Safety standard EN ISO 13855 for the positioning of safeguards

With safeguards on machinery, measures must be taken to guarantee the safety of human and machine. These measures are described in the standard ISO 13855 and ensure that the machine is brought to a safe state before the danger point can be reached. The safety distance must be selected in such a way that any dangerous movement comes to a standstill before any part of the body can reach the danger point.

The standard EN ISO 13855 “Safety of machinery – Positioning of safeguards with respect to the approach of the human body” defines the positioning of safeguards as well as the approach speed of humans. Both parameters need to be considered when designing safety measures and selecting the appropriate sensor technology. Different speeds and sizes are defined, depending on the direction and type of approach. Other aspects are also considered, such as indirect approach, the possibilities to circumvent safeguards and overrun measurement.

The successor standard EN ISO 13855:2024 came into force in November 2024. There have been some important changes and some areas have been tightened up. Calculation of the safety distance is more complex and more structured in the new version, and requires some intensive study.

An overview of the key changes and new requirements:

• New, more complex supplements are now specified for safety distances.
• There is a definition of what constitutes a sufficiently large step surface, which can thus be used as a reference point for measuring the safety distance, also in relation to ascent or descent.
• The calculation of the safety distance must now also include the change in the position of the danger point in relation to the person, once the safeguard has been interrupted.
• The standard was extended to include the calculation of dynamic separation distances for known and unknown human directions of approach.
• Forms for manual switches and foot switches have been added and the formula for two-hand switches has been changed.
• New limits for vertical ESPE devices have been defined.
• There are extended calculations for interlocking guards.

The adjustments and new features of ISO 13855:2024 has resulted in the following formula for calculating the safety distance:
S = (K x T) + D_DS + Z

It should also be noted that a distinction must be made between two types of approach.

1. Static approach:

When calculating the safety distance for someone approaching a fixed safeguard, the end result depends on the type of approach. However, the main formula still applies:
S = (K x T) + D_DS + Z

2. Dynamic approach for unknown human direction of approach:

If acceleration and deceleration are known and constant, the basic principle is the same as for the static approach, but an additional parameter S_M must be taken into account, which represents the change in the position of the hazard. This results in the following formula, which is to be used when the human approach direction is not exactly known:
S = (K x T) + D_DS + S_M + Z
 
S_M is calculated as follows:
S_M = v0 x T - (d/2) x tm² + (a/2) x tSRP/CS²