LNG (-162 C methane) storage tanks are designed per NFPA 59A and EN 1473 for fire and BLEVE risk. Full containment tanks use 9 percent Ni steel inner and pre-stressed concrete outer wall to contain leaks and radiation. FSRU, LNG terminals and peak-shaver plants follow the same principles.
Tank Types
- Single containment: single wall + external bund - legacy design
- Double containment: two tanks, outer holds liquid only
- Full containment: outer tank holds both liquid and vapor (modern)
- Membrane: Invar wall + concrete shell (GTT)
- Cover: concrete dome - radiation shield
BLEVE and RPT Risk
- BLEVE: pressurized liquid explosion - low for atmospheric LNG
- RPT (Rapid Phase Transition): LNG-water contact - physical explosion
- Pool fire: liquid pool fire - SEP 220 kW/m2
- Flash fire: vapor-cloud ignition - low overpressure
- Rollover: stratification breakdown - sudden flash
Impoundment Area
180,000 m3 tank, 100 percent capacity impoundment:
- Concrete bund height: per liquid volume
- Distance: tank half-diameter + 15 m
- Insulating concrete: -162 C durability
- Drainage: rainwater drain auto-valve
- Vapor fence: 4 m height, flame trap
Firewater System
- Deluge: tank shell 10.2 L/min/m2 (NFPA 15)
- High-expansion foam: vapor suppression, 1000:1 expansion
- Monitor: 4,000 L/min, 60 m range
- Dry chemical: 3,000 kg PKP for methane jet
- Water pond: 12,000 m3 seawater reservoir
Vapor Cloud Analysis
- Dispersion: PHAST, FLACS CFD modeling
- LFL: 5 percent (50,000 ppm)
- Hazard distance: 1/2 LFL boundary
- Exclusion zone: NFPA 59A Part 5 - no occupancy
- Flammable vapor fence: delay and dilution
LNG tanks with SprinkCalc
SprinkCalc computes LNG deluge design, impoundment sizing, firewater flow and vapor-cloud exclusion zone per NFPA 59A / EN 1473.
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Sources & Further Reading
NFPA 59A, EN 1473, SIGTTO, API 625, IGC Doc 03/17. NFPA 59A LNG code.