Engineering Protective Measures (Fixed/Interlocking Protection)
Created on 07.21
Engineering Protective Measures (Fixed/Interlocking Protection)
Objective: When hazards cannot be completely eliminated, use physical barriers to prevent personnel from entering hazardous areas.
Types and Selection:
1. Fixed Protective Devices:
Description: Permanently fixed to the equipment (e.g., welded or bolted), and can only be removed using tools.
Application: Hazardous areas that do not require frequent access (e.g., gearboxes, flywheels, drive shaft guards).
Requirements: Sufficiently robust and stable; designed reasonably with no sharp edges or burrs; sufficient safety distance from the hazard source (calculated); preferably opaque or with warning markings.
2. Interlocking protective devices:
Description: Opening or removing protective devices (doors, covers, light curtains, safety mats, etc.) automatically triggers shutdown or prevents hazardous movements from starting, and maintains a safe state until the protective device is fully closed and reset. Protective devices cannot be opened while the equipment is running.
Key Points: Interlocking functions must be reliable (high-reliability components, redundant design, monitoring), with priority given to forced disconnection (mechanical interlocking or safety relays/safety PLC control) over control circuit interlocking.
Types:
Mechanical Interlocking: Directly disconnects the power source or brakes via physical structures such as levers or cams.
Electrical interlocking: Uses limit switches, safety door switches, reed switches, etc., with signals fed into the safety control system (safety relays, safety PLC).
Non-contact interlocking: Such as safety light curtains, safety laser scanners, safety radars, capacitive sensing devices. Especially suitable for areas requiring frequent access or large equipment.
Key exchange system: Used in areas requiring multi-person collaboration or strict isolation, where the key represents “control authority.”
Application: Equipment requiring regular access to hazardous areas for operation, maintenance, calibration, or cleaning (e.g., injection molding machines, presses, robot workstation entrances).
3. Adjustable protective devices:
Description: Manually adjustable to accommodate different workpieces or operations (e.g., guide guards on sawing machines).
Requirements: Must be securely fixed after adjustment; adjustment mechanisms should be convenient and unlikely to move accidentally.
4. Self-closing protective devices:
Description: Automatically close via gravity, springs, or hydraulic/pneumatic systems (e.g., spring-hinged doors).
Application: Suitable for situations requiring quick temporary access (but typically still requires interlocking).
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