The case against the articulated tipper.
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■ 1 1979 Packington Estate Enteirises Ltd (PEEL) banned artictlated tipping vehicles from its andfill sites in the Midlands. The lecision was made because iree of them out of 10,000 a rticlateds which used the cornany's sites had toppled over then discharging domestic inustrial waste, while only one Igid vehicle had suffered a imilar fate out of 700,000 ischarges.
An extreme remedy perhaps, nd one that is estimated to aye cost the company about 250,000 per annum in lost avenue, but Mr C. A. R. Biddle, ianaging director of PEEL, beeves his action was necessary ) safeguard drivers and site emloyees.
Early this year, the company ailed for a national ban on the peration of articulated tipping ehicles after publishing a report had commissioned from Bris)l Polytechnic. The report's uthors, Dr R. C. Keen and M. J. itt, consulted waste disposal fficers, site operators, hauliers nd constructors and used their ndings in conjunction with Deartment of Transport statistics ) establish the probability of skin operation. They estimated the number of heavy articulated tipping vehicles at 120,000, and from a five per cent sample of this total 32 static roll-overs had been recorded over a seven-year period. A scaling up of the sample indicates that probably around 900 vehicles fall over every year.
The RHA says that waste accounts for about five per cent of tipper usage; there could be as many as 45 incidents in landfill each year. However, the report points out that the drivers' awareness may greatly reduce the number. The report's own survey of operators indicates only 10 stationary roll-overs per year. It also says that though injury to the driver or other operatives is rare, and vehicle damage small, some fatalities do occur. The case against the articulated tipper is strengthened when the number of incidents is related to the number of vehicles involved. Articulated vehicles account for 15 per cent of tipping operations yet 66 per cent of overturns. Outside of waste disposal operation they account for 54 per cent, implying a vulnerability seven to 11 times greater than that of rigid tippers.
The overall risk is estimated at one in 15,000 tips for articulated vehicles, and one in 300,000 tips for rigid ones. On waste disposal sites the frequency of overturn for articulated vehicles is increased to one in 5,000 tips while for rigid tippers these odds stay at one in 300,000.
The report concludes that articulated tipping vehicles are much more likely to overturn during discharge than rigid tipping vehicles, and that the current design of articulated tipping vehicles owes more to evolution and rule of thumb than the application of engineering analysis.
To hear a manufacturer's viewpoint, I visited Crane Fruehauf at Dereham in Norfolk, where I talked to the trailer company's technical manager, Trevor Chapman. He agreed with much of the report's findings, but said that his company had carried out stability tests as long ago as 1973, from which time all subsequent CF trailers have been built to greater stability standards.
Uneven ground conditions, ground slopes, sticking loads and side winds all contribute to the adverse conditions under which such vehicles have to work, but there are engineering solutions to improve stability.
At full tilt the maximum length 12.1m (39ft 9in) trailer needs a body angle of 40-45° under discharge. In this condition, the front of the body is higher than with the maximum weight rigids and contributes to an overall higher C of G. It is payload and volume which makes the articulated tipper more attractive to operate, and body length which makes it more susceptible to instability. In order to minimise the reaction at this stage, CF lowered the height of its chassis.
During tipping, almost all of the weight is transferred to the trailer's wheels. Deep cross-section tubes, with pivot points placed well forward of the rear, help to stiffen the chassis above the bogie and reduce chassis twisting.
Springs are designed to operate under compression but the various types react differently when the forces are reversed. The performance of multileaf springs can be improved to match that of monoleaf springs where the forces act in an upward direction. This might be done on one side when a vehicle is operating on uneven ground, by fitting lock and blocks.
However, monoleaf springs are preferred as the multileaf type is liable to lose its apparent stiffness suddenly and could cause the vehicle to fall over with little warning.
CF showed 7.5 degrees of tilt to be the maximum practical operational sideways angle of tilt using standard components.
The addition of a stabiliser mounted between the body and chassis could allow for a further three degrees of sideways tilt, but this would increase the unladen weight by about four cwt at a cost of approximately £300.
Air suspension is said to be the answer, but this would add up to £1,500 to the cost of the trailer.
Front-end or under-floor rams contribute very little to overall stiffness of the tipper trailer and twin rams have long since gone out of favour. Initially, two legs appear to be more stable than one, but positioned close together, the advantage is minimal. A failure or extra friction in one can result in uneven extension and induce a tilt not already there.
CF has produced an operator's handbook which provides the basic instruction in care, maintenance and operation of its tipping semitrailers.
Since the beginning of 1981, all overturns that caused injury have to be notified to the Health and Safety Executive. The number of reports has been very small.
As a direct result of PEEL's actions, inspector Ray Kelly said that he appreciated that more work was needed on the subject and on behalf of the H & SE understood to fund research on all aspects of tipping operation after consultation with the industry's representative bodies.