26.4.4 Method of Attachment
Portable magnets are generally of the permanent or electro-permanent type with a lifting capacity up to approximately 3 tonnes or of the battery type with a lifting capacity up to up to approximately 5 tonnes. They will usually be fitted with a lifting eye to facilitate easy connection to the lifting machine hook. Higher capacity magnets of the electro-permanent or electro type are often an integral part of the lifting machine.
Multiple magnets of all types may be used with advantage in conjunction with a lifting beam to lift long and/or flexible loads.
Figure 26.4.4-1 Typical portable permanent magnetic lifter with lifting eye
Figure 26.4.4-2 Electro-permanent magnetic lifter suspended via a chain sling
In the case of electro-magnets, the magnetic forces are only generated when the electrical supply is flowing. Failure of the electrical supply will cause the magnet to lose its lifting power instantaneously. Without additional safety features, their use is therefore limited to situations where a risk assessment has established that falling loads do not present a hazard to people. The warning devices and stand-by battery referred to above are intended to allow time for persons to leave the danger zone. In applications where it may be difficult to leave the danger zone within a safe period of time, further measures will be required. These may include a redundancy of the supply lines and control systems or a secondary mechanical holding system which can be deployed before exposing persons to danger.