5 - General equations for calculating the minimum distances and the overall system response time

Last edit: 13/07/2023

The protective measures must be positioned at the appropriate separation distance from the hazard. This distance should be calculated using the following formula:


S: minimum separation distance, in [mm]
K: constant parameter, in [mm/s]
T: overall system response time, in [s]
DDS: separation distance associated with a protective device, in [mm]
Z: supplemental distance factor, in [mm]


The factor K, specifically, represents the speed of movement of the upper limbs or body of a person approaching a hazardous zone.
K = 2000 [mm/s] when considering the horizontal movement of the upper limbs (hand and arm).
K = 1600 [mm/s] when considering a walking speed. It does not include other body movements that may affect the actual approach speed.
When the hazard arises from the movement of the machine, a combined speed of the machine and the person should be taken into account.

Instead, the distance of achievement DDS associated with an orthogonal approach to a detection zone is determined based on application issues:

  • reaching over the detection zone: DDO
  • reaching through the detection zone: DDT
  • reaching under the detection zone: DDU

The largest value among these is chosen as DDS:

DDS = max⁡(DDO, DDT, DDU)

The overall system response time can be calculated or measured. It includes portions of time that vary according to the type of machine, the safety devices applied and the elements of the SRP/CS or SCS involved in the safety function.
It is determined by the following formula:

T ≥ tSRP/CS + tME + tF

T: is the overall system response time used in the calculation to determine the separation distance
tSRP/CS: is the response time of SRP/CS or sSCS
tME: is the response time of the machine
tF: is the time relative to a tolerance factor for the machine, if necessary