Drilling in the basement It seemed like just another ordinary day on the job. An electrical contractor was working in a high-rise medical facility in the process of a major expansion. One of the contractor's electricians was running a high-powered electric drill to bore a 1-in. hole in the basement floor for installation of a driven ground rod. Foolishly, he hadn't taken the time to inspect as-built drawings for the location of any buried obstacles.
While drilling, he saw what appeared to be metal chips. Assuming he was going through one of the slab's reinforcement bars, he kept on drilling. Suddenly, he felt a difference in drilling pressure. At this moment, he began to question what he was actually drilling through and called for his supervisor, who contacted management.
Management, in turn, contacted their liability insurance carrier, who contacted us (forensic consulting engineers) to investigate the situation. We felt it prudent to open up the concrete in the area of the drilled hole. What we found was absolutely shocking: The electrician had actually drilled through a steel duct encasing a 13.8kV power feeder. One of our senior forensic engineers identified damage to the insulation on all three of the 4/0 AWG feeder cables. An inspection of the damaged cables during this investigation revealed the electrician would have inevitably lost his life had he drilled only an additional 1/16 of an inch. Therefore, in this case, the saying is not an exaggeration. The electrician literally did come within less than an inch of losing his life. In fact, one could characterize the electrician's life as both ill-fated and charmed-ill-fated because the odds of hitting the incoming feeder with his drill were extremely small (considering the large area of the basement) and charmed because seldom does one get any closer to the brink of death and live to tell about it.
Remedial solutions The facility's liability insurance carrier asked us to plan a remedial solution and manage the required corrective steps.
First, we immediately turned off the facility's normal power supply and started its emergency engine-generator set to provide power to critical loads. (Designed to provide limited emergency power only, it did not have the capacity to handle the total load.) Concurrently, load shedding went into effect.
Next, we quickly arranged to use a rented back-up generator set to augment the facility's emergency unit, which ensured a normal mode of operation at the medical center as soon as possible. (We made no effort to power certain nonessential loads.) We kept the additional standby unit outside the facility in a "ready" mode of operation. The facility purchased thousands of feet of 500kcmil cable temporarily installed for connection to various loads. This was somewhat complicated as different voltages were involved. However, the arrangement allowed most of the equipment not operating because of load shedding to function again. In one area of the facility where power was needed, running cables from the additional generator was impractical. Here, we ran feeder cables from a third generator, a small set dedicated to serve that load. A checklist assured no one had overlooked any details. For example, correct phase rotation of each generator was one such check.
Finally, we evaluated corrective alternatives. Splicing wasn't a viable option because workers had installed the 13.8kV feeder below the water line. (The facility was close to a large body of water.) Relocating the feeder to above grade also wasn't an option, due to the high costs involved. The only viable solution was to pull out the damaged cables, replace the damaged length of steel conduit with a new length, and pull in new 15kV cables.
With the temporary work completed, we prepared a flow chart covering the time needed to carry out the permanent work. From the chart, we determined the generators would be running for 16 hours.
Steps to repowering With the replacement cables installed, we performed hi-pot testing and installed heat-shrink type stress cones. Then, we verified every overcurrent protective device in every distribution panel was in the OFF position and placed safety tape with warning labels over the panels.
Next, the new cables were connected to the existing distribution equipment, and the existing loads were disconnected from the generators and reconnected to their original power sources.
Finally, the loads were reenergized from the normal utility power (via the new 15kV cables). As expected, the cable replacement and associated tasks only took the allocated span of 16 hours. This included a one-hour check of details before energizing the feeder.
Lesson learned The average duffer is elated when he gets a "hole in one." We know one electrician whose one hole cost the insurer of this facility $100,000.
Contractors and related trades who dig/drill into the ground should know safety requires identification of concealed hazards. In fact, when contractors plan to dig outside in New England, they can call the local area code where the work is located and then 344-7233 (Dig-Safe). A utility coordinator will provide guidance in choosing a safe location.
This same degree of caution is necessary for life safety when drilling inside a facility. Facility engineers and managers can learn from this experience and mandate an inspection of as-built electrical and mechanical drawings prior to drilling inside their facility or digging on the outside grounds. In effect, you must coordinate this effort with the engineer having access to all drawings for electrical systems as well as gas and water lines. And, there must be a clear understanding between this engineer and the worker doing the drilling as to its location and what impact, if any, the work may have on vital systems.
Drilling a hole in a medical facility basement to drive a ground rod almost cost an electrician his life. Only through pure good luck did his drilling dodge death. Had he checked as-built drawings, a $100,000 expense would have been avoided.
"He came within an inch of losing his life." We've heard this phrase used figuratively to describe a close call before. However, here's a case study where an electrician literally came within less than an inch of doing just that.