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Contributed by Adolfo Isassi

MMO vs Releasable Blocks

For canyoneering, when it comes to rigging releasable systems (rigging for rescue, contingency rigging), you will encounter a dizzying number of options and variations. Do you need to learn them all? Maybe. This will depend on the area you intend to canyoneer, the anchoring practices of that area, and how deep you want to take your training and learning.
For Entry Level canyoneering, when it is critical that you optimize your learning bandwidth, and avoid memorizing variations of the same concept, it pays off to learn two ways of rigging releasable:
  • A releasable block
  • A suspended releasable, like the MMO
Because the most important purpose of rigging releasable is that the rigging actually -releases – when needed, and one common factor that may get in the way of a smooth release, is a poorly located master point.
A poorly located master point is one that when loaded with the weight of the rappeler, it results in contact with a hard surface on a wall or floor, and prevents the releasable rigging from functioning properly. To an extent we have some control over the master point location when we link bolts, or tie webbing or cordage around single point anchors. But you will usually find that with limited natural anchor opportunities, or poorly located bolts, you will end with a master point making contact with rock.
Releasable blocks operate poorly, or not at all when in contact with rock.
When this happens, a MMO is a more reliable releasable system because even when it is in contact with rock, it will release and lower.
So, if you invest some learning and practice time, start by not learning 5 different releasable blocks. Instead, learn one reliable releasable block, and the MMO.

A releasable block that gets pinched up against the rock is essentially a static block. If it will not release when needed, it is useless.

When there is a risk of a releasable block getting pinched, switch to a suspended system, like the Munter-Mule-Overhand (MMO)

SIDE BAR:  Releasable systems that are rigged on the bag/pull side of the master point are Blocks.
Releasable systems that are rigged on the rappel side of the master point are Suspended systems. The same way there are many releasable blocks (Secure Compact 8, Euro 8, EMO, Totem Block, etc.) There are many suspended systems MMO, Suspended Descender, Assisted Braking Device, etc).

Reference: Professional Canyoning Handbook by CREPS & Petzl Foundation, Page 153