Incidents:Sixty foot fall on Thalehaha

Sixty foot fall on Thalehaha
Date	2012/02/21
Location	Rubio Canyon
Severity	Injury
Canyoneering-related	Yes
SAR involvement	No
Navigation problem	No
Environmental problem	No
Communication problem	No
Planning problem	No
Skills problem	No
Body movement problem	No
Rigging problem	Yes
Rappel problem	Yes
Insufficient gear	No
Gear failure	No

Summary

A canyoneer slips on Thalehaha and lets go with his brake hand. Despite the presence of an autoblock, he still falls most of the length of the waterfall.

Analysis

There is an extensive Bogley thread discussing the incident.

The primary failure was the rappeller taking his hand off the brake strand and then grabbing the rope above his descent device when he started to fall. The canyoneer at the bottom of the drop also failed to provide a good Fireman's belay, and the rappeller's incorrectly-rigged autoblock did not fully engage.

This incident was discussed twice on the Facebook group Southwestern Canyoneering; once on 2/22/2012 and once on 4/16/2014. It was also discussed on the Facebook group SoCal Canyoneering.

Preventative measures

Attention to brake hand placement

First and foremost, this accident could have been prevented by absorbing the initial slip with the rappeller's non-brake hand, or even by re-grabbing the brake strand rather than the rope above the device. Constantly reminding oneself and others in the group not to let go of the brake hand may have helped to avoid these errors.

Fireman's belay

If the canyoneer at the bottom of the rappel had given the rappeller a good fireman's belay, it is likely he could have arrested the fall.

Both hands on the rope

It is possible that the fall may not have occurred if the rappeller was holding onto the brake rope with both hands if he only absorbed the initial slip with one hand. On the other hand, not using the non-brake hand to steady himself with the rope above the rappel device may have increased the chance of slipping (and therefore falling), so it's not clear whether having both hands on the brake rope would be a net positive.

Autoblock inspection

Although an autoblock was present, it was not rigged properly. A more careful inspection may have resulted in rerigging it correctly before the rappel, which likely would have resulted in the autoblock arresting the fall. However, the frequent use of an autoblock may lessen the urgency of the never letting go of the brake rope which may have made this situation more likely. So, it's likely the use of an autoblock was a net negative as it provided two additional points of failure: rigging the autoblock, and brake hand complacency. A meticulously-inspected autoblock may have been a net positive, however.

Sequencing

The rappeller was less experienced than the camera man. If the rappeller had been sequenced first, the camera man could have inspected the rappeller's autoblock and may have detected and corrected the improper rigging, which may have led to the autoblock arresting the fall. On the other hand, the camera man would then not have been able to provide a fireman's belay.