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     Office of Air Quality, Permitting & Enforcement Division

               Mechanical Section Policy Memorandum


Date:  November 23, 1993              No.:  4

From:  Patrick N. Agumadu

Approved by:  Gary I. Wallin, P.E. 

Subject:  Standard Exemption No. 91 - Interpretation of
          Intent, Usage and Scope



The intent of Standard Exemption No. 91 is to allow the
installation or addition of silos to new or existing
operations.  Some form of mixing or blending can be authorized
under this exemption, provided the operation and movement of
materials are performed in enclosed systems and the exhaust
air is vented to a fabric filter.  There should not be any
pollutant other than particulate matter.

The exemption may be used in installing one or more cement,
sand, or any bulk mineral material silos with all the material
conveyed within closed conveyor systems (no front end loading
and no stockpiles).

The exemption may also be used in dry aggregate handling,
blending, bagging, product storage, and shipping provided that
none of these operations "sees the light of the day."


Standard Exemption No. 91 was originally intended to cover
bulk cement handling facilities, but later expanded to cover
all bulk mineral products, except asbestos.  Examples of such
bulk material handling operations are: 

1.  Standard Exemption No. 91 was approved for Texas 
    Industries, Inc to construct a cement storage and
    handling, dry aggregate handling, blending, bagging,
    product storage and shipping operations at their
    Sakrete Plant in Southeast Travis County. All emissions,
    including potential fugitive emissions are vented to a

2.  Halliburton Energy Service in Fresno also received 
    authorization under Standard Exemption No. 91 to construct
    a Bulk Material Handling Facility with some blending
    operation.  The blending operation is totally enclosed and
    vented to a baghouse.  In addition, the receiving and
    loadout operations are vented to bagfilters.

Necessary Action:   

Standard Exemption No. 91 DOES NOT cover the handling of
asbestos, stockpiles of any material and any open operation.

cc:  All Mechanical Section