Sphere & Bullet
Water spray for cooling and exposure protection on pressurised storage.
At a glance
- Hazard family
- Storage tanks
- Protected by
- Water spray, Hydrant, Water curtain, Gas detection, Flame detection
- Designed to
- NFPA 15, OISD‑STD‑116, IEC 60079‑29‑2
- Water spray on the vessel
- 10.2 L/min/m² of exposed surface
Design basis
- Water spray on the vessel
- 10.2 L/min/m² of exposed surfaceNFPA 15 — exposure protection
- Vertical supports and legs
- 10.2 L/min/m²NFPA 15
- Minimum nozzle pressure
- 1.4 bar (20 psi), unless listed for lessNFPA 15
Standards that apply
- NFPA 15Water spray fixed systems for fire protection.
- OISD-STD-116Fire protection for refineries and oil and gas processing plants.
- IEC 60079-29-2Selection, installation, use and maintenance of flammable gas detectors.
The risk
LPG and other liquefied gases are stored under pressure. A leak from a flange or valve can ignite as a jet fire, and a jet fire playing on the vessel heats the steel above the liquid level — where there is no liquid to carry the heat away. Weakened, the vessel can fail catastrophically: a boiling liquid expanding vapour explosion.
An unignited leak is dangerous too. The vapour is heavier than air, spreads low and far, and finds an ignition source somewhere else.
The scheme
Keep the steel cool, and catch the leak before it ignites:
- Medium velocity water spray over the whole vessel surface, legs and supports included, released on detection.
- Gas detection at low level around the vessels and in the drains.
- Flame detection to release the spray within seconds of ignition.
- Water curtains to disperse vapour and screen neighbouring plant, backed by hydrants and monitors.
Systems that apply
NFPA 15Fire Water Spray System
Medium and high velocity spray for vessels, transformers and process equipment.
NFPA 24Fire Hydrant System
Plant-wide ring main, hydrants, monitors and hose boxes, sized to the site.
NFPA 15Water Curtain System
Separation and exposure protection where spacing alone is not enough.
IEC 60079-29Gas Detection System
Flammable and toxic gas detection for process areas, with alarm and shutdown.
EN 54-10Flame Detection System
Optical flame detection for open process areas, fast enough to release deluge.
Products used
Deluge Valves & Systems · 9
Deluge Valve Cast Carbon Steel (Model PD-CS)
Cast carbon steel, 80 to 200 mm, 250 psi
Deluge Valve Cast Stainless Steel (Model PD-SS)
Cast stainless steel, 80 to 200 mm, 250 psi
Deluge Valve Aluminium Bronze (Model PD-AB)
Aluminium bronze, 80 to 200 mm, 250 psi
Deluge Valve Skid Cabinet
Pre-assembled and factory tested, with bypass
Deluge Valve Cast Carbon Steel (Model PD-ILV)
Inline globe pattern, cast carbon steel
Deluge Valve Aluminium Bronze (Model PD-ILVAB)
Inline globe pattern, aluminium bronze
Deluge Valve Cast Stainless Steel (Model PD-ILVS)
Inline globe pattern, cast stainless steel
Deluge Valve
Dry pilot, wet pilot and electric release
Wet Pilot Inline Deluge Assembly (Stainless Steel)
PD-ILVS with wet pilot trim, 80 to 200 mm
Spray Nozzles · 3
MVWS Nozzle Stainless Steel
Stainless steel 316, K-18 to K-102, 65° to 160°
MVWS Nozzle Brass
Brass, K-18 to K-102, 65° to 160°
MVWS Nozzle
Brass or stainless steel 316, K-18 to K-102
Strainers · 6
Fabricated Duplex Strainer
Twin baskets, cleaned without shutting down
Fabricated Basket Strainer
Top-removal basket, 2" to 24"
Fabricated Y Strainer
1" to 24", ASME Class 150 to 2500
Fabricated Tee Strainer
Graded filtration, 2" to 24", ASME 150 to 600
Fabricated Inline Strainer
Inline, 15 to 150 mm, 40 to 100 mesh
Strainer
Y-type, 1" to 24", threaded, socket weld or flanged
Questions we are asked
Why cool an LPG sphere that is not on fire?
Radiant heat or a jet fire from nearby heats the steel above the liquid, where nothing carries the heat away. Cooling keeps the steel strong enough to prevent a vessel failure.
Why are gas detectors placed so low?
LPG is heavier than air, so a leak spreads along the ground and collects in low points and drains.
Do the legs need spraying?
Yes. If the supports weaken in a fire the vessel can fall; NFPA 15 calls for them to be sprayed as well.
Related hazards
Projects on this hazard
- Photography to followTata Cummins
High velocity water spray system — Tata Cummins
High velocity water spray (HVWS) system for Tata Cummins at Jamshedpur. · Jamshedpur
- Photography to followTata Steel
Medium velocity water spray system — Tata Steel
Medium velocity water spray (MVWS) system for Tata Steel at Joda Mine. · Joda Mine
- 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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