Gavelli_edit.qxp 1/7/09 3:34 pm Page 88
Liquefied Natural Gas Explosion Hazards – Are They Real?
• a pressure vessel containing a liquefied gas, or low-boiling-point set by the local fire departments as evidence of the BLEVE hazard of
liquid, is exposed to intense heat from the outside; LNG. However, the evacuation areas were simply set in accordance
• the vessel insulation is absent or compromised; with the recommended distances for emergencies involving storage
• the liquid is heated up and the vapour pressure rises to the set tanks for any number of flammable gases involved in a fire,
23
and the
point of the relief system; fact remains that none of these accidents resulted in a BLEVE. This
• the vapour generation rate exceeds the flow rate through the demonstrates that the US-regulated double-shell tanker truck design
relief system; can withstand these types of accident.
• the vessel wall in contact with the vapour inside the vessel
weakens with exposure to high temperatures; and The Tivissa accident has triggered arguments that BLEVEs may also
• the vessel bursts, releasing the vapours. occur on LNG vessels.
24
As described earlier, a BLEVE requires heat
to be applied to a tank (e.g. from an external fire) of sufficient
During a BLEVE, the containment vessel may break into several intensity and duration to heat up the liquid inside the tank and
fragments, which may then be projected at a significant distance increase the vapour pressure at a rate that will overwhelm the
(depending on the pressure reached within the vessel prior to pressure relief and lead to failure of the tank. Given the large volume
failure); if the vessel contents are flammable, a fireball, flash fire or of LNG stored in an LNG carrier tank, the thick insulation and
vapour cloud explosion may also occur. multiple physical barriers (e.g. double hull, insulation, LNG tank
shell, etc.) that would protect the LNG cargo from an external fire, a
The possibility that BLEVEs may occur in LNG storage vessels has scenario that may lead to a BLEVE on an LNG carrier does not appear
been argued on several occasions with reference to LNG tanker credible. Furthermore, one must remember that the maximum
trucks and marine LNG tankers. To date, only one accident has been allowable pressure for LNG carrier tanks is in the order of 0.3 bar;
recorded in which an LNG tanker truck is widely believed to have therefore, even if the vapour pressure inside the LNG tank were to
suffered a BLEVE: on 22 June 2002 in Tivissa, Spain, a truck carrying exceed the strength of the tank, the strength of the explosion would
LNG rolled over, causing a portion of the LNG tank insulation to be minimal. The BLEVE potential of an LNG vessel subjected to a
become dislodged; a fire immediately started outside the LNG tank hypothetical ‘serious pool fire’ was analysed quantitatively by
and, approximately 20 minutes later, a small explosion occurred Pitblado, who concluded that “while tank failure is possible, it would
followed by a larger explosion.
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The truck driver was killed and not give rise to a major BLEVE”, and that the potential impact from
fragments from the truck were projected up to 257m away. The such a BLEVE would be “well below the scale of the initiating pool
strength of the explosion was calculated to be approximately 75kg fire event”.
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of TNT-equivalent. It should be pointed out that even though the
Tivissa accident is consistent with a BLEVE, there is no general Summary
agreement that this is indeed what happened. Even though the The general categories of severe explosion hazards most frequently
Major Hazardous Incident Data Service (MHIDAS) database did not used to oppose the siting of LNG facilities, onshore and offshore,
record the Tivissa accident as a BLEVE, LNG risk assessment experts have been reviewed. Given the large number of LNG terminals being
such as Pitblado accepted “that this had features of a classical BLEVE debated, and the even greater number of statements (through
and that there is no inherent property of LNG excluding BLEVE-like public comments to regulatory agencies, newspaper articles, blogs,
events”
22
although, as Pitblado points out, “US LNG trucks would be etc.), this review was not meant to be exhaustive but, rather, aimed
safer due to design features” including a double shell with insulation at grouping some of these arguments into a small set of
and structural supports in between. encompassing scenarios and to evaluate them based on publicly
available peer-reviewed scientific literature. Through this process,
Other road accidents involving LNG trucks (e.g. the 2006 truck known hazards (e.g. confined VCEs) have been recognised as such,
rollover in Massachusetts, and the LNG leak from a truck resulting in and have been separated from those hazards (e.g. unconfined
a fire in Nevada in 2005) have been mentioned as BLEVE ‘near flammable VCEs or floating bomb scenarios) for which there is no
misses’, using the wide evacuation areas (in the order of one mile) scientific supporting evidence. ■
1. Angela P, Pinna L, La Sfida del Secolo, Milano, Italy: Arnoldo 11. Cleaver RP, Cumber PS, Genillon P, A model to Predict the experiments and modeling, J Haz Mat, 2006;A132, pp. 119-
Mondadori Ed., 2006. Characteristics of Fires Following the Rupture of Natural Gas 140, 2006.
2. Bull DC, Elsworth JE, Hooper G, Quinn, CP, A study of Transmission Pipelines, Trans IchemE, 2001;79(Pt B):4. 18. Lovins AB, Lovins HL, Brittle Power, Andover, Massachusetts:
spherical detonation in mixtures of methane and oxygen 12. Bartenve AM, Gelfand BE, Makhviladze GM, Roberts JP, Brick House Publ. Co., 1982, chapter 8.
diluted by nitrogen, J Phys D: Appl Phys, 1976;9:1991–2000. Statistical Analysis of Accidents in the Middle Asia-Centre Gas 19. ‘Little Boy’, the atomic bomb exploded over Hiroshima, Japan
3. Cleaver P, Johnson M, Ho B, A summary of some experimental Pipelines, J Haz Mat, 1996;46:60–65. on 6 August 1945, was approximately equivalent to 15
data on LNG safety, J Haz Mat, 2007;140:429–38. 13. NTSB Pipeline Accident Report, Natural Gas Pipeline Rupture kilotons of TNT.
4. Parnaroukis M, et al., Vapor Cloud Explosion Study, Proceedings and Fire Near Carlsbad, New Mexico, NTSB/PAR-03/01, 19 20. CCPS, Guidelines for Evaluating the Characteristics of Vapor
Sixth International Congress on Liquified Natural Gas, 1980. August 2000. Cloud Explosions, Flash Fires and BLEVEs, Center for
5. Havens J, Prepared Direct Testimony submitted to FERC 14. Garrett JW, Oklahoma Gas Outage, Pipeline and Gas Journal, Chemical Process Safety, AIChE, New York, 1994.
docket CP04-58-000, 1 October 2005. 1987;17. 21. Planas-Cuchi E, Gasulla N, Ventosa A, Casal J, “Explosion of
6. Beale JP, The facts about LNG, CH-IV International report No. 15. Kinsman P, Lewis J, Report on a Study of International a road tanker containing liquefied natural gas, J Loss Prev
RPT-06903-01, 2006. Pipeline Accidents, Contract Research Report 294/2000, HSE Process Ind, 2004;17:315–21.
7. Riley TC, The risks and dangers of LNG, 2004. Available at: Books, 2000, Appendix N. 22. Pitblado R, BLEVE potential due to marine LNG vessel fires,
www.lngdanger.com 16. Williams Pipeline, Gas Pipeline SCC – Catastrophic Ruptures, J Haz Mat, 2007;140:527–34.
8. www.lavalledeitempli.net 1 May and 13 December 2003. Available at: www.corrosion- 23. Emergency Response Guidebook, Guide 115, 2005;178.
9. amici.golfo.ts.googlepages.com/home doctors.org/Pipeline/Williams-explosion.htm 24. Venart J, Letter to the editor, AIChE Process Safety Progress,
10. California Energy Commission Letter, 8 December 2005. 17. Luketa-Hanlin A, A review of large-scale LNG spills: 2005.
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HYDROCARBON WORLD VOLUME 4 ISSUE 1
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