Dry ice blast
cleaning is quickly establishing itself as a favored method of cleaning
in mold remediation (mold removal). Dry ice blasting is superior to cleaning mold
compared to traditional labor-intensive techniques such as sanders,
scrapers and wire brushes. The dry ice process cleans as thoroughly or
more so and in dramatically less time. Also, compared to soda
dry ice blast cleaning is as fast and creates far less mess.
Is Dry Ice?
Dry ice pellets
are made by taking liquid carbon dioxide (CO2) from a pressurized
storage tank and expanding it at ambient pressure to produce snow. The
snow is then compressed through a die to make hard pellets. The pellets
are readily available from most dry ice suppliers nationwide. For dry
ice blasting, the standard size is 1/8-inch high-density dry ice
Is Dry Ice Blasting?
It is a process in
which a blasting gun fires dry ice particles (rice-sized) at supersonic
speed to impact and clean a surface. The particles are accelerated by
compressed air, just as with other blasting systems. Upon impact the dry
ice sublimates (goes from a solid to a gas without passing through a
liquid phase). The substrate (surface) is left free of mold spores.
There are three
phases in the dry ice blasting process. Energy transfer works when dry
ice pellets are propelled out of the blasting gun at supersonic speed
and impact the surface. The energy transfer helps to knock off the
contaminant with little or no damage to the surface.
shock occurs when the freezing effect of the dry ice pellets hitting the
contaminant creates a micro-thermal shock (caused by the dry ice
temperature of -79º C) between the surface contaminant and the
substrate. This phase isn’t as much a factor for removal of mold as it
is with resins, oils, waxes, food particles and other contaminants. For
substances such as these, the thermal shock causes cracking and
delamination of the contaminant, furthering the elimination process.
The final phase,
gas pressure, has the dry ice pellet explode on impact and, as the
pellet warms, it converts to a CO2 gas, generating a volume expansion of
400 to 800 times. The rapid expansion underneath the contaminant on the
substrate forces off the contaminant from behind. The energy transfer
and gas pressure dynamics cause the contaminant to be relocated,
becoming airborne (as with mold spores) or falls to the ground. The mold
spores then need to be removed by HEPA filters. Since the dry ice
sublimates into a gas, no media remains to be cleaned up.
As for air system
requirements, a large number of applications using dry-ice blasting
equipment only require between 80 to 100 psi and 120 to 150 CFM. An
evaluation of system air is usually recommended to determine if the
facility has sufficient capabilities to run dry ice blasting equipment
at the levels desired for each specific application. Remediators
utilizing a stand alone diesel compressor would require a 185 CFM tow
blasting technology does not alter the mold-cleaning process very much.
Take the example of a second floor residence with no attic and having
drywall on walls and ceiling being infested with mold. First, the second
floor needs to be isolated from the first floor. Next, negative pressure
needs to be created using a HEPA-filtered air scrubber. If there is any
severely damaged carpeting and drywall, it should be double bagged and
discarded. For the sake of this example, we will say that one half of
the ceiling and all exterior wall drywall needed to be stripped and
At this point,
dry-ice blasting can be utilized to clean the plywood and support beams.
The blasting gun can easily be managed to target the desired mark.
Specific nozzle types best suited for cleaning wood can be utilized,
e.g. a fan-shaped nozzle, creating a pattern several inches wide, can be
used to “sweep” up and down boards and beams. The dry ice being
fired on the wood can typically remove mold in a way that is clearly
visible and in a methodical manner. Once the blasting phase is complete
and all surfaces have been vacuumed and cleared of sawdust and other
debris, mold remediators should follow up by applying a micro-biocide
spray to remediated areas to inhibit future growth.
A few details need
to be considered to operate dry-ice blasting equipment. Blasting in an
enclosed area is generally safe with proper ventilation. However,
because CO2 is 50 percent heavier than air, and containments may limit
ventilation enough where excessive levels of CO2 may accumulate, to
maintain negative pressure differentials exhaust air volume may need to
be greatly increased. In small areas or ones such as crawl spaces, great
care should be given to sustaining proper air levels. If the OSHA
Permissible Exposure Limit (PEL) for CO2 (5,000 ppm or 0.5 percent for
an eight-hour time-weighted average) is exceeded, supplied-air
respirators must be used.
Ear protection is
necessary, as the process can get very noisy. Second, because the
temperature of dry ice can be as low as –79oC (-109 oF), insulated
gloves should always be worn when working with it. It is also very
important that full personal protective equipment (PPE) is worn.
With dry ice
blasting as it pertains to mold removal, it is common to see a 60
percent time savings over other methods. Blasting can also effectively
and easily clean in tight spaces that would be difficult for hands or
tools to reach.
When the dry ice
changes from a solid to a gas, the volume expansion over surfaces such
as wood, concrete or stone efficiently results in a stripping effect
removing the mold from the surfaces. Typical results show less than 1
percent of toxic mold spores remain.
Dry ice sublimates
and leaves no media for cleanup. The blasting process will generate saw
dust, just as sanding would; however, when compared to other blasting
methods, the time and cost to address the secondary waste generated by
the media is eliminated.