Establishing derailment profiles by position for corridor shipments of dangerous goods

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  • Establishing derailment profiles by position for corridor shipments of dangerous goods

    F. F. SACCOMANNO Departtnetlt of Civil Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3G1

    AND

    S . M. EL-HAGE Transportation Planning, Mars/~all Macklin Monaghan, 80 Cornmerce Valley Drive East,

    Thorrthill, Ont., Canada W T 7N4

    Received November 15, 1989

    Revised manuscript accepted July 11, 1990

    The position of railcars carrying dangerous goods in a train can affect their involvement in a derailment. A model is presented, which minimizes the number of cars carrying dangerous goods derailing for different marshalling strategies and rail corridor conditions. An application of the model to the Sarnia-Toronto rail corridor is presented. The results of this analysis suggest that marshalling strategies for cars carrying dangerous goods need to be sensitive to corridor conditions that affect the causes of train derailments. Current Canadian Transport Commission directives governing the placement of cars carrying dangerous goods along a train were found to be ineffective in reducing their derailment probability when compared to a low-cost unregulated option. Effective marshalling strategies can substitute for speed controls on the shipment of danger- ous goods, resulting in a similar or improved derailment profiles and lower operating costs.

    Key words: dangerous goods, derailment, rail, marshalling, railcars.

    La position des wagons transportant des marchandises dangereuses peut avoir une influence sur leur comportement en cas de dkraillement. Un modkle qui limite le dkraillement de wagons de marchandises dangereuses selon diverses stratkgies de formation des trains et de conditions h l'intkrieur des corridors est prksentk. L'application de ce modkle au corridor Sarnia-Toronto est discutke. Les rksultats de l'analyse indiquent que les stratkgies de formation des trains transportant des matikres dangereuses doivent tenir compte de conditions du corridor ayant un impact sur les causes d'un dkraillement. Les lignes directrices actuelles de l'Office national des transports concernant la formation des trains comportant des wagons de marchandises dangereuses se sont rkvklkes inefficaces h rkduire les probabilitks de dkraillement en comparaison d'une option non rkglementke h faible co0t. Des stratkgies de formation des trains efficaces peuvent se substituer aux contrales de vitesse et entrainent des profils de dkraillement semblables ou amkliorks et des cotits d'exploitation plus faibles.

    Mots cle's : marchandises dangereuses, dkraillement, raille, formation des trains, wagons. [Traduit par la rkdaction]

    Can. J . Civ. Eng. 18, 67-75 (1991)

    Introduction For a given set of rail corridor conditions, the risks

    associated with the derailment of trains carrying dangerous goods (DG) can be reduced in two ways: (i) reducing the prob- ability that any railcar carrying DG is involved in the derail- ment block, and (ii) reducing the opportunity of incompatible DG being involved in the same derailment block.

    The involvement of DG cars in a derailment block is influenced by the position of these cars along a given train con- sist and by the placement of non-DG car buffers separating incompatible materials. Effective marshalling and buffering strategies seek to assign DG cars to points along the train that are less likely to derail in an accident situation. If such a derailment were to take place, these strategies seek to reduce the opportunity that incompatible materials are involved in the same derailment block. Incompatible materials situated close to one another in the same derailment block can increase the potential threat posed by the derailment. For example, in the 1979 Mississauga derailment, the major concern for emer- gency response personnel was the presence of three potentially explosive propane tankers in the same derailment block with a 90 t tank car carrying highly toxic chlorine. An explosion of

    NOTE: Written discussion of this paper is welcomed and will be received by the Editor until June 30, 1991 (address inside front cover). Printed in Canada / Imprime au Canada

    any one of the propane cars could have caused a rupture of the neighboring chlorine car, with potentially catastrophic effects for the neighboring population.

    The Canadian Transport Commission (CTC 1982) recog- nized the importance of position in railcar derailments by tabling in 1981 a special DG marshalling order. The major restrictions included in this order are summarized in Table 1. The most frequently applied restriction states that when train length permits, cars carrying DG must not be nearer than the 6th position from the locomotives block, occupied caboose, or any occupied car in the train. The central focus of this direc- tive is to provide a sufficient distance between derailed DG cars and operating train personnel. The term "when train length permits" in the CTC marshalling directive refers to any train consist having a sufficient number of non-DG railcars to provide a minimum 5-car separation where required. When train length does not permit, the CTC recommends that DG railcars must be placed near the middle of the train, and under no circumstances nearer than the 2nd position from the locomotive block.

    A number of important concerns are raised by these restric- tions regarding their consistency of application and their effectiveness in reducing DG derailments. A major factor con- trolling the placement of DG railcars along a train is the actual length of the train (no. of cars), a feature that is generally governed by traffic patterns along the corridor and by carrier

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  • CAN. J. CIV. ENG. VOL. 18. 1991

    TABLE 1. Position in freight o r mixed trains of cars containing dangerous commodities (CTC 1982)

    (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) Restriction o n position of D G c a r s t

    Placard Type of car group* A B C D E F G H I J K

    Any car 1 x x x x x x x x x x Tank car 2 x x x x x x $ x$ x x $ x All other 2 x x x Tank car 3 x x x x X X X X X X All other 3 X x X X X X X x Any car 4 x x x x x Tank car 5 X $ X $

    *Group 1 consists of explosives 1.1 and 1.2. Group 2 consists of explosives 1.3, 1.4, 1.5; flammable gases 2.1; nonflammable gases 2.2; poison gases 2.3; flammable solids 4.1,4.2,4.3; oxidisers 5.1, 5.2; poisons 6.1, 6.2 and corrosives. Group 3 consists of special commodities of the division 2.3. Group 4 consists of radio active materials. Group 5 consists of flammable liquids 3.3 and "empty placarded cars".

    fAn x entry denotes that restriction on position applies. Restriction A: When train length permits, DG cars must not be nearer than 6th from engine, occupied

    caboose, or occupied car. B: When train length does not permit, DG cars must be near middle of train but not nearer than

    2nd from engine, occupied caboose, or occupied car. C, D, E, and F: DG cars must not be placed next to car in placard groups 1 , 2 , 3, and 4, respec-

    tively. G: DG cars must not be placed next to engine. H: DG cars must not be placed next to caboose. I: DG cars must not be placed next to open-top car when lading protudes beyond car or when

    lading above car end is liable to shift. J: DG cars must not be placed next to any car piggyback or container with automatic heating

    or refrigeration, lighted heaters, stoves, lanterns, or internal combustion engines. K: DG cars must not be placed next to loaded flat car.

    +Except when train consists only of placarded tank cars. Except trailer-on-flat-car, container-on-flat-car, tri-level and bi-level cars, and any other car specially

    equipped with tie down devices for handling vehicles. Permanent end bulk head flat cars considered the same as an open-top car (column 13).

    scheduling restrictions. Given this dependence on train length, marshalling regulations for DG cars can be applied arbitrarily. Railcars carrying the same materials along the same corridor may be placed at different positions along the train, depending on car availability. In general, current regulations in Canada appear to have been developed without a clear understanding of the relationship between positions and derailment probabil- ity, a relationship that is complicated by the effect of speed and accident cause.

    This paper presents an approach for marshalling DG railcars that, for a given set of corridor conditions, minimizes their involvement in a derailment. The results of an application of the approach to the transport of DG along the Sarnia-Toronto rail corridor are discussed. This corridor application focuses on an evaluation of alternative marshalling strategies for an

    tional derailment probabilities, given the occurrence of a train derailment. This probability is a function of the train derailing at a specific point along its length, and having a certain number of cars involved in the derailment block. A position is subject to derailment only if it is situated in the critical block of cars following the initial point of derailment.

    In Canada, all train accidents having damages exceeding $850 are reportable to the Canadian Transport Commission (CTC) and have been included in this data base. The CTC rail accident data base used in this analysis consists of 805 train derailments covering the period 1983 - 1985 inclusive. Approximately 40 % of these derailments involve some type of dangerous material. Each accident record in the CTC data base includes information on train length, point of derailment, number of cars derailing, and causes of each derailment acci-

    assumed mix of material shipments and train consists. dent. While the involvement of a dangerous material in the total derailment block was indicated by the CTC in the data,

    Methodology the number of DG railcars actually derailing was not reported.

    As illustrated in Fig. 1, the methodology adopted in this study consists of four components: (i) establishing a relation- ship between the cause of the accident and the beginning of the derailment block; (ii) establishing a relationship between train speed, accident cause, and the number of cars involved in the derailment block; (iii) establishing a derailment probability distribution for each accident cause based on the position of the railcar along the train; and (iv) evaluating specific mar- shalling strategies for a given mix of dangerous and non- dangerous railcars and a set of rail corridor conditions.

    The basic thrust of this analysis is the estimation of posi-

    Point of derailment In this study, the initial point of derailment (POD) is

    assumed to depend on the cause of each train accident. For example, initial points of derailment associated with roadbed or track defects are assumed more likely to occur nearer to the front of the train than derailments associated with defects in the rolling stock (e.g., wheels, axle, and journal bearing failures). These latter derailments are more randomly dis- tributed throughout the train length. In this analysis, CTC rail accident data have been used to assess the statistical validity of this assertion.

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  • SACCOMANNO AND EL-HAGE

    I PROBABlLlN DISTRIBUTION OF POINT OF DERAILMENT I

    FOR A GIVEN TRAlN CONSIST AND POD

    BUFFERING DATA (DIFFERENT REGULATIONS

    DERAILMENT PROBABlLlN OF EVERY CAR IN A GIVEN TRAlN CONSIST. TRAlN SPEED,

    t

    NUMBER OF DC CARS DERAILING FOR A GIVEN MARSHALLING REGULATION. A N D A

    SPECIFIC RAlL CORRIDOR

    POSITION OF DC CARS IN A GIVEN TRAIN CONSIST AND MARSHALLING REGULATION

    EXPECTED NUMBER OF DC CARS DERAILING FOR A GIVEN TRAlN CONSIST A N D ACCIDENT SITUATION

    EVALUATION AND COMPARISON O F THE DIFFERENT BUFFERING A N D MARSHALLING REGULATIONS

    ~r

    ACCIDENT PROBABlLlN BY CAUSE OF DERAILMENT O N A

    SPECIFIC RAlL CORRIDOR

    FIG. 1. Model flow chart. (DC = dangerous commodity.)

    1

    -

    In obtaining a probability distribution for the POD, the dis- tribution of train lengths in the accident data base needs to be considered. Positions near the front of the train tend to be overrepresented in the accident data base, since these positions are available for short as well as for long trains. Positions further back in the train, however, are only available if the total number of cars in the train is sufficient to include these positions.

    The 1983- 1985 CTC accident data base provides a distri- bution of derailments for different train lengths. Visual inspec- tion of these data suggest a grouping of train length into two

    I categories: trains with fewer than 50 cars and trains with 50 or more cars. This grouping serves as a crude adjustment for total train length in the analysis of points of derailment.

    I Within each of these train length categories, car positions along the train were expressed in percentile form (NPOD). For example, in a 50-car train the 5th position was assigned the 10th percentile interval (0.1). The CTC accident data base was then classified by NPOD, train length, and accident cause.

    Analyses of variance techniques were used to assess the statistical effect of accident cause and train length on the normalized point of derailment. The results summarized in

    v

    Table 2 indicate that, while cause of derailment has a signifi- cant effect on NPOD, the effect of train length (alone or acting interactively with cause) was not significant. Accordingly, in the subsequent analysis, NPOD probabilities were estimated ignoring the effect of train length.

    Based on the CTC accident data base, point of derailment probabilities were estimated for each NPOD interval and derailment cause. The results of this analysis are summarized in Table 3. For roadbed defects, there is a 26% probability of initial derailment in the first 10 positions of the train, com- pared with a 10.9% probability for the same position when derailment is caused by wheel, axle, and journal failures.

    In establishing the probability distribution of derailment by position, only those cars located after the point of derailment need to be considered, since positions preceding the point of derailment are unlikely to be involved in the subsequent derail- ment block. This assertion is supported by the CTC accident data where nearly all derailments for the period 1983 - 1985 were characterized by a consistent front-to-rear progression beginning at the POD and ending at the rear of the train. Only two exceptions were found in the data base, both dealing with rear-end collision taking place in railyards.

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  • CAN. J. CIV. ENG. VOL. 18. 1991

    TABLE 2. Analysis of variance (effect of train length and cause o...

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