The use of the Safe Distance Scale Stick

by Mar 14, 2019Machine Safety

Firstly, access to any danger zone of a machine must be eliminated or restricted. The choice of restriction level and the means established to prevent access will depend on the nature of the danger zone and the need to access it. It can also depend on the proximity to the danger zone.

In the case where frequent access or access for operational purposes are not required, the first conceivable solution is eliminating access using a permanent protector.

Depending on the nature of the danger zone, three possibilities are provided for in the standards: access over, under and through the protector. In this blog, we will look at access through a permanent protector.

For many reasons (ease of fabrication, cost, weight and visibility needs), permanent protectors generally have openings that are theoretically accesses to the danger zone. For this reason, the design of permanent protectors is based on three parameters:

  1. The type of openings on the protector
  2. The size of the openings
  3. The distance to the danger zone

The combination of these three parameters for designing a permanent protector that meets standard requirements is described in CSA Z432 for machine safeguarding based on the international standard ISO 138572008 (adopted without modifications by CSA in 2015).

When permanent protectors are already installed, a conformity check it is generally necessary. Since the parameters to consider and the unreliable nature of the human eye in determining distances with precision, and the sometimes-high number of points to be check, the use of certain tools becomes very practical in terms of precision, avoiding mistakes and speed. Among the tools, the Safe Distance Scale Stick (‘’Gotcha Stick’’) is cited.

The stick is a tool that simulates the limb you wish to keep from the danger zone (e.g. finger, hand, arm). Performing the permanent protector’s conformity check is done simply by making sure that the stick cannot reach the danger zone when inserted through the openings of the protector, according to its smallest opening.

The image illustrated below shows a Safe Distance Scale Stick designed and produced by Intervention Prévention and is based on ISO/CSA 13857-2015.

The IP Safe Distance Stick is made up of two parts for two types of openings: slit and square (to evaluate circular openings in a protector, that square side must be used).

The first step to checking a protector’s conformity is identifying the type of opening and its smallest dimension. Afterwards, the Safe Distance Stick is inserted into the opening according to the smallest dimension facing the danger zone. If the danger zone can be touched, this means corrections must be made to the permanent protector or its installation distance from the danger zone.

If the fixed guard has multiple types of openings, the process needs to be repeated using the same steps.

In the case where the openings are shaped irregularly, comparability to a slit (namely width much larger than height)  or comparability to a square (width and height are of comparable sizes) are checked to decide what side of the Safe Distance Stick to use.


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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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Beloeil (Québec)
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