Asbestos was used for so long and in so many structures
that today there is a thriving industry dedicated to identifying
and removing asbestos-containing materials. AHERA mandates some institutions,
such as schools, to "inspect their buildings for asbestos and take
appropriate abatement actions using qualified, accredited persons
for inspection and abatement." (U.S.
Environmental Protection Agency, Asbestos in Schools, 2008).
Other commercial structures, while not subject to AHERA, must follow
Occupational Safety and Health Administration (OSHA) standards,
which state that "Employee exposure to asbestos must not exceed
0.1 fibers per cubic centimeter (f/cc) of air, averaged over an
8-hour shift" (Occupational
Safety and Health Administration, 2002). Accordingly, building
owners, while not required to remove asbestos containing materials
(ACM) from their structures
find that, to stay in compliance with OSHA, they should.
The first step in this process is to identify all the ACM in
a building. This process should be done by a trained asbestos
industrial hygienist. Asbestos industry workers take training
from state approved training facilities and receive a certification,
and in some states, a license. The worker must also take an annual
re-certification class (U.S.
Environmental Protection, Asbestos Training, Agency, 2008).
In addition, some states go above and beyond the federal requirements
Once a qualified asbestos consulting company has been contracted, industrial hygienists will sample a large variety of building materials, typically including flooring and associated glue, ceiling tiles, wall systems, insulations, fireproofing, caulks, baseboards, roofs, siding, and pipe wraps. A typical sample size is about 1 square inch for a non-friable material and a few tablespoons for friable materials. The samples are sealed in airtight containers and shipped to an accredited laboratory. This type of sample is known as bulk sample.
Laboratories are accredited and licensed by the federal government and, in some cases, state governments. Most asbestos laboratories will possess accreditation though the National Voluntary Laboratory Accreditation Program (NVLAP), which is a part of the National Institute of Standards and Technology (NIST). Some states, such as New York and California, also have laboratory accreditation programs. Many other states have license programs.
Typical bulk sample analysis is performed by polarized light microscopy (PLM), which uses an optical microscope to measure various optical properties of minerals/materials observed. All minerals possess certain uniquely identifying optical properties. A few examples of these are: refractive index, sign of elongation, and extinction angle. Two types of asbestos may possess the same sign of elongation and extinction angle but have differing refractive indexes. If the analyst measures enough of the optical properties they can positively identify whether a mineral is asbestos and what type of asbestos it is. For asbestos the most important optical property is refractive index. Refractive index is the measure of how much the speed of light is reduced as it enters a medium. A refractive index of 1.5 means that light is slowed down by 1.5 times. Refractive index can also be described as a measure of how much a light ray refracts or bends as it passes through a medium. An easy way to visualize this is how your feet appear distorted while standing in swimming pool. That is because water has a refractive index of approximately 1.34. As the light rays move from the air to the water they slow down by 1.34 times as they refract and bend.
The optical microscopes used for asbestos analysis typically magnify the sample 40 to 400 times. While this sounds like a lot, in certain types of samples, such as floor tiles, the asbestos can be so small it is beyond the resolution of optical microscopy. For samples with asbestos too small to resolve with PLM a Transmission Electron Microscope (TEM) can be used. Typical TEMs can magnify a sample millions of times. The TEM offers the analyst more than just high magnification to help identify particles; it also can show the diffraction pattern, or atomic structure, of a mineral and the chemical composition. The chemistry of a mineral is checked by energy dispersive x-ray analysis (EDXA). As the stream of TEM electrons hits the particle it excites the electrons within the particle causing them to jump to other electron shells. This causes other higher energy electrons in the atom to fill the spots of the original lower energy electrons. As they do so, they give off a tiny packet of energy at a certain level that differs for all atoms. The EDXA can measure this packet of energy, thereby determining the chemical make up of the particle. EDXA combined with diffraction can positively identify any mineral.
When the laboratory completes the analysis, the results are reported to the consultant and the building owner. They then make the determination on how to remove or contain the asbestos containing material (ACM). Removal of the ACM is done by first building a containment barrier around the ACM to be removed. Then qualified asbestos workers, wearing special protective clothing and respirators to prevent exposure to asbestos, remove the ACM. The ACM waste must be disposed of following all local and federal guidelines and placed in special hazardous materials landfills. During removal, the industrial hygienist monitors the ambient air quality by taking air samples for analysis using phase contrast microscopy (PCM). This monitors the fiber in air concentration and to insure that workers are wearing the proper respirator. PCM does not identify asbestos but does give a relative total "fiber" count. These fibers can be anything: asbestos, fiberglass, mineral wool, cellulose, synthetic fibers, etc.
After the workers complete the final cleaning of the containment, the industrial hygienist takes a set of final air samples. Air samples are typically run for at least two hours to collect 1,200 or more liters of air. These samples are typically analyzed by TEM in order to positively identify if asbestos is present. If the samples are below predetermined clearance criteria, the abatement is complete and the containment can be torn down. If the samples fail, the area must be re-cleaned and new samples taken.
For large office buildings with a lot of asbestos this process can take years and cost millions of dollars.
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List of Visuals
- Picture 7: Chrysotile Asbestos as seen under 100x magnification with PLM
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- Picture 8: Chrysotile fibers seen under19,000x magnification with TEM. Fibers are 1 to 4 microns long
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- Picture 9: Chrysotile Diffraction Pattern, or crystal structure, seen with TEM
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- Picture 10: Chrysotile Asbestos chemical composition as measured with TEM showing Magnesium, Silica and Iron. The copper is equipment based
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