Driving home at the end of a long day at the station, my phone rang. Looking at the incoming caller, I knew instantly that this was probably not going to be good news. I answered and heard the Fire Captain say: ‘We’ve had a foam system activation at the hangar, we need you to come and check it out.’ These are all the words that no one in this industry ever wants to hear.
The ensuing investigation determined that the system was activated due to workers welding outside of the hangar. The flame detectors had detected reflections from this welding and caused the system to activate.
There has been much written and many discussions on the fire-suppression changes addressed in the latest edition of NFPA 409. But there has been relatively little discussion on the detection requirements necessary for the operation of these systems. The requirements for foam suppression systems have been brought into question and other methods of protection are being utilized. This is primarily due to the large number of false activations that were being noticed. The foam system activates and dumps on the hangar without there ever having been a fire. This is an issue that could be tied to fire detection.
Fire-detection systems are required to be installed in all Group I, II and IV hangars, and within Group III hangars conducting hazardous operations. These fire-detection systems are required to be installed and supervised in accordance with NFPA 72. All alarms are required to be transmitted to a constantly attended location. Supplementary and low-level foam protection systems are required to activate with the primary system. For deluge systems, or closed-head sprinkler systems, listed flame or heat detectors are to be used.
Problems with detection
Aircraft hangars are unique structures. They are unique due to the value of the assets they house and protect. They are unique due to their size and configuration. And they are unique due to the types of operations that may be performed within their boundaries. The combination of these unique qualities can be problematic for fire detection.
The large size and expanse of the building leaves room for the possibility of obstructions or blind spots within the detector’s field of view. Large movable hangar doors create constantly varying conditions. Detectors must be set up to detect flames in the open and closed positions of the door. When these doors are open that allows for flames outside of the hangar to be detected. These flames can be from jet engine exhaust, blackbody radiation from other aircraft and equipment, construction or outside work being performed with an open flame source, or the detectors can become impaired from frequent and extended exposure to sunlight. Aircraft environments utilize a large amount of radio frequencies in their avionics, radar and communications. This can sometimes lead to radio frequency interference. All of these conditions could lead to a false activation of the hangar fire suppression system.
These risks demonstrate a need for more effective detection solutions. In response to these issues and in an effort to reduce and prevent false activations, the 2022 edition of NFPA 409 includes new clarifying annex information and the addition of Annex C, Type Qualification of Aircraft Hangar Radiant Energy-Sensing Flame Detectors and Controls. The purpose of this annex section is to ‘inform users about detectors and how the environment plays a role in their selection’. Included in the new annex information is clarifying guidance on how to effectively ‘reduce the probability of an inadvertent activation’. This guidance includes the following:
- The suppression system should only be activated by two or more simultaneous alarm signals.
- Flame detectors should be installed so that all areas are within the range and cone of vision of more than one detector.
- Detectors should be mounted in locations that allow for clear view under the aircraft, minimize obstructions to the field of view.
- Detectors should be aimed to ensure that they view only the area of interest and do not extend outside of the hangar.
- Flame detectors should be located at a sufficient distance from sources that could cause false alarms.
- Close attention to the manufacturers’ recommendations should be followed to reduce the effects of radar and radio frequency emissions.
In summary, this list provides guidance for what a fire-detection system must be capable of in order to avoid inadvertent system discharges and false alarms. They need to provide full coverage of the area to be protected. This would include above the aircraft, beneath the aircraft, and only within the space to be protected, not the outside areas. They need to be resistant to false-alarm sources. They need to only detect real fire within the space to be protected. Detection devices need to be resistant to radio frequency interference.
Innovative detection solutions
There are three system types that meet these criteria and are best suited for fire detection within aircraft hangars, these include multi-spectrum detectors, intelligent visual flame detection (iVFD) and the Fire Rover system.
NFPA 409 provides the recommendation that ‘multiple-spectrum optical flame detectors tend to provide the most advantageous detection and false alarm immunity characteristics’.
Multi-spectrum flame detectors utilize multiple infrared wavelengths to determine the presence of fire and differentiate flame-producing from non-flame-producing waves. False-alarm and false-fire sources can be rejected easily based on the identification of the specific wavelength energy.
Intelligent visual flame detection (iVFD) detects fire and flame using CCD sensors. This produces live video of the fire. The video processed by the CCD sensors allows for the fire’s shape, movement and growth to be analysed. This confirms that a fire is actually occurring, and aids in the elimination of false alarms and activations. An added benefit of iVFD is that the video footage is recorded and can be live streamed to an ‘operator’ for real-time viewing and fire confirmation.
Fire Rover utilizes a combination of these detection methods and tools to detect and extinguish actual fire and prevent false alarms and system activations. Fire Rover utilizes state-of-the-art thermography and video analytics to pinpoint and detect fires in their infancy and identify hotspots before flare-up. The thermal data and high-definition video are monitored in real-time by trained personnel at a central monitoring site. An added benefit of the Fire Rover system is that it also provides fire suppression. These are stand-alone units that can be deployed in a field setting or installed directly to an existing fire-protection system. The trained personnel receive the detection signal and information, they confirm whether an actual fire is occurring, and when a fire is confirmed the suppression nozzles can be remotely controlled by the operator. Fire Rover’s use of advanced analytics with human verification virtually eliminates the risk of an unintentional discharge.
The high asset value that an aircraft hangar protects demands a high level of fire protection and detection. False alarm activations, which lead to inadvertent suppression-system discharges, can no longer be tolerated within these facilities. The use and guidance of the performance-based design and risk assessment, permitted in the 2022 edition of NFPA 409, allow for the use, installation and implementation of these new technologies to better protect hangar facilities and aviation assets.
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