Disregard for lock-out/tag-out at a cheese factory isn't enough to overshadow a contractor's responsibility to safe design
Every few hours, the production line crew at a Northern California cheese factory would change cleaning tasks on machines that required lock-out/tag-out procedures widely known by the employees but rarely followed. Although such carelessness with safety procedures was the primary factor that led to an accident involving a member of the crew, the situation also raised questions about both the location of the production line disconnect and the installing contractor's responsibility for designing a safe system.
The victim of the accident knew the lock-out/tag-out procedures well — so well, in fact, that she had been entrusted with teaching them to new hires. Upon returning from break to relieve another employee — whom she had recently trained — who had been cleaning a concealed screw auger with limited access, she asked if he had locked out the machine, and he replied that he had. Without verifying that the equipment was de-energized, she began her cleaning duties by sticking her arm up into the chute to more thoroughly clean the auger cavity. The auger was, in fact, energized, and her arm was promptly cut off.
Setting the scene. The curd production line on which the victim was working processed milk into whey, which, when strained, left behind the curd that was then lifted to a holding hopper. Beneath the hopper was a short screw auger that would direct the curd to one of two barrel filling chutes, depending on which direction the auger turned. Every night at about midnight, the crew would shift to clean-up mode, using high-pressure steam and hot water to clean the cheese from every nook and cranny of the production machinery, as required by the USDA. The company had written instructions against hand cleaning and used equipment built with food grade polished welds to facilitate automated cleaning. But despite these precautions, the employees often found it necessary to reach up into the chutes to remove cheese that would stubbornly cling to the blades — a practice that wasn't approved by the company's cleaning policies (Photo 1).
Before beginning the cleaning process, the employees were supposed to lock-out and tag-out the machine by following a circuitous route through the production line tables into a hallway and through two rooms to the motor control center (MCC) about 150 ft away (Photo 2). A sign-out sheet was available for logging each lock-out/tag-out request, for which the employees had all supposedly received their own locks and keys upon starting work. The process broke down, however, because some employees never received locks, prompting crew members to take other employees' locks from a common box and leave the key. In fact, some would fail to lock-out the equipment altogether before cleaning. In spite of the written procedures, the actual training practice involved passing information verbally from one employee to the next with no consistency or quality assurance.
The victim had intended to save time by relying on her predecessor's lock-out/tag-out procedure for her own safety, violating the universal lock-out/tag-out rules by not personally checking the safety switch and not applying her own lock. When she asked if he had locked out the equipment he assumed she was just checking to see if he had followed safety procedures while he cleaned the machine. He had already finished his task, removed his lock, and restarted the machine. The situation was made worse by the noise in the process room, which made it difficult to determine whether the barrel fill auger was operating or idle.
Workman's compensation insurance paid for the employee's medical bills and short term lost wages, but her earning power was significantly curtailed by the accident. Her attorney brought suit on her behalf against the process equipment manufacturer and the electrical contractor that had connected the automation control wiring and installed the power wiring to the MCC.
Sorting out the responsibilities.
Even though the Exception to 430.102(B) in the 2002 National Electrical Code stipulates that the presence of lock-out/tag-out makes it acceptable to locate a disconnect out of sight of the barrel filler, the electrical contractor accepted responsibility for an improper location of the switch. However, the lock-out/tag-out procedure doesn't eliminate the need to know the equipment status when closing the disconnect. What if one employee began to work within equipment that had been locked-out by another employee, only to have the original employee remove his lock and restore power? Had the position of the switch been visible, it might have changed the outcome of this event.
Even though it wasn't required by the NEC, the presence of an electrically latching main power contactor, controlled by start-stop buttons on the barrel fill auger machine, would have certainly prevented this accident.
Because of the admission regarding the safety switch location, the electrical contractor's liability insurance company settled out of court for the full amount of the claim. The electrical contractor was no longer part of the suit, but its insurance company could recover any money received as a result of any percentage of liability on the equipment manufacturer's part. The case now focused on whether the lack of a latching relay was a design defect and, if so, the percentage of the responsibility for the faulty design the two defendants were liable for.
Deposition testimony showed that the cheese manufacturing industry is relatively small and isolated with only a few equipment suppliers who know the production procedures well. They know that daily cleanup and the accompanying lock-out/tag-out is universal. Their equipment is integrated with process controllers that can start equipment automatically. However, the one wild card is that despite the routine nature of cheese making, humans tend to introduce random variation in their behavior under such conditions. In this case, that random event was a careless disregard for lock-out/tag-out procedures. In the absence of universal engineering design standards, the art of prudent design would require the equipment manufacturer to anticipate this possibility and include a start-stop station in the barrel fill auger control panel mounted on the machine. These latching contactors are very common, yet aren't universally required or considered necessary by any codes or standards.
How much is expected of a contractor?
Although this is certainly a poster case for the importance of following lock-out/tag-out procedures religiously, it also raises several important questions for electrical contractors. In California, the law generally requires electrical circuits and systems to be designed by licensed engineers. However, licensed electrical contractors may design systems they install themselves.
Where the electrical power system interfaces with complex third party machinery, and a part, such as a latching contactor, could be located in either system, does the “license to design” legally require the contractor to, in essence, watch over the design of the equipment manufacturer? Who is responsible for assuring that such a contactor is installed? If a contractor chooses not to design the installation, can he avoid such design responsibility from a legal standpoint? To what degree should the electrical contractor be expected to anticipate the behavior patterns of the users of its installed systems?
This case closed with a settlement from the equipment manufacturer's insurance company, demonstrating that its attorneys were convinced that not only would the latching contactor most likely be deemed necessary by a jury if the case went to trial, but that the manufacturer would have some responsibility for providing that device.
Manufacturer responsibilities aside, several sections of the NEC anticipate user activity with requirements that emphasize the safety of the end-user. Safety measures like protection for wires exposed to abrasion, shielding for live parts, enclosed junctions, grounding for exposed metal, space provisions around panels, and nail plates for vulnerable wiring underscore this fact and raise questions about the contractor's responsibility to the end-user. Does this legally put contractors on notice that they should be looking for trouble caused by errant user behaviors when installing power systems? Like it or not, the answer may be “yes,” making the installer a tempting target for attorneys.
Crawford is a forensic electrical engineer in Sandpoint, Idaho.