http://www.servicor.com/Quick-Quote/Air-Flow-Calculator.aspxThere are NO industry standards that dictate air change rates, ACPH is a dependent variable. The cleanroom contractor selected should have experience in the design and commissioning of these rooms such that the average velocity and room architectural configuration will lead to the desired level of particle control, in the state (e.g., as-built, at-rest, or operational) as defined by the cleanroom design/construction contract. ACPH = (Avg. room velocity x 60)/(room height), Room CFM = (ACPH x Room volume)/60Air velocities for cleaner classes of cleanrooms tend to fall in the lower end of the recommended range while velocities for less clean classes tend to exceed the upper end of the range, but neither should normally fall below the lower end of the range. Ranges shown are those typically used. For 100% HEPA filter ceilings an average active filter face velocity of 100 fpm will normally provide an average room velocity of 80-90 fpm. For Class 1000 and less clean classes, it is always preferable to provide MORE filters, and to run them at lower velocities.Parameters shown are valid for a standard cleanroom with ceiling height not-to-exceed 10 feet. Cleanrooms with greater than 10 feet internal height - such as those for high bay aerospace applications - must be examined on an individual basis.Class 10 requires 99.999 on 0.12 micron or better ULPA filters.Class 1 requires 99.9995 on 0.12 micron or better VLSI filters.