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Sampling and Analysis at Libby
EPA has collected thousands of environmental samples in Libby from air, dust and solids. The samples have been collected from the Grace mine and from residences, businesses and other properties in Libby and Lincoln County. To ensure health and safety, workers with the potential to contact asbestos wear personal air samplers, and stationary air samplers are set up in various locations. Samples are collected by trained personnel.
- Air Samples – Collected with small, portable pumps worn by individuals, or larger, stationary pumps set up in one location. Air is drawn through a filter at a specific rate for a given time period. Asbestos and other breathable particles are trapped on the filter, which is sent to the lab for analysis.
- Indoor Dust Samples – Collected using a micro-vacuum that sucks dust-sized particles from specific areas (such as a windowsill). Air is drawn through a filter, which is sent for analysis. Results help determine if asbestos is present in the dust and might be stirred up into the breathing space. Asbestos may have settled as dust or been tracked inside on shoes or other items.
- Solid Samples (soil, mine waste, or vermiculite) – Collected from yards, gardens, driveways and excavations. Yard and driveway soil samples are generally taken from the upper six inches of soil, while garden soil samples are deeper. Waste samples are taken from open areas and may be taken from any depth. Vermiculite samples are generally taken from inside homes or other buildings. These solid samples may be taken to determine initial concentrations or to verify that a cleanup has been successful. They are generally collected using a small trowel or gloved fingers.
Do Sample Crews Wear Respirators When Sampling Residential Yards?
The use of respirators is complicated and is governed, in part, by OSHA regulations for worker safety. Workers may sometimes wear respirators outside if conditions show that they are potentially exposed to hazardous levels of asbestos and other contamination eight hours/day, six days/week, in Libby and at other sites. As a safety precaution, EPA encourages people who suspect or know that vermiculite is present in their homes or yards to refrain from disturbing the material.
Methods for asbestos analysis vary in complexity and are selected based on data needs. Simplistically, samples are visually identified under a microscope by a trained technician. Observed fibers are viewed at various magnifications and counted according to the rules and capabilities of each method. Depending on the method, results can indicate the type and amount of asbestos present, and also the dimensions of each counted fiber. Analytical techniques currently in use or proposed for use in Libby are:
- Phase contrast microscopy (PCM) - The traditional technique for measurement of asbestos fibers in air and upon what many regulations are based (e.g., occupational exposure). Results are often used to estimate health risk from asbestos in air. PCM has limited utility because it cannot differentiate between asbestos and non-asbestos fibers. Thus, PCM use in Libby has been limited to specific purposes, often in conjunction with another analytical technique such as TEM.
- Polarized light microscopy (PLM) - Used to visually estimate the percent of asbestos in bulk samples, such as soil and insulation materials. It can differentiate between asbestos types, but cannot reliably detect asbestos in low concentrations (below one percent). Thus, PLM is being used in Libby as a screening method.
- Transmission electron microscopy (TEM) - TEM is more complex than PCM or PLM, and it uses a more sophisticated analytical instrument. TEM can distinguish between asbestos and non-asbestos fibers and asbestos types. It can be used at higher magnifications, enabling identification of smaller asbestos fibers than can be seen by other techniques. In Libby, two TEM methods (AHERA and the more complex ISO 10312) are used, depending on the data need.
- Infrared spectroscopy (IR) - This is a developmental, rapid-screening method for use in determining the presence of Libby amphibole asbestos in soil at low concentrations. It is needed because PLM is not reliable for screening concentrations less than one percent.
- Scanning electron microscopy (SEM) - SEM is similar to TEM. It is capable of distinguishing asbestos fibers from non-asbestos fibers and is capable of higher magnifications than PCM. Its range of visibility is more limited than TEM. SEM is also limited in its ability for mineral identification.
In Libby, air samples are analyzed by PCM and TEM methods. Indoor dust samples are analyzed by TEM and, on occasion, PLM. Water samples are analyzed by TEM. Solid bulk samples (soil, mine waste and bulk insulation) are analyzed by PLM, and a respirable fraction is sometimes analyzed by TEM. SEM and IR may be used to analyze bulk samples for low levels of asbestos (concentration estimates below one percent). Method applications are regularly reviewed along with the advancement of new test methods.
EPA is very interested in the size of the asbestos fiber, particularly those longer than 5 microns and thinner than 0.5 microns.These fibers are thought to be more dangerous, because they are more difficult for the body to expel.
- Less than 5 microns.
- Between 5 and 10 microns.
- Greater than 10 microns.
A micron is too small to see with the naked eye. There are 25,400 microns in an inch!
All analysis is conducted by accredited national laboratories following protocols outlined in detailed, site-specific quality assurance plans.