cause of electrocution while welding ?

[jmpdiesel]

dear all
a strange incident happened in my workshop on 25th of sept. a technician who was working on a railroad wagon reportedly got electrocuted and died on the spot.welding work was being carried out on the wagon while he was working.Four other technicians were also working on the same wagon and they did not feel the shock.welding was being done by a AC welding machine with an O.C.V of 70 V AC.No other 230 V AC machine was being used on the wagon. we could not find the specific reason of electrocution but there were burn marks on both of his palms as he was fitting a gear in the wagon by holding it.The strange fact is that how come a person can die by 70V AC current ??? why didnt others feel the shock??? after the incident the machine was checked and there was no leakage AC current in it and the shop was completely dry.
Another interesting fact is that one month before this incident a fitter felt the shock while working on another wagon placed at the same berth and welding was being carried out by the same machine.Thankfully he survived.But this time we were not lucky enough.
Can anybody throw some light on the cause of death??
We are still unaware of the specific cause so that we can take corrective action.
Members may like to discuss

[Gadget]

Welcome to the forum JMP.
I know 70 amps seems low but I can vouch for the fact it can be enought to kill. I got tangled up with both leads of a welder with a carbon arc setup. Managed to get one carbon in each hand. The only thing that saved me was I was shaking so violently the carbon rod broke. Both hands were smoking and I had no muscle control at all. I figured I was a goner and now consider myself very lucky.
Bottom line, be very careful when welding. You ARE using enough power to kill.
Again welcome and thanks for the reminder.
Dan

[matteh99]

To really know what happened you would need to really see the cart and the setup. Somehow he managed to to become a path for the welding current. The current will divide up between its possible paths proportionally. If there are two paths for the current and path A is 1 ohm and path B is 1000000 ohms then a million times more current will flow through path A than path B. To be safe you want all of the pieces you are welding on to be as electrically connected as possible. If you do manage to put your self in parallel with the welding current most of it will flow through the work piece and not you.

A simple example would be putting a piece on a welding table with the work clamp attached to the table. If you lean against the table, hold the piece with one hand and weld with the other you put your self in parallel with the welding current. If there is a good connection between the table and piece nothing bad happens and you weld away. If the piece is rusty, painted, anodized, or otherwise not connected well to the table and your hand is well connected the same situation as listed above could be shocking. The resistance of your part of the circuit is the same but the resistance between the work piece side and table is higher meaning more current will flow through you and less through the work piece.

As far as one person being ok and another getting killed being sweaty and the amount of contact area has a huge impact on your bodies resistance. With dry hand holding the probes of my ohm meter I measure around 2000000 ohms. The internet says with sweaty hands on a large surface area your resistance can be as low as 2000 ohms. That could defiantly make the difference between life or death.

This site has some really good info on what it takes to get electrocuted. Ohm's Law (again!) : ELECTRICAL SAFETY

Eric

[huck_this]

Is this wagon on the train tracks while being welded? Where was the grounding lead and where was the guy welding? How far was the deceased working from the welder? Was the deceased in contact with the ground surface? Was he standing on the tracks?

There are a lot of factors here. One thing to remember. Always keep the grounding lead as close as possible to where you are welding.

[ksmeggy]

It's not the volts that kill, it's the amps. Usually, Ohm's law applies and amps are directly proportional to volts, but not necessarily with a welding machine. I understand even the old buzzboxes start their arc at a much higher voltage than the machine operates on, once the arc is started. However, there's another element at work, the collapsing magnetic field over the coil of wire that makes up a welding transformer: if you cut the supply to this coil sharply, mid-cycle, you can develop a higher voltage between both the welding leads and the input leads, than what was used to feed the machine (this is how a car coil can develop 20,000 Volts from a 12V battery). Still, this type of voltage surge is almost never fatal, because what kills is amps, not volts. Milliamps, to be precise, going through the heart.

The fellow had burn marks on both his palms? Well, if you draw a line through the path of least resistance, from one palm to the other, the path leads straight through the heart. It takes many amps to cause burn marks on you palm (I don't know the exact number because it depends on skin type, air humitidy, whether he was sweating, etc). But probably more than 30-50 amps to cause a visible burn. 50 amps going in one palm and out the other practically guarantees enough current (a few milliamps) through the heart to cause it to stop.

The most probable cause is improper grounding on a piece someone was welding on. If he then grabbed something with both hands, he completed the circuit needed to make a path for the ground (in one palm, out the other). This is reasonably common occurence when a grounding clamp is placed somewhere on a large steel structure or object, and is then forgotten while one or more persons welds around it. Just because you place a piece of metal on or beside a metallic structure, doesn't mean there is a clear path for current to flow to ground.

I have been a master electrician since 1991, I've been welding since about then as well. I've shocked myself any number of times doing just this; you tend to forget about your ground clamp when you're welding away at something. I find welders, like electricians, sometimes get a little cavalier about the small shocks we get from time to time. 99.9% of the time, no harm is done.

If I had to make a suggestion, I would say bring someone in to give a safety seminar on electricity in general welding, and whatever specialized methods your shop uses. And inspect the equipment you're using, replace any worn or burnt leads and grounding means, as well as employee's insulating boots and welding gloves.

[torqueman]

My condolences to the family. My first thought was what ksmeggy suggest. If both plams were burnt the voltage went though one and out the other. I assume he was wearing rubber soled boots and not standing in water. Since it will take the path of least resistance you would think he would received less than a full load. The human body is a conductor but not like steel is. It would suggest to me he was the only path to ground.

[KHK]

Are you sure that the welder is guilty?
What type of lighting was in use? Voltage? Type of power? D or Y

Fatial electric shocks has to do with body resistence. You need .005 amps accross the heart to be fatal, for he AVERAGE person. This can vary quite a bit depending on physical condition, amount of hydration, ect.

Hand to Hand shock;
A 70 volt circut has a 50 volt peak power so E=IR, 50=.005R,
10,000 Ohms=R so any body resistence 10,000 or lower can be fatal
A 120 volt circut has 85 volt peak power so E=IR, 85=.005R,
17,000 Ohms=R so any resistence 17,000 or lower can be fatal
This is true 120 times per second. 60 high and 60 low

Then there is the enviroment, humidity, sweaty hands, feet. Type of shoes type of walking surface. All of these things will effect the body resistence.

Usually hand to hand shocks are the worst. They have the heart in the current path. Hand to foot usualy not so bad.

I have seen a tech get third degree burns on both hands from a 5 amp 480 volt circut. I have also seen a tech get knocked over from a 100 amp 12,000 volt circut with no harm to him.... Go figure, the both of them should be dead!!

The people doing the welding should grind to bear metal, then connect the ground clamp to that area, and ground as close to the weld as possible.
I would scrap the welder. Make sure that the welder is destroyed, not taken home for a hoby welder.

[ksmeggy]

Fatial electric shocks has to do with body resistence. You need .005 amps accross the heart to be fatal, for he AVERAGE person. This can vary quite a bit depending on physical condition, amount of hydration, ect.

Hand to Hand shock;
A 70 volt circut has a 50 volt peak power so E=IR, 50=.005R,
10,000 Ohms=R so any body resistence 10,000 or lower can be fatal
A 120 volt circut has 85 volt peak power so E=IR, 85=.005R,
17,000 Ohms=R so any resistence 17,000 or lower can be fatal

Last time I measured: resistance for dry skin, hand to hand, gripping multimeter leads:
1,500 - 2,000 ohms, dry skin
< 200 ohms, sweaty skin

BUT: gripping multimeter leads gives a very small contact area, on a somewhat calloused part of your body; pushing with your palms against a metal object gives a much larger surface of contact, and the more force you exert the better the contact. Once the current gets through the skin (dry outer skin & fatty layer), the human body itself is an excellent conductor, with similar properties to a bucket of salt water. If I dipped my hands in salt water and firmly gripped 2 metal bars, I would wager I could get the resistance between the two, through my body, down into the 20 ohm range (this would make an ordinary telephone potentially lethal; people have been killed using older telephones in the bath).

In 25+ years working with electricity, the only time I've ever personally gotten a burn mark was from a moment of carelessness with a 240 Volt circuit (turned off the wrong breaker, didn't double-check), on a very hot day.

My comment was not intended to 'blame the welder'. I actually think it was possibly another welder who broke an arc nearby while he was positioning a piece of material (ie, was he helping someone align a piece while the other welder tacked it in place?). If he had burns on both palms, it is highly unlikely that he was himself welding when the incident occurred, which leaves as a possibility that his (live) whip came into contact with a piece he was holding (most experienced welders have an instinctive means of preventing this from happening). If the incident was caused by a faulty trouble light, tool or something, that would normally be pretty obvious just from looking at the scene.

[matteh99]

Last time I measured: resistance for dry skin, hand to hand, gripping multimeter leads:
1,500 - 2,000 ohms, dry skin
< 200 ohms, sweaty skin

The last time I measured I was closer to the 1500,000, to 2,000,000 ohm range dry. I think people are a odd thing to measure the resistance of there are a ton of variables.

Back to the original question. I would say hire a pro to take a look at the welding and electrical setup. Everyone here has given good advice but without seeing the whole setup, cart, welder, lighting, other electric tools, where people were working etc. we are all just guessing.

Eric

[vault]

an open wound will greatly lower the resistance. If a person were to get even a small cut that came in contact with the piece it or got a scrape, nick from working on the piece it could have lowered the body resisance enough.