There are often deadly hazards lurking underground on excavation sites.
Rupturing or breaking underground utilities such as electrical power cables and
pipelines can result in serious injuries or even death.
A Worksite Story A construction crew was using an auger to dig a hole for
anchoring a utility pole support cable. Suddenly the auger hit a small plastic
gas line. Escaping gas soon reached a nearby building, where it ignited about
20 minutes later. Four people died and 15 were injured. In addition, three
buildings were destroyed and more than a dozen others had extensive damage.
In the middle of the city, out in the suburbs, and perhaps
even in the middle of nowhere, there is a pretty good chance that one or more
utility line or other underground installation is buried beneath the surface.
Striking a buried utility while excavating the soil can not only cause
disruption of services to the general public, it could also result in someone
getting seriously injured or killed. So today we will review some steps to help
prevent striking underground utility installations at excavation sites.
Never dig until after all underground utilities have been
marked. We must first contact our state’s One Call Notification Center, who
will then notify their members to mark the approximate location of their buried
utility lines at the excavation site. The amount of lead time we must allow for
the lines to be marked varies is dictated by state law. But we must usually
allow at least two to three working days, excluding holidays and weekend, and
then we must confirm the utilities have been marked before we start to
excavate. Paint, stakes, or flags of various colors will be placed to identify
the approximate location of the utilities buried at the site.
Locate any underground utilities that are present inside the
“tolerance zone” by hand digging or utilizing other non-destructive digging
measures approved by the Competent Person. The tolerance zone is the area along
each side of each existing utility line that has been marked. The tolerance
zone varies from state to state, but usually ranges from 18 to 24 inches from
each side of the utility line. But in some States, believe it or not, the
tolerance zone is as much as 30 to 36 inches from each side of the utility.
Support exposed utility lines, if necessary, so they do not
collapse under their own weight. This could require placing a heavy timber or
pipe across the top of the trench, and then tying a rope from the timber or
pipe to the utility line to support its weight.
Ease up when you get near the underground utility when
digging with hand tools. You want to avoid damaging the utility line as you are
digging, so slow and easy does it!
Immediately report any damage you accidentally cause to a
buried utility, no matter how minor, to your Supervisor or the Competent
Person. The same applies to any damage you discover that was caused during
previous excavation operations. Damage to a buried utility that goes unrepaired
could worsen over time and cause the line to crack, corrode, or rupture.
Use caution when back-filling near
utility lines in excavations. Dumping a large load of backfill soil directly
onto an unsupported utility line could cause it to break. So firmly backfill
the area beneath the utility line with soil before placing and compacting soil
over the top. If you are ever in doubt about these or other important
procedures you should follow while digging near buried utility lines or
installations, ask your Supervisor or the Competent Person for help. Better
safe than sorry!
Before digging:
* Look for paint or flags marking locations of electrical lines. Electrical lines should
also have a warning device, such as a range control or limit. You should know how each is marked.
* Review marked-out areas. They may not be exact. If not sure, call the utility company to verify before digging.
* Plan to dig by hand when working within 2 feet of a mark-out, to make sure you do not hit a utility line or conduit with heavy equipment. Ask your supervisor to identify the expert who will review the work area before work begins and as needed during your shift.
When digging, look for:
*Signs of previous digging
*Changes in soil types
*Asphalt patches or depressions
*Concrete, plastic, or gravel
If you hit a line, you must report it! If it’s a gas line, evacuate everyone, secure the area, and call the fire department.