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

DOE-STD-1066-99

User Guidance for Selection, Use and Testing of Fire Protection Features

for High Efficiency Air Filtration Systems

Filtration systems are designed to remove radioactive and other hazardous particulate from air handling

systems before recirculation or discharge to the outside. A fire in a nuclear facility may result in an

appreciable quantity of radioactive material becoming airborne in a form that is easily dispersed. Several

design measures are used to assure the survivability of the filtration system long enough for skilled

firefighters to attack and extinguish all but the most serious fires.

Table C.1 summarizes the general selection criteria for filters and filter enclosures. Combustible frames

are allowed in all cases and in fact wood frames are commonly used. Although the wood frames may

have a fire retardant treatment to delay ignition, they still burn once ignited. Other combustibles include

the organic binder that holds together the fiber filter media, sealants that attach the media to the frame,

as well as accumulations of dust and particulate. Some filters may have noncombustible frames that are

subject to melting or distortion when heated. The glass fibers in the "paper" media curl and melt when

exposed to sufficient heat. Appendix B summarizes the effects of heat on the filter media. Although

nuclear ventilation HEPA filters are qualified to assure a filter efficiency of at least 97% after exposure

to air at 700 plus or minus 50 degrees F for 5 minutes, they may fail after longer exposures to lower

temperatures or more rapidly at higher temperatures. A typical fire produces temperatures more than

double the temperature used in the qualification test.

The recommended arrangement for fire protection systems protecting HEPA filters is illustrated in Figure

C.1. There are two separate water-based fire suppression systems. One is designed to protect the filters

from fire and the other to extinguish a fire that has reached the filters. The first system is an automatic

deluge spray system located in the plenum upstream of the filters and separated from the filters by a

demister. The second is a manual deluge spray system directed at the first stage of filters. The

automatic system is usually a deluge sprinkler system designed to meet the requirements of NFPA

Standard 13. The manual system is usually a fixed water spray system designed in accordance with

NFPA Standard 15. However, the reverse may be suitable in certain circumstances, provided that the

performance parameters are met. The term "deluge spray system" is used throughout this standard to

provide flexibility for the cognizant fire protection engineer to select the appropriate system.

Operation of the automatic deluge spray system is initiated by heat detectors located in the ducting. The

detection system opens a deluge valve, allowing water flow to the nozzles. The spray nozzles are either

open sprinkler heads from which the fusible link has been removed or special purpose nozzles designed

to produce a particular pattern. The automatic system is also equipped with a locked bypass valve that

can be manually opened if the detection system or the deluge valve fail to operate. The purpose of the

automatic system is to cool the air stream so that the filters can continue to function during a fire in the

facility. The demister is intended to protect the filters from water damage. Closed head pilot sprinklers

are sometimes used in place of an electrically operated heat detection system to open the deluge valve

to the nozzles. In this case, the pilot sprinklers serve only as temperature sensors and do not spray

water.

Wetting is a particular problem for filters. Unlike qualification tests for some other fire resistant materials,

the test standards used to qualify HEPA filter media do not require multiple wettings. In fact, the media

is permitted to lose up to 50% of its strength after a single 15 minute soaking period. There is no

requirement for the media to return to full strength after drying and no limitation on further reduction in

strength after subsequent soakings. Testing of both new and used filters verifies that they do lose

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