Since the entirety of fire sprinklers systems normally depend on heat to actuate a sprinkler – it is an important topic.
Before I ever started in shop drawing design. I prepared bid packages that specified important aspects of system design. One of the luxuries of living on the front-end (some say "theoretical") side of design was delegating the sprinkler temperature selection.
Selecting appropriate sprinkler temperatures is not difficult. That said, making an egregious error with a temperature too low could cause an inadvertent discharge. Considering how much damage this could do, there’s quite a bit of liability there.
Temperature is one of the three concepts I look to address when designing sprinkler systems in commercial kitchens.
Consideration #1: Heat
In high school I worked a few years in a kitchen. I hated it. It was stressful, always hot, and the cook line seemed to play the same six songs on repeat.
Even now when I hear The Hand that Feeds by Nine Inch Nails, my palms start to sweat. I get thrown back to that smoky, steamy kitchen and getting yelled at for bringing out entrees while the salad course wasn’t finished. Despite it being in a country club, it was awful.
Maybe I’m sensitive (if not dramatic), but when I design sprinkler systems for kitchens I’m acutely aware of how hot those spaces can be.
We want sprinklers to operate early enough in a fire when they can be effective. We also don’t want unintentional activation with a temperature too low.
NFPA 13 directs sprinklers to be ordinary or intermediate temperature unless specific heat-producing sources or hazards exist.
For commercial cooking equipment, if a sprinkler could experience ceiling temperatures over 100 degrees F (38 C), then they must at least be intermediate temperature (NFPA 13 2002-16 220.127.116.11, 2019 18.104.22.168).
I’ve never measured temperatures on the cookline but I would suspect this would be easy to achieve.
NFPA 13 also directs temperature selection to be based on nearby heat sources (in 22.214.171.124 2002-16, 126.96.36.199 2019).
NFPA 13 identifies temperature guidance for similar residential heat-producing sources. Sprinklers located 9 to 18 inches from a kitchen range, for instance, should be intermediate-temperature. Sprinklers 18 inches or more away from a kitchen range can be ordinary-temperature. Wall ovens have the same rules.
I've often located sprinklers within the center of cooklines as intermediate-temperature sprinklers. This allows a little grace from the edge of heat-producing sources. I'll then check specific appliances for anything that could cause higher temperatures and adjust accordingly.
Kitchen hoods that would otherwise form large obstructions can be excluded from sprinkler protection
when they contain a separate fire extinguishing system.
Consideration #2: Spacing Near Hoods
Exhaust hoods are required above cooking equipment that produces grease-laden vapors. NFPA 96 goes further to require that the equipment and exhaust system must also be protected.
One way to achieve this requirement is by sprinklers, but this method is rare. Pre-engineered wet chemical systems are designed specifically for cooking hazards. They are also often supplied directly with hood equipment.
If a fire extinguishing system is a part of the hood, NFPA 13 relaxes nearby sprinkler protection:
NFPA 13 188.8.131.52 (2007-2013), 184.108.40.206 (2016), 220.127.116.11 (2019) Hoods containing automatic fire-extinguishing systems are protected areas; therefore, these hoods are not considered obstructions to overhead sprinkler systems and shall not require floor coverage underneath.
NFPA 13 18.104.22.168 (2007-2013), 22.214.171.124 (2016), 126.96.36.199 (2019) Cooking equipment below hoods that contain automatic fire-extinguishing equipment is protected and shall not require protection from the overhead sprinkler system.
In regards to sprinkler spacing, the front-edge of a protect exhaust hood is essentially a solid wall.
If portions of a hood are not protected, the hood would be considered an obstruction and coverage would need to be provided below the hood.
Consideration #3: Obstructions & Conflicts
Commercial kitchens are often tightly-designed areas intended to maximize the preparer’s efficiency. End result: high-density of equipment and appliances in small areas.
This is the case along the ceiling as well. Lights, diffusers, and sprinklers become secondary and must shift to the narrow remaining ceiling. With hoods and the need for cooling comes large ductwork. These can limit the pipe layout serving sprinklers in kitchens and requires careful coordination.
It’s not always easy to tell from plans, but floor-to-ceiling storage is common.
Reflected ceiling plans often show a continuous ceiling between one cookline and its adjacent counter. However, there are often heat lamps, pot and pan storage, and a myriad of boxes and other food supplies stored above head height to the ceiling.
I try to space sprinklers in these areas directly above walking spaces that can tolerate storage in-between the cooklines.
What has been your experience with suppression systems for commercial kitchens? What challenges have you come across? Let us know here.
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Joseph Meyer, PE, owns/operates his own Fire Protection Engineering practice in St. Louis, Missouri. See bio on About page.