MEMORANDUM

          SUBJECT:  National Emission Standards for Hazardous Air Pollutants: Halogenated Solvent
          Cleaning

          FROM:     Scott Throwe, Branch Chief
                    Chemical Industry Branch

          TO:       Nhien Pham
                    Nidhi O'Meara



     We welcome the opportunity to assist you in monitoring compliance with Subpart T, the
national emission standards for halogenated solvent cleaning.  As discussed in a recent
conversation with my staff, guidance is needed to evaluate compliance with the equipment
standards for batch cold cleaning machines.   Specifically, you requested guidance on determining
compliance with §63.462(a)(1).  

     Owner or operators of an immersion batch cold solvent cleaning machine complying with
§63.462(a)(1) must employ a tightly fitting cover that shall be closed at all times expect during
parts entry and removal and a water layer at a minimum thickness of 2.5 centimeters (1.0 inch) on
the surface of the solvent within the cleaning machine.   To determine the thickness of the water
layer on the surface of the solvent, a clear pipette may be immersed and extended beyond the
solvent-water interface.  Once the pipette has been immersed, plug the end of the pipette to
prevent any air from entering the top of the pipette and remove the pipette from the machine.  A
visual inspection of the contents inside the pipette will enable you to determine the water layer
thickness.   

       Please contact Tracy Back at (202) 564-7076 with any further questions regarding
Subpart T.