What is an interlocked machine guard?
An interlocked guard is connected to the machine control system so hazardous operation is prevented or stopped when the guard is not closed. It is used where operators need repeat access and a fixed guard would make the task impractical.
The interlock is only one part of the solution. Door construction, reach around the opening, stopping time, retained energy, defeat resistance and the position of reset controls all influence whether access is safely controlled.
- Access frequency and task
- Machine stopping time
- Reach and whole-body entry
- Foreseeable defeat or bypass
When is guard locking considered?
Guard locking may be required where the hazard cannot reach a safe condition before a person could enter, including machinery with run-down time or retained pressure, heat or movement. The release principle also needs to suit power loss and emergency conditions.
Device selection should follow the risk assessment and required safety performance. Oxford Machine Guarding can provide the physical guard and agreed access hardware, with specialist safety-control validation included only where defined within the project team.
- Run-down and safe-stop behaviour
- Power-to-lock or power-to-unlock assessment
- Emergency release where required
- Mechanical mounting and alignment
Reset and restart need deliberate design.
Closing a guard should not create an unexpected restart. Reset locations should support a clear view of the protected zone, and whole-body access may require additional measures to prevent a person being trapped or overlooked.
On connected packaging equipment, the design also establishes which machines stop when a door opens and how upstream or downstream zones are affected. These interface decisions should be recorded before manufacture.
- No unexpected restart
- View of the safeguarded space
- Zone and conveyor interfaces
- Recorded functional requirements
