ASHRAE Journal - June 2014 - 53

Technical FeaTure
Fea

alkali and animal or vegetable fats, which with heat,
produces a soapy foaming action that reduces the temperature of the fuel below its auto-ignition temperature.
An engineer from the cooperating restaurant chain
worked with the largest manufacturer of wet chemical
systems to verify satisfactory performance during test
fires in samples of the chain's custom-made fryers.

Impact of UL Standard 300

Hybrid Systems: Wet Chemical and Water
Hybrid systems are very similar to wet chemical systems in terms of suppressant piping, nozzles, blow-off
caps, detectors, gas cartridges, agent tanks, cable, piping,
and pulley elbows. The difference is that the tank valve
is changed to allow the wet chemical to discharge to the
hazard area first, and then the valve automatically allows
potable water to flow through agent piping and nozzles.
The water is provided by the facility's potable water supply, or by means of an optional water tank, with a lockable (open) valve to ensure a continuous supply of water.
Accessories are the same as for wet chemical-only systems.
Coinciding somewhat with the introduction of these systems, overlapping designs of pipes and nozzles were introduced as alternatives to customary appliance-specific pipe
and nozzle designs. Appliances could then be changed or
rearranged under the hazard zone, without the need for
moving pipes and nozzles. Depending on local jurisdiction
requirements, dedicated piping and
nozzle protection might be required
for appliances such as upright broilers,
"salamander" over-fired broilers, and
chain broilers because these appliances
are generally not open on top to allow
the downward flow of wet chemicals
and water.

UL Standard 300 was published in 1992, and it became
effective in 1994. The standard covers the fire testing of pre-engineered fire extinguishing systems with
commercial cooking equipment. Among other revised
requirements, the fryer reignition issue spurred inclusion of more rigorous tests for fryer fires, and it recognized the transition from animal fats to vegetable oils
with higher auto-ignition temperatures.
To improve test pre-conditions, there were several
revisions, including:
* Changing the test appliance from
a fabricated pan simulating a fryer,
to a commercial fryer with specified
heating and cooling rates;
* Changing pre-burn after auto-ignition from one minute to two minutes;
* Revising the fryer condition during pre-burn from fuel-off to fuel-on;
Figure 2: Wet chemical system release assembly
Electronically Operated Fire
and
cabinet and agent cylinder.
Suppression and Hood Cleaning System
* Specifying a minimum grease
The newest type of fire suppression
auto-ignition temperature for cooking
system builds on the experience gained from earlier
oil of 685°F (363°C).
systems, with notable advances. These systems combine
Changes in the overall test requirements included:
* Flames in the appliance must be completely extin- electronic fire detection and microcomputer controls to
guished upon complete discharge of the extinguishing perform appliance, hood plenum, and lower duct fire
suppression.
agent;
When fire is detected, unlimited cold potable water is
* For deep fat fryers, woks, and ranges, the system must
not permit reignition of the grease or cooking oil for 20 sprayed for a preset time through hood, duct, and appliminutes, or until the temperature of the grease or cooking ance nozzles, with overlapping coverage. Detergentoil decreases at least 60°F (15°C) below its observed auto- based surfactant is injected continuously to lower the
surface tension of the water, allowing it to more quickly
ignition temperature, whichever is longer; and
* For all appliances other than deep fat fryers, woks, coat the burning fuel and enhance its cooling properties
and ranges, the system must not permit reignition for to help prevent reignition.
A significant advance with these systems is use of
five minutes.
UL-listed electronic fire detectors to sense both the
All UL-listed fire suppression systems were required to
temperature and the rate of temperature rise, either
be retested to UL 300. Dry chemical systems were no lonof which can trigger activation. The standard temperager compliant with UL 300, and all wet chemical systems
ture setting is 360°F (182°C) and other temperatures
required modifications to meet the UL 300 Standard.
J u n e 2014

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