Banner EZ-SCREEN­ Safety Light Curtain Systems - Manual (Page 17)

Reducing or Eliminating Pass-Through Hazards
A pass-through hazard is associated with applications where personnel may pass through a safeguard (which issues a stop command to
remove the hazard), and then continues into the guarded area, such as in perimeter guarding. Subsequently, their presence is no longer
detected, and the related danger becomes the unexpected start or restart of the machine while personnel are within the guarded area.
In the use of light screens, a pass-through hazard typically results from large safety distances calculated from long stopping times, large
minimum object sensitivities, reach-over, reach-through, or other installation considerations. A pass-through hazard can be generated
with as little as 75 mm (3") between the defined area and the machine frame or hard guarding.
Eliminate or reduce pass-through hazards whenever possible. While it is recommended to eliminate the pass-through hazard altogether,
this may not be possible due to machine layout, machine capabilities, or other application considerations.
One solution is to ensure that personnel are continually sensed while within the hazardous area. This can be accomplished by using
supplemental safeguarding, such as described by the ANSI B11.19 of safety requirements or other appropriate standards.
An alternate method is to ensure that once the safeguarding device is tripped it will latch, and will require a deliberate manual action to
reset. This method of safeguarding relies upon the location of the reset switch as well as safe work practices and procedures to prevent
an unexpected start or restart of the guarded machine.
WARNING: Use of EZ-SCREEN Type 2 for Perimeter Guarding
If an EZ-SCREEN Type 2 is installed in an application that results in a pass-through hazard (e.g., perime-
ter guarding), either the EZ-SCREEN Type 2 System or the Machine Primary Control Elements (MPCEs)
of the guarded machine must cause a Latched response following an interruption of the defined area.
The reset of this Latched condition may only be achieved by actuating a reset switch that is separate from
the normal means of machine cycle initiation.
Lockout/Tagout procedures per ANSI Z244.1 may be required, or additional safeguarding, as described by
ANSI B11.19 safety requirements or other appropriate standards, must be used if a passthrough hazard
can not be eliminated or reduced to an acceptable level of risk. Failure to observe this warning could
result in an increased risk of harm.
Supplemental Safeguarding
As described in Calculating the Safety Distance (Minimum Dis-
tance) on page 13, the EZ-SCREEN Type 2 must be properly posi-
tioned such that an individual can not reach through the defined
area and access the hazard point before the machine has stopped.
Additionally, the hazard can not be accessible by reaching around,
under, or over the defined area. To accomplish this, supplemental
guarding (mechanical barriers, such as screens or bars), as descri-
bed by ANSI B11.19 safety requirements or other appropriate
standards, must be installed. Access will then be possible only
through the defined area of the EZ-SCREEN Type 2 System or
through other safeguarding that prevents access to the hazard
(see
Figure 4. An example of supplemental safeguarding on page
17).
The mechanical barriers used for this purpose are typically called
"hard guarding'; there must be no gaps between the hard guarding
and the defined area. Any openings in the hard guarding must
comply with the safe opening requirements of ANSI B11.19 or oth-
er appropriate standard.
Figure 4. An example of supplemental safeguarding
EZ-SCREEN® Type 2 Light Screen Instruction Manual
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