Those of you who recieve EC&M magazine have already read the "Forensic Casebook" column with this name. I'll give a quick recap - then make a few points that were absent from the article.
The story is quite simple; a dairy worker was using a trailer-mounted power washer to clean up the milking area when he was electrocuted. This, by itself, is a sad tale. Yet, as with so many such tales, the death was more a matter of 'when,' rather than 'if.' The column posits a current path from the washer, along the hose, through the worker, and into the grounded structure. I don't question that.
The two points I want to address are equipment selection and maintenance.
The power washer - a trailer mounted unit - had an "open dripproof" motor on it. Supplied that way by the manufacturer, it had alread been replaced once because of moisture and corrosion damage. There was no supplimental enclosure; just a motor and pump sitting on a trailer.
I have a problem with that design; such a machine is sure to get wet, from every direction, in both use and in transport. A TEFC motor is clearly called for. That's my take.
Keep in mind that it matters not that every component was UL listed; the final assembly was not. I don't know if UL has a standard specific to this type of machine - if it does, I cannot imagine the machine being in compliance.
The lesson here is: buy the RIGHT equipment. Machinery is not a commodity, with all "pressure washers" being the same, and the purchase price being the only thing that matters.
This lesson is confirmed by my other issue: maintenance. The pressure washer was freely coated with manure, straw, and other debris. The capacitor cover and 'peckerhead' were held on with a bungee cord. The power cord and plug were damaged. In short, this machine was an accident waiting to happen.
Likewise, the receptacle that was used was severely corroded. It matters not that a "Bell box" was used; the NEC requires that equipment be suitable for its' location, and specifically mentions corrosion as a factor.
A side note: Dairy operations are very corrosive locations, with great amounts of moisture and harsh cleaning / sanitizing agents used. An ordinary receptacle and aluminum box are just not adequate. Try to imagine what equipment you would use if asked to install a receptacle inside your shower, and planned to powerwash the receptacle with bleach and oven cleaner every day. That's what we're up against.
The article addresses the lack of a GFCI receptacle. I doubt that such a device would have worked in this environmnent. A recent article in the IAEI magazine discussed the ways corrosion can prevent a GFCI from operating. A dairy is one place where the use of a GFCI breaker might be a better choice; you can locate the panel away from the wet / corrosive area.
The various signs of damage to the electrical parts suggests that there were regular mishaps at this dairy. Personally, I begin to start thinking in terms of 'criminal negligence' in a death like this.
