<P> Irradiation is used by the United States Postal Service to sterilize mail in the Washington, D.C. area . Some foods (e.g. spices, ground meats) are sterilized by irradiation . </P> <P> Subatomic particles may be more or less penetrating and may be generated by a radioisotope or a device, depending upon the type of particle . </P> <P> Fluids that would be damaged by heat, irradiation or chemical sterilization, such as drug products, can be sterilized by microfiltration using membrane filters . This method is commonly used for heat labile pharmaceuticals and protein solutions in medicinal drug processing . A microfilter with pore size 0.2 μm will usually effectively remove microorganisms . Some staphylococcal species have, however, been shown to be flexible enough to pass through 0.22 μm filters . In the processing of biologics, viruses must be removed or inactivated, requiring the use of nanofilters with a smaller pore size (20 - 50 nm) are used . Smaller pore sizes lower the flow rate, so in order to achieve higher total throughput or to avoid premature blockage, pre-filters might be used to protect small pore membrane filters . Tangential flow filtration (TFF) and alternating tangential flow (ATF) systems also reduce particulate accumulation and blockage . </P> <P> Membrane filters used in production processes are commonly made from materials such as mixed cellulose ester or polyethersulfone (PES). The filtration equipment and the filters themselves may be purchased as pre-sterilized disposable units in sealed packaging or must be sterilized by the user, generally by autoclaving at a temperature that does not damage the fragile filter membranes . To ensure proper functioning of the filter, the membrane filters are integrity tested post-use and sometimes before use . The nondestructive integrity test assures the filter is undamaged and is a regulatory requirement . Typically, terminal pharmaceutical sterile filtration is performed inside of a cleanroom to prevent contamination . </P>

What control process is used to destroy something of no value