Safety of Machinery

Safety of Machinery: Interlocking devices associated with guards

 

In April 2015 important changes will be made to Machinery Safety standards used within the European Machinery Directive 2006/42/EC impacting end users & machine builders alike.

The Machinery Directive 2006/42/EC (formerly 98/37/EC) references various standards, most notable the machinery safety standards such as EN ISO 13849-1 and EN 1088.

A new standard “EN ISO 14119:2013 Safety of machinery - Interlocking devices associated with guards - Principles for design and selection” comes into full force on 30th April 2015, and replaces the previous standard EN 1088.

 

OPERATOR BEHAVIOUR – INTERLOCK DEFEAT

In 2013 the UK Health & Safety Executive (HSE) published a report highlighting research which implied that operator defeating of safety devices is widespread within the UK engineering industry, involving a variety of machine types and techniques. The 2013 research focused on Computer Numerical Control (CNC) machines, but the characteristics of the individual (e.g. risk perception, knowledge of risks), and the environment (e.g. machine design and procurement), are common factors and exert an important influence on operatives’ behaviours.

 

EN ISO 14119

The new EN ISO 14119 standard has a distinct focus on the defeat of guarding systems, and provides specific guidance on counter measures which should be implemented to minimise the potential for successful interlock defeat, and reduce the operator incentive of attempt to defeat interlocks as their operation has limited interference on machinery operation or slow down of production.

EN ISO 14119 will replace all national standards on this subject, and will have an important impact on both machinery builders creating new machinery, and end users who may modify or maintain their own machinery as there are requirements relating to maintenance, function testing, and replacement of components.

 

KEY CHANGES

The standard offers a number of approaches which can be considered. These include prevention of access to the interlocking device, stopping operators using substitute actuators via coding, and the addition of defeat monitoring.

Importantly the standard now specifically covers coded actuators, using RFID or magnets, and assigns coding levels as follows:

 

Actuation principle examples

Actuator examples

Type

Mechanical

Physical contact / force

Uncoded

Rotary Cam

Type 1

Linear Cam

Hinge

Coded

Shaped actuator

Type 2

Trapped Key

Non-contact


 

Inductive

Uncoded

Suitable ferrous metal

Type 3

Magnetic

Magnet, solenoid

Capacitive

Any suitable object

Ultrasonic

Any suitable object

Optic

Any suitable object

Magnetic

Coded

Coded magnet

Type 4

RFID

Coded RFID tag

Optic

Optically coded tag

Note: These “types” are not hierarchical and should not be confused with other product “types” for example light curtains.

 

INSTALLATION (Minimum Safe Distance)

The standard clarifies a common misunderstanding about interlocking guards; regarding the minimum separation distance between the guard door and the hazard. Interlocked guards are required to be installed at a minimum distance such that a person cannot access a hazard before it is controlled (e.g. the machine stops).

This means that interlocked guards with guard locking may be required. The minimum distance is calculated according to ISO 13855.

 

With only a couple of months until the old EN 1088 standard loses the presumption of conformity, machine builders and manufacturing end users must take steps to ensure their designs and operations embrace the new requirements.