Filter Media.—Intake air filter media shall consist of cotton flannel, wool flannel, spun metal, activated carbon, activated alumina, nonwoven fabric, absorbent cotton fiber, electrostatic, or other suitable materials which, under conditions of intended use, are non-toxic and non- shedding and which do not release toxic volatiles or other contaminants to the air, or volatiles which impart any flavor or odor to the product. Chemical bonding materials contained in the media shall be non-toxic, non- volatile and insoluble under all conditions of use. Disposable media are not intended to be cleaned and re-used.

Filter Performance.—The air supply system and/or ducting shall be such that the air supply is caused to pass through suitable air filters properly installed before coming in contact with product-contact surfaces of the drying system. Supply air filters for air which will be heated before it comes in contact with the product shall be of a design selected to operate at a face velocity, and installed in a manner which will allow the filter manufacturer's rating to be 90 percent or higher, when tested in accordance with the ASHRAE Synthetic Dust Arrestance test.^A

Supply air filters for air which will not be heated before it comes in contact with the product shall be of a design, selected to operate at a face velocity, and installed in a manner which will allow the filter manufacturer's rating to be 85 percent or higher when tested in accordance with the ASHRAE Atmospheric Dust Spot Method.^A

Filter Media.—Air intake and pipeline filters shall consist of fiberglass, cotton flannel, wool flannel, spun metal, electrostatic material, or other equally acceptable filtering media, which are non- shedding and which do not release to the air, toxic volatiles, or volatiles which may impart any flavor or odor to the product.

Disposable media filters shall consist of cotton flannel, wool flannel, spun metal, nonwoven fabric, U.S.P. absorbent cotton fiber, or suitable inorganic materials which, under conditions of use, are non-toxic and nonshedding. Chemical bonding material contained in the media shall be nontoxic, nonvolatile, and insoluble under all conditions of use. Disposable media shall not be cleaned and reused.

Filter Performance.—The efficiency of intake filters shall be at least 50 percent as measured by the National Bureau of Standards' "Dust Spot Method"^B using atmospheric dust as the test aerosol.

The efficiency of either air pipeline filters or disposable filters shall be at least 50 percent as measured by the DOP (Dioctyl 1-phthalate fog) test^C.

Piping.—Air distribution piping, fittings, and gaskets between the terminal filter and any product or product-contact surface shall be sanitary milk piping, except where the compressing equipment is of the fan or blower type. When the air is used for such operations as removing containers from mandrels, other nontoxic materials may be used.

Air Supply Equipment.—The compressing equipment shall be designed to preclude contamination of the air with lubricant vapors and fumes. Oil-free air may be produced by one of the following methods or their equivalent:

1. Use of a carbon ring piston compressor.

2. Use of oil-lubricated compressor with effective provision for removal of any oil vapor by cooling the compressed air.

3. Water-lubricated or nonlubricated blowers.

The air supply shall be taken from a clean space or from relatively clean outer air and shall pass through a filter upstream from the compressing equipment. This filter shall be located and constructed so that it is easily accessible for examination, and the filter media are easily removable for cleaning or replacing. The filter shall be protected from weather, drainage, water, product spillage, and physical damage.

MOISTURE REMOVAL EQUIPMENT.—If it is necessary to cool the compressed air, an aftercooler shall be installed between the compressor and the air storage tank for the purpose of removing moisture from the compressed air.

FILTERS AND MOISTURE TRAPS.—Filters shall be constructed so as to assure effective passage of air through the filter media only.

The air under pressure shall pass through an oil-free filter and moisture trap for removal of solids and liquids. The filter and trap shall be located in the air pipeline downstream from the compressing equipment and from the air tank, if one is used. Air pipeline filters and moisture traps downstream from compressing equipment shall not be required where the compressing equipment is of the fan or blower type.

A disposable media filter shall be located in the sanitary air pipelines upstream from and as close as possible to each point of application or ultimate use of the air.

AIR PIPING.—The air piping from the compressing equipment to the filter and moisture trap shall be readily drainable.

A product-check valve of sanitary design shall be installed in the air piping downstream from the disposable media filter to prevent backflow of product into the air pipeline, except that a check valve shall not be required if the air piping enters the product zone from a point higher than the product overflow level which is open to the atmosphere.

The requirements of this section do not apply when the compressing equipment is of the fan or blower type. See illustrations depicting various air supply systems.

Note.—For additional details, see 3-A Accepted Practices for Supplying Air Under Pressure in Contact With Milk, Milk Products, and Product-Contact Surfaces.

^A The method of making these tests will be found in the following reference: Method of Testing Air Cleaning Devices, ASHRAE Standard 52-76. Available from The American Society of Heating, Refrigerating, and Air- Conditioning Engineers, Inc., 345 E. 47th St., New York, New York 10017.

^B Dill, R. S., A Test Method for Air Filters. Transactions of the American Society of Heating and Ventilation Engineers, 44:379, 1938.

^C DOP-Smoke Penetration and Air Resistance of Filters, Military Standard No. 282, section 102.9.1 Naval Supply Depot, 5801 Tabor Avenue, Philadelphia, Pennsylvania 19120.