Answer to Question #10654 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements

The following question was answered by an expert in the appropriate field:

I am interested in information regarding the calibration of vacuums, for example, high-energy particulate air (HEPA) systems. These vacuum cleaners are used for decontamination of loose particulates from equipment and personnel. The limit for HEPA is 99.97 percent efficiency at the 3 micron particle size. Is there a procedure/apparatus to determine if a vacuum and filter are still within the limit?

Yes, there are accepted procedures that are used for testing the integrity of HEPA filters used in vacuum cleaners. The tests involve introducing a known concentration of aerosol particles of an acceptable size into the inlet of the vacuum cleaner and measuring the concentration of the aerosol particles as they exit in the exhaust. These measurements will confirm whether or not the HEPA filter(s) is performing according to specifications. You can get an idea of the kind of setup that is suitable by looking at this description at a Brookhaven National Laboratory site. Attachment 9.3 shows a graphic of the setup. 

In order to perform such a test, one must have available an aerosol generator that produces the desired size distribution of particles. The standard material used in the past and still widely used has been an oily substance called dioctyl phthalate (DOP). Concerns with possible carcinogenicity of the DOP has led some individuals and groups to use alternative materials such as nontoxic polyolefin oils. By blowing air through small nozzles into a reservoir of the oil or by using other means, such as thermal generation in which the heated oil recondenses to form small droplets, the desired aerosols are generated. The aerosol concentrations are measured using an appropriate particle counter, a specialized device that provides a means, often a light scattering process, for determining the concentration of airborne particulates of the size range of interest that pass through the device. You can find a variety of information on aerosol generators and aerosol counters for use in filter testing by searching the Internet.

As a general practice, testing of the filters should be done when the vacuum cleaner is purchased (this validation is often provided by the manufacturer), whenever the HEPA filter(s) is changed, whenever anything has happened that leads you to believe the filter integrity may have been compromised, and otherwise on an annual basis as long as the vacuum cleaner is available for use.

There is a significant investment of money and time required to obtain the necessary equipment and become proficient in its use. If this is not practical, you may want to consider having a service company that deals with such assessments do the work for you, especially if the vacuum cleaner is not used frequently. You can find such companies by searching "HEPA filter testing services" on the Internet.

You can also find a variety of other sources that discuss the process and recommendations regarding filter testing. These include a number of standards for sale by the American Society of Mechanical Engineers (ASME) and affiliated groups:

  1. ASME N509, Nuclear Power Air Cleaning Units and Components, 2002 (Rev 2008).
  2. ASME N510, Testing of Nuclear Air-Treatment Systems, 2007.
  3. ASME-AG-1-2009,Code on Nuclear Air and Gas Treatment.

These are not aimed specifically at testing of vacuum cleaners, but the principles and many of the recommendations are applicable. There is more information available from some government agencies/groups in the United States and elsewhere. A good reference to review such sources is a book by R.C. and G.M. Brandys, In-Field Test Methods and Reference Standards for Portable High Efficiency Particulate Air Filtration (PHEAF) Equipment. The book deals with many aspects of testing and evaluation of air particulate cleaning systems, including specific references to HEPA vacuum cleaners, as can be seen from the Table of Contents available at the above link. I believe this book is available through Occupational & Environmental Health Consulting Services, Inc.

Good luck.

George Chabot, PhD

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