Silica and OSHA

The Occupational Safety and Health Administration (OSHA) is in final preparations for a hazard communication related to a Occupational Exposure to Crystalline Silica. This rule will basically set standards for exposure to silica dust during blasting (and other operations) in confined work spaces. Inhalation of silica is generally considered to increase the risk of silicosis.

According the OSHA, in 2005 "silicosis was identified on 161 death certificates as an underlying or contributing cause of death. Exposure to crystalline silica has also been associated with an increased risk of developing tuberculosis and other nonmalignant respiratory diseases, as well as renal and autoimmune diseases." The need for the exposure standard is the standardize monitoring, training for use with silica and compliance.

Of course, in an abrasive blasting environment the best way to avoid the hazards of silicosis is to use media that do not contain crystalline silica such as Crushed Glass Grit.

Crushed Glass - Gulf Coast Project

PaintSquare News recently posted an article - Uncontained Blast Medium OK'd for Gulf Coast Project - about the use of Crushed Glass Grit to remove a vinyl coating on a concrete surface. The US Army Corps of Engineers approved the use of this medium for abrasive blasting without containment since the Crushed Glass Grit does not contain free silica or toxic chemicals.

The article does a nice job of explaining the project and what issues needed to be considered prior to approval. Safety of the workers and the area surrounding the project were of prime importance.

I think the most interesting part of the article is the long discussion in the comments section. Ultimately, there really is no other reasonable option than to blast the surfaces. While concerns are raised regarding issues with potential hazards in the coating and with blasting concrete, the best choice for this project (and others like it) is Crushed Glass Grit.

(Not) Blasting with Sand

An excellent string on the ContractorTalk.com forum discusses the basics regarding blasting or not blasting with silica sand. There are some excellent basic questions about abrasive blasting and what is being used in the industry today. Some of the regular posters on the forum provid some very useful and pragmatic advice. Worth a quick read.

10 Blasting Bullets

10 quick abrasive blasting tips:

• Nozzle size determines the air requirement (CFM), not the pot size.
• Pressure systems are more efficient than siphon or gravity fed blasters.
• More air is always better.
• DRY AIR: Use a moisture separator on the blaster and cooler on the compressor.
• Ceramic nozzles are inexpensive but carbide nozzles last much longer.
• It's rare to blast above 110 PSI - typical is 80-90 PSI.
• Ear plugs are helpful, especially if you are near the compressor.
• Avoid using a longer blast hose than is necessary. A longer air hose is preferred.
• Proper protection is important, especially an air supply helmet in a closed or contained area.
• DO NOT blast with silica sand. There are plenty of 'healthier' alternatives that might even work better.
• Bonus Tip: Expect a loss of 5 PSI per 50 feet of air and blast hose.

Coal Slag

When coal is burned in a boiler to produce energy, the incombustible materials constitute three components: fly ash, bottom ash and bottom slag. There is growing concern about the potential hazards of coal waste due to contamination with heavy metals such as chromium, lead and arsenic.

Fly ash is the light 'dust' that is exhausted from the burning process. Improvements over the past 20 years at coal fired facilities has allowed as much as 99% of this ash to be captured for re-use in other applications. Bottom ash is the unburned material and fine particulate that is not expelled in the flue. A recent 60 Minutes expose discusses some of the hazards of fly ash:

Watch CBS News Videos Online

Boiler slag is the molten material (ash and incombustible) that is sent to a quenching water bath. The quenching process immediately fractures the molten material producing a coarse, hard, black, angular, glassy material sometimes call black beauty. This coal slag is used for a variety of industrial applications including abrasive blasting. The concern is that once the coal slag is blasted, the process releases the heavy metals into the air or they get absorbed by ground water.

While coal slag (which contains minimal crystalline silica) has historically been considered to be a safe alternative to silica sand, the EPA is reviewing whether to classify fly ash and other coal burning wastes as a hazardous material. There is no need to wait for the EPA to make a final determination. There are many alternatives to coal slag for blasting such as crushed glass grit and other more specialty types of blasting media.

Silicon Carbide

Silicon Carbide is manufactured from a high heat reaction of silica sand and carbon. While silicon carbide and silica share similar chemistry, Silicon Carbide used in abrasive blasting contains less than 1% free silica. Free silica or silicon dioxide is the compound that should be avoided (due to risk of silicosis) and not inhaled as a fine particulate. Details about Silicon Carbide can be found on a previous post.

Blasting Stone with Sand

Question: I am thinking of purchasing a small business doing stone engraving. My only concern is blasting with the silica sand which is what is being used right now. We plan to use a blasting room and filtered breathing system but I don't know how safe I can be using silica sand. I am curious about alternatives like silicon carbide and aluminum oxide and could use any tips and advice on how I can do this kind of work safely.

Response: Blasting with silica sand is definitely NOT recommended - even with a breathing apparatus. Both Aluminum Oxide and Silicon Carbide are more aggressive blasting media than sand and will provide quicker results and a better surface finish on stone. Both of these media can be used with standard abrasive blasting systems without modification. Of course, always minimize breathing any kind of dust when blasting.

Stone Engraving

Question: I am thinking of purchasing a small business doing stone engraving. My only concern is blasting with the silica sand which is what is being used right now. We plan to use a blasting room and filtered breathing system but I don't know how safe I can be using silica sand. I am curious about alternatives like silicon carbide and aluminum oxide and could use any tips and advice on how I can do this kind of work safely.

Response: Blasting with silica sand is definitely NOT recommended - even with a breathing apparatus. Both Aluminum Oxide and Silicon Carbide are more aggressive blasting media than sand and will provide quicker results and a better surface finish on stone. Both of these media media can be used with standard abrasive blasting systems without modification. Of course, always minimize breathing any kind of dust when blasting.

Crushed Glass Grit

The 'hottest' abrasive blast media right now seems to be Crushed Glass Grit. This media is sourced from recycled glass - mostly bottle (beer) glass. It is generally a mixture of clear, green and brown glass. Crushed Glass Grit has lots of great advantages:

• Clean, white-metal finish
• No free silica, heavy metals or other contaminants (like in many coal slags)
• Angular shape offers quick stripping (similar to silica in hardness)
• Cost effective use

Two issues to keep in mind when using Crushed Glass Grit: (1) Media is considered consumable and is not generally re-usable; (2) Source quality can vary dramatically - we use New Age Blast Media.

What experiences and performance have you had with Crushed Glass Grit?

Blast Cleaning Steel

Historically, steel has been blasted using silica sand. For obvious health reasons (potential silicosis hazard), silica is not a safe media to use. Many industrial contractors, municipalities and military facilities are now using Crushed Glass Grit to blast steel.

Crushed Glass Grit will remove paint, dirt, soils and rust leaving a 'white' metal surface. Depending on the grit size used, a micro-finish can be achieved so that the steel can be immediately primed and painted with no further preparation.

Produced from recycled bottle (mostly) glass, Crushed Glass Grit contains no free silica, heavy metals and is approved in many of the most stringent air quality districts. Crushed Glass Grit is also considered a green blasting media since it is 'neutral' to the environment.