System failure

Last week Ninja Treeworks had an accident on a work site.

We were hired by a friend to give him a hand pruning a couple of pollarded London plane trees. The trees are about 20m high, the lower part is covered in ivy. There were three climbers on site, A, B and C, as well as D, who took care of the ground work. A and B are both very experienced arborists, C has some experience in tree work, as well as being a very experienced rope access technician. 

The day started out wet and blustery, with quite heavy snowfall setting in soon after. We got the first tree done by mid-morning, by which time the weather had become decidedly unpleasant, so we decided to take a break in attempt to warm up a bit. While deinstalling our lines from the first tree, C got his cambium saver stuck, so after the break he headed back up again to retrieve it. Meanwhile A and B got a throwline into the second tree, ready for the access line to go in. Prior to ascending, C had had to lower the access line to get his ascent gear he had left there after the first ascent, then he pulled it up again and re-anchored it to the base of the tree, using a Petzl RIG, secured with two half hitches above it – to then commence his ascent.

In the meantime, D started up the chipper on the adjacent pavement to process the brush from the first tree. 

B then proceded to de-rig the access line, not realising C was still on rope in ascent, untied the two half hitches and pulled the lever, dropping C by approximately two meters before realising his mistake, realising there was way too much weight on the line – to then instantly release the lever. By the time his fall was arrested, C had impacted on a large limb hard with his butttock, had tried to grab on to it and in doing so hurt his shoulder.

Luckily C sustained no major injuries a couple of days rest could not sort. Yet the situation was very serious none the less, for conceivably,  if he had been higher up, maybe ascending limb to limb without any weight on the line, B would not have realised his mistake and would have deinstalled the RIG completely. In this scenario, when C reached the top of the ascent and had applied his weight to the line, this would have resulted in a 15m free fall to the ground. 

Obviously such a system failure leads to a great deal of upset, discussion and soul searching. What went wrong, where, why and how did we fail as a team, what factors were in play, how can we ensure this does not happen again.

First off, the use of access lines is a standard operating procedure in our company and is therefore used on a daily basis in a standardised format. All climbers are familiar with its installation, use and emergency procedures.

Without a doubt, at the core of this incident lies operator error on B’s part. Due to the ivy he had no clear line of sight to the access, due to the chipper running close by, he did not hear C ascending. These factors were further compiled by the fact that B was chilled, as well as low on blood sugar. The sum of the factors led to him developing a tunnel vision during the split second when he released the RIG. 

We were all deeply shocked and upset by a scenario none of us had ever envisaged, as visual control prior to any manipulation to the access line is what you might consider to be a no-brainer. 

But in this instance, a number of superficially small factors resulted in a system failure.

One of the things one discusses after such an event is whether a technical fix might have prevented it: had a I’D been used instead of the RIG, would it have mitigated the consequences of B’s tunnel vision? We did not reach a consensus in this matter. Yes, in this scenario, the anti-panic function on the I’D would have prevented C from being dropped as far as he was on the RIG. Having said that, in the alternate scenario, had he been ascending limb to limb, it would not have made a difference. On top of that, my personal opinion is that in certain rescue scenarios, the anti-panic function of the I’D could conceivably prove to be a hindrance over the RIG. So no, no obvious technical fixes.

What this accident does demonstrate clearly is that no one is safe from mistakes and accidents. Obviously, we like to think that competence, experience, as well as procedures and checks offer a degree of protection – while this is certainly true in many instances, external factors, such as cold, noise or heat can have a massive impact on our perception, sometimes without us even realising the degree by which our judgement is impaired.

I am certainly severely shaken by the whole incident, questioning my judgement and why I did not catch it in time, why I failed B and C. But I suppose the answer to that is that you simply cannot foresee every eventuality… and sometimes things simply go wrong. 

As a team our conclusions are, as I mentioned above, that small things can have a large impact, so be attentive to apparently small things: let your team mates know if you do not feel able to perform a task, recognise external factors that are having a negative impact on your form – and act accordingly, communicate with your team mates, put on an extra layer, eat something, hydrate, call it a day – whatever it takes.

This was certainly a humbling, revealing experience. I am deeply grateful the consequences were not more serious, am grateful to B, C and D for taking the time to debrief it thoroughly, as well as my people around me for letting me bend their ears, working through this one.

In that sense, please climb safe – and heed the small things.