310 GREENWICH STREET Block: 142 Lot: 25 BIN: 1083239 40 Harrison Street/Independence Plaza

NYC 9/11 Public Portal Document

TRANSMISSION ELECTRON MICROSCOPY TEM METHODOLOGY

Transmission Electron Microscopy (TEM) is a technique, which focuses an electron beam onto a thin sample mounted in the microscope column (under a vacuum). As the beam transmits through the sample, an image resulting from varying density of the sample is projected onto a fluorescent screen. Air samples for TEM analysis can be collected on either mixed cellulose ester or polycarbonate filters and are prepared using direct transfer techniques (as per EPA regulations). Direct preparation allows for the transfer of a carbon- coated replica of the filter material (with embedded fibers and particulates, etc.) right on to a copper grid suitable for TEM analysis. Indirect transfer techniques require an intermediate step that may break-up fiber bundles, resulting in an increased fiber amount.

Several methods exist for the preparation and analysis of air samples by electron microscopy. Most significant are the mandatory and non-mandatory TEM methods set forth as appendices to 40 CFR 763, Subpart E (AHERA Regulations). These methods are to be used for analysis of final clearance air samples on school abatement projects.

The analytical sensitivity is the airborne asbestos concentration represented by each fiber counted under the electron microscope. It is determined by the air volume collected and the. proportion of the filter examined. This method requires that the analytical sensitivity be no greater than 0.005 structures/cc.

Sampling pumps must be calibrated and their flow indicators must register more than 1 but no more than 10 liters/min. Two (2) field blanks are to be taken by removing the cap for not more than 30 seconds. A sealed blank is to be carried with each sample set. Th+is representative cassette is not to be opened in the filed. These samples are submitted to the laboratory for quality control purposes. The sampling should be conducted for a period of time to conform at least a volume of 1200 liters of air. The samples are later brought to a certified laboratory for the analysis.

NYC-WTC 000134783