Dry-Ice Blasting Inside and Out
April 11, 2006
Dry ice blast cleaning is an effective method of cleaning in mold remediation. And in the current age, where environmental concerns regarding industrial and commercial cleaning are growing, and traditional methods are coming under more intense scrutiny, companies are turning to alternative cleaning methods for other purposes as well.
What Is Dry-Ice Blasting?In the dry-ice blasting process, a blasting gun fires rice-size dry-ice particles 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, generating a volume expansion of 400 to 800 times. The rapid expansion under the contaminant on the substrate forces off the contaminant from behind. The energy transfer and gas pressure dynamics cause the contaminant to be relocated, either becoming (in the case of mold spores) airborne, or falling 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.
Mold Remediation ProcessDry-ice blasting technology does not much alter the mold-cleaning process. For example, picture a second-floor residence with no attic, with 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. In this case, let's say half the ceiling and all exterior wall drywall needs to be stripped and removed.
Here is where dry-ice blasting is utilized to clean the plywood and support beams. The blasting gun targets the desired mark, and specific nozzle types - those 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 will typically remove mold in a clearly visible, methodical manner.
Once the blasting phase is complete and all surfaces have been vacuumed and cleared of sawdust and other debris, the remediator should follow up by applying a micro-biocide spray to remediated areas to inhibit future growth.
Other UsesDry-ice blast cleaning is a very valid option for cleaning building exteriors. The fact that it utilizes a completely dry process is extremely valuable. Water is eliminated, leaving no secondary contaminant. There are no runoff or waste collection issues associated with dry-ice blast cleaning, reducing costs and removing a threat to waterways.
Beyond the obvious environmental issues, there are a number of other benefits associated with dry-ice blasting as it pertains to building-exterior cleaning. Dry ice:
- Eliminates slip hazard material.
- Eliminates use of dangerous solvents.
- Acts as a natural biocide.
- Is electrically non-conductive.
- Reduces damage and wear to building surfaces.
- Removes graffiti, mold, algae and other organic substances.
- Cleans steam or gas turbine engines, chillers, condensing units, and storage tanks.
- Removes or leaves in place existing coatings.
When removing organic materials from exterior siding, dry ice media offers a very effective "clean." The temperature of dry ice is -109 degrees. The severe cold is sufficient to kill all organic material it comes in contact with, including all forms of mold and algae. By doing so, when dry ice blasting removes materials off building walls, it completely removes the organic material's root structure thereby generating a longer lasting clean and reducing the frequency of cleaning maintenance.
Safety and OperationsA 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.
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 necessary for each specific application. For building exterior cleaning, a standalone diesel compressor is typically used and would require a 185 CFM tow behind compressor. If an airline longer than 100 feet is required, a larger compressor will likely be necessary to maintain sufficient pressure.
Cleaning removal rates of organic materials off building exteriors using dry ice are typically 5 square feet per minute or better. Usage can range regularly from 60 to 100 pounds or more per hour. Dry ice pellets are readily available throughout the United States from a number of different national suppliers. Dry ice can be delivered by the supplier to the jobsite, or you can schedule to pick up the media with your own truck. It is easily transferred from its storage container to an intermediary pail, and emptied into the hopper of the dry-ice blasting machine.