ASHRAE Journal - February 2015 - 24

TECHNICAL FEATURE

Fire system maintenance and performance.
Specified maintenance is required by codes, standards, and listings, with minimum performance
and other checks at least every six months. Newer,
electrically supervised fire systems can alert workers
to situations that might prevent systems from functioning properly. Also, modern fan controls can be
integrated with hoods and fire systems to anticipate
hazards and disable cooking appliances before a fire
event occurs.
Hood overhang and appliance placement. Design
overhang of hood fronts and ends over appliances
must be maintained, not only to aid hood capture and
containment performance, but also to minimize fires
spreading outside hoods. From another perspective,
appliances must be located within the design hazard
zone of the fire system and properly positioned under
fire system nozzles. When appliances are rearranged,
fire system piping and nozzles must be adjusted to conform to new appliance locations, unless overlapping
coverage is provided. Full height end panels, caster
locks, caster cups, and tethers are examples of appliance
locating mechanisms.
Clearance to combustibles. Clearance issues often
cause small fires to spread and increase damage. The
most frequent non-conforming issue observed by the
author is hoods and ducts mounted without required
clearances to nearby wood construction. Clearance
requirements are contained in model codes and standards, including the International Mechanical Code®,
Uniform Mechanical Code, and NFPA 96® Standard for
Ventilation Control and Fire Protection of Commercial Cooking
Operations.
Hood and duct integrity. In some of the previous
cases, code-required integrity of Type I hoods was compromised by improper design, construction, and installation. With cooking that produces grease and smoke,
requiring Type I hoods, it is common to specify:
* Listed hoods (UL 710 - Exhaust Hoods for Commercial Cooking Equipment);
* Listed grease filters (UL 1046 - Grease Filters for
Exhaust Ducts); and
* Listed exhaust fans (UL 762 - Power Roof Ventilators
for Restaurant Exhaust Applications).
The additional specification of factory-built, listed
duct products (UL 1978 - Grease Ducts) is a means of significantly improving duct integrity.
24

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FEBRUARY 2015

Hood, duct, and appliance cleaning. Depending on
the types of cooking and foods cooked, hoods and ducts
must be frequently and thoroughly cleaned to remove
flammable grease. Cleaning should also include removal
of grease from inside and around appliances. Hoods and
ducts over appliances with solid fuel cooking need more
frequent and aggressive cleaning to remove flammable
creosote as well as grease. Hoods are available with
daily self-cleaning functions for the hood plenum and
duct, and there is a professional organization that certifies commercial kitchen exhaust system cleaners and
supervisors.
Electricity and grease don't mix. When grease from
cooking deteriorates, its auto-ignition temperature
decreases as it carbonizes and becomes conductive.
This can lead to grease ignition in electrical connections and receptacles, and hood fire suppression
systems might not protect cramped areas behind
appliances.
Exhaust fan maintenance. Exhaust fan operation
is important; specified airflow carries heat toward
fire detectors, as well as grease into filters and other
cooking emissions out of the facility. Broken exhaust
fan belts are common, and preventive maintenance
should include periodic installation of new belts.
Exhaust air proving controls are recommended to
ensure that exhaust fans are running and exhaust air
is moving.
Solid fuel cooking. Reference 6 suggests, "Solid
fuel appliances dial up the threat with the addition of
highly combustible materials." While nearly all cooking releases grease particles and vapors from foods,
leading to deposit in hoods and ducts, solid fuels also
produce embers and creosote. With or without grease
deposits, creosote fires can ignite in hoods and ducts,
possibly above the position of conventional fire suppression system detectors. Also, conventional fire suppression systems have a fixed volume of suppressant
and they discharge the suppressant for a limited time-
in the range of 45 to 60 seconds. This time may be
insufficient to extinguish fires and prevent re-ignition,
particularly in burning hoods and ducts with creosote
deposits.
For solid fuel cooking, the author suggests that
designers and engineers consider specifying the latest
technology for commercial kitchen fire suppression
systems, such as systems with electronic monitoring

ASHRAE Journal - February 2015

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