Project Engineering
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5.1.3 Safety Clearance
5.1.3.1 General Information
The safety clearance is the minimum distance between the safety field of an ESPE and the danger zone.
It’s task is to prevent the danger zone from being reached before the hazardous motion is completed.
In accordance with ISO 13855, the safety clearance is influenced by the following factors:
• Stopping time of the machine (time from the triggering of the sensor to the completion of the hazardous
motion)
• Response time of the entire safety equipment (ESPE, machine, downstream safety evaluation)
• Approach speed
• Resolution of the ESPE
• Type of approach (vertical, horizontal or at an angle)
5.1.3.2 Calculating the Safety Clearance
The general formula for calculating the safety clearance S is:
S = (K × T ) + C or S = K × (t
1
+ t
2
+ t
3
) + C
S [mm]
Safety clearance, measured from the danger zone to the safety field
K [mm/s]
Approach speed
C
Additional clearance based on the relevant approach to the safety field
T [s]
Total response time (t
1
+ t
2
)
T [s]
Total response time
T = (t
1
+ t
2
+ t
3
)
t
1
[s]
Response time of the ESPE
t
2
[s]
Response time of the safety switching device
t
3
[s]
Machine over-travel time
d [mm]
Resolution of the ESPE
