Discussion: Establishing derailment profiles by position for corridor shipments of dangerous goods
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Design of crane runway girders for top running and underruning cranes and monorails: ' Reply
CARL GOLDMAN Department of Civil Engineering, Concordia University, 1455 de Maisonneuve Boulevard West, Montreal, Que.,
Canada H3G IM8
Received May 15, 1991
Manuscript accepted May 15, 1991
Can. I. Civ. Eng. 19, 191 (1992)
I agree with the comments of J. Sepp that quality soft minute details" for a successful crane runway design. I mounting with proper clips will be a benefit to the crane would also add that the engineer should study the bracing operation. The Gantrex company manufactures a specially of the building housing the cranes to avoid excessive deflec- designed pad and compatible crane rail clips. They have tions and vibrations, since a poorly designed building may done considerable research in this area and I suggest the lead to problems with crane operations regardless of how reader obtain this material before making a final judgement. well the runway is designed. This subject was beyond the
I am in full agreement with all the comments, especially scope of my paper. the final comment that the designer must consider "all the
i is cuss ion by J. Sepp. 1992. Canadian Journal of Civil Engineering, 19: this issue.
Establishing derailment profiles by position for corridor shipments of dangerous goods: ' Discussion
J. M. CRUDEN P.O. Box 69, Brigus, Nfld., Canada AOK IKO
Received July 3 , 1991
Manuscript accepted July 22, 1991
Can. I. Civ. Eng. 19, 191-194 (1992)
The authors suggest that (p. 74) "an end-of-train mar- shalling strategy can result in significant savings per year." While this may be true, it is also true that the potential hazard attending any derailment would not thereby reduce and would probably increase.
I personally (as part of the process of reviewing all avail- able Canadian Transport Commission (CTC) derailment files covering 1970 and subsequent years) created the CTC accident data base from which the authors used the 1983-1985 derailment data. Although I have been effectively retired from the federal public service since late 1986, I am sure my comments in this context continue to have high validity. Changes have been occurring in North American railway engineering practice during the past 10 years or so, but the process of modernization remains incomplete. Cana- dian railways may never fully apply all measures now avail- able to the making of their trackage as derailment-free as
'paper by F.F. Saccornanno and S.M. El-Hage. 1991. Cana- dian Journal of Civil Engineering, 18: 67-75. Printed in Canada / ImprimC au Canada
is possible with the full application of such innovations as swing-nose crossings, fully welded rail on main line outside yards, rail fastening conversion to control rail flexure (horizontal) and bending (both positive and negative), etc., so that wheel-rail impacts, due to rail excitation, especially at rail joints and at crossings of traditional design, may be limited to the maximum degree possible. Such moderniza- tion largely eliminates derailments and is by far the most desirable action, where economically feasible, in considering the safe transport of dangerous goods. Prevention of accidents is always preferable to the mere identification of immediate causes. The CTC computerized accident data base (covering all reportable rail accidents; dangerous goods leakages or involvement in accidents; hot boxes and related axle journal failures) was established to aid in accident prevention by identifying areas of high risk, amenable to corrective action.
The authors (pp. 70-71) state that CTC derailment data were regrouped into seven classes by cause, using the U.S. Federal Railway Association (FRA) classification system.
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This system is inappropriate to an appreciation of what corrective action is possible, as it fails to recognize the various modes of structural failure of track, where the design or the method of maintenance is inadequate to withstand applied static or dynamic forces. Such cases arise in (thermal or other) buckling, failure of fastener restraint against rail rollover or gage widening or against rail creep, dynamic rail failure under trains. In my opinion, the FRA system has other defects which make it unsuitable for a rational examination of the Canadian accident record, at least insofar as a regulatory agency is involved. For this reason I devel- oped the classification system as in the appended (1970-1985) statistics (Table 1).
The said statistics and an earlier version (1970-1980) are available in two reports, written and submitted by me to the Railway Transport Committee of the CTC in respect to: (a) Derailments on the Clearwater subdivision of C.N. Rail
near Messiter, B.C., at mileage 13.2 on 13 February 1981; at mileage 17.59 on 20 February 1981; and at mileage 12.11 on 13 March 1981 (CTC files 31385.3912, 31385.3913, 31385.3914).
(b) Derailment at Petawawa, Ontario, mileage 103.85, Chalk River subdivision of C.P. Rail on 24 February 1985 (CTC file 31385.3038).
The above reports, made under authority of section 226 of the Railway Act, were published by the Railway Transport Committee and are in the public domain. Apart from iden- tifying apparent causal factors in the subject accidents, both reports were used as convenient vehicles to draw to the atten- tion of Commissioners and other interested parties various matters perceived as of importance to the understanding of the past and current Canadian derailment records and of possible corrective action. Although much of the comment derived from my own experience as a railway engineer before coming to Canada (and from observations not always in agreement with the expressed opinions of Canadian railways as to what ought to have been experienced or observed), it was very largely supported by available bibliography. A number of internationally recognized authorities' publi- cations were quoted in support of the comment made, in each report.
The authors direct attention to the relative importance (or potential hazard) associated with various marshalling posi- tions for dangerous goods cargoes, in the event of a derail- ment, on a particular route. Regulations must, however, apply on a system-wide basis. Each railway subdivision has its own particular characteristics. Those that have, in the past, apparently played a part in derailments caused by dynamics are likely to do so again. They may be recognized (at least in their effects) from the accident record of derail- ment of through trains, which tend to occur in patterns accordingly.
The risk (or probability) of a derailment of a through train is identifiable in essence, therefore. It arises largely from the track design, construction, and maintenance specifics of particular trackage under its normal regime of operation. The latter is of particular importance as regards train speeds, types (especially unit trains), length, and tonnage. The wheel- rail dynamic excitations induced by the heaviest trains running at unrestricted speeds then generally relate directly to what derailments may occur, other than those caused by direct human failure or agency, for any particular subdivision.
Most derailments of an avoidable nature (approaching 200 per annum on 1970-1986 data) result from the free strain energy input to the track by the wheel-rail dynamics mentioned above. Where the strain energy is not adequately constrained by modern track fastener systems, negative bending of rails may attain amplitudes and accelerations such that cut spike rail fasteners are ejected from the track, permitting rail rollover or dynamic gage widening under a train, with catastrophic consequences. At lesser amplitudes (but not necessarily lesser accelerations), strain energy may be released into wheelsets in significant impacts. Car wheelsets rise and fall because of their springing and the interplay of dynamics, as the rail flexes under rolling loads. Such rise and fall can be appreciable. Impacts arise due to algebraically opposite acceleration vectors in wheelsets and rails. Such impacts can be severe and release significant free strain energy, causing either dynamic rail failure through overstrain or similar rupture of a wheel or spring or (presumably depending upon the degree of compression of springsets) an axle. Where axles are involved, it appears that a lesser degree of impact more often results in damage to axle journal bearings, such that friction develops, which if undetected may cause overheating (a "hot box") and journal failure. The latter may not cause derailment until some time later, commonly when the wheel concerned (no longer being adequately restrained laterally) fouls a switch or the checkrail at a crossing at grade.
Track improvements which tend to reduce impact, such as relaying jointed rail with continuous welded rail, will normally result in very major reduction in incidence of occurrence of defects in rolling stock such as those that can lead to derailment when not detected and repaired. This is very noticeable when the records of track improvement and derailment are compared. It is possible to identify a number of railway subdivisions where cases of derailment due to axle journal failure recurred repeatedly until track relaying, following which the incidence dropped to or near to zero. Insofar as the derailment patterns peculiar to particular sub- divisions is concerned, the detailed records appended to the two CTC reports quoted above illustrate the point quite clearly.
It is quite clear that the control of rail excitation dynamics and consequent rail-wheel dynamics is of first importance in the avoidance of derailments such as that at Mississauga on 10 November, 1979. Many minor derailments are reported, not because of the dollar value of reportable damage, but because of the presence of dangerous goods in the cargo of a derailed or slightly damaged car. It is virtually only in the derailment of a through train that a serious hazard arises from the release of dangerous com- modities into the surrounding area. Most derailments of through trains do not involve cars laden with dangerous cargo, nor such release in cases where they do. Most derailments of through trains in recent years involve long, heavy tonnage trains, on spiked rail 115 lb/yd (1 lb/yd = 0.496 kg/m) or lighter, at speeds such that the ratio of speed (in mph) squared divided by the rail weight (in Ib/yd) is greater than 10, with traditional spiked track (1 mph = 1.6 km/h). Where track is fastened with modern elastic fasteners, the same ratio would probably have to exceed 20 before any cases of derailment from avoidable causes arise.
Insofar as most derailments of through trains occur in
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the portion where dynamic excitation is fully developed, the safest location in a train for cars with dangerous lading must tend to be in the leading portion, immediately behind the 6th car behind the locomotive (to safeguard crew members). Such marshalling is not always operationally feasible and the 1982 regulation quoted by the authors recognizes this, while imposing various specific restrictions. Although the quantity of dangerous goods moved by rail has been increas- ing, most trains do not derail and those that do seldom result
in a significant dangerous goods release. For example, during 1984 there were 230 derailments of through trains. Of these, 56 (24.3%) had dangerous goods cars involved, and in only one case was a significant release of cargo (sulphuric acid) involved.
The conclusions drawn by the authors tend, therefore, to be somewhat irrelevant to the practical considerations involved.
Establishing derailment profiles by position for corridor shipments of dangerous goods: ' Reply
F. F. SACCOMANNO Department of Civil Engineering, University of Waterloo, Waterloo, Ont., Canada N2L 3Gl
S. M. EL-HAGE Transportation, City of Brampton, Brampton, Ont., Canada
Received July 22, 1991
Manuscript accepted July 22, 1991
I I Can. J. Civ. Eng. 19, 194-195 (1992)
~ Mr. Cruden raises a number of valid points concerning I the Canadian Transport Commission (CTC) rail accident I
data base and the need to consider track structural failure and dynamics in assessing train derailments. Many of his comments, however, touch on issues that are well beyond the scope and intent of our study.
In our paper, we attempted to show that the potential derailment of railcars carrying dangerous goods is affected by their position along the train consist. As a result, effective marshalling to positions with the lowest derailment potential can enhance the overall safety of transporting dangerous goods by rail. Observations taken from the 1983-1985 CTC rail accident data base suggested that involvement of railcars in derailments depends primarily on two factors: (1) the point at which derailment is initiated, and (2) the number of cars involved. The number of cars involved in a derail- ment block was found to depend on the train operating speed and on the cause of derailment. A similar relationship was suggested in the 1983 A.D. Little Inc. study of train derailments in the United States (referenced in the paper).
I A statistical analysis of the CTC accident data indicated that the point of derailment along the train depends primarily on the cause of derailment (Table 3 in the paper). For "track-related failures" (i.e., roadbed defects, rail and joint bar failures, and switch defects), a significant share of derailments took place within the first 10% section from
is cuss ion by J.M. Cruden. 1992. Canadian Journal of Civil Engineering, 19: this issue. Pnnlcd In Canada / Irnpr~rnc au Canada
the front of the train. Track-related derailments represented over 45% of all derailments in the CTC data base (Table 6 in the paper). Even considering all causes together,'the first 10% section of train length reflected over 10% of all derail- ments in the data base. From these results, it is difficult to accept Mr. Cruden's assertion that the safest position for railcars carrying dangerous goods is at the 6th position from the front of the train for all track conditions and derailment causes. Such an assertion does not appear to be supported by the available data, especially when track-related causes are being considered.
We cannot comment on Mr. Cruden's assertion that the U.S. Federal Railwav Association (FRA) cause codes do not adequately reflect track structural faiures causing train derailments. The U.S. FRA coding scheme includes an extensive list of failure possibilities. Our study was based on a highly aggregated representation of the U.S. FRA cause codes for the purpose of explaining derailment potential according to position and cause. The assumption is that a train derailment has already taken place. It was not our intention to use these cause codes to reconstruct at the micro level the accident failure process for the purpose of assigning fault.
Mr. Cruden is correct in suggesting that practical con- siderations require that regulations governing the placement of dangerous goods railcars be applied on a system-wide basis. However, this does not deny the fact that certain corridor features have a significant effect of the point of derailment and should be considered in assessing the pre-
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