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Pub Health 4310 Health Hazards in Industry

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Title: Pub Health 4310 Health Hazards in Industry


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

2
Lecture 19Chemical Based Products
  • Chapters 16-21
  • Chemical Based Products
  • Chemical Processing
  • Petroleum Refineries
  • Rubber Products
  • Acids, Ammonia, and Chlorine
  • Paint Manufacture
  • Plastic Products

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

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
    1920s, neoprene (chloroprene) and Buna rubber
    (styrene butadiene) in the 1930s
  • 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

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

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 1950s
  • 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

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

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
    gt85 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

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)

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

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

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

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

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

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

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

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

18
Chem Based Products Acids, Ammonia, and Chlorine
  • Ammonia - NH3
  • In the early 70s 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 31
    mole ratio is converted to ammonia (NH3)

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

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

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

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
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