Examples
Example: U.S.
Applications,
Model
K
= 63 in. per second (the hand speed constant set by OSHA)
Ts
= 0.32 (0.250 second is
specified
by the machine manufacturer; plus
20% safety factor; plus 20 ms for interface module IM-T-9A
response
time)
Tr
= 0.016 seconds (the
specified
response
time
of an LS2..30-600 EZ-
SCREEN Type 2)
Dpf
= 3 in
Substitute
the numbers into the formula as follows:
Ds = K x ( Ts + Tr ) + Dpf
Mount the EZ-SCREEN Type 2
emitter
and receiver so that no part of the
defined
area will be closer than 24.2 in. to the closest reachable hazard point on the
guarded machine.
Example: European
Applications,
Model
K
= 1600 mm per second
T
= 0.336 (0.250 second
specified
by machine manufacturer; plus
20% safety factor; plus 20 ms interface module response
time),
plus 0.016 seconds (the
specified
LS2..30-600 response
time)
C
= 8 x (30 - 14) = 128 mm (14 mm
resolution)
Substitute
the numbers into the formula as follows:
S = (K x T ) + C
S = (1600 x 0.336) + 128 = 665.6 mm
Mount the EZ-SCREEN Type 2
emitter
and receiver so that no part of the
defined
area will be closer than 665.6 mm to the closest reachable hazard
point on the guarded machine.
3.1.2 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 in) between the
defined
area and the machine frame or hard
(fixed)
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 safety requirements in ANSI B11.19 or other appropriate standards.
An
alternative
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 the Banner device for Perimeter Guarding
If a Banner device is installed in an
application
that results in a pass-through hazard (for example, perimeter
guarding), either the Banner device 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 cannot be
eliminated or reduced to an acceptable level of risk. Failure to observe this warning may result in serious bodily
injury or death.
EZ-SCREEN
®
Type 2 Light Screen
14
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