Brunel’s GWR Skew Bridge at Hanwell III - Disaster...

By 1847 the Great Western Railway had connected London to Exeter via Bristol, and the South Devon Railway was being built to extend the line to Plymouth. But on 22 May 1847, the Bucks Herald ran the following story, repeated in many other newspapers:
 
The railway bridge of the Great Western Railway over the turnpike road at Hanwell took fire on Thursday [20 May] at about 12 o’clock, and has become impassable. The scene was and is indescribable...
 
Although there was talk of ‘vile incendiaries’, it seems that a piece of lighted coal probably fell from an engine and set the timber bridge deck alight. The railway line and Uxbridge Turnpike were completely blocked. Trains had to stop either side of the bridge and
 
passenger[s] are obliged to alight, and walk, slide, or tumble down the embankment and scramble up again how they can.
 
Considering the height and steepness of the embankment, it must have been a major trauma for the passengers. At least eight of the cast iron girders had cracked from differential heating. Once more the bridge was shored up with timber and within a day or so, it was open for normal traffic.

Brunel must have been beside himself. In using wood to reduce dead weight, he had opened the bridge up to the ever-present danger of fire. And there was a further tragic consequence. The accident had been extensively reported in the national press, and it is possible that Brunel wrote to his friend Robert Stephenson to share his woes over cast iron girders. Stephenson’s own cast iron girder railway bridge over the River Dee had been open for nine months. The span length of his bridge was 100 feet, and he had achieved this by using three girders bolted end to end and strung with wrought-iron bars to provide extra tensile strength to the bottom flanges. On the evening of 24 May 1847, four days after the fire at Hanwell, the bridge failed as it was being crossed by a train. The engine and tender managed to get across but five carriages ended up in the river and the fireman and four passengers were killed. An excerpt from the subsequent accident report:
 
On the day of the accident, six trains had passed without any symptom of danger. On the afternoon of that day, immediately before the fatal train passed, about 18 tons of broken stone had been laid upon the planking as a protection against fire from the cinders of the engines, one of the bridges upon the Great Western Railway having been burnt about the same time through this cause.
 
The report went on to say that even with this extra eighteen tons, the load on the bridge would not have exceeded what it had previously withstood from trains, and the actual cause of the accident was likely to have been that the wrought iron tie rods had been incorrectly fitted. Nevertheless, the gravel laid as a fire retardant seems to have triggered the collapse. Both Stephenson and Brunel must have reflected with not a little discomfort on the risks of using cast iron girders.
 
A few months after the Dee Bridge accident, in August 1847, I K Brunel was called as a witness to the resulting public enquiry appointed ‘...to inquire into the Application of [cast] Iron to Railway Structures.’ Even before the enquiry started Brunel had written to the commissioners on the question of cast iron beams refusing to condemn their use. He wrote:

Who will venture to say ... that means may not be found of ensuring sound castings of any form ... and of a perfectly homogeneous mixture of the best metal? 

As a witness he was asked point blank to condemn trussed cast iron beams [as used on the failed Dee Bridge]; he replied:

By no means. But I should observe generally in answer to this question, that I avoid the use of cast iron whenever I can ...

Although Brunel and Stephenson were professional rivals, they were personal friends, and Brunel’s staunch defence of cast iron girders has been frequently ascribed to his personal loyalty to Robert Stephenson. The writer P S A Berridge comments:

...it was touch and go whether a charge of manslaughter would not be brought against Robert Stephenson.

However the multiple failures at Hanwell point to more than a little element of self-preservation. Had Brunel condemned the use of cast iron, the roads' commissioner, Sir Robert McAdam, might well have insisted on a complete rebuild of the Hanwell Bridge; he could even have demanded that it be closed to rail traffic until that had been done. The potential financial and reputational damage to the GWR—and Brunel—could have been considerable.
 
Brunel’s skew bridge at Hanwell had now ‘failed’ three times. The fire was clearly accidental but it could be argued that the extensive use of wood in an environment where the spillage of burning coals from steam locomotives was an ever present danger, was poor design practice and just asking for trouble. McAdam’s views have not been recorded, but there is indirect and circumstantial evidence to suggest that the bridge was securely shored up with timber for some considerable time. Nine months after the fire at an unrelated inquest into the deaths of two people from falling brickwork at Euston Station, counsel was making the point that there was no limit to the time that support scaffolding could be left in place if it was needed. His comments were reported in The Times:
 
There was an iron bridge at Southall, on the Great Western Railway, from which the scaffolding, although it had been erected many years, had not yet been removed. Much public inconvenience had arisen in consequence of there being danger of some accident in passing under the bridge...
 
The Morning Post version was slightly different:
 
The Great Western Railway Company ... had kept up the scaffold under an iron bridge erected near Hanwell for the last five years in consequence of some slight doubt as to its stability, and this in spite of great public inconvenience.
 
The barrister whose speech was being reported may have been indulging in some studied hyperbole, since it was at most nine months since the fire, but ‘many years’ or ‘five years’ is considerably longer than nine months. It is not impossible that either the Road Commissioners, or Brunel, or both, had decided to leave the timber framing in place under the bridge as a precaution following the second girder failure in 1839. Perhaps Brunel was repeating the ruse that was taking place at about the same time at his brick arch bridge at Maidenhead. Critics said it was too long and shallow and would fall down as soon as the centring (wooden support) was removed, and indeed some courses of bricks did become detached when this was done. The contractor conceded that he had allowed insufficient time for the mortar to harden and effected a repair. Brunel decided to have some fun at his critics’ expense, and instructed that the centring be left in place but eased so that it was not actually supporting the bridge, while appearing to do so. His stratagem was revealed many months later when the centring blew down in a winter gale leaving the bridge perfectly sound.
 
Meanwhile, the Hanwell Bridge needed to be rebuilt and from Brunel’s point of view he probably determined never again to use cast iron girders. The fire had spotlighted yet another disadvantage of cast iron; the report of the Railway Commissioners into the accident observes:

It would appear that, from the burning of the floor, the undersides of the girder would not be exposed to any great heat, while the upper parts were enveloped in flame, and that the unequal expansion has broken them on the underside first.
 
Cast iron is brittle and thus quite susceptible to damage from differential heating in the event of being involved in a fire.