User Guidance for Selection, Use and Testing of Fire Protection Features for High Efficiency Air Filtration Systems

DOE-STD-1066-99

strength after thorough soaking and that subsequent soakings may produce further incremental

reductions in strength. As illustrated in Figure C.1, a high efficiency demister is installed downstream of

the automatic deluge spray system to prevent water from soaking the filters. Section 14.8.2 of this

standard provides efficiency criteria for the demister.

Fires produce smoke that can cause rapid clogging of filters. Since the automatic spray deluge system

functions much like the scrubbers that are used to clean smoke stack exhaust, there is an expectation

that the automatic system may also reduce smoke clogging. However, the nozzles are not optimized for

smoke reduction. In limited research with spray nozzles it was found that smoke clogging was reduced

in some cases but increased in others. Therefore, premature manual activation of the spray deluge

system to knock down smoke is not recommended without further research to quantify results for specific

arrangements and combustible contents. Procedures, such as shutting down or throttling back the

blowers to prevent rupture of clogged filters during a fire, should be addressed in the authorization basis

documents.

The second fire suppression system is a manual deluge spray system. This system is employed only

if the filters begin to burn - it discharges water directly onto the first filter stage. Burning can not only

breach the filters but may also release particulate that has accumulated on the filters over time. Facilities

without this manual system must rely on firefighters to attack HEPA filter fires with high pressure hose

streams. The manual deluge system is intended to avoid unnecessary exposure of firefighters who must

otherwise enter the hazardous environment within the plenum and also to assure a more gentle

application of water, with the possibility that some filter stages may survive. The manual control valve

is normally locked in the closed position and only accessible to firefighters. Fire Department training

programs should address operating procedures for these valves.

Periodic testing of the fire suppression systems is needed to assure that all components remain

functional and to verify that debris has not blocked the nozzles, particularly those with a small orifice. The

most accurate method of testing would be to flow water periodically and observe the flow pattern from

the nozzles. However, the sensitivity of the filters to water damage makes this approach unsuitable for

the manual deluge spray system and undesirable for the automatic deluge spray system in the absence

of experimental data to set facility specific guidelines. Alternative nozzle tests may use a gas such as

air or carbon dioxide. If air is used, flow at the nozzle can be verified by deflection of a ribbon hanging

in front of the nozzle. Carbon dioxide "fog" may be directly visible at the nozzle but requires a more

robust piping design. Where existing designs and limited future use of a facility make modifications

impractical, then testing the automatic deluge spray system with water for up to one minute per quarter

is not expected to be detrimental to downstream filters over a period of several years provided:

o it is verified that there is no gross water carryover through the demister, and

o there is no significant increase in differential pressure across the first downstream HEPA filter during

or immediately after the test.

In any case, testing of both systems with water should be considered at the time of scheduled

replacement of filters.

C-4