In 1870, the first patent for an abrasive blasting piece was filed by Benjamin Tilghman, an American soldier from Pennsylvania. Supposedly, Tilghman’s idea came from seeing the effect of windblown sand on windows in the desert during his time in the military. His sandblasting cabinet, which used high pressure combined with sand and water, was a revolutionary invention that made surface finishing much more expedient and a true solution for industrial manufacturing. Abrasive blasting may have several associated hazards at any given time, so requirements regarding personnel protection in ANSI/ASSP Z9.4-2011 (R2021):Abrasive-Blasting Operations-Ventilation And Safe Practices For Fixed Location Enclosures are essential.
What Is Abrasive Blasting?
Abrasive blasting is more commonly known as sandblasting, since silica sand is a commonly used material as the abrasive—but it is not the only material used. ANSI/ASSP Z9.4-2011 (R2021) specifies that abrasives could include aluminum oxide, crushed glass, dry ice, glass bead, plastic, silicon carbide, and sodium bicarbonate. Abrasive blasting entails accelerating a grit of sand sized particles with compressed air to provide a stream of high velocity particles used to clean metal objects, such as steel structures, or provide a texture to poured concrete. Basically, it refers to the operation of forcibly propelling a high-pressure stream of abrasive material at a high velocity against a surface using compressed air in order to:
- Smooth a rough surface
- Roughen a smooth surface
- Shape a surface
- Remove surface contaminants
Sandblasting’s most common uses include stripping old, peeling and blistered paint from houses or buildings, stripping the surface of cars or other vehicles in order to apply new paint, restoring outdoor furniture, or stripping away concrete walkways and bigger structures to properly clean them. This process typically produces a large amount of dust from the abrasive, anything on the substrate being abraded, and/or the substrate itself. Thus, safety requirements, such as completing hazard evaluations and establish personnel protective equipment, for the abrasive blasting process are needed.
The ANSI/ASSP Z9.4-2011 (R2021) for Abrasive Blasting
ANSI/ASSP Z9.4-2011 (R2021) applies to all operations in fixed location abrasive-blast enclosures in which an abrasive forcibly comes in contact with a surface by pneumatic or hydraulic pressure or by centrifugal force. A large variety of solid materials may be used as abrasives with qualities varying from hard deep-cutting to soft polishing. These can be classified in the following six categories: 1) agricultural; 2) carbonaceous; 3) metallic; 4) slag materials; 5) plastic; and 6) nonmetallic minerals. This American National Standard specifies that the exhaust ventilation must:
- Keep the escape of dust from the enclosure to a minimum
- Maintain a reasonable visibility in blast-cleaning rooms and cabinets
- Provide for rapid clearance of the dust-laden air within the enclosure after the cessation of blasting to permit the enclosure to be opened
The standard does not apply to steam blasting, steam cleaning or hydraulic cleaning methods in which work is done without the aid of abrasives. It also does not apply to abrasive blasting conducted outdoors (e.g., bridges, water towers) even though temporary enclosures may be built at such locations.
What Are the Types of Abrasive Blasting?
There are multiple types of abrasive blasting that have pros and cons:
1. Sandblasting
Sand blasting machinery shoots dry silica abrasive particles at the surface of a part at high velocity. The sharpness of the abrasive (silica or quartz) and the consistency in size made it a great abrasive to use in giving uniform finished. However, the silica used is hazardous to health and can lead to Silicosis. As a result, this method is no longer preferred when it comes to abrasive blasting as the abrasive can be inhaled or leak into the environment.
2. Wet Blasting
Sandblasting, which uses high-pressure air streams, came before the invention of wet sandblasting: an industrial process in which pressurized wet slurry is applied to a surface for various cleaning or finishing effects. This makes using different types of abrasive medias much easier, and it provides operators with an easier cleanup process.
3. Vacuum Blasting
Vacuum blasting, also known as dustless blasting, involves a blasting machine that comes equipped with a vacuum suction that removes any propelled abrasives and surface contaminants—these materials are immediately sucked back into the control unit.
4. Centrifugal Blasting
Centrifugal blasting, also known as wheel blasting, is when a motor-operated blade wheel hurls the abrasives at incredibly high speeds towards the surface that needs cleaning. The blast wheel’s rapid spinning motion results in a highly efficient blasting process offering shorter time cycles.
5. Soda blasting
Soda blasting uses sodium bicarbonate as the abrasive, which is blasted onto the surface using air pressure. Sodium bicarbonate shatters on impact with the surface and exerts a force that clears up contaminants on the surface; it is a gentler form of abrasive blasting, requiring much less pressure exertion. This makes it suitable for softer surfaces such as chrome, plastic, or glass.
6. Steel Grit blasting
Steel Grit blasting uses spherical steels as abrasives. This method is commonly used when attempting to clean metal surfaces.
7. Bristle blasting
Bristle blasting is the only blasting that does not involve an abrasive being projected onto a surface in order to clean it. In this process, steel wire bristles are directly rotated against the surface of the material to remove contaminants.
8. Dry-ice blasting
Dry-ice blasting uses high-pressure compressed air pressure to shoot dry ice pellets (i.e., the solid form of carbon dioxide) that are projected at the surface to clean it.
9. Pencil blasting
Pencil blasting, sometimes referred to as micro-blasting, is when high-pressure air and fine powder are mixed together before being ejected out as an abrasive. It is specifically design to benefit small, intricate, and high-value parts and hence it can target and remove microns of material.
10. Bead blasting
Bead blasting is an air pressure powered abrasive blasting method that uses glass or steal beads. It does not change the dimension of the component as these beads are effective at cleaning, deburring, and peening metal surface. Although sandblasting is much quicker than bead blasting, it is harsher on the metal material and comes with increased health risks.
Dust Hazards from Abrasive Blasting
Abrasives, surface coating, encrusted substances, and base materials either chemically or physically attached to the blasted materials are shattered and pulverized during blasting operations. As a result, the dust formed might contain a significant number of particles of inhalable size, and the composition and toxicity of the dust particles should be considered when evaluating a potential health hazard. ANSI/ASSP Z9.4-2011 (R2021) details that prior to blasting, operators should perform and update, as necessary, a thorough evaluation of the potential health and/or explosion hazards from the blasting process. In making the hazard assessment the following should be evaluated:
- Composition and toxicity of the object being blasted
- Abrasive material
- Surface coatings
- Encrusted substances either chemically or physically attached to the blasted materials; and
- Composition and concentration of the dust generated by blasting
ANSI/ASSP Z9.4-2011 (R2021):Abrasive-Blasting Operations-Ventilation And Safe Practices For Fixed Location Enclosures is available on the ANSI Webstore.
