Method 18 Modifications

     Test Method 18, 40 CFR Part 60, Appendix A, was modified in
the April 22, 1994 issue of the Federal Register.  The Method
will, in most instances, require the performance of a recovery
efficiency study of the sampling and analytical system chosen for
the test.  If sufficient recovery of the target compound is
demonstrated, a correction factor will then be used to correct
the data collected during the test.

     Several testers have asked to use modified versions of NIOSH
ambient air sampling techniques for Method 18 sampling (adding a
water knockout trap before the adsorbent in order to remove
moisture).  With the promulgated modifications mentioned above,
as long as acceptable recovery efficiency is demonstrated for
each target compound, these techniques would be acceptable for
use with Method 18.  Please note:  if the water knockout is
analyzed for the recovery efficiency test, it must also be
analyzed during the compliance test.

     You may reach Rima Dishakjian at (919) 541-0443 if you have
any questions about this and other issues associated with Method
18.