The American Conference of Governmental Industrial Hygienists (ACGIH) recommended exposure limit for asbestos is:
Time weighted average: 0.1 fibers per cubic centimeter (f/cc). OSHA would list this as the permissible exposure limit or PEL.
The ACGIH defines a respiratory fiber as a fiber longer than 5 microns and at least three times as long as their diameter as determined by the membrane filter method at 400-450 X magnification using phase contrast illumination.
The TLV basis for the recommendation is pneumoconiosis, lung cancer and mesothelioma.