Taking a quick break for a snack after swimming, a 10-yr-old boy is electrocuted after dropping a few coins into a nearby vending machine.
After swimming at the city recreational center pool, 10-yr-old Brian needed a break and something to eat. Dripping wet, he walked out of the pool and onto the tiled floor in the center's lobby. Once in the lobby, he headed for the candy machine, the last in a row of three vending machines. As he dropped his coins into the machine, several nearby kids saw him suddenly jerk and shake violently. One individual raced to Brian's aid and received an electric shock upon touching the boy. Then, Brian fell to the floor. The recreational center manager immediately dialed 9-1-1. Despite life-saving measures given by pool lifeguards at the scene as well as continued resuscitation efforts by paramedics in the ambulance, Brian was pronounced dead at the hospital. The coroner declared “cardiac arrest secondary to electrocution” as the cause of death.
Because the pool was owned and operated by the city, the local government's risk management officer initiated an investigation into the accident. As good insurance practice dictated, the city identified and contacted the companies involved in the manufacture of the machines, the distributor that placed them at the site, and the company that stocked and serviced them. These companies, in turn, notified their insurance companies of the potential liability of their equipment or employees' actions. Because the case involved a fatality, most of the insurance carriers hired legal counsel, investigators, and expert witnesses.
Lawyers for the insurance carrier of the company that supplied, stocked, and serviced the candy machine hired our firm for forensic analysis. The parties that owned the two soft drink vending machines also retained experts. Each was faced with the same problem: Several questions had yet to be answered. What, if anything, was wrong with the vending machines? Was there an internal failure? Were the machines properly grounded? We had to answer these questions before determining the cause of the boy's death.
Whenever a product-related liability exists in a civil action, industry protocol dictates that all parties involved be notified of the accident and a date be set for a coordinated investigation. Once this was done, we conducted an inspection of the pool facility's electrical system and the three vending machines. (Specific requirements for notification and participation appear in ASTM E 860, Standard Practice for Examining and Testing Items That Are Or May Become Involved in Products Liability Litigation).
The initial stages of the investigation yielded few clues. Paying specific attention to the branch circuit that supplied the receptacle where the vending machines were plugged in, we inspected and tested the building's electrical distribution system for proper polarity and grounding integrity. Measurements of the open circuit voltage and voltage drop fell within acceptable limits. The grounding type duplex receptacle that supplied power to the vending machines had been installed in accordance with NEC 210.7, ensuring proper grounding continuity to the circuit breaker panel ground connection. We also found the panel was properly bonded to the service entrance grounding point, which was effectively grounded.
Next, we moved on to the next battery of tests. First, we used an appliance insulation tester (similar to a Megger) to ensure the motors and associated components of each machine had the proper electrical insulating qualities. As specified in Standard UL 471, Commercial Refrigerators and Freezers, we also tested the three machines for excessive leakage current to their frame, but they all fell within acceptable limits for both tests.
A visual inspection finally revealed the problem. While examining the three machines, we found several strands of copper conductor adhered to the bottom edge of one of the metal legs of the candy machine. We examined and tested the vending machine power cords next. In addition, the candy machine power cord plug had a broken grounding pin, and microscopic examination showed it had endured melt damage.
Next, we realized the officials who had initially responded to and investigated the accident had removed the power cord of one of the soft drink machines. Examination and testing of the cord revealed a portion of the cord was damaged, exposing the stranded energized conductor. The other soft drink machine's power cord was in good condition.
After the site inspection, testing, and examination of the vending machines and power cords, we knew the following conditions existed at the time of the accident: The power cord from one of the soft drink machines had been pinched under the candy machine's metal leg (Photos 1 and 2 above). The outer insulation of the cord gradually became damaged, and the energized conductor eventually made contact with the metal leg of the candy machine. This condition, coupled with the fact that the grounding pin on the candy machine's power cord was broken (Photo 3 above), caused the candy machine's metal cabinet to become energized. After recreating these conditions, we found the potential for almost full line voltage between the candy machine cabinet and the wet tiled floor — all the necessary circumstances for a fatal accident.
Despite these discoveries, several questions remained unanswered. Who last moved the machines? Who plugged the damaged attachment plug into the wall receptacle? Had anyone reported receiving shocks from the machine before the boy's electrocution? What inspection requirements should have been in place to ensure a safely operating machine?
Our investigation ended when all parties reached a confidential settlement. The recreational center placed rubber mats in front of the vending machines and instituted a safety inspection policy for the vending machines whenever distributors came to restock them. More importantly, the city electrical inspector began making periodic inspections of the recreational facility, including the vending machines.
Foley is President of Technical Consultants Group, Ltd., Denver. His firm specializes in electro-forensic engineering investigations.