Thursday, August 18, 2016

Is your safeguarding device actually protecting your workers?

Engineered controls are a popular method for restricting access to hazards; they include light curtains, safety  mats, area scanners and two hand controls.  An important consideration in the performance requirements of engineered controls is their safe distance.  This is the minimum distance that the device must be mounted from the hazard in order to effectively provide protection from the hazard. If the engineered control is not mounted at a safe distance it will not stop the machine in time to protect the worker!

The safe distance is dependent on the time taken to process the stop command, and how far an operator can penetrate the hazard zone before being detected by the device. The formula used to calculate safe distance (as referenced in CSA Z432-04 Safeguarding of Machinery) is:


Ds =K x (Ts + Tc + Tr + Tbm) + Dpf


Ds            = minimum safe distance between the safeguarding device and the hazard

K              = speed constant: 1.6 m/s (63 in/s) minimum, based on the movement being the

                    hand/arm only and the body being stationary

Ts            = worst stopping time of the machine/equipment

Tc            = worst stopping time of the control system


Tr            = response time for the safeguarding device, including its interface


Tbm        = additional stopping time allowed by a brake monitor (if installed)


Dpf          = maximum travel towards the hazard within the presence sensing device field that may

                    occur  before a stop is signalled.


A critical tool for calculating safe distance is the stop time measurement device.   If the stopping time for the equipment and its control system are unknown, the stop time device can be used to measure it.  The machine measures the time it takes the machine to stop after a stop signal is given.



Stop Time Demo



Ensure that your engineered controls are actually protecting your workers!


Posted by Kristin Petaski at 10:00 PM 0 Comments
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