Controlling Silica Exposures

in Construction

OSHA 3362-04 2009
Occupational Safety and Health Act of 1970

“To assure safe and healthful working conditions

for working men and women; by authorizing

enforcement of the standards developed under

the Act; by assisting and encouraging the States in

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safety and health.”

This publication provides a general overview of a

particular standards-related topic. This publication

does not alter or determine compliance responsibilities

which are set forth in OSHA standards, and the

Occupational Safety and Health Act. Moreover,

because interpretations and enforcement policy

may change over time, for additional guidance on

OSHA compliance requirements, the reader should

consult current administrative interpretations and

decisions by the Occupational Safety and Health

Review Commission and the courts.

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889-5627.
Controlling Silica Exposures

in Construction

Occupational Safety and Health Administration

U.S. Department of Labor

OSHA 3362-04

2009

Cover photo courtesy of the Center to Protect Workers’ Rights (CPWR)
This guidance document is not a standard or regulation, and it creates no new legal obligations.

The document is advisory in nature, informational in content, and is intended to assist employers in

providing a safe and healthful workplace. The Occupational Safety and Health Act requires employers to comply with safety and health standards promulgated by OSHA or by a state with an OSHAapproved state plan. In addition, pursuant to Section 5(a)(1), the General Duty Clause of the Act,

employers must provide their employees with a workplace free from recognized hazards likely to

cause death or serious physical harm. Employers can be cited for violating the General Duty Clause

if there is a recognized hazard and they do not take reasonable steps to prevent or abate the hazard.

However, failure to implement any specific recommendations contained within this document is not,

in itself, a violation of the General Duty Clause. Citations can only be based on standards, regulations, and the General Duty Clause.

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Occupational Safety and

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C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3

Contents

Overview 5

Stationary Masonry Saws 7

Handheld Masonry Saws 13

Hand-Operated Grinders 19

Tuckpointing/Mortar Removal 27

Jackhammers 33

Rotary Hammers and SimilarTools 39

Vehicle-Mounted Rock Drilling Rigs 45

Drywall Finishing 51

General Housekeeping and

Use of Dust Suppressants 56

OSHA Assistance 67

Regional Offices 69
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C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 5

Overview

This guidance document addresses the control of

employee exposures to respirable dust containing

crystalline silica, which is known to cause silicosis, a

serious lung disease, as well as increase the risk of

lung cancer and other systemic diseases. This document provides information on the effectiveness of

various engineering control approaches for several

kinds of construction operations and equipment,

and contains recommendations for work practices

and respiratory protection, as appropriate.

Quartz is the most common form of crystalline

silica. In fact, it is the second most common surface

material accounting for almost 12% by volume of

the earth’s crust. Quartz is present in many materials in the construction industry, such as brick and

mortar, concrete, slate, dimensional stone (granite,

sandstone), stone aggregate, tile, and sand used for

blasting. Other construction materials that contain

crystalline silica are asphalt filler, roofing granules,

plastic composites, soils, and to a lesser extent,

some wallboard joint compounds, paint, plaster,

caulking and putty. Cristobalite, a less common

form of crystalline silica, is formed at high temperatures (>1,470°C) in nature and by industrial processes. The ceramic and brick lining of boilers and vessels, some ceramic tiles, and volcanic ash contain

cristobalite.

The crystalline silica permissible exposure limit

(PEL) for the construction industry at 29 CFR

1926.55(a) is expressed in terms of millions of particles per cubic foot (mppcf). This PEL is based on a

particle count method long rendered obsolete by

respirable mass (gravimetric) sampling, which

yields results reported in milligrams per cubic meter

(mg/m3). In contrast with the construction PEL, the

crystalline silica PEL for general industry is based

on gravimetric sampling, which is the only method

currently available to OSHA compliance personnel.

Since the construction PEL is expressed in terms of

mppcf, the results of the gravimetric sampling must

be converted to an equivalent mppcf value. For

more information on the conversion of gravimetric

sampling results, please see Appendix E of OSHA

Directive CPL 03-00-007 (January 24, 2008). It can be

accessed at http://www.osha.gov/pls/oshaweb/

owadisp.show_document?p_ table=DIRECTIVES&

p_id=3790.

In this guidance, OSHA uses a benchmark 8-hour

time-weighted average exposure of 0.1 mg/m3 of

respirable silica dust as a point of reference in

describing control measures utilized by the construction trades. This benchmark is more conservative (i.e., lower) than the current construction PEL.

The benchmark is approximately equivalent to the

general industry PEL, is a single easy-to-use number

rather than a formula, and is expressed in terms of

the current gravimetric method rather than the

obsolete particle count method. Since this benchmark is generally more conservative than the construction PEL, employers who meet the benchmark

will be in compliance with the construction PEL.

OSHA notes that some organizations have recommended lower levels. For example, the National

Institute for Occupational Safety and Health (NIOSH)

recommends that respirable crystalline silica exposures be limited to 0.05 mg/m3 as a time-weighted

average for up to 10 hours (NIOSH, 2002). The

American Conference of Government Industrial

Hygienists (ACGIH) recommends that respirable

crystalline silica exposures be limited to 0.025 as an

8-hour time-weighted average (ACGIH, 2008). OSHA

is reviewing the construction and general industry

PELs for silica in its ongoing silica rulemaking.

The recommendations presented in this document are based on a review of information in the

published literature, NIOSH In-Depth Survey

Reports and OSHA inspection data. Engineering

control evaluations reported in the published literature were generally performed in controlled work

environments and may not reflect actual workplace

exposures experienced at construction worksites.

Moreover, potential silica exposure levels will

depend on the concentration of silica in materials at

construction sites, as well as factors in the work

environment (such as enclosed, semi-enclosed, or

open spaces and/or multiple operations generating

silica dust) as well as environmental conditions

(such as wind direction and speed). Therefore,

OSHA encourages employers to conduct periodic

exposure monitoring to confirm that engineering

and work practice controls are effective and that

appropriate respiratory protection is being used

where necessary. Controls continue to evolve and

OSHA encourages equipment suppliers and contractors to work with industrial hygienists to evaluate new designs and products to obtain objective

information that can be used to evaluate performance and support informed decisions on use.

If you choose to modify equipment, it is important to follow equipment manufacturers’ recommendations in order to ensure that modifications do

not adversely affect equipment performance and

that no additional hazards are created. Furthermore,

ground-fault circuit interrupters (GFCI) and water-
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Occupational Safety and

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tight/sealable electrical connectors should be used

with electric tools and equipment on construction

sites (OSHA, 1996). These features are particularly

important in areas where water is used to control

dust.

The document is divided into nine sections that

cover different construction operations. Eight are for

specific equipment or operations: Stationary

Masonry Saws, Handheld Masonry Saws, HandOperated Grinders, Tuckpointing/Mortar Removal,

Jackhammers, Rotary Hammers and Similar Tools,

Vehicle-Mounted Rock Drilling Rigs, and Drywall

Finishing. The other section addresses general

housekeeping operations and dust control through

the use of dust suppressants. These nine sections

draw heavily from OSHA’s experience, as is reflected in the numerous references to “OSHA case

files.” These files originated primarily from OSHA’s

Region 5 in conjunction with a Special Emphasis

Program for silica, and can be found in a report prepared for OSHA by Eastern Research Group (ERG).

This report, “Technological Feasibility Study and

Cost Impact Analysis of the Draft Crystalline Silica

Standard for Construction”, can be found in draft

form in OSHA’s docket H-006A, and at http://dockets.osha.gov/vg001/V037B/00/01/28.PDF.

The sections have been carefully written and

compiled; they include case studies, reference lists,

and technical notes. They offer information, advice

and recommendations on using wet methods, vacuum dust collection (VDC) systems, and work practices to control dust emissions from construction

operations. Many of these dust control systems are

readily available from vendors. By implementing

these recommendations, employers will more effectively minimize employee exposures to respirable

dust containing crystalline silica and will provide a

safer work environment for their employees.

For additional information about controlling silica exposures in construction, please see OSHA’s

website at http://www.osha.gov/SLTC/construction

silica/index.html.
Stationary Masonry Saws

This section covers gas- and electric-powered

stationary masonry saws. The term “silica” used

in this document refers to respirable crystalline

silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees produce dusts containing

silica when they cut, grind, crush, or drill construction materials such as concrete, masonry, tile and

rock. The small particles easily become suspended

in the air and, when inhaled, penetrate deep into

employees’ lungs.

Studies show that using a stationary masonry

saw to cut bricks, concrete blocks and similar materials can result in hazardous levels of airborne silica

if measures are not taken to reduce dust emissions.

Stationary saws should always be used with dust

control measures. At worksites without dust controls for these tools, studies have found that

employee silica exposures can be as high as 20

times the Occupational Safety and Health

Administration’s (OSHA) benchmark of 0.1 mg/m3

(milligrams per cubic meter of air) as an 8-hour

time-weighted average (TWA), an exposure approximately equivalent to OSHA’s general industry permissible exposure limit (PEL) (OSHA Case Files).1

Short-term exposures can be even higher.

This section describes methods available to

reduce employees’ exposures to silica when using

stationary masonry saws. OSHA encourages you to

use this information to evaluate or improve system

performance to reduce dust emissions. Technical

notes are found at the end of this section and are

referenced throughout the text.

Hazardous exposures to silica can occur when stationary

saws are operated without appropriate dust controls.

(Photo courtesy of the University of Washington.)

Two primary methods exist to control silica dust

while operating a stationary saw: (1) wet cutting,

and (2) vacuum dust collection. Ventilated booths,

when properly designed, can also reduce silica dust

exposure. All of these methods are easy to implement.

Wet cutting, when used properly, is an effective

way to reduce employee exposures to silica dust

and in most cases maintains exposures below the

allowable limit. Vacuum dust collection can significantly reduce silica levels, but may not reliably keep

them below 0.1 mg/m3 as an 8-hour TWA.

Silica Dust Control Measures

Wet Cutting

Most stationary saws come equipped with a water

basin that typically holds several gallons of water

and a pump for recycling water for wet cutting.2 If a

saw’s water supply system is not currently operating, the manufacturer may be able to supply the

necessary accessories to reactivate wet cutting

capability. Most suppliers stock these accessories

since water cooling prolongs the life of the saw

blade and tool.

Wet cutting is the most effective method for

controlling silica dust generated during sawing

because it controls the exposure at its source. Dust

that is wet is less able to become or remain airborne. Results obtained by OSHA and the National

Institute for Occupational Safety and Health

(NIOSH) at five construction sites indicate that wet

masonry saw operators’ exposures were routinely

below 0.1 mg/m3, and usually below 0.05 mg/m3,

not only when averaged over an 8-hour shift, but

also during just the period evaluated.3

At one jobsite, for example, NIOSH recorded a

respirable silica exposure level of 0.04 mg/m3 in the

breathing zone of an employee cutting concrete

blocks using a water-fed bench saw. The employee

operated the saw for approximately 5 of the 8

hours sampled (NIOSH, 1999a). Even if the employee had cut block for a full 8-hour shift, his estimated

exposure would have been 0.05 mg/m3.

In comparison, OSHA reported a significantly

higher exposure at another site on a day when wet

methods were not used due to cold weather. The

employee dry cut concrete block outdoors for a

similar period of time (nearly 6 hours), but in this

case experienced an 8-hour average exposure of 2

mg/m3 (OSHA Case Files).4

Employee exposures associated with uncontrolled dry cutting tend to be lower for employees

operating saws for a smaller percentage of their

shift, as well as for jobs involving materials with

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 7
lower silica content. However, among the nine results

obtained by OSHA and NIOSH, the average exposure

for dry cutting outdoors was 0.56 mg/m3 (with a

median of 0.25 mg/m3) for the periods sampled.5

These values exceed OSHA limits, and were associated with employees dry cutting for 10 to 60 percent of

the time sampled. At three construction sites,

employee exposures exceeded 2 mg/m3, presumably

during periods of intensive cutting lasting from 2

minutes to 6 hours (Lofgren, 1993; OSHA Case Files).

Maintenance. To minimize dust emissions from

saws equipped for wet cutting, keep pumps, hoses

and nozzles in excellent operating condition.

Regular saw maintenance reduces silica exposures

and ensures optimal operation of the equipment.

Saws and dust control devices should be on a routine maintenance schedule.

Maintaining a Water-Feed System

• Check the pump to ensure that it is working

properly and make sure that hoses are securely

connected and not cracked or broken.

• Adjust nozzles to ensure that water is directed

so that the maximum amount reaches the cutting area while still cooling the blade.

• Rinse or replace water filters at appropriate

intervals to ensure that the flow of clean water

is not restricted and to prevent damage to the

pump.

• Replace basin water when it gets gritty or

begins to silt up with dust. Depending on use,

this step may need to be repeated several

times per day to prevent the nozzle from clogging and to ensure that mist generated during

cutting does not carry extra dust from the recycled water.

• Dispose of water containing silica in a way that

prevents the silica from becoming resuspended in the air. If the silica is allowed to become

airborne, it can contribute to employee exposures.

• Consult the manufacturer for equipment operating specifications and recommendations that

apply to the specific saw model including electrical fault protection, such as a ground-fault

circuit interrupter (GFCI).

FreezingTemperatures. Freezing temperatures

complicate the use of water.6 Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Drain the system

when not in use. Large portable heating units are

commonly used to heat commercial and sometimes road and highway projects. If water freezes

on the ground, chip away the ice or use deicing

compounds or sand to control the slipping hazard.

Electrical Safety. Use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical

connectors for electric tools and equipment on construction sites (OSHA, 1996). These features are

particularly important to employee safety in wet or

damp areas, such as where water is used to control

dust. Although an assured equipment grounding

conductor program is an acceptable alternative to

GFCIs, OSHA recommends that employers use

GFCIs where possible because they afford better

protection for employees. (See 29 CFR 1926.404(b)(1)

for OSHA’s ground-fault protection requirements.)

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be more

airborne respirable dust present that is not visible

to the naked eye.

Vacuum Dust Collection Systems

When wet methods cannot be implemented, one

alternative is the use of vacuum dust collection

(VDC) systems. Stationary masonry saws with VDC

systems are commercially available and have the

ability to capture a substantial amount of dust.

With these systems, a vacuum pulls dust from the

cutting point through special fittings connected

directly to the saw (fixed-blade saws) or, alternatively, through a dust collection device connected to

the back of the saw (plunge-cut saws) (Croteau,

2000). A dust collector (exterior hood) mounted to

the back of a saw requires a high exhaust airflow to

ensure good dust capture between the saw blade

and dust collector.

Under experimental conditions, a VDC system for

a fixed-blade saw reduced short-term (15-minute)

exposures by 80 to 95 percent when compared to

uncontrolled masonry cutting. Because the saw

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produced unusually high levels of dust in the

enclosed, ventilated test area, the operators’ silica

exposure levels exceeded OSHA limits by a wide

margin, even with the VDC system equipment activated. However, the authors of the study reported

that uncontrolled silica exposure levels in the study

were considerably greater than those observed in

actual construction industry exposure assessment

studies. Consequently, use of the VDC system in an

actual construction setting could reduce silica exposure levels below OSHA limits (Croteau, 2000;

Croteau et al., 2002). Even when operators’ silica

exposure still exceeds OSHA limits, the level of

exposure could be substantially reduced through

the use of the VDC system.

Recommendations for Vacuum Dust Collection

Systems. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends

airflow of 25 cubic feet per minute (CFM) per inch

of blade diameter (ACGIH, 2007). If airflow is too

low, the hose may clog with particulate matter. A

study by Croteau et al. (2002), which tested an abrasive wheel saw, indicated that a ventilation flow

rate of 75 CFM and an air velocity of 3440 feet per

minute (FPM) should be considered the minimum

ventilation rate for a 2-inch diameter vacuum hose.

If the system provides a higher flow rate, then it is

acceptable to use a larger hose.

VDC systems can be purchased as a kit. These kits

should include a dust collector (exterior hood), vacuum, vacuum hose, and filter(s). The components

of a VDC system are discussed below.

• Dust collector (exterior hood): Be sure to use the

appropriate sized dust collector for the wheel

and if it is a retrofit on the saw, be sure to follow

the manufacturer’s instructions when installing

the device.

• Vacuum: Choose a vacuum with the appropriate

power and capacity for your job. Obtaining a

flow rate on a VDC system of 80 CFM or better

will give the best results while performing mortar removal (Heitbrink and Watkins, 2001).

• Vacuum hose: A flow rate of 80 CFM is best

maintained with a 11⁄2- to 2-inch diameter hose.

If the diameter is larger, the airflow velocity will

be reduced. If the diameter is smaller, airflow

resistance will be higher. Airflow resistance also

increases with hose length; excessively long

hoses should be avoided.

• Filters: Double filtration is important. The use of

a high-efficiency particulate air (HEPA) filter is

critical to prevent the escape of respirable silica

dust from the vacuum exhaust. HEPA filters are

at least 99.97 percent efficient in removing fine

dust particles from the air. A prefilter or cyclonic

separator in addition to a HEPA filter will improve

vacuum efficiency and extend the service life of

the more costly HEPA filter. A cyclonic separator

removes large particles that are capable of overloading or clogging the filter (Heitbrink and

Collingwood, 2005).7

• Systematic cleaning: Choose a vacuum

equipped with a back-pulse filter cleaning cycle.

Such auto-cleaning mechanisms will reduce the

time required for vacuum maintenance and

improve the overall efficiency of the dust collection system. If the vacuum does not have an

auto-cleaning mechanism, the employee can

periodically turn the vacuum cleaner on and off.

This allows the bag to collapse and causes the

prefilter cake to dislodge from the filter.

• Monitoring VDC efficiency: Purchasing a dust

collection system equipped with a static pressure gauge allows the employee to monitor the

system’s efficiency. Systems lacking a static

pressure gauge can be monitored visually. If a

dust plume increases and becomes more visible

where the dust collector meets the working

surface, the system is not working efficiently

(Heitbrink and Collingwood, 2005).

Tips for Operating a

Vacuum Dust Collection System

• Make sure that all hoses are clean and free of cracks.

• Ensure that appropriate filters and dust bags

are in good condition and changed or emptied

as needed (may be necessary several times per

shift under some circumstances).

• Check the entire system daily for signs of poor

dust capture or dust leaks.

• Use high-efficiency (HEPA) filters for maximum

dust control.

• Erect baffles on either side of the saw to

improve dust capture by rear-mounted dust

collection devices (exterior hoods).

• Review manufacturers’ operating specifications

and recommendations for your equipment.

Work Practice Controls to Enhance Vacuum

Effectiveness. Studies have shown that the effectiveness of VDC systems is enhanced by the use of

proper work practices (NIOSH, 1999; Croteau et al.,

2002). However, use of these work techniques without a dust collection system will not substantially

reduce dust exposures.

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With any type of vacuum system, employee protection from respirable dust is only as good as the filter in the vacuum. The less efficient the filter, the more

respirable dust will pass through with the vacuum

exhaust air. Locating the vacuum as far from employees as possible is one way to help limit exposure.

For optimal dust collection, the following measures are recommended:

• Keep the vacuum hose clear and free of debris,

kinks and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the dust collector and vacuum hoses.

• On vacuums with manual back-pulse filter cleaning systems, activate the system frequently (several times per day). Empty collection bags and

vacuums as frequently as necessary. Dispose of

collected dust in a way that prevents it from

becoming resuspended in the air.

• For best results, set up a regular schedule for filter cleaning and maintenance. For example,

institute a rule to clean the filter or change the

bag at each break. This will prevent pressure

loss and ensure that exhaust airflow stays constant on the VDC system.

• Remember, the absence of visible dust does not

necessarily mean that employees are adequately

protected from silica exposure.

Ventilation Booths

A booth (with fan) erected around a saw can help

reduce dust, but may require some experimentation.8 For example, one employer built a plywood

booth around the saw and installed a large

exhaust fan at the rear wall to pull dust away

from the employee, who operated the saw

through an opening in the front of the booth.9

Initial air sampling results indicated that the operators’ exposures to silica while cutting brick were

between 0.07 and 0.1 mg/m3. By modifying the

booth interior to better capture the plume of dust

released by the saw, the employer was able to

reduce exposures further, to 0.02 mg/m3 during

the period evaluated (OSHA Case Files).10

Tips for Designing an Effective Booth3

• Minimize the size of the operator opening to

reduce the chance of dust escaping into the

operator’s breathing area.

• Use a fan large enough to provide an average

of 250 feet per minute air velocity across the

face of the operator opening.

• Do not let the saw blade protrude beyond the

open face of the booth.

• Build a trapdoor into the lower back of the

booth to access the interior for cleaning and to

remove debris.

• Always position the booth so that the exhaust

fan does not blow dusty air on other employees. When possible, have the booth exhaust

downwind.

Fans

Fans are not effective dust control devices when

used as the sole control method and should not be

used as the primary method for managing dust.11

Fans can, however, be useful as a supplement to

other control methods. Use fans in enclosed areas,

such as bathrooms, where dust would build up due

to poor air circulation.

For the best effect, set an exhaust fan (the bigger,

the better) in an open window or external doorway.

Position the saw nearby, so that the fan captures

dust and blows it outside. Avoid positioning

employees between the saw and the fan. Also,

avoid positioning employees near the exhausted

air. An exhaust fan works best if a second window

or door across the room is open to allow fresh air

to enter.

Considerations

While dust control using vacuum dust collection

may be an attractive option in some circumstances,

it is not as effective as wet cutting for controlling

respirable dust. Respiratory protection may still be

needed to reduce employee exposures to levels of 0.1

mg/m3 or less when using vacuum dust collection.

Provide employees with respiratory protection

until air sampling indicates that their exposure is

adequately controlled.

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed

spaces. Cleaning should be performed with a

HEPA-filtered vacuum or by wet methods.

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Occupational Safety and

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Respiratory Protection and Engineering

Control Evaluation

Using a stationary saw without engineering controls can cause exposure to respirable silica to

reach 2.0 mg/m3 or higher. Therefore, it is important to utilize effective controls to reduce employee

exposures. Wet methods present the best choice

for suppressing dust while cutting with stationary

saws. Studies indicate that effective wet methods

can reduce exposures below 0.05 mg/m3, as an 8-

hour TWA. Stationary saws can be purchased with

water-fed equipment, or existing saws can be retrofitted with water-fed attachments. Respiratory protection should not be necessary when using effective wet methods.

In situations where wet methods may not be

appropriate or feasible, vacuum dust collection may

be an alternative control option. However, data indicate that vacuum dust collection alone can only

reduce exposures to 0.4 mg/m3

. Therefore, to supplement this control option, employees need to

wear a properly fitted, NIOSH-approved half-facepiece or disposable respirator equipped with an N-,

R-, or P-95 filter. A half-facepiece or disposable respirator can be used for exposures up to 1.0 mg/m3

.

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer,

the employer must establish and implement a written respiratory protection program with worksitespecific procedures and elements, including the

selection of respirators, medical evaluations of

employees, fit testing, proper usage, maintenance

and care, cleaning and disinfecting, proper air quality/quantity and training (see 29 CFR 1926.103).

Other employees in close proximity to the work

operations where silica dust is generated may also

need respiratory protection if effective controls are

not implemented. The level of respiratory protection is dependent on the employee’s silica exposure, which varies depending on factors in the work

environment (such as enclosed, semi-enclosed, or

open spaces and/or multiple operations generating

silica dust), environmental conditions (such as wind

direction and speed), and the percentage of silica

found in the material.

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important and

necessary to utilize effective controls (such as wet

methods and/or vacuum dust collection) in order to

minimize total exposures to silica-exposed tool

operators or potential exposures to other employees.

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine

proper respiratory protection, visit OSHA’s Web site

at www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2007. Industrial Ventilation, A Manual of

Recommended Practice, 26th Edition. American

Conference of Governmental Industrial Hygienists,

Cincinnati, OH.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Croteau, G.A. 2000. The effect of local exhaust ventilation controls on dust exposures during masonry

activities. MS Thesis. University of Washington. June,

2000.

Croteau, G.A. Guffey, S.E., Flanagan, M.E. and

Seixas NS. 2002. The effect of local exhaust ventilation controls on dust exposures during concrete

cutting and grinding activities. Am Ind Hygiene

Assn J. 63:458-467. July/August.

ERG. 2000. Site visit report - Masonry Training

Facility A. Eastern Research Group, Inc., Arlington,

VA. September, 2000.

Heitbrink, W.A. and Watkins, D.S. 2001. The effect

of exhaust flow rate upon the respirable dust emissions for tuckpointing operations. In: In-Depth

Study Report: Control Technology for Crystalline

Silica Exposures in Construction. U.S. Department

of Health and Human Services, Centers for Disease

Control and Prevention, National Institute for

Occupational Safety and Health. ECTB No. 247-18.

Heitbrink, W. and Collingwood, S. 2005. Protecting

Tuckpointing Workers from Silica Dust: Draft

Recommendations for Ventilated Grinder. The

Center to Protect Workers’ Rights (CPWR).

www.cpwr.com

Lofgren, D.J. 1993. Silica exposure for concrete

workers and masons. Appl Occup Environ Hygiene

8(10):832-836. October, 1993.

NIOSH. 1996. Preventing Silicosis and Deaths in

Construction Workers. Publication No. 96-112.

National Institute for Occupational Safety and Health.

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 1 1
NIOSH. 1999a. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 16 - Wet Cutting of Concrete Masonry

Units, File No. ECTB 233-116c. National Institute for

Occupational Safety and Health, Cincinnati, OH.

October, 1999.

NIOSH. 1999b. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 18 - Cutting Brick and Concrete Masonry

Units. ECTB 233-118c. National Institute for

Occupational Safety and Health, Cincinnati, OH.

November, 1999.

NIOSH. 2002. Pocket guide to chemical hazards. Pub.

No. 2002-140. National Institute for Occupational

Safety and Health, Cincinnati, OH. June, 2002.

OSHA. 1996. Ground-fault protection on construction

sites. Occupational Safety and Health Administration,

Office of Training and Education. May, 1996.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Shields, C. 2000. Database: Silica dust exposures

associated with construction activities (version date:

September 14, 2000). Occupational Safety and

Health Administration, North Aurora Office, IL.

Technical Notes

1 Laboratories have not used particle counting for

crystalline silica analysis for many years. Exposure

data is now reported gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using the

general industry PEL (0.1 mg/m3 of respirable quartz

as an 8-hour time-weighted average) as a benchmark to describe the effectiveness of control measures. The benchmark is approximately equivalent to

the general industry silica PEL. Other organizations

suggest more stringent levels. For example, the

National Institute for Occupational Safety and

Health (NIOSH) recommends that respirable crystalline silica exposures be limited to 0.05 mg/m3 as

a 10-hour time-weighted average (NIOSH, 2002).

The American Conference of Governmental

Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures be limited to

0.025 mg/m3 as an 8-hour time-weighted average

(ACGIH, 2008).

2 Some employers use a hose connected to an

external water source to provide a continuous flow

of fresh water in place of recirculated water. This

eliminates the need for pumps and filters, but

requires substantially more water and produces

more runoff.

3 Nine results contained in NIOSH, 1999a and

1999b; Shields, 2000; ERG, 2000; and OSHA Case

Files. The one exception was a result of 0.1 mg/m3.

4 The respirable silica concentration in the employee’s breathing zone during the period monitored

was 2.8 mg/m3.

5 Two results associated with exceptionally short

sampling periods (a 56-minute result of 7.5 mg/m3

and a 2-minute result of 3.1 mg/m3) were excluded

from this average, but included in the subsequent

text on periods of intensive cutting.

6 Some saws come set up for both water-feed and

vacuum dust collection for better employee protection in all situations.

7 For the system tested by Croteau et al. (2002), an

airflow of 70 cubic feet per minute (CFM) through

the vacuum controlled respirable dust better than

30 CFM. ACGIH (2007) recommends a still higher

airflow of 25 CFM per inch of blade diameter

(equivalent to 236 CFM for the saw tested). Low airflow can cause ducts to clog. For abrasive wheel

saws with vacuum dust collection, ACGIH recommends a minimum airflow velocity of 4,000 feet per

minute (FPM) through ducts to prevent dust from

settling. For a typical 2-inch diameter vacuum hose,

75 to 90 CFM will achieve that duct velocity. Larger

hoses are acceptable for larger vacuums that draw

more CFM of air. For example, 350 CFM of airflow

would create the recommended air velocity in a 4-

inch duct.

8 With careful experimentation, it is possible to construct a booth that controls exposures to levels

below OSHA’s limits. First, make adjustments to

control visible dust escaping from the front of the

booth. Then, conduct air sampling (preferably

under a variety of cutting conditions) to confirm

that the booth will also protect the operator from

respirable sized particles.

9 Booth dimensions were approximately 6 feet by

6.5 feet by 3.5 feet, with a 36-inch fan. Air moved

through the open face of the booth at an average

velocity of 250 feet per minute (FPM), consistent

with ACGIH’s recommendation for abrasive cut-off

saw booths.

10 Sampling periods at this site were of 318 to 462

minutes duration.

1 2

Occupational Safety and

Health Administration
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 1 3

Handheld Masonry Saws

This section covers gas-, air-, electric- and

hydraulic-powered handheld masonry saws.

The term “silica” used in this document refers

to respirable crystalline silica.

Employee operating a handheld masonry saw without

the use of appropriate dust controls. (Photo courtesy of

OSHA.)

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees produce dusts containing

silica when they cut, grind, crush, or drill construction materials such as concrete, masonry, tile and

rock. The small particles easily become suspended

in the air and, when inhaled, penetrate deep into

employees’ lungs.

Studies show that using a handheld masonry

saw to cut bricks, concrete blocks and similar materials can result in hazardous levels of airborne silica

if measures are not taken to reduce dust emissions.

Operating a handheld masonry saw outdoors

without dust controls can produce silica exposures

as high as 14 times the Occupational Safety and

Health Administration’s (OSHA) benchmark of 0.1

mg/m3 (milligrams per cubic meter of air) as an 8-

hour time-weighted average (TWA), an exposure

approximately equivalent to OSHA’s general industry permissible exposure limit (PEL) for construction

(OSHA Case Files).1 Short-term exposures or exposures from operating saws indoors can be significantly higher (up to 10 mg/m3

).

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne

respirable dust present that is not visible to the

naked eye.

This section describes methods available to

reduce employees’ exposures to silica when using

handheld masonry saws. Walk-behind saws are

addressed in a separate section for walk-behind surface preparation tools. OSHA encourages you to

use this information to evaluate or improve system

performance to reduce dust emissions. Technical

notes are found at the end of this section and are

referenced throughout the text.

Two main methods exist to control silica dust

while operating a handheld masonry saw: (1) wet

cutting and (2) vacuum dust collection.

Wet cutting, when used properly, is an effective

way to reduce employee exposures to silica dust and

in most cases maintains exposures below the allowable limit. Vacuum dust collection can significantly

reduce silica levels, but may not reliably keep them

below 0.1 mg/m3 as an 8-hour TWA.

When applying water to the blade, exposures of handheld saw operators to silica are considerably reduced.

(Photo courtesy of OSHA.)
1 4

Occupational Safety and

Health Administration

Silica Dust Control Measures

Wet Cutting

Water-fed handheld saws that are gasoline-powered, air-powered, electric-powered and hydraulicpowered are commercially available (Stihl, 2001;

Diamond Products, 2001; Partner Industrial Products,

2001). Water can be supplied to the saws either with

a pressurized portable water supply or with a constant water source, for example, a hose connected

to a municipal water supply.

Wet cutting is the most effective method for controlling silica dust generated during sawing because

it controls the exposure at its source. Dust that is

wet is less able to become or remain airborne. The

effectiveness of both a pressurized portable water

supply and a constant water supply was evaluated

by Thorpe et al. (1999). They found that respirable

dust levels were reduced by up to 94 percent for

pressurized portable water supply systems and up

to 96 percent for a constant supplying water source.

NIOSH reported that an employee dry cutting on

concrete outdoors was exposed to 1.5 mg/m3 of

silica as an 8-hour TWA (NIOSH, 1999c). A reduction

of 96 percent in respirable dust for this employee

would have resulted in exposure around 0.06 mg/m3

if the employee switched to a wet method.

Maintaining a Water-Feed System

• Check to ensure that hoses are securely connected and not cracked or broken.

• Adjust nozzles to ensure that water is directed

so that the maximum amount reaches the cutting area while still cooling the blade.

• Dispose of water containing silica in a way that

prevents the silica from becoming resuspended

in the air. If the silica is allowed to become airborne, it can contribute to employee exposures.

• Consult the manufacturer for equipment operating specifications and recommendations that

apply to the specific saw model including electrical fault protection, such as a ground-fault circuit interrupter (GFCI).

Maintenance. To minimize dust emissions from

saws equipped for wet cutting, keep hoses and nozzles in excellent operating condition. Regular saw

maintenance reduces silica exposures and ensures

optimal operation of the equipment. Saws and dust

control devices should be on a routine maintenance

schedule.

FreezingTemperatures. Freezing temperatures

complicate the use of water.2 Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Large portable

heating units are commonly used to heat commercial and sometimes road and highway projects.

Drain the system when not in use. If water freezes

on the ground, chip away the ice or use deicing

compounds or sand to control the slipping hazard.

Electrical Safety. Use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical

connectors for electric tools and equipment on construction sites (OSHA, 1996). These features are particularly important to employee safety in wet or

damp areas, such as where water is used to control

dust. Although an assured equipment grounding

conductor program is an acceptable alternative to

GFCIs, OSHA recommends that employers use

GFCIs where possible because they provide better

protection for employees. (See 29 CFR 1926.404(b)(1)

for OSHA’s ground-fault protection requirements.)

Vacuum Dust Collection Systems

Handheld saws can also be equipped with vacuum

dust collection (VDC) systems. Saws equipped with

VDC systems can be effective in controlling respirable silica exposure. One study by Thorpe et al.

(1999) found that a VDC system on the handheld

saw reduced mean respirable concrete dust concentrations from 8 mg/m3 to 0.7 mg/m3

. This represents

an 88 percent reduction in respirable concrete dust.

However, this study used a dust collection device

(exterior hood) that may not be commercially available.

Other studies have shown that handheld VDCequipped saws do not offer a reliable reduction in

exposure to dust. Two studies, Croteau (2000) and

Croteau et al. (2002), tested a handheld saw

equipped with a VDC system exhausting at 70 cubic

feet per minute (CFM). Unfortunately, this system

did not reduce respirable silica exposure. The studies concluded that the shape of the opening on the

dust collection device was not effective in capturing

the dust being emitted from the rotating blade. In

some cases, handheld saw and VDC system combinations might require the rotation of the blade to be

reversed to optimize dust collection (USF Surface

Preparation Group, 2002). However, such modifications generally must be performed by the manufacturer.

NIOSH obtained 8-hour TWA respirable silica

results between 0.117 and 0.388 mg/m3 for six

employees at two separate construction sites

(NIOSH, 1999a; NIOSH, 1999b). The employees used

no dust controls on this worksite. However, they

worked outdoors and used the handheld saw intermittently. The rest of the time on the worksite was

spent on activities that did not generate respirable
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 1 5

crystalline silica. If the handheld saw that was used

intermittently had been equipped with a VDC system, dust levels could have been reduced 75 percent, resulting in exposures between 0.03 mg/m3

and 0.01 mg/m3.

Although data on VDC-equipped handheld saws

used indoors were not available, one measurement

obtained from an employee cutting indoors without

a VDC system yielded a silica exposure of 10.3

mg/m3. The employee was a plumber cutting concrete floors around drains in a 16-story building.

Even if the employee achieved an 88 percent reduction in dust exposure using the VDC system

described by Thorpe et al. (1999), exposure still

would have exceeded 1.0 mg/m3.

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed spaces.

Cleaning should be performed with a HEPAfiltered vacuum or by wet methods.

Recommendations for Vacuum Dust Collection

Systems. The American Conference of Governmental

Industrial Hygienists (ACGIH) recommends airflow

of 25 CFM per inch of blade diameter. If airflow is

too low, the hose may clog with particulate matter.

A study by Croteau et al. (2002), which tested an

abrasive wheel saw, found a 2-inch diameter vacuum hose and a flow rate of 75 to 90 CFM achieved

an air velocity of 4,000 feet per minute (FPM).

Achieving this air velocity prevented particulate

matter from settling in the hose. If the VDC provides

a higher flow rate, then it is acceptable to use a larger hose.

VDC systems can be purchased as a kit. These

kits should include a dust collector (exterior hood),

vacuum, vacuum hose and filter(s). The components of a VDC system are discussed below.

• Dust collector (exterior hood): In most cases,

this is a retrofit on the saw; therefore, be sure to

follow the manufacturer’s instructions when

installing the device.

• Vacuum: Choose a vacuum with the appropriate

power and capacity for your job.

• Vacuum hose: A flow rate of 80 CFM is best

maintained with a 11⁄2- to 2-inch diameter hose. If

the diameter is larger, the airflow velocity of the

vacuum will be reduced. If the diameter is smaller, airflow resistance will be higher. Airflow

resistance also increases with hose length;

excessively long hoses should be avoided. Many

HEPA-filtered vacuum system kits include a variety of hose sizes for different tool applications.

• Filters: Double filtration is important. The use of

a high-efficiency particulate air (HEPA) filter is

critical to prevent the escape of respirable silica

dust from the vacuum exhaust. HEPA filters are

at least 99.97 percent efficient in removing fine

dust particles from the air. A prefilter or cyclonic

separator in addition to a HEPA filter will improve

vacuum efficiency and extend the service life of

the more costly HEPA filter. A cyclonic separator

removes large particles that are capable of overloading or clogging the filter. (Heitbrink and

Collingwood, 2005).3

• Systematic cleaning: Choose a vacuum equipped

with a back-pulse filter cleaning cycle. Such

auto-cleaning mechanisms will reduce the time

required for vacuum maintenance and improve

the overall efficiency of the dust collection system. If the vacuum does not have an auto-cleaning mechanism, the employee can periodically

turn the vacuum cleaner on and off. This allows

the bag to collapse and causes the prefilter cake

to dislodge from the filter.

• Monitoring VDC efficiency: Purchasing a dust

collection system equipped with a static pressure

gauge allows the employee to monitor the system’s efficiency. Systems lacking a static pressure gauge can be monitored visually. If a dust

plume increases and becomes more visible

where the dust collector (exterior hood) meets

the working surface, the system is not working

efficiently. When relying on this technique to

monitor the efficiency of the dust collection

system, try to locate the vacuum as far away

from adjacent employees as possible to help

limit their exposure to silica (Heitbrink and

Collingwood, 2005).

Work Practice Controls to Enhance Vacuum

Effectiveness. Studies have shown that the effectiveness of vacuum dust collection systems is

enhanced by the use of proper work practices

(NIOSH, 1999a; NIOSH, 1999b; NIOSH 1999c;

Croteau et al., 2002). However, use of these work

techniques without a dust collection system will not

substantially reduce dust exposures.

With any type of vacuum system, employee protection from respirable dust is only as good as the filter in the vacuum. The less efficient the filter, the more

respirable dust will pass through with the vacuum
1 6

Occupational Safety and

Health Administration

exhaust air. Locating the vacuum as far from employees as possible is one way to help limit exposure.

For optimal dust collection, the following measures are recommended:

• Keep the vacuum hose clear and free of debris,

kinks and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the dust collector (exterior hood) and

vacuum hoses.

• On vacuums with back-pulse filter cleaning systems, activate the system frequently (several

times per day). Empty collection bags and vacuums as frequently as necessary. Dispose of collected dust in a way that prevents it from becoming resuspended in the air.

• For best results, set up a regular schedule for filter cleaning and maintenance. For example,

institute a rule to clean the filter or change the

bag at each break. This will prevent pressure loss

and ensure that exhaust airflow stays constant

on the VDC system.

• Remember, the absence of visible dust does not

necessarily mean that employees are adequately

protected from silica exposure.

Fans

Fans are not effective dust control devices when

used as the sole control method and should not be

used as the primary method for managing dust.

Fans can, however, be useful as a supplement to

other control methods. Use fans in enclosed areas,

such as bathrooms, where dust may build up due to

poor air circulation.

For the best effect, set an exhaust fan (the bigger,

the better) in an open window or external doorway.

Position the saw nearby, so that the fan captures dust

and blows it outside. Avoid positioning employees

between the saw and the fan. Also, avoid positioning

employees near the exhausted air. An exhaust fan

works best if a second window or door across the

room is opened to allow fresh air to enter.

Considerations

While dust control using VDC may be an attractive

option in some circumstances, it is not as effective

as wet cutting for controlling respirable dust. Respiratory protection may still be needed to reduce

employee exposures below 0.1 mg/m3 as an 8-hour

TWA when using VDC.

Provide employees with respiratory protection

until air sampling demonstrates that their exposure

is adequately controlled.

Respiratory Protection and Engineering

Control Evaluation

Using a handheld saw without engineering controls

can cause exposures to respirable crystalline silica

to reach 1.5 mg/m3 during outdoor operations, with

indoor exposures being significantly higher (up to

10 mg/m3). Therefore, effective controls are needed

to reduce employee exposures below 0.1 mg/m3 as

an 8-hour TWA.

Effective wet methods provide the most reliable control for silica dust and are invaluable in

keeping silica levels below 0.1 mg/m3 as an 8-

hour TWA. Most handheld saws are manufactured

with water-fed equipment. Employees who use

saws that do not include water-fed equipment

should apply water directly to the cutting point.

Water should be applied at a minimum rate of

0.13 gallons per minute to ensure adequate dust

suppression outdoors. When effective wet methods are used outdoors, it is unlikely that supplemental respiratory protection will be needed

(Thorpe et al., 1999).

The use of wet methods during indoor operations can reduce silica exposures, but may not

reduce exposures below 0.1 mg/m3

. However,

when wet methods are used, exposures will not

likely exceed 1.0 mg/m3. When wet methods cannot reduce exposures below 0.1 mg/m3

, employees should supplement them with a NIOSHapproved half-facepiece or disposable respirator

equipped with an N-, R-, or P-95 filter.

In situations where wet methods may not be

appropriate or feasible, VDC systems may be an

alternative control option. Current data suggest

that the reduction in silica offered by VDC systems

is variable. For outdoor operations, using effective

VDC may reduce exposures below 1.0 mg/m3, but

not necessarily below 0.1 mg/m3. Therefore,

employees may need to wear a properly fitted,

NIOSH-approved half-facepiece or a disposable

respirator equipped with an N-, R- or P-95 filter

(see 29 CFR 1926.103).

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer, the employer must establish and implement a

written respiratory protection program with worksite-specific procedures and elements. These should

include the selection of respirators, medical evaluations of employees, fit testing, proper usage,

maintenance and care, cleaning and disinfecting,

proper air quality/quantity and training (see 29

CFR 1926.103).

Exposure control data are limited regarding the

use of a VDC system during indoor sawing opera-
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 1 7

Diamond Products. 2001. SpeediCut cut-off saws.

http://diamondproducts.com. Accessed

September 8, 2008.

Heitbrink, W.A. and Watkins, D.S. 2001. The effect

of exhaust flow rate upon the respirable dust

emissions for tuckpointing operations. In: InDepth Study Report: Control Technology for

Crystalline Silica Exposures in Construction. U.S.

Department of Health and Human Services,

Centers for Disease Control and Prevention,

National Institute for Occupational Safety and

Health. ECTB No. 247-18.

Heitbrink, W. and Collingwood, S. 2005. Protecting

Tuckpointing Workers from Silica Dust: Draft

Recommendations for Ventilated Grinder. The

Center to Protect Workers’ Rights (CPWR).

www.cpwr.com

NIOSH. 1995. Environmental surveillance report:

Concrete Coring, Inc., Enon, OH. U.S. Department

of Health and Human Services, Public Health

Service, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health, Division of Respiratory Disease

Studies, Morgantown, WV.

NIOSH. 1996. Alert: request for assistance in preventing silicosis and deaths in construction workers. DHHS (NIOSH) Publication No. 96-112. U.S.

Department of Health and Human Services, Public

Health Service, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health, Division of Physical Sciences

and Engineering, Cincinnati, OH.

NIOSH. 1999a. Control technology and exposure

assessment for occupational exposure to crystalline silica: Case 17 - dry cutting of concrete

masonry units. U.S. Department of Health and

Human Services, Public Health Service, Centers

for Disease Control and Prevention, National

Institute for Occupational Safety and Health,

Division of Physical Sciences and Engineering,

Cincinnati, OH. ECTB 233-117c.

NIOSH. 1999b. Control technology and exposure

assessment for occupational exposure to crystalline silica: Case 18 - cutting brick and concrete

masonry units. U.S. Department of Health and

Human Services, Public Health Service, Centers

for Disease Control and Prevention, National

Institute for Occupational Safety and Health,

Division of Physical Sciences and Engineering,

Cincinnati, OH. ECTB 233-118c.

NIOSH. 1999c. Control technology and exposure

assessment for occupational exposure to crystions. A handheld saw equipped with a VDC system cannot be relied upon solely to reduce exposures below 0.1 mg/m3

; therefore, employees may

need to wear a full-facepiece respirator equipped

with an N-, R-, or P-95 filter (see 29 CFR 1926.103).

Other employees in close proximity to the

work operations where silica dust is generated

may also need respiratory protection if effective

controls are not implemented. The level of respiratory protection is dependent on the employee’s

silica exposure, which varies depending on factors in the work environment (such as enclosed,

semi-enclosed, or open spaces and/or multiple

operations generating silica dust), environmental

conditions (such as wind direction and speed)

and the percentage of silica found in the material.

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important

and necessary to utilize effective controls (such as

wet-methods and/or vacuum dust collection) in

order to minimize total exposures to silicaexposed tool operators or potential exposures to

other employees.

Employers should conduct exposure monitoring periodically while controls are being used to

ensure that the controls are working properly and

that the appropriate level of respiratory protection

is being used.

For more information on how to determine

proper respiratory protection, visit OSHA’s Web

site at www.osha.gov. NIOSH’s Web site also provides information on respirators at

www.cdc.gov/niosh.

References

ACGIH. 2001. Industrial Ventilation, A Manual of

Recommended Practice, 24th Edition. American

Conference of Governmental Industrial

Hygienists, Cincinnati, OH.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Croteau, G.A. 2000. The effect of local exhaust

ventilation controls on dust exposures during

masonry activities. MS Thesis. University of

Washington. June, 2000.

Croteau, G.A., Guffey, S.E., Flanagan, M.E. and

Seixas, N.S. 2002. The effect of local exhaust ventilation controls on dust exposures during concrete cutting and grinding activities. Am Ind

Hygiene Assn J 63:458-467. July/August, 2002.
Technical Notes

1 Laboratories have not used particle counting for

crystalline silica analysis for many years. Exposure

data is now reported gravimetrically. However,

OSHA’s construction PEL for crystalline silica,

established in 1971, is still listed as a particle-count

value. (See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using 0.1

mg/m3 of respirable quartz as an 8-hour timeweighted average as a benchmark to describe the

effectiveness of control measures. The benchmark

is approximately equivalent to the general industry

silica PEL. Other organizations suggest lower levels.

For example, the National Institute for Occupational

Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be limited to 0.05

mg/m3 as a 10-hour time-weighted average (NIOSH,

2002). The American Conference of Governmental

Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures be limited to

0.025 mg/m3 as an 8-hour time-weighted average

(ACGIH, 2008).

2 Some saws come set up for both water-feed and

vacuum dust collection for better employee protection in all situations.

3 For the system tested by Croteau et al. (2002), an

airflow of 90 cubic feet per minute (CFM) through

the vacuum controlled respirable dust better than

70 CFM. ACGIH (2001) recommends a still higher

airflow of 25 CFM per inch of blade diameter

(equivalent to 236 CFM for the saw tested). Low airflow can cause ducts to clog. For abrasive wheel

saws with vacuum dust collection, ACGIH recommends a minimum airflow velocity of 4,000 feet per

minute (FPM) through ducts to prevent dust from

settling. For a typical 2-inch diameter vacuum hose,

75 to 90 CFM will achieve that duct velocity. Larger

hoses are acceptable for larger vacuums that draw

more CFM of air. For example, 350 CFM of airflow

would create the recommended air velocity in a 4-

inch duct.

talline silica: Case 21 - non-residential construction. U.S. Department of Health and Human

Services, Public Health Service, Centers for

Disease Control and Prevention, National Institute

for Occupational Safety and Health, Division of

Physical Sciences and Engineering, Cincinnati,

OH. ECTB 233-121c.

NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June, 2002.

OSHA. 1996. Ground-fault protection on construction sites. Occupational Safety and Health

Administration, Office of Training and Education.

May, 1996.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Partner Industrial Products. 2001. The Partner wet

cutting system. http://www.partnerusa.com.

Accessed September 8, 2008.

Shields, C. 2000. Database: Silica dust exposures

associated with construction activities (version

date: September 14, 2000). Occupational Safety

and Health Administration, North Aurora Office,

IL.

Stihl. 2001. Cutquick® cut-off machine accessories. http://www.stihlusa.com. Accessed

September 8, 2008.

Thorpe, A., Ritchie, A.S., Gibson, M.J. and Brown,

R.C. 1999. Measurements of the effectiveness of

dust control on cut-off saws used in the construction industry. Annals of Occup Hygiene 43 (7)

1443-1456. July, 1999.

Trakumas, S., Willeke, K., Reponen, T., Grinshpun,

S.A. and Freidman, W. 2001. Comparison of filter

bag, cyclonic, and wet dust collection methods in

vacuum cleaners. Am Ind Hygiene Assn J 62:573-

583.

USF Surface Preparation Group. 2000b. Sawtec

JS-90. www.surfacepreparation.com Accessed

September 8, 2008.

USF Surface Preparation Group. 2002. Personal

communication between USF and Laura Lewis of

ERG, Inc. January 28, 2002.

Zalk, D. 2000. Exposure assessment strategy for

the reduction of airborne silica during jackhammering activities. Presentation. American

Industrial Hygiene Conference and Exposition,

Orlando, FL. May 20-25, 2000.

1 8

Occupational Safety and

Health Administration
Using a grinder in poorly controlled conditions. (Photo

courtesy of OSHA Directorate of Construction.)

Adjustments in work methods and equipment,

when possible, can lower exposure levels. For

example, the use of jigs to increase the distance

between the employee and the point of work can

reduce exposure levels. Modifications in construction work methods for pouring, casting, finishing

and installing concrete can reduce the amount of

grinding required, which, in turn, can lower exposures.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne respirable dust present that is not visible

to the naked eye.

Silica Dust Control Measures

Vacuum Dust Collection Systems

Vacuum dust collection (VDC) systems for grinders

include a shroud, which surrounds the grinding

wheel, hose, filters and a vacuum to pull air

through the shroud. Many manufacturers offer

grinders with dust collection options. Employers

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 1 9

Hand-Operated Grinders

This section covers electric- and pneumatichand-operated grinders used for surface finishing and cutting slots. Angle grinders used for

tuckpointing are addressed in a separate section.

The term “silica” used in this document refers to

respirable crystalline silica.

Introduction

Employees produce dusts containing silica when

they grind on concrete and similar materials. The

grinders’ abrasive action generates fine particles

that easily become suspended in the air and,

when inhaled, penetrate deep into employees’

lungs. Exposure to fine particles of silica has been

shown to cause silicosis, a serious and sometimes fatal lung disease. Construction employees

who inhale fine particles of silica may be at risk of

developing this disease This section discusses the

methods available to reduce employee exposures

to silica during grinding activities.

Data compiled by the Occupational Safety and

Health Administration (OSHA) indicate that,

among employees who grind concrete, most are

exposed to silica at levels that exceed OSHA’s

benchmark of 0.1 mg/m3 (milligrams of silica per

cubic meter of air) as an 8-hour time-weighted

average (TWA), an exposure approximately equivalent to OSHA’s general industry permissible

exposure limit (PEL).1 In fact, on average, grinder

operators’ silica exposures (along with those of

tuckpointers) are among the highest in the construction industry.2 More than half of all grinder

operators experience silica exposures above 0.2

mg/m3 (milligrams per cubic meter of air).3 During

periods of intensive grinding, concrete finishers’

exposures can exceed 1.2 mg/m3 outdoors and

4.5 mg/m3 indoors (Lofgren, 1993; OSHA Case

Files).4

Vacuum dust collection systems are used to

reduce silica dust during concrete grinding operations. Vacuum methods can significantly reduce

dust emissions, but thus far have not been shown

to reliably keep silica levels below 0.1 mg/m3 as

an 8-hour time-weighted average (TWA).

Wet grinding is highly effective in reducing

silica exposures. Handheld water-fed grinding

equipment is commercially available for concrete

applications, granite grinding, and polishing operations. Conventional grinding equipment can be

retrofitted to add a water-feed capability.5
may also purchase equipment to retrofit grinders

for vacuum dust collection. The effectiveness of

vacuum systems depends on several factors,

including the user’s technique, the surfaces being

finished, and the efficiency of the dust collection

system.

The addition of the shroud and vacuum hose

may make it more difficult to work effectively while

reaching overhead.

Recommendations for Vacuum Dust Collection

Systems. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends

airflow of 25 cubic feet per minute (CFM) per inch

of blade diameter (for example, a 4-inch grinder

would need a vacuum with airflow of 100 CFM). If

airflow is too low, the hose may clog with particulate matter. However, employers should be aware

that rated airflows provided by manufacturers may

be different from actual airflow once attached to the

tool. A study by Croteau et al. (2002), which tested

an abrasive wheel saw, found a 2-inch diameter

vacuum hose and a flow rate of 75 CFM achieved

an air velocity of 4,000 feet per minute (FPM).

Achieving this air velocity prevented particulate

matter from settling in the hose.

VDC systems can be purchased as a kit. These

kits should include a grinder shroud (exterior hood),

vacuum, vacuum hose, and filter(s). The components of a VDC system are discussed below.

• Grinder shroud (exterior hood): Employees

should use a shroud appropriate for the grinder

and wheel size.

• Vacuum: Choose a vacuum with the appropriate

power and capacity for your job. Croteau et al.

(2002) found a flow rate greater than 70 CFM to

be effective.

• Vacuum hose: A 11⁄2- to 2-inch diameter hose is

usually best for smaller vacuums. If the diameter

is larger, the airflow velocity of the vacuum will

be reduced. If the diameter is smaller, airflow

resistance will be higher. Airflow resistance also

increases with hose length; excessively long

hoses should be avoided.

• Filters: Double filtration is important. The use of

a high-efficiency particulate air (HEPA) filter is

critical to prevent the escape of respirable silica

dust from the vacuum exhaust. HEPA filters are

at least 99.97 percent efficient in removing fine

dust particles from the air. A prefilter or cyclonic

separator in addition to a HEPA filter will improve

vacuum efficiency and extend the service life of

the more costly HEPA filter. A cyclonic separator

removes large particles that are capable of overloading or clogging the filter (Heitbrink and

Collingwood, 2005).

• Systematic cleaning: Regular cleaning of the filter is critical to maintaining high airflow. Choose

a vacuum equipped with a back-pulse filter

cleaning cycle. Such auto-cleaning mechanisms

will reduce the time required for vacuum maintenance and improve the overall efficiency of the

dust collection system. If the vacuum does not

have an auto-cleaning mechanism, the employee can periodically turn the vacuum cleaner on

and off. This allows the bag to collapse and

causes the prefilter cake to dislodge from the filter.

• Monitoring VDC efficiency: Purchasing a dust

collection system equipped with a static pressure gauge allows the employee to monitor the

system’s efficiency. Systems lacking a static

pressure gauge can be monitored visually. If a

dust plume increases and becomes more visible

where the shroud meets the working surface,

the system is not working efficiently. When relying on this technique to monitor the efficiency of

the dust collection system, try to locate the vacuum as far away from adjacent employees as

possible to help limit their exposure to silica

(Heitbrink and Collingwood, 2005).

System Maintenance. For optimal dust collection, the following measures are recommended:

• Keep the vacuum hose clear and free of debris,

kinks and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the shroud and ducts.

• On vacuums with back-pulse filter cleaning systems, activate the system frequently (several

times per day). Empty collection bags and vacuums as frequently as necessary. Dispose of collected dust in a way that prevents it from

becoming resuspended in the air.

• For best results, set up a regular schedule for filter cleaning and maintenance. For example,

institute a rule to clean the filter or change the

bag at each break. This will prevent pressure

loss and ensure that exhaust airflow stays constant on the VDC system.

• Remember, the absence of visible dust does not

necessarily mean that employees are adequately

protected from silica exposure.

2 0

Occupational Safety and

Health Administration
Grinder with attached VDC system. (Photo courtesy of

OSHA Directorate of Construction.)

Fans

Fans are not effective dust control devices when

used as the sole control method and should not

be used as the primary method for managing

dust. Fans can, however, be useful as a supplement to other control methods. Use fans in

enclosed areas, such as bathrooms, where dust

may build up due to poor air circulation.

For the best effect, set an exhaust fan (the bigger, the better) in an open window or external

doorway. Position the grinder nearby, so the fan

captures dust and blows it outside. Avoid positioning employees between the grinder and the

fan. Also, avoid positioning employees near the

exhausted air. An exhaust fan works best if a second window or door across the room is opened

to allow fresh air to enter.

Example: A four-foot square fan is placed in a

window exhausting to outside the building at

maximum fan speed. The fan will have the

strongest capture capability directly in front of the

fan face, but this quickly drops off. At two feet

away from the fan the capture capability is

reduced to 50 percent and at four feet the capture

capability is reduced to 7 percent of the capture

capability at the fan face. If the distance between

the grinding point and fan face is greater than the

length of the fan side (4 feet), dust capture would

probably not be effective (ACGIH, 2001).

Wet Grinding

Water provides excellent dust control during tasks

involving abrasive action on concrete. When applied

at the point where dust is generated, water wets

the dust particles before they can become airborne.

Water-fed equipment is regularly used to control

dust during granite and concrete grinding and polC O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 2 1

ishing operations, as well as during concrete and

masonry cutting with abrasive wheels. The wet

methods consistently keep employee exposures

below OSHA limits (Simcox et al., 1999; NIOSH,

1999). These tools include a nozzle or spout that

provides a stream of water to the grinding wheel.

For example, some equipment provides water

through a hole in a hollow shaft or a nozzle at the

edge of the wheel.

The National Institute for Occupational Safety

and Health (NIOSH) reported that an employee

reduced respirable dust levels by fitting an automatic water feed to a conventional handheld

grinder and exhaust shroud system used for tuckpointing (NIOSH, 2000a). Alternatively, a helper

can apply water by hand using a spray nozzle

(NIOSH, 1998). To be effective, the source must

constantly supply water to the point of operation.

The use of water systems on similar tools used

in the cut stone and stone products manufacturing industry has shown a reduction of exposures

well below 0.1 mg/m3 (NIOSH, 2000d and 2000e;

and OSHA Case Files). It is reasonable to assume

that such reductions can be achieved in the construction industry while using similar tools and

control methods.

Wet methods have advantages, but require

advance planning. The stone processing industry

has shown that water-fed grinders function well

to control dust even on uneven surfaces and near

corners and edges (problem areas for vacuum

dust collection equipment). Employees need

training, however, to become comfortable working with water-fed grinders. A wet surface looks

different from a dry one, and visibility during

grinding may be obscured by water spray and

slurry (OSHA Case Files). Slurry removal also

requires an extra step in the cleaning process (for

example, use of a wet-dry shop vacuum or rinsing the surface).6 Nevertheless, wet methods offer

reliable dust control during grinding.

Some surfaces might require extra cleaning

(for example, with a pressure washer or hose and

brush) after employees use wet methods. Avoid

splashing concrete slurry on vehicles or other

objects with specialty finishes.

Freezing Temperatures. Freezing temperatures

complicate the use of water. Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Large portable

heating units are commonly used to heat commercial and sometimes road and highway projects. Drain the system when not in use. If water

freezes on the ground, chip away the ice or use
deicing compounds or sand to control the slipping hazard.

Electrical Safety. Use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical

connectors for electric tools and equipment on

construction sites (OSHA, 1996). These features

are particularly important to employee safety in

wet or damp areas, such as where water is used

to control dust. Although an assured equipment

grounding conductor program is an acceptable

alternative to GFCIs, OSHA recommends that

employers use GFCIs where possible because

they afford better protection for employees. (See

29 CFR 1926.404(b)(1) for OSHA’s ground-fault

protection requirements.)

Adjustments in Work Methods

Employee Positioning

Where possible, exposures can be reduced if

employees work at a greater distance from the

grinding point. These reductions have been demonstrated for employees grinding on ceilings and for

employees sanding drywall. Dust falls on employees who stand directly below the grinding point. If

the grinder is attached to an adequately supported

pole, the employee can manipulate the grinder at a

distance from one side where the dust is less concentrated. While this method does not eliminate

exposure, it can help reduce the amount of dust in

the employee’s breathing area (NIOSH, 1995; OSHA

Case Files).

Grinding Wheel Size

A study comparing construction employees’ respirable silica exposure at nine construction sites

found that short-term exposure levels were about

30 percent higher for employees operating grinders

with 7-inch wheels than for operators grinding with

4.5-inch wheels. Additionally, diamond wheels used

for rougher, more aggressive grinding were associated with exposure levels approximately 60 percent

higher than those associated with abrasive wheels

used for fine finishing (Flanagan et al., 2003). Therefore, whenever possible, use a smaller rather than a

larger wheel, and use the least aggressive tool that

will do the job.

Construction Work Methods

Where practical, employers can reduce employees’

silica exposures by utilizing construction methods

and techniques that minimize the amount of grinding required. Examples include taking steps to minimize pouring/casting flaws and defects by ensuring

tighter fitting forms, improved finishing, grinding

2 2

Occupational Safety and

Health Administration

on pre-cast panels outdoors before installation inside, or using factory installed chase and grooves

on pre-cast structural concrete (ERG, 2002; OSHA

Case Files). Silica exposures may also be reduced if

grinding is done while the concrete is still “green”

(NIOSH, 2000b, NIOSH, 2000c). Additionally, for a

given amount of material removed from a surface,

less airborne dust will be generated if some of the

material can be removed as larger chips instead of

finely ground particles. An employee might use a

hammer and chisel or power chipping equipment

to remove most of the mass before using a grinder

to smooth the surface.

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled conditions,

and show the effectiveness of controls in reducing

silica exposures.

Case Studies - Silica Exposure Levels

Studies have shown that employees grinding concrete are exposed to potentially harmful levels of

silica unless dust levels are controlled.

Indoors. Case Study I: Among data obtained by

OSHA, grinder operators’ silica exposures exceeded

1.0 mg/m3 during OSHA inspections reported for

indoor construction sites. NIOSH reported an exposure level of 2.8 mg/m3 for a grinder operator finishing the walls, columns and floor inside an opensided parking garage (NIOSH, 2001).

Some of the highest indoor results are associated with overhead work (grinding on ceilings). For

example, OSHA reported exposures of 4.5, 4.5, 5.9,

and 7.3 mg/m3 for four construction employees

grinding slots and smoothing the ceiling of a mostly enclosed building (OSHA Case Files).

Outdoors. Case Study II: Exposures are somewhat

lower outdoors, where dust can disperse more

quickly, but results still indicate potentially harmful

employee exposures. For example, data compiled

by OSHA included results for three construction

employees who primarily performed concrete

grinding during the evaluation. The results indicate

that the employees’ silica exposures ranged from

nearly 0.4 to 1.2 mg/m3 during the air sampling

period. Even when results were averaged over their

full shift, exposures were still 0.15 mg/m3 to 0.3

mg/m3 (Lofgren, 1993; OSHA Case Files).7

Other Employees in the Area. Case Study III: Silica

dust released during uncontrolled grinding can

affect other employees in the area. NIOSH collected

area samples in the center of a room measuring 13
feet by 23 feet, while an employee used a grinder

on the concrete walls. The area samples indicated

that, over the course of a shift, a person (for example, an employee from another trade) could experience a silica exposure level of nearly 0.2 mg/m3 by

simply standing in the center of the room (NIOSH,

1998).8

Fortunately, bystander exposure can generally

be reduced to levels well below OSHA limits by

managing the dust. NIOSH found that when the

grinder operator’s exposure is reduced, bystander

exposure drops as well. At the site mentioned

above, the silica concentration in the middle of the

room fell below the limit of detection when grinder

operator exposures were reduced using either vacuum dust collection or wet-grinding methods

(NIOSH, 1998).

Case Studies - Vacuum Dust Collection

Several case studies provide insights about employees’ silica exposure when VDC systems are

used to control dust emissions. These examples

show that such systems significantly lower levels

of airborne silica, but may not reliably reduce the

grinder operator’s exposures to levels below allowable limits.

Case Study IV: OSHA evaluated employees grinding on outdoor concrete pier structures for about 3

hours during bridge construction. Without controls,

their daily average exposures to silica were 0.16

and 0.30 mg/m3 as 8-hour TWAs.9 OSHA then tested

a shrouded grinder connected to a backpack vacuum with a HEPA filter. The silica exposure dropped

to 0.02 mg/m3 as an 8-hour TWA10 (OSHA Case

Files).

Case Study V: At another construction site, an

employee operated a 7-inch grinder fitted with a

dust collection shroud connected to a drum vacuum. Full-shift air samples collected on two days

indicated a silica exposure level of 0.06 mg/m3 on

the first day and 0.11 mg/m3 on the second day

(OSHA Case Files). Exposure levels typically exceed

these values when dust controls are not used.

Case Study VI: Researchers collected air samples

for five days while one employee used various

grinders fitted with a vacuum dust-collection

shroud. The shroud was connected to a portable

electric vacuum, which included a high-efficiency

filter.11 While the operator performed grinding on

concrete walls inside a parking garage, breathing

area exposure levels ranged from 0.06 to 0.2 mg/m3

(Echt and Sieber, 2002; NIOSH, 2002b).

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 2 3

NIOSH (2001) obtained similar results from

another employee testing various grinders,

shrouds, and vacuums while smoothing concrete at

a parking garage site. The three 6-hour samples

collected on separate days indicated employee

exposure levels of 0.17, 0.18, and 0.26 mg/m3.

12

The results reported in these case studies are

notably lower than the exposure levels typically

associated with uncontrolled concrete grinding.

However, even when using a vacuum dust collection system, grinder operators’ exposures often

exceed 0.1 mg/m3.

Case Studies - Fans

Case Study VII: A fan set up in the doorway of a

small room was not adequate to remove the dust

generated during grinding. No other methods were

used to control dust. As a result, the grinder operator’s exposure to silica was 1.4 mg/m3 during a 2-

hour period. In another indoor space where

employees on a scaffold were grinding on a concrete wall, fans helped keep exposures at around

0.5 mg/m3 for the periods evaluated (1.5 to 4 hours)

(Lofgren, 1993).

Case Studies - Wet Methods

Case Study VIII: The results from two air samples

for a grinder operator and helper showed that

employees had low silica exposure when using

water spray while smoothing concrete walls. The

helper applied a spray of water from a hand-pump

garden sprayer can filled with tap water. The investigators concluded that by constantly spraying the

concrete just ahead of the grinder wheel, the

employees reduced their exposure levels by 90 percent (NIOSH 1998).13

Case Studies - Employee Repositioning

Two studies suggest that employee positioning is

an important determinant of silica exposure levels.

The following examples show a tenfold difference

in exposure recorded for employees using grinders

attached to poles while grinding concrete ceilings at

two (mostly enclosed) building sites. While employee position was a large factor, the type of work and

the silica content of the concrete also accounted for

some of the difference.

Case Study IX: At the first site, two grinder operators smoothed seams in a concrete ceiling using

grinders on long extension jigs. The jigs were supported at an angle on rolling scaffolds. The operators manipulated the grinders from the bottom end
of the jigs and were exposed to silica at levels of

0.184 and 0.415 mg/m3 (OSHA Case Files).14

Case Study X: Four operators at the second site

ground utility slots and smoothed junctions in concrete ceilings, holding the grinders above their

heads on short extensions fabricated from PVC

pipe. The employees’ exposure was exceptionally

high, ranging from 4.5 to 7.2 mg/m3. In this case,

the operators were removing more material (making more dust) and were positioned so that most of

the dust fell directly onto them (OSHA Case Files).15

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed

spaces. Cleaning should be performed with a

HEPA-filtered vacuum or by wet methods.

Respiratory Protection and

Engineering Control Evaluation

Using a hand-operated grinder without engineering

controls can cause exposures to respirable crystalline silica to reach 1.2 mg/m3 or higher while

working outdoors and 4.5 mg/m3 or higher while

working indoors. Effective wet methods are invaluable in keeping silica levels below 0.1 mg/m3 as an

8-hour TWA. When using effective wet methods, it

is unlikely that respiratory protection will be needed.

In situations where wet methods may not be

appropriate or feasible, VDC systems may be an

alternative control option. Current data suggest that

most grinding operations that utilize VDC systems

usually exceed 0.1 mg/m3, but generally do not

exceed 1.0 mg/m3

. Therefore, to supplement the

use of a VDC system, employees should wear a

properly fitted, NIOSH-approved half-facepiece or

disposable respirator equipped with an N-, R- or P95 filter. A half-facepiece or disposable respirator

can be used for protection at silica concentrations

up to 1.0 mg/m3.

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer,

the employer must establish and implement a written respiratory protection program with worksitespecific procedures and elements. These should

include the selection of respirators, medical evaluations of employees, fit testing, proper usage, maintenance and care, cleaning and disinfecting, proper

air quality/quantity and training (see 29 CFR 1926.103).

Where VDC systems and/or wet methods are not

feasible, the employee may be subject to wearing a

full-facepiece respirator equipped with an N-, R- or

P-95 filter in conjunction with a respiratory protection program, which is also outlined in and must

correspond with 29 CFR 1926.103. A full-facepiece

respirator equipped with an N-, R- or P-95 is adequate for silica concentrations up to 5.0 mg/m3

.

Other employees in close proximity to the work

operations where silica dust is generated may also

need respiratory protection if effective controls are

not implemented. The level of respiratory protection is dependent on the employee’s silica exposure, which varies depending on factors in the work

environment (such as enclosed, semi-enclosed, or

open spaces and/or multiple operations generating

silica dust), environmental conditions (such as wind

direction and speed), and the percentage of silica

found in the material.

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important and

necessary to utilize effective controls (such as wet

methods or VDC systems) in order to minimize

total exposures to silica-exposed tool operators or

potential exposures to other employees.

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine

proper respiratory protection, visit OSHA’s Web site

at www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2001. Industrial Ventilation, A Manual of

Recommended Practice, 24th Edition. American

Conference of Governmental Industrial Hygienists,

Cincinnati, OH.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Akbar-Khanzadeh, F. and Brillhart, R.L. 2002.

Respirable crystalline silica dust exposure during

concrete finishing (grinding) using handheld

grinders in the construction industry. Ann Occup

Hygiene 46(3):341-346.

Croteau, G.A., Guffey, S.E., Flanagan, M.E. and

Seixas, N.S. 2002. The effect of local exhaust venti2 4

Occupational Safety and

Health Administration
lation controls on dust exposures during concrete

cutting and grinding activities. Am Ind Hygiene

Assn J. 63:458-467. July/August.

Echt, A. and Sieber, W.K. 2002. Control of silica

exposure from hand tools in construction: Grinding

concrete. Appl Occup Environ Hygiene 17(7):457-

461. July, 2002.

ERG. 2002. Site visit report: Precast concrete product manufacturer facility B. Eastern Research

Group, Inc. September 26, 2002.

Flanagan, M.E., Seixas, N., Majar, M., Camp, J. and

Morgan, M. 2003. Silica dust exposures during

selected construction activities. Am Ind Hygiene

Assn J. 64(3):319-28. May-June, 2003.

Heitbrink, W.A. and Watkins, D.S. 2001. The effect

of exhaust flow rate upon the respirable dust emissions for tuckpointing operations. In: In-Depth

Study Report: Control Technology for Crystalline

Silica Exposures in Construction. U.S. Department

of Health and Human Services, Centers for Disease

Control and Prevention, National Institute for

Occupational Safety and Health. ECTB No. 247-18.

Heitbrink, W. and Collingwood, S. 2005. Protecting

Tuckpointing Workers from Silica Dust: Draft

Recommendations for Ventilated Grinder. The Center

to Protect Workers’ Rights (CPWR). www.cpwr.com

Lofgren, D.J. 1993. Silica exposure for concrete

workers and masons. Appl. Occup. Environ.

Hygiene 8(10):832-836. October, 1993.

NIOSH. 1995. In-depth survey report: A Laboratory

Comparison of Conventional Drywall Sanding

Techniques versus Commercially Available Control

(ECTB 208-11a). National Institute for Occupational

Safety and Health.

NIOSH. 1996. Preventing Silicosis and Deaths in

Construction Workers. Dept. of Health and Human

Services (National Institute for Occupational Safety

and Health, Publication No. 96-112).

NIOSH. 1998. Environmental surveillance report:

Construction site #16, Covington, KY. National

Institute for Occupational Safety and Health,

Morgantown, WV. June, 1998.

NIOSH. 1999. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 16 - Wet Cutting of Concrete Masonry

Units, File No. ECTB 233-116c. National Institute for

Occupational Safety and Health, October, 1999.

NIOSH. 2000a. In-depth survey report: Control

technology for crystalline silica exposures in construction: Exposures and preliminary control evaluation at various sites for Bricklayers Local #9,

Pittsburgh, PA (ECTB 247-12). National Institute

for Occupational Safety and Health, Cincinnati,

OH. February, 2000.

NIOSH. 2000b. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 25 – Concrete pipe manufacturing

(ECTB 233-125c). National Institute for Occupational

Safety and Health, Cincinnati, OH. March, 2000.

NIOSH. 2000c. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 27 – Pre-cast concrete shape manufacturing (ECTB 233-127c). National Institute for

Occupational Safety and Health, Cincinnati, OH.

March, 2000.

NIOSH 2000d. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case - 31 – A granite shed. (ECTB 233-131c).

National Institute for Occupational Safety and

Health, Cincinnati, OH, August, 2000.

NIOSH 2000e. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case-32 – A granite shed. (ECTB 233-132c).

National Institute for Occupational Safety and

Health, Cincinnati OH. August, 2000.

NIOSH. 2001. In-depth survey report for four sites:

Exposure to silica from hand tools in construction

chipping, grinding and hand demolition at Frank

Messer and Sons Construction Company, Lexington

and Newport, KY, and Columbus and Springfield, OH

(EPHB 247-15). National Institute for Occupational

Safety and Health, Cincinnati, OH. April, 2001.

NIOSH. 2002a. In-depth survey report: Control of

respirable dust and crystalline silica from grinding

concrete at Frank Messer & Sons Construction,

Newport, KY, and Baker Concrete Construction,

Dayton, OH (EPHB 247-21). National Institute for

Occupational Safety and Health, Cincinnati, OH.

May, 2002.

NIOSH. 2002b. In-depth survey report: Control of

silica exposure from hand tools in construction

grinding concrete at Frank Messer and Sons

Construction Company, Newport, KY (EPHB 247-

15c). National Institute for Occupational Safety and

Health, Cincinnati, OH. January, 2002.

NIOSH. 2002c. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

OSHA. 1996. Ground-fault protection on construction

sites. Occupational Safety and Health Administration,

Office of Training and Education. May.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 2 5
7 Results for the period evaluated were 0.39, 0.78,

and 1.2 mg/m3. If no additional exposure had

occurred, the associated 8-hour time-weighted

average (TWA) would have been 0.16, 0.31, and

0.34 mg/m3 for samples of 191 to 135 minutes duration. However, it is not uncommon for grinder operators to work at the same task for a full shift.

8 The average of four general area silica levels (0.14,

0.16, 0.16, and 0.27 mg/m3

) in the middle of the

room was 0.18 mg/m3. As expected, the grinder’s

exposure was higher (0.66 mg/m3) during the same

3-hour period.

9 The TWA is calculated by averaging the measured

exposure over a specific period of time (in this case

a full 8-hour shift).

10 Consultant provided only an 8-hour TWA result.

The construction firm did not continue use of the

backpack vacuum because its weight was considered too awkward (for bridge construction work).

11 The filter was rated as 99.99 percent efficient

when tested with respirable-sized particles in accordance with European Standard DIN 24184.

12 The employee primarily operated the grinder, but

performed concrete chipping for a brief period on

one day. The result of 0.18 mg/m3 suggests the

period of chipping had little impact on his total

exposure for the period sampled.

13 The sample pump worn by the operator faulted;

however, a high volume sample in the area indicated airborne concentration of 0.02 mg/m3

, the same

as the operator’s reported exposure level and much

lower than results for area samples during uncontrolled grinding. The result associated with the

helper was below the limit of detection for the 342-

minute sampling period. The grinder was operated

for about 80 percent of the time as the employee

smoothed walls in a room open to the outdoors on

one end and to an atrium on the other. During

uncontrolled grinding at the same site, NIOSH

obtained a result of 0.66 mg/m3 (grinding 75 percent

of the time). During this sampling period, the quickinterrupt electrical circuit breaker cut the power off

several times, possibly because water caused an

electrical short in this grinder.

14 These samples of 212 and 431 minutes in duration

resulted in 8-hour TWAs of 0.08 and 0.36 mg/m3.

15 The bulk silica concentration (30 percent) at the

first site was lower than at the second site (50 percent). However, the difference in silica content can

only account for roughly 40 percent of the large difference between exposure values for the two

processes. Results are associated with 8-hour TWA

values between 2.4 and 3.8 mg/m3 (if the employees had not had additional exposures) for samples

collected over 4 hours.

2 6

Occupational Safety and

Health Administration

Simcox, N., Lofgren, D., Leons, J. and J. Camp.

1999. Case Studies: Silica Exposure During Granite

Countertop Fabrication. Appl. Occup. Environ

Hygiene 14(9):577-582.

Technical Notes

1 Laboratories have not used particle counting for

crystalline silica analysis for many years. Exposure

data is now reported gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using the

general industry PEL (0.1 mg/m3 of respirable quartz

as an 8-hour time-weighted average) as a benchmark

to describe the effectiveness of control measures. The

benchmark is approximately equivalent to the general

industry silica PEL. Other organizations suggest more

stringent levels. For example, the National Institute

for Occupational Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be

limited to 0.05 mg/m3 as a 10-hour time-weighted

average (NIOSH, 2002c). The American Conference of

Governmental Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures be

limited to 0.025 mg/m3 as an 8-hour time-weighted

average (ACGIH, 2008).

2 Among data obtained by OSHA for common construction jobs, tuckpointers’ mean and median respirable silica exposures are the highest, with concrete

surface grinder operators second highest. Flanagan et

al. (2003) found that, at the nine construction sites

evaluated, concrete surface grinder operators had the

highest average exposure, with tuckpointers next

highest. Other groups evaluated included jackhammer operators, rock drillers, concrete saw operators,

crusher operators and employees performing cleaning activities at construction sites.

3 For data compiled by OSHA, the median exposure

level for handheld grinder operators exceeded 0.2

mg/m3.

4 Assuming exposure continued at the same level

for the entire shift, as is the case for some grinder

operators.

5 NIOSH (2000a) reported that an employee retrofitted grinding equipment used for tuckpointing.

Simcox et al. (1999) reported that several employers retrofit the grinders and polishers their employees used on granite.

6 Using more water will help keep the slurry thin and

unobtrusive, but can result in runoff if not controlled.
Tuckpointing/Mortar

Removal

This section covers the use of handheld angle

grinders for renovation of deteriorating mortar

in brick, stone and concrete block buildings

(tuckpointing/mortar removal). The term “silica”

used in this document refers to respirable crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees who use handheld angle

grinders to remove deteriorating mortar between

brick, stone and concrete block units generate significant amounts of silica-containing dusts. During

this operation, referred to as tuckpointing, small silica particles become suspended in the air and,

when inhaled, penetrate deep into employees’

lungs. Brick and building renovation masons have

been diagnosed with silicosis (Lyons et al., 2007).1

Air monitoring shows that typical silica exposure

levels for employees using angle grinders without

dust collection controls are in excess of the

Occupational Safety and Health Administration’s

(OSHA) benchmark of 0.1 mg/m3 (milligrams of silica per cubic meter of air) as an 8-hour time-weighted average (TWA), an exposure approximately

equivalent to OSHA’s general industry permissible

exposure limit (PEL).2 In fact, on average, tuckpointers’ silica exposures (along with those of surface

grinder operators) are among the highest in the

construction industry.3 Among data collected by

OSHA, more than half of employee exposures

exceed 1.0 mg/m3 during tuckpointing activities,

and frequently reach 2.4 mg/m3

. Even higher levels

are not uncommon (OSHA Case Files).4

This document describes methods available to

reduce employees’ exposures to silica when performing tuckpointing operations.

Although not widely used, vacuum dust collection systems are the most readily available means

for controlling silica dust during tuckpointing. With

careful work practices, this form of dust control can

lower silica exposures substantially. Nevertheless,

this method generally will not reduce dust levels

below regulatory limits and employers must take

additional steps to protect employees. Wet methods are not generally used for tuckpointing because

they deposit a slurry of mortar dust and water on

the brick, and the water used may penetrate the

building envelope.

Grinders who perform tuckpointing without dust controls

are frequently exposed to extremely high silica levels.

(Photo courtesy of CPWR.)

Silica Dust Control Measures

Vacuum Dust Collection Systems

Vacuum dust collection (VDC) systems for grinders

include a shroud, which surrounds the grinding

wheel, and a vacuum to pull air through the

shroud. Many manufacturers offer grinders with

dust collection options. Employers may also purchase equipment to retrofit grinders for vacuum

dust collection. The effectiveness of vacuum systems depends on several factors, including the

user’s technique, the surfaces being finished and

the efficiency of the dust collection system.

The addition of the shroud and vacuum hose

may make it more difficult to work effectively while

reaching above the shoulder, but improved visibility

due to reduced dust levels contributes to increased

efficiency.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do notrely only on visible dust to assess the

extent of the silica hazard. There may be airborne

respirable dust present that is not visible to the

naked eye.

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 2 7
Recommendations for Vacuum Dust Collection

Systems. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends

airflow of 25 cubic feet per minute (CFM) per inch

of blade diameter (for example, a 4-inch grinder

would need a vacuum with airflow of 100 CFM)

(ACGIH, 2007). If airflow is too low, the hose may

clog with particulate matter. A study by Croteau et

al. (2002), which tested an abrasive wheel saw,

indicated that a ventilation flow rate of 75 CFM

and an air velocity of 3440 feet per minute (FPM)

should be considered the minimum ventilation

rate for a 2-inch diameter vacuum hose.

VDC systems can be purchased as a kit. These

kits should include a grinder shroud, vacuum, vacuum hose and filter(s). The components of a VDC

system are discussed below.

• Grinder shroud: Use a shroud appropriate for

the grinder and wheel size that provides adequate visibility.

• Vacuum: Choose a vacuum with the appropriate

power and capacity for your job. A flow rate of

80 CFM or better on a vacuum dust collection

system will give the best results while performing mortar removal (Heitbrink and Watkins,

2001).

• Vacuum hose: Use the vacuum hose recommended by the manufacturer or that comes with

the equipment. Airflow resistance increases with

hose length; hoses more than 10 to 15 feet in

length should be avoided.

• Filters: Double filtration is important. The use of

a high-efficiency particulate air (HEPA) filter is

critical to prevent the escape of respirable silica

dust from the vacuum exhaust. HEPA filters are

at least 99.97 percent efficient in removing fine

dust particles from the air. A prefilter or cyclonic

separator in addition to a HEPA filter will extend

the service life of the more costly HEPA filter. A

cyclonic separator removes large particles that

are capable of overloading or clogging the filter

(Heitbrink and Collingwood, 2005).

• Systematic cleaning: Choose a vacuum equipped

with a back-pulse filter cleaning cycle. Such

auto-cleaning mechanisms will reduce the time

required for vacuum maintenance and improve

the overall efficiency of the dust collection system. If the vacuum does not have an auto-cleaning mechanism, the employee can periodically

turn the vacuum cleaner on and off. This allows

the bag to collapse and causes the prefilter cake

to dislodge from the filter.

2 8

Occupational Safety and

Health Administration

• Monitoring VDC efficiency: Purchasing a dust

collection system equipped with a static pressure gauge allows the employee to monitor the

system’s efficiency. Systems lacking a static

pressure gauge can be monitored visually. If a

dust plume increases and becomes more visible

where the shroud meets the working surface,

the system is not working efficiently (Heitbrink

and Collingwood, 2005).

System Maintenance. For optimal dust collection, the following measures are recommended:

• Keep the vacuum hose clear and free of debris,

kinks and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the shroud and vacuum hoses.

• For vacuums with back-pulse filter cleaning systems, activate the system frequently (several

times per day). Empty collection bags and vacuums as frequently as necessary. Dispose of collected dust in a way that prevents it from

becoming resuspended in the air.

• For best results, set up a regular schedule for filter cleaning and maintenance. For example,

institute a rule to clean the filter or change the

bag at each break. This will prevent pressure

loss and ensure that exhaust airflow stays more

constant on the VDC system.

• Remember, the absence of visible dust does not

necessarily mean that employees are adequately

protected from silica exposure.

Work Practice Controls to Enhance Vacuum

Effectiveness. Studies have shown that the effectiveness of vacuum dust collection systems is

enhanced by the use of proper work practices

(NIOSH, 1999; Croteau et al., 2002). However, use

of these work techniques without a dust collection

system will not substantially reduce dust exposures.

• Blade insertions: Place the left-hand side of the

shroud against the working surface before blade

insertion.5 This directs the dust into the shroud

as the blade cuts into the mortar joint.

• Blade depth: Per job specification, maintain the

full depth of the cut into the mortar. This allows

the shroud to remain flush against the working

surface and minimizes the dust that escapes

from the collection system.

• One-way movement: Avoid moving the grinder

back and forth along the slot as this will create

an open space ahead of the grinder and increase

dust escape. For better results, move the grinder
in one direction, making a second pass only if

necessary.

• Grinding direction: Grind counter to the direction of blade rotation to minimize escaping dust.

• Blade removal: Backing off the blade a few inches (2 to 4 inches) before removing it from the

slot will permit the vacuum to clear accumulated

dust.

• Force: Use normal (not excessive) force when

operating the tool to help keep the leading tool

edge flush against the working surface.

Leaving a large gap between the shroud and

uncut mortar (see Figure 1a) and not utilizing a high

enough airflow exhaust rate will allow dust to

escape and may expose employees to high levels

of respirable silica (Collingwood and Heitbrink,

2007). Reducing the size of the gap significantly

(see Figure 1b) and maintaining a high exhaust airflow rate ensures that most of the dust generated

from tuckpointing is captured.

Fiqure 1. Mortar Removal

1a. A large gap between the shroud and uncut mortar

permits air containing pulverized mortar to escape.

1b. Minimizing the gap between the shroud and uncut

mortar allows for good capture of pulverized mortar coming off the blade.

(Illustration courtesy of S. Collingwood and W.A. Heitbrink.)

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 2 9

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled conditions,

and show the effectiveness of controls in reducing

silica exposures.

Uncontrolled Exposures

Case Study I: Several silica samples were collected

at two unrelated building renovation sites. Neither

group of tuckpointers used dust controls. At the

first site, respirable silica exposures for all four

employees evaluated were greater than 1.4 mg/m3.

Exposure results were even higher at the second

location, where all tuckpointer exposure results

exceeded 2.4 mg/m3. At both sites, the highest tuckpointer exposures ranged from 7.0 mg/m3 to 8.0

mg/m3 (OSHA Case Files).

Case Study II: A foreman and a mason were evaluated while they performed tuckpointing on a humid

day with variable wind. Their respirable silica exposures were between 1.0 mg/m3 and 1.5 mg/m3

.

These levels exceeded regulatory limits and might

have been even higher had it not been for the

windy and humid weather conditions (OSHA Case

File).7

Controlled Exposures

Case Study III: NIOSH collected 13 respirable silica

samples for tuckpointers using angle-grinders

equipped with a VDC system consisting of a

shroud, hose and vacuum. Although exposures

were less than those uncontrolled exposures previously discussed, more than half of the employees

had exposures above 0.5 mg/m3 (NIOSH, 1999).

Case Study IV: A study showed the benefits of

using dust controls by comparing tuckpointers’

exposures with and without the use of vacuum dust

collection equipment. The dust collection system

consisted of a shroud on the grinder and a hose

attachment leading to a dust collection bag. Initial

tests showed that silica exposures with controls

were 37 to 47 percent lower than when controls

were not used, even though employees had difficulty using the shroud properly. Subsequently, the

manufacturer adjusted the shroud and rearranged

the handle and hose attachment to make the equipment easier to handle. In a follow-up test, the modified equipment reduced the employees’ respirable

silica exposure by 93 percent, from 4.0 mg/m3

(uncontrolled) to 0.3 mg/m3. While this reduction is

significant, the authors concluded that respiratory

protection is still required in order to provide

employees using dust collection equipment with

adequate protection (Nash and Williams, 2000).8
grinder will lower silica exposures; however, since

exposures may still exceed 0.1 mg/m3 with controls,

respiratory protection will be required to supplement the VDC system. When working in an open or

semi-enclosed area with a properly functioning

VDC system, the employee may be able to wear a

properly fitted, NIOSH-approved half-facepiece or

disposable respirator equipped with an N-, R- or P95 filter.

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer,

the employer must establish and implement a written respiratory protection program with worksitespecific procedures and elements. These should

include the selection of respirators, medical evaluations of employees, fit testing, proper usage, maintenance and care, cleaning and disinfecting, proper

air quality/quantity and training (see 29 CFR 1926.103).

When tuckpointing in enclosed areas or when

environmental conditions, such as wind, concentrate mortar particles in an employee’s breathing

zone, exposures may exceed 1.0 mg/m3 even with

effective controls. When working in enclosed areas,

the employer should supplement the VDC system

by providing a properly fitted NIOSH-approved fullfacepiece respirator with an N-, R- or P-95 filter. A

powered air-purifying respirator (PAPR) offers alternative protection for those who cannot wear a fullfacepiece air-purifying respirator. Such respiratory

protection is effective for exposures to silica up to 5

mg/m3 for a full-facepiece respirator and up to 10

mg/m3 for a PAPR with a fitted facepiece.

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important and

necessary to utilize effective controls (such as wet

methods and/or a VDC system) in order to minimize

total exposures to silica-exposed tool operators or

potential exposures to other employees.

Since tuckpointing even under controlled conditions can result in silica exposures in excess of 0.1

mg/m3, adjacent employees may need to wear respirators as well. The level of respiratory protection

is dependent on the employee’s silica exposure,

which varies depending on factors in the work environment (such as enclosed, semi-enclosed, or open

spaces and/or multiple operations generating silica

dust), environmental conditions (such as wind

direction and speed), and the percentage of silica

found in the material.

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

3 0

Occupational Safety and

Health Administration

Case Study V: Wet methods are not commonly

used for tuckpointing because they may deposit a

slurry consisting of mortar dust and water on the

brick. The applied water may also penetrate the

structure and damage the interior. However, in

some cases, wet methods can be used in tuckpointing operations. For example, in this case study, an

employee modified a tuckpointing grinder with

both a ventilation shroud and a small water application nozzle. During one hour of mortar grinding,

the employee’s respirable dust exposure (0.38

mg/m3) was less than 3 percent of the median value

for five results obtained for uncontrolled mortar

grinding in this study (13.3 mg/m3) (NIOSH, 2000).

In this case study, the employee used a handpump garden sprayer to pressurize the water,

which was applied to the blade at a rate slightly

less than a quart per minute through a nozzle made

of 1/16-inch copper tubing. A wet/dry shop vacuum

connected to the shroud removed the damp mortar

debris as it was generated. A 10-foot vacuum hose

extension (PVC pipe) allowed the employee to

stand an extra 10 feet away from the vacuum for

added protection from dust escaping from the vacuum.

This study was performed using an electric

grinder, which introduces electrical safety issues

because it is an electric tool being used in a wet

environment. One way to avoid possible electrical

safety issues related to the introduction of water is

to switch to a pneumatic grinder (NIOSH, 2000).

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed

spaces. Cleaning should be performed with a

HEPA-filtered vacuum or by wet methods.

Respiratory Protection and Engineering

Control Evaluation

It is not uncommon for respirable crystalline silica

exposures to reach 2.4 mg/m3 or higher while tuckpointing without engineering controls. Tuckpointing

is often conducted in situations or on materials that

do not permit the use of wet methods as an engineering control.

In these situations, VDC systems are recommended. A VDC system attached to the angle
appropriate level of respiratory protection is being

used.

For more information on how to determine

proper respiratory protection, visit OSHA’s Web site

at www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2007. Industrial Ventilation, A Manual of

Recommended Practice, 26th Edition. American

Conference of Governmental Industrial Hygienists,

Cincinnati, OH.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Collingwood, S. and Heitbrink, W.A. 2007. Field

evaluation of an engineering control for respirable

crystalline silca exposures during mortar removal. J

Occup Environ Hygiene 4:875-887.

Croteau, G.A., Guffey, S.E., Flanagan, M.E. and

Seixas, N.S. 2002. The effects of local exhaust ventilation controls on dust exposures during concrete

cutting and grinding activities. Am Ind Hygiene

Assoc J 63(4): 458-467.

Flanagan, M.E., Seixas, N., Majar, M., Camp, J. and

Morgan, M. 2003. Silica dust exposures during

selected construction activities. Am Ind Hygiene

Assn J 64(3):319-28. May-June, 2003.

Heitbrink, W.A. and Watkins, D.S. 2001. The effect

of exhaust flow rate upon the respirable dust emissions for tuckpointing operations. In: In-Depth

Study Report: Control Technology for Crystalline

Silica Exposures in Construction. U.S. Department

of Health and Human Services, Centers for Disease

Control and Prevention, National Institute for

Occupational Safety and Health. ECTB No. 247-18.

Heitbrink, W. and Collingwood, S. 2005. Protecting

Tuckpointing Workers from Silica Dust: Draft

Recommendations for Ventilated Grinder. The

Center to Protect Workers’ Rights (CPWR).

www.cpwr.com

Lyons, J.J., Sime, P.J., Ward, D., Watson, T.,

Abraham, J.L., Evans, R., Budev, M., Costas, K. and

Beckett, W.S. 2007. A breathless builder. Breathe

3:386-390.

Nash, N.T. and Williams, D.R. 2000. Occupational

exposure to crystalline silica during tuckpointing

and the use of engineering controls. Appl Occup

Environ Hygiene 15(1):8-10. January, 2000.

NIOSH. 1996. Preventing silicosis and deaths in

construction workers. Dept. of Health and Human

Services, National Institute for Occupational Safety

and Health. Publication No. 96-112.

NIOSH, 1998. Environmental surveillance report:

Construction site #16, Covington, KY. National

Institute for Occupational Safety and Health,

Morgantown, WV. June, 1998.

NIOSH. 1999. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 23―Masonry Tuckpointing (ECTB 233-

123c). National Institute for Occupational Safety and

Health, Cincinnati, OH.

NIOSH, 2000. In-depth survey report: Control technology for crystalline silica exposures in construction: Exposures and preliminary control evaluation

at various sites for Bricklayers Local #9, Pittsburgh,

Pennsylvania (ECTB 247-12). National Institute for

Occupational Safety and Health, Cincinnati, OH.

February, 2000.

NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for Occupational Safety and Health, Cincinnati, OH. June,

2002.

OSHA. 1996. Ground-fault protection on construction sites. Occupational Safety and Health Administration, Office of Training and Education. May,

1996.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Shields, C. 1999. Silica dust exposures from OSHA

construction inspections in the Chicago area 1996-

1998. Occupational Safety and Health

Administration. Aurora, IL, Area Office. Slide

Presentation.

Zalk, D. 2002. Personal communication between D.

Zalk, Lawrence Livermore Laboratory, CA. and W.

Long, Eastern Research Group, Inc., Arlington, VA.

October 29, 2002.

Technical Notes

1 These employees performed a variety of activities

involving silica-containing materials, including

abrasive blasting and work with fire brick (NIOSH,

1996).

2 Laboratories have not used particle counting for

crystalline silica analysis for many years. Exposure

data is now reported gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count

value. (See Appendix E to OSHA’s National

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3 1
Emphasis Program for Crystalline Silica, CPL 03-00-

007, for a detailed discussion of the conversion factor used to transform gravimetric measurements to

particle-count values). In this guidance, OSHA is

using 0.1 mg/m3 of respirable quartz as an 8-hour

time-weighted average as a benchmark to describe

the effectiveness of control measures. The benchmark is approximately equivalent to the general

industry silica PEL. Other organizations suggest

more stringent levels. For example, the National

Institute for Occupational Safety and Health

(NIOSH) recommends that respirable crystalline

silica exposures be limited to 0.05 mg/m3 as a 10-

hour time-weighted average (NIOSH, 2002). The

American Conference of Governmental Industrial

Hygienists (ACGIH) recommends that respirable

crystalline silica exposures be limited to 0.025

mg/m3 as an 8-hour time-weighted average (ACGIH,

2008).

3 Among data obtained by OSHA for common construction jobs, tuckpointers’ mean and median respirable silica exposures are the highest, with concrete surface grinder operators the second highest.

Flanagan et al. (2003) found that, at nine construction sites evaluated, concrete surface grinder operators had the highest average exposure, with tuckpointers next highest. Other groups evaluated

included jackhammer operators, rock drillers, concrete saw operators, crusher operators, and

employees performing cleaning activities at construction sites.

4 Among data obtained by OSHA, more than half of

employee exposures exceeded 1.0 mg/m3 during

3 2

Occupational Safety and

Health Administration

tuckpointing and the average exposure level was

2.2 mg/m3. Due to the high levels of dust, many of

the samples were collected for a period less than a

full shift. However, tuckpointers often work at this

task 8 hours per day. Thus, a similar level of exposure is assumed for the unsampled portion of the

shift. Even if employees had no further silica exposure beyond the period sampled, the median 8-

hour time-weighted average crystalline silica result

would exceed 0.5 mg/m3 and the average level

would be 1.5 mg/m3.

5 Assumes typical counter-clockwise blade rotation

(or whatever blade direction ensures that the dust

will be captured within the shroud).

6 Results from the two sites include 6 full and 2 partial shift samples. Employees at both sites indicated

they typically performed tuckpointing 8 hours per

day. Bulk samples showed that the mortar contained 20 to 40 percent silica at the first site and 30

percent silica at the second site (OSHA Case Files).

7 Bulk samples associated with these results indicate that the mortar contained 50 to 70 percent silica (OSHA Case File).

8 Initially, employees at two sites were monitored

for 5 to 7 hours each; in the follow-up test, sample

times were 1 to 2 hours. All results were reported

as 8-hour time-weighted averages. In the final test,

the respirable silica exposure without dust controls

was 4.08 mg/m3, compared to 0.31 mg/m3 with the

modified dust collection system (Nash and

Williams, 2000).
Employee chipping concrete with a jackhammer while

using a wet method. (Photo courtesy of NIOSH.)

Silica Dust Control Measures

Wet Methods

Wet methods reduce dust by wetting the material at

the impact point, before the dust gets into the air.

Wet particles are heavier and more likely to stick to

each other than dry particles and tend to settle

more quickly. Thus, wet methods decrease the

amount of particulate matter suspended in the air.

This form of dust suppression is effective for both

respirable and visible dust.

The ideal wet method of dust control uses the

minimum amount of water to get the maximum

result. Spray directed at the point of impact is optimal. The spray must not be too fine otherwise the

air motion around the jackhammer will not allow

the spray to contact dust at the impact point. For

example, employees operating 90-pound jackhammers reduced their silica exposure between 50 and

98 percent using just 1/8 gallon of water per minute

as a spray (Zalk, 2002).

Water for dust suppression can be applied manually, or using a semi-automated water-feed device.

Manual spraying

In the simplest method for suppressing dust, a dedicated helper directs a constant spray of water at

the impact point, while another employee operates

the jackhammer. The helper can use a hose with a

garden-style nozzle to maintain a steady and carefully directed spray at the impact point where material is broken and crushed.

An experienced helper will be able to adjust the

water flow to achieve the maximum dust suppression using the minimum amount of water, thus

reducing water run-off.

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3 3

Jackhammers

This section covers breaker hammers (jackhammers) used in the breaking and demolition of

concrete, asphalt and other materials. The term

“silica” used in this document refers to respirable crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees produce dusts containing

silica when they use breaker hammers (commonly

known as jackhammers) to chip and break rocks or

concrete. The hammer’s crushing action generates

small particles that easily become suspended in the

air and, when inhaled, penetrate deep into employees’ lungs.

The Occupational Safety and Health Administration

(OSHA) compiled exposure monitoring results for

construction workers using jackhammers outdoors

without dust suppression. Employee exposures frequently exceeded OSHA’s benchmark of 0.1 mg/m3

(milligrams of silica per cubic meter of air) as an 8-

hour time-weighted average (TWA), an exposure

approximately equivalent to OSHA’s general industry permissible exposure limit (PEL) for construction.1 The results showed operator exposures that

reached 0.8 mg/m3 during the period evaluated.

More than one-third of the jackhammer operators

experienced exposures between 0.1 mg/m3 and 0.5

mg/m3.

2 When breaking concrete indoors, operator

exposure levels were 3.0 mg/m3 or higher (NIOSH,

1983). Another set of exposure monitoring results

showed 178 jackhammer and chipping gun samples with a mean silica exposure of 0.15 mg/m3

(Flanagan et al., 2006).

This section discusses methods for reducing silica exposures among construction workers using

jackhammers. The principle means to control silica

dust from jackhammer operations is by wetting the

dust at the point of breaking or chipping (i.e., wet

methods). In comparison, an experiment was conducted testing the efficiency of dust collection on a

jackhammer. In the study, the jackhammer was

retrofitted with a commercially available rock drill

shroud connected to a vacuum dust collection system. The results of the study showed that the dust

collection system reduced respirable dust exposures by almost 60 percent (Echt et al., 2003).
Periodically picking up a hose and spraying the

general area is not effective. Simply pre-wetting the

concrete or asphalt prior to breaking the surface is

also ineffective (see Case Studies II and III, at Page

35). Because the jackhammer continues to break

through silica-containing material, dust is constantly produced. To be effective, spray application must

be continuous and directed at the point of impact.

Water Spray System

This alternative uses the same principle as manual

spraying, but eliminates the need for a helper to

hold the hose.

Jackhammers retrofitted with a spray nozzle

aimed at the tip of the tool offer a dramatic decrease

in silica exposure. Although water-fed jackhammers

are not commercially available, it is neither expensive nor difficult to retrofit equipment and parts are

available at well-stocked hardware stores (Zalk,

2000, 2001, 2002).

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne respirable dust present that is not visible to the naked eye.

Designing a water spray dust control system for

a jackhammer. Employers can design their own wet

method dust control system (NIOSH, 2008). The

system requires:

• A water source (e.g., a municipal tap, a tank

truck); a valve to control water flow from the

source (if the source does not have its own flow

control valve); and a hose or tubing to bring

water from the source to the jackhammer.

• Additional flexible, but durable, tubing to supply

water along the jackhammer to the nozzle.3

• A sturdy water flow control valve mounted on

the jackhammer to make minor adjustments in

the flow. A water flow rate of 350 ml/min (0.09

gallons/min) in conjunction with a spray angle

of 80 degrees (the angle included between the

sides of the cone formed by the water discharged from the nozzle) is recommended recommended for achieving optimal reductions in

silica exposure.

• A good-quality garden-style spray nozzle, which

can can provide either a spray or stream of

water.

• Fittings to connect the hose, valves and tubing,

and to mount the nozzle to the hammer body.

NIOSH has prepared a web-based practical

engineering pamphlet on the use of water spray

controls for jackhammers (NIOSH, 2008).

Using multiple jackhammers without dust controls

increases silica exposures for both operators and adjacent employees. (Photo courtesy of Kenneth Linch.)

System Maintenance. Routine maintenance

helps ensure that the equipment functions as

intended. Considerations include:

Clogged nozzles: Dust and debris can clog spray

nozzles. Check the nozzle frequently, especially if

the job starts looking dusty. Activate the spray for a

few seconds and observe the spray to be sure the

water flow is appropriate and directed at the tool

tip. The nozzle should be cleaned or changed if it is

dripping, spitting, squirting, or spraying at an odd

angle. Keep spare nozzles on hand for quick

changes at the worksite.

Spray angle: The spray nozzle position is critical. Check the water spray angle frequently.

• Is the spray focused on the breakpoint?

• Is the spray wetting the dust before it can disperse

from the tip of the hammer?

3 4

Occupational Safety and

Health Administration
Consistent water flow: Take steps to provide consistent water flow. Prevent interruptions from

kinked hoses, vehicular traffic running over hoses

and large drops in water pressure. Ensure an adequate supply of water.

Using a Water-Fed Jackhammer

Make sure that the water spray covers the tip of

the tool blade.

Adjust water flow as often as necessary. A

water flow rate of about 350 ml/min (0.09 gallons/min) is optimal in most circumstances.

Many factors affect the exact water requirement.

Water flow onto the impact point is an important

element in reducing silica exposure to the operator. However, the angle of water delivery is just

as important. A coned-shape spray angle of 80

degrees is recommended. This will provide the

greatest reduction in silica exposure to the operator. (Echt et al., 2003; Zalk, 2002; WorkSafe

Western Australia, 1996). More water is usually

not better.

As a rule of thumb, try to adjust the nozzle

and water flow to prevent visible dust release.

Employees may wish to keep a damp cloth

handy to wipe their protective faceshields or

eyewear.

FreezingTemperatures. Freezing temperatures

complicate the use of water. Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Large portable

heating units are commonly used to heat commercial and sometimes road and highway projects.

Drain the system when not in use. If water freezes

on the ground, chip away the ice or use deicing

compounds or sand to control the slipping hazard.

Enclosed Areas. A study of wet methods

showed that they work as well indoors as outdoors

for jackhammers (Zalk, 2000). However, the

decreased airflow in enclosed areas can increase

dust concentrations. Provide good fresh air circulation as an extra level of protection for jackhammer

operators working indoors or inside containments

as concentrations can increase quickly if controls

are not functioning optimally.

Water runoff. Comply with local requirements

for managing the used water. If a considerable

runoff is generated, it may be necessary to channel

the water to a point where it can be collected for

treatment.4

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled or poorly

controlled conditions, and show the effectiveness of

controls in reducing silica exposures.

Uncontrolled

Case Study I: Five jackhammer operators chipping

damaged sections of a concrete bridge deck for an

entire shift had silica exposures between 0.2 and

0.5 mg/m3. A sixth operator’s exposure was 0.09

mg/m3. In the same area, laborers’ exposures also

ranged between 0.2 and 0.5 mg/m3. The use of

compressed air to blow chips out of cracks may

have contributed to their exposures (Shields,

2000a). Results fell in this range at nearly half of the

construction sites for which OSHA compiled data.5

How Reliable are Wet Methods for Controlling

Respirable Silica Dust?

Wet methods are only as reliable as their application. If you can answer “Yes” to the following

questions, the dust control is probably working

well.

• Is there enough water and water pressure to

create a spray?

• Is the spray directed to envelop the area where

dust is released – at the tip of the tool?

• Does the operator make adjustments as needed to ensure that water spray is constantly

applied to the correct area?

• Is visible dust suppressed?6

Improper Use of Water to Control Dust

Case Study II: Employees at an indoor construction

site wet the surface before (but not during) jackhammer use. Their silica exposures were about 0.2

mg/m3 (OSHA Case File).

Case Study III: At a second indoor site, exposures

of more than 0.6 mg/m3 were reported for two

employees who inconsistently sprayed water while

operating jackhammers. These results significantly

exceed OSHA limits. A small fan in the window was

inadequate to blow contaminated air out of the

space and a cooling fan aimed at the employees

simply recirculated the dust (OSHA Case File).

Effective Wet Methods

Case Study IV: A construction employee was using

a jackhammer to break concrete on a bridge next to

a freeway while another employee continuously

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3 5
aimed a water hose at the breaking point. No silica

was detected in the first employee’s breathing area

over a 6-hour period. Air sampling results were well

below 0.1 mg/m3 (OSHA Case File).7

Case Study V: In an water spray to the impact

point. With dust control in place, exposure levels of

less than or equal to 0.1 mg/m3 were found both

indoors and outdoors (Zalk, 2000).

Air monitoring was conducted to measure silica

exposure levels while the employees operated the

equipment dry (no water flow). Additional monitoring was performed with the water turned on and

adjusted to carefully apply spray to the break point.

The experiment was repeated indoors, with the

employees breaking concrete in a shed on the

same parking lot, first using dry equipment, then

with the water on.8

Using dry methods, the employee exposure levels for silica were 0.2 to 0.8 mg/m3 outdoors and

approximately 0.9 to nearly 4.3 mg/m3 indoors. The

outdoor experimental results were within the range

observed for employees on construction sites operating jackhammers for the full shift. The indoor

results were somewhat higher than reported in

compiled OSHA samples.9

In this study, employee exposures dropped dramatically when dust was controlled by applying

water spray to the impact point. With dust control

in place, exposure levels of less than or equal to 0.1

mg/m3 were found both indoors and outdoors (Zalk,

2000).

Case Study VI: In this study, Echt et al., (2003) evaluated the effectiveness of vacuum dust collection

(VDC) and water-spray controls attached to a jackhammer. The water-spray control was very effective

in reducing respirable dust concentrations compared to the VDC control. The water-spray attachment delivered approximately 350 milliliters (ml)

of water per minute (0.09 gallons/min). This water

flow rate did not add a substantial amount of water

to the work surface.

Water spray controls that use commercially

available nozzles offer variable reduction in exposures based on flow rate and spray angle. A reduction in exposure to silica of approximately 40 percent was achieved using a flow rate of 250 ml/min

(0.07 gallons/min) at a spray angle of 60 degrees.

However, the reduction in exposure was increased

to around 70 percent with an increased flow rate at

300 ml/min (0.08 gallons/min) and a spray angle of

80 degrees (Echt et al., 2004).

Case Study VII: Brouwer et al., (2004) conducted a

study which investigated the effectiveness of water

application while using jackhammers and plate

compactors. Two types of jackhammers were analyzed in the study, heavy and light. The study

involved breaking concrete slabs in an inside area

of approximately 145,000 cubic feet with the heavy

jackhammer and breaking concrete floor tile with a

light jackhammer in a small enclosed bathroom

area of approximately 160 cubic feet. The water

flow rate on the light jackhammer was 190 ml/min,

while the flow rate was 170 ml/min for the heavy

jackhammer. Both jackhammers operated at 5 bar

pressure. The water holding tank, a backpack, held

a total of 15 liters.

Results of the silica exposure were calculated as

task-based time-weighted average concentrations.

Silica concentrations for the light jackhammer without the use of water ranged from 0.12 to 1.75

mg/m3 compared to the use of wet methods, which

resulted in exposures ranging from 0.04 to 0.67

mg/m3

. Results of the heavy jackhammer without

controls were 0.08 to 0.66 mg/m3. Exposure results

after wet methods were employed ranged from

0.02 to 0.36 mg/m3 respirable silica. (Brouwer et al.,

2004).

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed

spaces. Cleaning should be performed with a

HEPA-filtered vacuum or by wet methods.

Respiratory Protection and Engineering

Control Evaluation

Jackhammering without engineering controls or

using engineering controls in an ineffective manner

(for example, trickling water at the point of impact),

can cause exposures to respirable crystalline silica

that exceed 3.0 mg/m3

.

Selection and use of respiratory protection is

based on exposure, which is primarily affected by

four factors: Use of effective wet methods; length

of time jackhammers are in operation; indoor versus outdoor operations; and number of jackhammers in operation at a given time.

Effective wet methods provide the best option

for reducing silica exposures. Data show that outdoor jackhammering using effective wet methods

for operations under four hours duration will control exposures below 0.1 mg/m3

. Under such cir3 6

Occupational Safety and

Health Administration
cumstances, operators may not be required to wear

respiratory protection.

Because exposures can exceed 0.1 mg/m3, but

remain below 1.0 mg/m3, it may be necessary to

use a properly fitted, NIOSH-approved half-facepiece or disposable air purifying respirator

equipped with an N-, R- or P-95 filter under the following conditions:

• When operating a jackhammer outdoors with

effective wet methods for more than four hours.

• When operating multiple jackhammers outdoors

outdoors in close proximity (i.e., within 15 feet)

with effective wet methods for less than four hours.

• When operating a single jackhammer in enclosed spaces or indoors with effective wet

methods.

Because exposures can exceed 1.0 mg/m3, it

may be necessary to use a properly fitted, NIOSHapproved full-facepiece air purifying respirator

equipped with an N-, R- or P-95 filter under the following conditions:

• When operating multiple jackhammers indoors

while using effective wet methods.

• In situations where wet methods are not feasible

during any operation of two or more jackhammers.

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer,

the employer must establish and implement a written respiratory protection program with worksitespecific procedures and elements. These should

include the selection of respirators, medical evaluations of employees, fit testing, proper usage, maintenance and care, cleaning and disinfecting, proper

air quality/quantity and training (see 29 CFR 1926.103).

Other employees in close proximity to the work

operations where silica dust is generated may also

need respiratory protection if effective controls are

not implemented. The level of protection is dependent on the employee’s silica exposure, which

varies depending on factors in the work environment (such as enclosed, semi-enclosed, or open

spaces and/or multiple operations generating silica

dust), environmental conditions (such as wind

direction and speed), and the percentage of silica

found in the material.

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important and

necessary to utilize effective controls (such as wet

methods) in order to minimize total exposures to

silica-exposed tool operators or potential exposures

to other employees.

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine

proper respiratory protection, visit OSHA’s Web site

at www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2001. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Brouwer, D.H., Spee, T., Huijbers, R.F., Lurvink,

M.W.M., Fritjers, A.C.P. 2004. Effectiveness of dust

control by atomisation of water sprays on handheld

demolition and soil compacting equipment.

Tijdschrift voor toegepaste Arbowetenschap 4:68-74,

2004.

Croteau, G.A., Guffey, S.E, Flanagan, M.E. and

Seixas, N.S. 2002. The effects of local exhaust ventilation controls on dust exposures during concrete

cutting and grinding activities. Am Ind Hygiene

Assoc. J 63(4): 458-467, 2002.

Echt, A., Sieber, K., Jones, E., Schill, D., Lefkowitz,

D., Sugar, J., Hoffner, K. 2003. Control respirable

dust and crystalline silica from breaking concrete

with a jackhammer. Appl Occup Environ Hygiene

18(7): 491-495, 2003.

Echt, A., Sieber, K., Williams, D., Cantrell, A., Schill,

D.P., Lefkowitz, D., Sugar, J., Hoffner, K. 2004. Indepth survey report of a water spray device for suppressing respirable and crystalline silica dust from

jackhammers at E.E. Cruz Co.. South Plainfield, NJ.

Cincinnati, OH: U.S. Department of Health and

Human Services, Centers for Disease Control and

Prevention, National Institute for Occupational

Safety and Health, Report No. EPHB 282-11c2.

Flanagan, M.E., Seixas, N., Becker, P., Takacs, B.,

Camp, J. 2006. Silica exposure on construction

sites: results of an exposure monitoring data compilation project. J Occup Environ Hygiene. 3(3):144-

52.

NIOSH. 1983. Health hazard evaluation report:

Grand Gulf Nuclear Power Plant, Gibson,

Mississippi. HETA 83-132-1508. U.S. Dept. of Health

and Human Services, National Institute for

Occupational Safety and Health.

C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3 7
NIOSH. 1996. Preventing silicosis and deaths in

construction workers. U.S. Dept. of Health and

Human Services, National Institute for Occupational

Safety and Health, Publication No. 96-112.

NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June, 2002.

NIOSH. 2008. Water Spray Control of Hazardous

Dust When Breaking Concrete with a Jackhammer.

May, 2008. http://www.cdc.gov/niosh/docs/wpsolutions/ 2008-127.

OSHA. 1996. Ground-fault protection on construction sites. Occupational Safety and Health

Administration, Office of Training and Education.

May, 1996.

OSHA Case Files (Special Emphasis Program

Inspection Reports, 1996-1998).

Shields, C. 2000a. Database: Silica dust exposures

associated with construction activities. Occupational

Safety and Health Administration, North Aurora, IL.

September 14, 2000.

Shields, C. 2000b. Silica dust exposures from OSHA

construction inspections in the Chicago area 1996-

1999. Occupational Safety and Health

Administration, Aurora, IL, Area Office Slide

Presentation.

WorkSafe Western Australia. 1996. Silica dust on

construction sites. www.wt.com/au/safetyline/

d_pubs/silica.htm. March, accessed 04/15/97.

Zalk, D. 2000. Presentation at the American

Industrial Hygiene Conference and Exposition,

Orlando, FL. May 24, 2000.

Zalk, D. 2001. Personal communication between D.

Zalk, Lawrence Livermore Laboratory, CA, and W.

Long and A. Gandhi, Eastern Research Group, Inc.,

Arlington, VA. January 23, 2001.

Zalk, D. 2002. Personal communication between D.

Zalk, Lawrence Livermore Laboratory, CA. and W.

Long, Eastern Research Group, Inc., Arlington, VA.

October 29, 2002.

Technical Notes

1 Laboratories have not used particle counting for

crystalline silica analysis in many years and now

3 8

Occupational Safety and

Health Administration

report exposure data gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count

value. (See Appendix E to OSHA’s National

Emphasis Program for Crystalline Silica, CPL 03-00-

007, for a detailed discussion of the conversion factor used to transform gravimetric measurements to

particle-count values). In this guidance, OSHA is

using 0.1 mg/m3 of respirable quartz as an 8-hour

time-weighted average as a benchmark to describe

the effectiveness of control measures. The benchmark is approximately equivalent to the general

industry silica PEL. Other organizations suggest

more stringent levels. For example, the National

Institute for Occupational Safety and Health (NIOSH)

recommends that respirable crystalline silica exposures be limited to 0.05 mg/m3 as a 10-hour timeweighted average (NIOSH, 2002). The American

Conference of Governmental Industrial Hygienists

(ACGIH) recommends that respirable crystalline silica exposures be limited to 0.025 mg/m3 as an 8-

hour time-weighted average (ACGIH, 2008).

2 References: OSHA Case Files; Shields, 2000a [data

of 3/29, 5/1, 5/11, 7/8, 8/13, and 10/1/99].

3 Copper tubing, heavy rubber, plastic tubing, and

even hydraulic line have been used. The more flexible the tubing, the easier it is to adjust the nozzle

position when installing the system.

4 Under many conditions, 1/8 gallon per minute

water flow will generate little run-off. Requirements,

however, vary greatly by location. Contact the

municipal environmental quality department or

other appropriate authority to see if there are any

local requirements.

5 OSHA Case Files; Shields, 2000a [data of 8/13].

6 Although visible dust cannot be used to predict

the amount of respirable-sized dust in the air, if the

spray is not controlling the visible dust, it is probably not controlling respirable dust either.

7 Based on the limit of detection, the employee’s

respirable silica exposure was calculated to be less

than or equal to 0.037 mg/m3.

8 All sample durations were 1 to 3 hours.

9 This level is higher than typical on indoor construction sites, probably because the enclosed shed

used in the test was smaller and had less natural

ventilation than the indoor spaces evaluated for

OSHA’s data (primarily parking garages).
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 3 9

Rotary Hammers and

SimilarTools

This section covers use of rotary hammers and

similar tools to drill small diameter holes in concrete and other masonry construction materials.

The term “silica” used in this document refers to

respirable crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees produce dusts containing

silica when they cut, grind, crush, or drill construction materials such as concrete, masonry, tile, and

rock. The small particles easily become suspended

in the air and, when inhaled, penetrate deep into

employees’ lungs.

Using rotary hammers or similar tools to drill

small-diameter holes in concrete, bricks, masonry

blocks, tiles and similar materials can expose

employees to hazardous levels of airborne silica if

measures are not taken to suppress dust emissions.

At worksites without dust control, data compiled by

the Occupational Safety and Health Administration

(OSHA) show that employee silica exposures during this type of drilling can exceed the benchmark

of 0.1 mg/m3 (milligrams per cubic meter of air) as

an 8-hour time-weighted average (TWA), an exposure approximately equivalent to OSHA’s general

industry permissible exposure limit (PEL) by more

than three times (Lofgren, 1993).1,2 During periods

of active drilling, exposures can be as high as 0.78

mg/m3 (NIOSH, 1996).3

This section describes methods available to

reduce employees’ exposures to silica during

drilling of concrete and other silica-containing

materials. Three primary methods exist to control

silica dust while using rotary hammers: (1) vacuum

dust collection, (2) dust barriers or enclosures, and

(3) wet methods. Each of these methods is easy to

implement.

Vacuum dust collection methods can significantly reduce dust emissions during small-diameter

hole drilling operations. Dust barriers are helpful for

employees who drill holes only occasionally. Wet

methods are generally effective in reducing

employee exposures to silica dust and maintaining

exposures below OSHA’s limits, but are not appropriate with all tools.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne respirable dust present that is not visible

to the naked eye.

Silica Dust Control Measures

Vacuum Dust Collection Systems

Vacuum dust collection (VDC) systems are commercially available for handheld drills, usually as addon systems. The systems enclose the drill bit in a

suction ring (dust entrance), which includes a port

for attaching a vacuum to collect dust and concrete

particles generated during drilling.

Built-in Dust Collection Systems

Some tools that have built-in dust collection systems also use a suction ring and include an integral impeller (rotor blade) that draws dust into a

bag or receptacle attached to the drill body.

Built-in dust collection systems are convenient because they require no additional equipment, such as vacuums. However, built-in systems may not provide the same level of employee protection as vacuum systems. Fine particles

may pass through the lower-efficiency filter bags

or receptacles often used for built-in systems.

Also, built-in systems release the exhaust air

(and any particles that escape the filter) near the

employee’s face, while vacuums are typically

positioned several feet away.

Recommendations for Vacuum Dust Collection

Systems. VDC systems can be purchased as a kit.

These kits should include a dust collection device,
vacuum, vacuum hose and filter(s). The components of a VDC system are discussed below.

• Dust Collection Device: In most cases, this is a

retrofit on the rotary hammer; therefore, be sure

to follow the manufacturers’ directions on

installing the dust collector.

• Vacuum: Choose a vacuum with the appropriate power and capacity for your job. Obtaining a

flow rate on a vacuum dust collection system of

80 cubic feet per minute (CFM) or better will give

the best results with a variety of common tools

(Heitbrink and Watkins, 2001). In some circumstances, a lower flow rate may be sufficient.

Sheperd et al. (2009) found that for small hammer drills a flow rate of 49 CFM was sufficient to

capture more than 90 percent of the respirable

silica dust generated. Smaller, less expensive

vacuums may thus be adequate in some situations.

• Vacuum hose: Flow rates ranging from 50 to 80

CFM are best maintained with a 11⁄2- to 2-inch

diameter hose. If the diameter is larger, the airflow velocity of the vacuum will be reduced. If

the diameter is smaller, airflow resistance will be

higher. Airflow resistance also increases with

hose length; excessively long hoses should be

avoided. Many HEPA-filtered vacuum system

kits include a variety of hose sizes for different

tool applications.

• Filters: Double filtration is important. The use of

a high-efficiency particulate air (HEPA) filter is

critical to preventing the escape of respirable silica dust from the vacuum exhaust. HEPA filters

are at least 99.97 percent efficient in removing

fine particles of dust from the air. Vacuum cleaners with cyclonic pre-separators in addition to

HEPA filters provide superior and cost-effective

dust control when dust loading is high and high

airflow is needed to capture and remove the

dust. A cyclonic separator removes large particles that are capable of overloading or clogging

the filter (Heitbrink and Collingwood, 2005).

• Systematic cleaning: Regular cleaning of the filter is critical to maintaining high airflow. Choose

a vacuum equipped with a back-pulse filter

cleaning cycle. Such auto-cleaning mechanisms

will reduce the time required for vacuum maintenance and improve the overall efficiency of the

dust collection system. If the vacuum does not

have an auto-cleaning mechanism, the employee can periodically turn the vacuum cleaner on

and off. This allows the bag to collapse and

causes the prefilter cake to dislodge from the filter.

• Monitoring VDC efficiency: Purchasing a dust

collection system equipped with a static pressure gauge allows the employee to monitor the

system’s efficiency. Systems lacking a static

pressure gauge can be monitored visually. If a

dust plume increases and becomes more visible

where the exterior hood (suction ring) meets the

working surface, the system is not working efficiently (Heitbrink and Collingwood, 2005).

System Maintenance. For optimal dust collection, the following measures are recommended:

• Keep the vacuum hose clear and free of debris,

kinks and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the dust collection device and vacuum

hoses.

• Make sure that the vacuum bags and filters are

changed regularly, as often as necessary to prevent a decrease in airflow. Dust escaping from

the collection device can be a sign that airflow is

inadequate.

• For best results, set up a regular schedule for filter cleaning and maintenance. For example,

institute a rule to clean the filter or change the

bag at each break. This will prevent pressure

loss and ensure that exhaust airflow stays constant on the VDC system.

• Remember, the absence of visible dust does not

necessarily mean that employees are adequately

protected from silica exposure.

Dust Barriers

An employee who drills only an occasional small

hole in the course of a day may have relatively low

silica exposure. It is a good idea to minimize exposure to even small amounts of silica dust, so you

might want to experiment with techniques for capturing dust from a single small hole initially developed in the asbestos abatement industry.

One simple dust control method involves inserting the drill bit through a barrier, which is then

pressed against the working surface during drilling.

The dust exiting the hole collects against the barrier. If the barrier is damp, it forms a better seal

against the working surface and also moistens the

dust, thus capturing more dust and reducing the

amount that can escape when the employee

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removes the barrier. For example, employees

sometimes drill through shaving cream in an

upside-down waxed paper cup or through a damp

sponge to minimize exposure to asbestos (U.S.

GSA, 2001; Woods, 2000; LBL, undated).4 These

materials compress and are held in place by the

pressure of the advancing drill. Assuming the barrier material can make a good connection with the

surface, this method is appropriate for most materials that an employee might drill.

Tips for Devising a Dust Barrier for Occasional

Drilling. For optimal results, the following measures

are recommended:

• Insert the drill bit through the barrier until the tip

is just visible, and then set the tip against the

working surface in the correct position.

• Ensure that there are no gaps between the working surface and the barrier through which small

particles can escape and become airborne.

• Withdraw the drill bit by pulling it through the

barrier, so that the barrier collects any debris

drawn out with the bit.

• Dispose of dust and debris after completing

each hole. Handle the barrier carefully to minimize dust release.

• Add a moist material to the barrier to wet dust

and minimize release during disposal.

• When using a cup, use waxed paper, which will

compress under pressure, rather than

Styrofoam, which will crack.

• Do not allow the barrier to become overloaded.

For deeper holes, periodically check under the

barrier; it may be necessary to clean or empty it

before the hole is complete.

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed

spaces. Cleaning should be performed with a

HEPA-filtered vacuum or by wet methods.

Wet Methods

Wet methods are generally not appropriate for use

with electric rotary hammers unless the tools are

designed for use in damp environments. Pneumatic

drills, however, can be used for wet drilling, and

some come equipped with a water feed capability.

While designed primarily for use in explosive

atmospheres, water-fed pneumatic drills can also

be used to control silica exposures (CS UNITEC,

2003).

Wet methods are usually the most effective way

to control silica dust generated during construction

activities because wet dust is less able to become

or remain airborne. Although few specific data are

available regarding wet methods for drilling small

holes, studies have shown that drilling with waterfed bits or water spray at the bit-rock interface can

substantially reduce respirable dust generated by

rock drilling rigs (OSHA Case Files; Organiscak and

Page, 1996; NIOSH, 1999).

OSHA believes that wet methods can also help

control silica dust generated by smaller drills.

Controlled tests with a large-impact breaker (jackhammer) showed that an efficiently-operated, retrofitted spray-type water-feed system reduced

employee exposure to respirable silica (Zalk, 2000,

2002). Similarly, use of a water spray nozzle on a

pneumatic chipper was found to reduce exposure

to respirable silica dust by 70 percent (Sam, 2000).

Given the lower energy of handheld drills, a properly implemented water-feed system should significantly lower silica concentrations.

To ensure that dust emissions are minimized,

maintain the water supply equipment, including

pumps, hoses and nozzles in good operating condition. Track the water usage rate for different types

of jobs to predict the volume needed, and ensure

that enough water is available during the task.6

FreezingTemperatures. Freezing temperatures

complicate the use of water. Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Large portable

heating units are commonly used to heat commercial and sometimes road and highway projects.

Drain the system when not in use. If water freezes

on the ground, chip away the ice or use deicing

compounds or sand to control the slipping hazard.

Electrical Safety. Use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical

connectors for electric tools and equipment on construction sites (OSHA, 1996). These features are

particularly important to employee safety in wet or

damp areas, such as where water is used to control

dust. Although an assured equipment grounding

conductor program is an acceptable alternative to

GFCIs, OSHA recommends that employers use

GFCIs where possible because they afford better

protection for employees. (See 29 CFR 1926.404(b)(1)

for OSHA’s ground-fault protection requirements.)
Fans

Fans are not effective dust control devices when

used as the sole control method and should not be

used as the primary method for managing dust.

Fans can, however, be useful as a supplement to

other control methods. Use fans in enclosed areas,

such as bathrooms, where dust will build up due to

poor air circulation.

For the best effect, set an exhaust fan (the bigger, the better) in an open window or external

doorway so that the fan captures dust and blows it

outside. Avoid positioning employees near the

exhausted air. An exhaust fan works best if a second window or door across the room is opened to

allow fresh air to enter.

Example: A four-foot square fan is placed in a

window exhausting to outside the building at maximum fan speed. The fan will have the strongest

capture capability directly in front of the fan face,

but this quickly drops off. At two feet away from

the fan, the capture capability is reduced to 50 percent and at four feet, the capture capability is

reduced to seven percent of the capture capability

at the fan face. If the distance between the work

activity and fan face is greater than the length of

the fan side (four feet), dust capture would probably not be effective (ACGIH, 2007).

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled conditions,

and show the effectiveness of controls in reducing

silica exposures.

Case Study I: Three construction workers used

pneumatic and electric drills with 3⁄4-inch bits to drill

holes in the lower level of a concrete parking structure with poor ventilation. The employees used no

dust control methods and their silica exposure levels ranged from 0.1 mg/m3 to 0.3 mg/m3 (Lofgren,

1993).7

Case Study II: In an older Swedish study, an

employee used 6-millimeter (mm) bits to drill

numerous holes 50-mm deep (approximately 1⁄4-

inch by 2-inch holes) into concrete under experimental conditions. Without dust controls, the average respirable silica exposure level was greater

than 0.24 mg/m3 during the period evaluated. When

a dust extraction system was added to the drill, the

average respirable silica exposure was reduced to

less than 0.095 mg/m3.8 Investigators obtained similar results when they tested equipment with 10-mm

bits used for drilling 80-mm deep holes (approximately 3/8 inch by 31/8 inch). In this case, average

exposure decreased from 0.3 mg/m3 (no controls) to

less than 0.06 mg/m3 when dust extraction equipment was used (Hallin, 1983).9

In the same study, the operator tested equipment with a dust collection bag attached directly to

the drill. This condition had some of the highest

exposures reported for drilling with dust controls.10

The exposures were substantially lower than the

levels reported for uncontrolled drilling, but two of

the three results exceeded 0.1 mg/m3 (Hallin, 1983).

Respiratory Protection and Engineering

Control Evaluation

Using a rotary hammer or similar tool without engineering controls can cause exposures to respirable

crystalline silica to reach 0.3 mg/m3 or higher as an

8-hour time-weighted average. During periods of

active drilling, exposures can reach as high as 0.78

mg/m3 without controls. Therefore, it is important to

utilize effective controls to reduce employee exposures.

Both VDC systems and wet methods are generally effective in controlling exposures to below 0.1

mg/m3. However, wet methods are not appropriate

with electric rotary hammers that are not designed

to be used in wet environments. In these cases,

VDC systems offer the better option of control.

If the rotary hammer is being controlled by a

VDC system or wet methods, then respiratory protection may not be necessary. However, where

employee exposure exceeds 0.1 mg/m3 it may be

necessary to use a properly fitted, NIOSH-approved

half-facepiece or disposable respirator equipped

with an N-,R- or P-95 filter to supplement use of the

VDC system or wet methods methods (see 29 CFR

1926.103).

In any workplace where respirators are necessary to protect the health of the employee, or

whenever respirators are required by the employer,

the employer must establish and implement a written respiratory protection program with worksitespecific procedures and elements, including the

selection of respirators, medical evaluations of

employees, fit testing, proper usage, maintenance

and care, cleaning and disinfecting, proper air quality/quantity and training (see 29 CFR 1926.103).

Construction sites often involve many operations occurring simultaneously that can generate

respirable silica dust. Therefore, it is important and

necessary to utilize effective controls (such as wet

methods or VDC) in order to minimize total exposures to silica-exposed tool operators.

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Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine proper respiratory protection, visit OSHA’s Web site at

www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2007. Industrial Ventilation, a Manual of

Recommended Practice, 26th edition. American

Conference of Governmental Industrial Hygienists,

Cincinnati, OH, 2001.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati. OH,

2008.

CS UNITEC. 2003. Air Rotary Hammer Drill.

http://www.csunitec.com/ rotary/airrotary.html.

Accessed January 13, 2003.

Hallin, N. 1983. Occurrence of quartz in the construction sector (Report 1983-04-01). Bygghälsan—

The construction industry’s organization for working

environment, safety and health. Stockholm,

Sweden. April 1, 1983.

Heitbrink, W.A. and D.S. Watkins. 2001. The effect of

exhaust flow rate upon the respirable dust emissions for tuckpointing operations. In: In-Depth Study

Report: Control Technology for Crystalline Silica

Exposures in Construction. U.S. Department of

Health and Human Services, Centers for Disease

Control and Prevention, National Institute for

Occupational Safety and Health. ECTB No. 247-18,

2001.

Heitbrink, W. and Collingwood, S. 2005. Protecting

Tuckpointing Workers from Silica Dust: Draft

Recommendations for Ventilated Grinder. The

Center to Protect Workers’ Rights (CPWR).

www.cpwr.com

LBL. Undated. Asbestos management program,

appendix G, Bulk sampling procedure. Lawrence

Berkeley National Laboratory. Berkeley, CA.:

http://www.lbl.gov/ehs/ih/forms/AsbesProg.doc.

Accessed January 13, 2003.

Lofgren, D.J. 1993. Silica exposure for concrete

workers and masons. Appl. Occup. Environ. Hyg.

8(10):832-836, 1993.

NIOSH. 1996. Preventing silicosis and deaths in construction workers. U.S. Dept. of Health and Human

Services (National Institute for Occupational Safety

and Health, Publication No. 96-112). Cincinnati, OH.

NIOSH. 1999. Control technology and exposure

assessment for occupational exposure to crystalline

silica: Case 22 – rock drilling (ECTB 233-122c).

National Institute for Occupational Safety and

Health, Cincinnati, OH. November 19, 1999.

NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June.

Organiscak, J.A. and S.J. Page. 1996. Assessment of

airborne dust generated from small truck-mounted

rock drills. Report of Investigation No. 9616. U.S.

Department of the Interior, Bureau of Mines,

Pittsburgh, PA.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Sam, K. 2000. Control measures for reducing

employee exposure to concentrations of total and

respirable silica in the ready-mix concrete industry

during drum cleaning. Presentation at American

Industrial Hygiene Conference & Exposition.

Orlando, FL. May 24, 2000.

Shepherd, S., Woskie, S.R., Holcroft, C. and

Ellenbecker, M. 2009. Reducing Silica and Dust

Exposures in Construction During Use of Powered

Concrete-Cutting Hand Tools: Efficacy of Local

Exhaust Ventilation on Hammer Drills. Journal of

Occupational and Environmental Hygiene, 6:1,42-51,

2009.

U.S. GSA. 2001. Standard operating procedure for

asbestos operations and maintenance activities.

Appendix B: Cleaning above a drop ceiling--minicontainment methods. U.S. General Services

Administration, Kansas City, MO. July. http://safety.

gsa.gov/gsa/heartland/sops/acm_sop.pdf. Accessed

January 13, 2003.

Woods, David T. 2000. A common sense approach

to disturbing asbestos. Ind. Safety & Hyg. News

Online. www.ishn.com/CDA/ArticleInformation/features/BNP___Features___Item/0,2162,2572,00.html.

Accessed January 15, 2003.

Zalk, D. 2000. Presentation at American Industrial

Hygiene Conference & Exposition. Orlando, FL. May

24, 2000.

Zalk, D. 2002. Personal communication between D.

Zalk, Lawrence Livermore Laboratory, CA, and W.

Long, Eastern Research Group, Inc., Arlington, VA.

October 29, 2002.
Technical Notes

1 The three respirable crystalline silica results cited

are 0.3, 0.26, and 0.11 mg/m3, collected as 457-, 110-

and 177-minute samples, respectively (Lofgren,

1993).

2 Laboratories have not used particle counting for

crystalline silica analysis in many years and now

report exposure data gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using 0.1

mg/m3 of respirable quartz as an 8-hour timeweighted average as a benchmark to describe the

effectiveness of control measures. The benchmark

is approximately equivalent to the general industry

silica PEL. Other organizations suggest more stringent levels. For example, the National Institute for

Occupational Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be

limited to 0.05 mg/m3 as a 10-hour time-weighted

average (NIOSH, 2002). The American Conference

of Governmental Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures

be limited to 0.025 mg/m3 as an 8-hour time-weighted average (ACGIH, 2008).

3 This short-term respirable crystalline silica sample

was collected over a 45-minute period (NIOSH,

1996).

4 This technique, widely used for drilling asbestoscontaining materials, would also help control respirable silica-containing dust.

5 Water-fed drilling can include using small amounts

of water introduced into bailing air to suppress dust

and cool the bit, or water used instead of air to flush

debris from the hole. These studies indicate that

combining wet methods with local exhaust ventilation achieves even greater exposure reduction than

wet-methods alone.

6 Bit size, hole depth, substrate and weather all

affect the amount of water needed to control dust.

The usage rate must be adjusted for each individual

operation. For drill rigs with water injected into bailing air, about 1⁄2 to 1 gallon per minute is sufficient

(Organiscak and Page, 1996).

7 A bulk dust sample showed silica content of 12

percent in the concrete being drilled. During the

110- to 457-minute periods monitored, the employees’ silica exposures ranged from 0.11 mg/m3 to 0.3

mg/m3, with a median of 0.26 mg/m3.

8 Uncontrolled case for 6-mm bit: n = 6, median =

0.14 mg/m3, and range = 0.06 - 0.81 mg/m3.

Controlled case: n = 9, median = 0.08 mg/m3, and

range = 0.03 - 0.29 mg/m3

. Reported results are for

the 90- to 120-minute periods monitored. The lower

exposure levels may be due, in part, to the fact that

the employee in the controlled case drilled fewer

holes with each test drill while using dust collection

equipment, approximately 30 to 40 holes. Without

controls the employee drilled 40 to 90 holes with

each drill (Hallin, 1983).

9 Uncontrolled case with 10-mm drill bit: n = 4,

median = 0.295 mg/m3, and range = 0.28 - 0.33

mg/m3: Controlled case with 10 mm bit: n = 10,

median = 0.045 mg/m3, and range = 0.04 - 0.14

mg/m3. All sample durations were either 120 or 180

minutes (Hallin, 1983).

10 Of the three results for 120-minute samples associated with dust collection bags attached directly to

drills (0.04, 0.11 and 0.13 mg/m3

), two exceeded 0.1

mg/m3 and were among the highest 15 percent of

the 40 results obtained during controlled drilling

(Hallin, 1983).

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Vehicle-Mounted Rock

Drilling Rigs

This section covers drills mounted on trucks,

crawlers and other vehicles when used for

drilling rock or soil. The term “silica” used in this

document refers to respirable crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Employees produce dusts containing

silica when they use rock-drilling rigs mounted on

trucks, crawlers or other vehicles to drill into rock,

concrete, or soil. The small particles easily become

suspended in the air and, when inhaled, penetrate

deep into employees’ lungs.

Studies have shown that drilling into rock, concrete, or soil may produce hazardous levels of respirable silica if measures are not taken to limit and

control dust emissions. The National Institute for

Occupational Safety and Health (NIOSH), for example, found that a drilling rig operator at a construction site was exposed to 0.54 mg/m3 (milligrams of

silica per cubic meter of air) over the course of a

day (NIOSH, 1992b).

This level is more than five times the Occupational Safety and Health Administration’s (OSHA)

benchmark of 0.1 mg/m3 (milligrams per cubic

meter of air) as an 8-hour time-weighted average

(TWA), an exposure approximately equivalent to

OSHA’s general industry permissible exposure limit

(PEL).1 Furthermore, the U.S. Bureau of Mines found

that respirable silica concentrations averaged 2.13

mg/m3 in the immediate vicinity of small surface

drilling operations (U.S. Bureau of Mines, 1995).

Concentrations of respirable silica in soil and

rock may vary widely depending on the type of

underlying rock formation and history of volcanic

eruptions. For example, the preliminary site investigation of the Department of Energy’s Yucca

Mountain site indicated that soil concentrations of

cristobalite (a form of silica) ranged from 18 to 28

percent, and many job tasks were associated with

overexposure (CRWMS 1999). If a construction company will be doing substantial excavation at a site,

then obtaining a profile of the silica content of soil

and rock from bulk samples of the projected excavation represents good industrial hygiene practice.

Many times this information can be obtained as part

of the project design and provided to the contractor

as part of the description of existing site conditions.

This section describes methods available to

reduce employees’ exposures to silica when using

vehicle-mounted drilling rigs. The three primary

methods used to reduce dust emissions during rock

drilling are dust collection systems, wet methods

and operator isolation. OSHA recommends that

these drills always be operated using a combination

of dust control techniques.

Earth drilling rigs operated without dust controls are

capable of producing very high respirable silica levels

(Photo courtesy of NIOSH, 1992.)

Silica Dust Control Measures

Dust Collection Systems

Various types of dust collection systems are available for earth drills. Commonly used equipment

incorporates a movable suction duct attached to a

shroud (a flexible rubber skirt) that encloses the drill

hole opening and captures the cuttings coming

through the hole. Drilling equipment that does not

include these controls can be retrofitted by the manufacturer or a mechanical shop.

Dusty air pulled from the shroud enclosure usually passes through a flexible duct leading to a primary dust separator and a secondary filter system.

The dust separator often includes a self-cleaning

“back-pulse” feature that discharges the collected

particles to the ground. Some secondary filter systems are also self-cleaning. Finally, the exhaust air is

discharged to the atmosphere.

Design Considerations

Dust collection systems are commercially available

and work well in all climates and with all drill types.

If the systems are well designed, dust collectors

offer substantial dust reduction. Some important

design factors are described below.

Drill Bit Shroud Design. Conventional shrouds

are rectangular and constructed of four separate
pieces of rubber attached to the drill platform. Dust

can escape from each open seam or gap. Designs

that minimize the number of flaps and gaps can

help improve dust capture.

NIOSH tested a circular, slightly conical shroud

design that reduced gaps through which dust could

escape. Steel banding attached the shroud to the

drill deck, closed the single seam and helped hold

the shroud’s shape. A small trap door in the test

shroud allowed employees to shovel cuttings from

inside without distorting or lifting the shroud,

actions which can reduce dust collection efficiency.

Keeping cuttings cleared away is always important

for maintaining good contact between the bottom

of a shroud and the ground. In the tests, the singleseam conical shroud captured dust more efficiently

(99 percent) than a conventional square-shaped

shroud (95 percent) (NIOSH, 1998).

Adequate Airflow. The dust collector must be

designed to draw more air volume than the bailing

air volume used to flush cuttings from the drill hole.

To capture all the bailing air and dust using a conventional shroud, the airflow rate for the dust collector should be a minimum of three times the bailing

airflow rate (NIOSH, 1998). Improved shroud designs

may require somewhat less air, while less efficient

shrouds may require more. Air volume is generally

measured in cubic feet per minute (CFM).

Dust Collector Discharge Shrouds. A shroud or

sleeve enclosing the dust collection hopper discharge door can help reduce dust emissions. During

the dumping cycle, the sleeve guides particles to the

ground, thereby reducing dust that would otherwise

become airborne as material falls to the ground.

Heavy tarps or extendable coil-type flexible duct

materials make effective shrouds.

Tests of discharge door shrouds showed an 81

percent reduction in airborne dust during the dump

cycle (Page and Organiscak, 1995). Remember to

control material dumped from filter cartridges as

well. If possible, discharge this dust at a distance

from employees (OSHA Case File).

Exhaust Air Discharge Design. Dust exposures

can be further reduced by extending the primary

dust collection system exhaust port to release the

air farther away from employees. After an eight-foot

vertical PVC pipe was installed on the discharge

port, a test showed that airborne respirable dust

concentrations 100 feet downwind of the drill were

reduced by 62 percent (Organiscak and Page, 1996).

Extending the exhaust pipe away from employees

becomes particularly important if a secondary filter

is not used to capture the respirable silica particles.

If a flexible duct is extended near ground level,

avoid placing the opening where the exhausted air

will blow on other employees (including those

downwind). Instead, place the duct opening near

the ground where exhausted dust might deposit.

To minimize airflow resistance in the flexible duct,

run extensions in a relatively straight line, use the

same diameter as the discharge flexible duct and

keep added lengths to the minimum needed to

move the discharged air away from employees.

Maintenance Considerations

Dust collectors require routine care to ensure that

they are functioning as designed. Equipment that is

not well maintained can contribute to employee

exposure. Check the following points on a regular

basis.

Close Gaps in Shroud. To be effective, a shroud

must fully enclose the bit. Make sure that the

shroud on your equipment is in good condition.

Repair or replace torn or missing pieces and ensure

that gaps seal well. Tests show that simply maintaining the shroud in good condition can reduce

dust exposures by over 60 percent (Organiscak and

Page, 1996). For best results, lift the shroud as little

as possible.

If a well-maintained, well-sealed shroud leaks

dust, the airflow might be inadequate. Check the

condition of filters, the blower and ducts which are

possible causes of inadequate airflow.

Duct and Filter Maintenance. Clogged flexible

ducts and filters restrict dust collector airflow.

Visually inspect flexible ducts and filters often and

stay alert to signs of reduced flow (for example, an

increase in dust escaping from the shroud). Remove

material that accumulates in the flexible ducts;

deposited dust both restricts airflow and could be a

sign of filter or blower problems.2

If filters have an automatic cleaning cycle, be

sure that it is functioning as intended. Replace

clogged or damaged filters. During one drilling rig

evaluation, dust collector air suction was increased

from 2,165 CFM to 3,370 CFM when new filters were

installed (Page, 1991).

Fan Maintenance. Abrasive dust is destructive to

the fan motor, blades and drill bits. Routine maintenance is important for both. Experts recommend

scheduled inspections to check the following points

on the fan blower unit (ACGIH, 2001):

• Bearings and lubrication;

• Belt tension, wear and slippage;

• Excessive vibration;

• Coupling and belt alignment;

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• Fan impeller alignment and rotation;

• Excessive wear or caking on the impeller;

• Mounting bolts, set screws and bushings; and

• Safety guards.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne respirable dust present that is not visable to the naked eye.

Wet Methods

The proper use of wet methods requires a skilled

operator. In wet drilling, too much water can create

mud slurry at the bottom of the hole that can entrap

the bit, coupling and steel extensions. Too little

water will not effectively control dust emissions.

Studies indicate that the optimal water flow rate is

best achieved by slowly increasing the water to the

point where visible dust emissions are eliminated

(Organiscak and Page, 1996).3

While water injection methods work well for percussion, drag and button bits, special consideration

is required to protect bits with rollers (tri-cone bits)

from excess water on moving parts. A water separator described by the U.S. Bureau of Mines

removed all water except a slight mist from the bailing air, which improves dust control as explained

below (Page, 1991).

Water Injection at Bit. In wet drilling systems

that use forced air to flush cuttings from the hole,

water is introduced into the bailing air at the drill

head. The water serves to gather the small particles

into larger ones, thus reducing dust emissions. One

study of dust emissions during drilling found that

wet drilling was 29 percent more effective in reducing airborne respirable dust in the immediate drill

vicinity (where the operator would typically stand)

than a conventional dust collection system without

water (Organiscak and Page, 1996).

Wet drilling combined with a conventional dust

collection system offers even better dust control.

One exposure survey of rock drilling operations

showed that the combination of wet drilling with a

dust collection system resulted in a 42 percent

reduction in an operator’s respirable dust exposure

when compared to wet drilling alone (Zimmer, 1997).4

Water Injection at Dust Collector Exhaust. Tests

have shown that injecting small quantities of water

into the exhaust air discharge duct significantly

reduces respirable silica dust emissions. In a drill

site experiment, investigators placed a water tank

at a location suitable for a gravity feed and coupled it to the exhaust air discharge port using 1⁄4-

inch flexible tubing and a needle valve. Then they

turned the exhaust port so that it was slanting down

and added a 20-foot flexible duct that was also

slightly downward sloping, ending about one foot

above the ground, to allow material to fall out the

end. Water was trickled into the flexible duct at a

rate of one gallon per five minutes (0.2 gallons/

minute) (Organiscak and Page, 1996).5,6

When adding water to the discharge flexible duct

of the dust collection system, it is important not to

use too much, to avoid clogging problems. The flow

rate should be slowly increased until visible dust

emissions are significantly reduced. For better control, it is recommended that two valves be used to

adjust the water flow, one as a flow regulator and

the second as the on/off control. Add an in-line

water filter to keep debris in the water from blocking

the needle valve (NIOSH, 1997).

Even at ideal water flow rates, it will be necessary to check the flexible duct interior daily and

clear dust deposits that may form in it. A quickrelease clamp on the flexible duct will make the

process easier (Organiscak, 2002).

Operator Isolation

Drill operators using rigs with enclosed cabs can

reduce their potential silica exposure by spending as

much time as possible inside the vehicle cab while

drilling is in progress. To be effective, the cab must be

well sealed and ventilated. Door jams, window

grooves, power line entries and other joints should be

tightly sealed. Provide a slight positive pressure, using

filtered air, to prevent dust from leaking into the cab.

For the best dust control, use a high-efficiency particulate air (HEPA) filter. Some equipment permits the

operation of the drill from inside the cab.

An exposure survey found that if operators

spend time inside a fully enclosed cab and use wet

drilling together with a dust collection system, dust
exposures can be reduced up to 76 percent when

compared to wet drilling alone (Zimmer, 1997).

While the use of enclosed cabs substantially

reduces silica exposures, operators might be unwilling to keep windows and doors closed if the cab is

not air conditioned. Equipment might be upgraded

by installing aftermarket ventilation and air conditioning systems.7

Even in a sealed cab, dust already inside the cab

can become airborne. Clean cabs daily to remove

dust tracked in on boots or settled on surfaces.

Combining Methods for Better Dust Control

To effectively protect employees, dust control is

necessary at multiple points in the drilling process.

Table 1, below, summarizes the common sources of

airborne dust and the dust management methods

described in this section. Most of these techniques

can be used together to enhance employee protection from silica exposures.

Table 1: Summary of Dust ControlTechniques for

Vehicle-Mounted Rock Drilling

Source of Dust ControlTechniques

Primary Source: • Use wetdrilling/water

Dust released injection methods

from drill hole • Install dust collector

Dust escaping from • Maintain shroud

dust collector shroud condition

• Close gaps in shroud

• Avoid lifting or

distorting the shroud

during drilling

• Clear away cuttings

• Increase airflow rate

Airborne dust • Add a shroud to

released from dust discharge door

separator and filter • Inject water into dust

cartridge discharge collector discharge

port • Install a filter bag over

cartridge filter dump

discharge point

Fine particles in • Extend flexible duct

exhaust air from to release air at

dust collector a distance from

employees

Uncontrolled dust • Use enclosed cab

from drilling and other with filtered air

nearby activities • Stay upwind of dust

sources, when possible

• Watch for sources of

dust and make adjustments as needed

Table 2, below, ranks the efficacy of various combinations of available control technology for rock

drilling rigs and reflects the judgment of OSHA’s

contract consultant, ERG, based on their literature

review (ERG, 2003).

Table 2: Rating Dust Control Methods for

Vehicle-Mounted Rock Drilling Rigs

Control Method Rating

Wet drilling + dust collection *****

system + operator’s cab

Wet drilling + dust collecting  

system

Wet drilling + operator’s cab ** **

Wet drilling ***

Dust collection system ***

No control *

*= poor *****= excellent

Ratings are based on the method’s ability to

efficiently capture respirable dust and reliably

control employees’ exposure.

Source: ERG, 2003.

Work Practices

Proper work practices are also important in reducing potential silica exposures.

• When possible, equipment should be positioned

so that operators and others can work upwind

from a drill’s dust emissions.

• Put dust control equipment on a regular maintenance schedule.

• Train employees to watch for sources of dust

and to make necessary adjustments or repairs to

reduce emissions – and their own exposure.

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled conditions,

and show the effectiveness of controls in reducing

silica exposures.

No Dust Controls. NIOSH evaluated silica exposure for an employee dry-drilling rock when the

drill’s dust collector was out of operation. The 51⁄2-

hour sample indicated that the drill operator’s exposure was 0.54 mg/m3 when averaged over an 8-hour

shift. If the operator had continued the same work

for the full 8 hours, his respirable silica exposure

would have been 0.80 mg/m3, which greatly exceeds

allowable levels (NIOSH, 1992b).

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Multiple Dust Controls. In contrast, at another

construction site employees used multiple drills

with various dust controls to prepare granite for

blasting.8 OSHA measured a full-shift exposure

level of 0.054 mg/m3 (half the PEL) for an operator

using a water-injected drill fitted with a two-stage

dust collector.

This construction company used combined dust

controls to keep exposures consistently below the

PEL for all drill operators and their assistants (OSHA

Case File).9

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed spaces.

Cleaning should be performed with a HEPAfiltered vacuum or by wet methods.

Respiratory Protection and Engineering

Control Evaluation

Operating a rock drilling rig without engineering

controls can cause exposures to respirable silica to

reach 0.8 mg/m3 or higher (NIOSH, 1992b). Effective

controls, such as dust collection systems, wet methods and operator isolation can reduce exposures.

Operators of rock drilling rigs working in

enclosed, well-ventilated and sealed cabs should

not experience silica exposures in excess of 0.1

mg/m3 as an 8-hour time-weighted average.

However, those operators and helpers working outside of cabs, or those using cabs which are not

enclosed, well-ventilated and sealed, can experience

elevated exposures. OSHA estimates that exposures

would not normally exceed 1.0 mg/m3 with appropriate wet methods or dust collection systems in

place. Therefore, in addition to the controls, the

operators and helpers working in these conditions

may need to wear a properly fitted, NIOSH-approved

half-facepiece or disposable respirator with an N-, Ror P-95 filter. Such protection is adequate for exposures up to 1.0 mg/m3

. Where exposures exceed 1.0

mg/m3, higher levels of respiratory protection are

necessary (see 29 CFR 1926.103).

Since exposures may not be controlled to below

0.1 mg/m3 even with wet methods and/or dust collection systems, employees in close proximity to the

work operation where silica dust is generated may

need respiratory protection. The level of respiratory

protection is dependent on the employee’s silica

exposure, which varies depending on factors in the

work environment (such as enclosed, semienclosed, or open spaces and/or multiple operations

generating silica dust), environmental conditions

(such as wind direction and speed) and the percentage of silica found in the material.

In any workplace where respirators are necessary to protect the health of the employee, or whenever respirators are required by the employer, the

employer must establish and implement a written

respiratory protection program with worksite-specific procedures and elements. These should include

the selection of respirators, medical evaluations of

employees, fit testing, proper usage, maintenance

and care, cleaning and disinfecting, proper air quality/quantity and training (see 29 CFR 1926.103).

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine proper respiratory protection, visit OSHA’s Web site at

www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2001. Industrial Ventilation, A Manual of

Recommended Practice. 24th Edition. American

Conference of Governmental Industrial Hygienists.

Cincinnati, OH, 2001.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH,

2008.

CRWMS. 1999. Engineering File – Subsurface

Repository. Civilian Radioactive Waste Management

System Management & Operating Contractor.

BCA000000-01717-5705-00005 Rev 02, DCN 01. June,

1999.

ERG. 2003. Technological Feasibility Study and Cost

Impact Analysis of the Draft Crystalline Silica

Standard for Construction. Table 2, Ranking of dust

control technology, ERG composite of available

research on control technology. February, 2003.

NIOSH ALERT, 1992a. Preventing Silicosis and

Deaths in Rock Drillers. No. 92-107.

NIOSH. 1992b. Environmental surveillance report:

Breckinridge Construction Drilling, Westover, WV.

National Institute for Occupational Safety and

Health, Division of Respiratory Disease Studies,

Morgantown, WV, 1992.
NIOSH. 1997. Silica...it’s not just dust – What rockdrillers can do to protect their lungs from silica dust.

U.S. Dept. of Health and Human Services (National

Institute for Occupational Safety and Health,

Publication No. 97-118), available at <http://www.

cdc. gov/niosh/rock.html>. Accessed November 22,

2002.

NIOSH. 1998. New shroud design controls silica

dust for surface mine and construction blast-hole

drills. U.S. Dept. of Health and Human Services

(National Institute for Occupational Safety and

Health, Publication No. 98-150), 1998.

NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June, 2002.

Organiscak, J.A. 2002. Personal communication

between J. Organiscak, National Institute for

Occupational Safety and Health, Pittsburgh, PA, and

W. Long of Eastern Research Group, Inc. November

21, 2002.

Organiscak, J.A. and S.J. Page. 1996. Assessment of

airborne dust generated from small truck-mounted

rock drills. Report of investigation No. 9616. U.S.

Department of the Interior, Bureau of Mines,

Pittsburgh, PA, 1996.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Page, S.J. 1991. Respirable dust control on overburdened drills at surface mines. American Mining

Congress, Coal Convention. June 5, 1991.

Page, S.J. and J.A. Organiscak. 1995. Taming the

dust devil: an evaluation of improved dust controls

for surface drills using Rotoclone collectors.

Engineering and Mining Journal, pp. ww30 – ww31.

November, 1995.

U.S. Bureau of Mines. 1995. Dust collector discharge

shroud reduces dust exposure to drill operators at

surface coal mines. Technology News. No. 447.

March, 1995.

Zimmmer, A.T. 1997. Comparative evalution of dust

control technologies on percussion rock-drilling rigs.

Appl. Occup. Environ. Hyg. 12(12): 782-788.

December, 1997.

Technical Notes

1 Laboratories have not used particle counting for

crystalline silica analysis in many years and now

report exposure data gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using 0.1

mg/m3 of respirable quartz as an 8-hour timeweighted average as a benchmark to describe the

effectiveness of control measures. The benchmark

is approximately equivalent to the general industry

silica PEL. Other organizations suggest more stringent levels. For example, the National Institute for

Occupational Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be

limited to 0.05 mg/m3 as a 10-hour time-weighted

average (NIOSH, 2002). The American Conference

of Governmental Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures

be limited to 0.025 mg/m3 as an 8-hour time-weighted average (ACGIH, 2008).

2 To avoid clogging, ACGIH (2001) recommends

3,500 to 4,000 feet per minute (FPM) minimum air

velocity through ducts carrying rock or concrete

dust. Use a higher velocity of at least 4,500 FPM if

dust is moist or contains small chips.

3 Bit size, hole depth, substrate and weather all

affect the amount of water needed to control dust.

The usage rate must be adjusted for each individual

operation, but typically will be about 1⁄2 to 1 gallon

per minute.

4 Certain drill systems use large quantities of water,

rather than air, to flush cuttings from the hole. The

large volume of water in the hole usually controls

dust completely and additional devices, such as

dust collectors, offer very little extra benefit.

5 High air velocity and turbulence in the flexible

duct atomize the water drops to create a mist, which

captures dust as it moves down the length of the

duct (Organiscak, 2002).

6 To measure water flow rate, adjust the flow as

desired, then check how long it takes to fill a onegallon milk container.

7 To better exclude dust, pressurize the cab interior

by using a pressurization unit to introduce filtered

outside air into the cab. Studies show that 100 cubic

feet per minute (CFM) provides adequate pressure

(0.2 inches of water gauge) to keep dust from leaking into a well-sealed 100 cubic foot cab.

8 Bulk samples indicated the granite contained 30 to

40 percent crystalline silica.

9 Seven full-shift samples collected over six months.

Air-sampling data collected by OSHA and a company consultant were consistently below 0.061 mg/m3

,

with an average exposure level of 0.032 mg/m3

(OSHA Case File).

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Drywall Finishing

This section describes methods of controlling

silica exposures during drywall finishing tasks.

The term “silica” used in this document refers

to respirable crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Even when dust does not contain silica,

employees performing dusty jobs may be at risk.

Excessive exposure to airborne dust can contribute

to tissue injury in the eyes, ears and respiratory passages.

When sanding drywall joint compound, employees generate a substantial amount of airborne dust.

The smallest dust particles – the respirable particles

– are hazardous because they are deposited deep in

the lungs (Murray, J. and Nadel, J., 1994). Dust that

contains silica presents a particularly dangerous

hazard, but exposure to high levels of dust, whether

or not it contains silica, can also be harmful to

health. To avoid potentially hazardous exposures,

employers should implement effective dust control

measures during all drywall finishing activities.

The primary method for avoiding silica exposure, and thereby eliminating the risk of developing

silicosis, is to use only silica-free joint compounds.

Drywall finishers can also reduce their dust exposure by using vacuum dust collection equipment or

wet sanding methods.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be airborne respirable dust present that is not visible

to the naked eye.

Drywall Finishing Employees’ Exposures

The silica exposures of drywall finishing employees

are typically well below allowable limits, primarily

due to the low silica content of joint compounds.

Nonetheless, drywall joint compounds may contain

varying amounts of silica and drywall finishing

employees can be overexposed in certain circumstances. For example, by using a joint compound

containing just 3 percent silica, an employee could

exceed the Occupational Safety and Health

Administration’s (OSHA) benchmark of 0.1 mg/m3

(milligrams of silica per cubic meter of air) as an

8-hour time-weighted average (TWA), an exposure

approximately equivalent to OSHA’s general industry permissible exposure limit (PEL), during intensive periods of uncontrolled drywall sanding on ceilings. One study of drywall sanding, in which a silica-containing joint compound was used, found that

the respirable silica level exceeded 0.15 mg/m3

(NIOSH, 1997).1,2

The potential for silica exposure is also indicated

by the results of NIOSH tests of settled drywall dust.

NIOSH found that dust generated during drywall

sanding contained up to 6 percent silica (NIOSH,

1995). Other studies found that silica constituted up

to 3.7 percent of the airborne respirable dust collected in drywall sanding employees’ breathing zones

(NIOSH, 1997; Epling et al., 1999).3

Drywall sanding employees can also experience

total dust exposures substantially above OSHA limits. In one study, employees using hand sanders

without controls had exposures up to 143.1 mg/m3

of total dust. Similarly, employees using conventional pole-mounted sanders were exposed to up to

35.1 mg/m3 of total dust (CPWR, 1998).4

Although both of these exposures exceed regulatory limits, these results demonstrate that pole

sander use can reduce dust exposures by increasing

the distance between the employee and the point of

work. An earlier NIOSH study also found lower

exposures for employees using pole-mounted drywall sanders compared to handheld sanding

(NIOSH, 1995).

Additionally, NIOSH (1997) found that some of

the highest dust exposures occur when employees

sand joint compound in enclosed spaces, such as

closets or small rooms. Poor air exchange in these

areas causes dust levels to build up when dust controls are not used.

Increasing or decreasing dust dissipation (by

increasing distance to the employee or decreasing

air exchange) affects respirable dust levels as well

as total dust levels. For example, concrete finishers

using a long-angled jig to grind a ceiling had lower
silica exposures than employees grinding concrete

with equipment attached to a short section of pipe

and held directly overhead (OSHA Case Files).

Employees grinding concrete indoors had higher

respirable silica exposures than employees performing the same task outdoors, where dust could dissipate more quickly (Lofgren, 1993; NIOSH, 2001;

OSHA Case Files).

Silica-Free Joint Compounds

Many manufacturers offer joint compounds that

contain little or no silica. In a study of six brands of

joint compound purchased at retail stores, no crystalline silica was detected in three brands (NIOSH,

1997). The silica present in a sample of one of the

six products, however, was substantially different

from the percentage listed on the material safety

data sheet (MSDS) for that product.5 Nonetheless,

OSHA recommends that employers rely on manufacturers’ information and use proper methods to

minimize employees’ dust exposures, rather than

testing joint compounds themselves.

Regardless of a compound’s silica content, the

high levels of dust that drywall finishing may generate also poses a health hazard. Thus, OSHA recommends that employees always use dust control

measures when drywall sanding. The two principal

methods for controlling dust are (1) vacuum dust

collection systems and (2) wet sponging. Either

method is easy to implement.

Silica-Free Joint Compounds

• Check the label and the MSDS to identify the

product’s ingredients (usually listed in Section 3

on the MSDS).

• Avoid using joint compounds that contain crystalline silica or quartz (another common term

for crystalline silica).

• Always use dust control methods, regardless of

the joint compound’s silica content.

Vacuum Dust Collection Systems

Vacuum dust collection (VDC) systems for drywall

sanding equipment are commercially available, and

studies show that they significantly reduce total

dust concentrations. A NIOSH study of the effectiveness of several vacuum dust collection systems

showed reductions in total dust exposures ranging

from 80 to 97 percent, depending on the system

used (NIOSH, 1995).

Similarly, a second study of vacuum systems

reported reductions in total dust exposures of 96

percent when used during pole sanding and 95 percent for hand sanding. Both of the resulting exposure levels were well below regulatory limits for

total dust (CPWR, 1998).

Figure 1 shows the average reduction in airborne

dust measured for four drywall sanding operations—pole-mounted sanding and hand sanding

with and without vacuum dust control measures

from the CPWR study.6

Vacuum dust collection systems typically consist

of a sanding screen and a head, with a hose port to

connect a portable wet or dry vacuum. Vacuum

sanders can be handheld or pole-mounted.

A third study compared the effectiveness of various drywall sanding techniques. The ventilated

sander was the most effective in controlling exposures to respirable dust, reducing dust concentrations by 88 percent when compared to a block

sander (Young-Corbett and Nussbaum, 2009).

Using and Maintaining the Vacuum

Some dry sanding vacuum system manufacturers

recommend using a shop vacuum, while others

suggest using industrial vacuums (wet or wet/dry),

especially for heavy-duty sanding projects.

Vacuum performance depends largely on how

well the filters are maintained. When filters become

caked with dust, the vacuum’s airflow rate decreases

and dust is not captured as efficiently. Some drywall

sanding vacuum systems include wet dust collection (air bubbled through water) as a type of prefilter to extend vacuum filter life. Regardless of the

type of system used, put the vacuum on a routine

maintenance schedule and inspect it frequently.

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Tips on Filters

• Use high-efficiency filters for maximum dust

control. Typical shop vacuums might not have

adequate filtration systems.

• Regularly clean and/or replace filters. Determine

the rate at which vacuum filters become clogged

or filled and create an appropriate schedule for

cleaning and replacing the filters.

• If the vacuum has a “back-pulse” filter cleaning

cycle, periodically check this feature to maintain

the vacuum’s efficiency.

• Take precautions when cleaning or changing

vacuum filters, bags and canisters to prevent

accidental dust releases.

• Make sure that all vacuum hoses are clean and

free of cracks to maintain the correct airflow rate

and pressure. Check the entire system daily for

signs of poor dust capture or dust leaks and

repair accordingly.

• Encourage employees to watch for signs that

dust collection equipment is not working efficiently and to make adjustments as necessary.

Vacuum dust collection methods are likely to

reduce silica exposures to levels less than 1 mg/m3

while performing drywall finishing. If using a VDC

system, the exposure monitoring needs to be performed while it is in operation. This enables you to

check the adequacy of the VDC system as well as

seeing if it is necessary to use respiratory protection.

Tips for Selecting a Drywall FinishingTool with

Vacuum Dust Collection (NIOSH, 1995)

Most vacuum sanding tools offer dramatic dust

reduction. When choosing among tools, employers

can concentrate on those features that promote

employee acceptance, such as:

• A comfortable handle.

• A lightweight vacuum hose.

• A good connection between the hose and tool.

• Equipment that balances flexibility and stability

in the sanding head.

• Models that allow the user to maintain a comfortable posture.

Consider the practical aspects of equipment use.

For example:

• For wet collection systems, is it convenient to

change the water?

• Will the equipment be easy to clean?

• Will the vacuum be easy to service?

Wet Sponge Method

Wet methods are often the most effective means of

controlling dust because particles never have a

chance to become airborne. Drywall compound

manufacturers often recommend using wet finishing methods for dust control. (NIOSH, 1995). A laboratory study found that use of a wet sponge sanding

method reduced respirable dust concentrations by

60 percent when compared to a block sander

(Young-Corbett and Nussbaum, 2009).

The wet sanding method for drywall finishing

uses a sponge to wet the drywall joint compound

and remove residues. For wet sanding, saturate a

sponge with clean lukewarm water and wring it out

to prevent dripping. Then gently rub the high spots

using as few strokes as possible to avoid grooving

the joints. The sponge should be cleaned frequently.

In addition to reducing employee exposures,

wet finishing methods offer other advantages. For

example, wet methods often require less cleanup,

the wallboard face is not scuffed during finishing,

and joints are easier to conceal with paint than

joints that are dry sanded (USG, 2002). Wet finishing can be more complicated on poorly finished

joints because employees may find it difficult to

remove large amounts of joint compound with this

method. Therefore, employees should apply joint

compound smoothly so that little finishing is required.

Some contractors are concerned about the

increased drying time associated with wet methods.

All wet-sanded areas must dry thoroughly before

applying additional coats of joint compound or decorating. Some employees, however, already use

heat guns or space heaters to shorten joint compound drying times; these methods allow painting

to begin sooner, even after wet sanding. Further, the

time spent drying the joint compound might be offset by the time it would otherwise take to remove

dust particles from the walls before painting.

Tips for Using Drywall Sponges

• Use quality application techniques to minimize

excess joint compound on the surface.

• Use as few sanding strokes as possible to avoid

grooving the surface.

• Use drying aids to shorten drying time.

• Make sure that sponges and water buckets are

thoroughly cleaned after each use to prevent

dust from drying on the equipment and becoming airborne.

• Consult manufacturers’ recommendations for

wet sanding drywall compounds.
Respiratory Protection and Engineering

Control Evaluation

Employees who sand drywall without controls are

often exposed to high concentrations of dust. This

dust may or may not contain respirable silica,

depending upon the ingredients in the joint compound. If silica is a component within the joint compound, then it is likely that respirable silica will be

released as a particulate. Whether the dust contains

silica or not, exposures to drywall sanders are capable of exceeding the PEL for total dust, which is 15

mg/m3, as well as the PEL for respirable dust, which

is 5 mg/m3.

The use of silica-free joint compounds, wet

methods, and/or effective vacuum dust collection

methods are very effective in virtually eliminating or

suppressing silica and respirable dust. With the use

of such controls, it may be possible to eliminate the

need for respiratory protection to control exposures

to silica dust.

However, the use of silica-free joint compound

alone will not reduce exposures to respirable dust.

Data suggest that the use of wet methods and vacuum dust collection methods can also reduce respirable dust exposures below 5 mg/m3

. With the

addition of such controls, respirators may not be

needed for protection against respirable dust.

If wet methods or vacuum dust collection methods are not feasible, employees may be required to

wear appropriate respiratory protection. A NIOSH

approved half-facepiece or disposable respirator

with an N-, R- or P-95 filter can protect employees

exposed to up to 50 mg/m3 respirable dust.

In any workplace where respirators are necessary to protect the health of the employee, or whenever respirators are required by the employer, the

employer must establish and implement a written

respiratory protection program with worksite-specific procedures and elements. These sould include

the selection of respirators, medical evaluations of

employees, fit testing, proper usage, maintenance

and care, cleaning and disinfecting, proper air quality/quantity and training (see 29 CFR 1926.103).

Exposure monitoring for respirable dust should

be conducted periodically while wet methods or

vacuum dust collection methods are being utilized

to ensure that engineering controls are working

properly and that the proper level of respiratory

protection, if necessary, is being used.

For more information on how to determine proper respiratory protection, visit OSHA’s Web site at

www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed spaces.

Cleaning should be performed with a HEPAfiltered vacuum or by wet methods.

References

ACGIH. 2001. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Center to Protect Workers’ Rights (CPWR). 1998.

Drywall Dust Engineering Controls. Video VI-98.

Produced jointly with National Institute for

Occupational Safety and Health (NIOSH)

Engineering and Work Practices Controls Work

Group.

Epling, C., Gitelman, A., Desai, T. and J. Dement.

1999. Airborne exposures and ambulatory peak

expiratory flow in drywall finishers. Report OSH2-

98. Center to Protect Workers’ Rights.

Lofgren, D.J. 1993. Case studies: Silica exposure for

concrete workers and masons. Appl. Occup.

Environ. Hyg. 8(10):832-836. October, 1993.

Murray J. and Nadel J., Editors. Textbook of

Respiratory Medicine, 2nd Ed., 1994, Airway

Pharmacology, pp. 285-311.

NIOSH. 1984. Health Hazard Evaluation Report.

Grand Gulf Nuclear Power Plant, Port Gibson, MI.

Dept. of Health and Human Services (HETA 83-132-

1508). Cincinnati, OH.

NIOSH. 1995. In-depth survey report: a laboratory

comparison of conventional drywall sanding techniques versus commercially available control. ECTB

208-11a. National Institute for Occupational Safety

and Health.

NIOSH. 1997. Health Hazard Evaluation Report.

Center to Protect Workers’ Rights. Washington, DC,

Dept. of Health and Human Services Report (HETA94-0078-2660). Cincinnati, OH.

NIOSH 2001. In-depth survey report for four sites:

exposure to silica from hand tools in construction

chipping, grinding, and hand demolition at Frank

Messer and Sons Construction Company, Lexington

and Newport, KY, and Columbus and Springfield, OH

(EPHB 247-15). National Institute for Occupational

Safety and Health, Cincinnati, OH. April, 2001.

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NIOSH. 2002. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June, 2002.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

USG. 2002. Finishing and Decorating Gypsum

Panels/Wet Sanding. J-610/12-87.

http://www.usg.com. (Accessed November 16,

2002.)

Young-Corbett, D.E. and Nussbaum, M.A. (2009).

Dust Control Effectiveness of Drywall Sanding

Tools. Journal of Occupational and Environmental

Hygiene, 6:7, 385-389.

Technical Notes

1 A 382-minute sample resulted in a respirable dust

exposure level of 7.0 mg/m3 and a silica level concentration of 0.21 mg/m3

.

2 Laboratories have not used particle counting for

crystalline silica analysis in many years and now

report exposure data gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using 0.1

mg/m3 of respirable quartz as an 8-hour timeweighted average as a benchmark to describe the

effectiveness of control measures. The benchmark

is approximately equivalent to the general industry

silica PEL. Other organizations suggest more stringent levels. For example, the National Institute for

Occupational Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be

limited to 0.05 mg/m3 as a 10-hour time-weighted

average (NIOSH, 2002). The American Conference

of Governmental Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures

be limited to 0.025 mg/m3 as an 8-hour time-weighted average (ACGIH, 2008).

3 Epling (1999) collected 8-hour respirable crystalline

silica samples at two construction sites using a 10-

millimeter cyclone at 2.6 liters/minute (LPM) airflow

to achieve a 4-micrometer cut-point. Crystalline silica was quantifiable at 1.1 to 3.7 percent in four of

the six samples. NIOSH (1997) used Dorr-Oliver

cyclones at 1.7 LPM to collect 22 samples, of which

15 (68 percent) contained silica amounts between

the level of quantification (LOQ) and limit of detection (LOD). In the same report, NIOSH described

two additional respirable crystalline silica results

from another site as 0.04 and 0.08 mg/m3 for samples of 443 and 435 minutes duration.

4 These values were those reported in the CPWR

video, which may not have shown all measurements taken during the study. Respirable dust levels

were not reported (CPWR, 1998).

5 When the silica percentage is in doubt, some laboratories that specialize in environmental testing can

analyze a sample of the product to determine the

actual silica content. OSHA recommends, however,

that employers minimize employee exposure by

relying on manufacturers’ information and using

dust control methods rather than by testing joint

compounds themselves.

6 Data values were averaged from those presented

in the CPWR video, which may not include all values measured during the actual study.
General Housekeeping and

Use of Dust Suppressants

This section covers dust control methods for

general housekeeping activities at construction

sites, including site cleaning, material handling

and the use of dust suppressants. The term “silica” used in this document refers to respirable

crystalline silica.

Introduction

Exposure to fine particles of silica has been shown

to cause silicosis, a serious and sometimes fatal

lung disease. Construction employees who inhale

fine particles of silica may be at risk of developing

this disease. Silica dust can be generated when

materials such as ceramics, concrete, masonry, rock

and sand are mixed, blasted, chipped, cut, crushed,

drilled, dumped, ground, mixed or driven upon.

Employees at construction sites may be exposed to

silica dust during general housekeeping activities

such as sweeping, emptying vacuum cleaners and

using compressed air for cleaning. Silica exposures

may also occur whenever silica-containing dusts are

disturbed, such as during material handling. The

small particles generated during these activities easily become suspended in the air and, when inhaled,

penetrate deep into employees’ lungs.

Examples of Construction Materials

that Contain Silica

• Concrete

• Brick, tile and other masonry

• Mortar

• Asphalt

• Sand

• Many stone products (such as granite, slate

and sandstone) and rock aggregate1

In several studies of construction sites, silica

exposure levels rose when employees engaged in

general construction cleaning activities such as dry

sweeping, using backpack blowing equipment and

emptying vacuums used to collect concrete dust.2

For example, the National Institute for Occupational

Safety and Health (NIOSH) determined that a concrete finisher handling a vacuum bag containing

concrete dust was exposed to approximately 0.79

mg/m3 (milligrams of silica per cubic meter of air)

(NIOSH, 2001b).3 This level is more than five times

higher than the finisher’s average silica exposure for

the day, which already exceeded the Occupational

Safety and Health Administration’s (OSHA) benchmark of 0.1 mg/m3 (milligrams per cubic meter of

air) as an 8-hour time-weighted average (TWA), an

exposure approximately equivalent to OSHA’s general industry permissible exposure limit (PEL).4

While most employees do not handle vacuum bags

for their full shifts, this activity presents a significant

source of exposure for employees who may also be

exposed to silica from other sources.

Housekeeping Activities that Can Release

Airborne Dust Containing Silica

• Dry sweeping

• Using blowers or compressed air for cleaning

• Dumping bags of raw material

• Dumping wheelbarrow loads

• Breaking or crushing materials

• Spreading crushed materials (concrete, aggregate)

• Dropping, tossing, or pouring dusty materials

• Operating a vacuum with the air discharge near

a source of dust

• Emptying vacuums

• Driving over piles of dust or debris

• Other actions that disturb or create dust

This section describes several methods available

to reduce employees’ silica exposure during housekeeping and related activities. These methods

include general measures to suppress the creation

of dusts (use of water and other dust suppressants),

vacuuming, using cabs and enclosures, and modification of work practices. Many of these methods

can be used to reduce exposures to silica in a broad

range of construction activities in addition to housekeeping tasks.

Visible and Respirable Dust

Visible dust contains large particles that are easy

to see. The tiny, respirable-sized particles (those

that can get into the deep lung) containing silica

pose the greatest hazard and are not visible.

Most dust-generating construction activities produce a mixture of visible and respirable particles.

Do use visible dust as a general guide for

improving dust suppression efforts. If you see

visible dust being generated, emissions of respirable silica are probably too high. Measures

that control tool-generated dust at the source

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usually reduce all types of particle emissions,

including respirable particles.

Do not rely only on visible dust to assess the

extent of the silica hazard. There may be more

airborne respirable dust present that is not visible to the naked eye.

Silica Dust Control Measures

Dust Suppressants

Dust suppression is a dust control method that can

be applied to many different operations, such as

materials handling, rock crushing, abrasive blasting

and operation of heavy construction vehicles. Types

of dust suppressants include water (mists, sprays,

steam and fog), surfactants (including foams),

acrylic polymers, asphalt, chloride compounds,

lignin compounds, natural oil resins, organic resin

emulsions and petroleum-based oils and waste

products.

Dust suppression is generally effective in controlling respirable silica dust, although few data are

available regarding specific exposure reductions.

Many of these methods have also been successful

in reducing erosion and fugitive dust emissions

(PM10) regulated by the Environmental Protection

Agency (EPA).5

Water

Wet methods (i.e., methods involving the application of water) are often the easiest and most effective way to reduce potential silica exposures. Dust

that is wet is less able to become or remain airborne. Water can be applied in different ways to suit

the specific situation. For example:

• Wet mopping or spraying water, followed with a

wet vacuum or squeegee will collect dust and

create less airborne dust than dry sweeping.

• The point where dust will be generated or has

settled can be flooded by flushing surfaces with

water or wet scrubbing.

• Particles can be removed from surfaces by water

under pressure (pressure washing).6

Water can be used as a dust suppressant during

a variety of activities, including:

• Use of heavy construction vehicles on unpaved

surfaces: A water truck can spray the site

grounds.

• Blasting operations: A separate water hose can be

strung next to the hose containing the blasting medium; the two materials can be sprayed simultaneously.

• Materials handling and transport operations: It

is often most efficient to spray a material before

it reaches a transfer point so that the dust has

time to absorb the water before being disturbed.

Increasing moisture content decreases the

amount of dust generated (Plinke et al., 1992).

Construction employees can use a variety of

equipment to apply water, depending on the size

and type of the job. A spray or mist can be an efficient way to distribute adequate amounts of water

over a large area. For a small job, a portable garden

sprayer with a hand pump may be adequate; a larger job might require a garden hose with a mister

nozzle. On a demolition site, a fire hose can be used

to apply water rapidly over a large area, but employees must be able to control both the spray nozzle

and the water pressure or volume.

Start with a Gentle Spray or Mist

Avoid blasting dry dust with a forceful stream of

water. The energy of the water and surrounding

air can disturb the dust and cause it to become airborne before it is wet.

Instead, use a gentle spray or mist to moisten

the particles first. When washing large quantities

of dust from a surface, increase the water force

only after pre-wetting all the dust with a gentle

spray. Use the minimum amount of water needed

to get the job done, particularly where runoff is a

concern.

For optimal results:

• Use nozzles and flow regulators to control water

volume.

• Clean up water and slurry as soon as practical

(using a wet/dry shop vacuum or squeegees and

scoops). If allowed to dry, the dust contained in

the slurry may become a source of silica and

other dust exposure.

• Rewet surfaces as often as necessary to maintain

dust control.

Fogging Methods: Fog, fine particles of water,

can be an effective dust suppressant in certain situations because it provides a larger contact area than

do water sprays. Fog is most effective when the

water droplets are approximately the same size in

diameter as the dust particles to be suppressed. The

dust particles stick to the water droplets. The added

weight prevents the particles from remaining suspended in the air.
Water fog can be generated with a two-fluid system that uses water with compressed air to increase

impact force on the nozzle impinging device or a

single-fluid system where water is pumped at very

high pressure and hydraulically forced through a

very small nozzle opening.

Fogging works best in a pocket or covered area

where air movement is negligible, such as a sealed

material transfer point. Because material moistened

by fog dries quickly, this method has no lasting benefit and must be repeated at each transfer point of

the handling system. Fog is less effective in open

areas because the droplets may blow away before

contacting the dust. Fog may also reduce visibility

and condense on control room windows and may

freeze in cold temperatures and evaporate quickly in

low-humidity conditions (Westbrook, 1999).

Steam Methods: Steam is the gaseous state of

water. Like fog, steam can reach a larger contact

area than sprayed water. Also like fog, steam can

visually restrict operations and condense on surfaces.

Electrostatic Charging: Particles from most

industrial dust clouds possess either a positive or

negative charge, (Johnston et al., 1985). For this reason, electrostatically charged water sprays have

been studied as a dust suppressant method.

Electrostatic water sprays may enhance dust

removal by attracting oppositely-charged dust particles to the charged water droplets. An electrostatic

water spray emitter consists of a waterproof power

supply, a control panel for monitoring and adjusting

water and air supply rates, an insulated charging

coil and a siphon-type nozzle. Sources of clean air

and water are required, with a relatively long period

of time to interact (seconds) between the dust particles and water droplets for peak efficiency.

FreezingTemperatures. Freezing temperatures

complicate the use of water. Consider heating the

local work area, if practical, to prevent ice from

forming in the water-feed system. Large portable

heating units are commonly used to heat commercial and sometimes road and highway projects.

Drain the system when not in use. If water freezes

on the ground, chip away the ice or use deicing

compounds or sand to control the slipping hazard.

Electrical Safety. Use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical

connectors for electric tools and equipment on construction sites (OSHA, 1996). These features are particularly important to employee safety in wet or

damp areas, such as where water is used to control

dust. Although an assured equipment grounding

conductor program is an acceptable alternative to

GFCIs, OSHA recommends that employers use

GFCIs where possible because they afford better

protection for employees. (See 29 CFR 1926.404(b)(1)

for OSHA’s ground-fault protection requirements.)

Surfactants and Other Soil-Binding Materials

A surfactant is a highly concentrated soap or detergent that can be added to water to help control

dust. Surfactants are often referred to as “wetting

agents.” Surfactants break the surface tension of

water, allowing the water to penetrate deeper, to

better saturate the dust particles and slow evaporation. When using surfactants on a ground surface

(soil), the surface stays moist longer and fewer

water applications are needed.

Surfactants formulated to enhance dust particle

water absorption capabilities are not recommended

for materials handling system applications because

they will make dust particles stick to many other

surfaces, such as transfer points and conveyor belts

(Westbrook, 1999).

Surfactants formulated to alter the static surface

charge of dust particles are generally better for

materials handling systems. The surfactant molecules have a high affinity for other surfactants and

most other materials, regardless of any static surface charging. This enables the treated dust particles to agglomerate, having higher weight-to-surface area ratios and fewer tendencies to remain or

become airborne (Westbrook, 1999).

Surfactants can be applied in either a water or

foam spray. Both types rely on the water in the

blended solution to act as a carrier by which small

quantities of surfactant molecules become applied

to the dust particles. Both types reduce fugitive dust

amounts by up to 90 percent or more. Water/surfactant sprays generally consist of one part surfactant

to 1,000 parts water. (Westbrook, 1999).

In addition to surfactants, a number of other

compounds are used on soils to provide dust suppression. These compounds, discussed in greater

detail below, include:

• Acrylic polymers;

• Solid asphalt;

• Liquid asphalt;

• Chloride compounds;

• Lignin compounds;

• Natural oil resins; and

• Organic resin emulsions.

Petroleum-based oils and waste products should

not be used as a dust suppressant as this is a violation of multiple EPA regulations (Skorseth and

Selim, 2000).

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Acrylic Polymers

Acrylic polymers are synthetic plastic adhesives that

work as a ground surface dust suppressant by

chemically binding during curing, creating a surface

crust. Acrylic polymers may take up to 24 hours to

cure, depending on the temperature (colder temperatures result in longer cure times). They are considered environmentally safe, non-corrosive, nonleaching, and non-slippery when wet. Further, they

are flexible after curing. Users have found various

levels of success with acrylic polymers as a dust

suppressant on unpaved roads (Saunders, 2000).

Asphalt - Solids

Asphalt is obtained as a residue in the distillation or

refining of petroleum. Recycled asphalt from roads

or roofing material can be an economical dust suppression tool on unpaved roadways or when crushing rock. Using millings from asphalt roads as a

dust suppressant may have the added benefit of

helping county transportation authorities reduce

disposal or storage costs for the used material.

However, when used on unpaved roadways,

millings can contribute to the formation of road

ruts, resulting in higher maintenance costs.

Asphalt – Liquids

Liquid asphalts have been used in the past to treat

gravel roads for dust control. However, most localities, in compliance with EPA requirements, have

banned the use of liquid asphalt products due to the

large content of fuel oil or kerosene in these products (Skorseth and Selim, 2000).

Chloride Compounds

Popular in surface dust control and road stabilization, calcium chloride and magnesium chloride are

naturally occurring brines processed into a colorless, odorless liquid and into white flakes or pellets.

Used as water additives, chloride compounds are

hygroscopic and work as dust suppressants by

attracting moisture from the air. They resist evaporation. They exhibit high surface tension and low

vapor pressure, which helps bind or aggregate

smaller particles to larger and heavier particles

which are less likely to become airborne.

These properties make chloride compounds

effective in keeping unpaved surfaces damp and

reducing dust levels. They remain active even after

the ground has been tilled or rebladed. Chloride

compounds also lower the freezing point of water,

making them useful in cold temperatures.

However, these properties also give chloride

compounds the disadvantage of performing poorly

in low humidity. They can be corrosive without

inhibitor additives (though most products contain

the necessary inhibitors), may be harmful to vegetation and ground water, and may leach away with

precipitation. Further, they may be slippery when wet,

so slips and falls may be a concern for employees.

Lignin Compounds

Lignin sulfate and lignin sulfonate are powders that

are by-products of the wood pulping process.

Compounds in this category chemically bind soil

particles together by reducing the tension between

clay in the soil and water. They react with negatively-charged clay particles to agglomerate the soil.

Lignin compounds are used to coat ground surfaces, forming a crust as they cure.

Lignin compounds are water soluble and are

most effective in dry climates. They are immediately

active and remain effective after reblading. They

lower the freezing point of water, making them useful in cold temperatures.

Lignin sulfates and sulfonates leach away with

precipitation and may be slippery when wet. They

may also become brittle when dry and can be

harmful to ground water. Further, they work best

with a well-graded aggregate mix (a wide range in

grain sizes). They may have an unpleasant odor

when first applied, but the smell dissipates quickly.

Lignin compounds may also be corrosive to aluminum.

Natural Oil Resins

Natural oil resins represent another class of dust

suppressants. One popular example is soybean oil

resin, a by-product of soybean oil refining. Oil resins

are usually added to water to make a suspension

and applied to ground surfaces. For road stabilization, the oil can be applied in a spray with bituminous asphalt applicator equipment. The oil coating

leaves a residue that makes dust particles heavier

and makes them stick together like an adhesive, a

process known as agglomeration.

Used vegetable oil has also been explored as a

dust suppressant (Drenner and Trumbull, 2003). Due

to its relatively low cost, it may be an attractive

option in some situations, although its performance

duration may be limited. (Note that used vegetable

oil should not be confused with used motor oil.

Used motor oil is restricted or prohibited for use as

a dust suppressant in most jurisdictions.)

Vegetable oil has also been used as a dust suppressant in the agriculture industry, specifically to

reduce dust in grain storage and processing areas.

However, researchers disagree about its effectiveness.
Natural oil products are immediately active,

effective after reblading, non-corrosive, and environmentally safe. However, they may have an offensive odor, may become brittle when dry and may

leach away with precipitation. They may also be

slippery when wet.

Organic Resin Emulsions

Organic resin emulsions are natural resins, emulsified in liquid form such as pine tree sap. They bind

and adhere to dust particles as they cure and create

a surface crust. They are environmentally safe, noncorrosive, non-leaching, non-slippery when wet, and

waterproof. However, they may become brittle

when dry and need to be cleaned from equipment

quickly. These natural resins will take longer to cure

in colder temperatures.

Vacuum Methods

Vacuums offer a versatile option for collecting dry

debris from smooth and uneven surfaces, cracks,

expansion joints and irregular shapes. Wet/dry

vacuums can also collect water, slurry and damp

materials. Pneumatic vacuums may be used where

electricity is not available.

Vacuums do not produce the clouds of dust

often generated during dry sweeping or blowing

with compressed air, but they are not dust-free.

Vacuum cleaners with inadequate or damaged filters can increase employee silica dust exposures

due to the agitating action of the vacuum and incomplete filtration of fine dust particles (Heckel et

al., 2000). Employers must choose vacuum filter

media carefully.

Understanding vacuum filter ratings. Manufacturers’ vacuum filter descriptions can be confusing

and make comparison difficult; however, the filter

rating system itself is quite simple.

Rating systems indicate a filter’s ability to capture various sizes of dust. Two important pieces of

information are: (1) collection efficiency, or percent

of particles captured, and (2) the smallest size of

particles that will be captured at the stated efficiency.

For example, a high efficiency particulate air

(HEPA) filter is 99.97 percent efficient against particles as small as 0.3 micrometers (μm). Less-efficient

filters report ratings with either lower collection efficiency, larger particle size, or both. Compared to a

HEPA filter, a filter rated 70 percent efficient against

7 μm dust, for example, will not capture as many

fine particles; the uncaptured particles will be discharged with the vacuum’s exhaust air and perhaps

into the employees’ breathing zone.

Tips for Operating Vacuum Cleaners

• If necessary, train employees on the vacuum’s

self-cleaning features and the manufacturer’s

recommended methods for emptying canisters

or changing bags.

• Select a vacuum that allows employees to

clean filters without opening the vacuum and

remove full bags without exposing themselves

to dust (NIOSH, 2001b).

• Position vacuums away from sources of dust or

first vacuum the area where the canister will sit.

If a vacuum sits on a dusty surface, the exhaust

air can cause particles to become airborne.

• Keep the vacuum hose clear and free of debris,

kinks, and tight bends. Maintain the vacuum at

peak performance to ensure adequate airflow

through the shroud and ducts.7

• On vacuums with reverse flow cleaning systems, activate the system frequently (several

times per day, or more if necessary).

• Empty collection bags and vacuums as frequently as necessary to prevent decreased airflow.8 Follow manufacturers’ directions and do

not allow units to overfill. Dispose of collected

dust in a way that prevents it from becoming

resuspended in the air.

• Keep an adequate supply of bags at the worksite.

For greater employee protection, select a vacuum filter that has a higher efficiency against smaller

particles.

When purchasing filters (or a new vacuum), keep

in mind that the more efficient filters generally also

require more “lift” or suction power (measured as

“inches of water grade,” or “in. w.g.”). The higherefficiency filters are not available for vacuums with

low lift ratings.9

Higher-efficiency filters tend to be more costly.

Extend the service life of more expensive filters by

adding prefilters, which protect the fine-particle filter

by catching the larger dust. Low-cost prefilters can

be changed frequently with minimal expense.

Prefilters are available in various grades. Select a

relatively efficient prefilter that will capture most of

the dust. An inefficient prefilter will allow more dust

to pass, causing the high efficiency particle filter to

become overloaded more quickly (Trakumas et al.,

2001).

Filter surface area (the size of the filter if it were

spread out flat) is another feature to consider when

comparing filters. The greater the surface area of

the filter, the more dust it will hold. Vacuums also

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require less suction power to move air through filters with larger areas. Manufacturers often provide

information about filter surface area.

Cabs and Enclosures

Use material handling equipment for moving large

amounts of silica-containing dusty material. Select

equipment with enclosed cabs and positive pressure ventilation systems (to isolate operators from

dust) and air conditioning (to encourage operators

to keep windows and doors closed, so dust stays

out). Many cabs can be retrofitted to add a filtered

ventilation system and air conditioning.10

Put the cab on a regular maintenance schedule.

Check for leaking seals around windows, doors and

electrical wiring. Change ventilation system filters

on schedule. For maximum protection from exposure to small particles, use the most efficient filter

recommended by the cab manufacturer.

Clean the cab interior daily so that dust does not

accumulate and is not dispersed by the cab ventilation system.

Compressed Air

The use of compressed air to clean surfaces or

clothing is strongly discouraged. Using compressed air to clean work surfaces or clothing

can significantly increase employee exposure,

especially in enclosed and semi-enclosed spaces.

Cleaning should be performed with a HEPAfiltered vacuum or by wet methods.

Work Practices

Common sense work practices can help employees

limit their exposure to silica. Examples include:

• Clean up spills and waste before dust can

spread.

• Wear a rubber apron to keep wet dust off clothing. When it dries, the dust can become airborne.

• Whenever possible, work upwind of any dust

sources. This can be as simple as working from

the other side of the pile when shoveling debris.

• Keep roadways damp at sites where the surface

includes high silica aggregate or crushed concrete.

• Wet down silica-containing debris and rock spoil

piles prior to removal or disturbance.

Encourage employees to watch for dust sources

containing silica and make adjustments or use dust

control methods to reduce their silica exposure.

Dumping or Pouring Materials

The farther objects fall when dropped, the more

dust they will generate on impact. When dumping

or pouring materials (for example, debris into a

dumpster or raw materials into a mixer), minimize

drop distances by releasing materials close to their

destination level. Support the bag, bin, or barrow

just above the top of the pile and slowly add materials onto the pile. When a long drop is unavoidable,

use enclosed disposal chutes or slides.

Use wheelbarrow ramps of appropriate height

(not too tall for a small dump pile).

Moisten the dumpster contents, floors and walls

prior to adding any debris to reduce dust released

upon impact.

Spray the debris stream with water mist to help

suppress dust.

Sweeping

Take steps to limit the use of dry sweeping. Reduce

the quantity of debris and the distance and frequency of sweeping. Use a vacuum or wet mop, or moisten the material and scrape it into position.

Collect and transport debris by bucket or wheelbarrow from smaller local piles rather than pushing

it for longer distances to a central pile.

Avoid dry sweeping debris with sweeping compounds that contain quartz sand (crystalline silica)

as the grit.

Removing Debris from Slots or Uneven

Surfaces

Use a vacuum instead of a blower. Use vacuum

hose attachments sized for the situation. For example, remove tailings from handheld drill holes using

a HEPA-filtered vacuum.

Flush cracks with water instead of using compressed air.

Vacuums

Use vacuums with self-cleaning features (backpulse). Make sure that employees are fully trained

in vacuum operation.

Handle vacuum bags carefully and have a disposal receptacle nearby.

Avoid overfilling vacuum canisters or bags. The

extra weight makes bags difficult to handle and subject to tearing.

Avoid shaking or jarring the vacuum. Follow the

manufacturer’s instructions for recommended handling.

Avoid depositing or storing collected debris

where it will be disturbed or run over and become a

source of dust exposure for another employee.
Dust Control

Encourage employees who perform dusty tasks to

use dust control methods during their activities.

The less dust released, the less time required for

cleanup.

Case Studies

The following case studies indicate silica exposure

levels found under certain uncontrolled or poorly

controlled conditions, and show the effectiveness of

controls in reducing silica exposures.

Vacuum Bag as Exposure Source

Case Study I: NIOSH evaluated a concrete finisher’s

silica exposure while he operated a grinder with

vacuum dust collection equipment. Investigators

determined that a peak period of exposure (0.79

mg/m3

) occurred while the employee was handling

the vacuum bag containing concrete dust. This level

was more than five times higher than his average

silica exposure for the day (0.155 mg/m3). Because

the employee emptied the vacuum frequently

(approximately every 35 minutes during a 7-hour

shift), the vacuum bag dust probably made a substantial contribution to his total silica exposure for

the day (NIOSH, 2001b).

Case Study II. Researchers reported that, at another

construction site, a concrete finisher dumped full

vacuum bags on the ground, where they became a

source of dust exposure when a forklift drove over

them and when other employees swept up the

spilled dust. The same employee had initially

attempted to clean the vacuum filter by removing it

and pounding it on the ground. After he received

training on the vacuum’s self-cleaning feature, he

reduced downtime (and probably prolonged the

filter’s life) by using the vacuum manufacturer’s

recommended methods (Echt and Sieber, 2002).

Cleanup Activities

Case Study III. In a study of nine construction sites,

investigators measured respirable dust and silica

exposure of 10 employees performing cleanup

activities. During cleaning tasks, the tool associated

with the highest dust exposure was the backpack

blower (Flanagan et al., 2003).11

In the same study, dust exposures were higher

for employees who used a sweeping compound

than for employees who swept without a compound (Flanagan et al., 2003). The sweeping compound type was not reported, but some compounds

include crystalline silica (quartz sand) as grit, which

might be an additional source of silica dust during

sweeping (NIOSH, 2001a).

Using Box Fans

This study also found that dust exposure levels

were higher for employees performing cleanup

activities in areas where box fans were used, compared to cleanup in areas without fans (Flanagan

et al., 2003). Air blowing on sources of dust can

increase the amount of dust in the air.

Although the investigators report an average

employee exposure level of 0.03 mg/m3 (below

OSHA’s limits) for employees performing cleanup,

half of the employees’ exposure levels exceeded

0.05 mg/m3 (Flanagan et al., 2003).12

Dry Sweeping

Case Study IV. A study conducted at nine construction sites in Finland evaluated the relative average

respirable crystalline silica exposure levels for

employees’ dry sweeping after various stages of

demolition and construction, and compared them

with exposures when alternate cleaning methods

were used. Compared to dry sweeping, employee

exposures were approximately 50 percent lower

when the employees used squeegees to sweep

(scrape) surfaces and approximately 80 percent

lower when employees used vacuums (Riala, 1988).13

Using Steam

Case Study V. Testing was performed at two mineral processing plants to determine the effectiveness

of steam as a dust suppressant. Applying water

vapor as steam (0.22 percent water-to-product ratio

by weight) resulted in a 64 percent reduction in respirable dust. This compares to a reduction in respirable dust of 25 percent when the same amount

of water was applied as a water spray. Even when

the amount of water sprayed was increased to 0.5

percent (water-to-product ratio by weight), the

reduction in respirable dust (55 percent) was less

than that achieved with steam (Bureau of Mines,

1985).

Comparison Study I

A university study compared various types of dust

suppressants for use on unpaved roadways: asphalt

millings, calcium chloride, magnesium chloride, lignosulfonate (tree sap), soybean oil, and used fryer

oil. The researchers developed a scoring system

that took into account environmental impact and

dust suppression performance. Lignosulfonate

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C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 6 3

achieved the highest score. However, the authors

noted that a second application of the product was

needed. The two oil compounds scored evenly, just

below lignosulfonate, but the authors noted that the

vegetable oils required more intensive maintenance

than other dust suppressants. The roadway treated

with used fryer oil became rutted early in the study.

The two chloride compounds achieved scores

slightly less than the oils. All options significantly

outscored the untreated (control) section of roadway (Drenner and Trumbull, 2003).

Comparison Study II

Another university study compared the cost and

performance of three dust suppression and soil stabilization options (lignosulfonate, calcium chloride,

magnesium chloride), and the impact of no treatment on an unpaved roadway over 41⁄2 months. The

dust suppressants reduced fugitive dust emissions

by 50 to 70 percent compared to the untreated section. The researchers estimated that the untreated

test section of roadway would require maintenance

eight times per year versus twice a year for the

treated sections. The researchers noted pothole formation on the lignosulfonate-treated section of

roadway after the test period ended. When material,

labor, equipment and maintenance costs were tallied, researchers estimated an annual cost of more

than $20,000 per mile for an untreated roadway.

Calcium chloride, lignosulfonate, and magnesium

chloride treatments were estimated to have approximate annual costs of $11,000, $10,000, and $9,000

dollars per mile, respectively (Addo and Sanders,

1995).

Comparison Study III

NIOSH evaluated substitute materials for silica sand

in abrasive blasting. Among the many products

compared to silica sand was silica sand treated with

three different types of dust suppressants. Although

the report did not reveal the names and types of

dust suppressants, airborne testing revealed that

dust suppressants reduced respirable silica levels by

70 percent compared to untreated silica sand

(NIOSH, 1998).

Respiratory Protection and

Engineering Control Evaluation

Tasks performed during general housekeeping, such

as dry sweeping, dumping materials, emptying vacuum cleaners and using compressed air, can contribute significantly to employees’ exposure to respirable silica. Control methods including use of dust

suppressants, vacuuming, use of cabs and enclosures, and modification of work practices can be

applied to reduce silica exposure while performing

general housekeeping tasks. Utilizing these methods

in the manner that has been presented in this section will, in most if not all cases, allow employees

who are performing general housekeeping to perform the operation without respiratory protection.

Where engineering and work practice controls

are not sufficient to reduce employees’ exposure

below 0.1 mg/m3, respiratory protection may be

needed (see 29 CFR 1926.103). If respiratory protection is necessary, use a properly-fitted, NIOSHapproved half-facepiece or disposable respirator

equipped with an N-, R- or P-95 filter. In the occasional situation where general housekeeping tasks

are performed for a full 8-hour day, time-weighted

average silica exposures may exceed 1.0 mg/m3. In

these situations, a full facepiece respirator, which

provides greater protection than a half-facepiece

respirator, may be necessary.

In any workplace where respirators are necessary to protect the health of the employee, or whenever respirators are required by the employer, the

F gu e Compa son of S ca Exposu e

Du ng C ean ng Act v t es Examp es F om Case Stud es

0 75

3

8

5

Vacuuming

Using Squeegie

Dry Sweeping

Handilng Vacuum Bags

Appropriate Exposure Level (as a multiple of PEL)

if Activity Were Performed for a Full Shift
employer must establish and implement a written

respiratory protection program with worksite-specific procedures and elements, including the selection

of respirators, medical evaluations of employees, fit

testing, proper usage, maintenance and care, cleaning and disinfecting, proper air quality/quantity and

training (see 29 CFR 1926.103).

Uncontrolled housekeeping activities, such as

the use of compressed air, can contribute substantial excess exposure to nearby employees within a

short period of time. Alternate methods of cleaning

should be explored.

Employers should conduct exposure monitoring

periodically while controls are being used to ensure

that the controls are working properly and that the

appropriate level of respiratory protection is being

used.

For more information on how to determine proper respiratory protection, visit OSHA’s Web site at

www.osha.gov. NIOSH’s Web site also provides

information on respirators at www.cdc.gov/niosh.

References

ACGIH. 2001. Industrial Ventilation, a Manual of

Recommended Practice, 25th edition. American

Conference of Governmental Industrial Hygienists,

Cincinnati, OH.

ACGIH. 2008. Threshold limit values for chemical

substances and physical agents and biological

exposure indices. American Conference of

Governmental Industrial Hygienists, Cincinnati, OH.

Addo, J.Q. and Sanders, T.J. 1995. Effectiveness and

environmental impact of road dust suppressants.

Mountain-Plains Consortium Report No. 95-28A.

Beardwood, J. 2001. Dust gets in your eyes...lungs,

wallet, and other wear parts. Grading and

Excavation Contractor. www.forester.net/gx_0106_

dust.html.

Bureau of Mines. 1985. Adding steam to control

dust in mineral processing. Report of Investigation

No. 8935, 1985.

Drenner, J., and T. Trumbull. 2003. Preliminary

report on used fryer oil as a dust suppressant. P2

Highlight. (January) www.iwrc/org/p2highlt/p2current.cfm.

Echt, A., and W.K. Sieber. 2002. Case Studies:

Control of silica exposure from hand tools in construction: Grinding concrete. Appl. Occup. Environ.

Hygiene. 17(7):457-461. July, 2002.

Flanagan, M.E., N. Seixas, M. Majar, J. Camp, and

M. Morgan. 2003. Silica dust exposures during

selected construction activities. Am. Ind. Hygiene

Assn. J 64(3):319-28. May-June, 2003.

Grenier, M.G. and Bigu, J.. 1988. Suppression of airborne dust in hard rock mines by means of electrostatic water sprays. Appl. Ind. Hygiene. 3:251-257.

September, 1988.

Heckel, C.L., A. Quraishi, N.G. Carlson, and A.J.

Streifel. 2000. Evaluation of vacuum cleaners: A

method to evaluate the cleaning effectiveness and

airborne particle generation of vacuum cleaners.

Poster presented at 2000 American Industrial

Hygiene Conference and Exposition.

Hogan, T.J. 1996. Selected particulates: silica. In

Plog, B.A., J. Niland, and P.J. Quinlan, eds.

Fundamentals of Industrial Hygiene, 4th ed.

National Safety Council. Itasca, IL, pp. 180-182, 1996.

Johnston, A.M., J.H. Vincent, and A.D. Jones. 1985.

Measurement of electric charge for workplace

aerosols. Ann. Occup. Hygiene. 29:2, 1985.

McKernan, J. 2000. Personal communication

between J. McKernan of National Institute for

Occupational Safety and Health and L. Lewis of

Eastern Research Group, January 28, 2000.

NIOSH. 1998. Evaluation of substitute materials for

silica sand in abrasive blasting. Report prepared

under contract 200-95-2946. National Institute for

Occupational Safety and Health. Pittsburgh, PA.

September, 1998.

NIOSH. 1999a. Control technology and exposure

assessment for occupational exposure to crystalline

silica: case 04 -- a concrete finishing operation.

Report # ECTB 233-104c. National Institute for

Occupational Safety and Health, Cincinnati, OH.

April, 1999.

NIOSH. 1999b. Control technology and exposure

assessment for occupational exposure to crystalline

silica: case 15 – concrete cutting. Report # ECTB

233-115c. National Institute for Occupational Safety

and Health, Cincinnati, OH. November, 1999.

NIOSH. 2000. In-depth survey report: Control technology for environmental enclosures – an evaluation of in-use enclosures at San Joaquin Helicopter.

National Institute for Occupational Safety and

Health, Cincinnati, OH, 1999.

NIOSH. 2001a. Technology news: Sweeping compound application reduces dust from soiled floors

within enclosed operator cabs (No. 487). National

Institute for Occupational Safety and Health,

Pittsburgh, PA. March, 2001.

NIOSH. 2001b. In-depth survey report of exposure

to silica from hand tools in construction chipping,

6 4

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Health Administration
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 6 5

grinding, and hand demolition at Frank Messer and

Sons Construction Company: Lexington and

Newport, KY, Columbus and Springfield, OH. Report

# 247-15. National Institute for Occupational Safety

and Health, Cincinnati, OH, April, 2001.

NIOSH. 2002a. In-depth survey report of exposure to

silica from demolition of plaster ceilings at Frank

Messer and Sons Construction Company: Columbus,

OH. Report # 247-15b. National Institute for Occupational Safety and Health, Cincinnati, OH, January,

2002.

NIOSH. 2002b. Pocket guide to chemical hazards.

Pub. No. 2002-140. National Institute for

Occupational Safety and Health, Cincinnati, OH.

June, 2002.

OSHA Case Files (Special Emphasis Program

Inspection Reports from 1996-1998).

Plinke, M.A.E., Maus, R. and Leith, D. 1992.

Experimental examination of factors that affect dust

generation by using Heubach and MRI testers. Am.

Ind. Hygiene. Assn. J. 53(5):325-330. May, 1992.

Riala, R. 1988. Dust and quartz exposure of Finnish

construction site cleaners. Ann. Occup. Hygiene

32(2):215-220, 1988.

Saunders, Mark. 2000. Just say ‘No’ to

dust...maybe. Grading and Excavation Contractor.

May/June. www.forester.net/gec_0005_just.html.

Skorseth, K. and Selim, A.. 2000. Gravel Roads

Maintenance and Design Manual. USDOT, Federal

Highway Administration. November, 2000.

Smandych, R.S., Thomson, M. and Goodfellow, H.

1998. Dust control for material handling operations:

a systematic approach. Am. Ind. Hygiene Assn. J.

58:139-146. February, 1998.

Trakumas, S., Willeke, K., Ginshpun, S.A., Reponen,

T., Mainelis, G. and Freidman, W. 2001. Particle

emission characteristics of filter-equipped vacuum

cleaners. Am. Ind. Hygiene Assn. J. 62:482-493.

July/August, 2001.

Westbrook, T. 1999. Managing fugitive dust.

Presentation made at the Pollution Prevention

Seminar for the Mining and Mineral Industries,

Options for Reducing Dust Emissions, held in Mesa,

AZ, on September 16, 1999.

Technical Notes

1 Aggregates can contain up to 80 percent crystalline silica (Hogan, 1996). On the other hand, limestone and marble contain relatively little crystalline

silica, often less than 3 percent.

2 References: Flanagan et al., 2003; NIOSH, 2002a,

1999a, 1999b; OSHA Case Files; Riala, 1988.

3 NIOSH conducted video and real-time respirable

dust monitoring in the employee’s breathing zone

and simultaneously captured respirable dust on a

cassette for gravimetric and X-ray diffraction analysis. Results indicated the respirable dust on the filter

was 14.5 percent silica. This percentage was used to

calculate the approximate silica exposure associated

with the videotaped activities. NIOSH also sampled

the employee’s full shift using traditional methods.

Results indicated an 8-hour time-weighted average

respirable silica exposure of 0.155 mg/m3 (0.182

mg/m3 for the 410-minute period sampled) (NIOSH,

2001b).

4 Laboratories have not used particle counting for

crystalline silica analysis for many years. Exposure

data is now reported gravimetrically. However,

OSHA’s construction PEL for crystalline silica, established in 1971, is still listed as a particle-count value.

(See Appendix E to OSHA’s National Emphasis

Program for Crystalline Silica, CPL 03-00-007, for a

detailed discussion of the conversion factor used to

transform gravimetric measurements to particlecount values). In this guidance, OSHA is using 0.1

mg/m3 of respirable quartz as an 8-hour timeweighted average as a benchmark to describe the

effectiveness of control measures. The benchmark

is approximately equivalent to the general industry

silica PEL. Other organizations suggest more stringent levels. For example, the National Institute for

Occupational Safety and Health (NIOSH) recommends that respirable crystalline silica exposures be

limited to 0.05 mg/m3 as a 10-hour time-weighted

average (NIOSH, 2002b). The American Conference

of Governmental Industrial Hygienists (ACGIH) recommends that respirable crystalline silica exposures

be limited to 0.025 mg/m3 as an 8-hour time-weighted average (ACGIH, 2008).

5 PM10 is EPA’s designation for suspended particulate matter with a mass median aerodynamic diameter less than 10 micrometers (a particle size comparable to that of respirable dust). The amount of

this particulate matter is regulated in the National

Ambient Air Quality Standards, with the limits being

no more than 150 micrograms per cubic meter of

air (μg/m3) in a 24-hour period more than three

times in three years, and with an annual arithmetic

average not to exceed 50 μg/m3.

6 For better dust management, moisten loose dust

with a gentle spray before using higher pressure.

7 ACGIH recommends 3,500 to 4,000 feet per minute

(FPM) velocity (within the hose/duct) to keep concrete dust and particles released from grinding from

settling in the hose (ACGIH, 2001). For a typical 2-
6 6

Occupational Safety and

Health Administration

inch diameter vacuum hose, 75 to 90 cubic feet per

minute (CFM) will achieve that duct velocity (ACGIH,

2001). However, for maximum collection efficiency,

the shroud may require higher CFM.

8 NIOSH (2001b) showed that airflow through a vacuum dropped by two-thirds (from 87 to 31 CFM) as

the vacuum bag filled. The lower airflow was not

adequate to prevent dust from settling in the hose.

9 For some small vacuums, “pleated” filters with

large surface areas can help solve the problem of

low suction power.

10 Controlled tests of aerosol penetration into agricultural tractor cabs have shown that a retrofitted

cabin can filter out 99.6 percent of particles 0.3 μm

to 0.4 μm in diameter (NIOSH, 2000).

11 Flanagan et al., 2003, evaluated peak and average

respirable dust exposure using personal dust monitors to record multiple one-minute average results

during various phases of a task. Observers recorded

work variables for each minute.

12 Eleven crystalline silica samples associated with

employees performing cleanup were collected using

nylon cyclones and air sampling pumps. Results

were reported by major activity group (cleanup) as

geometric mean and as percent exceeding the

ACGIH TLV (0.05 mg/m3). Employees recorded their

own activities during the period sampled (sample

durations were not reported, but were less than fullshift) (Flanagan et al., 2003).

13 Riala (1988) analyzed respirable quartz using sedimentation to separate particles less than 5 μm from

total dust samples, rather than by sampling with a

cyclone. Additionally, respirable quartz was analyzed in 9 of 110 samples and estimated for the

remainder. The average breathing zone silica results

were 0.530 mg/m3 for dry sweeping, 0.33 mg/m3

when squeegees were used, and 0.06 to 0.10 mg/m3

during vacuum cleaning. Mean sample durations

were approximately 90 minutes. Cleanup worker

exposures were notably higher than reported by

Flanagan et al., 2003.
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 6 7

OSHA Assistance

OSHA can provide extensive help through a variety of

programs, including technical assistance about effective safety and health programs, state plans, workplace consultations, voluntary protection programs,

strategic partnerships, and training and education.

Safety and Health Program Management

System Guidelines

Effective management of employee safety and health

protection is a decisive factor in reducing the extent

and severity of work-related injuries and illnesses and

their related costs. In fact, an effective safety and

health management system forms the basis of good

employee protection, can save time and money,

increase productivity and reduce employee injuries,

illnesses and related workers’ compensation costs.

To assist employers and employees in developing

effective safety and health management systems,

OSHA published recommended Safety and Health

Program Management Guidelines (54 Federal

Register (16): 3904-3916, January 26, 1989). These voluntary guidelines can be applied to all places of

employment covered by OSHA.

The guidelines identify four general elements critical to the development of a successful safety and

health management system:

• Management leadership and employee involvement,

• Worksite analysis,

• Hazard prevention and control, and

• Safety and health training.

The guidelines recommend specific actions, under

each of these general elements, to achieve an effective

safety and health management system. The Federal

Register notice is available online at www.osha.gov.

State Programs

The Occupational Safety and Health Act of 1970 (OSH

Act) encourages states to develop and operate their

own job safety and health plans. OSHA approves and

monitors these plans. Twenty-four states, Puerto Rico

and the Virgin Islands currently operate approved

state plans: 22 cover both private and public (state

and local government) employment; Connecticut,

New Jersey, New York and the Virgin Islands cover the

public sector only. States and territories with their

own OSHA-approved occupational safety and health

plans must adopt standards identical to, or at least as

effective as, the Federal OSHA standards.

Consultation Services

Consultation assistance is available on request to

employers who want help in establishing and maintaining a safe and healthful workplace. Largely funded

by OSHA, the service is provided at no cost to the

employer. Primarily developed for smaller employers

with more hazardous operations, the consultation

service is delivered by state governments employing

professional safety and health consultants. Comprehensive assistance includes an appraisal of all mechanical systems, work practices, and occupational safety

and health hazards of the workplace and all aspects of

the employer’s present job safety and health program.

In addition, the service offers assistance to employers

in developing and implementing an effective safety

and health program. No penalties are proposed or

citations issued for hazards identified by the consultant. OSHA provides consultation assistance to the

employer with the assurance that his or her name and

firm and any information about the workplace will not

be routinely reported to OSHA enforcement staff.

Under the consultation program, certain exemplary

employers may request participation in OSHA’s Safety

and Health Achievement Recognition Program

(SHARP). Eligibility for participation in SHARP includes receiving a comprehensive consultation visit,

demonstrating exemplary achievements in workplace

safety and health by abating all identified hazards, and

developing an excellent safety and health program.

Employers accepted into SHARP may receive an

exemption from programmed inspections (not complaint or accident investigation inspections) for a period

of 1 year. For more information concerning consultation assistance, see OSHA’s website at www.osha.gov.

Voluntary Protection Programs (VPP)

Voluntary Protection Programs and on-site consultation services, when coupled with an effective enforcement program, expand employee protection to

help meet the goals of the OSH Act. The VPPs motivate others to achieve excellent safety and health

results in the same outstanding way as they establish a cooperative relationship between employers,

employees, and OSHA.

For additional information on VPP and how to

apply, contact the OSHA regional offices listed at the

end of this publication.

Strategic Partnership Program

OSHA’s Strategic Partnership Program, the newest

member of OSHA’s cooperative programs, helps

encourage, assist, and recognize the efforts of partners to eliminate serious workplace hazards and

achieve a high level of employee safety and health.

Whereas OSHA’s Consultation Program and VPP entail

one-on-one relationships between OSHA and individual worksites, most strategic partnerships seek to

have a broader impact by building cooperative relationships with groups of employers and employees.

These partnerships are voluntary, cooperative relationships between OSHA, employers, employee represen-
6 8

Occupational Safety and

Health Administration

tatives, and others (e.g., trade unions, trade and professional associations, universities, and other government agencies).

For more information on this and other cooperative programs, contact your nearest OSHA office, or

visit OSHA’s website at www.osha.gov.

Alliance Program

Through the Alliance Program, OSHA works with

groups committed to safety and health, including

businesses, trade or professional organizations,

unions and educational institutions, to leverage

resources and expertise to develop compliance

assistance tools and resources and share information with employers and employees to help prevent

injuries, illnesses and fatalities in the workplace.

Alliance program agreements have been established with a wide variety of industries including meat,

apparel, poultry, steel, plastics, maritime, printing,

chemical, construction, paper and telecommunications. These agreements are addressing many safety

and health hazards and at-risk audiences, including silica, fall protection, amputations, immigrant workers,

youth and small businesses. By meeting the goals of

the Alliance Program agreements (training and education, outreach and communication, and promoting the

national dialogue on workplace safety and health),

OSHA and the Alliance Program participants are

developing and disseminating compliance assistance

information and resources for employers and employees such as electronic assistance tools, fact sheets,

toolbox talks, and training programs.

OSHATraining and Education

OSHA area offices offer a variety of information services, such as compliance assistance, technical advice,

publications, audiovisual aids and speakers for special

engagements. OSHA’s Training Institute in Arlington

Heights, IL, provides basic and advanced courses in

safety and health for Federal and state compliance

officers, state consultants, Federal agency personnel,

and private sector employers, employees, and their

representatives.

The OSHA Training Institute also has established

OSHA Training Institute Education Centers to address

the increased demand for its courses from the private

sector and from other federal agencies. These centers

are colleges, universities, and nonprofit organizations

that have been selected after a competition for participation in the program.

OSHA also provides funds to nonprofit organizations, through grants, to conduct workplace training

and education in subjects where OSHA believes there

is a lack of workplace training. Grants are awarded

annually. Grant recipients are expected to contribute

20 percent of the total grant cost.

For more information on grants, training, and education, contact the OSHA Training Institute, Directorate

of Training and Education, 2020 South Arlington

Heights Road, Arlington Heights, IL 60005, (847) 297-

4810, or see Training on OSHA’s website at

www.osha.gov. For further information on any OSHA

program, contact your nearest OSHA regional office

listed at the end of this publication.

Information Available Electronically

OSHA has a variety of materials and tools available on

its website at www.osha.gov. These include electronic

compliance assistance tools, such as Safety and

HealthTopics, eTools, Expert Advisors; regulations,

directives and publications; videos and other information for employers and employees. OSHA’s software

programs and compliance assistance tools walk you

through challenging safety and health issues and

common problems to find the best solutions for your

workplace.

A wide variety of OSHA materials, including standards, interpretations, directives and more can be

purchased on CD-ROM from the U.S. Government

Printing Office, Superintendent of Documents, toll-free

phone (866) 512-1800.

OSHA Publications

OSHA has an extensive publications program. For a

listing of free items, visit OSHA’s website at www.osha.

gov or contact the OSHA Publications Office, U.S.

Department of Labor, 200 Constitution Avenue, NW,

N-3101, Washington, DC 20210; telephone (202) 693-

1888 or fax to (202) 693-2498.

Contacting OSHA

To report an emergency, file a complaint, or seek

OSHA advice, assistance, or products, call (800) 321-

OSHA or contact your nearest OSHA Regional or Area

office listed at the end of this publication. The teletypewriter (TTY) number is (877) 889-5627.

Written correspondence can be mailed to the nearest OSHA Regional or Area Office listed at the end of

this publication or to OSHA’s national office at: U.S.

Department of Labor, Occupational Safety and Health

Administration, 200 Constitution Avenue, N.W.,

Washington, DC 20210.

By visiting OSHA’s website at www.osha.gov, you

can also:

• File a complaint online,

• Submit general inquiries about workplace safety

and health electronically, and

• Find more information about OSHA and occupational safety and health.
C O N T R O L L I N G S I L I C A E X P O S U R E S I N C O N S T R U C T I O N 6 9

OSHA Regional Offices

Region I

(CT,* ME, MA, NH, RI, VT*)

JFK Federal Building, Room E340

Boston, MA 02203

(617) 565-9860

Region II

(NJ,* NY,* PR,* VI*)

201 Varick Street, Room 670

New York, NY 10014

(212) 337-2378

Region III

(DE, DC, MD,* PA, VA,* WV)

The Curtis Center

170 S. Independence Mall West

Suite 740 West

Philadelphia, PA 19106-3309

(215) 861-4900

Region IV

(AL, FL, GA, KY,* MS, NC,* SC,* TN*)

61 Forsyth Street, SW, Room 6T50

Atlanta, GA 30303

(404) 562-2300

Region V

(IL, IN,* MI,* MN,* OH, WI)

230 South Dearborn Street

Room 3244

Chicago, IL 60604

(312) 353-2220

Region VI

(AR, LA, NM,* OK, TX)

525 Griffin Street, Room 602

Dallas, TX 75202

(972) 850-4145

Region VII

(IA,* KS, MO, NE)

Two Pershing Square

2300 Main Street, Suite 1010

Kansas City, MO 64108-2416

(816) 283-8745

Region VIII

(CO, MT, ND, SD, UT,* WY*)

1999 Broadway, Suite 1690

PO Box 46550

Denver, CO 80202-5716

(720) 264-6550

Region IX

(AZ,* CA,* HI,* NV,* and American Samoa,

Guam and the Northern Mariana Islands)

90 7th Street, Suite 18-100

San Francisco, CA 94103

(415) 625-2547

Region X

(AK,* ID, OR,* WA*)

1111 Third Avenue, Suite 715

Seattle, WA 98101-3212

(206) 553-5930

* These states and territories operate their own

OSHA-approved job safety and health programs

and cover state and local government employees

as well as private sector employees. The

Connecticut, New Jersey, New York and Virgin

Islands plans cover public employees only. States

with approved programs must have standards that

are identical to, or at least as effective as, the

Federal OSHA standards.

Note: To get contact information for OSHA Area

Offices, OSHA-approved State Plans and OSHA

Consultation Projects, please visit us online at

www.osha.gov or call us at 1-800-321-OSHA.