Emergency Stop System Requirements
Emergency stop systems on conveyor belts exist for one purpose: to allow any person near the conveyor to stop it immediately if they observe a dangerous condition or if they or a colleague is in danger of injury. The system must be reliable, accessible, and clearly identifiable. Failure of an emergency stop system during an incident can result in fatality.
Pull-Wire Emergency Stop: The Primary System
Pull-wire (or pull-cord) systems run the full length of the conveyor on one or both sides. A wire is strung at approximately waist height, anchored at intervals and connected to a series of switches. Pulling the wire at any point along its length, in either direction, triggers the nearest switch and stops the conveyor.
Spacing Requirements
- MSHA (USA): maximum 30m between anchor points / switch locations
- Australian standard: maximum 50m, but 30m is best practice
- European (EN 620): maximum 50m for outdoor, 30m for enclosed underground
- Best practice recommendation: 20β?5m spacing for all mining conveyors
Wire Specification
- Wire diameter: minimum 3mm stainless steel or galvanised steel
- Wire colour: yellow or orange β?high visibility, contrasting with surroundings
- Activation force: 50β?50 N (must be activatable by a person in distress or wearing gloves)
- Travel before activation: maximum 150mm deflection before switch triggers
Switch Requirements
- Latching type β?once tripped, switch remains open until manually reset
- Manual reset at switch location β?prevents remote reset without physical inspection of the tripped location
- Fail-safe design β?wire break (wire cut or anchor failure) must trigger stop, not allow bypass
- IP65 minimum for outdoor; IP67 for underground wet
Additional Emergency Stop Points
- Drive end: Mushroom-head push button at motor control panel, easily accessible to drive operator
- Tail end: Push button at tail pulley β?critical for operators loading material
- Loading point: Additional button where operators are stationed during loading
- Control room: Master stop that stops all conveyors in sequence or simultaneously
Testing Programme
| Test | Frequency | Method |
|---|---|---|
| Pull-wire function test (each switch) | Monthly | Pull wire at each switch β?verify conveyor stops |
| Wire break simulation | Quarterly | Disconnect wire at one anchor β?verify stop triggers |
| Reset confirmation | With each function test | Verify remote restart is blocked until manual reset |
| Response time measurement | Annually | Measure belt stop time from pull to full stop β?must be β? seconds |
| Visual inspection (all hardware) | Monthly | Check wire tension, anchor condition, switch housing |
β οΈ Never Defeat or Bypass Emergency Stops
Bypassing, tying off, or defeating pull-wire emergency stops for any reason β?including "to keep production running while a switch is repaired" β?is an unacceptable safety violation in all jurisdictions. If a pull-wire switch requires repair, the conveyor must be locked out until repair is complete, or a temporary replacement switch must be installed before restarting. Lives depend on these systems functioning correctly.
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