Testing of conveyor pull wire activated emergency stops

Conveyor systems are used extensively throughout the mining and quarrying industry. As with any plant, they must be subjected to regular maintenance and testing. Part of any conveyor maintenance schedule should include testing of the pull wire activated emergency stops. A number of recent structured inspections has found that the testing of these devices has either not been sufficient or has not been undertaken correctly. Most testing was found to involve simply pulling the pull wire in one direction as hard as required to activate the emergency stop. This basic test fails to test a number of other key requirements of pull wire activated emergency stops.

One source of information relating to the testing of conveyors is Australian Standard AS 1755-2000, 'Conveyors-Safety requirements'. The standard states that where used as an emergency stop control, a pull wire activated device shall comply with the following requirements:

1. Breaking, slackening or removal of the pull wire shall activate the device.
2. Where electrical continuity is monitored in the pull wire:
   1. the slackening requirements of Item (a) need not apply
   2. the conveyor shall stop in the event of the pull wire being broken or removed.
3. The force required to operate the pull wire activated device shall not exceed 70 N when applied midway between supports and at right angles to the axis of a pull wire with less than 300mm movement and 230 N along the axis of the wire.
4. The design and distance between pull wire supports shall be such that the wire moves freely when pulled and does not become disengaged from the support.
   NOTE: A maximum spacing of 6m should apply.
5. Materials used for pull wires shall be of adequate strength, be protected against environmental conditions and be suitable for handling without the need for additional protection being worn by operators.
   NOTE: Where more than one switch is used in a pull wire system, a visual indicator should be provided to indicate which switch has been activated.
6. The switch shall be activated when the pull wire is pulled in any direction.

Tests carried out on conveyor pull wire activated devices should ensure all requirements of Australian Standard AS 1755-2000 are taken into account. The results of any service, maintenance and testing of conveyor pull wire switches should be kept as a record, not only to verify the testing but to monitor any deterioration that may cause an unacceptable level of risk.

Authorised by Peter Minahan - Chief Inspector of Mines

Contact: minesafetyandhealth@dnrm.qld.gov.au

Issued by Queensland Department of Natural Resources and Mines