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Guard Interlocks

industrial accidentAn interlocking device is a mechanical, electrical or other type of device, the purpose of which is to prevent the operation of the hazardous machine functions under specified conditions, normally when a guard door remains open.

interlocks are an integral component of the safety related control function and where there are more than one  than one interlocks fitted to a machine assembly, generally where there are more than one (1) moveable door, these interlocking functions are connected electrically to the safety relay in series.

industrial accidentInterlocking devices have a guard door position monitoring function that senses whether the guard is closed or not and produce a stop command when the guard is not in the closed position. Some interlocking devices also have a guard locking function to keep the guard locked whilst the hazardous function is present.

BS EN ISO 14119:2013 specifies four (4) functional types of interlocking devices, namely;

  1. TYPE 1 Interlocking. Is an interlocking device with mechanically actuated position switch, with an un-coded actuator, e,g, a hinged interlocking device.
  2. TYPE 2 Interlocking. Is an interlocking device with mechanically actuated position switch with coded actuator, e,g. a tongue actuated position switches.
  3. TYPE 3 Interlocking, is an interlocking device with non-contact actuated position switch with un-coded actuator, e,g, a proximity switch.
  4. TYPE 4 Interlocking, is interlocking device with non-contact actuated position switch with coded actuator, e,g, RFID tag actuated position switches

It will be beneficial to the reader at this stage to understand some of the terminology used when we discus interlocking devices, namely;

“Interlocking Guard” is a guard associated with an interlocking device so that, together with the control system of the machine, the following functions are performed;

  • the hazardous machine functions protected by the guard cannot operate until the guard is closed.
  • if the guard is opened whilst hazardous machine functions are operating, a stop command is given.
  • when the guard is closed, the hazardous machine functions protected by the guard, can operate, however, the closure of the guard does not by itself start the hazardous machine functions.

 

NOTE: ISO 12100:2010, Section 3.27.4, describes how an interlocking guard can contain or be equipped with one or more interlocking devices and which can be of different types, thus giving some diversity to the system.

“Interlocking guard with a start function” is a special form of interlocking guard which, once it has reached its closed position, gives a command to initiate the hazardous function(s) without the use of a separate start control, however, ISO 12100:2010, in Section 3.27.6 gives clear and detailed provisions regarding the condition of use, namely;

 

industrial accidentEach of the areas cost are real and necessary, however, how can the defendant in claims negligence defer or indeed by-pass costs? The answer is good safety management by a dedicated person with full authority by senior management for cultural change in relation to safety ownership and responsibility.

JGMA can assist companies to implement this cultural change in short but worthwhile in-house training.