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Asbestos Air Sampling Methods

Asbestos is the name for a group of related dangerous minerals that affect the lungs if inhaled. It was used in building materials before 1980 and can be released during demolition. The major forms of asbestos used were chrysotile, amosite and crocidolite. Chrysotile, also known as white asbestos, makes up 90 percent of the asbestos used in the United States in buildings. Air sampling is used to measure the presence and concentration of the fiber both inside and outside of buildings.

  1. NIOSH Method 7402

    • The National Institute for Occupational Safety and Health (NIOSH) Method 7402 uses a transmission electron microscope (TEM) to analyze air samples for asbestos.

      Method 7402 uses a filter apparatus that draws air through a filter. The equipment uses 25 mm diameter cassettes and 0.45 to 1.2 micrometer pore size filters to collect the fibers. The filter has this small pore size to allow air through but to capture fibers. The sample rate is 0.5 to 16 liters per minute, so 100 to 1300 fibers can be captured per mm cubed of filter space.

      Circular areas from three of the four quarters of the filter are cut out and mounted on a slide. The slide is placed in a petri dish which contains several filters soaked in acetone and left to stand, covered, for two to four minutes. The slide is then dried using an evaporator, and replaced in an acetone-rich environment. The transmission electron microscope is then used to get diffraction patterns and energy-dispersive X-rays (distinctive appearances of the fibers under the TEM) and the patterns are compared to known patterns of asbestos. The filter is then counted for visible fibers.

    NIOSH Method 7400

    • NIOSH Method 7400 uses the same sampling conditions as Method 7402. After sampling, a wedge of approximately 25 percent of the filter is cut and mounted on a slide and 250 microliters of acetone is dripped on. About 3 microliters of triacetin is dripped on and the coverslide mounted. A phase contrast microscope is then used to count the fibers that are longer than 5 micrometers on the filter.

    EPA Modified Yamate Method

    • The Environmental Protection Agency uses the Modified Yamate Method to collect air samples of asbestos. This method uses the same general collection idea as the NIOSH methods but has specified volumes for collection. These are a minimum of 560 liters of air and a maximum of 3,800 liters. The same 25 micrometer filter is used, and the procedure also uses transmission electron microscopes to analyze the filter.

    EPA Superfund Method

    • The Superfund Method also uses TEM and a 25-micrometer filter, but recommends a sample volume of 15,000 liters of air where necessary. In places such as urban areas, the sample volume can be 5,000 liters or less, and in rural areas, the sample can be 10,000 liters or less, as filters can be overloaded with fibers if too much volume is passed through the filter.

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