How do you know all the asbestos fibers are out of the air? Air testing. Asbestos fibers are not visible to the naked eye.
There are several types of asbestos clearance testing.
Asbestos PCM Analysis
Asbestos PCM air sample testing analysis is a method that follows a prescribed standard called the NIOSH 7400 Method.
Asbestos PCM samples use a light microscope to detect all fibers visually. The microscope can be hand carried; one of the advantages of this method is mobility. Samples can even be analyzed on-site, which decreases the turnaround time required for obtaining results. The microscope magnifies objects approximately 400 times their actual size. Yes, a phone can also magnify 400 times. This is not the preferred method, as fibers from other building materials may also be present. There is no separation of asbestos fibers from other building material fibers.
The main disadvantage of the Phase Contrast Microscopy methodology is that it is not asbestos specific. The analyst counts any fiber that falls into a field of view that is greater than or equal to 5 μm in length, with a 3:1 aspect ratio (three times longer than its width).
PCM asbestos analysis is intended for Worker Safety use, not asbestos clearance.
Asbestos PCM air samples with results <0.01 f/cc (fibers per cubic centimeter) are acceptable for worker safety in accordance to OSHA’s PEL for worker safety.
Asbestos PCM air samples with results >0.01 f/cc (fibers per cubic centimeter) are not acceptable for worker safety in accordance to OSHA’s PEL for worker safety. These samples are shown as FAIL.
Asbestos TEM Analysis
Asbestos TEM (Transmission Electron Microscope) air sample testing uses electrons to create images, fine crystal patterns and analyzes the chemical makeup of fibers or structures encountered in the air sample.
The machinery required is not mobile and is very sophisticated.
It magnifies objects at least 20 times their actual size. This method also is asbestos-specific; so specific that it can indicate the type of asbestos fibers in the air sample.
This method is most appropriate for final clearance samples either due to regulation (AHERA) or liability issues. By law, schools, public buildings, hospitals, etc., must, by law, use this method. This is also most appropriate for litigation and real estate transactions.
Asbestos TEM air samples with a result of <70 s/mm² (structures/millimeter squared) have achieved final clearance. Lab results show asbestos fibers to be non-detect.
Asbestos TEM air samples with a result of >70 s/mm² (structures/millimeter squared) indicate asbestos abatement is necessary.
Asbestos Tape Lifts
Scotch-type clear tape is gently pressed on hard surface contents that have been cleaned of asbestos fibers. This is a presence or absence only test.