Plant maintenance and safety interlocks – myths and facts

In a recent article entitled “Unsafe Maintenance”, Judith Hackitt, chair of the UK’s Health and Safety Executive, examined some of the reasons why so many serious accidents and even fatalities continue to occur within processes related to the maintenance of machinery and equipment.

Trapped key interlocks ensure that machinery is maintained in a safe and efficient manner

Judith identified several common attitudes, concerns or faults which can ultimately lead to the safety of maintenance workers being compromised:

  • Time pressure – while machinery is stopped, money is being lost.
  • A focus on addressing everyday risks such as slips and trips, rather than mitigating the potential risks involved in machine maintenance.
  • A failure to plan maintenance activities or consider the best and safest ways to carry them out.
  • A perception that safety equipment will slow down production.
  • An absence of basic safety equipment, such as lockout / tagout and “Castell key arrangements”, which prevent access to running machinery and accidental start-up during maintenance activities.
  • A lack of the necessary ability to safely maintain equipment.


Trapped key interlocks can address all of these issues. It would be helpful to challenge some of the common industry misconceptions and separate fact from fiction.

“Mechanical trapped key interlocks slow down production; sensor-type safety solutions are much faster and just as safe.”

MYTH – A well designed safety interlocking system will work in harmony with existing manufacturing processes.

 “A well designed trapped key interlock can ensure the highest levels of safety integrity.”

FACT – The secret to a good safety system is a comprehensive risk assessment and understanding of the maintenance requirements. Trapped key technology will enforce these procedures.

 “I have to choose between implementing a trapped key system or a lockout / tagout system.”

MYTH – Trapped key interlocks and lockout / tagout can be combined to deliver an integrated safety system that covers planned and unplanned maintenance intervention.

 “Trapped key interlocks are expensive and inflexible.”

MYTH – With a wide installed base, trapped key interlocks have a long heritage of flexibility across heavy and light manufacturing operations. They are often found in excellent working condition even after decades of use, providing years of cost-effective safety.

“Interlocks are complicated and confusing.”

MYTH – Being process-driven, trapped key interlocks are easy to use, regardless of language or technical expertise.


Allied to thorough risk assessments and clear method statements, trapped key interlocks ensure that machinery is maintained in a safe and efficient manner by:

  • Dramatically reducing process risks and enforcing routines.
  • Isolating a machine’s power supply before work can begin.
  • Creating a robust process in areas where noise and communication could be an issue.
  • Performing in harsh and difficult manufacturing environments.

By: David Hughes, Sales Director, Castell Safety International Ltd.

Tags: ,

Leave a Reply