Title: Pub Health 4310 Health Hazards in Industry
1Pub Health 4310Health Hazards in Industry
- John Flores
- Lecture 19
- Chemical Based Products
2Lecture 19Chemical Based Products
- Chapters 16-21
- Chemical Based Products
- Chemical Processing
- Petroleum Refineries
- Rubber Products
- Acids, Ammonia, and Chlorine
- Paint Manufacture
- Plastic Products
3Chem 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
4Chem 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
5Chem 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
6Chem 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
7Chem 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
8Chem 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
9Chem 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)
10Chem 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
11Chem 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
12Chem 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
13Chem 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
14Chem 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
15Chem 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
16Chem 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
17Chem 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
18Chem 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)
19Chem 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
20Chem 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
21Chem 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
22Chem 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