Why use Interlocks


Despite tighter statutory requirements for the guarding of dangerous machinery and an increased awareness of the need to design for operator safety, avoidable industrial accidents continue to occur.  In virtually all cases some form of guarding was in use at the time.

This section explains how and where interlocking can be used to augment existing safety systems, and effectively protect personnel. Later sections describe in detail the use of interlocking systems in industry.      

The fundamental principles on which all machine guarding is based, is the construction of a secure barrier to stop a worker being able to come into contact with a dangerous part of a machine.  However, guarding is only effective while machine operation does not require human intervention.  To ensure that when workers need to access a machine they do so under safe controlled conditions, further safety measures must be provided.

Even in highly automated environments there is a frequent need for personnel to gain access to machinery.  With an assembly robot, for example, in addition to the need for local programming, there are other day-to-day requirements for regular access to the area around the robot.  Maintenance, servicing, cleaning, part loading, fine tuning and in-production adjustments are just some of the circumstances under which workers must enter perimeter guarding.

As soon as a worker needs to access a machine, a new and unpredictable element enters the safety system.  It should be safe to assume that a maintenance engineer will turn a machine off before unlocking the guard, and that a simple “work in progress” indicator will ensure that no one inadvertently restores power to the machine while work is being carried out.  It should be possible to rely on common sense and safe working practices.

The catalogue of industrial accidents caused by human error indicates that this is not the case.  Ignorance, forgetfulness or haste can instantly negate the most thorough safe working practice regulations. To be effective, a machine guarding system must accommodate the need for frequent access and positively control the conditions under which access is allowed.

It is important that users, as well as manufacturers, identify potential hazards and specify the relevant safety control measures at the earliest possible stage.  Using hazard analysis and risk assessment techniques this should take into account the design and operation of the machine in the context of its working environment, together with the nature of the production process itself.