Abrasive Blasting Media that Reduce Exposure to Silica

Using alternative blasting media that do not contain crystalline silica and are designed to minimize dust production can help reduce airborne concentrations of respirable crystalline silica and other hazardous substances.

Description:

Abrasive blasting is a process that removes soils, discoloration, and coatings from metal, concrete, or masonry surfaces.  It can also be used to add texture to a surface so that new coatings adhere more strongly.  Abrasive blasting involves directing a pressurized stream of abrasive material against the surface until the desired effect is achieved.  Silica sand has traditionally been one of the most commonly used blasting media.  However, when silica sand impacts the blasted surface at high speeds, the grains of sand fracture and create copious dust and respirable crystalline silica.  Using an alternative blasting medium can help reduce worker exposure to silica and other hazardous substances.
 

There are a wide variety of blasting media that can be used in place of silica sand.  These may include coal slag, steel shot, glass, grit, walnut shells, and garnet. However, even though these materials do not contain silica, there can be crystalline silica in the base material being blasted.  When impacted by the blasting media, the crystalline silica in the base material can become airborne.  Milder blasting media like dry ice, baking soda, sponges, and water jets are silica-free and designed to minimize the dust created when the blasting medium strikes the surface of interest. 

Sponge blasting involves shooting small pieces of specially made grit sponge at the surface of interest.  As the pieces of sponge strike the surface, they adhere to and remove the top layer.  Sponge blasting creates very little airborne dust, and the sponge pieces can often be reused.  It also reduces the likelihood of ricochet.

 

SpongeJet® B-VAC™ Pro 4

Fully integrated, mobile system

Price: $100,000 (verified 5/7/19)

 

Photo courtesy of spongejet.com

 

Soda blasting is a gentle abrasive blasting method that uses sodium bicarbonate (baking soda) as the blasting medium.  It is ideal for soft materials like wood and can also be used in restoration projects.  It usually requires a much lower blasting pressure. Although the baking soda can’t be reused, it is non-toxic and biodegradable, and creates a much lower volume of waste than traditional sandblasting.    

 

The Soda Works Buster Blaster 100 Mobile Unit

Fully integrated and mobile

Price: $42,500 (verified 5/7/19)

 

Courtesy of sodaworks.com

 

 

Risks Addressed:

Abrasive blasting using silica sand creates extremely high levels of airborne respirable crystalline silica (RCS) particles that are small enough to penetrate into the lower lung.  This can cause cancer, chronic obstructive pulmonary disease (COPD) and silicosis, an incurable lung disease that leads to death.  Even if the blasting medium does not contain silica, many common construction materials (brick, block, mortar, concrete, etc.) have a high silica content and will release RCS into the air when hit by the blasting medium.  The Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for respirable crystalline silica in the construction industry is 50 micrograms per cubic meter (μg/m3), expressed as an 8-hour time weighted average (TWA). Uncontrolled sandblasting has been shown to produce up to 27,000 μg/m3 of RCS, or about 540 times the current PEL (Jennison & Cocalis 1995).
 
Even if the blasting medium and base material are silica-free, they can still produce hazardous respirable dust.  Coal slag has been used as a silica sand alternative, but research shows that it can contain beryllium and may cause a type of metal poisoning called berylliosis (Mugford 2017a).  Copper slag and crushed garnet have also been used as silica sand substitutes even though they can contain various toxins like arsenic (Mugford 2017b) and have been shown to cause lung damage and inflammation when inhaled (Hubbs et. al. 2001).

How Risks are Reduced:

Blasting with silica sand creates extremely high levels of silica-containing dust.  This dust is a combination of particles that are dislodged from the surface being blasted as well as pulverized abrasive material.  By substituting a silica-free abrasive that reduces dust, you can minimize exposure to silica and other hazardous airborne contaminants.

Effects on Productivity:

Using a silica-free abrasive blasting medium that reduces dust can improve visibility and accuracy.

Additional Considerations:

The likelihood of exposure to silica or other harmful airborne contaminants while abrasive blasting depends on many factors, including the blast pressure, surface coating, and base material.  If a paint or coating contains hazardous substances like lead or hexavalent chromium, these hazards will be present in any dust created by the blasting process. 
 
Some of the substitutes mentioned above may be of limited utility when blasting a metal surface to impart a profile. When performing any type of blasting, OSHA requires a type CE NIOSH-certified blasting airline respirator with positive pressure blasting helmet.  Abrasive blasting can also be extremely loud.  It may frequently be necessary to use double hearing protection. 
 
For more information on safer abrasive blasting, please visit https://www.cdc.gov/niosh/topics/blasting/default.html.

Contributors:

Sara Brooks, MPH - CPWR - The Center for Construction Research and Training

Mike Kassman, MAHP, CHST, PA-AIC, APT: CPWR - The Center for Construction Research and Training

Alan Echt, MPH, DrPH - National Institute for Occupational Safety and Health

 

Hazards Addressed:

  • Paints & Coatings
    • Perform abrasive blasting
    • Prepare surfaces with mechanical devices