Outrigger Interlock Systems May Vary Considerably

By R. Bruce Wright, CPCU, with thanks to Allan Brown, CLCP, of SPEC, Inc.

Many of you will have heard me say during my visits that I wear many hats during these consultations. These hats include the data collection hat, the system safety program review hat, and the safety advisor hat, among others. As I meet with folks around the country, talking with operations and safety experts at utilities and reviewing their experiences, I get a chance to hear about all kinds of claims and losses that have happened at utilities. In fact, I learn about many, many types of errors and failures, far more than any single company's safety officer will ever experience, or so I certainly hope! This leads me to one of the most valuable services I think I can offer, which fits under what I will call the “Guess what new weird and wonderful problem I just heard about?” hat. Wearing this hat provides me with a chance to share lessons I have learned with everyone in the program, providing all participants with the chance to benefit from these lessons for free, avoiding the costs of the accidents. You probably recall hearing me say at some point that experience is the best teacher, but learning from other peoples’ experiences is far cheaper! This article covers the latest example. (I have left out some details, since the claim is still open, but the lesson is too important to delay sharing with you.) The story comes in three parts.

Part 1- I first learned about this incident, an accident that I didn’t know was possible, when I met with a Operations Manager recently. Due to a series of compounding circumstances—an urgent emergency, a night time call out, the several workers needed arriving at different times, the rush to get things done quickly—an error occurred that led to a significant loss. Fortunately, no one was hurt, but there was significant property damage, running well up into serious money. Significantly, no one involved knew it was possible to make the mistake that led to the damage, just as I didn’t.

Over the years there have been significant improvements in the safety equipment on utility trucks. While all of the improvements are valuable, one of the most obviously useful is the system of outrigger interlocks now used on buckets and diggers that requires deployment of the outriggers before the cranes, buckets, or digger units can be operated, deployed, or “un-cradled.” This system uses relays and pressure sensing devices to ensure that the stabilizers, or outriggers, are extended and in sufficient contact with a stable surface to provide support, before the equipment is used. I had always believed that these systems were 2-way safety systems- that they also required that the aerial devices be returned to their cradles before the stabilizing outriggers could be retracted, but I have now learned that this is sometimes, but not always, the case. The utility where this happened reported that the crew loaded a pole, which required them to put out the outriggers and lift the arm in order to provide clearance for the loading operation. After the pole was loaded onto the derrick unit, somehow their crew was able to retract the outriggers and drive off with the arm still extended, which led to this costly loss.

Let’s not spend any time wondering how the crew made this mistake. Of course it involved human error, but take it from me, the circumstances were such (Remember, it was a matter of urgent emergency, in the dark, with multiple workers pitching is as they arrived, that required extra loading in a hurry.) that it is not hard to see how events conspired to lead up to the mistake. The thing we always tell our clients is don’t fix the blame, fix the process. Here, management had previously believed that the interlock system was just that ‘fix,’ but found out to their dismay that it was not.

Part 2 of this lesson was provided by another contact, with whom I met only a few weeks later. With this event fresh in my mind, I brought it up during this meeting too and discovered that this second utility used the same brand of equipment themselves. Furthermore, they too didn’t know that their system offered only 1-way protection, not 2-way. As a result of our conversation, my contact there said he would see to it that they tested their equipment to verify the issue, and if it existed, see what could be done. Here’s what they passed along to me in an email:

From: Allan Brown [ABrown@spec.coop]
Sent: Wednesday, November 28, 2012 10:07 AM
Cc: bruce@synebar.com;
Subject: Altec transmission software upgrade

Importance: High

In a recent conversation with Mr. Bruce Wright -- a safety consultant to our GL carrier -- he shared the details about an accident (at another company) in which a crew had loaded poles on an Altec bucket. … They had raised the boom to make room for the poles, and in the rush to get to the job they raised the outriggers and began to drive off with the boom still in the air. The fact that this was done at night probably accounts for the fact that no one on the crew noticed the potential problem.

We didn't think this was possible until we tested the theory on a few units. Versalifts don't permit it, but for some unknown reason Altec does. Altec says they can't modify the existing outrigger/boom interlock (which allows the boom to be raised only after the outriggers are down, but not the reverse), but they can modify the software such that if the boom isn't completely cradled, the transmission can't be moved out of neutral. I've spoken to Dale and he agrees that we need to make this change.

Randy will be making arrangements with Altec to schedule the modification in the near future.

Allan D. Brown, CLCP

Director of Risk Management

South Plains Electric Cooperative, Inc.

As a result of their investigation they are now retrofitting 20 pieces of Altec equipment with the transmission interlock!

Part 3- With my curiosity now fully fueled, I fired up my computer and began to do some further research. I found that the standard for outrigger interlocks promulgated by ANSI was revised in 2009. Here’s what the 2009 edition of the American National Standard for Vehicle Mounted Rotating and Elevated Aerial Devices has to say:

4.5.5 Outrigger Interlock Device – When an aerial device is equipped with outriggers, and their use is required to pass the stability tests of this standard, an interlock device shall be provided that prevents the boom from being operated from the stowed position until the outriggers have been deployed.

Deployment may be sensed when the outriggers meet resistance or by receipt of an indicative response that the outrigger deployment is beyond a predetermined position. The lifting of an outrigger during operation shall not disable boom functions. An interlock override switch may be provided; however, the override mode of operation shall disable automatically.

(Note that it says nothing about any interlock system needing “re-cradling” protection.)

Armed with that information I next contacted Altec directly. The advisor I spoke to on their technical support line stated that they offer a variety of configurations of interlocks that meet the ANSI standard and also meet the widely varying specifications of their customers. While outrigger interlocks are standard equipment and have been for nearly 2 decades, the standard equipment devices only require outrigger deployment before using equipment, not the reverse. However, Altec offers options including a transmission interlock system as well as a parking brake interlock system that can prevent the vehicle being moved until the equipment is back in the proper stowage cradle. He went on to report that they offer over-rides as well, to meet customer needs. As an example, he said that some customers want to be able to over-ride the interlocks if a vehicle becomes stuck in mud and needs to be winched. (It isn’t clear to me why an operator would want to winch free a stuck vehicle without cradling the bucket, but so be it.)

The bottom line is simply this. Every utility needs to know what type of safety equipment and interlock systems its vehicles have. If you aren’t completely certain, you should test your units yourself to verify what they have. You probably have vehicles of different ages and from different manufacturers. Even if they are all the same age and maker, they could still differ in their equipment. Once you know what you have, you can make sensible decisions on what retrofitting should be done and you can make sure that all of your workers know which systems are on what vehicles until you can make them all meet the uniform standard you and your operations experts decide is most appropriate for your utility. Don’t make the mistake I made and ass/u/me they’re all alike!