Design Criteria for Sprinklers in Industrial Oven?

8/6/2024

I am working on a design for a wet sprinkler system in an industrial oven. This oven has steel mandrils with fiberglass strands coated in epoxy rolled through them, heated to 350 degrees. Then, they are rolled through another machine that blows ambient-temperature air onto the mandrils to cool them down. This process forms fiberglass/epoxy-reinforced conduits.

There are (3) total exhaust ducts, one penetrating the roof and two extending 5'-0" above the top of the machine and into the open building. No dipping, flow coating, or spraying happens in this machine. Strictly heating and cooling.

I am guided by NFPA 13's rules on ducts, but I don't believe NFPA 33's design criteria would apply here. I am also guided to NFPA 13 2022 9.3.8 and A9.3.8, but I am unclear on whether 15 psi is required at each head based on the wording.

My thinking is that a 0.2 over the whole oven would be the design criteria, protecting the hazard (OH2) in a non-FM building.

What would your design criteria for this be?

Would you calculate the heads in the exhaust ducts?

Would you put heads in the exhaust ducts that don't extend through the roof or say they're protected by the overhead system?

I have my thoughts, but a lot is left up to interpretation. Thank you for any information.

P.S. in the attached file, (2) ducts that don't extend through the roof are shown as actually extending through the roof. There is a revision drawing I am waiting on.

Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe

7 Comments

Peter Howard

8/6/2024 07:43:00 am

I think you might be in NFPA 86.

NFPA 86 (2019)

9.1 General. A study shall be conducted to determine the need for fixed or portable fire protection system for ovens, furnaces, or related equipment.

9.1.1 The determination of the need for fire protection systems shall be based on a review of the fire hazards associated with the equipment.

9.1.2 Where determined to be necessary, fixed or portable fire protection systems shall be provided.

9.1.3 Written procedures shall be established outlining actions to be taken in response to an unintended fire involving an oven system.

-------

After that it basically does direct you to use the code for the type of protection system required. (Section 9.2) But I think you have to do the study to verify what that is first.

Glenn Berger

8/6/2024 08:24:18 am

Peter's answer above contains the correct path forward. Typically ovens will have fire protection installed from the mfg.

Chris

8/6/2024 08:44:05 am

I have encountered an Oven before, but it has been a long time. We had started with a dry system in the oven. The piping left the oven, ran about 20' over, and hit the DPV. We kept having tons of issues with the oven heating the air and causing unexpected over-pressurization. It was a really interesting and crazy experience... The DPV kept tripping and we couldn't figure out why? Our best guess is that the clapper got so hot that it was boiling the water on the other side, causing it to vaporize and turn into gas and dramatically increasing the pressure to the point that it tripped the valve.

There used to be a code reference that said that an oven should use a deluge valve, but I am struggling to find it now... I feel like this is a strong key, as there won't be the issue of trying to balance the pressures with this option. Also, I would maybe run it 100' or so away so that the piping can cool from the surrounding air before it hits the valve.

Also, the sprinklers themselves are stupid expensive. I recall them costing something like $600 each? I would confirm with your supplier and your estimator ASAP.

Dan Wilder

8/6/2024 10:55:54 am

With doing a similar oven for a private defense MFG creating carbon reinforced seats and helmets for aircraft, we omitted wet sprinkler protection in lieu of a dry chem within the oven due to the potential steam discharge potential (within a closed/sealed oven) and that life safety hazard to the surrounding area. The ducting was protected with a dry sprinkler system using quartzoid sprinklers. In this case with the ducting exhausting into the interior, I would still put in sprinklers for any duct between the oven and the fans at a minimum.

The overhead system extending in front of the oven was covered under a .2 density with ultra-high temp sprinklers (for any sprinkler close to duct) and high temp sprinklers extended 25' in all directions (per insurance recommendations at the time)...it may have added draft curtains around the perimeter as well, it was a while ago.

Jack G

8/6/2024 03:54:53 pm

Mfpa 86 requirements for industrial ovens and furnaces.
1. Automatic and manual fire protection systems: ( fps)
Class A&B ovens with combustible materials must have an approved automatic ( fps). Class A-B operate at near or atmispheric pressures.
Class C&D ovens should have fixed fire extinguishing system ( ffes) to protecr against hazards like overheating spills and ignition.
2. Explosion vents:
Vents should be distrubeted around the ignition source and require warning signs. Class A ovens require explosion signs.
3. Mechanical ventilation:
Class A ovens use mechanical ventilation to dilute flammable vapoes to a lwvel that is too low to ignite.
Fire protection systems for ovens are straightforward and the 4 classes of furnaces are defined to make it easier to tell the usage and whar the furnace is rated for. The systems could be wet dry preaction deluge ( open-closed heads) foam.
1964-?80 nvf furnaces that made silicon ( 4x8 ft) sheets for circuit boards. 110 feet high, like a tower. Bunch of small class A ovens each year since.
Identify your ovens, classify thecombustibles, protect per nfpa 86 and applicable phamplets for your system design

Jesse

8/6/2024 04:57:12 pm

Oh man I love questions like this one. Really gets me back to my HPR roots.

While you've made the case for a 13 design using OH2, I think you'll need to be looking at NFPA 86

David Williams

8/8/2024 04:54:53 pm

That's funny... back when I was a plant engineer, I designed an oven to incinerate the debris left on screens that create the screen pattern on the back of hardboard. (the process eliminated a dangerous boiler chemical dip process). 900 degree F.. electric elements every 6 inches to cover the 5' x 16' screens. So we were an incinerator and expected to have fire in there (although the amount of wood fiber that we were burning off was only enough to sort of smolder... we never thought about sprinklers or fire protection although the building it was in (hardboard mill) certainly had protection. Is it all NFPA 86?

Design Criteria for Sprinklers in Industrial Oven?

Leave a Reply.

ALL-ACCESS

SUBSCRIBE

COMMUNITY

YOUR POST

PE EXAM

FILTERS

ARCHIVES

PE PREP SERIES