Touching a tree or anything outside your machine while in the cab will kill you. Touching the ground in an attempt to escape the cab will kill you too. So stay inside, windows shut.
Tuesday, November 8, 2011
This past weekend we had unprecedented damage from an early snowstorm. Trees were down across all the roads in town, and many took powerlines down with them. I had to clear a dozen or more large trees just to reach the highway, less than half a mile from my house.
I used the front end loader on my tractor to break up the tree jams, and pick up the brush and move it aside so cars could pass. Anyone who’s ever run a loader knows that’s heavy and dangerous work as the trees bend and snap. You’re glad to be in a roll cage enclosed cab with some of those limbs come back to whack you in the face!
To clearing the road I’d scoop under a load of tree debris, lift it high, and dump it in the woods. That process went along uneventfully until I picked up a load of brush that was tangled with bare electric power lines. There are lots of stories online telling you to stay away from power lines. There are very few stories that talk about what you should do if you get up close and engaged with them. Today, I’d like to share my thoughts with you.
The conventional wisdom says that it’s fatal to contact live electrical power lines. That is certainly the case much of the time, but not always.
If you hit live power lines with a loader, backhoe, or crane, and you are inside an enclosed cab on the machine, you can probably emerge unscathed, provided you keep your wits about you and follow these steps.
When your machine touches the line, it immediately becomes energized to the voltage in the wires. If you are sitting in the cab, you get energized too. You don’t actually feel anything but a tingle, as no current is flowing through you, but you are suddenly in a very dicey position.
As long as you remain in the cab, the wires can’t touch you, and the current flows through the metal of the machine. If you get out of the cab, or a wire gets in, all that changes. If you touch anything outside the cab, the power line current will flow from the cab frame, into you, and out of you into whatever you touch. That's almost always lethal.
That’s how most people who have accidents on construction equipment get killed. They hit a line, and then jump off the machine. That’s usually a fatal error. The ground under the machine is energized as the current flows through the wire, into the machine, and into the surrounding earth. The dirt within five to ten feet of the machine is going to be energized to a dangerous level. So you can be safe in the cab, but dead if you jump on the ground.
The wires present another danger. If the wire is outside, touching your loader frame, you are safe. If the wire gets inside, or touches you, you are toast. So don’t open the windows or doors.
If anyone sees you in this fax, wave them away, but do not open the doors. If they approach you, they are likely to be electrocuted by the field you are currently immersed in. Hopefully, no one else is around you.
The final danger is that the energy in the wire will disable the machine, leaving you unable to escape. When the energy flows into the machine’s steel frame, it has to go somewhere. That somewhere is ground, through the steel tracks or rubber tires that the machine sits on. That point of contact with the ground becomes a hot spot, both figuratively and literally. A tracked machine, sitting on steel tracks, could have the grease in the tracks burst into flame. A wheeled loader will have smoke coming from the tires as they begin to melt. Both situations call for fast action.
Disengage the machine from the wires, look around for other hazards, and back away. If the machine’s arms are tangled, remember the rig has enough power to break the wires, but you have to make sure you back clear, wherever they land. That is absolutely vital. Wires may be dark, and hard to see against downed trees or a dark roadway. It’s essential that you back at least twenty feet away from them before exiting the cab. If the ground is wet, back farther.
If for some reason you cannot back away, remain in the cab and use a cell phone or radio to call for help. When seeking help, the only thing someone can do is cut the power remotely. Any attempts to approach your energized machine will be lethal to potential rescuers. It’s far better and safer to get your machine out of danger under its own power.
Hopefully, you will never encounter powerlines in a construction machine. If you do, just remember. Stay inside. Keep your head. Disengage and back clear.
Once clear, flag the area as dangerous from a safe distance. When walking near downed wires it’s possible to step from an area with no charge to a lethally charged area with no visible indication of what is about to happen. In that sense, downed lines are more dangerous than the deadliest snake, because they do not even have to touch you to kill you.