The first hood system I ever tested, I pulled the manual station, heard the release click, and started writing it up. The cook walked over and asked why his fryer was still hissing. The gas valve hadn't closed. The cable was fine, the station was fine, and the valve was sitting there wide open because nobody had checked the one thing the whole system exists to do besides dump agent.
That's the real lesson of this inspection. The agent is half of it. The other half is everything the system is supposed to shut off or tell somebody about when it goes.
What you're actually inspecting
A restaurant hood suppression system is a pre-engineered wet chemical setup. A tank, a cartridge, piping up to nozzles over the fryers, griddle, range and plenum, and a release that works either by fusible links on a cable or by an electric detection scheme. The two documents you keep running into are NFPA 17A for the system itself and NFPA 96 for the hood and duct. Your AHJ may adopt different editions, so check what yours enforces.
The manufacturer's installation and service manual is the real checklist. Ansul, Kidde, Buckeye, they all differ in the details. Get the manual for the exact model on the wall. Don't work from memory.
How often
Usually every six months. Most places read NFPA 17A and 96 that way, and most insurance carriers expect it. Some jurisdictions want proof of that visit on file with the fire marshal, some don't care until a fire happens. Check your AHJ.
Longer cycles exist for the agent cylinders. Six year maintenance and twelve year hydrostatic testing come up for stored pressure wet chemical tanks, but the intervals depend on the cylinder type and the manual, so look it up for the unit in front of you.
The walk, in order
Start before you touch anything. Talk to the kitchen manager. Has the appliance line changed? Somebody swapped a six burner range for a charbroiler and nobody told the hood company, and now a nozzle is aiming at the wrong thing. That's the most common deficiency I find.
Then, roughly:
- Look at the hazard. Nozzle coverage has to match the appliances actually under the hood now, not what was there at install.
- Check nozzles for grease buildup and make sure the blow-off caps are on.
- Check the tank, the gauge or pressure indicator, the cartridge, the date on the tag.
- Replace the fusible links. Many shops do this every visit. Use the rated link for that system, because temperature rating depends on the design, and the manual lists it.
- Trip the system with a manual pull, or by cutting a link, and watch what happens.
- Confirm the gas valve closes, electric to the appliances drops, and the makeup air does what the local rules say.
- Reset, re-arm, new links, new tag.
Step six is where I got burned. Don't skip it.
What the trip is supposed to do
| Event on trip | What should happen | Pass or fail |
|---|---|---|
| Gas valve | Closes, needs manual reset | Check by hand |
| Appliance power (shunt trip) | Drops on every appliance under the hood | Verify each one |
| Exhaust fan | Keeps running | Verify |
| Makeup air | Usually shuts off, varies by AHJ | Check local rule |
| Fire alarm panel | Alarm or supervisory signal | See below |
| Fusible link count | 4 links in a typical line, all replaced | Log it |
Those numbers are what a mid size restaurant might have, not a standard. Count yours on site.
The fire alarm part
If the building has a fire alarm panel, the hood system usually talks to it through a monitor module on the release's switch contact. Whether that lands as an alarm or a supervisory is an AHJ call. Some want the whole building to evacuate when a fryer goes off, some want a supervisory so the cook isn't fighting an evacuation. I'd get that in writing before the next job.
How that contact gets wired depends on the release assembly and the module you're landing it on. I'm not going to give you terminals here, because they change by model and revision. Read the installation sheet for both devices, and treat any wiring drawing from a different job as a suggestion at best. For why the monitor circuit is supervised the way it is, end of line resistors explained covers it. Trip it from the hood side, then confirm the panel shows the right event, then confirm it clears after reset.
Don't forget the extinguisher
A Class K extinguisher should be within reach of the cooking appliances. It's a separate inspection with its own tag, so don't let the hood visit be the only time someone looks at it. There's a rundown in NFPA 10 extinguisher inspection requirements.
Paperwork that survives an audit
Tag the tank. Write the date, your cert or license number, what you replaced, what you found. If the nozzle layout didn't match the appliances, say so on the report in plain words, with a photo, and tell the owner before you leave. Don't fix a hazard mismatch by guessing. Call the manufacturer or the company that designed it.
Deficiencies get a copy to the owner and, depending on your area, to the AHJ. I keep every report. Three years later someone always asks.
I built FireDeck for the fire alarm paperwork side, so I'm biased, but the retyping of the same device list into the next form is the grind that made me do it.
Hood systems are mostly boring until the one day they aren't. Pull the station. Watch the gas valve.