Pub Health 4310 Health Hazards in Industry

1. Pub Health 4310Health Hazards in Industry John Flores Lecture 19 Chemical Based Products

2. Lecture 19:Chemical Based Products • Chapters 16-21 • Chemical Based Products • Chemical Processing • Petroleum Refineries • Rubber Products • Acids, Ammonia, and Chlorine • Paint Manufacture • Plastic Products PH 4310 - Health Hazards in Industry, Lct 19

3. Chem Based Products – Rubber Products • Introduction: • Natural rubber and synthetic rubber polymers are used to make all kinds of industrial products like tires, belting, hoses, footwear, rainwear, and chemically protective clothes including gloves, aprons, and respirator facepieces • Rubber products are made with coating techniques, extrusion, calendaring, and compression molding • Rubber workers in the US number around 200,000 in about 1500 plants • A number of epidemiological studies completed on this industry have found: • Excess colon, prostate, and pancreatic cancers in rubber workers, • Excess stomach cancer in compounding workers, • Excess lung cancer in curing operators, • Leukemia in tire builders, • Excess deaths from bladder cancer, • A higher rate of leukemia in white workers • Other cancers including esophageal, biliary and liver cancer, lymphoma, and multiple myeloma, and • Increased respiratory morbidity and pulmonary function decrement in tire plant processing workers PH 4310 - Health Hazards in Industry, Lct 19

4. Chem Based Products – Rubber Products • Materials • More than 3 million metric tons of natural or synthetic rubber are used annually to make rubber products • Natural rubber is harvested from tropical rubber tree by collecting the milk-like serum (latex) from the inner bark of the tree • The natural latex is an aqueous solution containing rubber which must be precipitated out for processing • A preservatives such as ammonia, formaldehyde, or sodium sulfite is added to the precipitated rubber so that the rubber can be baled for shipment • Natural rubber has great plasticity, but limited elasticity, so vulcanizing the rubber reduces its plasticity but increases its elasticity • Vulcanizing is the cross-linking of rubber molecules with sulfur compounds • The vulcanizing conditions (time, temperature, and pressure) and chemical additives, permit the modification of the material for a specific product type • Synthetic rubbers were developed during the past century • Thiokol rubber (polysulfide) was developed in the 1920’s, neoprene (chloroprene) and Buna rubber (styrene butadiene) in the 1930’s • Synthetic rubbers are often blended with natural rubber • Styrene-butadiene makes up half of the rubber manufactured in the US with half of this amount going towards tire manufacturing PH 4310 - Health Hazards in Industry, Lct 19

5. Chem Based Products – Rubber Products • Materials (cont.) • Natural or synthetic rubber products (cont.) • Both synthetic and natural rubbers have limitations for certain operations • Various additive chemicals are added to the rubber to overcome many of these limitations • The addition of chemicals is called “compounding” and it is the point at which many toxic chemicals, many in powder form, become potential exposures • In compounding operations, the first material added is an accelerator, then the plasticizer, reinforcing agents, antioxidant, fillers, and colorants, the material is then mixed and stored as sheet stock and is called “master batch material” • Master batch material is stored until it is ready for processing, which requires that the material go through a warm-up mill, then the vulcanizing agent is added so that the material can be used in the product to be manufactured • Additives • Various rubber processing chemicals are needed in order to fabricate the finished rubber product and to ensure that product has specific characteristics • These additives are usually organic materials and are added in small quantities • Sulfur is the most important vulcanizing agent and is used elementally or in one of many organic forms • Vulcanizing agents can be added to the initial batch or as the rubber is being prepared for final fabrication PH 4310 - Health Hazards in Industry, Lct 19

6. Chem Based Products – Rubber Products • Materials (cont.) • Additives (cont.) • Accelerators are used to hasten the vulcanizing process • Inorganic lead or aniline compounds were the first accelerators used in this industry, now the principle accelerators used are a series of organic thiazole compounds • Activators are used to give the rubber batch certain properties • Common activators are zinc oxide, fatty acids, litharge, magnesium oxide, amines, and amine soaps • Stabilizers are used to protect the polymer during extended storage before its end use • Antioxidants are added to protect the finished product, important antioxidants used are arylamines and phenols • An antioxidant containing 0.25% B-naphthylamine as a contaminant was identified as the agent causing bladder cancer in rubber workers in England in the 1950’s • This material was banned and excess bladder cancers are no longer seen in the UK rubber worker population • Antiozonants are added to protect against environments with high ozone levels, such as in LA • Organic lubricants can be added to the rubber to increase its viscosity and workability • Lubricants include coal tar, petroleum oils, ester plasticizers, liquid rubbers, fats, oils, and synthetic resins • The final additives are the pigments which are principally used to give the rubber color but can also add reinforcement, filler, or extender for the finished product • Common pigments are carbon black, zinc oxide, clay, and silicates PH 4310 - Health Hazards in Industry, Lct 19

7. Chem Based Products – Rubber Products • Manufacturing Processes • Compounding and Mixing • Three major raw materials are sent to the mixer, rubber stock, carbon black, and chemical additives • Before the bale of rubber stock can be sent to the mixer, it must be cut into manageable and weighable pieces with a guillotine cutter to match the required weight of rubber for the particular recipe • Since carbon black and most compounds added to the mix are in powder form, the batch mixing can be a very dusty process requiring the weigh stations to be exhausted • If possible, small quantities of chemicals should be prepackaged in plastic for direct placement into the batch to eliminate dust exposures • With the exception of small job shops, carbon black is added to the batch using a closed pipe delivery system which has greatly reduced dust exposures from carbon black • The recipe of mixed components are dumped onto a conveyor and dumped into the mixer • In most rubber manufacturing sites, the mixers used to prepare the master batches are Banbury Mixers • The Banbury Mixer is a high torque, low RPM mixer that shears materials between 2 thick blades and a mixer wall as a ram forces the mixing materials to the mixer blades • The rubber batch is mixed until there is a uniform dispersion of the ingredients • Once the mixing is complete the Banbury mixer charge (product) is dumped onto a drop mill that is located directly under the mixer on a lower floor • The 2-roll mill has rolls 2-3 ft in diameter which rotate in different direction and at different speeds • This process generates considerable heat requiring the rolls to be cooled with water PH 4310 - Health Hazards in Industry, Lct 19

8. Chem Based Products – Rubber Products • Manufacturing Processes (cont.) • Compounding and Mixing (cont.) • When the drop mill processing is complete the rubber is slit and sheeted onto a conveyor • The sheeted rubber stock is then cut into slabs and each slab is dipped into an anti-tack solution to prevent it from sticking together • The anti-tack material is often based from talc, clay, or soapstone • The rubber material now has all of the components of a finished product except the vulcanizing agent, rubber in this form is called “master batch” • Exposure Hazards associated with compounding and mixing are: • Chemical additive dusts during pre-weighing and compounding • Use of a computer controlled weighing system eliminates the exposure hazard • Additive dusts, condensed fumes, and oil mist during charging of the Banbury Mixer, also noise >85 dBA during mixer use • Partially enclosing hood has been the most effective engineering control to minimize these hazards • Dumping mix onto the drop mill releases volatile fractions of oils, high vapor pressure organic compounds, or possible degradation products if the roller are not cooled adequately • Drip mills are usually equipped with canopy hoods to remove the hot process contaminants • Because working at the drop mill often requires the operator to work over the moving rollers, the mills are supplied with emergency shut off guards to prevent anyone from being pulled into the rollers PH 4310 - Health Hazards in Industry, Lct 19

9. Chem Based Products – Rubber Products • Manufacturing Processes (cont.) • Compounding and Mixing (cont.) • Exposure Hazards (cont.): • The anti-tack dipping exposes the worker to talc, clay, and soapstone dusts • Make sure through analysis that the anti-tack materials do not contain asbestos materials • Using wet process is best method to control exposures • Processing • General rubber manufacturing follows all of the basic process steps as found in tire manufacturing • In tire manufacturing, 3 pieces must be fabricated • The tire bead, which is a rubber coated steel wire ring that holds the tire onto the wheel rim • The ply-stock, which is rubber coated fabric used in multiple layers to build the overall structure of the tire, • And the solid rubber tread, which is the road bearing element • Although automation has been tried for tire building, the manual build-up method continues to be the method of choice • Tire building process • Rubber is processed from the feed mill for each part (could be from the same mill or a different one depending on the product specs) PH 4310 - Health Hazards in Industry, Lct 19

10. Chem Based Products – Rubber Products • Manufacturing Processes (cont.) • Processing (cont.) • Tire building process (cont.) • In the making of the bead, shredded rubber is mixed with a solvent to make it viscous and to allow for coating of the wire ring • The solvent cement is made in a separate areas (cement house) to mix the flammable solvents and conform to fire code • At one time benzene was used, but white gas or hexane has replaced it • This viscous rubber (cement and shredded rubber mix) is used to cover the metal ring, which is then covered with a rubberized fabric to finish this part of the process • To manufacture the ply-stock, calendaring rollers are used with a reinforced fabric and a lump of rubber • As the fabric passes through the calendar, the rubber coats it to a specified thickness while filling any fabric voids with rubber • The continuous web is then cooled as it rolls off the calendar and is cut to length • In manufacturing the tread, rubber is fed from a feed mill to an extruder • The material enters a heated screw feed barrel where it is compressed and forced out of a die that shapes the rubber according to the desired shape and size of the tread • Tread is then picked up on a conveyor, its cut to length, then a roller spreads glue onto the underside of the tread so that it can be bonded to the tire carcass PH 4310 - Health Hazards in Industry, Lct 19

11. Chem Based Products – Rubber Products • Manufacturing Processes (cont.) • Processing (cont.) • Exposure hazards • Tire building is mostly done by hand with little automation, so heat stress, noise, and ergo hazards are probably the norm • Potential inhalation of glues and solvents during the preparation of the bead, the mixing of the glue, and the gluing of the tread onto the tire carcass • Use of local exhaust generally is acceptable to keep exposures within acceptable limits • Assembly • The 3 components for the tire are set up at the tire builders station, the set up is called a “book” • The tire building machine is basically a rotating cylinder sized for a certain tire size and acts as a template for the particular tire to be built • The tire is built by placing the beads onto the rotating cylinder, then tackifier is added to the visible rubber • A layer of ply stock is added onto the tackifier, this is repeated until the correct number of ply are in place • Once all ply are in place, more tackifier is added onto the last ply, then the tread is added • The tackifier is usually white gasoline that may have some aromatic content • The completed tire is called a “green tire” since it has not gone through the vulcanization (curing) process • Exposure hazards • Particulate exposures are very low, but solvent exposures can be high, especially if the tackifier contains benzene at % levels PH 4310 - Health Hazards in Industry, Lct 19

12. Chem Based Products – Rubber Products • Manufacturing Processes (cont.) • Curing • To prepare the “green” tire for curing, the tire must first be sprayed with a parting material • Traditionally the parting material was petroleum based, but due to some environmental concerns, it is now water based • Once coated, the tire is taken to the curing area where the operation can be automated or conducted manually • In manual curing: • The operator places the tire onto a flexible bladder, which is then placed inside a clam-shell press • The bladder is inflated with either steam or hot water which forces the tire form against an aluminum mold that contains the tread profile • The curing press is then heated to 100-200 ºC (210-390 ºF) for 20-60 min, to cure (vulcanize the tire) • Vulcanization, the cross linking of the rubber, is what gives the tire its great strength and elasticity • Automated curing • In a high production facility, the operator spots the “green” tire onto loading station at the curing press • The tire is picked up automatically and positioned in the cavity of the press, it closes, and curing begins • Exposure hazards • The curing cloud (organics) released during opening of the press, is the primary exposure during curing • There have bee studies (Rappaport, 1978, and Scand., 1982) indicating mutagenicity of the fume • Other hazards include, heat stressors from steam and convective heat loads, and noise from air and steam PH 4310 - Health Hazards in Industry, Lct 19

13. Chem Based Products – Rubber Products • Control Technology • Dust • In general the smaller the particle or the more extensive the grinding of a granular material, the greater the dust hazard during handling, transport, and processing • Purchasing the most course product suitable for the project reduces risk • The use of water to suppress dust has been effective as seen with applying anti-tack compounds • Prior to wet methods, housekeeping and significant dust exposures were the norm • Solvent Vapors • Application of a small amount of solvent is needed to ensure good bonding of rubber layers • Use of benzene prior to 1950, instead of white gas, may be responsible for excess leukemia seen in tire builders • Curing Fume • The most difficult air contaminant to control is the curing fume from curing and compression molding • Studies have indicated excess lung cancers in curing room workers, Ames tests have shown the fume to be mutagenic to bacteria, excess respiratory morbidity is linked to this work population • Use of local and dilution ventilation are needed to keep workers cool and remove contaminated air • Fixed or flexible curtains should be dropped as low as possible to reduce face area • A minimum face velocity of 80 fpm should be achieved at the canopy face • Replacement air should be supplied adjacent to the curing line and not directly next to the canopy • Worker should be positioned outside of the hood PH 4310 - Health Hazards in Industry, Lct 19

14. Chem Based Products – Rubber Products • Control Technology (cont) • Ventilation designs for rubber processing • ACGIH and Plastics Research Association of Great Britain have recommended specific vent designs for rubber processing equipment PH 4310 - Health Hazards in Industry, Lct 19

15. Chem Based Products – Acids, Ammonia, and Chlorine • Acids • Hydrochloric Acid • Hydrogen chloride can be prepared by reacting sulfuric acid with sodium chloride to sodium bisulfite, which also reacts with sodium chloride to hydrogen chloride and sodium sulfate • The acid is made by absorbing the hydrogen chloride gas into water • In the US, most of the hydrochloric acid is formed as a by-product in the chlorination of organics • Hydrogen, benzene, chlorine, and a catalyst are reacted to form chlorobenzene, leaving hydrogen chloride as a reaction product • The benzene and chlorobenzene are recovered first, leaving hydrogen chloride which can be mixed with water to make hydrochloric acid • Exposure hazards • The principle hazard of producing hydrochloric acid is exposure to either the leakage of gas and vapor from the system or the tail gas from the scrubber • The design of absorption towers adequately protects workers and the nearby community from these gas exposures • Common hydrochloric acid safety and handling procedures provide good operating practices, protective clothing, and eye and respiratory protection recommendations PH 4310 - Health Hazards in Industry, Lct 19

16. Chem Based Products – Acids, Ammonia, and Chlorine • Acids (cont.) • Nitric Acid • The principle production method for making nitric acid is the high pressure ammonia oxidation process • Air and ammonia are passed over a heated platinum – rhodium catalyst which causes the ammonia to oxidize yielding nitric oxide (NO), the nitric oxide is then oxidized to from nitrogen dioxide (NO2) • The concentration of ammonia must be less than the lower limit of flammability (15.5% in air) to prevent the formation of an explosive atmosphere • The NO2 is absorbed into water through a bubble-cap plate column to yield 50-70% nitric acid (HNO3) • Exposure hazards • Nitric acid recovery plants have the potential for significant exposures to nitrogen oxide(s) from liquid or gas leaks and during on-stream sampling • Emissions from exhaust stacks or nitrogen dioxide scrubbers can cause exposures to nitrogen oxide(s) since the tail gas stream may contain as high as 0.3% (3000 ppm) • Ammonia exposures can occur during leaks from storage tanks, gauge glasses, valves, and process lines • Ammonia concentrations if high enough can also create a fire or explosion hazard • Controls • Air cleaning of exhaust streams is done by reducing the oxides or by absorbing them into alkaline liquors • A good respiratory protection program is needed to protect employees from the respiratory hazards of ammonia and nitrogen dioxide in the event of emergency escape and entry into areas of high concentrations PH 4310 - Health Hazards in Industry, Lct 19

17. Chem Based Products – Acids, Ammonia, and Chlorine • Acids (cont.) • Sulfuric Acid • The process to create sulfuric acid involves the catalytic conversion of sulfur dioxide (SO2) to sulfur trioxide (SO3) which is then absorbed into water • Sulfur dioxide can be obtained from burning elemental sulfur (releasing 8-11% SO2), roasting sulfide ores (7-4% SO2) or from various metallurgical process streams in which SO2 is present in process streams • The conversion of sulfur dioxide to sulfur trioxide involves the use of a converter tower containing several beds of pentavalent vanadium catalyst pellets • The reaction in the converter (2SO2 + O2 = 2SO3) is conducted at 400-600 ºC (750-1110 ºF) • After reaction at the converter, the gas is sent to the economizer and absorption tower, the tail gas of this stream can contain as much as 2000 ppm of SO2 • In a modification of the converter process, a stream is taken off prior to the last converter stage and conveyed directly to the absorber reducing the tail gas stream to 100-300 ppm • Exposure hazards • Significant sulfur dioxide and sulfur trioxide exposures can occur from fugitive leaks and off-gas emissions • Due to toxicity, both emergency escape and re-entry respiratory protection equipment must be available • Exposures to ammonium vanadate or vanadium pentoxide catalyst can occur at the converter • Controls • Maintain the closed process to minimize leaks and emission and provide overflow containment for tank ruptures • Minimize contact through good handling techniques and PPE, and avoid storing acids near reducing agents PH 4310 - Health Hazards in Industry, Lct 19

18. Chem Based Products – Acids, Ammonia, and Chlorine • Ammonia - NH3 • In the early 70’s ammonia ranked 2nd or 3rd on the list of top chemicals produced and top on the list for value of product • Ammonia markets • The major market for ammonia is fertilizer (80-85%), • The minor market is for fibers and intermediates (5%), and • Small markets for explosives, metallurgy, pulp and paper, and other miscellaneous applications • A number of processes are used for the manufacture of ammonia, and all are based on the catalytic formation of ammonia from hydrogen and nitrogen • Natural gas (source of Hydrogen) and nitrogen from the air can be used to make ammonia • After desulfurization, natural gas is sent to a primary reformer, where it is cracked over a nickel catalyst using steam at 815 ºC (1500 ºF) to produce hydrogen and CO • The produced CO is sent to a secondary reformer and reacted with steam to produce CO2 and more H2 • A 2-stage shift converter uses an iron catalyst in the 1st stage, and a copper catalyst in the 2nd stage to remove CO2 with triethanolamine, organic solvents, or hot carbonate to form a pure H2 – N2 environment • The hydrogen and nitrogen, which remains in a 3:1 mole ratio is converted to ammonia (NH3) PH 4310 - Health Hazards in Industry, Lct 19

19. Chem Based Products – Acids, Ammonia, and Chlorine • Ammonia - NH3 (cont.) • Hazards • The principle hazard of ammonia manufacturing is the accidental gas releases from piping • Ammonia is also a fire hazard, and can explode violently if gas to air mixtures reach 16-25% • Controls • A respiratory protection program utilizing escape and re-entry respiratory protection is necessary • Protection against skin and eye irritation protection must be provide where contact may occur PH 4310 - Health Hazards in Industry, Lct 19

20. Chem Based Products – Acids, Ammonia, and Chlorine • Chlorine - Cl- • Chlorine gas is made from the electrolytic decomposition of sodium chloride brine by two methods • The diaphragm cell process, produces about 75% of the US supply of chlorine • The mercury cell chloralkali process is used to produce the other 25% • The diaphragm cell • An electrolytic cell with upward projecting carbon or metal anodes and a steel cover for the cathode • The steel cathode has projecting fingers that interleave the anodes, the cathode fingers are also covered with vacuum-formed diaphragm • Process: • A purified solution of sodium chloride is fed into the cell, chlorine forms at the anode and bubbles to the surface of the cell where it is withdrawn • The brine liquor overflow (spent brine) contains approximately 11.5% NaOH and 15% NaCl, this brine is concentrated in evaporators to a 50% caustic soda • The hazards of the diaphragm cell involve accidental releases of chlorine gas and exposures to caustic soda PH 4310 - Health Hazards in Industry, Lct 19

21. Chem Based Products – Acids, Ammonia, and Chlorine • Chlorine - Cl- (cont.) • The mercury cell chloralkali process • A low voltage-high amperage (84,000) DC electrolytic cell using carbon- or titanium-based anodes and a flowing mercury cathode • The cell is a long steel chamber 4-ft wide, 40-ft long, and 1-ft deep, containing approximately 3-tons of mercury • The cell is sloped so that the mercury will flow from the inlet to the outlet by gravity • Process: • The sodium chloride brine is electrolytically dissociated to chlorine gas and a sodium-mercury amalgam by-product is formed • The chlorine is collected and liquefied as the final product • The sodium-mercury amalgam flows to a companion electrolytic cell called the denuder or decomposer • At the denuder, the amalgam becomes the anode, graphite is used for the cathode, and caustic soda is the electrolyte • Hydrogen and sodium from the amalgam are released, the sodium forms caustic soda, and the denuded mercury is re-circulated back to the electrolytic cell • The by-product, caustic soda, is often reacted with chlorine to form sodium hypochlorite PH 4310 - Health Hazards in Industry, Lct 19

22. Chem Based Products – Acids, Ammonia, and Chlorine • Chlorine - Cl- (cont.) • The mercury cell chloralkali process (cont.) • Hazards • Potential exposures still exist in this process, but the major health hazard is the inhalation of mercury vapor and dust of mercury salts • Mercury vapor can be released from the hydrogen stream released from the decomposer • It can also be released in the exhaust and leakage at the end boxes of the cell • Chlorine is a corrosive and inhalation hazard • Caustic soda is a skin and eye hazard • Effective controls include • Control of fugitive losses at mercury circulating pumps and boxes of the cells with local exhaust ventilation • Reduction of mercury vapor exposures in the cell room by by using cleaner brine and switching to titanium-based anodes (maintenance reduced) • Placing gaskets at all connection points • Instillation of a central vacuum cleaner for spill removal and routine flushing of the floor with water • Setting up a personal hygiene plan requiring requiring work clothes changes and providing respiratory protection for selected maintenance operations • Use of continuous monitoring to alarm when mercury vapor if in the air PH 4310 - Health Hazards in Industry, Lct 19