NIOSH 7402

NIOSH 7402 is a standardized laboratory method published by the U.S. National Institute for Occupational Safety and Health for counting and identifying asbestos fibers in air samples using transmission electron microscopy (TEM). It is typically used as a companion to NIOSH 7400, which uses phase-contrast microscopy to count all fibers regardless of type; NIOSH 7402 then determines what fraction of those fibers are actually asbestos.

Origin

The method was developed by NIOSH as part of its Manual of Analytical Methods, with the TEM-based 7402 protocol first issued in 1989 to address a known limitation of PCM: that it cannot distinguish asbestos fibers from non-asbestos fibers of similar size. It has since been revised several times to reflect improvements in electron microscopy and counting rules.

Significance in Asbestos Context

For a patient or family trying to reconstruct a workplace or environmental exposure, NIOSH 7402 results are often the most reliable air-monitoring evidence available, because they confirm whether the airborne fibers were truly asbestos and identify which type (chrysotile, amosite, crocidolite, etc.). Industrial hygiene records, OSHA inspection files, and insurance loss-control reports frequently contain 7400/7402 results from the worker's job site. These numbers can support claims that exposure levels at a particular plant, shipyard, or job task exceeded safe limits, and the fiber-type identification can help link exposure to specific products or defendants whose materials contained that mineral.

Example Sentence

His attorney subpoenaed the refinery's industrial hygiene file and found NIOSH 7402 results from the 1980s showing crocidolite and amosite fibers in the insulators' breathing zone.

Related Terms

NIOSH 7400, Transmission Electron Microscopy (TEM), Phase Contrast Microscopy (PCM), Fiber Counting, Industrial Hygiene, OSHA Permissible Exposure Limit

Notes

• Ask your legal team to request historical industrial hygiene records, OSHA inspection reports, and insurance loss-control surveys from each worksite. 7400 and 7402 data are often buried in these files.
• If only NIOSH 7400 (PCM) data exist, the total fiber count may overstate or understate asbestos exposure; a qualified industrial hygienist can estimate the asbestos fraction or argue that PCM-only data understate risk because PCM misses thin fibers visible only under TEM.
• Preserve any old air-sampling reports, union safety files, or employer 'right-to-know' documents you find at home. These often contain the only surviving fiber-type identifications for a given job site.
• Fiber-type results (chrysotile vs. amphibole) can be important for product identification, because specific manufacturers used specific asbestos types in their insulation, gaskets, or friction products.