Underwriters Laboratories, Inc. (UL) is renowned world leader in independent safety certification that certifies products against certain criteria which is suitable and appropriate for safety of the people and citizens. The UL 900 standard is designed to determine combustibility and the amount of smoke generated for air filter units under test. The classification for HVAC air filters confirms that the filters will meet requirements for most General ventilation and HVAC applications.
It should be noted that the test classifies the Filters only under clean conditions and not after it is used in any systems. This is because, after installation and running for a period of time, the combustibility and smoke generation of an air filter will depend upon the type, nature and quantity of the material accumulated inside the filter and hence only clean filters are subject to testing procedures.
The standard separately rates both washable and throwaway filters, used for the removal of dust and other airborne contaminants from HVAC systems, Air Handling units and recirculated systems. This is in conjunction and conformance with the Standards of the National Fire Protection Association (NFPA) for Installation of Air Conditioning and Ventilating Systems.
As per the main clause from the standard, a UL 900 Classified Filter is an air filter which, when clean, will burn moderately when attacked by flame, or emit moderate amounts of smoke, or both. The air filter unit shall not produce flame or extensive sparks, which are sustained beyond the discharge end of the test duct described in the Standard, when subjected to the flame exposure test. In addition, the burn shall not cause the development of an area of more than 9 square inches as measured below the smoke-density time curve.
Additionally, the adhesive material used for coating the filtering media, or other parts of an air filter unit, shall have a flash point of not less than 325 degrees F, Cleveland Open-Cup Method ASTM D92-5a (ANSI Z11.6- 1966).
It is important to note that the toxicity of the products of combustion, resulting from a filters exposure to flame, is outside the scope of UL 900, as is the filter’s particle capture efficiency before or after flame exposure.
To get filters tested and listed under UL 900, an application is submitted to Underwriters Laboratories. This application will involve the filter media material data sheets, frame material data, glue data sheets and all other raw materials used for manufacturing the filter element. Once the data sheets and applications are approved several samples are sent to UL lab for testing. All the samples need to pass the testing criteria for UL.
A listing is granted only if the samples pass the test procedures of UL and UL members will visit the factory for inspection of manufacturing process and raw materials used. UL 900 stickers can be attached to the filters only after the filter factory inspection is also successfully completed.
There will be follow up service where UL representative will visit the factory on a quarterly basis and inspect the filter elements. The representative may ask for additional samples for testing if required during each visit. Moreover, samples will need to be submitted for testing on an annual basis also.
There may be similar filter products manufactured in the factory which may have the same appearance, but with different raw materials as inputs. These filter elements cannot use the UL Label. Thus, the UL authorities ensures that the filter customer gets the authentic UL products which maintains the quality as per the UL 900 standard.
It is important to note that currently, there is only one UL 900 classification for air filters. The decision to sunset the dual-class Standard, Class 1 and Class 2, was made in September of 2009.
(All above information & Data are derived from Book records of Filtration Standards & Other related standards, research papers and its related webpages)