AS A DESCENT CONTROL DEVICE
When used to control a descent, the MPD design allows for easy adjustment
of the friction for the size of the load, rope type, and environmental and
terrain conditions. The speed of the descent is controlled by the friction of
the rope applied against the Fixed Brake V-Groove. Always start with the
running end held fi rmly back toward the anchor, parallel to the load end.
Reduce the friction by varying the angle at which the running end enters the
MPD. Maximum friction is applied when the Secondary Friction Post is used.
AT NO POINT SHOULD THE RUNNING END OF THE ROPE HAVE AN ANGLE
OF LESS THAN 90º TO THE LOAD END OF THE ROPE.
Edge transitions can be the most challenging part of an operation. Using the
MPD as a descent control device allows for a high degree of responsiveness
and control. As the rescuer or rescuer and patient approach the edge, it is
very easy to take in rope through the MPD to prepare for the edge transition.
Pretensioning of the Main Line is also simplifi ed because of this.
TO LOWER
To lower, fi rmly grip the running end of the rope and tightly hold it against
the Fixed Brake V-Groove, bringing it back toward the anchor and parallel to
the load end, creating an “S-shaped” bend in the rope as it passes through
the MPD. Pass the rope over the Secondary Friction Post for heavier loads if
needed. Unlock the Parking Brake and then fi rmly grip the Release Handle.
For the most comfortable hand operating position, before pulling outward on
the handle, give a slight clockwise turn of the wrist, then pull out to engage
the release mechanism.
10 m [33 ft] of the descent), it is recommended to convert from hand-tight
Belay Line tension to shared tension between the Main Line and Belay
Line. Should the Main Line system fail from this point on, a Shared Tension
system will minimize rope stretch and provide a considerably reduced
arresting distance as compared to a conventional untensioned belay. It
will also help mitigate other hazards, such as an inadvertently slack Belay
Line or rope-induced rockfall, since the now-tensioned Belay Line will be
suspended above the terrain between contact points, just like the Main Line.
SHARED TENSION SYSTEMS
Shared Tension Systems are essentially two lowering systems in place of
one lowering system and a belay, with each line supporting approximately
half the load. If either system should fail, the increased load on the other
descent control device will cause an increase in rate of descent. While the
MPD is an effective belay device capable of safely arresting a falling load,
when used as a descent control device you are manually overriding the
belay function. This could result in increased stopping distances
if not using proper technique.
Therefore, in a Shared Tension lower it is imperative that the running end
rope of the Belay Line be held back toward the anchor, maintaining the
“S-shaped” bend as the rope runs through the MPD.
If there is a sudden
change in speed or tension on the rope running through the MPD,
the belayer must immediately let go of the Release Handle
(disengage) while maintaining a fi rm grip on the running end of the
rope to ensure the braking mechanism activates and arrests the load
in the shortest distance possible
.
!
!
YOU MUST LET GO OF THE RELEASE HANDLE WHILE MAINTAINING A FIRM
GRIP ON THE RUNNING END OF THE ROPE TO ACTIVATE THE BELAY!
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AS A BELAY DEVICE
The MPD is designed to be used as a belay device to arrest a falling load
should the Main Line system fail. It is recommended that during edge
transitions, while either lowering or raising loads, that the Belay Line tension
be kept hand tight and without slack in the line. Stumbles by the rescuer or
litter tender(s) are most likely to occur during edge transitions, which may
result in the ropes being run across edges that can potentially damage or
cut them. It is less likely to damage both ropes if the Belay Line remains
untensioned during these transitions. Additionally, greater descent control
can be achieved if only one rope manages the rate of descent during edge
transitions.
If the Main Line system completely fails during an edge transition (e.g.
anchor failure or improper system connection), and if both ropes are
suspended above the terrain, as when using a high directional, then a
dynamic fall onto the Belay Line is likely. Among rescuers, this is widely
recognized as potentially the worst case dynamic event in rescue work.
While every effort should be made to rig and operate systems to minimize
the potential for such dynamic events, the MPD is designed and has been
tested to arrest a 1 m fall onto 3 m of static rope with a rescue-sized load
and limit the peak force below 15 kN (3,372 lbf) with no more than 1 m
(3.3 ft) stopping distance (as advocated by the British Columbia Council of
Technical Rescue Belay Competency Drop Test Criteria). Such a dynamic
event is severe and warrants that all involved equipment be retired and
properly disposed of after the operation is safely completed.
BELAYING A LOWERING SYSTEM
When belaying a lowering system, once the rescuer has good control of the
load and is in the correct descent path (this often occurs within the fi rst
ALWAYS MAINTAIN A FIRM GRIP ON THE RUNNING END OF THE ROPE
DIRECTED BACK TOWARD THE ANCHOR IN AN “S-SHAPED” BEND BEFORE
ENGAGING THE RELEASE HANDLE.
Begin lowering by rotating the handle slowly counterclockwise all the
way to completely unseat the Moving Brake from the rope, controlling
the rate primarily with friction on the Fixed Brake V-Groove. Maintaining
the “S-shaped” bend in the rope will improve the function of the braking
mechanism in the event it is needed and will increase the service life of
the Moving Brake, reducing the potential for rope creep through the device.
Load
Anchor
S-shaped bend
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