CHEMICAL ENGINEERING TRANSACTIONS VOL. 57, 2017 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Sauro Pierucci, Jiří Jaromír Klemeš, Laura Piazza, Serafim Bakalis Copyright © 2017, AIDIC Servizi S.r.l. ISBN 978-88-95608- 48-8; ISSN 2283-9216 Essential Points in the Emergency Management in Transport Accidents which Can Lead to a BLEVE-Fireball Behrouz Hemmatian, Joaquim Casal, Eulàlia Planas* Centre for Technological Risk Studies (CERTEC). Universitat Politècnica de Catalunya·EEBE. Eduard Maristany 10. 08019- Barcelona (Catalonia, Spain) eulalia.planas@upc.edu Huge amounts of hazardous materials are transported by rail and road, being from time to time involved in traffic accidents. In these cases, flammable materials such as, for example, LPG, can originate a severe accident if a loss of containment takes place: a BLEVE explosion usually followed by a fireball. This type of accident, which often follows the domino effect sequence of fireexplosion, has caused the death of many people, including firefighters and spectators, the mechanical and thermal effects reaching significant distances. A historical survey has been performed on 167 accidents obtained from diverse databases. The results thus obtained have been used, together with the adequate mathematical models, to analyze the time to failure that can be expected and to estimate the lethality reach of the diverse effects –overpressure, ejected fragments, thermal radiation. Finally, a set of considerations concerning the safety and emergency measures that should be adopted in these accidents are commented. 1. Introduction Approximately 40% of major accidents occur during transportation. In fixed plants usually people involved know what to do in such a case and emergency plans are ready to be applied. Nevertheless, if the accident occurs during transportation, especially in road or rail modes, often other people can be affected. A typical case is that of a road tanker transporting a hazardous material which has undergone a traffic accident. Often a number of spectators remain relatively near the tanker, especially if there is a fire. These spectators take a “safety distance” based on the fire radiation. But an explosion –possibly a BLEVE– can occur at any moment (D’Aulisa et al., 2014; Hemmatian et al, 2015). And if the explosion is followed by a fireball, this distance will not be enough at all. Such accidents can be very severe (Busini et al., 2011) and a few principles should be clear for the emergency management in order to decrease or avoid the consequences on people. Here, the results obtained from a historical analysis and from the application of BLEVE and fireball mathematical models are used to define several simple measures which should be taken in these accidents, with an especial emphasis on the transportation of LNG and LPG. 2. Analysis of past accidents 2.1 Historical survey A historical analysis has been performed (Hemmatian, 2016) on a set of 167 BLEVE accidents occurred after 1st January 1961, the largest sample of BLEVE accidents studied until now. The Major Hazard Incident Data Service database (MHIDAS, 2007) was used to obtain most of the data. Other sources were: Analysis, Research and Information on Accidents (ARIA, 2012); Major Accidents Reporting System (MARS, 2012); Failure and Accidents Technical information System (FACTS, 2010). The lacking information in some accidents was searched from other sources such as the U. S. Chemical Safety Board (CSB, 2012), US. National Transport Safety Board (NTSB, 2013) or the National Fire Protection Association (NFPA, 2012). DOI: 10.3303/CET1757074 Please cite this article as: Hemmatian B., Casal J., Planas E., 2017, Essential points in the emergency management in transport accidents which can lead to a bleve-fireball, Chemical Engineering Transactions, 57, 439-444 DOI: 10.3303/CET1757074 439 Table 1 shows the substances involved in the 167 accidents analyzed. 247 substances were identified, as in some of the accidents more than one substance were simultaneously involved. LPG was by large the most frequent material (66% of BLEVEs), followed by vinyl chloride (6%) and oil (6%). Table 1: Substances involved in BLEVEs (% calculated for 167 accidents) Substance Number of accidents Percentage LPG 111 66 Vinyl chloride 10 6 Oil 10 6 Gasoline/Petrol/Diesel/Kerosene 8 5 Ethylene oxide 7 4 Carbon dioxide 6 4 Water 5 3 LNG 5 3 Other chemical substances 85 52 Total 247 149 Transport implied almost half of the BLEVEs (Table 2; some accidents had different origins). When analyzing “all” accidents (Haastrup et al., 1990; Vílchez et al., 1995), approximate values of 40% for transport are found; for the case of BLEVE this percentage increases up to 47%. Among BLEVEs that occurred in transportation, 57% involved rail tankers, 37% occurred with road tankers, 6% in ships and 1% in pipelines. Table 2: General origin of BLEVEs (% calculated for 167 accidents) General origin No. of accidents Overall percentage Transport 78 46.7 Storage area 39 23.4 Transfer 22 13.2 Process plant 19 11.4 Other activities 15 9.0 Total 173 103.7 2.2 Transport accidents which can lead to a BLEVE When a road or rail tanker transporting a flammable liquid (as, for example, LNG or LPG) undergoes a traffic accident or a derailment, the following accidental sequence can occur: damage of thermal insulation → loss of containment → ignition → flames impingement on the vessel → pressure increase → SRV opening → more flames impingement → BLEVE of the vessel. This sequence can take a variable time, depending on the specific circumstances. If the flames impinge on a non-insulated vessel wall, the explosion can occur after one minute, after one hour or, even, can never occur. If there is a certain delay, two things will happen: a) as the fire is something “attractive” for many people, probably a certain number of spectators will come to look at the accident, and b) the firefighters will come and will try to control the emergency. The spectators will adopt a “safety distance” (for example, of the order of 100 m) according to their experience and knowledge (in most cases, quite limited) of which are the hazards that a large fire can imply. However, even though this distance could be enough for a relatively large pool fire, it is completely insufficient if a BLEVE followed by a fireball takes place. And this is the reason why in such accidents spectators can be wounded or even killed. Furthermore, many firefighters have also died, due to the uncertainty concerning the time to failure; even though in industrialized countries firefighters are more and more aware of the convenience of evacuating in the situations which can lead to a BLEVE, still accidents occur in which the explosion happens while they are trying to extinguish the fire, with the associated severe consequences. In such situations, the measures taken during the emergency are essential to reduce the consequences of the event; two representative cases have been described in the literature (Planas et al., 2004 and 2015). 2.3 Amount of hazardous material involved For safe transportation of hazardous materials by rail and road, several regulations exist in different countries. The UN Recommendations on the Transport of Dangerous Goods (2011) is the basis for many national and 440 international regulations. Here, the common classes of rail and road tankers used for transportation of LPG and LNG have been taken from the US Department of Transportation. The report from Molag and Kruithof (2006) has also been considered for defining the various scenarios. The tankers and their specific parameters considered in this study are summarized in Table 3: Table 3: Capacities of different rail and road tankers Rail tankers Road tankers Volume (m3) Filling degree (%) at loading temp. and Prupt (kPa)* Volume (m3) Filling degree (%) at loading temp. and Prupt (kPa)* Propane 127.1; 121.1; 110; 94.1; 63 90% → 1137 kPa 86% → 1500 kPa 81% → 2000 kPa 64; 45.4; 34.1; 24.6; 13.2; 10.6; 2.8 86% → 1500 kPa 81% → 2000 kPa Butane 127.1; 121.1; 110; 94.1; 63 90% → 1137 kPa 86% → 1500 kPa 81% → 2000 kPa 64; 45.4; 34.1; 24.6; 13.2; 10.6; 2.8 85% → 700 kPa 76% → 1500 kPa Methane 111 91% → 206.8 kPa 87% → 482.6 kPa 85% →689.5 kPa 56 94% → 103.4 kPa 93% → 137.9 kPa 91% → 206.8 kPa 90% → 275.8 kPa 89% → 344.7 kPa 87% → 482.6 kPa 85% → 689.5 kPa *Loading temperature: 289 K for propane and butane and 113 K for methane. Different volumes of rail and road tankers are used in the transportation of LPG. Rail tankers range between 63 m3 and 127.1 m3, and road tankers range between 2.8 m3 and 64 m3 (Leffler, 2014). In the case of LNG, the capacities of 111 m3 and 56 m3 have been considered for rail and road tankers, respectively. The maximum filling degree is in fact determined by the existing regulations (which are not the same for all countries) and by the properties of the transported material. In the EU, this is regulated by the European Agreement concerning the International Carriage of Dangerous Goods by Road (ADR); the maximum allowed filling degree in the worst conditions (i.e., at the conditions at which the safety relief valve will open) is 95%. Thus, this assumption condition will be assumed for the diverse calculations here. 3. Effects and consequences from BLEVE-fireball 3.1 Overpressure To find the corresponding consequences on people, the Probit function can be used. For direct overpressure effects (as usually transportation accidents will occur in non-congested zones) the lethality due to pulmonary hemorrhage can be estimated as a function of ΔP (overpressure, N·m-2) by using Eq. (1) (Casal, 2008): PY Δ⋅+−= ln91.61.77 (1) At short distances ΔP varies with the direction (Birk et al., 2007), but it is not necessary to take this into account. For 1% of lethality, a threshold value of 103 kPa is obtained. The corresponding distances for propane, butane and methane (assimilated to natural gas) have been calculated for different vessel pressures and volumes. The reach for lethality due to ΔP direct effects is quite reduced (< 15 m for road tankers and < 20 m for rail tankers), as could have been expected: the value required for lethality is rather high and ΔP decreases quickly with the distance. If other criteria are applied (0.35 bar/15% lethality, 0.5 bar/50% lethality) the reach increases. 3.2 Ejected fragments As for the ejected fragments, diverse vessel breaking patterns are found (Gubinelli and Cozzani, 2009; Tugnoli et al., 2014). Among them, the one dividing the vessel in one bottom and the rest is the most frequent one (60% of cases). The prediction of the range of ejected fragments is rather difficult. However, a few authors have proposed expressions to calculate in an approximate way the maximum distance which can be reached by the fragment originated from cylindrical vessels (those used in transportation). Baum (1988) proposed the following expressions, where m is the mass of substance contained in the vessel (kg) and is the range (m): 441 For tanks < 5m3 vol.: l = 90·m0.33 ; for tanks > 5 m3 vol.: l = 465·m0.1 (2) The resulting distances for different values of vessel volume have been calculated (Figure 1). Very large distances can be covered by the fragments (much larger than those found for overpressure). This is due to the special way usually found in cylindrical tanks fragmentation, which gives rise to relatively aerodynamic fragments which travel in a way similar to that of a rocket or a missile; thus, ranges larger than one kilometer can be reached. Instead, for the case of spherical vessels, shorter distances are reached (the maximum distance registered for a large fragment of these vessels is 600 m). Figure 1: Distances reached by the ejected fragments (road tankers). Another aspect which should be considered is the direction followed by the fragments. Whereas for a spherical vessel this cannot be predicted due to the irregular shape of fragments, for cylindrical tanks (those found in road and rail transportation) often the fragments are ejected following the vessel longitudinal axis. Although this is completely true in some cases (see, for ex., the Tivissa accident, Planas et al., 2015), there is some scattering; Holden and Reeves (1985) suggested that in 62.5% of cases the fragments were ejected in the main axis direction, with a scattering covering an angle of 45º. Nevertheless, depending on the vessel failure mode, they can also be ejected in other directions 3.3 Fireball thermal radiation BLEVE will be almost always followed by a fireball if the contained substance is flammable. In this situation, predicting the effects of fire and its thermal radiation is crucial from the point of view of emergency management. Thus, the threshold values for thermal radiation were calculated for 1% lethality (with and without protection; protection is considered when, as in the case of firefighters, special resistant dresses are used), and 1% first and second degree burns, as well as the corresponding distances. In all cases, large distances are required to avoid consequences on people, much higher than those corresponding to the overpressure wave. 3.4 Lethality distances The values obtained from the data exposed in the previous sections allowed the calculation of the distances corresponding to the lethality threshold (1% lethality) for both blast and thermal radiation, as well as for first and second degree burns. As blast damage reach is much shorter in all cases than thermal effects, only thermal effects and fragments distances were taken into account here to consider the order of magnitude that evacuation distances should cover. The values obtained for the maximum distances corresponding to thermal radiation thresholds have been summarized in Table 4. Approximate distances of 500 m (LPG) and 400 m (LNG) have been obtained for the typical tanks used in road transport, and 670 m (LPG) and 520 m (LNG) have been obtained in the case of rail transportation. These values, together with those obtained for the ejection of fragments (Table 5), give an idea of the order of magnitude of the evacuation distances that should be considered in these types of accidents. 0 5000 10000 15000 20000 25000 30000 35000 40000 0 200 400 600 800 1000 1200 1400 T ot al m as s (k g) Distance (m) Propane Butane Methane 442 Table 4: Maximum distances for thermal radiation consequences (m) Propane Butane Methane Rail Road Rail Road Rail Road 1% lethality (protected) 370 270 370 265 280 205 1% lethality (unprotected) 430 310 425 305 325 240 1% second degree burns (unprotected) 440 320 440 315 335 245 1% first degree burns (unprotected) 670 490 665 480 515 380 Table 5: Maximum distances for ejected fragments reach (m) Propane Butane Methane Rail Road Rail Road Rail Road 1390 1295 1410 1310 1350 1265 4. Time to failure Once a pressurized vessel is subjected to the action of flames, its temperature and pressure will increase; this can lead to its collapse or it can stand, depending on the circumstances. Even if the vessel cannot stand, its failure can occur in a relatively short time or after a long time. In the San Juanico accident (México, 1984) the first BLEVEs occurred 69 s after (supposedly) one or more jet fires impinged on the vessels; however, in the Zarzalico accident (Planas et al., 2015), the tank stood during 70 min a very strong fire. The following circumstances can have a significant influence: i) Existence of a safety valve, which will keep a certain pressure value; it can not guarantee that the vessel will not explode, but could imply a certain delay in the explosion (Molag and Kruithof, 2006); however, it could also imply an additional heat input from the jet fire. ii) Existence of passive fire protection, which can delay the failure of the equipment one hour or more, or even avoid it (Paltrinieri et al, 2009; Birk, 2014). However, if a traffic accident or a derailment has occurred, the protective layer can be damaged and it will not protect anymore the vessel wall from the fire. The impingement of a high momentum jet fire can also erode it. iii) The mass contained in the vessel: the higher the filling degree, the smaller the probability that the flames impinge on the unprotected wall. iv) If the flames impinge on the vessel wall above or below the liquid level. Above the liquid level the wall is not protected –cooled– by the liquid and its heating can originate the failure, even if a safety valve avoids the pressure to exceed a certain value. To show how the time to failure of a pressurized vessel subjected to the action of a fire can vary, information on a few representative accidents (Hemmatian et al., 2015) occurred during transportation has been included in Table 6. It is clear from these data that the time to failure can range from a couple of minutes or even less to up more than one hour or, simply, can never happen. Table 6: Time to failure for different cases (transportation) Date Place Sequence Material Time to failure 1980 USA Fire→BLEVE Petrol road tanker 3 min 1970 USA Fire→BLEVEs LPG rail tankers First car in 5 min, 6 cars in 40 min 1987 Australia Fire→BLEVE LPG rail tanker 15 min 2002 Spain Fire→BLEVE LNG road tanker 20 min 1972 USA Fire→BLEVE Propylene road tanker 25 min 1973 USA Fire→BLEVE LPG rail tanker 30 min 1970 France Fire→BLEVE Propane rail tanker 40 min 1970 USA Fire→BLEVE Ethylene oxide rail tanker 45 min 2011 Spain Fire→BLEVE LNG road tanker 70 min 1976 USA Fire→BLEVE Isobutane rail tank 1.5 h 5. Conclusions In road or rail transportation of dangerous materials, especially flammable liquids or liquefied flammable gases, if there is a situation (fire affecting a tank) which can potentially lead to a BLEVE, the following potential mechanical and thermal effects should be considered: overpressure, ejection of fragments and thermal radiation. While the effects of overpressure wave cover a relatively short distance, those associated to ejected fragments can reach long distances and the thermal radiation –if a fireball occurs– can cover an important area. The following points should be taken into account and applied in the management of the emergency in order to avoid or reduce the consequences on people: 443 - If fire is affecting the tank, the explosion –probably followed by a fireball– can occur at any moment, from the first minute up to several hours after the beginning of the emergency. - Even if the tank is thermally insulated, an impact or jet erosion can have damaged the insulation and the situation should not be considered safe. - The fact that a safety relief valve is activated does not imply a safe situation, a BLEVE can still occur. - Although in cylindrical tanks fragments are prone to be ejected approximately along the tank main axis, depending on the failure mode they can follow other directions. - As the explosion can occur at any moment from the beginning of the accident, immediate evacuation of people to a safe distance must be applied. - People should be evacuated to a distance of at least 700 m and preferably –if possible– to 1200 or 1400 m. - Unless there is the need of rescuing someone from the trucks or wagons that suffered the accident, the firefighters should withdraw to the same distances too. Acknowledgments The authors thank the Spanish Ministry of Science and Innovation (project CTM2014-57448-R) for sponsoring this research. They also thank Mr. Jamal Hematian and Mr. Ken Black from National Steel Car Ltd., Canada. References ARIA, 2012. Analysis, Research and Information on Accidents. www.aria.developpement-durable.gouv.fr Accessed 10/04/2013. Baum M. R., 1988. Destructive failure of pressure vessels: preliminary design for fragment velocity and the extent of the hazard zone. J. Pressure Vessel Technol., 110 (2), 168-176. Birk A. M., 2014. Cost‐effective application of thermal protection on LPG road transport tanks for risk reduction due to hot BLEVE incidents. Risk Analysis, 34(6), 1139-1148. Birk A. M., Cunningham H. H., 2007. J. Loss Prev. Process Ind., 20 (3) 194-206. Busini V., Pontiggia M., Derudi M., Landucci G., Cozzani, V., Rota R., 2011. Safety of LPG rail transportation. Chem. Eng. Trans. 24, 1321-1326. Casal, J., 2008. Evaluation of the Effects and Consequences of Major Accidents in Industrial Plants. Elsevier, Amsterdam. CSB. 2012. U.S. Chemical Safety Board. www.csb.gov. Accessed 10/04/2013. D’Aulisa A., Tugnoli A., Cozzani V., Landucci G., Birk M. A. 2014. CFD modelling of LPG vessels under fire exposure conditions. AIChE J. 60 4292-4305. FACTS. 2010. Failure and ACcidents Technical information System. www.factsonline.nl. Accessed 10/04/2013. Gubinelli G., Cozzani V., 2009. Assessment of missile hazards: evaluation of the fragment number and drag factors. J. Hazard. Mater. 161 (1), 439-449. Haastrup P., Brockhoff L., 1990. Severity of accidents with hazardous materials: a comparison between transportation and fixed installations. J. Loss Prev. Process Ind. 3(4), 395-405. Hemmatian B., Planas E., Casal J., 2015. Fire as a primary event of accident domino sequences: the case of BLEVE. Rel. Eng. & System Safety, 139, 141-148. Hemmatian B., 2016. Contribution to the study of Boiling Liquid Expanding Vapor Explosions and their mechanical effects. PhD thesis. UPC. Barcelona. Holden P. L., Reeves A. B., 1985. Fragment hazards from failures of pressurized liquefied gas vessels. IchemE Symp. Ser. 93, 205-220. Leffler, W. L., 2014. Natural Gas Liquids: A Nontechnical Guide. PennWell Books. MARS, 2012. Accident Reporting System (MARS). emars.jrc.ec.europa.eu. Accessed 10/04/2013. MHIDAS. 2007. Major Hazard Incident Data Service. Health and Safety Executive, London. Molag M., Kruithof A., 2006. BLEVE prevention of a LPG tank vehicle or a LPG wagon, TNO Report R2005/364. Apeldoorn. NFPA. 2012. National Fire Protection Association (NFPA). www.nfpa.org. Accessed 10/04/2013. NTSB., 2013. U. S. National Transport Safety Board. www.ntsb.gov. Accessed 10/04/2013. Paltrinieri N., Landucci G., Molag M., Bonvicini S., Spadoni G., Cozzani V., 2009. Risk reduction in road and rail LPG transportation by passive fire protection. J. Hazad. Mater. 167(1), 332-344. Planas E., Gasulla N., Ventosa A., Casal J., 2004a. Explosion of a road tanker containing liquefied natural gas. J. Loss Prev. Process Ind., 17(4), 315-321. Planas E., Pastor E., Casal J., Bonilla J. M., 2015. Analysis of the BLEVE of a liquefied natural gas road tanker: The Zarzalico accident. J. Loss Prev. Process Ind., 34, 127-138. Tugnoli, A. Gubinelli, G., Landucci, G., Cozzani, V. Assessment of fragment projection hazard: probability distributions for the initial direction of fragments. J. Hazard. Mater., 279C (2014) 418-427. 444 http://www.csb.gov/