By coincidence I have recently received photos of two separate incidents involving vehicle accidents at pipeline facilities. No names, no pack drill, but I am grateful to the pipeline owners for permission to show these images and discuss the implications.
(If some of my comments below appear critical of the design of the facilities and their protection, I’m not singling out anyone. There are a lot of pipeline sites around that suffer from the same shortcomings. I hope everyone can learn from the examples here.)
The first incident was clearly vandalism:
The site appears to be in a rough area and the owner has taken a variety of precautions to protect it, include bollards that are clearly effective:
I don’t know how deep these bollards have been sunk into the ground, but it must be a lot more than the 600 mm that is common. This is an example of a site where the possibility of vehicle impact was anticipated and mitigated effectively.
The second incident was an out-of-control vehicle. No-one knows how fast it was going but it clearly wasn’t just sauntering along:
Perhaps the most interesting photo of this event is the last. All of the impact energy has been absorbed by the security fence. The almost pristine state of the guardrail, which in the photos above is underneath the car, suggests that the car was airborne at the time of impact. A closer look at the picture shows what looks like a low earth mound at the left which might have been responsible for launching the car.
In this case it looks as if the possibility of vehicle impact had been anticipated (hence the guardrail) but the mitigation was not very effective. In fact if the earth mound was meant as protection then it was counterproductive (but it might have been for some other purpose or just temporary construction spoil).
I think there are a few lessons to be learned from these incidents:
- Vehicle impacts on facilities really do happen. They are not captured in the APIA/POG pipeline incident database because that records only defined events that involve buried pipelines, so the frequency of other types of incidents is not known. I only learned of these two by chance.
- It is possible to design effective protection against at least some vehicle impacts, as illustrated by the first incident above. Properly engineered bollards with good foundations are one form of protection.
- Standard chain-wire security fencing may be quite effective at catching errant vehicles, even though it is only meant to keep out errant people. (Having been mucking around lately with chicken-wire garden enclosures I’ve developed a personal appreciation of just how tough wire mesh can be.) But you would not want to rely on it.
- Earth mounds are sometimes used for protection but clearly need to be properly designed or they may make an incident worst.
It is also worth commenting on the use of guardrail. Guardrail is ubiquitous alongside roads where its purpose is to deflect a wandering vehicle back onto the carriageway. In that role it is quite effective, but when hit by a vehicle the angle of attack is very small indeed. Guardrail is also deliberately designed to yield. The rail itself is somewhat flexible, the C-section posts are also flexible, and the posts are embedded to only shallow depth. It follows that guardrail is not effective protection against impacts at 90 deg (or many much smaller angles). In the second of the two incidents above I think the chain-wire fence probably had a lot more energy absorbing capacity than the bit of guardrail. Energy absorption is what it’s all about.
(There is probably information on guardrail design and function in the traffic engineering literature but I haven’t looked recently. My comments above are based on information received quite some time ago when we were considering it at vulnerable sites during design of a new pipeline; we didn’t use it.)
The threat of vehicle impact comes up from time to time in safety management studies. The workshops usually agree on one of two alternatives, depending on the circumstances of the specific site:
- Erect a large earth mound between the site and road (but designed so it doesn’t become a launching ramp)
- Engage a suitably qualified traffic engineer to advise on the best means of protection