UDC: 539.43

The Kelvin Hall fairground accident by L P Pook, Department of Trade and Industry, National Engineering Laboratory, Fatigue Division, East Kilbride, Glasgow G75 OQU.

‘The spread of information about failures within the technical community is essential and it is a sad refection on society that legal and political constraints are doing so much to prevent this spread, Max S M Saltsman 1. Details of such a failure are described here.

Keywords: Fatigue failure, health and safety.

Introduction

A fairground ride, known as the ‘Concorde Flyer’, was installed at the Kelvin Hall , Glasgow for the 1978 Christmas Carnival. On Boxing Day (26 December 1978) one arm fractured, the car attached to the arm overturned, and two passengers were killed. An official inquiry into the accident was held by Sheriff J Irvine Smith under the Fatal Accidents and Sudden Deaths Inquiry (Scotland) Act 1976. The findings 2 of this inquiry are the source of most of the material presented.

The Concorde Flyer

The Concorde Flyer consisted of ten cars each rigidly attached to an individual arm which was in turn attached, by a pivot, to a central hub. The arms were approximately 3 m long. Each was a low carbon structural steel welded assembly consisting of 100 mm x 50 mm rectangular hollow sections along the leading and trailing edges cross- braced by square hollow sections. Each car was fitted with a single wheel which ran on a circular track incorporating a large and a small hill. The hub was driven by an electric motor fitted with appropriate control gear. The normal speed of operation was 8-9 revolutions per minute. Fatigue stresses were produced in the arms as the cars were forced uphill and ran downhill.

Failure Analysis

The accident occurred on Boxing Day 1978 during the Kelvin Hall Christmas Carnival. The machine was boarded, and started up. After about two revolutions the arm which was attached to one car fractured where it was welded to its pivot box at the hub. Detailed examination by the Health & Safety Executive showed that the failure had originated at the leading edge of the arm.

Fig. 1 shows the leading edge structural details in the vicinity of the failure. The trailing edge structure was

similar. The pivot box consisted of a 100 mm square hollow section with 38 mm thick end plates welded on. A 63 mm diameter pivot passed through the end plates and was fillet welded to one inner face. The 100 mm x 50 mm hollow section, which formed the leading edge of the arm, was fillet welded to the pivot box along 3 sides. The fourth outer side had a 100 mm x 6 mm side plate attached by longitudinal fillet welds. This side plate was in turn attached to the pivot box by a partial penetration fillet weld which was perpendicular to the applied stress, and not visible externally. The assembly was completed by the addition of the top and bottom plates which were 6.2 mm and 5.2 mm thick respectively.

A fatigue crack had originated at the partial penetration fillet weld and grown slowly through the weld. It then grew into the welds attaching the top and bottom plates to the arm. The rest of the failure was ductile fracture, probably in a single continuous action. Fatigue cracking would have been noticeable, on visual examination by an expert, for some time before the accident. After the accident visual examination revealed cracks on five further arms, and more cracks were found on the arm which failed. Laboratory examination revealed still more cracks. One crack had been painted over, and paint had penetrated the crack.

Fig. 1

There is no doubt that fatigue was the immediate cause of the accident. This resulted from poor detail design, coupled with inadequate inspection procedures.

History of the Concorde Flyer

The history of the Concorde Flyer is outlined below. The sheriff who conducted the fatal accident inquiry

Structural details in the vicinity of failure

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requirements of the bye-law. commented that it had not been found possible to establish the precise nature of the defects appearing in the machine, or the precise nature and dates of repairs carried out.

The Concorde Flyer was first commissioned in 1976. The designer and manufacturer both had considerable experience of fairground rides. After it was commissioned the machine gave trouble and modified parts were supplied by the manufacturer.

At the Kelvin Hall Christmas Carnival of 1976/77 at least one of the arms fractured. As a result the owner contacted the manufacturer and repairs were carried out, but the nature of the damage and repairs is unclear.

About December 1977 the owner was still dissatisfied with the machine and accordingly asked the designer to plan modifications. These included shortening the arms by about 0.6 m, compensating for this by extending the central hub, and modifying the method of attaching the arms to the hub. The modifications were completed early in 1978, and the machine was recommissioned about Easter 1978. (In 1978 Easter Sunday was on 26 March.)

Soon after an arm fractured while the machine was at Greenock, and the owner instructed a local engineering firm to carry out repairs. They apparently welded a metal splint to the fractured arm.

Subsequently the owner arranged for alternations to be made to all the arms. These included the addition of the cover plates shown on Fig. 1 and alterations to attachments at the hubs. The designer of the machine was not consulted about these final modifications.

Safety Certificates

In 1976, following several fairground accidents, the Government issued a 'Guide to safety at fairs'. The guide 3

did not have any legal force. Its introduction notes that:

'The guide does not try to take account of the many individual variations in premises and amusement devices that are to be found. It is intended, rather, as an indication of the standards to be aimed at.'

Safety certificates are prescribed by the guide, and these had been adopted as a requirement by the Showmen's Guild (the trade association of fairground operators). These certificates cover structural, mechanical and electrical safety. Also, under a bye-law, a licence was required from Glasgow District Council to operate the Concorde Flyer within Glasgow. At the time of the accident three safety certificates, certifying that the machine had been independently inspected, were in force. Two were in the form recommended by the guide, and taken together, appeared to satisfy the requirements of the Showmen's Guild. The third appeared to satisfy the

The first safety certificate was issued on 31 March 1978 by an engineer, who had been appointed by the Showmen's Guild as an inspector, and covered structural and mechanical safety. It stated that he had inspected the machine with regard to its structural and mechanical safety, and its condition was such that it did not present a danger to the public. The certificate further stated that as part of his examination he had observed a fully loaded test run, which in fact was not the case. The emergency braking system, required by the guide, was not working at the time of the inspection. The sheriff commented that the certificate was 'admittedly not worth the paper it was written on'.

The second certificate, issued by another inspector appointed by the Showmen's Guild, and dated 8 May 1978 certified that the machine had been examined for the purpose of electrical safety and had been found to be safe. This certificate appears to have been in order.

After the machine had been installed in the Kelvin Hall for the Christmas Carnival it was examined visually on behalf of Glasgow District Council by three officials. These were two electrical engineers and a man variously described as a builder or joiner. Their inspection appeared to be mainly concerned with ensuring that the machine had been correctly reassembled after transport to the Kelvin Hall. In evidence to the inquiry it was stated that they did not observe any 'hairline' cracks or other defects, and did not consider that the modifications which had been carried out affected safety. As a result of their recommendations, the third certificate, a 'licence for a public show' was issued by Glasgow District Council on 5 December 1978.

Discussion

The inquiry revealed a situation where a number of errors and omissions, each non-critical in itself, had linked up into a chain of coincidence which resulted in catastrophe. A particular concern of the inquiry was how was it that what should have been obvious cracks escaped notice? Apart from the inspections actually carried out, there were opportunities for cracks to be noticed each time the machine was dismantled for transport and reassembled at a new location. The sheriff commented that the evidence revealed a situation where 'everyone was leaving it to everyone else'. It is possible that cracks were in fact noticed, but that their significance was simply not appreciated.

From a technical viewpoint there are two main points of interest neither of which was brought out in the inquiry. The first follows from the fact that the earlier failures in the arms were almost certainly due to fatigue, from which it would follow that the various repairs carried out were actually attempts to prevent further fatigue failures. A

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sequence of events, where repeated but unsuccessful attempts are made to strengthen welded structures against fatigue by welding on additional material , is often observed. The practice is repeatedly denounced by fatigue specialists. In this particular case the end result was that the detail design in the vicinity of the failure was poor from both fatigue and inspection viewpoints.

The second point is why was it that the arm failed completely, whereas the earlier failures were no more than an expensive nuisance ? The answer is probably that a boxed in structure, such as that of the arm at the time of the failure, has poorer static strength characteristics than the original more open and redundant design in that ductile tearing is more likely to lead to complete failure.

Concluding remarks

In a fatal accident inquiry the court is required to establish the facts concerning an accident, but not to apportion blame in either a criminal or civil sense. The act also makes provision for recommendations to be made in appropriate circumstances. The sheriff made a number of recommendations, mostly of an obvious nature. Some of these covered points where recommendations of the ‘Guide to safety at fairs’ had not been followed. This is how

matters stood in 1980 when the findings of the inquiry were published. Fairground safety procedures are now much tighter. There were no prosecutions for criminal negligence and the question of civil liability appears to have been settled out of court.

Acknowledgements

This paper is published by permission of the Director, National Engineering Laboratory, Department of Trade and Industry. It is Crown copyright.

References

(1) Saltsman, M. S. M., “Political and social decision making in relation to fracture, failure, risk analysis and safe design procedures”. In TAPLIN D M R (Ed), ‘Advances in research on the strength and fracture of materials,’ 0,Ufoi-d: Pergamon Press, 4, (1 978), 20 1-206.

(2) Irvine Smith, J., “Findings of inquiry into the death of Thomas John McDonald and Clare McDonald”, Sheriff Clerk‘s Criminal Office,Glasgow, (1980).

(3) Anon: “Guide to safety at fairs”, HMSO London (1976).

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