1. WJH FAA Technical Center John W. Reinhardt
Fire Safety Section, AAR-440 Atlantic City Int’l Airport, New Jersey 08405

2. OBJECTIVES
To 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.

3. CONSIDERATION
The 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).

4. ADOPT 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, 2000
In 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 considerations
NFPA 750 represents a significant advancement in water mist technology and the knowledge base associated with its application.

5. SCALING APPROACH
Characterize the WMS/N2 system that passed the MPS tests using the NFPA 750 standard and other techniques
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.

6. CHARACTERIZATION OF WATER MIST
NFPA 750 Section A-5-2 (Appendix A)
System Flow Rate
System Operating Pressure
General Water Requirements
Nozzle Characteristics
Nozzle Spray Characteristics
Nozzle Installation Parameters
Activation Device
General Design Parameters

7. CHARACTERIZATION OF WATER MIST (CONT.)
NFPA 750 Section A (Appendix A)
Will characterize FAA’s WMS/N2 system using the recommended method to determine the cumulative volumetric distribution of water droplets
NFPA 750 Section B-1 (Appendix B – Water Mist Droplet Size Characterization and Measurement)
If the equipment is available, will characterize FAA’s WMS/N2 system using one of the following techniques: optical imaging, diffraction, or Doppler refraction (Sauter Mean Diameter, Dv0.10).

8. CHARACTERIZATION 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 water availability.

9. NITROGEN MEASUREMENT
The 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).
COMPUTER MODELING
Task group member recommended usage of computer modeling techniques to facilitate scaling analysis using critical characterized parameters. It may be used If provided by task group member.

10. STATUS
The characterization of the FAA’s WMS/N2 has been initiated using the NFPA 750 standard.
Test fixtures to determine water mass in the fire zone is under construction
Searching for a Phase Doppler Particle Analyzer or similar equipment to measure particle size distribution and velocity of the mist on the fire zone. Anyone who owns one and is willing to share the equipment please contact John Reinhardt at or