Large amounts of hazardous materials are transported every day. The historical survey performed on the accidents occurred indicates that road accidents with LNG are very infrequent (less than 1% of road accidents involved this substance). Considering all accidents involving hazardous substances, there is in fact a significant amount occurring during transportation. Since avoiding accidents completely is impossible, studies on accidents occurred are important to get experimental data to improve safety in the future. In this paper, the explosion of a road tanker transporting liquified natural gas is analyzed. The explosion took place because of the heating of the tank by the fire which started with the road accident. It is not clear whether the flames (approximately 13m high) were due to the truck fuel or to a release of LNG or, more probably, both. The remains indicate that there was flame impingement on the right side of the tank, which was not in contact with the LNG. In any case, after 20 min of the exposure to fire, the tank exploded. The explosion seems to have followed the two-step mode: the formation of an initiating crack, followed by a two-phase discharge and then the restart of the crack with the catastrophic failure of the vessel. The calculations made by using the overpressure estimated from the effects observed would indicate a lower pressure inside the tank, just before the explosion, than that required to have been a BLEVE according to Reid (1976) criterion; however, the liability of this result is limited by the lack of homogeneity of the blast wave, which in the case of pressurized vessel is significantly differential with respect to the diverse directions. According to a less restrictive criterion (CCPS, 1994), this accident could be considered to have been a BLEVE. The mechanical effects were very severe. A significant part of the energy released in the explosion was manifested in the breakage and distortion of the tank and the truck structure (that had been previously heated by the fire) and the ejection of fragments. The energy converted into the pressure wave seems to have been relatively low. This is confirmed by the final state of a car located at a few meters of the explosion (Fig. 7). This reinforces the theory that only a limited part (40-50%) of the overall energy released in the explosion must be considered for the calculation of the pressure wave. As for thermal radiation, the analysis of the effects and consequences shows that practically the whole contents of the tank could have been involved in the fire ball. Finally, concerning the trajectory of the fragments, this accident again shows that, in the case of cylindrical tanks, the main fragments usually follow a unidirectional path along the tank's main axis. The insulation used in the tank was polyurethane, a combustible and self-extinguishing substance. Replacing it with a non-combustible insulation (mineral wool, for example) and substituting the aluminium lining for a steel plate would increase the safety.
Explosion of a road tanker containing liquified natural gas
Journal of Loss Prevention in the Process Industries ; 17 , 4 ; 315-321
2004
7 Seiten, 19 Bilder, 1 Tabelle, 15 Quellen
Aufsatz (Zeitschrift)
Englisch
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