We have a 119-gallon double-wall fuel tank for our diesel fire pump.
Our tank rep believes we only need (2) vents total: (1) an emergency vent for the interstitial space and (1) a combined normal/emergency vent for the primary tank. We have received pushback that we need (3) vents: (1) normal for the primary tank, (1) emergency for the primary tank, and (1) emergency for the interstitial space. We are having difficulties finding any requirements either allowing or not the combination of the emergency and normal vent lines of the primary tank (NFPA, building code, or UL 142). Do any of you know if the combination of these vents is typically allowed? What do you typically see for the venting of a diesel fire pump fuel tank? Note, this job does fall under 2022 California Building Code, but I am still interested in what is common even outside of California. Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
5 Comments
Dan Wilder
1/24/2025 08:35:45 am
Are you speaking to the actual tank openings or how to pipe those tank openings out?
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Ken Thackery
1/24/2025 10:15:35 am
If you have a double wall tank you need 2 vents, the tank will come with 2 threaded openings. Tank size dictates vent size. We did 3 750gpm diesel pumps this year and vent size was 2", we're doing a 2500 gpm now and they're 4", due to larger tank size. The pump submittals will tell you vent size and the fuel tank will be ordered accordingly through your pump rep. Also if you go to Clark fire.com there is tool to size pump exhaust and louvers for combustion/exhaust air. note: the inner/outer wall space is very very small so it can look like there is no gap but there is.
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Jack G
1/24/2025 10:38:16 am
NFPA-20, 2019 11.4.1.6 indicates the vents for the diesel tank.
Reply
COLIN LUSHER
1/24/2025 11:31:01 am
I'm interested to see the responses here too. Most are saying only 2 vents required for a double wall tank. But I work with Patterson tanks mostly, and each tank has four (4) vent outlets; 1 main vent for inner and outer tank, and one emergency vent for inner and outer tanks. I've always piped them separately. Would love to know if any of these can be manifolded. NFPA 20 is clear that inner tank and outer tank vents cannot be manifolded, but can the main vent and emergency vents for each tank be manifolded? Four vents out the wall seems excessive.
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Todd E Wyatt
1/24/2025 02:51:16 pm
Per the "2022 California Building Code, Title 24, Part 2 (Volumes 1 & 2) with July 2024 Supplement updated", the applicable Referenced Standard is NFPA 20 - 2019 which is referenced in 412.2.4.1, 913.1, 913.2, 913.2.1, and 913.5.
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