An article from CBC earlier this year reported that beavers had chewed through an underground fiber and had knocked 900 customers in Tumbler Ridge, British Columbia off broadband for 36 hours. The beavers had chewed through a 4.5-inch conduit that was buried three feet underground. This was an unusual fiber cut because it was due to beavers – but animals damaging fiber is a common occurrence.
Squirrels are the number one source of animal damage to fiber. It’s believed that rodents love to chew on fiber as a way to sharpen their teeth, which grow continuously throughout their life. For example, squirrel teeth grow as much as eight inches per year, and the animals are forced to gnaw to keep teeth under control and sharp. For some reason, squirrels seem to prefer fiber cables over other kinds of wires hanging on poles.
I remember reading a few years ago that Level 3 reported that 17% of their aerial fiber outages were caused by squirrels. A Google search turns up numerous network outages caused by squirrels. I have a client with a new fiber network, and the only outage over the last year came from a squirrel chewing through the middle-mile fiber route that carried broadband to and from the community.
ISPs use a wide variety of techniques to try to prevent squirrel damage – but anybody that has ever put out a bird feeder knows how persistent squirrels can be. One deterrent is to use hardened cables that are a challenge for squirrels to chew through. However, there have been cases reported where squirrels still partially chew through such cables and cause enough damage to allow in water and cause future damage.
A more common solution is to use sort of physical barriers to keep squirrels away from the cable. There are barrier devices that can be mounted on the pole to block squirrels from moving higher – but these can also be an impediment for technicians. Another kind of barrier is mounted where the fiber connects to a pole to keep the squirrels away from the fiber. There are more exotic solutions like deploying ultrasonic blasters to drive squirrels away from fiber. In other countries, ISPs sometimes deploy poison or obnoxious chemicals to keep squirrels away from the fiber, but such techniques are frowned upon or illegal in the US.
What was most interesting about the beaver fiber cut was that the cut was far underground – supposedly out of any danger. In parts of the country there are similar threats to buried fiber from pocket gophers. There are thirteen species of pocket gophers in the US that range from 5 to 13 inches in length. The two regions of the country with pocket gophers are the Midwest plains and the Southwest. Gophers live on plants and either eat roots or pull plants down through the soil.
Pocket gophers can cause considerable damage to buried fiber. These rodents will chew through almost anything and there have been reported outages from gophers chewing through gas, water, and buried electric lines. Gophers typically live between 6 and 12 inches below the surface and are a particular threat to buried drops.
There are several ways to protect against gophers. The best protection is to bury fiber deep enough to be out of gopher range, but that can add a lot of cost to buried drops. I have a few clients that bore drops to keep them away from gophers. Another protection is to enclose the fiber in a sheath that is over 3 inches in diameter. Anything that large and tubular is generally too big for a gopher to bite. Another solution is to surround the buried fiber with 6 – 8 inches of gravel of at least 1-inch size – anything smaller gets pushed to the side by the gophers. Unfortunately, all of these solutions add a lot of cost to fiber drops.
An unexpected risk for aerial fiber is from birds. Large birds with sharp talons can create small cuts in the sheath and introduce water. Flocks of birds sitting on a fiber can cause stretch and cause sag. That may sound like a small risk, but when I lived in Florida is was common to see hundreds of birds sitting shoulder to shoulder on the wires between two poles. While most people would find that many birds to be an interesting sight, being a broadband guy, my first reaction was always to see which wire they were sitting on.