2.5.5 Other Features

Protection DevicesIn accordance with most modern legislation cranes manufactured with a rated capacity of 1 tonne or more must be fitted with devices to warn the operative and prevent dangerous movements of the load in the event of overload. However, it should be noted that older equipment may not be fitted with such devices and, if not, consideration should be given to upgrading them.

Overload protection devices take different forms but are usually set to allow a load slightly in excess of the SWL to be raised. This protects the hoist from accidental overload but allows for dynamic loading.

Older cab-controlled cranes usually had a driver operated foot brake on the long travel motion. These have to be replaced with automatic brakes when the crane is converted to pendant control. The crosstravel motion was slower and below a certain speed there was not usually a brake fitted. This is not always addressed when cranes are converted to pendant control. There may be some of these still in service and if so, their acceptability should be reviewed. Modern cranes should have brakes on both the long and cross travel motions. These are actuated on release of the controls. Unlike the hoist brake, which is designed to arrest the load in the shortest possible distance, travel brakes are designed to stop the motion more gently to minimize load swing.

The hoist motion should always have an upper limit switch to prevent over hoisting. This is a safety device and should not be used as a positional limit switch. If for operational reasons a positional limit is required, a secondary system should be used. Most manufacturers can supply these.

Most modern cranes will also have a lower limit switch to prevent over lowering. Many older cranes did not have a lower limit but relied instead upon having sufficient rope for the bottom hook to reach the floor. This should be borne in mind when relocating such a crane.

Most older cranes were not fitted with limit switches on the long travel and cross travel motions and relied instead on the skill of the operator. The main reason is that simple limit switches can only cut the power supply. Unless this is done at a position which allows for the full speed stopping distance, they will be ineffective. However, positioning them to allow for stopping from full speed will considerably limit the floor area covered by the crane. Modern electronics can provide an effective solution and should be considered if the risk assessment shows that it needs to be addressed.

If more than one crane is operating on the same supporting structure or track, anti-collision control should be considered unless the risk of collision can be controlled by other means. Again, modern electronics can provide a solution.

For portal and semi portal cranes operating in an area where people may be present, anti-collision control to protect personnel should be considered. For further information please refer to the statement in 1.A6.4.8.6.1 Motion limits.

There should be a lockable isolator switch which can disconnect the power supply to the down shop conductors. This should be mounted in an easily accessible position and clearly identified as the isolator for the crane. There should also be a separate lockable isolator or crane disconnector switch on the crane at the point where the power supply enters the control cabinet.

All crane controls must incorporate an emergency stop button coloured red on a yellow background. Unlike the other buttons this must not be of the self-resetting type and should require manual resetting once actuated. It must be in a readily accessible position and this will normally be with the crane controls, for example in the operator’s cab or in the pendant push button box.

When remote controls are used, the control station should always include a stop button. However, it may also be necessary to have a separate hard-wired emergency stop button to provide functional safety. This addresses the possibility of a malfunction in the control electronics causing a motion to start without an operator command at a time when the control station is unmanned or out of reach. The separate emergency stop button enables anyone in the vicinity to take action.

This approach may not be practical in situations where there is more than one crane on the supporting structure or the supporting structure is very long. However, the problem can also be addressed by good management of the remote-control station. (See section 2.11 SAFE USE OF ELECTRIC BRIDGE AND GANTRY CRANES dealing with safe use) An additional emergency stop is not required if the following conditions apply:

In addition some of the risks arising from an unmanned control station can be addressed as follows:

The control station can have a separate ‘hold to run’ button which holds in the main contactor. This requires two-handed operation but will automatically de-energise the main contactor when the control station is left unattended. If fitted, this facility should have the same level of integrity as the emergency stop, i.e. a single fault shall not lead to loss of safety function and, whenever reasonably practicable, shall be detected at or before the next demand on the safety function.