This tale will explain why you need to take the utmost care and realize your surroundings when working in a sensitive networking environment. We have seen it all from crews cutting cables in the ceiling that they thought were dead to something as simple as a guy knocking a plug for a network switch out of the outlet. In the network cabling environment you always need to be aware of your surroundings and always check the space you have been working in for any connectivity issues and obvious problems. This practice will help you avoid having these common mistakes happen very often.
An existing single mode fiber optic cable within a large metropolitan hospital was damaged by a cable pulling crew. The crew was pulling a new 12 strand armored fiber. One of the guys in the middle of the run did not have a ladder. He was pulling the armored cable from the ground. There was a bundle of about 20 armored fiber cables coming through a hole in the wall above the ceiling. The new cable being pulled was laying on top of the larger bundle of fiber. As he was pulling from his spot on the ground he was pulling the new cable down on the existing bundle. He was burning the outer jackets of the existing cables. All of the cables would have survived except for the one in the middle of the bundle that was not armored. The new armored cable burnt right through it very easily.
This knocked out 3 floors of one wing in a very busy Hospital. We were called in for emergency repair work. We were able to patch it up temporarily that night. A couple of days later we did a permanent replace. When we started troubleshooting we had no idea where the problem was. We only knew there was a crew working in the data center the night before. We shot a laser light through the fiber from one of the connectors in the data center using our LAN tester. When we looked around we saw a beaming red light in the ceiling. As we looked closer the hole through the wall where the large bundle of fiber was coming through was lit up red like a Christmas tree. We had isolated the problem to this area. We were able to pull back some slack and we were surprised by what we pulled out from inside the wall.
The fiber cable had been cut clean through. We knew we had a important task ahead of us, as the hospital was counting on us to bring the network back up as soon as possible. At least we had found the problem and we could now shift our focus to getting the repair done quickly.
The moral of this story is use the proper equipment and some common sense! Simple laws of physics will tell you, you can't pull down on a cable that is rubbing against another cable or bundle of cables for an extended period without catastrophe. This was very costly to fix and created an embarrassing situation for the contractor.