How to use a prusik-hitch self belay when rappelling

The prusik-hitch self belay technique can be used to help protect a rappeller from losing control of a rappel.

Source: This article was adapted from the CMC Rope Rescue Manual, Revised 4th edition, Edited by James A. Frank. Copyright © 2013 by CMC Rescue, Inc. All Rights Reserved. Excerpted With Expressed Written Permission. Order a copy today at 1.800.235.5741, www.CMCrescue.com.

CMC reminds us that, like a bottom belay, the prusik-hitch self belay does not protect against failure of:

1. the anchor,
2. the equipment,
3. or a mistake in rigging. 

There are several systems used, each requiring reactions by the rappeller. The simplest method to set up a self belay is to attach a prusik above the descender and clip it into the harness, as shown below.

One hand is the brake hand that controls the rappel and the other slides the prusik down the rope.

The prusik-hitch self belay with a figure 8 rappel device.

If the rescuer loses control of the rappel, the prusik should grab the rope and stop him.

Caution: Like all prusik-hitch-based systems, the self belay is dependent on selecting prusik material that will grip the rope reliably when the rappeller lets go of the hitch.

It also depends on the rappeller letting go of the prusik hitch. The loss of control of the rappel may cause the falling person to panic and the instinctive reaction is to grab the rope. If that hand is tending the prusik hitch, it is possible to pull the knot down the rope with you.

The correct response is to let go of the prusik hitch, allowing it to grab the rope. It has been CMC's experience in classes that the student will most often let go of the prusik hitch if the rappel begins to move too fast and heat builds up in the hand.

While this setup works well with a figure 8-type descender, CMC says it is not as convenient with brake bar racks, which require the use of two hands, one hand on the bottom bar and the other holding the rope. As a result, a hand is not available to tend the self belay. While the hand that controls the spread of the bars can be used for the belay, the rescuer has to stop each time he wants to adjust the bars.

One solution to this issue, according to CMC, is a simple tactical rappel setup.

How to handle a stuck prusik hitch

It the self belay prusik hitch activates, either intentionally or unexpectedly, the rescuer's weight will have to be unloaded from the prusik hitch to loosen it.

A hard pull on the prusik hitch with both hands may get it to slide.

An extra prusik or ascender, along with an etrier or foot sling, can be used to take the rescuer's weight off the hitch in order to free it. Attach the etrier above the decender and stand up as discussed below.

What if you do not have extra gear, or you are not strong enough to free the prusik hitch by brute force?

CMC recommends the following procedure to free a stuck prusik, and it recommends you practice it with someone experienced with this technique, and that you do it close to the ground until you are proficient with it.

1. Lock off the descender with a single wrap.
2. Form a bight in the rope below the descender and put one foot in the bight with the knee bent.
3. Bring the rope from the bight over the top of the descender, still bending the knee, and then wrap the rope two more times around the descender for a total of three wraps.
4. Stand up in the bight to take the weight off of the prusik hitch. Lossen the hitch and slide it down.
5. Sit back down in the harness. Unlock the descender, making sure not to load the prusik hitch.