Fixed / Cone Roof Tanks
Top pourers and foam chambers discharging onto the liquid surface.
At a glance
- Hazard family
- Storage tanks
- Protected by
- Foam, Hydrant
- Designed to
- NFPA 11, OISD‑STD‑116, OISD‑STD‑117
- Foam application rate
- 4.1 L/min/m² of liquid surface (minimum)
Design basis
- Foam application rate
- 4.1 L/min/m² of liquid surface (minimum)NFPA 11 — fixed-roof tanks
- Discharge time, flash point 37.8–93.3 °C
- 30 minutesNFPA 11 — fixed-roof tanks
- Discharge time, flash point below 37.8 °C, or crude oil
- 55 minutesNFPA 11 — fixed-roof tanks
- Discharge outlets per tank
- 1 up to 24 m diameter; 2 to 36 m; 3 to 42 m; 4 to 48 m; 5 to 54 m; 6 to 60 mNFPA 11 — fixed-roof tanks
Standards that apply
- NFPA 11Low-, medium- and high-expansion foam.
- OISD-STD-116Fire protection for refineries and oil and gas processing plants.
- OISD-STD-117Fire protection for petroleum depots and terminals.
The risk
Under a fixed roof there is a vapour space above the liquid, and it can hold a flammable mixture. An ignition inside the tank lifts the roof — the roof-to-shell seam is built to fail first so the shell stays standing — and leaves a fire across the whole liquid surface.
A surface fire on a large tank radiates enough heat to threaten every tank around it, and with crude oil or other heavy products it carries the risk of boilover.
The scheme
Put foam onto the surface gently, and keep the neighbours cool:
- Foam chambers or pourers on the shell, with vapour seals, deflect foam down the inside of the shell so it spreads across the surface without plunging in.
- Foam solution is supplied from outside the bund, from a bladder tank or inductor.
- Water spray cools the shell of the tank on fire and the tanks exposed to it.
- Hydrants and monitors back up the fixed systems, and foam makers on the bund wall deal with any spill.
Systems that apply
Products used
Foam Equipment · 12
Foam Bladder Tank Horizontal with Ratio Controller
Horizontal, 1,000 to 15,000 litres
Foam Bladder Tank Vertical with Ratio Controller
Vertical, 200 to 7,500 litres
Foam Concentrate Tank
Atmospheric, horizontal, 200 to 10,000 litres
Foam Mixer (For fixed roof tank)
Fixed roof tanks, glass vapour seal, 50 to 150 NB
Foam Pourer Cone Roof Tank
For cone roof tanks, fixed orifice plate
Foam Pourer Floating Roof Tank
For floating roof tanks, 50 to 80 NB inlet
HOV (Hydraulically Operated Valve)
Auto open, manual close, 40 and 50 NB
Foam Inductor
Inline, 3% or 6% induction, 50 to 200 NB
Foam Nozzle
Air-aspirating, upright and pendent, K-3.0
Foam Maker (For Floating Roof Tank)
For floating roof tanks, 50 to 80 NB inlet
Foam Pourer
Fixed roof tank application, with vapour seal
Foam Bladder Tank with Ratio Controller
Vertical 200 to 7,500 L, horizontal 1,000 to 15,000 L
Spray Nozzles · 1
Sprinkler Foam-Water
Air-aspirating, upright and pendent, K-3.0
Questions we are asked
Why does foam go in through the shell, not over the roof?
Foam chambers on the shell deflect foam down the inside wall so it spreads gently across the surface. Foam dropped onto the liquid would plunge in and break down.
What does the vapour seal do?
It keeps tank vapour out of the foam line while the system is idle, and breaks under foam pressure when the system operates. It should be inspected regularly and replaced after every discharge.
How many foam outlets does a tank need?
It depends on the diameter: under NFPA 11, one outlet up to 24 m, rising to six at 60 m.
Related hazards
Projects on this hazard
- Photography to followIOTL
Foam system — IOTL
Foam based fire fighting system for IOTL at Vadinar. · Vadinar
- Photography to followAirports Authority of India
Foam system — Airports Authority of India
Foam based fire fighting system for Airports Authority of India at Kolkata. · Kolkata
- Photography to followGAIL
Hydrant system — GAIL
Fire hydrant system for GAIL at Vijaipur. · Vijaipur
- Photography to followTISCO
Hydrant system — TISCO
Fire hydrant system for TISCO at Noamundi. · Noamundi
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