Transition Protection
Transitions are protected at a point in the transition where the
perimeter or the diameter is equal to or less than the maximum
size duct that can be protected. The nozzle(s) must be located
in the center of the area at that point, or center of the module
protected when more than one duct nozzle is required.
Note:
Nozzles to protect ducts with a transition that is more than
4 ft (1.2 m) in height, will be required to be positioned in
the opening of the transition from the hood 2 to 8 in. (50
to 203 mm) into the opening using standard duct nozzle
design parameters.
See Figure 4-4.
FIGURE 4-4
000174
Electrostatic Precipitator Protection
Some restaurant ventilating ducts have an electrostatic precip
-
itator installed at or near the base. These precipitators are
generally small and are used to aid in the cleaning of exhaust air.
Ducts with precipitators located at or near the base can be
protected using duct nozzle(s) above the precipitator and 1/2N
nozzle(s) for the precipitator. One 1/2N nozzle must be used
for each cell being protected. This nozzle is stamped with 1/2N,
indicating that it is a 1/2-flow nozzle and must be counted as 1/2
flow number.
When protecting ducts equipped with precipitators, the duct
nozzle(s) must be installed above the precipitator and aimed to
discharge downstream. If the area above the precipitator is a
duct, the nozzle(s) must be positioned according to duct protec
-
tion guidelines. If the area above the precipitator is a transition,
the transition guidelines must be followed.
The 1/2N nozzle must be centered 10 to 26 in. (254 to 660 mm)
below the precipitator and aimed to discharge at the center of
each precipitator cell. However, if it is physically impossible to
mount the nozzle at 10 to 26 in. (254 to 660 mm) due to precip
-
itator placement, the nozzle may be mounted closer than 10 in.
(254 mm). See Figure 4-5.
* IF PHYSICALLY IMPOSSIBLE AT 10 TO 26 IN. (254 TO 660
mm
), NOZZLE MAY BE
MOUNTED CLOSER THAN 10 IN. (254
mm
).
FIGURE 4-5
000196
Note:
For protection of Pollution Control Units (PCUs) or air
scrubbers with or without ESPs, contact Technical Services for
non-UL listed recommended application.
DUCT
TRANSITION
4 FT
(1.2 m)
MAX.
DUCT
NOZZLE
SEE DUCT FOR
TRANSITION
PROTECTION
PRECIPITATOR
10-26 IN.*
(254-660 mm)
NOZZLE FOR
PRECIPITATOR
PROTECTION
SECTION 4 – SYSTEM DESIGN
UL EX3470 ULC EX3470
PAGE 4-4 REV. 11 2014-SEP-01
R-102 Restaurant Fire Suppression Manual