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Course 851 - Silica Dust Safety in Construction

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Silica Dust Control Strategies

control strategies

Controlling the exposure to silica in construction can be done by applying engineering controls, administrative actions, and personal protective equipment (PPE), similar to practices in other industries. These prioritized control strategies are called the “Hierarchy of Controls.”

  1. Engineering controls include strategies that eliminate or reduce the hazard (silica dust) itself. Examples include such things as treating material so it does not create dust, replacing silica with another material, isolating, containment, and using ventilation systems.
  2. Administrative/work practice controls include limiting workers’ exposure time and providing showers.
  3. Use of personal protective equipment (PPE) includes wearing proper respiratory protection and protective clothing.

In this module, we will discuss these control strategies in more detail. It is important to know the best control exposure to silica dust, a higher priority control strategy may actually be less effective. For more information on the Hierarchy of Controls, check out Course 704, Hazard Analysis and Control, Module 5.

Engineering Controls

As mentioned earlier, if possible, we want to do something about the hazard first. Then we don’t have to worry so much about employee behaviors. Engineering controls attempt to do that.

If silica products are used, OSHA requires engineering controls to be used first wherever possible. This type of control involves a mechanical process to eliminate or reduce the amount of silica dust.

The most effective way to eliminate the silica hazard is to eliminate the silica! Doing that is not possible for many masonry operations, but engineering controls are possible and especially important for many applications.

For instance, where abrasive blasting is done outside, substitution of silica with some other material can be used. Substituting the silica means using a different, safer material, like plastic beads, corn cobs, walnut shells, etc., in place of the silica-containing substance.

There are two basic types of engineering control methods:

  1. Wet methods: As we mentioned earlier, wet methods for cutting, drilling, hammering and grinding is the most effective method for controlling airborne silica dust because it controls the exposure at its source. In most cases, wet methods keep exposures below the allowable limit.
  2. Dry methods: The most common dry control method is vacuum dust collection (VDC). This engineering control method can significantly reduce silica levels, but may not reliably keep them below 0.1 mg/m3 as an 8-hour TWA. VDCSs include a dust collector (hood or shroud), vacuum, hose and filter(s).

Wet Methods

wet
  • Cutting: Wet cutting is the most effective method for controlling silica dust generated during sawing because it controls the exposure at its source. Wet dust is less able to become or remain airborne. Wet masonry saw operators’ exposures usually well below 0.1 mg/m3.st stationary saws come equipped with a water basin that typically holds several gallons of water and a pump for recycling water for wet cutting. Handheld saws spray water that is held in separate containers.
  • Drilling: Wet drilling systems pump water through the drill stem to prevent dust from being released into the air. The drill operator controls the flow using a control valve. Some drills are equipped with a flow meter.
  • Hammering: Wet methods are generally not appropriate for use with electric rotary hammers; however, pneumatic drills can be used for wet drilling and some come equipped with water-feed capability. The best way to control silica dust when using a jackhammer is with wet methods, where water is constantly sprayed to reduce the amount of dust that gets into the air. Wetting the surface with a spray or mist of water at the point where the jackhammer’s tip strikes the surface material helps reduce the amount of airborne dust.
  • Grinding: Wet grinding is highly effective in reducing silica exposures. 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. Wet methods consistently keep employee exposures below OSHA limits.

Dust Suppression

Dust suppression is a wet 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.

  • Pre-wetting surfaces: When blasting, a separate water hose can be strung next to the hose containing the blasting medium. When using heavy construction vehicles on unpaved surfaces, a water truck can spray the site grounds.
  • 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.
  • 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. Electrostatic water sprays may enhance dust removal by attracting oppositely-charged dust particles to the charged water droplets.
  • 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.
  • 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.
iQ 360 Vacuum Masonry Chop Saw
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Dry Control Methods

Cutting: When wet methods cannot be used, one alternative is the use of vacuum dust collection (VDC) systems. Stationary masonry and hand-held 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. A dust collector mounted to the back of a saw requires a high exhaust airflow to ensure good dust capture between the saw blade and dust collector.

Dust Collection when Drilling - DeWALT
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Drilling: Dry collection systems require an enclosure around the area where the drill stem enters the ground. The enclosure is made by hanging a rubber or cloth shroud from the underside of the drill deck. The enclosure is ducted to a dust collector that has a fan outside of the filter opposite the drill hole. The fan creates a negative pressure inside the enclosure capturing dust as it leaves the hole during drilling.

Rock drilling equipment should use enclosed positive-pressure cabs with air conditioning and filtered air supply to isolate the operator from the dust. Older cabs can be retrofitted with systems that filter, heat, and cool the air.

Grinding: Vacuum dust collection 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 may also purchase equipment to retrofit grinders for vacuum dust collection.

wet
If vacuum systems are not available, use respiratory protection.

Hammering: Vacuum dust collection systems are the primary way to control dust when using rotary hammers. The drill bit is surrounded by a shroud attached to a vacuum to collect dust and bits of concrete. VDCSs are available in a variety of designs and should include a dust collection device (shroud), vacuum, hose and filter(s).

Blasting: Crystalline silica, in the form of finely ground quartz sand as an abrasive blasting agent, is used to remove surface coatings prior to repainting or treating, a process that typically generates extremely high levels of airborne respirable crystalline silica. To minimize exposure during dry abrasive sand blasting, dust collection systems can be installed on the equipment. Also, the workspace may be enclosed, or ventilation hoods may be used.

Isolation, Containment and Ventilation

wet

Isolation: Methods can be used to isolate or increase the distance between the employee and the point of work can reduce exposure levels. For instance, 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.

Employee Positioning: Where possible, exposures can be reduced if employees work from a position that minimizes exposure. For instance, greater distance from the grinding point, especially when grinding on ceilings and sanding drywall when the dust can fall directly on the employee.

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.

Ventilated containment structures: Exhaust ventilation systems in containment structures can be effective in capturing and removing silica dust. However, task requirements may make this method infeasible. Both the structure and exhaust systems should be properly designed to be effective.

Ventilation Booths: A booth (with fan) erected around a saw can help reduce dust, but may require some experimentation. 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.

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 would build up due to poor air circulation.

Vacuums for general cleaning: 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. Use pneumatic vacuums 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. Employers should choose vacuum filter media carefully.

Instructions

Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Which of the Hierarchy of Controls strategies are used to eliminate or reduce silica dust hazards?

2. What is the most effective method for controlling airborne silica dust because it controls the exposure at its source?

3. Vacuum dust collection systems for _____ include a shroud, hose, filters and a vacuum to pull air through the shroud.

4. What methods increase the distance between the employee and the point of work to reduce silica dust exposure?

5. Which of the following should not be used as the primary method for managing silica dust?


Have a great day!

Important! You will receive an "error" message unless all questions are answered.