Introduction Castell Trapped Key Interlocks


Trapped key interlocking ensures that a process is followed and cannot be circumvented or short cut. The transfer of a key ensures that wherever personnel find themselves, in either starting or shutting down operations, they can be assured that they are safe.

There are three simple steps in designing a trapped key system, what is being isolated, how many access points are there and what type of access is required.

A key is used to start the process and remains trapped whilst the machine is running. The only way to remove the key is to isolate the hazard.

This key is then used to gain access to the dangerous area and remains trapped in position while the gate or door is opened. The key can only be removed when the gate or door has been shut. In this way the key is either trapped when the machine is running and access cannot be gained, or the key is trapped while access is gained and the machine cannot be started.

Designing interlock systems

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

These are:

What is the operational flow to start and stop equipment?

• What is being isolated?

• Is there more than one system that needs to be isolated to make access safe?

• Is there a time delay required for safe access?

• How many access points are there?

• What is the type of access? Full body or part body?

• Severity of the possible injuries?

• What is the possibility of avoiding the hazard?

• What is the nature of the hazards?

• What are the energy sources present?

• What is the operating environment?