The Guard That Was Too Close: Machine Access vs Safety Clearance
A machine guard (interlocked door) mounted 100 mm from a moving belt. The operator reached around the guard to clear a jam. The belt caught his sleeve. The guard was there, but it was too close — the operator could reach the hazard without opening the door. This is about minimum safety distances for fixed guards.
The reach-over rule
A fixed guard must be mounted far enough from the hazard that the operator can’t reach over or around it. The distance depends on the guard height. A guard that’s too low lets the operator reach over it. A guard that’s too close lets the operator reach around it.
| Guard height | Minimum distance to hazard |
|---|---|
| 1200 mm | 100 mm (reach over) |
| 1400 mm | 300 mm |
| 1600 mm | 500 mm |
| 1800 mm | No reach-over (guard is high enough) |
These are per ISO 13857. The numbers are conservative. If the guard is 1200 mm high and the hazard is 100 mm away, the operator can reach over. We needed either a taller guard or more distance.
What we did
1. Extend the guard. We added a 600 mm extension to the top of the guard, making it 1800 mm high. Now the operator can’t reach over. The guard blocks access from above.
2. Increase the distance. We moved the guard 300 mm away from the belt. Even if the operator leans over, they can’t reach the belt. The distance plus the height makes the hazard unreachable without opening the interlocked door.
3. Add a fixed guard where reach isn’t needed. The section of the guard that the operator doesn’t need to open (the back and sides) is fixed. Only the front door is interlocked. The operator can’t remove a side panel to reach the hazard.
The interlock door
The interlocked door has a safety switch that opens the control circuit when the door opens. The machine stops. The door can’t be bypassed (no override key in production). If the door is opened during operation, the machine stops within its stop time (0.5 seconds for the belt conveyor).
The jam-clearing procedure
The operator reached around the guard because clearing a jam without opening the door was faster. We added a small access panel (interlocked) specifically for jam clearing. The operator opens the panel, clears the jam, and closes it. The machine restarts. No more reaching around the guard. The procedure is documented and trained.
The guard rule: A guard that’s too close is as bad as no guard. Per ISO 13857, the distance from guard to hazard depends on guard height. If the operator can reach over or around it, the guard is decorative. Extend the guard, increase the distance, and provide a proper interlocked access panel for maintenance.
