The battery isolator switch on a generator set used to power a washing plant failed to danger. Users of similar equipment are advised to note the contents of this alert and carry out checks on equipment they operate.
The generator set was fitted with a battery isolator switch shown in the attached image. The purpose of the isolator is to isolate power from the battery to the starter motor of the generator set as a means of achieving secure isolation during maintenance, for example.
In normal operation, the generator is started and stopped from a control panel that is in a different location from the battery isolator.
The isolation procedure involved
- shutting down the plant in the normal way
- switch the battery isolator switch to the ‘OFF’ position
- remove the key from the battery isolator switch
- move the lockable flap to cover the barrel of the lock
- secure the flap with a multi hasp padlocking device
- operators add their personal locks to the multi hasp
- attempt to star the generator set by normal means
By chance it was discovered that the battery isolator key had fallen from the barrel of the lock WHILE THE GENERATOR WAS RUNNING.
This was immediately reported as a near hit and investigated by site management.
The investigation showed that the barrel of the lock was worn and it was possible to remove the key in the ON position. In fact, the key was so loose in the lock barrel that vibration had caused it to fall out.
Clearly the key should be retained in the lock barrel in the ON position and is designed only to be removed in the OFF position.
The failure created a hazardous situation where the key could be removed from the isolator without isolating power from the battery. An operator may lock the flap in position believing that the battery is isolated when in fact it isn’t. Isolation has not been achieved and the safety of operatives working on the plant is then entirely dependent on the final TRY OUT step of LOTOTO to reveal the defect.