Clean Manufacturing: Air Filter Adherence to Flammability Standards Ensures Safety of Cleanroom Fan Filter Units
Can filter units play a critical role in proper cleanroom operation; however, the relative safety of their role and performance can be jeopardized if the air filter used does not meet accepted Underwriters Laboratories Inc. (UL) flammability standards. Non-compliance of air filter units to the applicable UL standards are a risk to both the OEM manufacturer who produces a cleanroom fan filter unit with a non-complying air filter, as well as the maintenance technician who may inadvertently replace a complying air filter unit with an "it fits" replacement unit that does not meet the flame safety requirements.
The two predominant UL standards that apply to fire safety with regard to air filters used in cleanroom fan filter units are UL 94 HF-1 and UL 900. These standards apply to both the air filter media and the entire air filter assembly. To minimize the risks of potential fire and smoke hazards with the cleanroom fan filter unit, it is important to verify that any air filter used meets both UL 94 and UL 900 standards.
Essentially, UL 94 HF-1 covers any plastic parts used in the construction of the air filter. Plastic specimens representing a cross section of the various air filter plastic components are exposed to set amounts of heat and flame in a controlled environment to determine such things as burn rate, flame drip and self-extinguishing performance once the heat and flame source is removed. Among the test results indicating compliance with UL 94 HF-1 are a burn rate to not exceed 1.5 inch (38.1mm) per minute over a 4.0 inch (101.6mm) span and flame drip, in which no specimens drip molten flaming particles capable of igniting dry absorbent surgical cotton placed 12 inches (305mm) below the specimen. In addition, an ignited specimen caused by heat and open flame exposure must cease to burn within two seconds after a test flame is removed.
UL 900 compliance focuses on the determination of combustibility and amount of smoke released from both washable and throwaway air filter units used to remove dust and other airborne particles from the circulated air stream. Testing for UL 900 compliance includes flame exposure and spot flame tests conducted on air filter unit specimens in which smoke generation is scientifically gauged utilizing photocell technology. To be compliant, Class 1 and Class 2 air filter units must demonstrate significant flame or spark control characteristics when subjected to specified flame-exposure and spot-flame tests. Because combustibility and smoke producing characteristics can be greatly impacted by the amount and types of particulates trapped in an air filter, UL 900 testing applies only to a clean air filter. Consequently, in order to stay within the compliance realm, it is important that the fan filter unit be regularly maintained by routinely cleaning or replacing the air filter.
Complete, uncondensed descriptions of the testing methods and compliance requirements for UL 94 HF-1 and UL 900 are available directly from UL. Your cleanroom fan filter unit manufacturer should also be able to provide flammability information on any air filter used in their system. Also, the air filter manufacturer can be an important source of flammability information.
Air filter manufacturers, whose products are used in cleanroom fan filter unit applications, routinely select media and frame materials that are known to meet UL 94 HF-1 and UL 900 testing standards. One of the latest innovations in media suitable for cleanroom fan filter units has been the introduction of Quadrafoam media that is rated UL 94 HF-1. Quadrafoam is non-hazardous and pH neutralized for longer filter life. For applications where microbial contamination is a possibility, Quadrafoam media includes an anti-microbial additive with a fungus growth rating of zero.
Most cleanroom fan filter units require an air filter with an integrated, supportive frame and grid system to maintain the media in its optimum position. Air filter frames and grids are subject to the same flammability considerations as the media. The variety of filter frames available range from metals, such as aluminum and steel, to plastic. Plastic frame materials have increased in popularity as they have achieved flame retardant status and provide flexibility not associated with more rigid metal frame materials. The latest flame retardant polypropylene materials used by air filter manufacturers should meet or exceed the UL 94 HF-1 and UL 900 standards.
There are just a few basic rules for consideration to minimize the risks of fire and smoke from air filters used with cleanroom fan filter units. They include: 1) Select a fan filter unit manufacturer who makes it known that they specify UL 94 HF-1-, UL 900-compliant air filters; 2) Clean or replace air filters regularly per the fan filter manufacturer's recommendation (based on your specific cleanroom application); 3) Always replace a UL 94 HF-1-, UL 900-compliant air filter with the fan filter unit manufacturer's original parts; 4) Don't hesitate to contact any reputable air filter manufacturer serving the industry if you suspect there might be a fire or smoke hazard issue with existing equipment.
The air filter component of the fan filter unit plays a critical role in maintaining the environmental quality of the cleanroom. Safety begins when potential fire and smoke hazards are minimized by the fan filter unit manufacturer who originally specifies a UL 94 HF-1-, UL 900-compliant air filter. Safety is maintained on-site when the compliant air filter is properly cleaned or replaced as necessary. Thus cleanroom operators can be assured that their system will perform properly and operate while maintaining compliance with regard to UL standards.