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         Office of Air Quality, New Source Review Program

               Mechanical Section Policy Memorandum


Date:  December 20, 1994                          No.:  17

From:  Skip Clark, P.E. 

Approved by:  Gary Wallin, P.E. 

Subject:  Standard Exemption No. 24



The intent of Standard Exemption No. 24 was to cover sand or
investment molds from the time they are made until they are
broken apart.  No other equipment, or processing was intended
for this exemption.  Also, the size of the castings is limited
to 100 pounds or less per casting.


Historically, molds for castings that are less than 100 pounds
per casting do not tend to emit large amounts of particulate
matter or other pollutants while they are being formed and/or
used.  The 100 pound per casting is defined as the actual
weight of the casted part, irregardless of how much is
actually melted to cast that part.  If the company wants to
melt 125 pounds of metal to make sure of enough melt to fill
the mold, the excess is not counted toward the weight of the
casting.  The potential to emit air containments is mainly
concentrated in the furnace area and the break-out and sand
reclamation systems.

Larger mold making equipment can be covered under Standard
Exemptions Nos. 23 or 44.  The melting and holding furnaces
that are used in these processes may be covered under Standard
Exemption Nos. 7, 17, 58 or 96.

Necessary Action:  


cc:  All Mechanical Section