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July 2, 2009

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Technical hitch

Is the increasing mechanisation of the hardware used

in the construction industry taking the focus away

from the safety and protection of the ‘soft tissue’ of the workforce, wonders David Jones.

Recent times have seen much innovative development in the mechanisation of construction plant, particularly around the fast interchange of working tools and bucket attachments on to dipper arms. Being able to use a vast range of tools with a single machine is an attractive option, particularly in the current financial climate.

Most of these add-ons can be directly attached to the dipper arms of the machines with simple pin joints, so that they form an integral working part of the machine as originally designed and manufactured for the job. In use, the machine as a whole should be regularly serviced and maintained in accordance with the original manufacturer’s specification.

Plant such as excavators is not normally factory-fitted with a quick-hitch device by the original manufacturer. Instead, these components are usually bought from an independent dealer and subsequently retrofitted to the machine.

They are available in a used condition from myriad sources and, more often than not, they come with little, or no proper information. (The only detail that was offered with a recent example for sale on the Internet was that the piece of equipment came off a five-tonne machine and would fit any digger with the same pin centres!)

Figures 1 and 2 show another second-hand quick-hitch coupler that was discovered for sale on the Internet, with no information other than pin size and spacing for fit.

The danger here is obvious: directly transferring the working load of the excavator bucket on to the dipper arm of the machine and then swinging it around above the heads of those on a construction site without being certain about its condition, or the safe load it is capable of supporting, is madness.

The construction industry has seen a spate of incidents over the last two years or so, in which the buckets on the dipper arms of mechanical excavators became detached and fell on to victims with, in some of the cases, fatal consequences. In 2008, four deaths were caused by such incidents, and there have been others this year so far.

The common factor appears to be the use of semi-automatic quick-hitch couplers, although there were also reported accidents involving other types of coupling devices.

The Strategic Forum for Construction (SFfC) is currently looking into this as an urgent issue (see below). The causes of the problem are not yet fully understood, as the investigation is ongoing, but there appears to be some association with the essential use of safety pins to control the risk of the machines falling apart.

A voluntary agreement is now in place in the UK not to manufacture any further semi-automatic quick-hitch couplers, which is fine as far as new equipment goes but it does not address the problem of the existing equipment in current use, or of the second-hand sales market.

Know the risks


The measurable units of impact and probability by which the risk posed by a piece of mechanical equipment is assessed can only reliably be identified by looking at the whole procurement chain in a construction project. It starts with the initiation and commissioning by the client and ends when the piece of machinery is actually taken off site.

But how many clients actually have enough competent knowledge and understanding of the plant and equipment that will be brought into use on their project?

Moving along the procurement chain, do many designers have that necessary knowledge and understanding? And what about the project managers?

Then there are the contractors, many of whom don’t actually own the mechanical plant that is brought on to site but rely on sub-contractors and hire companies to provide and/or operate the equipment for them.

Mechanical plant and equipment is complex and needs expertise and special skills to maintain and operate. The top end of the procurement chain generally has very little, or no knowledge at all on the detail of it, even though the client does have ultimate responsibility to maintain safety in their undertakings.

However, the reality of downward delegation means control of the safety, maintenance and management aspects of the piece of equipment is often handed down to the plant supplier, or operator.

Most quick-hitch manufacturers adopt similar installation procedures for parts like hoses, high-pressure solenoids, and fittings. But there are exceptions to this rule — for instance, where a quick-hitch manufacturer uses low-pressure solenoids. The difference in the operating pressure of each solenoid creates extreme risk and high potential for serious mechanical/operation failure, should the solenoid and quick-hitch not match up with each other.

But how would the upper echelons of the procurement chain know that such a risk is lurking in the project?

Consider this, more detailed scenario: a second-hand machine fitted with a low-pressure solenoid is retrofitted with a new quick-hitch, which requires a high-pressure solenoid. In such an instance, the fitter may assume the ‘old’ solenoid will do the same job and proceeds to fit the new quick-hitch to the existing pipe-work, unaware of the high risk he has just created. In such instances, the quick-hitch will continue to operate, even with the wrong solenoid fitted, and appear to be perfectly safe.

Unknown to the operator, however, when they next apply excess force to a digging attachment using this incorrect configuration, the moving jaw controlled by the hydraulic ram in the quick-hitch mechanism could be forced off the rear pin of the attachment, owing to inadequate pressure being sent by the control solenoid to keep the ram securely engaged.

Pressure in the system is still high enough to send the ram to max stroke and thus avoid auto-lock failure at this point.

The operator will only be aware there is something wrong when the bucket falls off the quick-hitch, resulting in serious injury or death to anyone working underneath.

The safety pin is therefore absolutely vital, and what makes the issue even more complicated is that some of the devices have safety pins while others do not. An operator can easily forget that his piece of equipment should have a safety pin manually fitted, or he may think he has a fully automatic quick-hitch coupler.

If there are any weak points in the procurement chain, the operator is the last chance to maintain safety.

Along with the condition of the mechanical equipment itself, operator training is undoubtedly the other most important factor when using any quick-hitch device.

It is imperative that operators fully understand the relationship between their excavator and any quick-hitch used with it. They must, for example, know exactly how the locking system on the quick-hitch works for maintenance/operation purposes, and fully understand how the excavator is able to control each function of the quick-hitch.

Although the speed and ease with which tools can be interchanged is a major benefit, using more securely attached devices — which do take the operator longer to affix — is a far safer option.

Tasks should be properly planned so that the operator can use each individual tool for as long as possible before a change is required, thus reducing the need for frequent changes, and consequently making the task safer.

Play by the rules


Of course, it’s not all down to the operator and their competence (and there are also concerns over whether current training in this area is sufficient to guarantee it).

The time has come for the whole procurement chain to rethink the way in which it deals with mechanical plant and equipment on site.

Clients, designers, supervisors, surveyors, engineers, contractors — the whole team of CDM duty-holders — could adopt a more holistic attitude to controlling these risks by ensuring they have a better understanding of the operation of site plant.

Just think of the improvement in safety culture if clients actually set some rules on the type of plant procured, and prevented inferior and unsafe equipment from being used on their projects. These rules could be applied to the early plans that eventually translate into tender specifications.

The procurement team is under statutory duties when undertaking any work but some parts of the construction industry continue to get it wrong, or simply ignore the rules.

The industry has had to comply with the Construction (Design and Management) Regulations since 1995, and the revised version since 2007, but even before then, we had, and still have, the Provision and Use of Work Equipment Regulations 1998 (PUWER), which clarify all the various parties need to know:

who is responsible for the coordination of the equipment;

that changes in conditions of use need to be reported to that person;

whether there are any limitations on the use of the equipment; and

how the equipment can be used safely.

Around even longer than PUWER are the Supply of Machinery (Safety) Regulations, which, since 1992, have placed a duty on those who use plant and equipment on their project — whether owned/provided by them or others — to ensure it meets certain criteria. These regulations deal robustly with conformity assessment procedures for second-hand equipment; require a Certificate of Adequacy; demand EC-type examinations; define the term “modification” as “even of a minor nature”; and require the production of a ‘Technical File’ to harmonise standards.

Conclusion


At the May meeting of the Strategic Forum for Construction — which brings together the HSE, contractors, client groups, the professions, plant associations, training organisations, manufacturers’ groups, and more — it was revealed that the estimated number of all types of quick-hitch devices currently in use is probably around the 100,000 mark, so the enormity of the task is clear.

In the meantime, practitioners and those in management and control of construction projects could improve the situation greatly, simply by being more aware of the problem, imposing effective control on the type of plant and tools that can be brought on to their sites, making greater use of technical specification, and improving training in construction plant and equipment. Increase your own knowledge and understanding of plant and machinery, know what you need, then specify what others have to provide to do the job properly and safely on your sites.

Until the SFfC has concluded its current work on this problem, it is possible in the meantime to take reasonable steps to minimise the risk by, at least, restricting the use of potentially unsafe semi-automatic quick-hitch devices and looking to safer alternatives.

Further information


At the end of December 2007, the HSE issued a safety alert to users of excavators fitted with quick-hitch devices, outlining the precautions to be taken when relying on these devices, and warning of robust enforcement action where they are found to be in use without adequate precautions.


David Jones has been active in construction safety since 1995.

http://www.hse.gov.uk/construction/quickhitch.htm

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