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Silica FAQs

Robert Bowers, P. Eng., ICPI Director of Engineering

ICPI Director of Engineering, Robert Bowers, P. Eng., receives questions from members in need of advice and tips regarding silica.

The following questions arose from the participants in the recent ICPI webinar, "Preventing Silica Exposure of the Jobsite." After consultation with the presenters, Rob Bowers summarized these responses.  The webinar recording is available on the Webinars and On-Demand Learning page. The recording is FREE to members as part of the Contractor Webinar Series and costs $70 for non-members.

Respirable Crystalline Silica References

ICPI's statement regarding OSHA Silica Standard dated September 25, 2017 - https://www.icpi.org/newsroom/osha%E2%80%99s-occupational-exposure-crystalline-silica-rule-force

Small Entity Compliance Guide for the Respirable Crystalline Silica Standard for Construction  (link is external)

Small Entity Compliance Guide for the Respiratory Protection Standard (link is external)

Online tool to Develop a Respirable Crystalline Silica Exposure Control Plan provided by The Center for Construction Research and Training - https://plan.silica-safe.org/ (link is external)

Sample Respirable Crystalline Silica Exposure Control Plan provided by Zurich Insurance North America (link is external)

Occupational Safety and Health Administration Standard 29 CRF

Table 1: Specified Exposure Control Methods When Working With Materials Containing Crystalline Silica

29 CFR Parts 1910, 1915, and 1926 Occupational Exposure to Respirable Crystalline Silica; Final Rule as published in the Federal Register (link is external)

Part 1910 Occupational Safety and Health Standards, Subsection 134 - Respiratory Protection  (link is external)

Part 1910 Occupational Safety and Health Standards, Subsection 1053 - Respirable crystalline silica (link is external)

Part 1926 Safety and Health Regulations for Construction, Subsection 1153 - Respirable crystalline silica (link is external)

Answers to Post-Webinar Questions:

1. Is there a template available we can follow to implement the safety program/manual for silica? Currently, contractors can make use of the following generic construction industry tools.

Online tool to Develop a Respirable Crystalline Silica Exposure Control Plan provided by The Center for Construction Research and Training (link is external)

Sample Respirable Crystalline Silica Exposure Control Plan provided by Zurich Insurance North America (link is external)

2. Regarding OSHA's statement that certain tasks on table one do not require medical monitoring IF an employee does not perform that or other tasks which require an APF 10 for more than 30 days...Do we have an interpretation of is that 30 instances or a total of 30 days with more than 240 hours of work exposure (totaling 30 days)? The Small Entity Compliance Guide states, “Employers must make an initial or periodic medical examination available to employees who will be required by the silica standard to wear a respirator for 30 or more days per year in the upcoming year (the next 365 days). "If the employee is required to wear a respirator at any time during a day, even if it is just for a few minutes, that counts as one day of respirator use.”

If an employee is required to perform a task that requires a respirator, as a contractor and employer, you will be required to comply with the related OSHA Standards. a. A Respiratory Program per 29 CFR 1910.134 Federal OSHA Standard. The Respiratory Program includes:

Medical evaluation questionnaire

PFT – Pulmonary Function Test

Respirator fit test

Written respiratory program with documented training

b. In addition, the Silica Standard 29 CFR 1910.1053 and 29CFR 1926.1153 program requirements include the respiratory program listed above AND the following:

Physical Exam

TB Test

Chest X-Ray – must be read by a NIOSH-certified B Reader

Written silica exposure control plan with documented training

3. Does the IQ saw meet the requirement of not having to have a respirator for a standard paver cut and is there written data to support the requirement which can be used as part of an employer’s written silica exposure control plan? iQ Powertools has reported they have objective air monitoring test data to confirm that the tool, when used per manufacturer’s recommendations, meets the OSHA Silica Permissible Exposure Limit (PEL). Contact iQ Powertools to obtain this test data.

When a manufacturer tests its equipment, if the work practice and materials used match the job site conditions, OSHA will allow this data to be used as objective data as part of a written silica exposure control plan. Remember, to comply with the standard, OSHA requires an employer to have a written silica exposure control plan.

Since cutting concrete with a vacuum assisted saw is not listed in Table 1 of the standard, the employer must follow the Alternative Exposure Control Methods to determine the levels of respirable crystalline silica that employees are exposed to. This can be done using the performance option; or the scheduled monitoring option as directed by the standard. Following the performance option will require Objective Data that demonstrates employee exposure to respirable crystalline silica associated with a particular product or material or a specific process, task, or activity. The data must reflect workplace conditions, that closely resemble, or could result in higher exposures, than the processes, types of material, control methods, work practices, and environmental conditions in the employer’s current operations.

Examples of objective data are information such as: a. Air monitoring data from industry-wide surveys; b. Calculations based on the composition of a substance; c. Area sampling results and exposure mapping profile approached; and d. Historical air monitoring data collected by the employer.

4. Do smaller residential projects have the same rules and regulations as larger commercial projects? Yes. The Federal and state OSHA standards apply to all employers, large and small, nationwide. It applies to all projects, large and small, nationwide. In the past, you may have worked on smaller residential projects and never saw an OSHA inspector. Smaller residential projects are harder for them to find. But, if they drive by and see you working, they will probably stop and do an inspection. ICPI recommends that you be prepared, comply with the standard, have a silica exposure program in place and protect the health of your workers.

5. What about homeowners that are working on their own homes? OSHA standards do not apply to homeowners working on their own property or to contractors who work by themselves. “29 U.S.C. § 654, 5(a)1: Each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees.” The caveat is that OSHA does not cover workers who are not employees. However, OSHA has determined that exposure to respirable crystalline silica at a level under 50 µg/m³ over an eight-hour period time weighted average (TWA) is a safe Permissible Exposure Limit (PEL). It would make sense that homeowners and single contractors not jeopardize their health and work to be below the PEL.

6. What if you are using a table saw but dry cutting with a vacuum attached? a. Is this acceptable? As mentioned above, dry cutting concrete with a vacuum system is not listed in Table 1 so you would have to comply with the Alternate Exposure Control Methods. Determining if this would reduce the exposure level below the Permissible Exposure Limit (PEL) can only be determined after Air Monitoring Data is collected using a worker performing that task with the equipment, materials and site conditions in question. It may be possible to confirm the operator, and those in the immediate area, are safely under the Permissible Exposure Limit (PEL), if you have objective test data.

b. Can you use a respirator in addition to the vacuum? Use of a respirator will reduce the exposure level by the respirator’s Assigned Protection Factor (APF). As an example, if a worker is exposed to an environment that has a measured respirable crystalline silica level of 400 µg/m3 per 8-hr day TWA and they use a respirator with an APF of 10, the calculated exposure level will be 40 µg/m3 per 8-hr day TWA which is less than the regulated PEL. However, if the worker uses a respirator for more than 30 days a year, they will have to comply with 29 CRF 1910.134 - Respiratory Protection. In addition, the employer must comply with the additional respirator requirements from the Silica Standard. (See Question 2.b)

7. I thought I was told that none of the tools present in today’s markets provide the necessary filtration to ensure compliance with the new PEL limits. a. Is this true? False. There are many tools with vacuums attached or integrated, from various manufacturers, that could be used to drill, grind, chip, and cut concrete, asphalt and masonry materials that will safely keep an employee under the 50 µg/m³ over an eight-hour period time-weighted average.

b. If so, then even if you have vacuum saws you must then have respirators? The tools available are getting better and better at reducing the exposure to respirable crystalline silica. If it can be demonstrated with Air Monitoring Data collected using a worker performing the task with the equipment, materials and site conditions in question, that exposure levels are below the Permissible Exposure Limit (PEL) then a respirator is not required. However, if the dust reduction systems are not function at 100% effectiveness or the conditions change from those present when the Air Monitoring Data was collected, it is possible that an OSHA inspection could conduct a test and determine the exposure level is more than the PEL. That is why ICPI recommends when cutting concrete with a saw, the use of a respirator is a good practice.

8. When OSHA’s Table One does not give specific control method of using a commercial vacuum system for some tasks, and does for others, may we assume we can use a commercial vacuum system IF we obtain test results, as OSHA outlines, that would prove we can perform the task below the PEL? Yes. As mentioned previously, if the exposure control method is not included in Table 1, the Alternate Exposure Control Method must be utilized. Table 1 currently does not include dry cutting concrete with a saw using a vacuum dust reduction system. The first step of the alternative exposure control method is to determine the levels of respirable crystalline silica that employees are exposed to. This can be determined by collecting Air Monitoring Data using a worker performing that task with the equipment, materials and site conditions in question. These results may prove the exposure levels are below the Permissible Exposure Limit (PEL) and even the Actionable Exposure Limit (AEL). However, it will still be necessary to comply with the Alternate Exposure Control method and, “use engineering and work practice controls, to the extent feasible, to limit employee exposures to the PEL, and supplement the controls with respiratory protection when no other alternative is available. As well as keep records of employee exposure to respirable crystalline silica.”

9. Does the protection requirement pertain to just the individual using the saw to cut & not installers that are not in the immediate area? Part of the written control program should contain information on methods used to restrict access to the area. The plan must include a description of the procedures used to restrict access to work areas, when necessary, to limit the number of employees exposed to respirable crystalline silica and the levels to which they are exposed, including exposures generated by other employers or self-employed workers. When Table 1 requires respiratory protection, employers must provide respirators to all employees engaged in the task.

It would make sense that persons working in the restricted area would need the same level of protection afforded to the worker whose task was generating the respirable crystalline silica.

10. How do you perform an air monitoring test? An air monitoring test is typically conducted using the following equipment: Air sample pump, calibrator or rotameter, air sampling cassette filter, cassette filter holder, cyclone, tubing and clip. A small tube runs from the pump over the shoulder and is clipped on the chest or collar near the worker’s breathing area. This test can be done with or without a respirator. The worker them performs the task that needs to be analyzed. As the pump runs, air taken from the vicinity of the worker’s breathing area is filtered to collect all dust present. Once the testing is complete, the length of time the pump runs and the volume of air sampled is then recorded. The cassette filter is then analyzed in a lab to determine the mass of respirable crystalline silica captured. This number is then factored to consider the volume of air the worker would breathe in an 8-hour day compared to the volume of air sampled by the pump over the period of time that the air sample was taken.

Here is a link to a video from ALS Global that will be useful to contractors wanting to understand how to use air monitoring equipment to perform a test themselves: https://www.youtube.com/watch?v=O5knJEGGa7k (link is external)

11. Isn't it true that the current studies show that even cutting with a vacuum saw or wet you still would be required to have a respiratory system? There are numerous studies that have been done with results both above and below the Permissible Exposure Limit (PEL). Remember, if an employer has objective test data to confirm the tools, work practices and materials being used, creates and exposure level under the Permissible Exposure Limit (PEL) then no respirator is required.

The intent of the OSHA Silica Standard is to limit employees’ exposure to silica and keep them in a safe work environment. OSHA has determined that 50 µg/m³ over an eight-hour period time-weighted average (TWA) is a safe, maintainable limit.

12. Does an N95 Mask count as a respirator? Yes. OSHA recognizes the N95-rated, 2 strap mask as a respirator with an Approved Protection Factor (APF) of 10. Please reference OSHA’s Small Entity Compliance Guide for the Respiratory Protection Standard as well as 29 CRF 1910.134 - Respiratory Protection standard. As with any respirator, they must be fit tested. Refer to Question 2 for more information regarding a respiratory program.

13. What about Techniseal NextGen? Techniseal’s NextGel stabilized joint sand is reported by the manufacturer to generate substantially less dust when it is spread and compacted into the joint compared to other joint sand. Obtaining objective data from the manufacturer could confirm this. Alternately, collecting Air Monitoring Data using a worker spreading and compacting the joint sand with the equipment, materials and site conditions in question would be needed to confirm the exposure level.

14. What is the contact information for lab that does air monitoring testing? There are three main components to get Objective Data, i.e. a silica air monitoring test report.

Obtain air monitoring equipment (air pump, calibrator, air sampling cassette, hoses and a clip)

Conduct air monitoring tests – which is typically done by Industrial Hygienists.

Analyze the collected samples.

Here are links to two Industrial Hygiene companies that can help you obtain Objective Data.

Galson Labs – Air Sampling Equipment Rental and air sampling and analysis http://www.sgsgalson.com/ (link is external)

EMSL Analytical, Inc. – Provides Industrial Hygienists and air sampling & analysis https://www.emsl.com/ (link is external)

15. Are there procedures to clean up after cutting pavers? a. If wet cutting, what is the suggested clean up procedure of the slurry? If you are using a wet table saw, remove the slurry from the saw and allow it to dry, solidify and then dispose of with other site waste. Handle with care as to not reintroduce the dust into the atmosphere where it could be inhaled by someone. If cutting in place with a saw that has a water attachment and the slurry is on the paver surface, use large volumes of water to rinse before the slurry dries and permanently stains the paver surface. Scrub with a stiff bristle brush if necessary.

b. Once dust is collected, what is the procedure for proper disposal? The Housekeeping section of the standard requires that when cleaning up dust that can contribute to employee exposure to respirable crystalline silica, employers must:

Not allow cleaning by dry brushing and sweeping, unless methods such as wet sweeping and HEPA-filtered vacuuming are not feasible;

Not allow cleaning of surfaces or clothing with compressed air, unless the compressed air is used together with a ventilation system that effectively captures the dust cloud or no other cleaning method is feasible.

This section of the written plan would include cleaning methods that are acceptable (e.g., wet sweeping), cleaning methods that are unacceptable because acceptable cleaning methods are feasible (e.g., dry sweeping or blowing), and special instructions (e.g., use local exhaust ventilation if compressed air must be used). Hygiene-related subjects, such as not using compressed air to clean clothing, could also be addressed in this section of the written exposure control plan.

Remember the intent of the OSHA Silica Standard is to limit employees’ exposure to silica and keep them in a safe environment. Care and common sense apply to the proper disposal of the collected dust. Do not reintroduce the dust into the atmosphere where it could be inhaled by someone. Here are some options.

Mix the collected dust with water and allow to dry and solidify, then dispose of with other site waste.

Put the collected dust into a sealed container or trash bag for disposal with other site waste.

Mix it with moist native soil on the job site.

Additionally, the paver industry has used the terminology “sweeping” joint sand. To help differentiate the clean-up task from the necessary interlocking concrete pavement construction step, it is suggested that you use the terminology “applying” or “spreading” joint sand. Use of the term sweeping will probably attract unnecessary attention from an OSHA inspector because of the almost complete prohibition on dry sweeping. Keep in mind, the Permissible Exposure Limit still needs to be considered.

Have additional questions regarding silica? Please contact ICPI, at 703-657-6900.

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Getting to the Root of the Problem

Robert Bowers, P. Eng., ICPI Director of Engineering

Getting to the root of the problem. ICPI Director of Engineering, Robert Bowers, P. Eng., receives questions from members in need of advice and tips regarding the best practices to use when constructing paver driveways.

One recent questions referred to a residential driveway. A client wanted to install a 2,000 sf paver driveway due to the roots from 100+ year old oak trees that had damaged the existing driveway. The clients wanted a solution that would give them an attractive, stable driveway, yet would not hurt the roots of the trees.

Any cutting or compaction near the roots would result in excessive stress on the trees, possibly causing it to die a couple years, so what is the best way to install concrete pavers over existing roots without damaging the root system?

Obviously cutting the roots back to install the paver base would not be an option. Alternately, installing the aggregate base on top of the existing root mat would also present problems. Compacting the aggregate base could injure the root system. Over time the roots would grow towards the surface, through the base and bedding sand in their search for water. Eventually this would cause movement and buckling of the paver surface.

Image above: Cracking caused by tree roots (http://www.qualityincalifornia.com/2011/09/cracking-from-tree-roots.html) A better solution would be to consider a permeable interlocking concrete pavement (PICP) system. PICP is typically constructed on uncompacted subgrade. A plus for the tree roots. PICP will detain water under the pavement surface to allow it to infiltrate into the subgrade. Another plus for the trees. Tree roots also require air. In a typical PICP base, 40% of the volume is air. Again, another plus for the trees. This open volume also give the trees root plenty of space to grow before surface movements are become a problem. When you add it all up, PICP systems make sense when you consider the impact and needs of the surrounding trees.

A similar situation occurred at Louisiana State University. The landscape architect used PICP systems in areas around 200+ year old oak trees. The open graded aggregate base of the PICPs reduce the compacted forces from students walking on the soil, and PICP delivers water and air to the tree roots. The trees on campus that once showed visible signs of distress are now thriving.

Image above: LSU’s campus where PICP systems were installed to reduce the compacted forces from students.

Image above: PICP systems installed on LSU’s campus in areas around 200+ year old oak trees.

Have an engineering or technical question? Robert is always ready to respond with the latest technical resources and information.

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Paver Patio Points

Robert Bowers, P. Eng., ICPI Director of Engineering

As the weather gets warmer, consumers start to create their outdoor dream space.

ICPI Director of Engineering, Robert Bowers, P. Eng., receives questions from members in need of advice and tips regarding the best practices to use when constructing raised patios. 

One of the most recent questions was related to a residential permeable interlocking concrete pavement (PICP) patio. Typically a PICP system uses a layer of ASTM #2 stone as the subbase, a 4 in. (100mm) layer of ASTM #57 stone above as the base and a 2 in. (50mm) layer of ASTM #8 stone on top as the bedding layer. Given this is a residential patio application, could the contractor only use a layer of #57 stone for the base or would it need to incorporate #2 stone as well?

The response, ASTM #2 stone provides better structural support for heavier, repetitive loads. It also tends to stay in place better than ASTM #57 stone, once it has been compacted. The drawback to using ASTM #2 stone is that it will typically require heavier compaction equipment and the need to manage another material on site. Given this project is a residential patio and will only experience light pedestrian loading, the ASTM #2 stone subbase is probably not necessary. It was also recommended that a highly permeable geotextile be placed between the ASTM #57 stone and the subgrade to improve separation between the open aggregate and the subgrade soil.

The system of ASTM #2 / #57 / #8 layers of aggregate are recommended because it has been demonstrated to work on numerous projects. However, an engineer familiar with the design of PICP systems may choose to utilize different aggregates.

Another question asked about the recommended installation best practices for a raised patio against brick veneer on a house? The response referred to the ICPI Advanced Residential Technician student manual.

When constructing a raised patio against an existing structure considerations should include: 1) creation of an air gap between the building’s exterior cladding and the raised fill using a retaining wall facing the building and 2) considering the additional load the raised patio will place on the foundation wall of the building.

Considering item 1, it is important to address water and moisture issues. It is important to ensure that rainfall landing on the patio surface is directed away from the house. Typically, a minimum grade of 1.5% is ideal to ensure that water flows across the surface. If the slope is lower than this, the water won’t move rapidly off of the patio. Slopes can be increased up to 4% to help speed the movement of water, but the pavement surface will be pitched. Tables and chairs will be on a noticeable slant, and the area can become a slipping hazard if ice forms on the patio surface. For larger patio areas, surface drains may be constructed to remove water from the surface. For smaller patios, it may be appropriate to have surface water flow across the patio, over the top of the retaining wall, and onto the garden or patio below. The use of stabilized joint sand may be appropriate to ensure that it is not removed by falling or flowing water.

Raised patio construction will likely affect the house. In most cases, there are two types of exterior walls: a) below grade foundation walls and b) above grade exterior walls. During construction, the compaction of fill places large dynamic loads on the adjacent walls. Placement of fill next to a building wall also increases the lateral load applied to the walls. The fill material used to construct the patio has moisture in it that can affect the building if the fill contacts the exterior walls. Below-grade foundation walls are typically constructed using concrete or concrete masonry units (CMU) waterproofed on the exterior with a drainage system incorporated at the base. Foundation walls are designed to withstand moisture against them continuously.

An above-grade exterior wall of a house can be constructed from materials such as wood, vinyl or aluminum siding, cement board, stucco, mortared clay, concrete brick, mortared stone or mortared veneers. These exterior wall materials are designed to support the load of the building above, and to resist the penetration of water. Placing compacted soil next to these types of siding can trap moisture in and against them, which leads to deterioration and eventually failure. Deterioration is accelerated when freeze-thaw conditions also exist. For raised patios with compacted fill material against the exterior wall, it is best to construct a stress relief wall leaving an air gap between the raised patio and the exterior wall. The stress relief wall can be constructed like any other segmental retaining wall on a raised patio project, but the face of the wall faces the exterior wall of the building. The air gap created needs to have drainage so any water that finds its way into the gap can drain out. It is also appropriate to encourage air circulation in the space to minimize condensation and allow the space to thoroughly dry out.

For item 2, when additional fill is placed adjacent to a building, lateral load applied to the foundation wall will increase. This is true even when a stress relief wall is used. For buildings with unbalanced fill conditions, like a basement, the weight of the additional fill can exceed the lateral strength of the foundation wall and can cause the wall to bulge and eventually blow out in to the basement area, potentially causing a collapse of the structure. Extra load is applied from the raised patio fill, but no extra resistance is provided by the foundation wall. Caution should be taken when taking on an unbalanced fill project, and an engineer should be consulted to ensure the stability of the project.

Image Above: Drawing from the ICPI Advanced Residential Installer Course manual.

Have an engineering or technical question? Robert is always ready to respond with the latest technical resources and information.

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The Use of Geotextile in Permeable Pavement

Robert Bowers, P. Eng., ICPI Director of Engineering

ICPI Director of Engineering, Robert Bowers, P. Eng., receives questions from members in need of advice and tips regarding permeable paver driveways.

One recent question referred to a residential permeable pavement driveway, and when to use geotextile versus when to not.

Sometimes called filter fabric, geotextile is made of synthetic fibers formed into a sheet that are designed to allow water and gases to pass through them, while retain soil particles. Geotextile separates and contains the base from the underlying soil subgrade. It allows the base to shed water, and prevents the soil around it from working its way into the base.

Without geotextile, the soil will work its way into the base and weaken it. This is a slow process that happens when the soil is saturated with water or during periods of thawing. Geotextile stops this process and extends the life of the base by many years. Geotextile is recommended for use over silt and clay soils. It is not essential in sandy soils.

The decision to use a geotextile in permeable pavement should be based on the same criteria used when considering use of a geotextile for the traditional interlocking concrete pavement: 1) confinement of the base aggregate and 2) separation of the base aggregate from the subgrade soil. Confinement and separation created by the geotextile will help ensure that the base in a pavement system will function longer than a base that is not wrapped in a geotextile.

However, the selection criteria also requires that the geotextile have a high level of permeability. Typically, geotextile manufactures report the materials ability to pass water through it as the permittivity. The greater number, the faster water will pass through.

The member went on to ask if they should use the same woven geotextile as specified for traditional paver systems?

If the soil is structurally sound, like a sand-gravel mixture, the use of non-woven needle punched geotextile should work. It was suggested that a thicker non-woven needle punched geotextile, such as an 8 oz., be used because of the damage it would experience from compacting larger angular aggregate on top of it.

If the soil is weaker, like silt or clay, the use of a woven geotextile would be appropriate. However, it was recommended to look for a geotextile with a higher permeability to allow the water collected in the system to pass through the geotextile and infiltrate in the subgrade unimpeded. Typical slit-tape woven geotextile would not be suitable because of its low permittivity. It is recommended to use a mono-filament, multi-filament or fibrillated-filament type woven geotextile.

Have an engineering or technical question? Robert is always ready to respond with the latest technical resources and information.