Watch any television documentary about the second world war and one can only be astounded at the advances in technology that have taken place since 1945. Aircraft and vehicles have advanced such that the transport of that period has already become consigned to the status of museum exhibits. Step back to the first world war (1914-1918) and the contrast is even more striking with horse-drawn and early petrol driven solid-tyred vehicles in use and the aeroplane replacing the airship in aerial warfare.
It is a sobering thought therefore that it was between these two periods in history, in 1931, that the need for the load moment indicator (LMI) was first recognised and the first European legislation was introduced to require its use. What progress has been made since that time? Initially, early cranes were rated to carry a fixed and constant maximum load at any radius and the only requirement was that they should be clearly marked accordingly with that maximum capacity. When cranes developed so that the permitted load could change with radius, the need for an automatic device to warn of overload was recognised and the LMI was born out of that need to eventually develop into the LMI – or safe load indicator or rated capacity indicator – as we know it today.
Governments and indicator manufacturers in Europe followed the development of the crane with regulations and products to match the crane technology of the time. This process peaked in the 1980s with some excellent standards that clearly defined the performance standards that should be expected. These still form the basis for safety expectations in the European Union until some flesh can be added to the bones of the Machinery Directive by the completion of the new European standards.
Seventy years after the introduction of the LMI, the latest European Machinery Directive simply states that cranes with a maximum working load of not less than 1,000kg or an overturning moment of not less than 40,000Nm must be fitted with devices ‘to warn the driver and prevent dangerous movements of the load’ in the event of overload. Apart from the fact that ‘the device’ rather than the operator is now required to take the initiative to ‘prevent dangerous movements of the load’, little seems to have changed in the basic requirement over the course of 70 years.
The 1930s must have been a very safety-conscious period in Britain because 1931 also saw the introduction of the Highway Code, the first guidance on how to drive a car on public highways. This publication has changed out of all recognition since it first appeared, constantly being amended to reflect the dramatic changes in the motor cars that we drive and how we use them. Our cars are faster, safer, and more capable and we now expect the safety protection that has followed their development. Collapsible steering columns, safety belts, anti-lock braking, air bags, crumple zones, side impact protection. These are features that we have come to expect when we buy a new car. Our natural survival instinct means that we welcome every safety feature that is offered.
The development of the crane has been even more dramatic and far more varied than that of the motor car and yet, when it comes to the use of even the most basic safety instrumentation, arguments still rage in the industry as to whether an LMI should be fitted at all. It is as if there is some macho feeling that the crane operator really should not need this irritating device to dictate what he can and cannot do. It is reminiscent of the early resistance to the compulsory wearing of seat belts. We must remember, however, that it is not only the crane operator that is the potential victim in a crane accident.
Much, of course, stems from the out-dated myth that electronic LMI systems are unreliable. This had justifiable roots in the 1970s when electronic systems were first introduced. Many were complex hybrid electro-mechanical systems and some were produced by electronics companies seizing an opportunity in a new market but with no previous experience of placing their precious equipment in the then often damp and vibration prone environment of the mobile crane. No one told them when they looked in that nice dry cosy cab in the OEM’s factory that one rainy day the operator would leave the window open right over their poorly protected equipment.
Essentially, the case for reliability has long been proven by those with specialised experience in the business. It would be folly to ignore, however, that in any newly emerging market, there will be good and bad, experienced and inexperienced, bidders for the business and it behoves the buyer to beware.
Some detractors of electronic LMI systems crave for a return to the reliability of the mechanical systems of the 1950s. For the man operating a fleet of old mechanically operated cranes in a remote location far from civilisation, one must have a degree of sympathy for his desire for something mechanical that he can maintain and fix in the event of a problem. The reality, however, is that for the current manufacturing cost of that mechanical indicator, he could buy guaranteed electronic reliability several times over.
The real problem is the price that we place on safety and the fact that in reality, our man really doesn’t want to pay the price, mechanically or electronically, to realise his dream solution.
Reliability can, of course, be purchased. Take a trip on an aeroplane. Do you worry that a single electronic failure will bring it down? I doubt that you do because you know that the essential circuits are duplicated, perhaps triplicated, to ensure back up continuity in the event of failure. LMIs could have duplicated circuits if we were prepared to pay for them. It need not be excessively expensive and would allow continuous safe operation while providing the facility to carry out repairs at relative leisure.
Another factor held against the LMI, again based on historical heresy, is the belief that the operator can drive any crane ‘by the seat of his pants’. In the good old days when men were men and the old lattice boom cranes were built strongly with their rating charts based purely on stability, this was partially true. Even then, however, there was a dangerously fine line between a crane feeling ‘light’ and it tipping on its face. The warning of disaster provided by the LMI prevented many accidents in that period, though we will never be able to known exactly how many.
Unfortunately, few modern cranes have simple stability-only based ratings, and it has been necessary to find new solutions to match the current technology of the mobile crane.
‘Training’ is the final argument for the irrelevance of the LMI. LMIs are just a poor substitute for proper training, it is sometimes argued. Teach the operator to find out the exact weight of the load and then train him to be able to read his rating chart so that he is aware of his safety margin at all times. Is this real in today’s world? Once again, history lends some credence to the argument. On older cranes with simple rating charts, it was a relatively simple matter to check the lifting capacity against the radius and then, with some means of measuring or otherwise being aware of that limiting radius, drive the crane within its designed limitations.
We must recognise that the modern telescopic mobile crane is a very different animal to the simple stability-based lattice boom that we have described and it can bite with little warning! It may have a multiplicity of rating charts, changing constantly depending on the exact combination of boom angle, length and slew position and a variety of other possible inputs. The charts are no longer simple to read or easy to follow closely while carrying out a lift. Each duty may contain a mixture of stability and strength related ratings. The operator needs all of his concentration for the execution of the lift at that critical time.
What of the additional benefits offered by the LMI? Some now provide a simple data logging feature at no extra cost. Others provide data logging of the minutiae of every lift to facilitate objective planned maintenance and management control of the crane-owning business. These features offer potential cost savings to the owner that more than offset the additional purchase price of the LMI. That can easily be justified by the potential for damage to the crane alone.
So where are we now? Seventy years – a lifetime – has passed. Is there really anyone out there who still believes that the case for the LMI has not been well and truly proven? The time has come for them to be mandatory worldwide.