ETL 1110-3-484
26 Sep 97
10.4.3 System Arrangement. Arrange nozzle assembly control valves to minimize the time-delay
between system actuation and foam discharge from the nozzles. For most applications,
proportioners will be located downstream of alarm check valves in nozzle system risers centrally
located in fire protection equipment rooms. The foam-water solution will be supplied to
individual automatic water control (deluge) valves in the hangar area. For alteration of existing
systems where fire protection water is supplied to multiple riser manifolds within the hangar area,
it may be feasible to omit alarm check valves and supply nozzles directly from automatic water
control valves.
10.4.4 Discharge Requirement. Design nozzle systems to produce a minimum application rate of
4.1 L/min/m2 (0.10 gpm/ft2) over the under-aircraft area to be protected. This application rate is
applicable to the area beneath the wings and fuselage of the aircraft. As a practical matter, nozzle
systems cannot be designed to cover just the "shadow areas" of the aircraft. Nozzle discharges
should impact the floor in front of or beside the protected aircraft. The objective is to achieve
gentle application of foam onto burning fuel presumed to exist beneath the aircraft. Determine
the area of coverage of each nozzle and provide a flow rate that achieves the required application
rate. For example, if the discharge from one or more nozzles covers an area of 400 m2 (4300 ft2),
the flow rate of a single oscillating nozzle, or the combined flow rate of multiple fixed nozzles,
needs to be approximately 1640 L/min (430 gpm) in order to achieve the minimum application
rate.
10.4.5 Nozzle Type. Nozzles can be either fixed or oscillating type. Use fixed type nozzle
systems except in unusual situations where only oscillating type will provide the required
performance. Fixed nozzle systems are more reliable than oscillating because they are not
dependent upon water or electric-powered oscillating mechanisms to perform effectively. Also,
fixed nozzles are less suspectable to incorrect alignment after installation. Historically, oscillating
nozzles have experienced numerous problems with maladjustment. Often times, the angle of
nozzle elevation has been found changed from original setting. In some cases, this has resulted in
damage to aircraft where discharges were directed onto the protected aircraft, rather than under
the aircraft.
10.4.5.1 Fixed Nozzle Systems. Available fixed nozzles used in hangar applications have a
discharge characteristic generally less than that of oscillating nozzles. Consequently, multiple
fixed nozzles, with varying discharge rates and patterns, are typically used in a tree or manifold
arrangement. The combined flows of individual nozzles can approximate the flow of a single
oscillating nozzle. For fixed nozzle systems, use nozzles 75 mm (3 in) or less in length.
Generally, flow rates of individual fixed nozzles should be limited to 473 L/min (125 gpm) or less.
10.4.5.2 Oscillating Nozzles. Use oscillating nozzle systems only when fixed nozzle systems
cannot provide effective performance. If fixed nozzles are not used, the reasons must be clearly
addressed and substantiated in the design analysis. Where oscillating nozzles must be used,
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