Interlocking device and sensitive device

by Jan 8, 2019Machine Safety

Many alternatives are available to allow for efficient control of access to the danger zones of equipment. The choice of one or many of these alternatives is mainly based on the need to access the danger zone, the frequency and the nature of the tasks to be performed inside the danger zone.

The Regulation respecting occupational health and safety clearly states the type of access control according to the need for access in article 182. The article states:

Controlling the danger zone: Subject to section 183, a machine shall be designed and built so as to make its danger zone inaccessible, failing which it shall be equipped with at least one of the following protectors or protective devices:

(1)  in the case where no one will have access to the machine’s danger zone while it is in operation:

(a)  a permanent protector;
(b)  a protector fitted with an interlocking device;
(c)  an interlocked protector fitted with an interlocking device;
(d)  a sensor device;

(2)  in the case where at least one person will have access to the machine’s danger zone while it is in operation:

(a)  a protector fitted with an interlocking device;
(b)  an interlocked protector fitted with an interlocking device;
(c)  an automatic closing protector;
(d)  an adjustable protector;
(e)  a sensor device;
(f)  a two-hand control.

In this blog, we will look at the second part of this article, namely the situation in which at least one person has access to the danger zone of the machine while it is in operation. More specifically, it will explore interlocking devices and sensor devices. The other types of protectors will be handled in other blogs of the same series.

The regulation prescribes the minimum requirements to abide by in article 175 for interlocking protectors, article 176 for interlocked protectors and 179 for sensor devices.

More details, that complete the requirements stated in the regulation articles, are provided in the CSA Z432-16 standards based on ISO 14120-2015 and ISO 12100-2010 (reviewed in 2015). In addition, since the solutions that require the integration of a protector fitted with an interlocking device, an interlocked protector or sensor device are always carried out using the parts of control systems relating to safety, the provisions of ISO 13849-1-2015 and ISO 13849-2 must be complied with. This ensures the reliability of security systems based on these devices.

According to ISO 12100-2010, a protector fitted with an interlocking device (interlocking guard in the standard) must be associated with an interlocking device so that, together with the control system of the machine:

  • the hazardous machine functions “covered” by the guard cannot operate until the guard is closed.
  • if the guard is opened while the machine operates, a stop command is given for all of the machine’s hazardous functions
  • when the guard is closed, the hazardous machine functions can operate, but not before a reset and start command initiated by the operator

Interlocked protectors equipped with an interlocking device (interlocking guard with guard locking in the standard), ensure the same functions as protectors fitted with an interlocking device. However, they guarantee the total disappearance of hazards before the protector can be opened/unlocked after a stop command is given by the worker. This device is applicable when hazards remain after stoppage of the machine.

Sensor devices provide almost the same hazard exposure reduction than that of an interlocking device. However, for sensor devices, machine stoppage isn’t provoked by the displacement of a protector, but rather the activation of an element sensitive to the presence of a body or parts of a body in the danger zone or in proximity of it.

These devices are not applicable when the hazard isn’t localized (e.g. projections, temperature, noise, etc.). In addition, calculations based on the distance to the danger zone, the estimated speed to reach the danger zone and the safety system response time must be performed before implementing a solution using a sensor device.

Finally, it is necessary that the environment in which these devices are used be taken into consideration (dust, humidity, temperature, etc.). Otherwise, failures leading to unwanted shutdowns (loss of productivity, higher probability of circumvention) or loss of safety functions can occur.

For more information, you can read our other blogs and you can contact us for our expertise in machine safety.

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Intervention Prévention Inc.

Intervention Prévention concentrates its operations in the field of work safety, offering specialized services following Standards CSA Z462 – Workplace Electrical Safety, CSA Z460 – Control of Hazardous Energy: Lock-out and Other Methods, and CSA Z432 – Safeguarding of Machinery.


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