NEW CRITERIA
Now,
Underwriters Laboratories (UL) has simplified its Standard UL 900 for
evaluating a filter’s combustibility and smoke generating potential
when the filter is exposed to direct flame. The designations UL Class
2 and UL Class 1 designations are now outdated. UL 900 covers both
washable and throwaway filters used for the removal of dust and other
airborne particles from mechanically circulated air in equipment and
systems.
The vast majority of air filters have
historically tested as UL Class 2. The criterion for this filter
classification is that when tested, the clean air filter burns
moderately when attacked by flame, or emits moderate amounts of
smoke, or both. A UL Class 1 filter, when clean, did not contribute
fuel when attacked by flame and emitted only negligible amounts of
smoke.
Some municipalities required the UL
Class 1 product through local codes. In many cases, because of the
different construction of Class 1 and Class 2 rated products, the
user paid two to three times the cost of a UL Class 2 product.
Additionally, there was a widespread
misconception within engineering circles that a UL Class 1 product
was “fireproof.” This was not the case, since a Class 1 product
could burn if submitted directly to an open flame, although it was
less likely to contribute combustion byproducts. Both classes, when
clean, would self-extinguish when the flame source was removed from
contact with the filter.
In the future,
filters will only be required to meet the requirements that were
formally recognized as UL Class 2. Filter frames and labels will
carry one marking to designate that they meet the requirements of the
standard. Most filter manufacturers have started the conversion
process and will be in compliance well before the effective date of
May 2012. The Underwriters Laboratories website provides complete
listings as to which manufacturers follow the procedures as
prescribed in the Standard and which of their filters are in
compliance.
It is important to note, after a
period of service, that the combustibility and smoke generation of an
air filter depends upon the nature and quantity of the material
collected by the filter. The test requirements of this Standard, for
classification purposes, apply only to air filters in a clean
condition. This is a critical step forward. UL is a recognized leader
in independent safety certification and has facilitated a simplified,
cost-conscious revision.
For more information
on this subject, see
www.filterair.info/ULCert.
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