ASBESTOS

MEDIA - AIR

Transmission Electron Microscopy (TEM)

AHERA (40CFR Part 763, subpart E, Appendix A)
The TEM method outlined in this section of the Asbestos Hazard Emergency Response Act (AHERA) is required by the EPA for testing and clearing air samples in schools after abatement activities. The AHERA method is considered “state of the art” for detection of asbestos in air. The AHERA method will detect and record asbestos structures as small as 0.5 µm in length making it the most sensitive method for the detection of asbestos in air.

NIOSH 7402
NIOSH 7402 is a TEM method typically employed when clearance samples repeatedly fail NIOSH 7400 (PCM) testing. If the fibers causing the PCM samples to fail are suspected of being non-asbestos, the building owner can take advantage of the TEM's increased capabilities to qualify each fiber as asbestos or non-asbestos. The method then calculates the ratio of asbestos fibers to non-asbestos fibers. This percentage can then be applied to original PCM results, giving a concentration of asbestos structures per cubic centimeters (versus total fibers per cubic centimeters). NIOSH 7402 is also utilized by consultants for quality control or better guarantee the absence of asbestos in the air.

ISO 10312
Ambient Air - Determination of Asbestos Fibres - Direct-Transfer Transmission Electron Microscopy Method
This international standard is applicable to the determination of airborne asbestos in a wide range of ambient air situations including, the interior atmospheres of buildings, and for detailed evaluation of any atmosphere in which asbestos structures are likely to be present. ISO 10312 includes the measurement of the lengths, widths and aspect ratios of the asbestos structures.

EPA Level II
Methodology for the Measurement of Airborne Asbestos by Electron Microscopy, July 1984
Authored by Yamate, Satish and Gibbons in 1984, this is an older (obsolete) TEM method that is divided into three increasingly stringent levels of analysis depending on the concentration of fibers and need of the consultant. Many consider the “Yamate - Level II” method to be the foundation of the AHERA TEM method.

ASTM D6281-06
Standard Test Method for Airborne Asbestos Concentration in Ambient and Indoor Atmospheres as Determined by Transmission Electron Microscopy Direct Transfer
This test method is an analytical procedure using Transmission electron Microscopy (TEM) for the determination of the concentration of asbestos structures in ambient atmospheres and includes measurements of the dimensions of asbestos structures and asbestos fibers found within the structures from which aspect ratios are calculated. This method is necessarily complex as it reports precise detail about the measurements of the often complex structures encountered in a typical air sample.

This test method was adapted from International Standard ISO 10312 Air Quality - Determination of Asbestos Fibres - Direct Transfer Transmission Electron Microscopy Method.

Phase Constrast Microscopy (PCM)

NIOSH 7400
Asbestos and Other Fibers by PCM
NIOSH 7400 is routinely used to determine concentration of detectable fibers (asbestos AND non-asbestos) in air. Fibers < 5.0 µm and/or < 0.25 µm in diameter will not be detected or recorded by this method. NIOSH 7400 alone cannot distinguish between asbestos and non-asbestos fibers.

A low count result does not guarantee a low concentration of asbestos. Likewise, a high 7400 count does not necessarily indicate a high asbestos concentration. A TEM method (NIOSH 7402) is required to be used in conjunction with NIOSH 7400 to definitively qualify fiber identification.

NIOSH 7400 (OSHA with TWA's)
Time Weighted Averages are used for determination of compliance with OSHA limits. A NIOSH 7400 result is mathematically “weighted” to determine the workers exposure in terms of an eight (8) hour shift. Regulatory agencies often limit exposures for workers based on an eight (8) hour shift (or Time Weighted Average).