DRY ICE BLASTING
Here is some information on the dry ice blasting process for mold removal and advantages/disadvantages of using this process. For information on companies in the area using this method contact TP Environmental Consulting. The most important part of using this process is picking a experienced company. I recommend the company should have at a minimum over 5 years experience and you utilize a professional consultant to oversee the project. The cost of the consultant will be minimal compared to the cost of the dry ice process.
The advantage of dry ice blasting over soda blasting is that the dry ice (solid state carbon dioxide) will go from a solid to a gas (sublimation). In layman’s terms, there is no dry ice to clean up afterwards. Again, the debris generated will need to be cleaned up though and this could be extensive. The space needs to be well ventilated and oxygen levels monitored. Supplied air respirators may be needed.
The main disadvantage to dry ice blasting is the cost and complexity. Many say it is only cost effective on larger projects. For something small, a wire brush or sandpaper may be a better option for semi-porous surfaces.
Sanding or Blasting creates more particulates than it’s worth trying to clean and protect (workers). There is no contractor yet who can show me they clean up after sanding or blasting as well as they can washing/cleaning. They leave way too much dust behind.
Sanding or Blasting is not a safe or easy way to go. And certainly not cost effective as it is always much more expensive.
I know cleaning is safer, better, easier, etc. than blasting or sanding. And when used with restrained removal, it is very cost effective, and safe for the occupants.
What 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 pellets.
What 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.
Micro-thermal 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 behind compressor.
Mold Remediation Process
Utilizing dry-ice 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 removed.
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. However more mold spores are released into the air during the process which requires more air scrubbing during the process thus increasing cost.