Standards / Machinery Safety

Positioning of Safeguards

EN ISO 13855 is the European standard for positioning safeguards with respect to the approach speeds of parts of the human body. It provides the method for calculating how far a presence-sensing device, two-hand control or guard must sit from a hazard so that the machine reaches a safe state before the hazard can be reached.

Scope

EN ISO 13855 applies to the positioning of safeguards including electro-sensitive protective equipment such as light curtains, pressure-sensitive mats, two-hand control devices and interlocked guards. It defines approach speeds for the hand, arm and body, and the method of combining them with the overall stopping performance of the machine.

Exclusions & Related Standards

• The reach distances that prevent a hazard being reached at all, independently of stopping time, fall under EN ISO 13857.
• The construction of guards falls under EN ISO 14120.
• The reliability of the safety function is determined under ISO 13849.
• Emergency stop devices are not safeguards and fall under EN ISO 13850.

Key Requirements & Marking

The minimum distance is derived from the approach speed of the relevant body part, the overall stopping performance of the machine including the response times of the detecting device and the whole control chain, and an allowance related to the resolution of the device. Because the calculation depends on the machine stopping performance, it has to be revisited whenever anything affecting stopping time changes.

The distance follows from approach speed, total stopping performance and the resolution of the device.

Testing Overview

Assessment involves measuring the overall stopping performance of the machine from the moment the device is actuated to the cessation of the hazard, verifying the response time of the detecting device and the control chain, and confirming the installed distance against the calculated minimum.

Selection Guide

Select device resolution for what must be detected: a device resolving an arm will not detect a finger, so fine resolution is required where a hand can enter. Ensure no one can stand between the device and the hazard, or provide additional detection or a reset positioned outside the danger area. Treat any muting or blanking arrangement as part of the safety function.

Inspection, Care and Maintenance

• Recalculate the distance whenever brake performance, tooling or control response changes
• Measure stopping performance periodically rather than relying on the original figure, as brakes degrade
• Verify that muting and blanking behave as intended and cannot be left active
• Confirm that the device cannot be approached from a direction it does not cover
• Check that the device has not been moved closer to the hazard for operational convenience

Once past the sensed plane a person is no longer detected, which the layout or a second device has to address.