Dry ice blasting is a form of media blasting, similar to sand blasting, plastic bead blasting, or soda blasting but substitutes dry ice as the blasting medium. Dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it.

Method

Dry ice blasting involves propelling pellets at extremely high speeds. Upon impact, the pellet sublimates almost immediately, transferring minimal kinetic energy to the surface on impact and producing minimal abrasion. The sublimation process absorbs a large volume of heat from the surface, producing shear stresses due to thermal shock. This is assumed to improve cleaning as the top layer of dirt or contaminant is expected to transfer more heat than the underlying substrate and flake off more easily. The efficiency and effectiveness of this process depends on the thermal conductivity of the substrate and contaminant. The rapid change in state from solid to gas also causes microscopic shock waves, which are also thought to assist in removing the contaminant.

Equipment

Dry ice blasting generally uses one of two delivery systems to combine compressed air with ice and accelerate particles out of the delivery nozzle:

Single-hose technology uses a single hose to deliver air blasts and dry ice. The single hose system can use a longer hose than the double-hose counterpart without a significant drop in pressure when the ice leaves the hose. The additional power comes at the cost of increased complexity. Single-hose systems are used when the surface to be cleaned has a heavier build-up or when the surface to be cleaned is vertical or at a greater height than the hopper and gas compressor.

Double-hose dry ice blasting was developed before the single-hose system. Compressed air is delivered in one hose, and ice pellets were sucked out of a second hose by the venturi effect. Compared with a single-hose system, the two-hose system delivers ice pellets with less force than a single-hose system. Theoretically two-hose systems have a limit to the vertical distance between the machine and applicator. This limit however is well in excess of 7.62m or 25 feet. Two-hose systems are generally less costly to produce due to a much simpler delivery system and they allow finer particles of ice to be delivered with lower velocity as the late combination of warm air with cold ice results in less sublimation in the hose. The latter properties allow for more delicate surfaces to be cleaned.

Uses

Dry ice blasting can be used to clean food processing equipment to effectively decontaminate surfaces. It may also be used to clean some equipment without disassembly and without producing fire or electrical hazards. The EPA recommends dry ice blasting as an alternative to many types of solvent-based cleaning. Dry ice blasting can clean numerous objects with differing, complex geometries at once.

Safety

Carbon dioxide is increasingly toxic starting at concentrations above 1%, and can also displace oxygen resulting in asphyxia if equipment is not used in a ventilated area. In addition, because carbon dioxide is heavier than air, exhaust vents are required to be at or near ground level to efficiently remove the gas. At normal pressure dry ice is −78 °C or −108 °F and must be handled with insulated gloves. Eye and ear protection are required to safely use dry ice cleaning equipment. Compared to other blasting-cleaning methods, dry ice blasting produces fewer waste products and does not require clean-up of a blasting medium.