Thud. “Uggh.” I heard it this weekend—the sound of coverall-ed flesh smacking limestone. Luckily, very luckily, the caver fell backwards wedging across the top of the canyon. He had a death grip on his rack, which was rigged to the rope, but no longer attached to him.
He was a victim of Sudden Accidental Disconnect (SAD), also known as rollout. Under the right circumstances, it is easy to disconnect a rappel rack from a carabiner. If the carabiner, connecting the rack to the harness, is unlocked and the rack is momentarily unweighted and things line up just right, the rack will pop out of the carabiner. Here’s a simplified example of how fast this can happen.
SAD has killed at least two cavers and it almost got my buddy. He was crossing a simple, standing rebelay. He rigged his rack, fiddled with the bars and removed the cows tail. When he sat down on the rack, he quickly realized it was no longer attached. Somehow, in the fiddling and reaching, the rack eye had levered open the carabiner gate and slid out. A simple mistake and a some luck is all it takes.
Don’t worry, it is very easy to prevent with the Rappel Test. Since everyone knows a QAS should always be above an untested descender, simply slide the QAS down and rappel a couple inches proving the descender works and is attached. Then, and only then, can the QAS be removed and properly stowed. The Rappel Test can catch other mistakes, not just SAD.
1. Engage QAS.
2. Rig descender.
3. Rappel an inch or two.
4. Circle one: pass/fail. Fail=repeat test.
5. Stow QAS.
It is also possible to lessen the threat of SAD by replacing the locking carabiner with something more secure or a screw link. However, nothing will lessen importance of always doing the Rappel Test before each descent. Note that SAD is not an equipment problem. It is fully due to operator error.
Please, take the Rappel Test. Everytime.
I also posted this on Cavechat.