Ongoing quest to boost crane safety

The National Slate Mining Museum in Llanberis has one exhibit that may make you shudder – a company hospital. In the heyday of the mine, it was a matter of fact that slate workers were maimed and injured on an industrial scale. Thankfully, nowadays we live in more enlightened times.

Cranes are a potentially life threatening piece of equipment. Street Crane and many other crane builders always include basic equipment function training during commissioning and project handover so that operators are familiar with simple crane controls and how use the crane to move a load safety. More frequently customers are demanding that this training is a much more detailed training session to include detailed analysis and information on hook loading slinging techniques.

As crane builders we can help with crane safety by adding additional control equipment such as variable frequency drives to facilitate smooth acceleration and deceleration with minimal load swing. This used to be a function of the crane operators skill but many modern cranes now offer this load control without the need for such special skills.

Harmonisation of European standards for crane and hoist design, though initially driven by a desire to standardise and remove barriers to cross-border trade, has also helped drive improvements in safety. The process began with the all-embracing Machinery Directive of 1995, but these principles have now been refined in specific regulations governing power driven hoists, overhead crane design standards and the electrical requirements of hoisting machines. Special regulations have also been introduced for handling hot metal and other hazardous material which make strict requirements for systems redundancy.

Electrical control is a key area of safety. Overload protection and the use of limit switches are mandatory in the EU. This prevents crane abuse by exceeding the safe working load and also avoids loads being lifted too far, jeopardising the load and crane mechanisms. These and other critical electrical controls are now duplicated to provide a back-up that takes over in the event of failure in the primary circuit.

Braking is a crucial safety factor. For example, the Street Crane hoist brake acts externally on a hoist gearbox shaft, not an extended motor shaft. This design allows the brake to be easily inspected and serviced, it contributes to a cooler brake in use and produces lower working temperatures in the hoist motor as heat generated by the hoist brake is not conducted over. Hoist motors therefore run cooler and more reliably with less heat stress.

European legislation now demands the provision of a secondary emergency brake on all cranes handling molten metal. Street’s answer to this is to fit a large external disk to the main cable barrel with braking by means of an external set of callipers. This is automatically activated if the hoist speed exceeds the design speed by 10% or more, arresting movement to prevent a potential runaway situation. The external callipers are not just a highly efficient form of braking, but easy to access for inspection or maintenance. In addition to molten metal, this type of hoist may be used with other hazardous substances such as nuclear materials.

Crane and hoist configuration can also contribute to greater safety in operation. Twin hoist cranes are now much more common. Not only do they provide more flexibility in material handling, but when dealing with larger and more awkward loads, they improve stability in transit and give more options when picking and placing the load. Remote radio controls are also almost universally specified now as they allow the crane operator more freedom of movement and control from a position of safety and good visibility.

We have come far since the heyday of slate mining in Llanberis and industrial safety is now a prime concern for all manufacturers and equipment suppliers. Training and hazard awareness is a key element in this and the quest to improve physical safety in all aspects of mechanical handling continues.