Restaurant Adds Appliances to a Wet Chemical Hood System
A fast-food restaurant has a wet chemical system protecting a hood over two fryers and a griddle. The owner replaces the griddle with a larger model and adds a third fryer, and simultaneously installs a higher-CFM exhaust fan. The appliance installer tells the owner the existing suppression system is 'grandfathered' and can stay as is because the hood itself is not being changed. The hood has a listed grease duct with one elbow and a rooftop fan. The manual pull station is about 8 ft from the cooking equipment. The cylinder tag shows the last semi-annual service was 14 months ago.
1. Is the 'grandfathered' claim correct? Justify your answer.
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No. Kitchen wet chemical systems are designed from the appliance manufacturer's listed design and installation manual - nozzle quantity, spacing, aiming, and agent quantity are all tied to specific appliances, specific dimensions, and specific arrangement.
- Changing the griddle to a larger unit and adding a third fryer changes the hazard: more cooking surface, more fuel, and a different nozzle count and coverage requirement.
- The larger exhaust fan changes plenum airflow, which the design manual addresses and which affects whether the plenum nozzle arrangement still works.
- The existing cylinder was sized for the original nozzle count and appliance set. There is no basis to assume it has reserve capacity.
A hood that is unchanged does not make the system unchanged. The design basis has to be re-established, by the manufacturer's listed manual or the manufacturer's engineered design, and approved by the AHJ.
2. What must be verified or recomputed before the system is placed back in service?
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Work from the appliance cut sheets for the new griddle and the third fryer:
- Are the new appliances listed in the manual at the installed spacing from the hood and from each other? If an appliance isn't covered, the manual's rules cannot be extrapolated - get the manufacturer's engineered design or choose a covered appliance.
- Nozzle count, spacing, and aiming for the new appliance set, including maximum single-nozzle coverage and appliance-to-nozzle distance.
- Plenum and duct protection: confirm the duct nozzle and plenum coverage still comply with the added airflow; verify the fan shutdown is interlocked.
- Agent quantity and cylinder size for the new total nozzle count, plus the required spare cartridge/expellant.
- Fusible links: correct temperature ratings and locations for each appliance and for the hood/plenum, per the manual.
- Fuel and power shutoff re-verified for every appliance, including the new fryer, and for the added exhaust fan.
- Manual pull station accessibility along the egress path.
- Full functional/acceptance test of detection, actuation, agent discharge (or the manufacturer's approved test method), and shutoffs.
The technician cannot simply add nozzles in the field; any deviation from the listed manual requires manufacturer involvement and AHJ acceptance.
3. What documentation and training should accompany the work, and how do you handle the overdue service?
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Overdue service first. The 14-month gap is a deficiency in its own right. Perform complete maintenance per the standard and the manufacturer before returning the system to service, and document the gap.
Documentation:
- Revised as-builts and a new appliance inventory list showing every protected appliance and its nozzle(s).
- Agent quantity calculation for the new nozzle count.
- Functional test record for detection, discharge, and all shutoffs, signed by the installer and witnessed or accepted by the AHJ.
- Updated cylinder and system tags reflecting the new design.
- Notification to the AHJ and, where required, the insurance carrier.
Training: kitchen staff on the relocated/extended protection, the manual pull station location and use, what to do after a discharge (do not reset, call the service company, no cooking until re-accepted), and the cleaning routine that keeps nozzles and links unobstructed.