Dry ice blasting is nothing new.  Discovered in the 1970’s and perfected in the late 1980’s, it has been used to remove grease, paint, rust and even clean tire rubber-molds.  Now it’s being introduced to a whole new market and application:  mold remediation.  In this application, it not only proves itself practical but also a necessity in certain types of remediation activities.

Dry ice, or CO2, blasting combines the best of both worlds by effectively mixing chemical action with brute force.  Similar to sand or even soda blasting, CO2 blasting delivers an aggressive force to dislodge contaminants on contact.  And, although, the material used in CO2 blasting is softer than conventional blasting material, it is still a good match for wood and metal material.  Still, what CO2 blasting lacks in force, it more than compensates in chemical energy.  In pellet form, CO2 will hold a temperature of –79 degrees Celsius (less than negative 110 degrees Fahrenheit) that will spontaneously cool the impact area allowing contaminants to contract and dislodge.  Then, upon impact, the pellet will convert from a solid to a gas, leaving nothing but the removed contamination as residue.  This phase conversion, or sublimation, not only helps to dislodge any contaminants, but also expands in size at such a rate that it dislodges any remaining material.  This conversion results in a volume increase of nearly 700 times the original size of the CO2 pellet – enough to lend additional impact energy.

Clearly, CO2 blasting offers specific benefits other than just acting as an aggressive remediation tool.  Just like any other media blasting process, it can often reach hard to remediate areas such as those in an attic on the underside of roof sheathing riddled with nails.  Previously, it would have been less expensive and more effective to replace the roof and the sheathing than to hand sand each square inch of the sheathing.  Now, CO2 blasting makes this job simple.  Even better, unlike soda or sand blasting, CO2 blasting will leave no residue other than the spores and contaminants being removed. 

CO2 blasting can be performed with the use of commercially available equipment precisely designed for this purpose.  Due to temperature and pellet size differences, standard media blasting units will not work.  Common prices for CO2 blasting equipment range from $15,000 to $80,000, excluding an air compressor, depending on the type and size of the unit desired.  Other than size, CO2 blasting equipment is available in two basic formats:  direct feed or siphon feed.  Siphon feed units supply ice pellets and air to the wand via two separate hoses.  Once at the wand tip, the unit then uses the air to pull pellets from the other hose and mixes them just prior to release.  The result is a lower priced unit that while still effective, is limited in power and spray head options.  A direct feed unit, on the other hand, mixes CO2 and air at the equipment base to provide a consistent, more powerful result.  Often these units will allow for wider spray heads and the ability to vary CO2 output, creating a more powerful or more detailed cleaning.

Beyond basic CO2 blasting machinery, additional equipment and supplies will be required.  Most CO2 blasting machines require an air compressor capable of 80-100 psi and 120-250 cfm.  While you may be able to get 80-100 psi from a basic handheld compressor, you will need a large, commercial-grade, tow-behind air compressor to deliver the amount of cfm (cubic feet per minute) of air volume required.  Additionally, expect to use approximately 40-60 pounds of dry ice per hour during blasting operations.  For this you will need to contact a local CO2 supplier and request either a pellet or shaved version of dry ice.  Most people prefer the pellet form to the shaved form, but it is not as readily available.  Plan several days in advance, as this may need to be shipped from another city for use.  Also consider that not only will you have to calculate the amount of ice you plan to use, but also how much of that ice will sublimate (otherwise known as evaporation) prior to use.  Expect to lose an additional 60-100 lbs. a day from this alone.  That means that you will frequently order more than 400 lbs. of CO2 pellets at a time.  It also means that CO2 blasting must be planned well in advance and jobs should be grouped to avoid additional costs.

Safety is another concern that must be taken into account when conducting CO2 blasting.  Full-face respirators (for eye protection and respiratory protection), ear muffs (for noise protection), PPE suits, and leather gloves as well as nitrile gloves (for cold and contamination protection) are a must when working with CO2 blasting.  Keep in mind that as CO2 is –79 degrees Celsius, it will burn your skin and should not be used in any manner that may cause harm.  Although this may be common sense, never fail to discuss this risk with people performing this work and make available MSDS material for their review.  Static charges may also be a consideration in CO2 blasting, or, for that matter, any blasting process.  As the CO2 pellets pass through the wand, static electricity can build and then release when the technician completes the circuit by touching a metal object.  By taking actions to ground the wand or your technician, you might be able to avoid this problem.  Additional safety measures, such as oxygen level monitoring, are also important.  When working in containment, it is also crucial to have vibrating O2 sensors to notify technicians when the oxygen level drops below acceptable levels.  Chose only vibrating sensors that attach to an armband, as you will be unable to hear any audible alarms during blasting. 

Although oxygen level is a common concern for most people contemplating CO2 blasting, with frequent air changes, it may never become a problem.  Just make sure that you not only consider enough air exchanges for remediation activities, but also for CO2 blasting.  A digital manometer is not an option in CO2 blasting, it is a requirement.  Check it often and make sure that one person’s sole responsibility is to ensure containment throughout the job and verify with the manometer.  Keep in mind that CO2 blasting requires even more than the standard 4 changes per hour.  Not only will the CO2 expand at a rate nearly 700 times the original size, but you will also be forcing nearly 120-150 cfm’s of air from the air compressor into the containment.  Now, of course, you won’t be constantly blasting for an entire hour, but if you did, you’d have an additional 7200 to 9000 cubic feet of air (120 – 150 cfm * 60 minutes) to consider in your containment planning calculations.  That means that you would need an additional 4 to 5 2000 CFM HEPA machines just to create enough negative pressure to counteract this problem.  Although this isn’t exact, it’s a good estimate to start with and it frequently will be enough to cover any additional air pressure that the CO2 sublimination creates.  Just make sure that you not only protect containment by having enough negative air machines, but you also still provide enough HEPA supplied air from the outside as well.  I typically look for about a 1:2 ratio of HEPA supplied air machines to HEPA negative air machines.  In addition, you might also want several HEPA air scrubbers to help pick up any debris that is released in the process of blasting before it settles somewhere else.  Position these air scrubbers in proximity to the blasting equipment for the best effect.  Total, CO2 blasting will require far more HEPA filtration equipment and monitoring equipment than any remediation project you may have been involved with thus far.  Very rarely will you use less than 6 HEPA filtering machines and 1 monometer on any CO2 blasting project.  Plan accordingly.

Just as dry ice has definite applications, it also has significant limitations.  As you may have already concluded, CO2 blasting is not for small or discrete projects.  The setup and dismantling time alone makes it a large loss remediation tool.  As a matter of fact, unless you do several hundreds of thousands of dollars a year in remediation services, it may not even be worthwhile investment.  CO2 blasting is also not a tool to be used on every fire, vandalism, or even microbial claim.  Not only is the setup time consuming, but the cost may be high.  Even after purchasing the equipment, CO2 material costs can be quite high, depending on shipping and availability.  And even if these costs are acceptable, you may have to wait 3-7 days for material to arrive.  CO2 blasting is also typically less aggressive than soda or sand blasting resulting in less than satisfactory results if the damage is severe.  Always offer a test to your customer prior to committing to a blasting method.  This will not only save money and time, but also your reputation.

CO2 blasting, in addition to having logistical and investment limitations, also has several practical limitations.  As with any other type of blasting technique, CO2, blasting is not a cure all.  If the extent of the contamination is limited in scope or too serious to risk aerosolizing the contaminants, you may want to consider total removal rather than blasting.  If you do decide to use CO2 blasting, always utilize proper containment with additional critical barrier to be used in the event that negative pressure fails.  Extra HEPA machines to be used primarily for active scrubbing are always recommended during and after blasting.  Additionally, take the extra effort to not only clean as a final step, but also throughout the job.  It is not unusual to clean 4-5 times after concluding CO2, blasting operations. 

If CO2 blasting is your best option, make sure you educate not only your technicians, but also your customers.  Many customers, insurance companies and testing companies alike are unfamiliar with CO2 blasting.  Unfortunately, this lack of knowledge can translate into misconceptions quite quickly.  Before you know it, your efforts to conduct CO2 blasting can be rejected on the grounds that it is “too expensive”, “too dangerous”, or even “ineffective”.  And although this may not be the case, these misconceptions can quickly become obstacles if you haven’t laid the proper knowledge base.  Try to educate before the job.  Discuss the CO2 blasting option with testing companies before working with them and turn this obstacle into a benefit for your sales growth.  Additionally, make sure to review results and a CO2 Material Data Safety Sheet with the customer.  Carefully explain how you plan on exhausting the leftover CO2 and point out how it is a naturally occurring chemical in the environment.  Above all, don’t rush into the process.  Discuss, answer questions and educate – you will be happy with the result.

CO2 blasting is certainly not for everyone and not for every project, but it is definitely a resource worth exploring if you have the volume and the project to work with.  When you find that proper application, you will not only be pleased with the effectiveness, but also the time and money it saves.