In 1995 we performed one of the first negative exposure assessment trials allowed by the 1994 OSHA asbestos regulations. The results showed that high levels of asbestos fibers were released from dry demolition of drywall with joint compound reported to contain less than 1% asbestos – an average of 0.25 fibers per cubic centimeter of air. They also showed that point counting hides this reality. That is now well known amongst the best consultants, but not in 1995, as that was before the now rampant inappropriate use of point counting for non-friable materials.
An insurance company had purchased a 50-some story high rise building constructed in 1974/5. They thought they had purchased a building free of asbestos. Indeed, the plans for the building are prominently marked with wording prohibiting use of asbestos. One of our competitors was first hired, and they were finding less than 1% asbestos content in the drywall joint compound, but apparently did not have a good working relationship with the managers. The managers then hired Dames & Moore (now part of AECOM), and they in turn hired us to handle the project for them due to our extensive expertise and well-established business relationship providing asbestos and lead-consulting for them in California. In 1994 we performed a complete asbestos survey of the building. While the structural steel fireproofing does not contain asbestos, we did find it in drywall joint compound in much of the building, vinyl floor tile, and flooring mastics.
We planned and designed the negative exposure assessment trial. A licensed asbestos abatement contractor,TEG (now part of NorthStar Group Services, Inc.) was hired, and they built a negative pressure containment to perform dry removal of drywall with all of the PLM joint compound results less than 1%, simulating what would happen in normal demolition work. The workers wore high-level respiratory protection (full-face supplied air respirators).
Since the owners thought they had bought an asbestos-free building, they and the managers were very anxious, so they hired another consulting company, Law / Crandall (merged into MACTEC, then AMEC) to also run air samples during the negative exposure assessment, with us as the lead consultant. We agreed with Law / Crandall to use the same laboratory. A total of 30 air samples were collected, with each consulting company collecting different total air volumes. Of the 30 samples, 11 were readable by the laboratory, with the following results from Transmission Electron Microscope analysis, expressed as fibers per cubic centimeter of air: 0.2456, 0.4592, 0.3200, 0.087, 0.16, 0.21, 0.13, 0.18, 0.27, 0.43, and 0.27. The average was 0.25 fibers per cc.
We also collected 20 samples of the drywall joint compound which had been demolished, and submitted them for PLM point counting (400 points), for a total of 8,000 points. There was an asbestos fiber on just one point, and 5 off point. Counting 1,000 points per sample, as some now try to do, would surely not have made a significant difference. The correlation between the air sample results and the point counting results is very low.
The negative exposure assessment gave the managers the solid information they needed to justify spending the money needed for abatement in areas being renovated for new tenants.
Despite the fact that the best consultants know that point counting of non-friable materials such as drywall joint compound is not appropriate, there are currently some consultants and laboratories promoting point counting as a way to avoid asbestos abatement. The laboratory prices for re-analysis of samples are:
$40 each sample for the most accurate method, the Transmission Electron Microscope Chatfield method
$35 for 400 point count without gravimetric reduction
$60 for 400 point count with gravimetric reduction
$60 for 1,000 point count without gravimetric reduction
$70 for 1,000 point count with gravimetric reduction
(all 3 day turn around prices).
That makes it obvious that the point counts are currently being used by ill-informed or corrupt consultants to hide the asbestos, as there is no cost justification for using them.
The laboratories used on the project were Southwestern Electron Microscopy & Environmental Laboratories, Inc., Forensic Analytical and Balsam Environmental Consultants (owned by Dames & Moore).