There is no OSHA regulation stating how often general industrial hygiene testing should be done. However, it should be done every one to two years, depending on what chemicals or particulates are being generated. Most of the larger manufacturers follow this schedule so recent data are always available. Many clients of Environmental Safety Consultants have different areas tested each year, so that all areas are tested at least every two years. If manufacturing methods change, then the testing must be done at that time. Those method changes include the chemicals, stock materials, or procedures. Regulations can change, as well, lowering the permissible limits, which may warrant retesting if the most recent results were below the old limit but above the new one. Of course, noise is usually tested in the plant annually and the audiometric testing for the workers must be done annually.