By Tom Justice, CAFS, NCT, Zene

The first edition of the UL 900 Standard for air filter units was issued back in September 1965 and has evolved over the years to the most recent designation as an American National Standard (ANSI) which occurred on February 14, 2012; ANSI/UL 900. It currently consists of the Eighth Edition dated April 21, 2015.

Most of us in the filter industry have been involved at some time or another with the UL 900 standard and anyone in the industry for more than a year has certainly developed a definite opinion on this subject. For those new to the industry, the standard covers the requirements to determine “the amount of smoke generated and the combustibility of air filter units of both washable and throwaway types used for removal of dust and other airborne particles….”. Smoke generation of an air filter unit is dependent upon the type and quantity of material collected on the filter during a specific service life, hence “the test requirements of this standard, for classification purposes, apply only to air filter units in a clean condition.” Following the clean state “it is intended that maintenance and inspection practices should be followed as proposed in Appendix B of NFPA 90A”. 1

The fact that we classify clean filters, which are only really clean for a brief time during the service life, has always been a point of contention for fabricators. However looking past this, the Certified Air Filter Specialists (CAFS) have an obligation to understand the requirements of NFPA 90A and insure that their customers remain in compliance. Since it’s inception, UL 900 has been incorporated into building codes throughout North America becoming a part of the legal landscape. In any litigious environment the end user sees the knowledgeable professional as adding value to the products they purchase.

Like any number of standards, UL 900 provides a uniform test protocol. What gives UL 900 its teeth is the listing and follow-up program. When a manufacturer choses to list a product with UL, they are given a file number. Then the product is tested in accordance with UL 900 and must meet the following requirements:

  • No flame beyond the end of the test duct.
  • Less than 25 sparks sustained beyond the end of the test duct.
  • Less than 9 square inches of smoke measured below the smoke density time curve.

Once a product is listed, it is incorporated into the follow-up service for quarterly inspections at each manufacturing location. This is where the standard gets its teeth. The inspection compares current production to the UL file, looking for any variations in both process and materials. The material designation along with the supplier and amount of material used must match with what is on file. The inspector may go so far as to check the calibration of any instruments used for measurements.

The standard has seen numerous changes as noted by the fact that it is now in its eight revision, however the most notable change was the removal of references to Class I and Class II. Comments or proposals for changes or revisions to the standard are most often solicited from the Standards Technical Panel (STP), which is made up of consumers, manufacturers, supply chain, general interest, etc. however proposals may be submitted by groups or individuals via a Proposal Request in UL’s On-Line Collaborative Standards Development System (CSDS) at .

As with any standards document, changes are a necessity if the standard is to remain a viable document in step with changing requirements. This demands the active involvement of a standing standards committee made up of a broad cross section of the industry from manufacturers to users. It is difficult to imagine that any standard could remain an active document for more than 20 years without such input. While UL 900 has seen numerous changes there are still a number of issues, which call for resolution.

  • Is the current standard at odds with new sustainability requirements and initiatives, specifically for recycled, compostable and biodegradable products? Which requirement takes precedence, the acute or the chronic threat? And more often than not recycled products are the creation of numerous untraceable sources and may be compounded or blended in varying quantities. UL is very specific in traceability as well as composition and usage which makes variable sourcing impossible.
  • As companies are forced to compete globally, they are faced with numerous and non-uniform fire code requirements dependent on the geographic locale. In Europe the most common standard is DIN53438. Related to this are DIN4102 and EN13501. And very different is the French fire classification NF P92-507 for construction materials. However we have only to look across our own border to note the impact of non-uniformity. When the U.S. removed references to Class I and Class II, Canada did not follow suit, choosing instead to retain the old system.
  • While uniformity is an issue in itself, there has to my knowledge never been a scientific comparison made as to the stringency of these various international requirements and which requirements provide adequate protection. My favorite comment came while researching this article and is one which points to these differences. After numerous e-mails with one colleague, he finally retorted, “Why are you Yanks so concerned about smoke and flame?”
  • And last but not least there has been a definite outcry from fabricators that the test is inconsistent, e.g. “a product passes but then fails on the annual follow up service. What we don’t know without further research is whether the variation is in the test or in the raw material components of the filter.

These issues affect all of us in the supply chain in some fashion or another. As we can drive for answers to these issues it is difficult to imagine any organization better positioned to pull the stakeholders together than NAFA.

1 – UL/ANSI 900 Standard for Safety for Air Filter Units, Eighth Edition., April 21, 2015


Back to Index