Although the number of Americans working in agriculture has steadily decreased over the past few decades — and the amount of mechanization has conversely increased — one aspect of life on the farm has not changed. By every account, it is still one of the most dangerous jobs in the country, with a yearly average of 39.5 deaths per 100,000 workers, according to the April 2010 article, “Most Dangerous Jobs in America,” from cnnmoney.com.
Unfortunately, the dairy farm worker described in this case learned of these occupational hazards firsthand, as he became part of this tragic statistic some years ago — when the lack of GFCI protection at the power washer he was using to clean the milking stations combined with a deadly arc-tracking incident at the corroded plug receptacle interface to shock and ultimately electrocute him.
Setting the stage
After a dairy operation took on a major expansion project in 1988, a multi-section, wood-framed, steel building was added onto the east side of the original hip-roof barn. This new addition split into a free-stall barn and a holding pen for cows entering the milking area. The south half of the old barn was converted into a milking parlor. Cows entered the milking parlor along either lane and were held in place by a gate — six per side. The pit area extended most of the length of the parlor, allowing the operator to have easy access for cleaning and hooking up milking devices.
The dairy farm owner, Mike, had purchased a new pressure washer from ABC Mfg. two years prior to the accident that originally contained a 120V, 2-hp, capacitor-start-capacitor-run induction motor, which drove a water-pump with an output of 2-gal/min. at 1,500 lb.
Failing only four months later, Mike brought the pressure washer back to ABC for repairs. According to ABC representatives, the original open-drip motor apparently failed due to the high amount of moisture and corrosion. Nevertheless, ABC replaced it with another open-drip unit that was more tightly sealed against water intrusion and replaced the original 1-ft line cord with a longer one.
Although ABC instructed Mike to move the unit to a drier area that offered more protection, Mike insisted he had to keep it in the milking parlor, because this was the only part of the building that didn’t freeze in the winter. After this repair, the power washer continued to be used in the milking parlor multiple times a day. Typically sitting on the elevated portion of the milking parlor (just west of the pit entrance), the power washer plugged into a duplex receptacle that was originally mounted on the lower pit wall next to the stairs.
Ryan had worked at this dairy farm near his home for the past 13 years. While not a glamorous job, it was stable and allowed him a steady income. By all accounts, he was a competent and dependable employee. Ryan’s main duty was to take care of the basic needs of the dairy cows — feeding, watering, and moving them in and out of the pens. He was also responsible for cleaning the milking parlor after the twice-daily milking operations — a task he’d completed countless times before.
On the day of the accident, Ryan finished feeding the cows at approximately 7 p.m. The nightly milking was completed around the same time, so he walked over to the barn to begin cleaning the parlor. Typically, he would use a water hose to spray down the milking units and hook them up to the sanitizer system. After starting the sanitizer system, he would then turn on the pressure washer and thoroughly spray down the area to clean away any manure and debris. The whole process took approximately 10 to 15 min.
Meanwhile, another hired man, Luke, had arrived at the farm to help Mike sort out some steers for future sale. At approximately 7:15 p.m., Mike told Luke to run over to the milking parlor and ask for Ryan’s help. As Luke entered the milking parlor, he noticed the power washer was running, but couldn’t see Ryan anywhere.
He quickly found Ryan lying unconscious on the floor holding the power washer wand. Luke ran over to check on him, shutting off the power washer on his way. Luke threw the wand to the side and checked Ryan’s vitals. Finding no pulse, he ran back outside to find Mike, who immediately called 911. Despite multiple attempts to resuscitate Ryan, he never regained consciousness and was later pronounced dead at the hospital.
Emergency personnel originally speculated that sudden cardiac arrest was the cause of death, not necessarily unusual for a male in his mid-40s. However, a subsequent autopsy revealed Ryan was not suffering from any significant underlying health problems or diseases. The autopsy did reveal an unusual burn injury on his right hand and wrist — and another injury to his left arm. This discovery, along with other circumstances surrounding the incident (use of a power washer in a wet environment), led the pathologist to conclude that Ryan was most likely electrocuted.
After the accident, Mike and his wife continued to use the power washer for a few days until the coroner notified them that Ryan might have been electrocuted. Mike then hired his regular electrician to come out and examine the dairy barn and power washer for any problems. The electrician measured continuity of the power washer equipment grounding system between the ground prong of the plug and the power washer housing. After that, they pulled the machine outside and left it exposed to the elements. At some point, the unit was transferred into the custody of a forensic engineering firm hired by the insurer of the dairy farm.
The electrician also replaced the original power washer receptacle with a ground-fault interrupting (GFCI) receptacle. The original receptacle was so corroded that he could not unscrew it from the junction box. While prying it out of the box, the unit fractured. The receptacle remains were later thrown into the trash. However, fortunately the electrician later recovered the pieces after learning of possible legal action.
The legal team for Ryan’s estate notified other parties that may have been at fault, inviting them to attend inspections of the dairy farm and the power washer — actions that typically occur prior to a lawsuit being filed. The insurer of the power washer manufacturer, ABC Mfg., hired our forensic engineering firm to investigate Ryan’s death and determine what role, if any, the power washer may have played in the accident.
Investigation and analysis
The power washer was made up of a pump and motor assembly mounted on a wheeled cart. The pump pressurized water that was directed to a hose-connected spray wand. The internal circuitry was fairly simple. Power traveled down the line cord, through an external on/off switch, entered the motor housing, and energized the motor windings. The motor also contained an integrated thermal protector to guard against overheating.
At the time of the accident, the pressure washer was in rough condition, encrusted with manure and other debris. In addition, the unit showed indications of physical abuse. The junction box covering the motor fixture wires as well as one of the capacitor covers had broken away from the motor housing. Photographs taken shortly after the accident show that the fixture wiring junction box was held in place with bungee cords (Photo 1).
Electrical tests and measurements showed that the on/off switch was not damaged and functioned properly. Although some of the internal conductors and fixture wires showed indications of damaged insulation, there was no evidence of arc-tracking or other abnormal current paths.
Resistance measurements of the line cord indicated that there was no electrical short between the line cord conductors. The plug blades were wired to the proper line cord conductors. However, there was evidence of melting on the ends of the hot and neutral plug blades where they would have mated with the receptacle wipes. In addition, there was evidence of arc-tracking across the plug face between the hot and ground plug blades (Photo 2).
The ground connection between the line cord and the motor housing depends on this physical connection between the fixture wire junction box and the motor housing. Although we found it to be damaged during our inspection, according to the electrician, there was continuity on the grounding path from the ground blade to the motor housing shortly after the accident.
The motor manufacturer provided an in-line thermal protector along with the motor leads. The manual-reset thermal protector is designed to open the circuit if the motor overheats (due to a fault, locked rotor condition, etc.,) and prevent damage to the motor windings. However, at the time of our inspection, the thermal protector was disconnected. In all probability, moisture and corrosion from the poor operating conditions caused the motor to overheat and resulted in the perceived nuisance tripping of the thermal protector. Rather than replace the thermal protector, an unknown party cut it out of the circuit.
Two hoses were tied together to form a complete hose of 30.8 ft and terminating at a quick-connect fitting for a 3-ft, pistol-grip spray wand. The hose was electrically continuous from the pressure washer end to the quick-connect fitting at the wand. In practice, when physically connected to the pressure washer, the hose would be grounded through the power washer equipment-grounding conductor. Additional analysis was conducted in the following areas as well.
Milking parlor receptacle
As mentioned previously, the receptacle was removed from the junction box soon after the accident. During our later examination, the receptacle housing and faceplate showed signs of severe contamination. Dirt, straw, and manure were found on the surfaces of the receptacle junction box and faceplate.
The lower receptacle had a burn pattern across the face, between hot and ground (Photo 3) that mirrored the pattern on the pressure washer plug.
The ground bus was severely damaged and was separated into three sections. The edges of the bus sections were oxidized and appeared severed due to the corrosion (Photo 4). Only one of the three sections of the ground bus was still attached to the grounding conductor. This separation in the ground bus is a safety hazard. Any ground-fault current within the receptacle or on items plugged into the receptacle will not have a low-resistance current path back to the panel that could trip the overcurrent protection. This allows fault current to continue to seek other paths back to the grounded transformer.
Current path resulting in electrocution
In order to be shocked, a person must become part of a current path. During a typical ground-fault event, current flows through multiple paths and the least resistant path will carry most of the current. Stray current paths can form through mediums such as water, soot, and other contaminants. Normally, if the equipment and circuit grounding system is intact and properly bonded to the grounded (neutral) conductor at the service entrance, the ground-fault current will be enough to trip the over-current protection device (OCPD).
The physical evidence of arc-tracking across the plug face of the milking parlor receptacle shows that electric current flowed from the hot blade of the plug (120V) to the ground blade of the plug (0V). This current path allowed the grounded components of the power washer (including the hose and wand) to become energized. Over time, as the plug arc-tracking and the physical degradation of the receptacle increased, it would cause the potential fault current path to decrease in resistance.
Of course, the human body will also conduct current. Although not a good conductor when compared to copper, it takes only takes a relatively small amount of current to cause damage — 100mA across the heart is enough to induce ventricular fibrillation (i.e., a heart attack), and it takes only 1A to produce the type of burning found on the victim’s body.
As he did that day, Ryan normally wore insulated rubber boots while he was washing the milking parlor. Thus, while he was performing his daily tasks, he was normally insulated from electrical ground, and his body did not conduct significant fault current (if any was present). Over time, as the plug arc-tracking and the physical degradation of the receptacle increased, it would cause the potential fault current path to decrease in resistance.
The cattle gates in the milking parlor were all bonded to the main panel. Unfortunately, the integrity/quality of the grounding system was not tested during the investigation. It is unknown whether the gates were improperly acting as a grounding electrode or if they were properly bonded to the grounded conductor at the service. Depending on the quality of the grounding system, this could create a dangerous hazard wherein any personnel contacting the cattle gates could place themselves in-line with ground-fault current should the OCPD not trip.
The autopsy photographs showed a burn on Ryan’s right hand consistent with the shape of the pistol grip on the wand and a smaller burn on his right wrist consistent with the location of the hose. There were two wounds on his left arm where the skin was broken — and current would be able to flow through his body to another electrically grounded surface. These wounds show that, based on a confluence of events, Ryan most likely became part of the current path when he eventually held the power washer wand in his right hand and touched the grounded steel frame of the cattle gates with his left arm and/or hand (click here to see Figure).
The owner/operator of the power washer manufacturing business (ABC Mfg.) started out building and/or repairing other manufacturer’s units. However, after several years, it began building and selling its own units. The company based its power washer designs on the units it had worked on in the past. Its electrical parts supplier helped with any design issues and recommended the appropriate components. Although UL-rated components were used, the power washer unit as a whole was never submitted to Underwriters Laboratories (UL) for testing. In addition, the manufacturing representatives were ignorant as to the NEC requirement for a GFCI, regarding it as a cause of nuisance tripping.
In the case of the artifact pressure washer, if the unit suffered an internal ground fault, a GFCI in the pressure washer cord would detect that not all of the current was returning on the neutral conductor and then trip the circuit. However, if ground-fault current passed to electrical ground at the plug face, as was the case in this accident, a GFCI in the pressure washer cord would not detect this leakage. The current in the hot and neutral conductors, as seen by the downstream GFCI, would remain the same.
The expert representing Ryan’s estate blamed the cause of the accident on a ground fault within the pressure washer. In that case, an integral GFCI could have prevented the accident. However, we did not find physical evidence in the pressure washer to indicate a ground-fault path internal to the pressure washer. Instead, the physical evidence indicated that the fault current tracked across the plug face to the pressure washer ground, energizing Ryan’s body. Thus, a GFCI located in the pressure washer line cord of plug would not have prevented this accident.
Receptacle and pressure washer maintenance
The milking parlor is a wet and corrosive environment according to the 1987 NEC, Sec. 547 - Agricultural Buildings.
“547-1(b) Corrosive Atmosphere. Agricultural buildings where a corrosive atmosphere exists. Such buildings include totally enclosed and environmentally controlled areas where (1) poultry and animal excrement may cause corrosive vapors in the confinement area; (2) corrosive particles may combine with water; (3) the area is damp and wet by reason of periodic washing for cleaning and sanitizing with water and cleansing agents; (4) similar conditions exist.”
In such an environment, harsh conditions exist for all electrical appliances and systems. In 1987, there was no separate section of the code dedicated to duplex receptacles in agricultural buildings; however, all switches, circuit breakers, controllers, and fuses located in a corrosive atmosphere were required to have a “weatherproof, corrosion-resistant enclosure designed to minimize the entrance of dust, water, and corrosive elements,” and were to be equipped with a “telescoping or close-fitting cover.” The receptacle that was installed in the milking parlor in 1988 appeared to meet this requirement when the receptacle caps were closed.
However, Sec. 410-57 of the 1987 NEC required that all receptacles located in damp or wet locations be provided with a “weatherproof enclosure, the integrity of which is not affected when the receptacle is in use (attachment plug cap inserted).” The receptacle in the milking parlor did not meet this requirement. When a plug is inserted in the receptacle, the receptacle cover is open, allowing moisture, corrosive vapors, and debris to contact the electrical components of the plug and receptacle. As the pressure washer was left plugged into the receptacle at all times (without a sealed cover), it was not properly protected.
The 1987 NEC specifically required GFCI protection only on receptacles in wet or damp locations in dwellings and hotels. By 2002, the NEC required GFCI receptacles in wet or damp locations in agricultural buildings as well. The receptacle that was located in the milking parlor was not a GFCI receptacle and did not meet this requirement.
If the failing receptacle had been properly used, protected, and maintained prior to the accident, Ryan’s death may have been prevented. Leaving the cover on the receptacle between uses of the pressure washer would have minimized the damage to the receptacle and kept its face free of moisture and contaminants that could contribute to arc-tracking. Having a qualified electrician examine the electrical equipment at regular intervals — and replacing damaged equipment — would have ensured that the receptacle and housing met the provisions of the current NEC. This means that the receptacle should have been protected by a sealed, in-use cover, thereby preventing arc-tracking on the plug face, and/or replaced with a GFCI receptacle.
Even though we believe an integrated GFCI device would not have prevented this accident, the manufacturer of the power washer was nonetheless ignorant of the NEC safety standards regarding its product. The design and construction of the unit also violated several other sections of the applicable UL standard that would have made the unit safer.
Finally, the physical evidence of deterioration and modifications made to the pressure washer indicate that the dairy farm employees, possibly including Ryan himself, repaired their own equipment without the benefit of electrical expertise or safety concerns. Cutting out the thermal protector in the motor circuit, using a bungee cord to attach the fixture wire junction box to the motor, and using electrical tape to repair a cracked switch faceplate are all modifications to the pressure washer that compromised its safe use. If they had purchased an approved device from the start — and used and maintained it in a proper manner — the accident may not have occurred.
Many times, it takes a multitude of failures to cause a tragic accident. If any one of them were taken out of the equation, Ryan might still be alive. Eventually, the lawsuit against our client, ABC Mfg., was settled out of court prior to trial. Further legal procedures are unknown, but based on our findings, the owner of the dairy farm could have faced OSHA sanctions/fines over his unsafe work spaces, equipment, and processes.
Paris is a forensic electrical engineer with Anderson Engineering, New Prague, Minn. He can be reached at firstname.lastname@example.org.