Dry Ice (Reply)

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Hello All -

Here are a couple of observations and comments. First of all, good article from Mr. Holland, however, there were a few technical errors associated with it, which I will address in a moment.

Next, I have only been associated with a couple of hundred mould remediation projects, and as such, my comments are from that limited perspective - presumably the remediation guys have been involved in perhaps thousands - I don't know.

Having said that, in those hundreds of projects, I have never encountered a single project where dry ice blasting would be an appropriate remediation action. I have been involved in many, many blasting projects (needle, bead, corn, CO2, sand, and walnuts). But,the efficacy of the method to abrade the surface of the contaminated material is not the issue, neither is the speed, nor cost, and my post didn't attempt to address those issues.

Mr. Redington, I agree with you, in that I have seen CO2 blasting used in remediation projects, where it was used cheaper than other methods (such as scraping with a toothbrush), but that doesn't automatically make it an <I>appropriate</I> method. Efficacy of the method notwithstanding, and cost or speed of the method notwithstanding, I have never seen a single case where a blasting technique, of any kind would be <I>appropriate</I> in mould remediation. I have been involved in hundreds of mould remediation projects where it <I>could</I> have been used, and hundreds where it <I>would</I> have been effective, but in no cases where it would have been <I>appropriate</I> and where the remediation would have been any more successful by it's use over more conventional, cheaper, faster, methods.

The crux of my argument lies within the concept of what is, (and is not), <I>appropriate</I> remediation - of which probably 100% of remediators would disagree, and the overwhelming majority of doctors, mycologists, microbiologists, Industrial Hygienists, other scientists and insurance companies would agree. I would be happy to give an classic example, if asked.

Regarding the HEPA issue. It is a common misconception that smaller particles are not captured as well as larger particles and that when particles become smaller than 0.3 µm they become more and more difficult to capture. In fact, the opposite is true. The reason the 0.3 µm aerodynamic diameter is selected (or in some cases other sizes) is because there is an inverted capture curve surrounding that size; i.e. it is the most difficult size to capture. Particles larger than the selected size and particles smaller than the selected size are captured with <U>greater</U> efficiency.

The particle physics which drive the capture efficacy are very well understood, and only break down at particle sizes too small to be of interest to this group. I have placed depictions of two such capture curves on my web site at:

http://www.forensic-applications.com/Examplephotos/capcurve.jpg

and

http://www.forensic-applications.com/Examplephotos/N95capcurve.jpg

It is interesting to note that these are the types of myths I see propagated in three day wonder certified mould classes. I just gave a lecture to the NACHI folks on mould issues, and at the end, one of the participants was almost in tears since he had just returned from an expensive three day "mould class" in Arizona given by a self-proclaimed "mold expert." But he found out in one hour of my lecture that virtually everything he learned in his three day class was incorrect and would get blasted (CO2 or otherwise) if it ever went to court.

So ... Devil's advocate? Nah...just an Industrial Hygienist's perspective.

Cheers,

Caoimhín P. Connell

Forensic Industrial Hygienist

www.forensic-applications.com

<SMALL> (The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG </SMALL>