Banner MM-TA-12B Instruction Manual page 16

System Installation
3.1.4 Pass-Through Hazards
A "pass-through hazard" is associated with applications where personnel may
pass through a safeguard (at which point the hazard stops or is removed), and
then may continue into the hazardous area. Subsequently, their presence is no
longer detected, and the safeguard can not prevent the start or restart of the
machine. The related danger is the unexpected start or restart of the machine
while personnel are within the hazardous area.
In the use of safety light screens, a pass-through hazard typically results from
large separation/safety distances calculated from long stopping times, large mini-
mum object sensitivities, reach over, reach through, or other installation consid-
erations. 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.
Reducing or Eliminating Pass-Through Hazards
Measures must be taken to eliminate or reduce pass-through hazards. One solu-
tion is to ensure that personnel are continually sensed while within the hazardous
area. This can be accomplished by using supplemental safeguarding, including:
safety mats, area scanners, and horizontally mounted safety light screens. While
it is recommended to eliminate the pass-through hazard altogether, this may not
be possible due to cell or machine layout, machine capabilities, or other applica-
tion considerations.
An alternate method is to ensure that once the safeguarding device is tripped it
will latch, and require a deliberate manual action to reset. This type of supple-
mental 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.
The reset switch or actuating control must be positioned outside the guarded
area, and provide the switch operator with a full unobstructed view of the entire
guarded area and any associated hazards as the reset is performed. The reset
switch or actuating control must not be reachable from within the guarded area
and must be protected (through the use of rings or guards) against unauthorized
or inadvertent operation. A key-actuated reset switch provides some operator
control, as it can be removed by the operator and taken into the guarded area.
However, this does not prevent unauthorized or inadvertent resets due to spare
keys in the possession of others, or additional personnel entering the safeguard-
ed area unnoticed.
The reset of a safeguard must not initiate hazardous motion. Also, before each
reset of the safeguard is performed, safe work procedures require that a start-up
procedure be followed and that the individual performing the reset verify that the
entire hazardous area is clear of all personnel. If any areas can not be observed
from the reset switch location, additional supplemental safeguarding must be
used: at a minimum, visual and audible warnings of machine start-up.
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MM-TA-12B Muting Module
Instruction Manual
WARNING . . .
Pass-Through
Hazards, Presence-
Sensing
Safeguarding Devices, and
Muting
If the presence-sensing safeguard-
ing device (PSSD) is guarding an
application in which personnel
have access into the sensing area
or field (for example, a machine
operator at the point of operation)
while the PSSD is muted, all pass-
through hazards must be eliminat-
ed. The individual must be sensed
continually while in the safeguard-
ed area; this will prevent initiation
of a machine cycle if the mute
ends while the individual is within
the hazardous area. See Appendix
B for examples.
If the pass-through hazard cannot
be eliminated, as in entry/exit
applications, the individual must
be detected entering the safe-
guarded area and the hazardous
motion must stop immediately.