Effectiveness of safeguards using safety distances

Safety distances

To ensure that a potential hazard can be shut down quickly enough, the safeguard must be installed at an appropriate distance. This provides protection for the upper and lower limbs.

The safety distance (S) is defined in EN ISO 13855 and depends in particular on the following factors:

  • t1 = Reaction time of the safeguard itself.
  • t2 = Reaction time of the machine, i.e. the machine's stopping performance as a reaction to the signal from the safeguard
  • C = Potential approach towards a danger zone undetected by the safeguard, e.g. reaching through two beams of a light curtain undetected, depending on the distance of these beams
  • K = Anticipated approach speed of the human body or parts of the human body. This factor is defined in EN ISO 13855 as 1 600 mm/sec for walking speed and 2 000 mm/sec for hand speed

The distance to be implemented is therefore S = K* (t1 + t2) + C

Safety distances for other population groups

EN ISO 13857 examines the safety distances required to prevent hazard zones being reached by the upper and lower limbs. It is worth stressing that this standard makes it clear that different anthropometric data (size, length of limbs…) may apply for other populations or groups (e.g. Asian countries, Scandinavia, children) and that this could give rise to other risks. Application of this standard may therefore be restricted, particularly in the public domain or when exporting to other countries.

Standard Title
EN ISO 13857 Safety of machinery
Safety distances to prevent hazard zones being reached
by upper and lower limbs


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