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Record Type: Instruction
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Directive Number: CPL 2-2.7
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Subject: Crystalline Silica
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Information Date: 10/30/1978
OSHA Instruction CPL 2-2.7 October 30, 1972
OSHA PROGRAM DIRECTIVE #300-3
TO: Field and National Offices/OSH
SUBJECT: Crystalline Silica
1. PURPOSE
This directive provides guidelines to be followed in inspections, and
where necessary, the issuance of citations, regarding exposure to silica
in the workplace.
2. DOCUMENTATION AFFECTED
This directive cancels the Silica Sampling Data Sheet of January 3,
1972.
3. DOCUMENTATION REFERENCED
a. Field operations Manual, Chapter XIII.
b. OSHA Standard Method for Respirable Gravimetric Dust Sampling.
c. Guidelines for Control of Occupational Exposure to Crystalline Silica
and Abrasive Blasting.
4. BACKGROUND
a. Chemical Data. Crystalline silica, also called alpha silica or generally
free silica, is silicon dioxide (SiO2). In pure, natural form, SiO2 crystals
are minute, very hard, translucent, and colorless. The physical properties
are: molecular weight, 60.09; melting point, 1710 C; boiling point, 2230
C; and vapor pressure, 10 mm Hg at 1732 C. Most mined minerals contain
some Si02. "Crystalline" refers to the orientation of SiO2 molecules in
a fixed pattern as opposed to a nonperiodic, random molecular arrangement
defined as amorphous (such as diatomaceous earth). The three most common
crystalline forms of silica encountered in industry are: quartz, tridymite,
and cristobalite. Quartz is a silicon dioxide polymorph with a composition
of 46.7% Si and 53.3% 0 crystallized in the hexagonal system. Tridymite
is a silicon dioxide polymorph with a composition like quartz, but containing
sodium aluminum silicate. It is crystallized in the ortho-rhombic system.
Cristobalite is also similar to quartz but with various impurities. Structurally
cristobalite is in the cubic or tetragonal system. Silicates, composed
of the SiO2 tetrahedron structural unit, are also sources of crystalline
silica (usually less than 1%). The silicates include: mica, soapstone,
talc (non-asbestos and fibrous). tremolite, and Portland Cement.
OSHA Instruction CPL 2-2.7 October 30, 1972
b. Fire, Explosion Potential, and Reactivity. Under extremely unusual
circumstances. fine airborne dust can propagate an explosion: usually a
strong source of ignition is required (welders' torch, boiler furnace).
In a closed container in the laboratory, dust explosion can be initiated
with a spark due to static electricity. The lower explosive limit will
depend on particle size. particle distribution in air, particle velocity,
and the mixture of dust (organic content, presence of gases, etc.).
c. Other Relevant Information. This section is for information purposes
only, not for compliance action.
(1) Common Processes. Silica is present in almost every process where
natural minerals are handled. It is prevalent in foundries where it has
several uses, in the manufacture and use of abrasives, in the construction
industry as an ingredient of materials or byproduct of activities, and
in the manufacture of glass and Pottery. Some of the processes in which
occupational exposures are to be expected are described below.
(a) Glass Manufacture. The four main divisions of the glass manufacturing
industry are flat glass. container glass, specialty (or technical) glass,
and fiber glass. The end products in fiber glass are silicates. Fibers
should not be confused with crystalline silica as they represent a different
health problem. The major portion of all glass batches is silica sand.
Washed sand is commonly used. The amount of fine particulates has been
reduced by washing. The unloading of dry sand from boxcars, either by power
scoop or by shovel and wheelbarrow, may produce large quantities of fine
silica dust.
(i) Processes. The various types of glass manufactured in the modern
glass industry are made by two processes: the older pot process and the
more common tank method. Heat stress may be associated with both processes.
(A) Pot process. The pot process is used primarily for the manufacture
of high-quality glass and for small quantity specialty glass. The pots
vary in size up to those capable of holding two tons of ingredients, for
the silicosis cases reported in the glass industry. The pots are made of
different types of clay combined with flint or silica flour. Pot glass
is manufactured in furnaces. waste heat causes considerable convective
air currents, therefore, breathing zone silica levels may be high throughout
the furnace areas. Pot melting of glass may necessitate hand shoveling
and hand filling of the pots. Optical and specialty glasses also frequently
contain heavy metals, such as lead, barium, etc. During the hand-filling
process, multiple exposures to dust of other ingredients, such as heavy
metals, may occur.
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(B) Tank process. The tank method is used for high volume production
requirements, such as window glass, television tubes, container glass,
etc. Glass tanks of current design provide for enclosed continuous feeding
of batch ingredients. This system reduces if functioning properly.
(ii) Repairs. The blocks and bricks used in the construction of the
furnaces and tanks contain silica in significant amounts. Silica brick
contains tridymite as its principal constituent. Dust concentrations may
be a problem to maintenance employees working on tanks. The hazard is caused
by cutting and chipping of blocks and bricks to be fitted into furnace
structures. Introduction of prefabricated furnace blocks and parts has
reduced the need to cut at the site of installation.
(b) Portland Cement. Another major use of silica is in the manufacture
of Portland Cement. In this process, the raw materials used may be divided
into four categories. These are: those supplying the lime component (calcaneous),
the silica component (siliceous), the alumina component (argillaceous),
and the iron component (ferriferous). The processing of the raw materials
into cement involves four stages:
(i) Size reduction to obtain fineness and increased surface area to
allow the chemical reactions to occur. (ii) Blending, correction, and homogenization
of raw mix to obtain desired composition and uniformity. (iii)Burning to
form new compounds, which liberates carbon dioxide. (iv) Heat pulverization
of kiln product with addition of gypsum.
The various components are usually moved from raw material storage by
overhead crane and deposited in roughly the desired proportions which can
be controlled. some of the sources of dust are quarrying, crushing, grinding,
the rotary kiln. screens, bagging operations, and the loading and unloading
from transportation vehicles. Heat stress may be associated with these
processes. Almost identical exposures can occur in cement block and brick
making, in brick kilns, and in kiln repair. The possibility of dual jurisdiction
with MESA may exist.
(c) Pottery Industry. The silica in the pottery industry is present
as flint. In the production of pottery there are six basic processes: preparation
of the body ingredients, forming and shaping, biscuit firing, application
of glaze. gloss firing, and decoration.
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OSHA Instruction CPL 2-2.7 October 30, 1972
Dust exposure may be a hazard in the transfer of raw materials from
boxcars to storage bins. The dust hazard may also exist in the preparatory
stages that follow such as: calcining, crushing, and grinding of flint,
stone. etc. These preparatory processes may be carried out in another plant.
The possibility of dual jurisdiction with MESA may exist. In the slip house
the body ingredients are blended in water, and:
(i) Plastic clay is produced by filtering and pugging. (ii) Casting
slip is produced by blunging. (iii) Dust for pressing is produced by drying,
grinding, and disintegrating.
Dust may arise from dry pressing, grinding, or evaporated blend. The
plastic clay, dust. or casting slip then enters the forming and shaping
phases. Plastic clay shaping is now primarily a mechanical operation. Dust-pressed
articles are produced by compacting pre-dried body-dust by hand or mechanical
pressing. After shaping, the ware may be dried and finished and is then
ready for biscuit firing. Outside the slip house. flatware brushing is
one of the dustiest occupations and requires control measures. The other
finishing steps have less potential for dust hazard; however, multiple
hazards should be expected in the glazing process. Rubber bands holding
together drying forms are a source of fine dust when dry.
(d) Foundries. The foundry environment varies primarily with the kind
of material poured. The exposure to silica dust in the foundry environment
can be described by following the process from melting to cleaning.
(i) In the melting process the metals or alloys are melted in a furnace
of the cupola, electric arc, electric induction, or open-hearth type. Silica
exposure in the melting process, however, may be minimal. The primary hazard
is exposure to metal fumes and dust. The production of iron castings is
accomplished by re-melting scrap along with pig iron in a furnace called
a cupola. The cupola may be a source of carbon monoxide, metal fumes and
dust. In an electric arc furnace, melting is achieved by heat transfer
from the arcs that are sprung from the electrodes to the metal charge.
Electric furnaces may give rise to large amounts of iron oxide and various
other fumes depending on the composition of the steel being formed. In
an electric induction furnace a high frequency current is passed through
the primary coil, thus inducing a much heavier secondary current in the
charge (metal), which results in heating it by resistance to the desired
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OSHA Instruction CPL 2-2.7 October 30, 1972
temperature. In this process, melting is quite rapid, so that there
is only a slight loss of the easily oxidized elements. In the open-hearth
furnace, both the hearth and the charge resting on it are exposed to the
direct action of the flame employed in converting the solid charge into
the liquid state. If a large tonnage is continually required, the open-hearth
furnace is used.
(ii) Mold and core making presents multiple hazards due to the use of
silica and the great variety of binders and mold making processes. Molds
may be coated with flint or silica flour. After the initial forming, molds
may be preheated and cooled, and the surface may be retreated to prevent
metal adhesion. Cooled molds may be called chills. Resin binders and solvents
(primarily alcohols) may be used, therefore multiple exposures are possible.
(iii)Pouring operations generate gases and vapors from the destructive
distillation of sea coal mixed into the molding sand and synthetic gates.
When sea coal is used in mold making, evaluation for coal tar pitch volatiles
may be indicated. Multiple air contaminants are generated in the pouring
operation. CO2 and CO may be generated when organic materials in the mold
are heated. Numerous organic components have been identified in foundry
fumes. The temperature of the metal to be cast in the mold. Where pouring
is done on the floor, the general practice has been to minimize these hazards
by providing high ceilings with air outlets as high as possible and inlets
near floor level.
(iv) After pouring, the molds are allowed to cool, with time depending
on size of the cast and the metal.
(v) After cooling, the external molds are opened or broken in an operation
called shakeout. Dust concentrations are high during shakeout and cleanup
operations. An effective control for the shakeout operation is the relatively
complete enclosure with sufficient exhaust volume, removed at the top of
the enclosure to maintain an inflow of at least 200 FPM at all openings.
(vi) Core knockout is a process in which the mold portion from the inside
of the cast is removed resulting in the dispersion of silica dust. The
use of compressed air jets to blow out the last of the core sand produces
excessive airborne dust concentrations. A side hood arrangement may be
effective in controlling exposures depending on the size of the cast. Vacuum
may be used to control dust in the core knockout process.
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OSHA Instruction CPL 2-2.7 October 30, 1972
Other operations generating dust are the transfer to return conveyer.
transfer to elevator, transfer to and from belt conveyers. sand screens.
tailing pipes, sand mixers and receiving points on sand bins. Since core
sand is reused several times. it may become progressively finer. This may
increase the number of respirable size particles in the air.
(vii)Grinding. After the cast has been shaken out and the core mold
removed, the cast has.to be rough ground to remove mold defects. The cast
may still have a lot of fine particles embedded in or adhering to its surface,
which become airborne upon grinding. Noise may be a major problem in this
operation. Several engineering controls are proven and available. depending
on the size of the cast, to control this problem.
(e) Abrasive Blasting. This process is used to clean, smooth, or prepare
surfaces for additional treatment or appearance (such as buildings, bridges.
ships, etc.). Abrasive blasting is the high velocity bombardment of a surface
by an abrasive material (wet or dry) propelled by primarily pneumatic pressure.
Three basic techniques may be encountered: dry, wet. and airless (centrifugal).
A vacuum can be used to control dust when a pneumatic blast nozzle is used.
Noise is a major hazard in addition to dust. The dust generated in any
blasting process is a combination of the fragmented blasting media and
the material dislodged from the surface treated. Where a fragmentable abrasive,
such as sand, shells, cobs, glass beads, metal shots or slag, is used,
or where a fragmentable surface, such as a sand casting, a painted or scaly
surface, or masonry, is blasted, the dust generated varies in particle
size and chemical composition. The particle size of the blasting agent
decreases upon rehandling or reuse: liberation of more silica sand in the
respirable size is possible if silica is present in either the agent or
surface. Due to the volume of sand used for some stationary operations,
complete respiratory protection is necessary not only for the sand blaster,
but also for the entire work area if the blasting is not done inside an
effective enclosure (i.e., buildings, ships, etc.). Where an employee is
inside the enclosure, together with the production parts to be sand (or
shot) blasted, full protective clothing must be considered. The contamination
of the clothing with secondary contaminants and blasting agents may occur.
(2) Signs and Symptoms of Disease. Upon repeated exposure to dust containing
crystalline silica, a fibrous lung condition called silicosis may develop.
Signs such as labored breathing and early fatigue may indicate silicosis;
however, they can arise from many other causes. Diagnosis of silicosis
can be made by a physician only and is difficult to make without a work
history. The progress of silicosis
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OSHA Instruction CPL 2-2.7 October 30, 1972
can only be stopped; the lung condition cannot be cured. The incidence
of tuberculosis is high among silicosis patients.
5. INSPECTION PROCEDURES
a. Pre-Inspection Preparation
(1) The inspection team or the assigned CSHO shall:
(a) Review any previous case files on the plant to be inspected, noting
the size of the plant area, number of employees, and volume of expected
activities. (b) Search applicable standard industry classification code
in the state directory of industries (usually a Chamber of Commerce publication)
for similar plants. Review the case files of similar plants to become familiar
with problems to be expected. (c) Use other technical information or literature
to increase the understanding of expected activities. (d) Review all information
obtained by the requesting officer if the plant inspection is a referral
visit.
(2) The team or the assigned CSHO shall also:
(a) Estimate the time to be spent at the plant. (b) Estimate the number
and type of airborne contaminant samples to be taken. Review "OSHA Standard
Method for Respirable Gravimetric Dust Sampling." Determine weights of
all filters to be used in sampling which will require gravimetric analysis.
(c) Establish availability of all supplies necessary before the planned
sampling. (d) A respirable dust (crystalline silica) sampling train shall
consist of a nylon cyclone, cassette, tubing and a personal air sampling
pump. (e) Check air sampling pumps for calibration or calibrate for 1.7
liters per minute with sampling train. Log calibrations of sampling trains,
including component numbers and calibration results. (f) Obtain or prepare
the necessary number of cassettes plus 10% spares. (g) Prepare field log
book and/or sampling work sheets to record the following information for
each intended sample to substantiate entries required for OSHA Form 1 and
others:
(i) Employer's name; (ii) Substance sampled and sampling procedure used;
(iii) Work activity and location sampled; (iv) work load in area (above,
below, or at normal); (v) Number of employees in area: (vi) Information
on employee sampled:
(A) Name, address. and telephone number; (B) Social Security number,
if possible
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OSHA Instruction CPL 2-2.7 October 30, 1972
(C) Time spent per day at that activity; (D) Type of respiratory protection
and other protective equipment.
(vii) Instruments or pump used (and serial number); (viii) Sample identification
and cassette number (or numbers); (ix) Sample starting time and ending
time; (x) Starting flow rate and ending flow rate. if applicable; (xi)
Weather conditions; (xii) Other remarks.
(h) As other contaminants besides dust may be in the atmosphere, consider
and prepare other sampling trains or capture media if combination of anticipated
contaminants warrants it. Consult available OSHA standard methods. (i)
Check, calibrate and log calibration of direct reading instruments to be
used in the survey (such as sound level meter, CO analyzer). (j) Check
camera and verify film and camera operation. (k) Obtain and check personal
protective equipment. When preparing for an inspection of a plant with
dusty conditions, in addition to the normal protective equipment, obtain
a respirator equipped with cartridges or filters appropriate for anticipated
exposures. (l) Suggested list of sampling supplies should include strong
tape, Tygon tubing, scissors, sampling pump belts, plastic bags (Whirl-pack),
and a clipboard. (m) Review other applicable sub-parts of OSHA Health and
Safety Standards anticipated during the inspection. (n) Obtain and become
familiar with copies of reference documents. (o) Discuss the preparation
for the plant visit with appropriate supervisor. b. Inspection
(1) Upon entering the workplace, the CSHO shall contact plant management,
identify himself, and state the purpose of the visit.
(2) Opening Conference. The CSHO shall obtain a process flow chart and
plant layout, and determine production volume and activity cycles. If the
plant facilities layout chart is not available, the CSHO shall sketch a
plant layout subsequently during the inspection, identifying major operation
areas, distribution of major equipment, building identification, existing
and planned engineering controls, and approximate dimensions of the plant
property. Determine if the plant production level is normal or unusual
due to maintenance shutdowns, accelerated production, etc. If the production
is down, proceed with inspection, but do not perform full scale sampling
until normal production is resumed.
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OSHA Instruction CPL 2-2.7 October 30, 1972
(a) The opening conference shall be continued with a discussion of specific
health hazard-related information.
(i) Determine the form(s) in which silica arrives at the plant and the
approximate sequence of the process in which it is used; request the Safety
Data Sheets, if available. (ii) Obtain plant management statement regarding
safeguards, precautions, protective equipment, and routine procedures used
for protection of employees in plant operations. Ask about any known experience
of employee illness or symptoms exhibited or complaints with regard to
health matters. (iii) Obtain complete labeling and placarding information
of chemicals used in the operation,.if any. (b) The CSHO shall obtain the
following additional information either by direct interview, or partial
interview, or record review. Plant management shall be requested to provide
the information not readily available in a letter to the Area Director.
(i) Monitoring Program. If the plant has an air sampling program or
spot samples have been taken at the plant, the-CSHO shall note:
(A) Collection equipment used, and calibration record if any: (B) Sampling
and analytical methods employed; (C) Frequency of sampling, if performed
regularly; (D) Specified locations of sampling in the plant. if used; (E)
Names of persons who have performed sampling, including names of outside
consultants; and (F) Date of most recent sampling run. Obtain:
((1)) Time of sampling, with respect to work cycle; ((2)) Duration of
individual sampling runs; ((3)) Specific sampling locations with respect
to process and work stations; and ((4)) The sampling results.
(ii) Medical Program.
(A) What types of medical examination are provided (such as preplacement,
annual or special tests for silica exposure) and by whom, in-house or contract
physician? (B) What are the medical protocols or reasons for providing
other physical examinations? (C) Where are the physical examinations conducted?
(iii) Record Keeping Program.
(A) What types of records are being maintained? (B) When was the particular
record keeping started?
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OSHA Instruction CPL 2-2.7 October 30, 1972 (C) How and where records
are kept (such as medical records with employee's personnel record. protective
equipment records in the warehouse, training program record with the safety
engineer, etc.)? (D) Are heath-related records reviewed and correlated
with other available records (air monitoring, training, and maintenance
records)?
(iv) Employee Training and Information Program (including new employees).
(A) Who informs the employee about the potential health hazards associated
with silica exposure? (B) How often does employee training take place,
specifically on health hazards of silica? (C) What written training materials
are provided? Include a copy. (D) Is the employee able to review his or
her individual health-related records? (E) Are emergency procedures taught
and practiced in the plant? Include copies of procedures. (F) Is the function
and use of protective equipment and engineering controls taught? written
instructions for the selection and use of respirators shall be established
according to 29 CFR 1910.134(b)(1). Obtain a copy. (G) Obtain copies of
minutes of recent safety meetings.
(v) Personal Hygiene Program.
(A) What type of locker and lunch facilities are provided? (B) What
type of shower facilities are provided? (C) What procedures are used for
encouraging good personal hygiene practices? (vi) Personal Protective Equipment
Program.
(A) Are respiratory protective devices provided? If so, what type? (B)
For abrasive blasting is the type C supplied air, positive pressure, demand
type abrasive blasting respirator worn according to 29 CFR 1910.94(a) and
30 CFR Part 11? (C) What is the program for repair and maintenance of all
respiratory protective devices? (D) what are the policies and procedures
for issuing personal protective equipment? (E) How is dirty protective
clothing or equipment cleaned, decontaminated and/or disposed? (vii) Engineering
Controls and Related Preventive Maintenance Program. Provide for each system:
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OSHA Instruction CPL 2-2.7 October 30, 1972
(A) Control system identification and type; (B) Design capacity; (C)
Approximate date installed: (D) Collection system; (E) Preventive maintenance
plan; (F) System performance measurement program. (viii) Housekeeping Program.
(A) What is the method used for floor cleaning and the frequency of
it? (B) What is the method of removal of dust from work surfaces in the
plant? (C) What equipment is used in the housekeeping process, such as
vacuum cleaners, mops, flooding, sweeping, etc.? (D) Is refuse picked up
regularly? (E) Is there an in-plant disposal site of production wastes?
(3) Walk Through Inspection
(a) Prior to the start of the in-plant inspection, the CSHO shall have
or wear appropriate protective equipment. The use of personal protective
equipment shall not be less than that required in the plant area. (b) Start
at the production material receiving point and follow the production flow.
Observe conditions, processes, physical and chemical agents used, worker
activities, and existing engineering (c) The CSHO shall identify and record
on plant layout or on a separate sketch the following:
(i) Potential sources of health hazards.
(A) Note the temperature, noise. and dust conditions in each area. (B)
Note areas adjacent to the silica process. (C) Record other materials used
in the process. Their use rate, brand names, preferably the chemical names,
and storage areas shall be noted. (D) Observe all silica dust accumulations
on ceiling, walls, floors and equipment. Note possible sources. (ii) Location
and number of exposed employees.
(A) Note number of employees in each area. Note the number of workers
potentially exposed to silica or other health hazards and obtain their
job titles and/or job descriptions.
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OSHA Instruction CPL 2-2.7 October 30, 1972
(B) Provide opportunity for conversations with employees during inspection
concerning knowledge of the hazards, reason for and methods of protective
equipment and engineering controls. (C) Note permanent work stations with
respect to plant processes. (D) Note the use of protective devices. (E)
Note the appearance of work clothing (as an indication of potential exposure).
(iii) Types of engineering controls.
(A) Note openings (in tunnels or buildings) to external environment
and the plant air flow patterns. (B) Identify all ventilation systems.
(C) Note maintenance work practices on process equipment if there is an
opportunity. (iv) Housekeeping.
(A) Enter sanitary facilities and observe the conditions. (B) Note adequacy
of general housekeeping procedures. (C) Note the availability of cleaning
equipment and supplies.
(v) Other.
(A) Photograph potential health hazard areas, equipment, engineering
controls and safety hazards and situations which should be a part of the
inspection report. (B) The CSHO shall arrive at conclusions and opinions
deliberately and slowly. Appearances can be deceiving with respect to airborne
concentrations of silica.
(4) Sampling. For sampling purposes, select employees who have apparent
maximum potential exposure and also employees representative of other work
operations. The CSHO shall:
(a) Attach sampling devices to the selected employees. Follow OSHA Standard
Methods. (b) Set the sampling rate at 1.7 liters per minute. (c) Check
flow meter setting and sample collection frequently throughout the sampling
period. (d) Minimum total sampling time is 7 hours, unless the operation
time is shorter. (e) Replace the cartridge with a new one as deemed necessary;
do not overload! (f) Perform area sampling to determine effectiveness of
engineering controls (this result shall not be used for citation). (g)
Keep at least one cassette as a blank, per day of sampling, expose it to
the plant environment and immediately reseal. Air shall not be drawn through
the blank.
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OSHA Instruction CPL 2-2.7 October 30, 1972
(h) dust concentrations shall be determined by gravimetric analysis
in the area office and crystalline silica determinations shall be performed
on the same samples by the laboratory. (i) In case of potential multiple
contaminants (silica, lead, arsenic etc.), samples shall be collected for
each suspected contaminant separately, according to appropriate OSHA Standard
Method. (j) Perform measurements and as many noise engineering control
checks as feasible. (k) Complete other engineering control survey before
leaving plant. (l) Interview employees, and observe for symptoms of health
impairment. (m) Arrive at conclusions and opinions slowly. Sampling results
will not be returned instantaneously. Appearances can be deceiving with
respect to airborne concentrations of silica. (5) Closing Conference
(a) After completing the sampling, surveying all engineering control
systems, and reviewing available plant records, the CSNO shall discuss
the findings with management and labor representatives together or in separate
meetings.
(b) Management and labor shall be advised of possible violations pending
results of laboratory analysis of samples. (c) CSHO shall be prepared to
discuss the Crystalline Silica and Abrasive Blasting Guidelines with the
employer. Guidelines shall be considered as good practice recommendations,
not regulations. 6. REPORT
a. The CSHO shall calculate the permissible exposure limit (PEL) of
silica samples collected according to the following procedure:
(1) Obtain material identification and per cent silica analysis from
the laboratory. (2) Use the formula for gravimetric method provided for
respirable quartz in Table Z-3, 1910.1000, to calculate the PEL. For cristobalite
and tridymite, one half of the value calculated shall be used to determine
PEL. (3) Example: A respirable dust sample is weighed and the time-weighted
average is calculated to be 3.6 mg/M3. The laboratory reports the composition
of the dust to be 13% quartz, 8% tridymite and 10% czistobalite. Calculate
the permissible exposure limit of each component.
Quartz: 10 mf/M3 0.66 mg/M3 (PEL) -------- = (13 %+ 2)
Tridymite:10 mg/M3 X 1/2 = 1 mg/M3 X 1/2 = 0.50 mg/M3 -------- (PEL)
(8% + 2)
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OSHA Instruction CPL 2-2.7 October 30, 1972 Cristobalite:
10 mg/M3 X 1/2 = 0.83 mg/M~ X 1/2 = 0.42 mg/M --------- (PEL) (10% +
2)
In this case, employee exposure to the individual components exceeds
the permissible exposure limits.
b. A complete technical report shall be compiled using all information,
observations, photographs, and other data collected in accordance with
this program directive. The report shall be concluded with recommendations,
if any, for citations under OSHA standards or general duty clause and for
proposed penalties. c. The report shall include descriptions of unusual
sources or conditions of airborne contaminations. d. The report shall also
include descriptions of exceptional or well-designed engineering controls
observed and surveyed.
7. CITATIONS
Consult Chapter XIII, Section G, of the Field Operations Manual for
specific instructions on the issuance of citations where violations involving
exposure to silica are concerned.
8. EFFECTIVE DATE
This directive is effective immediately and shall be retained until
further notice.
Morton Corn Assistant Secretary of Labor
Distribution: A-1 E-1 B-2 HEW-1 C-2 NIOSH Regional Program Directors-1
D-4&5 NACOSH-1 Training Inatitute-4
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U.S. DEPARTMENT OF LABOR Occupational Safety and Health Administration
WASHINGTON, D.C. 20210
Office of the Assistant Secretary
Dear Sir:
The nature of work at your establishment in and Health Administration
(OSHA) that crystalline silica may be used in your manufacturing process.
As you know, the present permissible exposure limit to weighted average
concentration for an 8-hour period. If the employee exposure is found to
be in excess of the permissible limits, you must implement feasible engineering
or administrative controls or maintain an effective respiratory protection
program should such controls be found infeasible. The National Institute
for Occupational Safety and Health has recommended that the permissible
exposure limit for silica be lowered to .05 mg/M3, as determined by a full-shift
sample up to a 10-hour working day, 40-hour work week. This recommendation
is currently being considered by OSHA.
As an interim measure until such time as a complete standard is promulgated
we are forwarding herewith recommended guidelines for protection of your
employees against the risk of disease resulting from exposure to silica.
These recommendations involve preventive steps of good housekeeping, personal
hygiene, medical surveillance, monitoring and measuring of exposure levels,
employee training, respirator information and abrasive blasting work practices
which should ensure a reduced health risk for those of your employees who
are involved in such manufacturing processes. The issuance of these guidelines
does not alter our intention to continue our compliance activities.
The wide use and multiple applications of silica in our nation's industries
combine to make silica a major occupational health hazard. Therefore, voluntary
compliance with the enclosed nonmandatory guidelines would further the
overall objective of the Occupational Safety and Health Act - to assure
so far as possible, safe and healthful working conditions.
Your cooperation in this matter is greatly appreciated. Protection of
your employees from overexposure to silica is, I am confident, our common
goal.
Bert M. Concklin Deputy Assistant Secretary
OSHA Instruction CPL 2-2.7 October 30, 1972
Guidelines for Control of Occupational Exposure to Crystalline Silica
and Abrasive Blasting
In accordance with the Occupational Safety and Health Administration's
(OSHA) standard for air contaminants (29 CFR 1910.1000), employee exposure
to airborne crystalline silica shall not exceed an 8-hour time-weighted
average limit (variable) as stated in 29 CFR 1910.1000, Table Z-3. or a
limit set by a state agency whenever a state-administered Occupational
Safety and Health Plan is in effect. The first mandatory requirement is
that employee exposure be eliminated through the implementation of feasible
engineering controls. After all such controls are implemented and they
do not control to the permissible exposure limit, each employer must rotate
its employees to the extent possible in order to reduce exposure. Only
when all engineering or administrative controls have been implemented,
and the level of respirable silica still exceeds permissible exposure limits,
may an employer rely on a respirator program pursuant to the mandatory
requirements of 1910.134. Generally where working conditions or other practices
constitute recognized hazards likely to cause death or serious physical
harm, they must be corrected pursuant to Section 5(a)(1) of the Occupational
Safety and Health Act. In addition to these mandatory requirements, the
National Institute of Occupational Safety and Health has recommended that
the limit be lowered to 0.05 mg/M3, as determined by a full-shift sample
up to a 10-hour working day, 40-hour work week. This recommendation is
currently being considered by OSHA. Pending such consideration, the following
recommendations are made to ensure that employee exposure to respirable
silica is controlled to the permissible exposure limit. For these guidelines.
silica means crystalline silica.
1. MONITORING
a. Each employer who has a place of employment in which silica is occupationally
produced, reacted, released, packaged, repackaged, transported, stored,
handled, or used should inspect each workplace and work operation to determine
if any employee may be exposed to silica at or above the permissible exposure
limits. Indicators that an evaluation of employee exposure should be undertaken
would include:
(i) Any information or observations which would indicate employee exposure
to silica or other substances; (ii) Any measurement of airborne silica:
(iii) Any employee complaints of symptoms which may be attributable to
exposure to silica or other substances; (iv) Any production, process, or
control change which may result in an increase in the airborne concentration
of silica, or whenever the employer has any other reason to suspect an
increase in the airborne concentrations of silica.
b. Air Monitoring
(i) Employee exposure measurements should represent the actual breathing
zone exposure conditions for each employee. Any appropriate
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OSHA Instruction CPL 2-2.7 October 30, 1972
combination of long-term or short-term respirable samples would be acceptable,
but total sampling time may not be less than 7 hours. In case of abrasive
blasting operations, substances other than silica should be sampled and
analyzed. (ii) Accuracy of Measurement. The method of monitoring and analysis
should have an accuracy of not less than plus or minus 25% for concentrations
of airborne silica equal to or greater than the permissible exposure limit.
(One method meeting this accuracy requirement is available in the "NIOSH
Manual of Analytical Methods," Government Printing Office Stock No. 1733-00041)
(iii) Frequency of Monitoring. Where the employer has determined that employees
are exposed to silica or other substances in excess of the permissible
exposure limit, monitoring should be-repeated quarterly.
2. MEDICAL SURVEILLANCE
Each employer should institute a medical surveillance program for all
employees who are or will be exposed to airborne concentrations of silica
or other substances above the permissible exposure limit. The employer
should provide each employee with an opportunity for a medical examination
performed by or under the supervision of a licensed physician and should
be provided during the employee's normal working hours:without cost to
the employee.
a. Medical Examination
(i) Each employer should provide a medical examination which includes
a complete medical history and physical examination, an annual chest roentgenogram
(x-ray) and pulmonary function tests to each employee exposed to silica
in excess of the permissible exposure limits. In the abrasive blasting
trade, attention should be paid to potential scarring of cornea.
(a) A chest roentgenogram (posteroanterior 14" by 17" or 14" by 14")
classified according to the 1971 ILO International Classification of Radiographs
of Pneumoconioses. [ILO U/C International Classification of Radiographs
of Pneumoconioses 1971, Occupational Safety and Health Series 22 (rev)
Geneva, International Labor Office, 19721.
(b) Pulmonary function tests including forced vital capacity (FVC) and
forced expiratory volume at one second (FEV 1) to provide a baseline for
evaluation of pulmonary function and to help determine the advisability
of the workers using negative- or positive-pressure respirators. It is
recognized that providing such medical examination and record keeping of
medical data may be difficult for those abrasive blasting establishments
employing transient workers.
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OSHA Instruction CPL 2-2.7 October 30, 1972
(ii) Medical examinations should also be made available: (a) To employees
prior to their assignment to areas in which airborne concentrations of
silica are above the permissible exposure limit; (b) At least.annually
for each employee exposed to airborne concentrations of silica above the
permissible exposure limit at any time during the preceding six months;
(c) Immediately, upon notification by the employee that the employee has
developed signs or symptoms commonly associated with chronic exposure to
silica.
(iii) Where medical examinations are performed, the employer should
provide the examining physician with the following information:
(a) The reason for the medical examination requested; (b) A description
of the affected employee's duties as they relate to the employee's exposure;
(c) A description of any personal protective equipment used or to be used;
(d) The results of the employee's exposure measurements, if available;
(e) The employee's anticipated or estimated exposure level; (f) Upon request
of the physician, information concerning previous medical examination of
the affected employee.
b. Physician's Written Opinion
(i) The employer should obtain and furnish the employ with a written
opinion from the examining physician containing the following:
(a) The signs or symptoms of silica exposure manifested by the employee,
if any; (b) A report on the findings of the chest roentgenogram and pulmonary
function tests; (c) The physician's opinion as to whether the employee
has any detected medical condition which would place the employee at increased
risk of material impairment to the employee's health from exposure to silica
or other substances or would directly or indirectly aggravate any detected
medical condition; (d) Any recommended limitation upon the employee's exposure
to silica or other substances or upon the use of personal protective equipment
and respirators; and (e) A statement that the employee has been informed
by the physician of any medical condition which requires further examination
or treatment.
(ii) The written opinion obtained by the employer should not reveal
specific findings or diagnoses unrelated to occupational exposure to silica
or other substances. (iii) If the employer determines, on the basis of
the physician's written opinion, that any employee's health would be materially
impaired by maintaining the existing exposure to silica or other substances,
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OSHA Instruction CPL 2-2.7 October 30, 1972
the employer should place specific limitations, based on the physician's
written opinion, on the employee's continued exposure to silica or other
substances.
3. TRAINING
a. Each employee who may be potentially exposed to silica or other substances
should be apprised at the beginning of his or her employment or assignment
to such an exposure area of the hazards, relevant symptoms. appropriate
emergency procedures, and proper conditions and precautions for safe use
or exposure. b. Instruct affected employees to advise the employer of the
development of the signs and symptoms of prolonged exposure to silica and
other substances. c. Inform employees of the specific nature of operations
which could result in exposure to silica or other substances above the
permissible exposure limits, as well as safe work practices for the handling,
use, or release of the silica and the types and function of engineering
controls. d. Instruct employees in proper housekeeping practices. e. Instruct
employees as to the purpose, proper use, and limitations of respirators.
f. Provide employees with a description of, and explain the purposes for,
the medical surveillance program. g. Inform employees where written procedures
and health information are available on the premises. h. Advise employees
of the increased risk of impaired health due to the combination of smoking
and silica dust exposure.
4. PERSONAL PROTECTIVE DEVICES
a. Personal Protective Devices Program. Engineering controls shall be
used to maintain silica dust exposures below the prescribed limit. When
the limits of exposure to silica cannot be met by limiting the concentrations
of silica in the work environment by engineering and administrative controls,
an employer must utilize a program of respiratory protection to protect
every employee exposed. b. Respirator Selection and Usage
(i) The employer should select and provide an appropriate respirator
from the table on the next page. When abrasive blasting is done, the type
C supplied-air, positive pressure, demand type abrasive blasting respirator
shall be worn according to 29 CFR 1910.94(a) and 30 CFR Part 11. (ii) Employees
experiencing frequent and continuous breathing difficulty while using respirators
should be evaluated by a physician to determine the ability of the worker
to wear a respirator. (iii) A respiratory protective program meeting the
requirements of 29 CFR 1910.134 shall be established and enforced by the
employer. (iv) A respirator specified for use in higher concentrations
of airborne silica may be used in atmospheres of lower concentrations.
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OSHA Instruction CPL 2-2.7 October 30, 1972 Recommendations for Respirator
Usage at Airborne Silica Concentrations Above the Permissible Exposure
Limit
_____________________________________________________________________
|Concentrations of | Respirator Type* | |Airborne Silica | | |in Multiples
of | | |the Standard | | |____________________|______________________________________________|
|Less than or | Single use (valveless type) dust respirator.| |Equal to
5x | | |____________________|______________________________________________|
|Less than or | Quarter or half mask respirator with | |equal to 10x |
replaceable dust filter or single use (with | | | valve) dust respirator.
| | | | | | Type C, demand type (negative pressure), | | | with quarter
or half mask facepiece. | |____________________|______________________________________________|
|Less than or | Full faceplate respirator with replaceable | |equal to
100x | dust filter. | | | | | | Type C, supplied-air respirator, demand
type| | | (negative pressure), with full facepiece. | |____________________|______________________________________________|
|Less than or | Powered air-purifying (positive pressure) | |equal to 200x
| respirator, with replaceable applicable | | | filter.** | |____________________|______________________________________________|
|Greater than 200x | Type C, supplied-air respirator, continuous | | |
flow type (positive pressure), with full | | | Facepiece, hood, or helmet.
| |____________________|______________________________________________|
*Where a variance has been obtained for abrasive blasting with silica
sand use only Type C continuous flow, supplied air respirator with hood
or helmet.
**An alternative is to select the standard high efficiency filter which
must be at least 99.97% efficient against 0.3 um dioctyl phthalate (DOP).
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OSHA Instruction CPL 2-2.7 October 30, 1978
(v) Employees shall be given instructions on the use of respirators
assigned to them, on cleaning respirators. and on testing for leakage.
(vi) When employees are exposed to other toxic substances in addition to
silica, appropriate combinations of respiratory protection shall be provided.
c. Only those respiratory protection devices shall be used which have
a "Tested and Certified" number issued by the National Institute of Occupational
Safety and Health to the manufacturer of the device. d. There should be
an established in-plant procedure and means and facilities provided to
issue respiratory protective equipment, to return used contaminated equipment,
to decontaminate and disinfect the equipment, and to repair or exchange
damaged equipment. Record keeping of these activities is mandatory.
5. PROTECTIVE CLOTHING
Where exposure to airborne silica or other substances is above the permissible
exposure limit, work clothing should be vacuumed before removal unless
it is wet. Clothes should not be cleaned by blowing or shaking.
6. HOUSEKEEPING
a. All exposed surfaces should be maintained free of accumulation of
silica dust, which, if dispersed, would result in airborne concentrations
in excess of the permissible exposure limit. b. Dry sweeping and the use
of compressed air for the cleaning of floors and other surfaces should
be prohibited. If vacuuming is used the exhaust air should be properly
filtered to prevent generation of airborne respirable silica concentrations.
Gentle washdown of surfaces is preferable if practical. c. Emphasis should
be placed upon preventive maintenance and repair of equipment. proper storage
of dust producing materials, and collection of dusts containing silica.
Sanitation shall meet the requirements of 29 CFR 1910.141.
7. PERSONAL HYGIENE FACILITIES AND PRACTICES
a. All food, beverages, tobacco products, nonfood chewing products.
and unapplied cosmetics should be discouraged in work areas. b. Employers
shall provide an adequate number of lavatories, maintained and provided
with soap and towels. c. Where employees wear protective clothing or equipment,
or both, in-plant change rooms should be provided in accordance with 1910.141(e).
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OSHA Instruction CPL 2-2.7 October 30, 1978
8. ENGINEERING CONTROLS
a. Dust Suppression. Moisture, mists, fogs, etc.,should be added where
such addition can substantially reduce the exposure to airborne respirable
silica dust. b. Ventilation. Where a local exhaust ventilation and collection
system is used in a building, it should be designed and maintained to prevent
the accumulation or recirculation of airborne silica dust into the workplace.
The system should be inspected periodically. Adequate measures should be
taken to ensure that any discharge will not produce health hazards to the
outside environment. c. Additional Control Measures. When mobile equipment
is operated in areas of potential silica exposure, engineering controls
should be provided to protect the operator from such exposure.
9. ITINERANT WORK
a. when employees are exposed to airborne silica at temporary work sites
away from the plant, emphasis should be placed on respiratory protection,
protective clothing, portable engineering controls, and provisions for
personal hygiene and sanitation. Training of employees should be provided
to protect them as well as others from airborne silica dust exposure to
the extent practical.
10. ABRASIVE BLASTING
a. Introduction
(i) Consult standards listed in 29 CFR 1910.94(a). (ii) The nature of
dust generated in any abrasive blasting process is the combination of the
fragmentation of blasting media and the material dislodged from the surface
treated. Where fragmentable abrasives such as sand, shells, alumina, glass
bead or metal shot is used, or where a fragmentable surface such as sand
casting, a painted or scaly surface, or masonry is blasted, the airborne
dust generated will vary in particle size and chemical composition. Noise
associated-with abrasive blasting operations is also a significant hazard.
Heat stress may also be a potential hazard. (iii) Engineering controls
for noise and dust should be considered even if they cannot reduce the
exposures to permissible exposure limits but will significantly reduce
noise and dust exposure to the employees. (iv) Maximum respiratory protection
should be provided when silica sand is used as the abrasive agent, or sand
castings are cleaned by blasting. (v) All production and control systems
used in a stationary abrasive blasting process should be designed or maintained
to prevent escape of airborne dust or aerosols in the work environment
and to assure control of the abrasive agents.
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OSHA Instruction CPL 2-2.7 October 30, 1978
b. General
(i) Selection and maintenance of protective equipment.
(a) Refer to the table on page 5 to select appropriate respiratory protective
equipment. (b) Air-supplied helmets, ricochet hoods. dust respirators,
ear muffs and safety glasses should be an individual issue item, identified
with and used by one employee only. Such equipment should be reissued to
another employee only after complete cleaning, repair and decontamination.
(c) Means should be provided to vacuum, clean and store air supplied respiratory
equipment after each shift of use. Storage should be in a clean enclosure
such as locker, footlocker, or plastic container. The employees should
be trained to maintain the issued equipment in clean condition for his
own protection. (d) Replacement of prescription or plane safety glasses
should be made if multiple pitting or etching is visible in the center
of the lenses. (e) Replacement of faceplates in air-supplied helmets, ricochet
hoods. or full face masks should take place when a side-on light source
produces obscuring visible reflections and glare from the etched spots
and pit holes in the faceplate. Mylar coating, or similar transparent plastic
material, is recommended to protect the glass or plastic faceplate. (f)
Length of air hose may not be altered from the manufacturer's specifications.
(g) The condition of protective equipment should be checked daily by the
employee. Rips, tears, and openings which expose skin to abrasive agents,
should be mended. Functional tests for leaks, proper respiration, and good
connections should be performed on the complete air supply system.
(ii) Air supply - portable.
(a) The breathable air supplied to the helmet or ricochet hood should
be drawn from an oil and carbon monoxide free air compressor. In itinerant
work, it should be located upwind from the main air compressor to prevent
entry of combustion gases into breathable air. (b) Breathable air supply
system should be equipped, if possible, with audible alarm at the helmet
or hood to warn the user of low air pressure.
(iii) Hearing protection. Suitable hearing protection, providing at
least 20 dBA reduction in noise level experienced, should be worn inside
the helmet or ricochet hood unless hearing protection is an integral part
of such helmet or hood. (iv) Heat stress. Cooling of breathable air, supplied
to the blasting helmets or ricochet hoods. should be considered depending
on season and exposure of the employee to heat sources.
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OSHA Instruction CPL 2-2.7 October 30, 1978
c. Work Practices
(i) Indoors blasting cabinets and glove boxes.
(a) Negative pressure should be maintained inside during blasting. (b)
The enclosure should be as complete as practical. (c) When the inside of
the blasting cabinet is cleaned, respiratory protection should be utilized.
(d) If blasting creates excessive noise. a change of nozzle configuration
or application of noise control materials to the enclosure should be considered.
(e) Cabinets should be maintained in good repair including the presence
of gaskets.
(ii) In-plant blasting rooms.
(a) Negative pressure should be maintained inside during blasting. The
room should have exhaust capacity of one air change per minute. (b) Minimum
recommended protective equipment of an abrasive blaster working inside
a blasting room, in the open, in enclosed space, or outdoors is: safety
boots or toe guards;. durable coveralls, closeable at exists, ankles and
other openings to prevent entry of abrasive dust and rubbing of such; respiratory,
eye, and hearing protection; and gauntlet gloves. (c) If abrasive blasting
is automated, the room should not be entered before at least six air changes
have occurred, as respirable-size dust particles stay airborne for a considerable
length of time. (d) In the room, a cleanup method other than broom sweeping
or compressed air blowing should be used to collect the abrasive agent
after blasting (e.g. vacuum cleaning). If the blasting agent is removed
manually. respiratory protection should be used.
(iii) In-plant work area.
(a) If occasional but regular abrasive blasting must be performed inside
a building without enclosures, respiratory protection should be provided
for all employees in the area. Portable engineering control devices should
be used at the location to collect all of the used abrasive agent as it
is applied. (b) When airborne abrasive blasting dust becomes sufficiently
heavy in an area to cause a temporary safety hazard by reduced visibility,
or a marked discomfort to the unprotected employees not engaged in abrasive
blasting, such operations in the affected area should be discontinued until
the airborne dust is removed by exhaust ventilation and the settled dust
has been removed from the horizontal surfaces in the area. If such operations
have to continue, appropriate respiratory protection should be provided
to those employees remaining in the area, provided visibility is adequate.
(c) If wet blasting is employed, airborne dust hazard may exist after evaporation
of water.
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OSHA Instruction CPL 2-2.7 October 30, 1978
(iv) Confined space. A confined space is a compartment or tank or similar
enclosed space in which abrasive blasting, or a preexisting atmosphere.
may cause the employee to be overcome by conditions hazardous to life and
where egress may be difficult if normal body functions are impaired.
(a) Before starting work, open all access hatches, trap doors, etc.,
to aid natural ventilation. Mechanical ventilation should be used, picking
up air at the furthest point away from the opening if natural ventilation
will not cause a complete air change. Consider the other potentially hazardous
materials present. such as solvents, crusts of chemicals, or old paint,
with regard to explosion or fire potential when blasted. (b) A "buddy system"
should be used - for each employee inside a confined space, another employee
should be available to assist in a potential emergency. (c) For respiratory
protection, a self-contained breathing apparatus or air-supplied hood should
be utilized. (d) Adequate lighting that meets the requirements of the National
Electrical Code, article 502, should be provided. (e) If the space is mechanically
ventilated, means should be provided to collect dust before release to
the open atmosphere.
(v) Outdoors. (a) Blaster should be protected in a manner equivalent
to that mentioned in 29 CFR 1910.94(a)(5). (b) The pot man should wear
the same protective devices available to the blaster, depending on the
distance and wind conditions relative to the blasting location. (c) Prudent
care should be taken to prevent the dust cloud from spreading to other
work areas. (d) Hearing protection and respiratory protection should be
available to all other employees in the area if their presence is required.
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