Trapped-key safety systems control an agreed sequence of isolation, access and return to service. The key arrangement must be selected through a machine-specific risk assessment. Define every hazardous energy source, access point and person-entry scenario before choosing locks or an exchange unit.
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Describe the sequence of isolation, access and return to service, including every person and access point involved. Review the hazards and energy sources that must remain controlled. Have the key-exchange arrangement assessed as part of the complete safety system, with escape, lost-key and restart procedures included in validation.
These are questions for the safeguarding review, not a generic installation design. The full machine and its operating tasks determine the required arrangement.
Identify hazardous motion and stored or supplied energy, including connected machinery. Agree how the required safe condition is established and verified. Removal of a control key should not be assumed to isolate every hazard without checking the actual system.
Map entry gates, removable sections and other foreseeable access. Separate routine operation from cleaning, blockage clearance and maintenance. Include the route a person takes inside the area and the hazards that remain during each task.
State whether one or several people may enter, whether they can lose sight of each other and who controls return to service. Have the assessment define the required personal-control arrangement. One access key is not automatically sufficient for every multi-person task.
Prepare a state diagram showing which key is available or trapped at each stage and which action it permits. Assign unique identifiers and controlled ownership. Review spare, replacement and lost-key handling so an unintended key cannot undermine the agreed sequence.
Review how a person leaves the safeguarded area and how the area is checked before a deliberate restart. Include visibility, trapped-person scenarios and emergency response. Returning a key must not be treated as proof that every person and hazard is accounted for.
Agree design responsibilities, drawings, the assessed safety functions, inspection and validation records, user instructions and periodic checks. Test the defined sequence and foreseeable incorrect actions under a controlled validation plan before the system is released for use.
The right choice changes with hazards and foreseeable access for trapped-key machinery access control, machine motion and stopping behaviour, your line layout and required results.
For the engineering review, provide an access map, energy-source list, task descriptions and a proposed sequence of operating states. The competent design and validation team should resolve isolation, personal control, escape, lost keys and restart together. Keep approved diagrams and key records with the machine documentation, and review them when the machine or access task changes.
Use the selection guide to compare the scope, then send the specification checklist with your application enquiry.
Your final solution for trapped-key machinery access control must reflect the law, current standards and site-specific risks that apply to your installation.
A trapped-key concept should be reviewed as a sequence of controlled states, including what happens when several people or several access points are involved. The arrangement must follow the machine-specific safeguarding and isolation assessment.
Identify electrical, pneumatic, hydraulic, gravity and other hazards relevant to the installation. Record what must be isolated, restrained, dissipated or otherwise controlled before access. The presence of a key-operated device does not establish that every hazardous condition has been addressed.
Show who receives permission to open a gate and how people inside retain control of the conditions needed for their protection. Include whole-body entry and more than one person. Have the competent designer assess the appropriate arrangement; a single shared access key is not a complete description of a multi-person work method.
List an open gate, a person still inside, a missing key and a change of shift as scenarios to resolve during design. Define an authorised response without using uncontrolled duplicate keys or bypassing the intended sequence. Keep key identification and custody in the operating arrangements.
An added gate or connected machine can change the original assumptions. Update the isolation and access diagram and the associated verification before the revised arrangement is used. Retain clear instructions for return to service, including the distinction between completing the access sequence and deliberately starting production.
Review trapped-key access planning — explore the existing guidance
Further reading: HSE safe-intervention principles, HSE machinery safety.