Let Go!

Arc Flash Safety January 2018

“Let go” current is the magnitude of current that causes muscles to involuntarily contract—i.e., your fingers will close and lock onto the conductor. If nothing breaks the current path, such as the tripping of a ground-fault circuit interrupter or someone removing the victim from the circuit, the results are often fatal.

Two events I was involved with included an investigation of a job-related incident, and the other was at home. One survived and one did not.

On the job

The first situation was an expert witness case of mine where a technician was downloading energy data from data ports mounted on the outside of several rooftop units (RTU) for an audit of the system’s performance. This was a sensitive facility, so a security escort was required.

Normally, this is a routine procedure, but one of the RTUs had no port—now what? He opened an access hatch on the RTU to see if it was possibly on the inside. Sure enough, there it was. He laid on his back and wiggled his way in just far enough to reach the port and plug in. The security person reported hearing a loud groan followed by the tech’s feet kicking. By the time the escort realized what was happening, it was too late.

What happened? Working his way into the RTU, the tech grabbed a component to better position his body—but the component was energized. The current path was across his chest and stopped his heart. The equipment had been incorrectly modified, which resulted in one phase remaining energized—even though the switch was in the off position. 

Before you ask—due to the nature of his work only involving a laptop and outside data ports, he was never properly trained in the hazards of electricity.

To address incorrect installations and modifications, the 2018 Edition of NFPA 70E added 110.1(B), Inspection: “The electrical safety program shall include elements to verify that newly installed or modified electrical equipment or systems have been inspected to comply with applicable installation codes and standards prior to being placed into service.”

At home

When my son was a senior in high school, he had a rock band that practiced at our house most afternoons (which motivated me to stay at the office later). One afternoon, I received a call from him, and he sounded pretty shaken up. Much to my surprise, he seemed to have taken a sudden interest in what Dad does and began asking questions about grounding, electric shock and current. This was not a normal conversation, and since my office was close to home, I was out the door in a flash. When I arrived, he and his bandmates were in the basement with all of the amplifiers humming—still quite stunned.

They had decided to “borrow” an old, inexpensive metal pole light from my workshop area and put in a few colored bulbs for effect. However, the light did not work. In their usual teenage style, they just left it there. A short time later, my son—who was playing guitar—reached out and grabbed the microphone, which was on the stand and simultaneously grabbed the light. At that moment, he let out a high-pitched shriek that could have shattered windows. Although the whole event happened in an instant, his bandmates all thought the same thing about the performance: “Cool! We can work with that shriek.” However, almost at the same time, he collapsed to the floor.

What happened? It turned out the old light’s metal base was sharp and had cut the cord’s phase conductor. The light’s base was right on the conductor and—without a ground—the whole thing was energized. When he grabbed the microphone that was grounded through the amplifiers and then grabbed the energized pole of the light, he was across 120 volts to ground and could not let go. He collapsed, pulling the light with him. This broke the circuit, and the fall ultimately saved his life.

Understanding the possible cardiac effects, I took him to our local clinic where they performed a blood test to determine if there was any heart muscle damage. The attending physician indicated no damage to the heart, but he did notice burns to his fingers where he was latched onto the light. We missed that through all of the commotion. He still has the scars today.

Whether on the job, at home or anywhere, the hazards of electricity lurk just around the corner for its next unsuspecting victim. 

NFPA 70E is one of the most important standards for electrical safety—in the workplace and at home. Don’t be a victim!

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