New machinery safety standard welcomed
11 March 2019
An ISO document devoted specifically to trapped key interlocking answers many questions that have arisen relating to performance levels, key coding, and power interlocking and will provide more choice for users of interlock devices and systems.
Fortress Interlocks believes the introduction of ISO/TS 19837:2018 – Safety of Machinery – Trapped Key Interlocking Devices – Principles for design, selection and configuration – is a welcome addition to the existing suite of machinery safety standards.
Perhaps the most critical question addressed is where mechanical or hybrid mechanical/electrical systems sit in relation to performance
levels introduced in ISO 13849.
Trapped Key Interlocking has its roots in the rail and power distribution industries where sequential control was, and still is, critical to safe, continuous operation. In the 1960’s trapped key interlocking was gradually utilised by the manufacturing sector, where isolating machinery before gaining access, was the requirement.
Machinery with multiple energy sources and access points can be easily safeguarded using trapped key interlocks. Fortress Interlocks has developed specialised products over the years which can isolate air and hydraulic supplies as well as electrical power in sequence before allowing access points to be opened.
When ISO14119:2013 Safety of Machinery – Interlocking device associated with guards, Principles for design and selection, was published trapped key interlocking had become no more than an annex, even the scope was clear that it did not provide all the specific requirements for trapped key systems. In many respects ISO14119:2013 served to confuse users and potential users familiar with decades of trapped key interlocks installations.
ISO/TS 19837:2018, three years in the making, is a welcome addition to the existing suite of machinery safety standards. Perhaps the most critical question addressed is where mechanical or hybrid mechanical/electrical systems sit in relation to performance
levels introduced in ISO 13849.
Power Interlocking is now more properly referred to as 'Isolation control through direct mechanical action' and falls within the Safety Related Part of The Control System. This coupled with the section 'Validating performance level' makes evaluating performance levels for trapped key systems much clearer.
The difference between actuators and keys is cleared up, following the confusion created in ISO14119:2013, and both are addressed in the Terms and definitions and Symbols and abbreviated terms sections.
The need for a schematic detailing the trapped key system operation and establishing key coding appears under 'Key Transfer Plan' and will provide users with an excellent tool in the system design phase as well as a documented system layout after installation. Key coding and management is also addressed extensively.
A much-needed standardisation of symbols to represent trapped key interlocks will make it easier for customers to understand schematics, and the excellent pictorial examples throughout the document are useful for those building a trapped key interlock system.
Jo Smith, Fortress managing director, says: “The publication of ISO/TS 19837 will help to keep trapped key interlocking at the forefront of machine safety in the future, it is very much welcomed by Fortress. We have worked hard to ensure Fortress products meet the most stringent safety standards and our trapped key interlocks are no exception. It is good to finally have a document that helps our customers understand better how trapped key interlocks fit within the international machinery safety standards.