Providing Safety
ISO-document for Trapped Key Interlocking

ISO-document for Trapped Key Interlocks

ISO / TS 19837: 2018 clarifies the design of mechanical interlock systems

A clear distinction between actuators and keys

What exactly does ISO / TS 19837: 2018 mean?
ISO / TS 19837:2018
is the first international ISO document specifically dedicated to Trapped Key Interlocking and is used as the starting point for design, selection and configuration. It answers many of the questions related to performance levels, key encoding and power interlocking. This is an important step forward that will create more choices for users of interlock devices and systems.

Trapped Key Interlocking originated in the rail and power distribution industries where sequential control is crucial for safe and continuous operations. In the 1960s, Trapped Key Interlocking was gradually introduced by the manufacturing sector, where isolating machinery before gaining access was required.

Machines with multiple energy sources and access points can be easily safeguarded using Trapped Key Interlocks. Over the years, Fortress Interlocks has developed specialised products, which can isolate air, hydraulic supplies and electrical power in sequence before allowing access points to be opened.

When ISO 14119: 2013 got published, Trapped Key interlocking was no more than an attachment. It was clear that this document did not contain all the specific requirements for Trapped Key systems. ISO 14119: 2013 in many ways confused users and potential users who had been familiar with their implemented trapped key interlocks installations for decades.

ISO / TS 19837: 2018, in the works for three years, is a welcome addition to the existing set of machine safety standards. Perhaps the most critical question remains where mechanical or hybrid mechanical / electrical systems stand in relation to the performance levels introduced in ISO 13849.

Power Interlocking is now more appropriately referred to as “Isolation control through direct mechanical action” and falls within the Safety Related Part of The Control System. This in combination with the section “Validating performance level” makes evaluating performance levels for Trapped Key systems a lot clearer.

The confusion that arose in ISO 14119: 2013, regarding the difference between actuators and keys is solved in ISO / TS 19837: 2018 both are addressed in the “Conditions and Definitions” and “Symbols and Short Terms” sections.

The need for a schematic overview of the trapped key system operation and establishing key coding appears under “Key Transfer Plan” and provides users with an excellent resource in the system design phase and a documented system layout after installation. You can also find that Key coding and management are discussed in detail here.

The standardization of symbols to represent trapped key interlocks makes it much easier for customers to understand the schematics. The outstanding graphic examples in the document are also useful for who is building a Trapped Key Interlock system.

Jo Smith, Fortress Managing Director: “The publication of ISO / TS 19837 will help keep Trapped Key Interlocking at the forefront of machine safety. This is very much appreciated by Fortress Interlocks. We have worked hard to ensure that Fortress products meet the strictest safety standards and our Trapped Key Interlocks are no exception. It is good to finally have a document that helps our customers to better understand how Trapped Key Interlocks fit into international machine safety standards. “


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