Abrasive Blasting: Equipment, Media, and Safety — Shipbuilding / Marine Fabrication

Objective. Students will describe the components of a dry-abrasive blast system, select appropriate blast media for steel and aluminum substrates, and explain safety controls including pressure vessel inspection, blast suit requirements, and respiratory air quality.

What Is Abrasive Blasting?

Abrasive blasting — commonly called sandblasting — is the process of propelling a stream of abrasive media at high velocity against a surface to clean it and create a surface profile. In marine fabrication, proper surface preparation is critical: paint and coatings applied to an inadequately prepared surface will fail prematurely, leading to corrosion, structural damage, and costly rework. SSPC (now AMPP) and NACE standards define cleanliness grades; blasting to Near-White Metal (SSPC-SP 10) or White Metal (SSPC-SP 5) is common for marine structures before applying protective coatings.

Components of a Dry-Abrasive Blast System

Understanding every component helps you operate safely and troubleshoot problems.

Compressor: The air compressor generates the compressed air that drives the entire system. It must deliver adequate volume (measured in cubic feet per minute, or CFM) and pressure (measured in PSI) for the nozzle size in use. Moisture and oil in compressed air contaminate the surface and the breathing air supply — both are serious hazards.

Moisture Separator / Air Dryer: Installed downstream of the compressor, this device removes water vapor and oil mist from the air before it enters the blast pot or the respirator supply line. A clogged or bypassed separator is a common failure point.

Blast Pot (Pressure Vessel): The blast pot holds the abrasive media and meters it into the air stream. It is a pressure vessel subject to ASME and OSHA inspection requirements. Never open, adjust, or repair a pressurized blast pot. Before any demonstration or maintenance, the pot must be depressurized and locked out/tagged out (LOTO) per OSHA 29 CFR 1910.147.

Deadman Valve: A spring-loaded remote control handle held by the blaster. When the blaster releases grip — due to a fall, injury, or loss of control — the valve automatically shuts off air and media flow. The deadman valve is a primary safety device; never tie it open or bypass it.

Blast Hose: Heavy-duty, static-dissipating hose carries the abrasive-air mixture from the blast pot to the nozzle. Inspect hose couplings and the hose body before each use; abrasive wear can thin the hose wall, creating a blowout hazard. Use whip checks (safety cables) at every coupling.

Nozzle: The nozzle accelerates the media to working velocity. Venturi-style nozzles are most efficient. Nozzle bore diameter and condition directly affect blast pressure and media flow rate. A worn nozzle wastes air and reduces cleaning rate.

Blast Helmet with Supplied-Air Line: The blaster wears a heavy-duty protective hood (blast helmet) that covers the head, face, and neck. It integrates with a supplied-air respirator that delivers breathing-quality air directly to the blaster — not filtered ambient air, but a separate, dedicated air supply.

Selecting Blast Media

Choosing the right media matters for substrate compatibility, surface profile, and recyclability.

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Steel substrates tolerate aggressive media such as steel grit or steel shot because contamination from iron is not a concern on steel. Steel grit produces a sharp, angular profile that promotes coating adhesion.

Aluminum substrates require non-ferrous media. Never use steel grit or steel shot on aluminum: iron particles embed in the soft aluminum and cause galvanic corrosion under the coating. Garnet, aluminum oxide, and plastic media are appropriate choices. Plastic media is preferred when substrate damage must be minimized.

Surface profile is the anchor pattern measured in mils (thousandths of an inch). Coating manufacturers specify a minimum and maximum profile; exceeding the maximum leaves peaks that penetrate the coating film, creating corrosion initiation points.

Respiratory Safety and Grade-D Breathing Air

Abrasive blasting generates airborne dust that is immediately dangerous to life and health (IDLH). Silica-containing media (such as conventional sand) is prohibited on job sites in the US due to silicosis risk. Even permissible media produce high dust concentrations. A supplied-air respirator (SAR) — not a filtering facepiece — is required for blasters.

OSHA 29 CFR 1910.134 specifies that breathing air supplied to workers must meet Grade D quality as defined by the Compressed Gas Association (CGA). Grade-D air limits carbon monoxide (CO) to 10 ppm or less, carbon dioxide to 1,000 ppm or less, and has no objectionable odor. Oil mist must be controlled. Air compressors used for breathing air must be positioned to prevent engine exhaust from being drawn into the intake — a common and deadly mistake.

Carbon monoxide monitoring is essential. CO is colorless and odorless; a CO monitor on the supply line or at the compressor intake is the only reliable detection method. Verify monitor function before every blast shift.

Pre-blast air quality checklist:

1. Confirm compressor intake is upwind of exhaust sources.

2. Inspect and drain moisture separator.

3. Verify CO monitor is calibrated and operational.

4. Check supplied-air hose connections to helmet.

5. Confirm Grade-D air certification for the air source if using bottled air.

Lockout/Tagout Before Demonstration or Maintenance

The blast pot is a pressure vessel and an energy source. Before any inspection, uncoupling hoses, or clearing blockages: depressurize completely, close the inlet valve, apply a lockout device and tag, and verify zero energy by checking the pressure gauge. All workers in the area must acknowledge the lockout before work begins. Never assume the pot is empty.

Personal Protective Equipment Summary

Blast helmet with supplied-air respirator (mandatory for blasters)
Leather or equivalent heavy gloves
Leather or abrasion-resistant clothing / blast suit
Steel-toed, puncture-resistant boots
Hearing protection (compressors and blasting produce high noise levels)
Bystanders must be kept clear of the blast zone or wear appropriate PPE

Key terms9

Blast PotA pressurized vessel that holds abrasive media and meters it into the compressed-air stream; subject to ASME pressure-vessel inspection requirements and must be depressurized and locked out before any maintenance.

Deadman ValveA spring-loaded remote shutoff handle held by the blaster; automatically stops air and media flow if the blaster releases grip, preventing runaway hose injuries.

Grade-D Breathing AirThe minimum air quality standard defined by the Compressed Gas Association and required by OSHA 29 CFR 1910.134 for supplied-air respirators; limits carbon monoxide to 10 ppm or less and carbon dioxide to 1,000 ppm or less with no objectionable odor.

Surface ProfileThe anchor pattern depth created by abrasive blasting, measured in mils (thousandths of an inch); must fall within the coating manufacturer's specified minimum and maximum range for proper adhesion.

Supplied-Air Respirator (SAR)A respirator that delivers breathing-quality air from a remote, dedicated source (compressor or cylinder) rather than filtering ambient air; required for abrasive blasting due to IDLH dust concentrations.

Whip CheckA safety cable or wire attached across hose couplings to prevent a pressurized hose from whipping violently if the coupling fails.

Ferrous ContaminationIron or steel particles embedded in a substrate surface; on aluminum, embedded ferrous particles cause galvanic corrosion under coatings and must be avoided by using non-ferrous blast media.

SSPC-SP 10 / Near-White MetalA surface cleanliness standard (now maintained by AMPP) requiring removal of nearly all mill scale, rust, and contaminants, leaving only light staining on no more than 5 percent of the surface; commonly specified for marine protective coatings.

Moisture SeparatorA device installed downstream of the compressor that removes water vapor and oil from compressed air before it reaches the blast pot or the breathing air supply line.

In class: System walk-around demonstration: instructor powers down and locks out the blast pot, then guides students through each component (compressor, moisture separator, blast pot, deadman valve, blast hose, nozzle, blast helmet with supplied air) explaining function and common failure points. · Media comparison exercise: students examine and handle samples of steel grit, steel shot, garnet, aluminum oxide, and plastic media; they record hardness, angularity, and recyclability characteristics and match each media to appropriate substrate and desired surface profile. · Respiratory air quality discussion and Grade-D air demonstration: instructor explains the OSHA Grade-D breathing air standard for supplied-air blast helmets and demonstrates use of a carbon monoxide monitor; students complete a checklist for pre-blast air quality verification.
Materials: Blast pot (properly tagged out for demonstration), blast hose and nozzle samples, deadman valve, blast helmet with supplied-air line, CO monitor, media sample set (labeled jars), surface profile comparator kit, OSHA 29 CFR 1910.134 reference handout on breathing air.
Check: Oral quiz: instructor asks each student to name all major blast system components and their function, identify the correct media for aluminum versus steel, and state the minimum respiratory requirement for blasting; all three must be answered correctly to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.