reclaim—a valuable ingredient of the rubber mixture, a product from processing old rubber products, is produced in auxiliary factories ('Provodnik'—in Moscow, 'Krasny Treugolnik'—in Leningrad). Old rubber (galoshes, tires) is sorted under a canopy, cleaned of mechanical impurities, washed in special washing pits, crushed on a chopper machine, passed through a magnetic separator that retains metal parts, and loaded into a tank for pickling. The latter is done with either 15% sulfuric acid or caustic soda with heating; during this process, cotton fabrics from rubber products are hydrolyzed and removed by washing. Then follows devulcanization, i.e., heating the crushed rubber at a temperature of 160-180° and pressure of 8-10 atm for 8-10 hours in special 'devulcanization' boilers, after which the reclaim is rolled on American rolls, then on refining rolls, from which it comes out in the form of a thin sheet 0.1-0.2 li thick, possessing a certain plasticity. Main hazards: 1) contamination and wetting of the face, hands, and clothing, 2) inhalation of dust during sorting, crushing, and passing through the magnet, 3) inhalation of vapors of sulfuric acid and caustic soda during pickling, 4) exposure to radiant heat, elevated temperature of devulcanization gases (presence of H₂S is assumed), 5) danger of injury and burns during devulcanization, and 6) inhalation of specific vapors of heated old rubber when cutting devulcanized rubber and during its calendering. Calendering and mixing. The ingredients of the rubber mixture, accurately weighed according to the formula, are mixed in calendering workshops on rolls or mixers. The purpose of calendering is the uniform distribution of ingredients throughout the entire mass of rubber and giving it plasticity. During calendering, in addition to significant physical stress, the following should be noted: a) unfavorable meteorological conditions (high temperature, especially in summer, reaching 28-30° with significant relative humidity 60-70% and low air movement speed), b) contamination of the air with dust from ingredients mixed with rubber (dustiness of 10-20 mg/m³, sometimes poisonous), and c) danger of serious injury when hands get into the gap between rolls. Hygienically more rational is mixing in closed mixers (of the 'Banbury' type): dusting is less here and there is no danger of serious injury. Rolls of calendered rubber go to calenders, where they are passed between one pair of rolls, then between a second pair with a smaller gap, etc., until a sheet of the required thickness is obtained. For calender operators, in general, the same unfavorable sanitary conditions are typical as for calender operators. Preparation of glue and rubberized fabrics. For gluing products and manufacturing rubberized fabrics, glue—a solution of rubber mixture in gasoline with a consistency of 40% to 80%—is used. It is manufactured in 'glue-mixing' workshops in special mixers, during loading and unloading of which large amounts of gasoline vapors (from 2 to 5 mg/l) enter the air. For glue-mixers, in addition, the following is characteristic: 1) standing position, 2) significant physical stress.—Rubberized fabrics are manufactured in rubberizing or gumming shops on spreading machines (tables with plates heated by steam to 80-100°).

In front of the plate is placed a roll of fabric, which as it passes through the system of rollers, has a layer of rubber glue applied to it by a special knife; the fabric then passes over a hot plate and dries from the heat, i.e., the benzine contained in the glue is released, and at the other end of the spreading machine the fabric is wound onto a rotating reel. The air from the hot plate heats up and even in winter the temperature in the workshops reaches 20-25° with a humidity of 25-30% (in summer the temperature rises to 30° and higher with an increase in relative humidity to 50-60%). The concentration of benzine in the air sometimes reaches 10 and more mg/l; the usual concentration is 4-6 mg/l. From the friction of the fabric against the iron plate, static electricity charges are formed, which at a certain voltage produce sparks, from which the benzine vapors over the plate and the fabric itself can ignite. Frequent flashes, especially in winter, are typical for the spreading workshops. Assembly and gluing. In the manufacture of small items, gluers prepare the blanks, i.e., trim rubber parts, glue the product with rubber glue, and send it for vulcanization. In mass production (galoshes, tires), the blank is separated. Trimming of rubber and textile parts is done both manually with a knife according to a template and on cutting machines (band knives, stamping presses, diagonal cutting machines, etc.). These works are characterized by: 1) strain on attention and vision; 2) work standing with a forward tilt of the body and curvature to the right; 3) danger of cuts and 4) inhalation of talc dust, with which the parts are dusted, and textile dust when cutting textile parts. Trimmed parts before assembly are coated with glue in the places that are to be glued. In galosh production this is done in coating workshops. Drying is also done here in drying cabinets (50°). The temperature in the workshop is somewhat elevated (20-22°) from the drying cabinets, which also contributes to the evaporation of benzine from the glue (concentration of benzine in the air-2-4 mg/l). In addition, coaters get their hands dirty with gasoline glue. Assembly of products is done by gluers, who constitute the most numerous profession. In the assembly of galoshes and small items (vikkel, canning rings, toys, medical items, etc.), women are employed almost exclusively, as this does not require significant physical exertion. The assembly of galoshes is currently done on conveyors that transfer a last (aluminum or cast iron) from one worker to another, on which the galosh is assembled. On both sides of the conveyor sit 26 workers each; one side assembles the right, the second side assembles the left galosh. The galosh is assembled from 17 parts by placing them on the last in a certain order, and for gluing them, rubber glue is used, placed in open cups in front of the workers. In this profession, with individual gluing, workers were often poisoned by benzine vapors, as a significant part of the coating was concentrated in the galosh workshop, where the concentration of benzine vapors reached 4-5 mg/l; when working on the conveyor, the main hazards are: 1) abundant amount of frequent small movements; 2) noise from the impact of metal lasts and tools, etc.; 3) inhalation of benzine vapors (0.5-1.5 mg/l); 4) irrational working posture, etc. Assembly of automobile tires is done on corresponding forms, which weigh up to 165 and more kilograms. A layer of rubberized fabric is placed on the form, onto which several more layers are glued one on top of another, between which rubber interlayers are placed; on top is glued the "protector" (profiled rubber surface), and on the opposite side the tire ends with "wings" - both made of massive and strong rubber. Assembly is accompanied by lubricating the parts to be glued with glue, from which benzine continuously evaporates, the concentration of which in the air is quite high. The work also requires great physical exertion and is done in irrational forced working positions. A number of products are made on extrusion machines by "molding", which eliminates part of the gluing and the associated evaporation of benzine from the glue. The extrusion machine used for this is built on the principle of a meat grinder, where the loaded rubber is kneaded and extruded through a heated nozzle in the form of a tube of the required diameter and wall thickness. This is how some tubes, laboratory and medical tubes, bicycle chambers, etc., are prepared, and for the chambers, the edges of the tubes are ground on corresponding machines and then glued at the edges. To prevent the tubes from sticking together, they are abundantly dusted with talc, which creates high dustiness at extrusion machines (around 15-30 mg/m³). In addition, extrusion machine operators are in danger of burns from heated parts of the machine, bruises when adjusting it, and severe trauma when the hand gets into the loading hole. The air temperature from the machine is always elevated. When grinding auto and bicycle chambers, a significant amount of rubber dust enters the air of the workshops. Some products (soles, heels, toys, bulbs for enemas) are made by extruding rubber in a mold, in size and profile completely corresponding to the product being made. In the manufacture of seamless products (chirurgical gloves, nipples, condoms, etc.), a large amount of benzine vapors enters the air of the workrooms. Production is carried out by dipping wooden or glass forms into liquid glue with subsequent drying of the product - Varnishing. After assembly, some products (galoshes) are varnished, which is a solution of linseed oil with rosin in a solvent, which is ligroin, less often turpentine. Ligroin is a petroleum distillation product, boiling at 110-200°, and is more toxic than gasoline. Other impurities (lead litharge) are sometimes added to the varnish. When cooking varnish, "oil-boiling" gases enter the air, in which acrolein is assumed to be present. Varnishing is done in varnishing workshops by dipping the galosh with the last into varnish, placed in boxes built into the work table, or on special conveyor machines, followed by even spreading of the varnish over the surface of the galosh with a bare hand. Sometimes varnishing is done with a brush. The main professional hazards of the varnisher: 1) work standing with a forward tilt of the body; 2) significant physical exertion; 3) contamination of hands (up to the elbows) and clothing with varnish and 4) inhalation of toxic vapors of these varnishes (concentration of ligroin varnish vapors in the varnishing workshop of the "Red Bogatyr" plant-1.0-1.5 mg/l). Vulcanization is carried out in vulcanization kettles of various capacities and in vulcanization presses (hot plates, between which the product to be vulcanized is clamped in a mold) at a temperature of 135-140° and a pressure of 2 to 3.5 atmospheres. Vulcanization lasts from 15 minutes to 3 hours and more. In kettles, vulcanization is done by rolling in carts on which the products are placed; at this time the kettle is heated to 80°. Workers serving vulcanization equipment load and unload products, screw the lids of the kettles with bolts, monitor the temperature and pressure during vulcanization and regulate them. When unloading vulcanization equipment, large amounts of "vulcanization gases" enter the workshop air, the composition of which is not exactly known; the presence of sulfur compounds and a number of carbon compounds is assumed. Workers serving vulcanization equipment are subjected to: 1) significant physical exertion; 2) exposure to high temperature and radiant energy; 3) unfavorable meteorological conditions (temperature reaching 25-35° with low humidity); 4) exposure to "vulcanization gases" and 5) danger of burns and bruises from vulcanization equipment and heavy products in molds. Removal of products from molds for small items does not require great physical exertion. For removal of large items (sleeves, automobile tires), which is mostly done manually, significant physical exertion and danger of trauma are typical. In galosh production, preliminary cleaning of lasts from varnish is done by treating them with solvent naphtha, which contains large amounts of aromatic hydrocarbons (benzene and its homologs). Finishing, sorting and rejection. Most rubber products immediately after removal from molds are subjected to sorting and rejection, which are characterized by strain on vision and attention. Some products are also subjected to finishing: turning, grinding, etc., done on lathes. The main professional hazards: 1) strain on vision; 2) contamination of the air with rubber dust (40-60 mg/m³); 3) standing working position with a forward tilt of the body and 4) danger of trauma, etc. Ebonite, or hard rubber (ebonite plates, sticks and tubes, uterine tips, etc.) differs from rubber by a higher sulfur content in the mixtures, reaching 50%, a higher vulcanization temperature (165-170°) and a longer vulcanization time. In equipment in ebonite workshops, vulcanization equipment (kettles and presses), lathes and grinding machines predominate.

These workshops are characterized by the following features: 1) higher temperatures in the workshops, 2) finer and more volatile dust released during turning and grinding (according to Uspensky, at the 'Kaucuk' plant in 1925/26, the dust content ranged from 5 to 125 mg/m³ with particle sizes from 16 to 527 μ), and 3) higher sulfur compound content in vulcanization gases. Occupational hazards. 1. Unfavorable meteorological conditions (vulcanization workshops, cutting workshops, calendering workshops, etc.). 2. Dust. The highest concentration of inorganic dust is observed in chalk workshops, at injection molding machines, and at mixing calenders; organic dust - at lathes and grinding machines for rubber and ebonite, and at rag calenders; talc dust - in many assembly and cutting workshops when rubber is dusted. The dust is mainly neutral (chalk, talc, kaolin, etc.), so one can expect non-mechanical irritation of the respiratory tract and pathological phenomena of the stomach when swallowed. Previously, and now very rarely, lead vulcanization accelerators were used, with which acute and chronic lead poisoning were recorded. Currently, instead of lead compounds, organic accelerators are used; some of them have a poisonous effect on animals. In the coming years, the use of other organic compounds containing aniline and its derivatives is planned. Unlike lead compounds, organic accelerators are used in small quantities. Carbon black also deserves attention, which has been increasingly used in plants in recent years. 3. Gases. a) Gasoline, in terms of the number of workers exposed to it, should be ranked first among production hazards. In cutting, coating, and some assembly workshops, the concentration of gasoline vapors is almost 10 times higher than the maximum allowable limit - 0.5 mg/l. Therefore, there is always a danger of acute poisoning and chronic poisoning phenomena among these groups of workers. In 1914, a series of mass acute poisonings were recorded at the 'Triangle' plant in St. Petersburg and the 'Conductor' plant in Riga. Individual cases of acute poisoning have also been observed in recent years. Clinic and prevention of gasoline poisoning - see Gasoline - gasoline from the point of view of occupational hygiene; treatment of acute poisoning - see Poisoning. b) Ligroin, a heavy petroleum fraction, pollutes the air during varnish manufacturing and varnishing of galoshes. It is significantly more poisonous than gasoline. According to Geronimus and Gladyshevskaya (All-Union Institute of Health Improvement and Labor Organization), a concentration of 40 mg/l causes almost 100% mortality in white mice (gasoline 'Galosh' causes such toxic action at 70-80 mg/l). An examination of varnishers at the 'Red Bogatyr' plant by Vishnevskaya, Safonov, and Khozak (All-Union Institute of Health Improvement and Labor Organization) showed the presence of polyneuritis with predominant damage to sensitivity and vegetative apparatus caused by ligroin varnish. There is no developed symptomatology of poisoning with ligroin vapors. The course of acute and chronic poisonings has much in common with those of other petroleum distillation products, in particular gasoline, which is lighter than ligroin, and kerosene, which is heavier than it. c) Turpentine is also used for dissolving varnish. In recent years, it has been displaced from production by ligroin. It causes skin and mucous membrane irritation, kidney damage, etc., in workers. d) Oil-boiling, varnish-boiling, and factis gases, to which varnish-boilers and factis workers are exposed. During oil boiling, a series of aldehydes is formed, among which the presence of acrolein, a strong irritant of mucous membranes, is assumed; during factis boiling - hydrogen sulfide, causing strong irritation of the respiratory tract and lungs. Chronic phenomena are reduced to headaches, anemia, digestive disorders, etc. e) Vulcanization gases are released when unloading products from vulcanization units. They contain sulfur compounds (H₂S and SO₂ are assumed) and carbon compounds (CO is assumed). In experiments on white mice, they had an irritating effect on mucous membranes, excitement, and narcosis. -595

Rubber production. Similar in composition and properties are devulcanization gases released during the regeneration of old rubber. 4. Muscle strain: a) general physical strain when lifting and moving heavy loads (assemblers and removers of tires, spiral sleeves, etc., vulcanizers, calenderers, etc.), b) forced body position during work (for rubber and ebonite turners, grinders, cutters, etc.), c) monotonous tiring frequent small movements (for galosh makers, varnishers, assemblers of small items, etc.). 5. In a number of professions, workers are exposed to noise and floor vibration. 6. Traumatism quite vividly reflects the specific features of rubber production. The number of accidents is relatively small and has noticeably decreased in recent years (according to the Bureau of Safety Engineering of the Rubber Association in 1932, 37 cases were registered per 1 million man-hours). The severity of accidents, calculated in terms of the number of days of incapacity per case, is also not high (8-9 days per case). The distribution of accidents by material causes shows that about half falls on manual work, manual movement of heavy loads, and transport vehicles, and about one third on executive mechanisms. The most frequent and severe traumatism is observed in the professions of calenderers, calandermen, assemblers of heavy products, removers of products from heavy molds, vulcanizers, cutters, etc.

* Morbidity. The overall level of morbidity is comparatively low. Thus, according to morbidity data published by the Moscow Regional Social Insurance Fund, the number of cases of disability per 100 insured persons for 1928 amounted to 163.4, and the number of days of disability amounted to 1,584.8. The distribution of disability cases by classes and forms of disease reveals certain specific characteristics of rubber production. Thus, the indicators for diseases of the nervous system are somewhat elevated, amounting to 7.9 cases and 116.4 days of disability per 100 insured persons in the rubber industry. Among diseases of the nervous system, hysteria and "neurasthenia" stand out, amounting to 2.7 cases per 100 insured persons in the rubber industry. The increased morbidity in the class of nervous diseases and especially functional neuroses can be linked to the effect of gasoline vapors, mentioned above, and to a number of other factors. This is confirmed by the fact that in those productions (such as the production of industrial equipment at the "Kaucuk" plant), where the concentration of gasoline vapors is comparatively low, the corresponding indicators are lower and amounted in 1931 (according to statistical materials of the All-Union Institute for Health Improvement and Labor Organization) to 6.1 cases for nervous diseases, and for hysteria and neurasthenia only 0.8 cases per 100 insured persons. Materials from a selective medical examination of workers at the same plant conducted in 1932 by the All-Union Institute for Health Improvement and Labor Organization showed an increased number of functional neuroses among workers in the calendering shop, where there are rather high concentrations of gasoline vapors in the air (see above). The aforementioned morbidity data (for 1928) also note some increase in indicators for the class of diseases of the circulatory system, which can be linked to significant physical strain and other factors, and for the class of diseases of the digestive system, which can be explained by the swallowing of dust, the influence of unfavorable meteorological conditions, etc. The results of a detailed examination of the health status of workers at the "Krasny Bogatyr" and "Kaucuk" plants, conducted in 1924-1925 (Tikhomirov, Kresin and others), do not contradict the data of general morbidity statistics. In terms of pathological notes (6.15 at the "Krasny Bogatyr" plant and 5.5 at the "Kaucuk" plant), Rubber Production occupies one of the leading positions. For individual diseases, pathological involvement revealed the same tendency: increased involvement of the nervous system, organs of vision (conjunctivitis), organs of circulation, respiration and digestion, which in most cases is associated with unfavorable working conditions for rubber workers. In addition, phenomena of clinical anemia with hemoglobin content of 60-70% were revealed (see Benzin - gasoline from the point of view of occupational hygiene). Measures to improve working conditions. Since the main cause of the sanitary unsatisfactory condition of production is the artisanal organization of the production process, poor sealing and mechanization, the radical resolution of a number of hygiene problems must go along the path of reconstruction of production and change in the technological process. The fight against dustiness in chalk workshops, heavy physical strain and associated trauma and morbidity is possible only through mechanization and sealing of production processes with the use of continuous-action equipment, pneumatic transport and sieving, automatic weighing, etc. Palliative measures are: a) artificial ventilation with local dust extraction, b) rational special clothing, c) use of mechanical transport, d) installation of showers, etc. In calenders, health measures should go in the direction of maximum introduction of closed-type mixers, in equipping calenders and calenders with protective devices, in setting up a rational ventilation system, ensuring sufficient cubic capacity of work premises, etc. To combat the danger of poisoning from gasoline, the most radical measures are: a) transition to the production of products by molding, which is currently technically difficult to implement, b) replacement of gasoline glue with aqueous dispersions of rubber, which has already been resolved in the laboratory and will probably be implemented practically in the near future. In addition: a) since gasoline is a mixture of hydrocarbons and other compounds with varying physico-chemical and toxic properties, the fight against it should be directed toward finding the least toxic gasoline, i.e., its hygienic standardization; b) great preventive importance has not only the chemical but also the toxicological analysis of gasolines entering production; this has been practiced in recent years at the "Krasny Bogatyr" plant for gasolines suspected of toxicity; c) great importance is attached to rational supply-exhaust ventilation. Thus, at the "Krasny Treugolnik" plant (1926-29) when the ventilation installations were not operating, the concentration of gasoline in the galosh-assembly shop was 1.1-3.6 mg/l, in the "macintosh-glue" workshop - 2.6-5.8 mg/l, and when they were operating respectively - 0.46-0.84 mg/l and 1.12-1.25 mg/l; d) great importance also has rational organization of labor. Thus, at the "Krasny Bogatyr" plant with the transition from individual assembly of galoshes to conveyor assembly and the allocation of gluing operations in a separate room, the concentration of gasoline decreased from 5-7 mg/l to 0.5-1.0 mg/l. Improvement of working conditions when varnishing galoshes with ligroin varnish is possible through mechanization and sealing of the production process. Palliative measures: varnishing with a brush and rational ventilation. Along the path of sealing the production process and installing ventilation, improvement of labor in oil-boiling, varnish-boiling, factice and vulcanization workshops should proceed. To combat muscular strain and trauma when carrying heavy loads and manual work, it is necessary to mechanize intra-factory transport, introduce mechanical lifting structures, etc. Rational organization of labor (rationalization of the workplace, lighting, etc.), use of professional selection for a number of professions can also significantly improve the working conditions of rubber workers. Sanitary peculiarities of rubber production due to the use of synthetic rubber. - In the second five-year plan, the rubber industry began to master synthetic rubber, i.e., to replace natural rubber, obtained from the milky sap of tropical plants and being an imported product, with synthetic (artificial) rubber, made from alcohol (by the method of Academician Lebedev) and being a Soviet product. According to the plan for the second five-year period, consumption of synthetic rubber by rubber plants should amount in 1937 to about 90% of all rubber consumed by the rubber industry. Synthetic rubber has a number of features distinguishing it from natural rubber, due to which working conditions also acquire certain characteristic features. These features of synthetic rubber basically come down to the following. 1. Presence in it of easily volatile substances, the exact composition of which has not yet been studied in detail. They represent a mixture of various unsaturated hydrocarbons, mostly consisting of pseudobutylene, formula CH₃-CH=CH-CH₃, boiling at a temperature of 4-10° with an admixture of butadiene 1,3, formula CH₂=CH-CH=CH₂, boiling at a temperature of -4°, and other unsaturated hydrocarbons with higher molecular weight. Besides hydrocarbons, diethyl ether and some other substances may be present in this mixture. This mixture has a sharp and unpleasant odor. There are no exact data for judging the toxic effect of these gases. Observations made in plants producing synthetic rubber, as well as existing literature data on the effect of unsaturated hydrocarbons, give reason to assume that inhalation of this mixture of gases is not indifferent to health. An irritating effect on the mucous membranes (conjunctivitis, laryngitis, bronchitis, etc.), an adverse effect on the nervous system and possibly on the blood can be expected. Workers engaged in cutting rubber and in calendering shops are most exposed to these gases, to a lesser extent - workers in cutting and assembly shops, etc. 2. Presence of residues of metallic sodium in synthetic rubber. This can lead to ignition of gases present in synthetic rubber when moisture comes into contact with it. Flashes from these causes have been observed when calendering synthetic rubber and when mixing rubber mixture in closed "bembe" mixers. Even with flashes of synthetic rubber, there is a danger of burns to workers. In addition, metallic sodium present in synthetic rubber and caustic soda, formed in it from the oxidation of metallic sodium and the absorption of moisture, can cause burns and ulcers upon contact with the skin.

Ulcers from alkali burns heal slowly even with appropriate treatment and pose a danger of contamination and infection. 3. The need for large quantities of carbon black when using synthetic rubber. This can lead to increased air pollution with carbon black in chalk workshops during transportation and hanging of the carbon black, and in calendering workshops during its mixing with rubber and other ingredients of the rubber mixture. 4. Increased consumption of rubber cement and rubber solvents (gasoline, kerosene, etc.) due to the lower adhesiveness of raw rubber made from synthetic rubber. This can lead to an increase in the concentration of petroleum product vapors in the air, if the power of ventilation systems is not increased simultaneously with the increase in solvent vapors. Measures to improve working conditions when using synthetic rubber mainly come down to the following. 1. Reducing the amount of volatile substances contained in synthetic rubber by processing it in vacuum mixers with gas extraction from it; this measure is already partially carried out in factories producing synthetic rubber. It is advisable to establish laboratory control over the gas content of samples of synthetic rubber entering production in order to prevent samples with an excessive content of volatile substances from entering production. 2. Neutralization of the metallic sodium contained in synthetic rubber by adding naphthenic acids to it or by thoroughly mixing the synthetic rubber in a mixer. When working with synthetic rubber containing metallic sodium, the use of gloves is necessary. 3. Mechanization of operations with carbon black or the use of briquettes made from carbon black, "carbon black mother", etc. 4. Reconstruction of ventilation systems in the direction of increasing their power and rational arrangement of air ducts, ensuring the most complete removal of gases from workplaces. This mainly applies to calendering and assembly workshops. 5. Implementation of a number of fire prevention measures during storage, transportation, and processing of synthetic rubber.