From: emv@msen.com (Edward Vielmetti)
Newsgroups: comp.infosystems.gopher
Subject: Gopher Threat to Fiber Networks
Date: 15 Oct 1992 06:08:07 GMT
Organization: Msen, Inc. -- Ann Arbor, Michigan
NNTP-Posting-Host: garnet.msen.com
X-Newsreader: TIN [version 1.1 PL6]

yanked from telecom, for your reading enjoyment.  if you are installing
gophers near your fiber plant take some care.   --Ed

Don Kimberlin (Don.Kimberlin@f730.n250.z1.FIDONET.ORG) wrote:
: [originally posted in Fidonet BROADCAST conference, with some spelling
: corrections]
: 
: Here's a just a bit of "real world" about fiber optic cable and those
: overblown statements about the apparent invincibility of fiber optic
: cable ... those things that trumpet phrases like, "Impervious to harm
: and interruption ... non-metallic and interference-proof!"... and so
: on.
: 
: In fact, practical fiber optic cable of the type planted in the ground
: for intercity use has at least two important natural enemies, both of
: which have caused, and continue to cause failures of those cables,
: gophers and lightning.  Both have been significant causes of failure
: of preceding cable technologies in the twisted copper pairs and
: coaxial cables of the earlier analog era.
: 
: A recent edition of "Lightguide Digest" published by AT&T technologies
: tells quite openly how AT&T's RL series of fiber optic cable is
: constructed to attempt to avoid both kinds of natural enemies.
: 
: First addressing the gopher threat, the article describes it as a
: "gnawing problem" that "is growing."  It says, "the fact is well
: established that rodents such as gophers will gnaw through unprotected
: buried cables.  Information collected in the 1950s indicated that
: gopehrs infested more than 60 percent of the continental U.S." An
: accompanying figure shows a distribution of gopher areas to include
: almost all the area west of the Mississippi River plys most of
: Florida, Georgia and about a third of Alabama.  The article goes on,
: "To grind down incisors which grow approximately 12 inches per year,
: gophers spend 10 percent of their time, which means more than 90,000
: bites per week, gnawing various items including fiber optic cable."
: The bite pressure exerted by a gopher on fiber optic cable is said to
: reach as high as 18,000 pounds per square inch.
: 
: The habits of the gopher are described as a creature that keeps a home
: territory of several hundred square feet, saying that cables buried
: through gopher territories are the victims of repeated gnawing
: attacks. Reports have been made of gophers completely severing
: all-dielectric fiber cables in Ohio, an area not previously thought to
: be in the "gopher zone," and Colorado reports indicate gophers there
: are a widespread threat to unprotected fiber optic lines.
: 
: Two methods are the only ones known to be effective against gopher
: attack:
: 
: One is to place the nominal 1/2-inch diameter fiber cable in a 2-1/2
: to 4 inch diameter rigid PVC conduit, an expense communications
: companies would rather avoid.  The other is to use a cable with a
: stainless steel sheath around its fiber optic contents ... which makes
: the cable conductive, increasing the risk of lightning striking the
: cable and literally blowing the cable in pieces. Indeed, the article
: reports that one Mountain Bell fiber cut was caused by gnawing through
: a two-inch outer conduit, anyway.  Larger cement or ceramic conduit
: might be used, but that would increase costs of placing cable evern
: more.
: 
: To attempt gopher protection, AT&T has two calbe designs in its RL
: series. The first, for direct burial in rural areas, is called Primary
: Rodent- Lightning (Primary RL) Sheath. It consists of a corrugated
: stainless steel armor layer bonded to an outer polyethelyne jacket
: that contains a surrounding layer of wire strength members. The visual
: representation of this cable winds up looking very much like
: transoceanic deep-sea cables that have evolved over more than 130
: years of submarine telegraphy around the world, the only difference
: being that the center of the cable is hollow, providing for a variety
: of forms of fibers inside. The other type, called the Lightguide
: Express Entry Rodent-Lightning LXE-RL Sheath, has but two strength-
: member wires in its jacket and a layer of "Water-Blocking/Lightning
: Tape" located under its stainless steel jacket.
: 
: The article goes on to describe how such cable types are actually
: tested and rated for gopher resistance.  A sample of cable is buried
: in a closed-off area (underground barricades to contain the gophers
: within a confined area) with ten gophers that have nothing else to
: gnaw on. Ratings of one to five indicate whether any given gopher
: managed to inflict damage ranging from cutting the outer jacket to
: completely biting the cable in two.  The final rating of a given cable
: is the averaage of the scores of the ten different gophers placed in
: the area to attack the cable.
: 
: The gophers used for the test are provided by the Denver Wildlife
: Research Center of the U.S. Department of Agriculture, and the gopher
: most often supplied is the common plains "pocket gopher" called Geomys
: Bursarius, a small animal only 7 ot 9 inches in length that rarely
: weighs more than half a pound.
: 
: The other hazard that arises to intercity fiber optic cables, since
: metallic sheaths must be used to prevent gopher damage, and wires
: along the cable must be added to provide "strength" so the cable can
: be pulled and handled, is lightning.
: 
: One of the lesser-understood factors about buried metallic conductors
: is that since they are often more conductive than the surrounding soil
: they are buried in, they are better, more attractive conductors to
: lightning than the dirt that surrounds them.  This means that
: lightning can, and is, actually attracted to even buried cable, and
: that momentary lightning currents in the metallic members of those
: cable can rise high enough to actually melt a hole in the cable.
: 
: Indeed, buried fiber optic cable can be struck in open rural areas,
: resulting in failure of the cable until the damaged section is
: replaces.  One notable such case happened to MCI in a buried cable
: west of Jacksonville, Florida, where a lightning bolt that seemed to
: appear out of nowhere stabbed down into a buried fiber cable in an
: open field. Even more dramatic is the piece of damaged RL cable on
: display in the Charlotte, NC office of AT&T, which can be seen to have
: split open from the forces exerted on it when struck by lightning.
: That piece of damaged cable was struck with such force when it was
: buried four feet under an open soybean field near Davidson, NC. The
: cableman who repaired it stated that on the surface, a hole about the
: size of a golf ball had been made in the dirt, with spherical balls of
: dirt thrown back up around the hole where the lightning struck the
: ground on its way down to reach the metallic elements of the fiber
: cable.
: 
: So, now you have some facts to bear in mind the next time you hear
: some salesman touting the apparently impervious, uniterruptible nature
: of fiber optic cable plant. It has the same sort of failure potentials
: that previous cables have had for decades!
: 
: 
: Don Kimberlin - via FidoNet node 1:250/98
: INTERNET: Don.Kimberlin@f730.n250.z1.FIDONET.ORG
: 
Newsgroups: comp.infosystems.gopher