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Trapped Key Interlocking

A trapped key interlock works by immobilizing a part/parts until the correct sequence has been followed. A key is trapped—making movement impossible—until the other keys in the sequence have been set to their correct status. This is commonly used to make gates, valves, etc. safe in environments where equipment can be dangerous if not operated correctly.

The benefits of this system include:

  • Reduced human error
  • Less downtime
  • Guaranteed compliance

Plus, our systems are customizable and designed to last, which means that once you have fitted a solution that works for your specific needs, you won’t have to think about it again any time soon.

Locked state (Isolation)
The moving part is immobilized by the breakers and the key is trapped. This key cannot be removed because the other two keys have not been inserted.

Unlocked state (Access)
The two keys are inserted, which releases the previously trapped key. Once the breakers are off the part can move freely.

STI’s trapped key interlocks boast a number of benefits, including:

  • It removes the possibility of human error by making it impossible not to follow the correct sequence
  • It protects both people and equipment
  • It improves efficiency by reducing the number of setbacks and manufacturing breaks caused by incorrectly followed operations
  • It makes employees feel safe at work
  • It helps sites achieve regulatory compliance, particularly with the European Machinery Directive 2006/42/CE and EN ISO 13849-1:2008 (Safety of Machinery – safety-related parts of control systems)
  • It can be used for a multitude of processes (our engineers can customize it according to specific needs)

Points to consider when identifying components

To design interlock components into an integrated safety system there are a number of key questions that need to be addressed.

  • The operational flow to start and stop equipment
  • What is being isolated
  • The number of systems that need to be isolated to make access safe
  • Time delay requirements for safe access
  • The number of access points
  • The type of access (full body or part body)
  • The severity of the possible injuries
  • The possibility of avoiding the hazard
  • The nature of the hazard
  • The present energy sources
  • The operating environment
  • Use of risk assessments as a guide to examine how the integrated safety system functions

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