3OBJECTIVESTo determine the critical parameters required to scale a water mist system combined with nitrogen, used as an aircraft cargo compartment fire suppression system that have met the MPS.
4CONSIDERATIONThe scaling consideration of the water mist/N2 fire extinguishing system is for cargo compartments of volume sizes of 719 ft3 (298 in x 125 in x 42 in) and 6252 ft3 (590 in x 164 in x 80 in).
5SCALING APPROACHCharacterize the WMS system that passed the MPS tests using the NFPA 750 standard.Characterize nitrogen system.Use defined system parameters and transpose them to different scale cargo compartment, paying close attention to the vertical plane (z-axis). Adjust system as needed in scaled compartment to provide same critical parameters values.
6CHARACTERIZATION OF WATER MIST (CONT.) Water collection (mass flow) on a 18” by 18” pan located on the fire zone at 36” above the cargo compartment floor in order to determine the amount of water wetting the defined combustible surface.
7ADOPT NFPA 750 – STANDARD ON WATER MIST FIRE PROTECTION SYSTEMS This NFPA document was prepared by the Technical Committee on Water Mist Fire Suppression Systems and acted on by the National Fire Protection Association, Inc. on November It was issued by the Standards Council on January 2000, with an effective date of February 11, 2000In developing this standard, the committee addressed system components and hardware, system types, installation requirements, design objectives, hazard classifications, calculations, water supplies, atomizing media, plans, documentation, acceptance criteria, and maintenance considerationsNFPA 750 represents a significant advancement in water mist technology and the knowledge base associated with its application.
8CHARACTERIZATION OF WATER MIST NFPA 750 Section A-5-2 (Appendix A)System Flow RateSystem Operating PressureGeneral Water RequirementsNozzle CharacteristicsNozzle Spray CharacteristicsNozzle Installation ParametersActivation DeviceGeneral Design Parameters
9NITROGEN MEASUREMENTThe measurement of the nitrogen volumetric concentration, in the scaled cargo compartment, will be achieved by determining the oxygen volumetric concentration in the hypoxic condition (using gas analyzers). The time to reach an inert condition with nitrogen will also be considered during the scaling of the system.
10I. SYSTEM FIRE PERFORMANCE OBJECTIVE - Fire Suppression CHARACTERIZATION OF WATER MIST/N2 SYSTEMI. SYSTEM FIRE PERFORMANCE OBJECTIVE - Fire SuppressionII. WATER MIST SYSTEM (NFPA 750 – Standard on Water Mist Fire Protection Systems) – The Environmental Engineering Concepts water mist system was a balanced high-pressure, Class I system (i.e., at least 10% of the spray is less than 200 microns).
11II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)1. System Flow Rate (Minimum and Maximum)a. Flow rate – from 0.54 gpm (1 zone activated) to 1.84 gpm (4 zones activated)b. Flow rate per unit area – lbs/min*ft22. System Operating Pressure (Minimum and Maximum)a. Nozzle operating pressure range - from 550 psig (4 zones activated) to 1150 psig (1 zone activated).b. Pump/cylinder operating pressure range – for pump model Giant P217A the inlet pressure is up to 90 psig and the discharge pressure is up to 2500 psigc. Pump inlet and outlet pressure and flow rate requirements – the inlet pressure is from 20 (minimum) to 90 psig (maximum), the discharge pressure is up to 2500 psig (1250 psig used during the fire tests), the pump will produce a volume of up to 3.36 gpm.
12II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)3. General Water Requirementsa. Quantity/duration – 9 gallons (continuously discharging for 5 minutes)b. Quality – Special consideration should be given to the quality of water that will flow through the water mist system. Water with total dissolved solids (DS) counts of greater than 500 parts per million (ppm) or water with high calcium carbonate levels or PH levels above 7.5 may not be satisfactory and could lead to excessive nozzle blockage and nozzle maintenance.c. Temperature – Above freezing point, preferable at standard room temperature. The pump relies on the water running through it to keep it cool.d. Pressure – Correct water pressure and supply rate is essential to the pumps operation. The water supply pressure must be maintained between a minimum of 20 psi and a maximum of 90 psi to operate the pump.
13II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)4. Nozzle Characteristicsa. Type(s)/model numbers – EEC/MicroCool nozzle, nozzle orifice is " (0.63 mm) in diameterb. Flow rate (minimum and maximum) – gpm to 0.23 gpmc. Operating pressure (minimum and maximum) – 1025 psig to 1150 psig5. Nozzle Spray Characteristicsa. Spray angle – 27º, nozzle pointing down verticallyb. Drop size distribution – Droplet sizes range from 70 to 100 microns (Class I), provided by manufacturer. No access to PDPA systemc. Momentum/velocity – 3.89 feet per second (obtained by using high speed film)
14II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)6. Nozzle Installation Parametersa. Distance above floor – 65" above floorb. Distance below ceiling - 1" below ceilingc. Distance above hazard – (i.) For bulk load test – 29" above hazard, (ii.) For containerized test - 1" above hazard, (iii) For surface burn test - 11" above hazard(minimum and maximum), and (iv) for aerosol can explosion test - 41" above hazard.d. Nozzle spacing - 16" between nozzles (8 nozzles per zone)e. Zone spacing - 30" between zonesf. Orientation – nozzles pointing down verticallyg. Minimum distance from walls and obstructions – Atomization nozzles should never be pointed towards and allowed to spray on any close object or surface otherwise the fog will condense; a distance of 18" to 24" should be preserved. Use a nozzle plug to block off the fog if this cannot be avoided.
15II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)7. Activation Devicea. Type/model number – Manual activationb. Activation, temperature – 1 minute after ceiling temperature reached 200ºF8. General Design Parametersa. Pipe requirementi. Size – 3/8” diameter stainless steel tubingii. Operating pressures – up to 2500 psig b. Fittingsi. Type – compression fittings ii. Operating pressure – up to 2500 psig
16II. WATER MIST SYSTEM (CONT.) CHARACTERIZATION OF WATER MIST/N2 SYSTEMII. WATER MIST SYSTEM (CONT.)8. General Design Parameters (Cont.)c. Pumpsi. Valves, fittings, and filters – drain valves, NPT type fittings (with swivel), twin filter components of 10 and 5-micron unitsii. Power requirements – 120 Vac (Motor), 24 Vdc (Relays)iii. Operating pressure and flow rates – See Section 2.c System Operating Pressureiv. Water requirements – See Section 3. General Water Requirements
17III. NITROGEN SYSTEM CRITICAL PARAMETERS CHARACTERIZATION OF WATER MIST/N2 SYSTEMIII. NITROGEN SYSTEM CRITICAL PARAMETERS1. Cylinder valves and fittings – Two Matheson 3020 Series Regulators, CGA 580, with a maximum inlet pressure of 3500 psig, and a flow rate of CFM (at 500 psig) per regulator.2. Cylinder capacity – 16 High Pressure Size T cylinders, 1.73 ft3 each3. Cylinder operating pressures – 2500 psig4. Volumetric Concentration – 90% N2 in air5. Flow Rate – initial rate at 500 psig was CFM (average = CFM)6. Time for Initial Protection – an average of 12.5 minutes7. Fire/Explosion Protection Time – 180 minutes (infinite if OBIGSS system used)
18TC-10 CARGO COMPARTMENT (2000 FT3) CHARACTERIZATION OF WATER MIST/N2 SYSTEMTC-10 CARGO COMPARTMENT (2000 FT3)WMS/N2 INSTALLATION
19CHARACTERIZATION OF WATER MIST/N2 SYSTEM TC-1013 Zones/95 Nozzles
20B-737 CARGO COMPARTMENT (719 FT3) CHARACTERIZATION OF WATER MIST/N2 SYSTEMB-737 CARGO COMPARTMENT (719 FT3)WMS/N2 INSTALLATION
21CHARACTERIZATION OF WATER MIST/N2 SYSTEM B-7379 Zones/72 Nozzles
22B-777 CARGO COMPARTMENT (6252 FT3) CHARACTERIZATION OF WATER MIST/N2 SYSTEMB-777 CARGO COMPARTMENT (6252 FT3)WMS/N2 INSTALLATION
23CHARACTERIZATION OF WATER MIST/N2 SYSTEM B-77725 Zones/180 Nozzles
25WATER COLLECTION TEST RESULTS Placed 18”x18” pan on scaleCollected weight samples every 30 secondsCollected samples for 5 minutesRan tests 10x per cargo size
26TC-10 WATER COLLECTION TEST CHARACTERIZATION OF WATER MIST/N2 SYSTEM 1 Zone/8 Nozzles On
27B-737 WATER COLLECTION TEST CHARACTERIZATION OF WATER MIST/N2 SYSTEM 1 Zone/8 Nozzles On
28B-777 WATER COLLECTION TEST CHARACTERIZATION OF WATER MIST/N2 SYSTEM 1 Zone/8 Nozzles On
29TC-10 Class E WATER COLLECTION TEST CHARACTERIZATION OF WATER MIST/N2 SYSTEMWATER COLLECTION TESTTC-10 Class E1 Zone/8 Nozzles On
30CHARACTERIZATION OF WATER MIST/N2 SYSTEM 3.8 lbs1.5 lbs1.4 lbs0.9 lb
31The NFPA 750, Standard on Water Mist Fire Protection, provides an excellent guideline to characterize an aircraft cargo compartment water mist fire suppression system.The water collection test provides a simple and inexpensive method to determine the amount of water available on the combustible surface. This water, accumulated on the surface, cools the burning surface and provides liquid for oxygen dilution during the fire suppression process. This test does not provide particle size distribution, flux density, nor spray momentum, but it offers a quick and an inexpensive way to compare the WMS/N2 system in various compartment sizes.
32After performing the water collection test on the WMS/N2 system in the B-737 and B777, it was observed that the water accumulated in the pan was the same or was more than the water accumulated during the TC-10 test.The above statement can not be made for the TC-10 Class E compartment. The amount of water accumulated on the combustible surface needs to be increased; this can be achieved by reconfiguring the installation or adding more zones.