Rockwell Automation Publication 450L-UM001D-EN-P - December 2019 69
Installation and Wiring Chapter 6
Regardless of the calculated safety distance, the protective field of a GuardShield
safety light curtain is never mounted closer than 152.4 mm (6 in.) from the point
of operation to the pinch point hazard.
In the United States, two formulas are commonly used to calculate the safety
distance.
• The OSHA formula is the minimum requirement for the calculation of
the safety distance.
• The ANSI formula, the formula we recommend, incorporates additional
factors to be considered when calculating the safety distance.
OSHA Safety Distance Formula
The OSHA safety distance formula as specified in CFR29 Subpart O1910.217 is
as follows:
Ds = 63 × T
Ds Safety Distance in inches (1 in. = 25.4 mm)
63 Is the OSHA recommended hand speed constant in inches per
second (63 in./sec = 1600 mm/sec)
T Is the total stop time of all devices in the safety circuit, which is
measured in seconds. This value must include all components that
are involved to stop the hazardous motion of the machinery. For a
mechanical power press, it is the stopping time that is measured at
approximately the 90° position of the crankshaft rotation.
IMPORTANT The T number must include the response times of all devices, including the
response time of the safety light curtain, the safety light curtain controller (if
used), the machine control circuit, and any other devices that react to stop the
hazardous motion of the machinery. Not including the response time of a
device or devices in the stop time calculation results in insufficient safety
distance for the application, which results in operator injury.
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