• Record Type:
    OSHA Instruction
  • Current Directive Number:
    CPL 02-02-007
  • Old Directive Number:
    CPL 2-2.7
  • Title:
    Crystalline Silica
  • Information Date:
Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

OSHA Instruction CPL 2-2.7 October 30, 1972


TO: Field and National Offices/OSH

SUBJECT: Crystalline Silica


This directive provides guidelines to be followed in inspections, and where necessary, the issuance of citations, regarding exposure to silica in the workplace.


This directive cancels the Silica Sampling Data Sheet of January 3, 1972.


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.


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.

(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.


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

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.


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

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.


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


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.

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?


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:

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.


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.

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.


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)


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.


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.


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



Occupational Safety and Health Administration


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.


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

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.


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.


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,

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.


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.


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.


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).

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.


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.


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.


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).


OSHA Instruction CPL 2-2.7 October 30, 1978


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.


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.


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.

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.


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.

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.

Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.