Electrical Equipment Utilized in Final Filter Enclosures

DOE-STD-1066-99

liquids in any quantity should not be permitted. In addition, the storage of spare filters

inside the filter plenum should not be permitted.

14.5.2

All electrical equipment located in the filter plenum should comply with NFPA 70 and all

electrical wiring located in the filter enclosure should be in metal conduit.

14.5.3

Processes Subjecting Final Filter Plenum to Flammable and Combustible Vapors

14.5.3.1

When operations or processes involve flammable or combustible liquids

that produce vapors, the concentration of the gases or vapors inside the

final filter plenum should not exceed 25 percent of their lower flammable

limit inside the filter enclosure.

14.5.3.2

Fixed combustible gas analyzers should be provided in the final filter

enclosure when the process involves gases or vapor with analyzer alarms

set to sound an alarm at 25 percent of the lower flammable limit. These

alarms should be transmitted to a continuously manned location.

14.5.4

Processes Subjecting Final Filter Plenum to Pyrophoric Dust Particles

When operations or processes involve pyrophoric materials that may subject the final filter

plenum to the pyrophoric dust particles, a method to remove the dust particles before

reaching the final filter enclosure, such as a prefilter, should be required.

14.5.5

Processes Subjecting Final Filter Plenum to High Dust Loading, High Moisture

Air, Acid, or Solvent Environments

Operations sometimes may involve processes that may subject the final filters to airstreams

carrying high moisture content, high dust loading, acids, and solvents that may rapidly

degrade, plug or disintegrate the final filter medium or separators. When operations

involve these sorts of airstreams, preventive methods should be utilized to stop the

degradation impact on the final filters. These can include, but are not limited to, more

frequent filter change outs, prefilters, scrubbers or traps, filters rated for the particular

environment, and the use of alternative chemicals. When chemical degraders to HEPAs

are utilized, including hydrogen fluoride (HF), nitric acid (HNO3), and perchloric acid

(HCLO4), processes should include scrubbers, traps, or other methods to remove the

chemical before the final HEPA filters.

14.6 Prefilters, Duct Entrance Filters, and Fire Screens

14.6.1

Prefilters and Duct Entrance Filters

Protection of the final filter plenum from dust and particulate loading should be

accomplished by using duct entrance filters or prefilters or a combination of both as follows:

14.6.1.1

All gloveboxes, hot cells, and fume hoods connected to containment

ventilation systems should be provided with at least moderately efficient