Material Use Guide
OSHA Fact Sheet – Crystalline Silica Rule: Construction
The inserted “Fact Sheet” from OSHA covering the crystalline silica rule for construction is a brief resource to which the contractor may refer for OSHA guidance regarding compliance with the new rule, what activities should be monitored and other
Industrial Hygiene Assessment
This section of the booklet contains briefings of assessments obtained by SPEC MIX at certain jobsites where SPEC MIX products and silo systems were on site. SPEC MIX hired ARS Environmental to evaluate four jobsites across the country of different size and with aggregates of different composition to get across section of the average worker’s exposure to dust on a jobsite when mixing materials. A contractor may wish to use this information to better understand and evaluate the mixing stations on your projects
Work Control Practices for SPEC MIX Silo
SPEC MIX products and silo systems, when used properly and as designed, increase jobsite efficiency and consistency while minimizing exposure to dust. Like any other tool on site, it is of the utmost importance that the user is properly trained on its use to ensure that workers are not putting themselves at risk. This section of the booklet focuses on suggested Work Control Practices Guide intended to help train on-site personnel to use SPEC MIX silo systems and products in a safe way that should reduce unnecessary exposure to dust. Note that not all jobsite conditions are the same and that a contractor will need to assess the conditions at the mixing station to determine what, if any, adjustments need to be made to keep an employee in a position to reduce dust exposure.
This section of the booklet contains a suggested Written Control Plan for the SPEC MIX mixing station. Your competent designee may use this form as a template when evaluating the unique mixing conditions on your jobsite to help develop a plan for mixing. This plan can be kept on file and used to educate employees as well as notify safety inspectors to the plan that your company has set in place for mixing materials on site.
SPEC MIX Preblended Materials
SPEC MIX products are preblended cement, aggregate and performance admixtures that are specifically designed for the application and consistent from the first to the last batch. This section of the booklet contains a listing of our basic product mixes.
SPEC MIX Silo Systems
This section of the booklet includes all of the SPEC MIX silo systems that are available for use on construction sites today. Each silo system offers the contractor specific efficiency advantages to help maximize mixing station efficiency.
SPEC MIX Engineering Controls
Should a jobsite condition make it necessary to incorporate additional protection, SPEC MIX does offer engineering controls that can be implemented at the contractors’ option to help additionally reduce exposure to dust. This section of the booklet identifies two controls. It is important to note that proper training on how to use the silo systems and products can often create an on-site environment that reduces exposure to dust.
Who is affected by the construction standard?
About two million construction workers are exposed to respirable crystalline silica in over 600,000 workplaces. OSHA estimates that more than 840,000 of these workers are exposed to silica levels that exceed the new permissible exposure limit (PEL). Exposure to respirable crystalline silica can cause silicosis, lung cancer, other respiratory diseases, and kidney disease. Exposure can occur during common construction tasks such as using masonry saws, grinders, drills, jackhammers and handheld powered chipping tools; operating vehicle-mounted drilling rigs; milling; operating crushing machines; and using heavy equipment for demolition or certain other tasks. The construction standard does not apply where exposures will remain low under any foreseeable conditions; for example, when only performing tasks such as mixing mortar; pouring concrete footers, slab foundation and foundation walls; and removing concrete formwork.
What does the standard require?
The standard requires employers to limit worker exposures to respirable crystalline silica and to take other steps to protect workers. The standard provides flexible alternatives, especially useful for small employers. Employers can either use a control method laid out in Table 1* of the construction standard, or they can measure workers’ exposure to silica and independently decide which dust controls work best to limit exposures to the PEL in their workplaces. Regardless of which exposure control method is used, all construction employers covered by the standard are required to:
• Establish and implement a written exposure control plan that identifies tasks that involve exposure and methods used to protect workers, including procedures to restrict access to work areas where high exposures may occur.
• Designate a competent person to implement the written exposure control plan.
• Restrict housekeeping practices that expose workers to silica where feasible alternatives are available.
• Offer medical exams—including chest X-rays and lung function tests—every three years for workers who are required by the standard to wear a respirator for 30 or more days per year.
• Train workers on work operations that result in silica exposure and ways to limit exposure.
• Keep records of workers’ silica exposure and medical exams.
What is Table 1?
Table 1 matches common construction tasks with dust control methods, so employers know exactly what they need to do to limit worker exposures to silica. The dust control measures listed in the table include methods known to be effective, like using water to keep dust from getting into the air or using ventilation to capture dust. In some operations, respirators may also be needed. Employers who follow Table 1 correctly are not required to measure workers’ exposure to silica and are not subject to the PEL.
Table 1 Example: Handheld Power Saws
If workers are sawing silica-containing materials, they can use a saw with a built-in system that applies water to the saw blade. The water limits the amount of respirable crystalline silica that gets into the air.
Alternative exposure control methods
Employers who do not use control methods in Table 1 must:
• Measure the amount of silica that workers are exposed to if it may be at or above an action level of 25 μg/m3 (micrograms of silica per cubic meter of air), averaged over an eight hour day.
• Protect workers from respirable crystalline silica exposures above the permissible exposure limit of 50 μg/m3, averaged over an eight-hour day.
• Use dust controls to protect workers from silica exposures above the PEL.
• Provide respirators to workers when dust controls cannot limit exposures to the PEL.
When are employers required to comply with the standard?
Construction employers must comply with all requirements of the standard by June 23, 2017, except requirements for laboratory evaluation of exposure samples, which begin on June 23, 2018.
Additional information on OSHA’s silica rule can be found at www.osha.gov/silica.
OSHA can provide extensive help through a variety of programs, including technical assistance about effective safety and health programs, workplace
consultations, and training and education.
OSHA’s On-site Consultation Program offers free and confidential occupational safety and health services to small and medium-sized businesses in all states and several territories across the country, with priority given to high-hazard worksites. On-site consultation services are separate from enforcement and do not result in penalties or citations. Consultants from state agencies or universities work with employers to identify workplace hazards, provide advice on compliance with OSHA standards, and assist in establishing and improving safety and health management systems.
To locate the OSHA On-site Consultation Program nearest you, call 1-800-321-OSHA (6742) or visit www.osha.gov/dcsp/smallbusiness . For more information on this and other health-related issues impacting workers, to report an emergency, fatality, inpatient hospitalization, or to file a confidential complaint, contact your nearest OSHA office, visit www.osha.gov , or call OSHA at 1-800-321-OSHA (6742), TTY 1-877-889-5627
As OSHA’s new crystalline silica rule for construction was being developed, SPEC MIX took a proactive approach to better understanding how this rule will affect its silo systems and material used on site. In 2016, ARS Environmental Health, Inc. was contracted to run a series of three industrial hygiene assessments of workers’ exposure to respirable dust and crystalline silica while using SPEC MIX products and silo systems. A follow-up test was run in September of 2017 on one additional jobsite.
2016 Material Mixing Assessment
In 2016, three jobsites (Chicago, IL; Statesboro, GA; Scottsdale, AZ) were selected for evaluating a workers exposure to respirable dust and crystalline silica when using SPEC MIX silo systems and materials. The employees who were working the mixing stations were fitted with a personal sampling pump with a respirable dust cyclone (pictures 1 & 2) and monitored for two continuous days.
These jobsites had crews of between 8 and 12 workers, mixed between 4 and 7 double batches of material per worker, and loaded between 1 and 4 bulk bags per day (pictures 3 & 4). The employees who were mixing the materials also preformed other jobsite activities including building scaffold, shoveling mortar and grout, driving the forklift, carrying brick and block, cutting brick and block, and laying block. They were generally exposed to all conditions on site.
Prior to the assessment, the workers who performed the mixing tasks were given SPEC MIX Work Control Practices training on how to best approach these tasks in a safe and responsible manner. In some cases the silos did employ an upper silo shroud, but not all silos. There were no engineering controls used between the silo and the mixer beyond the standard material dispensing chute.
The analysis of the samples collected showed that the workers monitored on these jobsites had an exposure level below the PEL (PERMISSIBLE EXPOSURE LIMIT) and below the Action Level of OSHA’s New Crystalline Silica Rule for Construction in an 8 hour working day (Table 1).
2017 Material Mixing Assessment
In September of 2017, an additional study was commissioned in Dallas, TX using industrial hygienist ARS Environmental Health, Inc. The Dallas market was specifically selected because the mason sand/aggregate in this part of the country is known to have a high content of silica (quartz). The analysis was performed on a large project employing two masonry subcontractors with over 50 workers onsite. The employees who were working the mixing stations were fitted with a personal sampling pump that included a respirable dust cyclone while monitored for two continuous eight hour days.
The employees at the mixing station on this jobsite mixed between 13 and 52 double batches of material and loaded between 7 and 13 bulk bags per day. The employees who were mixing materials spent the majority of their time at the mixing station, mixing materials, loading silos and performing other tasks related to the mixing of materials. They were generally exposed to all conditions on site.
Prior to the assessment, the workers who performed the mixing tasks were given SPEC MIX Work Control Practices training on how to best approach these tasks in a safe and responsible manner. The silos did have engineering controls installed, specifically, an upper silo shroud and a mixer shroud (pictures 1 & 2).
The analysis of the samples collected showed that the workers monitored on this job site had an exposure level below the PEL (PERMISSIBLE EXPOSURE LIMIT) and below the Action Level of OSHA’s New Silica Rule for Construction in an 8 hour working day (Table 2).
We note that some jobsites will include other activities, such as sawing concrete, which will produce dust that these assessments did not report. Where those activities occur on the jobsite, contractors will need to consider them in making their own assessments.
SPEC MIX silo delivery systems are designed to increase productivity on site while adding to jobsite safety by reducing physical injury with their ergonomically correct design. The standard gravity or mechanical silos should also limit workers exposure to construction site mixing dust when the following best practices are incorporated into everyday use.
Loading the Silo:
1. Position silo in an area of open wind, avoiding enclosed
or confined areas. (If silo enclosures are necessary for
winter work, provide engineering controls to minimize dust
2. Position the bulk bag over the top of the silo centered over
the fill port and safety ring.
3. From the loading platform, position yourself so you are not
downwind from the filling port to minimize exposure to dust
4. Lower the bulk bag to a position just above the safety ring.
5. Using the safety hook or your hand, reach under the safety
ring and open the b-locks on the inner and outer chutes at
the bottom of the bulk bag to dispense material into the silo
6. Climb down the ladder as the material dispenses into the
silo to minimize exposure to dust while filling the silo (picture 3).
7. Using the forklift, continue to adjust the position of the bulk
bag over the silo to keep the chute of the bulk bag as close
as possible to the fill port to reduce dust.
If positioning upwind when loading the silo is not
possible or if the contractor should want to use
additional measures to reduce exposure to dust
when loading a SPEC MIX silo system, the contractor
should employ its own engineering controls or may
contact SPEC MIX to explore additional manufacturer’s
Silo Mixing Procedures:
1. Position silo in an area of open wind, avoiding enclosed
or confined areas. (If silo enclosures are necessary for
winter work, provide engineering controls to minimize dust
2. Position the silo so the mason tender can be positioned
with a crosswind over the mixer or upwind to keep dust
from blowing into the face of the worker while mixing. Many
SPEC MIX silos are equipped with rotating gates that allow
for the handle to be moved without moving the silo itself.
If necessary, remove the mixer from under the silo and
reposition it in a different direction to keep the operator from
standing in a downwind position (picture 1).
3. Fill the mixer with sufficient water to receive the material.
It is beneficial to keep the initial batch wetter than required
for final use to ensure complete hydration of the aggregate,
reducing dust when charging the mixer and increasing board
life of the final product (picture 2).
4. When opening the gate, take a stance that is away from the
discharge of material to limit exposure to dust.
5. Open the gate with even force and only as wide as needed
to allow for a good steady flow of material into the silo
mixer. Opening at too great of a distance can cause product
surges that have the potential to increase airborne particles.
When the desired amount of material has been dispensed
into the mixer, shut the gate with even force, maintaining
distance from the mixer (picture 3).
6. As the wind shifts, make sure to position yourself with a
cross wind or upwind to continue to avoid exposure to dust.
If necessary, turn the mixer a different direction (picture 4).
If positioning upwind when mixing is not possible or if
the contractor should want to use additional measures
to reduce exposure to dust when loading a SPEC MIX
silo system, the contractor should employ its own
engineering controls or may contact SPEC MIX to
explore additional manufacturer’s engineering controls.
Mixing 80 Pound Bag Product:
Always position the mixer with either a cross wind or upwind
from work to keep dust from blowing into the face of the
worker while mixing. This may require a change in the mixer
position as the wind direction changes daily (picture 5).
If positioning upwind when loading a silo or mixing is not possible or if the contractor should want to use additional measures to reduce exposure to dust when loading a SPEC MIX silo system, the contractor should employ its own engineering controls or may contact SPEC MIX to explore additional manufacturer’s engineering controls.
SPEC MIX Silo Upper Shroud:
1. Install the Silo Upper Shroud into the fill port at the top of the silo. The end of the tube with the skirt should be positioned just above the top of the silo and draped down to close any air gaps between the Upper Dust Shroud and the
silo (picture 1).
2. Position the bulk bag over the Silo Upper Shroud and lower the bulk bag so it compresses the upper shroud.
3. Reach under the safety ring, pull the upper dust shroud down from the bulk bag and release the inner and outer b-lock by hand or with the safety hook (picture 2).
4. Release the upper dust shroud to allow it to compress against the bulk bag.
5. Climb down the ladder as the material dispenses into the silo to minimize exposure to dust while filling the silo (picture 3).
6. Reposition the bulk bag as needed to keep a tight seal between the upper dust shroud and the bulk bag.
SPEC MIX Mixer Shroud:
1. Install the Mixer Shroud to the silo slide gate chute ring.
2. Cut the chute of the Mixer Shroud at the desired height to allow the shroud to hang over the mortar mixer so that the shroud falls down over the sides of the mixer drum approximately 2” in every direction (picture 4).
3. Strap the chute of the mixer shroud over the silo chute on the chute ring.
Additional Helpful Mixing Tips:
1. If the mixer cannot be repositioned, the use of a windscreen to block wind direction that is creating an upwind condition can be helpful.
2. When mixing in enclosed areas, the use of an evacuation fan can be helpful.