26 Sep 97
10.3.4 Sprinkler Spacing. Space sprinklers in aircraft storage and servicing areas uniformly
throughout the protected area so spacing does not exceed 12.1 m2 (130 ft2) per sprinkler. Note:
This spacing is consistent with NFPA 409, 3-2.2.3 and NFPA 13, 4-2.2.4.
10.3.5 Design Density. Design foam-water sprinkler systems to provide a minimum discharge
density of 6.5 L/min/m2 (0.16 gpm/ft2) for the entire design area. Design for sprinkler discharge
to be uniform between sprinklers on individual sprinkler systems. Strive to limit densities to a
maximum variation of 20% above the design or minimum design density. Variation below the
minimum is not permitted. This means that where a sprinkler discharge provides a design density
of 6.5 L/min/m2 (0.16 gpm/ft2), no other sprinkler, on the same system, should provide a density
greater than 7.82 L/min/m2 (0.192 gpm/ft2). In other words, if sprinklers are spaced uniformly to
12.1 m2 (130 ft2) each, all sprinklers in the design area should discharge a minimum of 78.7 L/min
(20.8 gpm) and a maximum of 94.6 L/min (25.0 gpm).
10.3.5.1 Maximum Variation in Discharge. A specified maximum variation in discharge is a
means to quantify uniform discharge. Although this concept was originally applied to deluge
sprinkler systems where all sprinklers flow, it can also be applied to closed-head systems. While
this may seem like a questionable design requirement, particularly for closed-head systems,
significant excess discharge can unnecessarily increase water supply and AFFF concentrate
requirements. However, designers should use only reasonable conventional piping configurations
in order to satisfy this somewhat subjective design parameter.
10.3.6 Design Area. Design area is related to the total discharge from sprinklers expected to
operate in an anticipated fire scenario. Design area can be specified in terms of the number of
complete sprinkler systems expected to be actuated by a fire, or it can be specified in terms of the
floor area equating to the number of sprinklers over such an area. Design area for DoD hangar
applications can involve as many as three complete sprinkler systems or floor areas of more than
2230 m2 (24,000 ft2). The required design area will be specified in the applicable DoD criteria.
10.3.7 Sprinkler System Configuration. To facilitate limiting the maximum variation in
discharge noted above, configure piping systems to achieve a reasonably balanced discharge when
all sprinklers on a system are flowing. Among other things, this requires an evaluation of the roof
configuration and slope. For buildings with a sloped roof, for example, locating crossmains at or
near the peak of the building, with branch lines running down the slope, will result in a more
balanced system. Such an arrangement results in a pressure gain at lower level sprinklers due to
flow from higher to lower elevations. This gain will offset at least a portion of the friction loss in
the branch line, yielding similar discharge pressures between sprinklers.
10.3.7.1 Sprinkler Riser Nipples (Sprigs). Locate sprinkler branch lines close to the underside of
the hangar roof deck so maximum allowable sprinkler deflector distances can be achieved without
having to install sprinklers on individual riser nipples or sprigs as they are commonly referred to.