Self-Cleaning Viscous Liquid Filters

DOE-STD-1066-99

These types of filters utilize a viscous liquid for cleaning purposes. They should be avoided for uses

where radioactive materials are handled because they produce radioactive sludge that requires

disposal. These types of filters would also require special fire protection systems because of the

combustible nature of the liquid.

Moving Curtain Single Pass Rolling Prefilters

One noteworthy type of prefilter is the moving curtain single pass rolling prefilter. This type of prefilter

involves fresh filter media being manually or automatically fed across the face of the filter, while the

dirty media is rewound onto a take up roll. When the roll is exhausted, the take up media is disposed

of and a new media roll is then installed. Fire tests involving this type of prefiltering were performed

in 1980 by Lawrence Livermore National Laboratory utilizing a modified commercial moving curtain

filter. The purpose of testing this type of filter was to find a way to limit the amount or eliminate

aerosol smoke that may be produced in a fire that can plug a final HEPA filter.

The tests

demonstrated that prefilters of this type could limit aerosol plugging of HEPA filters produced during

fire. However, the subject final test report stated that prefilters of this type were an "experimental

prototype" and that this type of prefilter "would have limited application as a pure fire protection device"

for containment ventilation systems in current use.3

Electrostatic Precipitator Prefilter

Another type of prefilter that has been utilized at DOE facilities is the electrostatic precipitator (ESP)

prefilter. This prefilter imparts an electrical charge to particles in the air flow stream, causing the

particles to adhere to collector plates. The ESP prefilter has been used to extend the life of final

HEPA filters when processes involve larger diameter airflow particles. A certain level of fire protection

could be achieved with an ESP prefilter during a fire if the particles expected as products of

combustion can be properly collected on the filter throughout the fire for the particular air flow capacity

of the process. Most commercially available ESP prefilters cannot catch the smaller airborne particles

and smoke particles associated with a burning fire. However, more work needs to be done on ESP

prefilters to understand what particle sizes associated with fire an ESP can effectively filter out. When

ESP prefilters are used they should be made of noncombustible materials and, as with any prefilter,

careful attention should be directed to prevent dust loading on it during its use. Also, ESP prefilters

should not be used where explosive concentrations of gases or dusts are present.

Alvares, N., D. Beason, W. Bergman, J. Creighton, H. Ford, and A. Lipska. 1980. Fire Protection

Countermeasures for Containment Ventilation, UCID-18781, Lawrence Livermore National Laboratory, Livermore,

California

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