Air Date: 2-17-2012| Episode: 236
Particles & Aerosol Physics – More than Meets the Eye & Field Testing Air Filtration Devices – This week we will discuss the issues that make performing field tests of air filtration devices and HEPA vacuums such a challenge...
Particles & Aerosol Physics – More than Meets the Eye & Field Testing Air Filtration Devices – This week we will discuss the issues that make performing field tests of air filtration devices and HEPA vacuums such a challenge. Tony Havics, PE, CIH,CHMM Wane Baker, PE, CIH and Tom Yacobellis are coming on to discuss the reason particles behave the way they do, the challenges in determining how well we are capturing these particles and the limitations of our instruments and equipment when it comes to particle capture and measurement. The Air Filtration Device Standards Development Committee (AFD) of the Indoor Environmental Standards Organization (IESO) will be continuing its research efforts by conducting a three-day testing program of HEPA-filtered negative air type or collection machines in mid March. The purpose of this event is to gather additional data to complete the development of an ANSI/IESO Standard for the field evaluation of portable HEPA-equipped air filtration devices. The committee is seeking multi-channel laser particle counters from various manufacturers and the assistance of manufacturers’ representatives who are proficient in their use.
Air Filtration Device Testing
Today’s episode of IAQradio featured a roundtable discussion on HEPA filtered air filtration devices with Tony Havics, Wane Baker and Tom Yacobellis. Tony, Wane and Tom volunteer on the IESO Air Filtration Device (AFD) Committee which is developing a testing standard for AFDs. While Tony and Wane are more scientific types, Tom is a hands-on field guy.
Nuggets mined from today’s broadcast:
· Interesting history of the origin of HEPA filter. Takeoff on a German gasmask filter captured during World War II. Used in the Manhattan Project as a mechanism to prevent the escape of radioactive contaminates. Today’s HEPA filters are made from glass fibers to be heat resistant and other suitable materials.
· Particle- is a small localized object to which can be ascribed several physical properties such as volume or mass.
· Aerosol- is a colloid suspension of fine solid particles or liquid droplets in a gas.
· Aerodynamics- the shape and density of particles are important. Most deeply penetrating size particles are 0.1 micro meters in size.
· Isokinetic sampling- the technique for collecting airborne particulate matter in which the collector is so designed that the airstream entering it has a velocity equal to that of the air passing around and outside the collector.
· More accurate method of sampling incorporating the same velocity, speed and direction of the airstream.
· False sense of security. While HEPA filtration is called for in multiple industry standards and guideline documents in real world situations it is very common for even brand new HEPA filters to leak significantly and pose a cross contamination risk. IESO is conducting testing on air filtration devices and has undertaken the development of writing a standard.
· Current state of the art for onsite testing of HEPA filter efficiency uses laser particle counter, a duct length of 8X-10 X duct outlet diameter, collection of 3 sets of 1 minute duration samples from the airstream. Ultraviolet particles and UV lights can be used to determine AFD filter failure points.
· Soft spot. HEPA filters lose efficiency on 10 nanometer size particles.
· Aerodynamic equivalent diameter- the aerodynamic equivalent diameter is the diameter of a sphere, with density -1g/cm³, that has the same terminal settling velocity under gravity a the airborne particle considered.
· Agglomeration- the sticking of particles to one another or to solid surfaces, is a natural phenomenon.
IAQ newsman Glenn Felman had good news to share, the RIA and Clean Trust signed a Memorandum of Understanding agreeing to cooperate and the joint IESO-RIA IESO/RIA Standard for Determining Impact of Fire-related Particulate in HVAC Systems was approved by ANSI.
Today’s music: “Particle Man” by They Might Be Giants
Z-Man Signing Off