High expansion foam for DOD aircraft hangars revisited
In January 2014, the accidental activation of a high expansion foam system in King Aircraft Hangar at Eglin Air Force Base in Valparaiso, Fla,. resulted in the death of a civilian contractor (see my April 2014 column). This fatal accident, along with several other accidental discharges at Air Force hangars, resulted in a worldwide survey/evaluation of existing Air Force hangar fire protection systems. We have not seen any official reports yet. However, based on recent changes in project work scopes, it appears results of some sort are in. These changes are revisions to be made to "ETL 02-15 Fire Protection Engineering Criteria - New Aircraft Facilities, dated December 3, 2002."
This column will present some of these proposed criteria. Now, it is time for the obligatory disclaimer. If you are currently involved with or planning to be involved with the design of a high expansion foam system for an Air Force aircraft hangar, please confirm the applicable criteria with the government project manager or the AHJ.
There are some interesting aspects about the new criteria. The first is that it borrows heavily from concepts and components used by the Navy in their criteria for AFFF systems for aircraft hangars (see November and December 2012 columns).
The second is the requirement that several of the components be proprietary. Let us look at some of these changes.
No more bladder tanks
Foam concentrate storage tanks are required to be vertical, double-walled, high density cross-linked polyethylene storage tanks. This is definitely a good move. Bladder tanks were often used as an alternative to highly unreliable foam concentrate pumping systems. The next change described below eliminates that reason. Bladder tanks also required highly specialized care during maintenance; a skill I have yet to see at many DOD installations.
Foam proportioning by inductor
Foam proportioning must be by a single foam inductor for each foam-water riser. Inductor must be one manufactured by Viking Fomtec or an Air Force approved equal (no such thing).
Use of flow control valves
The foam deluge valve must be a Viking J-1 Flow Control Valve with trim package for electric releasing, remote re-setting, and opening/closing speed control. Use of any other flow control valve requires approval from the Air Force (good luck on that).
Foam discharge stop stations
Provide foam stop stations of the "dead man" type. The stop stations must be used in conjunction with valves and equipment that will prohibit or stop the discharge of foam/water from the foam suppression system, i.e., the Viking J-1 Flow Control Valve or “approved equal” (again, good luck on that). A manual foam stop station will be provided at the location of each manual foam releasing station. Once depressed, and so long as the button is held down, the stop station will prevent/stop discharge from the foam system regardless of whether or not the foam system was activated automatically or manually, and whether or not the activation occurred prior to, or after the stop station was pressed and held. When the foam stop station button is depressed under full flow, the time to fully close the flow control valve will not exceed 15 seconds.
The 15-second limit is a measure implemented because of the Eglin accident. An abort capability was provided in the Eglin hangar, but it required the station to be operated for 90 seconds to close the valve. The station was operated during the incident, but not long enough before the operator felt a need to evacuate. Hence the discharge was not stopped. The abort station will be identified by a sign which will have a white background with a minimum 1/2-inch-wide blue border with “STOP FOAM SYSTEM” in blue lettering not less than three inches high. The manual stop station will require a tamper cover and will be located on the lower center portion of the sign. The word “STOP” will be written in minimum one-inch-high red lettering placed directly above the manual stop station.
Rated fire pump pressure limitation removed
The maximum rated fire pump size of 2,500 gpm has not changed, but the maximum permitted pressure rating of 125 psi has been removed. This is a very good idea. Given high pressure losses through the foam inductor and flow control valves, it may be difficult to limit the pump-rated pressure to 125 psi.
No pre-primed systems
Pre-priming of any foam solution piping is not permitted. All solution piping must be sloped to be self-draining back to the riser.
A proprietary Foam System Control Panel (FCSP)
The FSCP must be Det-Tronics Eagle Quantum Premier Fire Detection/ Releasing System, equipped with redundant controllers and furnished complete with minimum 60-node Safety Systems Software (S3). FSCP alarm, supervisory and trouble signal reporting to the Fire Alarm Control Panel must be via discrete dry contact output points.
A return to a requirement for optical flame detection
Optical flame detection will be the X3301 Multispectrum IR Flame Detector manufactured by Det-Tronics. Optical flame detection system will use triple infrared (IR) flame detectors listed/approved for the expected fuel hazards in the hangar bay. It appears that the purpose of the triple IR optical detectors is to be cross-zoned with the water flow or pressure switch in the sprinkler system in order to activate foam discharge. ETL 02-15 currently requires only operation of the water flow or pressure switch of the wet pipe or pre-action sprinkler system serving the hangar bay in order to initiate foam discharge. This modification is the single most important change in terms of limiting accidental system discharges. The Air Force appears to have finally realized that reliance on a sprinkler water flow alone was not a good idea. Now that optical detection is back in the Air Force hangar fire protection repertoire, they may wish to consider using triple IR for foam discharge activation (as the Navy does) and eliminate the water flow alarm switch activation from the equation. By requiring detection by at least two or three optical detectors, one achieves a dramatic increase in time to extinguish (you do not have to wait for ceiling level sprinkler activation), while minimizing chances of a false activation.
Provide blue beacons not less than 400 cd (208/120VAC) powered from a dedicated emergency. The FSCP will control beacon initiation.
Electrical installation changes
All fire alarm circuiting in the hangar bay must have watertight conduit/connections and NEMA 4X junction boxes, back boxes and enclosures. Initiating devices such as start stations, stop stations and flame detectors requires conduit to enter the bottom of the back box, and the low point of the conduit will be provided with a drain. Where the conduit is in a hazardous classified area, breathers shall be provided in isolated portions of the conduit (i.e., sealed off from the remaining conduit system). Drains and breathers shall be rated for the hazardous classification in which they are installed, but shall not be less than NEMA 4X. This change will reduce the false discharges occurring as the result of water from leaky roofs entering raceways and shorting out devices.
Location of addressable devices
Install releasing modules and monitor modules integral to the release of the foam system in a normally occupied, conditioned space within the building. This revision appears to come from Air National Guard, who learned the lesson that electronic devices can get flaky when used outside of their recommended temperature and humidity ranges.
Surge Protection Devices (SPD)
Provide SPD to protect all power supply circuits to FACP and FSCP panels. Provide SPD to protect all fire alarm circuits leaving or entering the building. Devices mounted on an exterior wall do not require an SPD when lighting protection is provided on the building. SPDs are intended to minimize the potential for “phantom alarms” resulting from surges.
I do not think there is any way to completely prevent accidental foam system discharge without rendering the system useless for protection of aircraft. These measures are good changes, and will significantly reduce false discharges, improve system stability, reliability and maintainability. n
Samuel S. Dannaway, PE, is a registered fire protection engineer and mechanical engineer with bachelor’s and master’s degrees from the University of Maryland Department of Fire Protection Engineering. He is past president and a Fellow of the Society of Fire Protection Engineers. He is president of S. S. Dannaway Associates Inc., a 15-person fire protection engineering firm with offices in Honolulu and Guam. He can be reached via email at SDannaway@ssdafire.com.