Accident Investigation Question

hexreader

Joined Apr 16, 2011
581
Doesn't the current need to reach your heart to kill you?

I don't see how any of the incidents reported here could cause significant current through the heart.

...... but I am no expert, I just watch the TV science programs
 

Gdrumm

Joined Aug 29, 2008
684
We have a Limit Switch on some machine that delivers a slight shock if someone hands are sweaty, etc.

A few injuries have occurred when they jerk away from it, and hit their hand on something nearby.

We teach them how to reset the Limit with a tool, but they sometimes forget.

Anyway, if he received a slight shock enough to recoil his head, then he may have hit his head on a pipe, and that knocked him out.

Are some people more susceptable to electrric shock than others?

I knew a guy one time who could hold a spark plug wire up near his tongue while the engine was running, and you could see the sparks jumping over to his tongue. He was a little bit retarded *(before or after, I'm not sure)
 

KMoffett

Joined Dec 19, 2007
2,918
has your investigation determined the current path?
Since this a line powered device, it would be prudent to look for possible "leakage" currents from the line through the case or any of the output terminals to ground. "If" the person was rendered unconsciousness, it's more likely from a high voltage AC source than 9VDC...just from my experience in Biomedical Electronics service.
This is a test circuit to simulate the body when measuring leakage currents with medical equipment. One end is grounded and the other is touched to various points of exposed metal (case, connectors, controls...) on the powered device that is being tested. Using the ACV range on a DMM, 1mV=1uA of leakage current.
http://www.mddionline.com/sites/default/files/mddi0407p54b.jpg
http://www.mddionline.com/sites/default/files/mddi0407p54a.jpg
If I remember right the maximum allowable leakage for "industrial" devices is 5mA AC.

Ken
 

debe

Joined Sep 21, 2010
1,389
This sounds like someone trying for a monetry payout. Iv worked on 24V DC with salt water around in a marine enviroment on boats & the best i could get was a slight burning sensation. If the plug pack was a modern SMPS there is a posability of a break down from mains side to DC side. Has it been checked for leakage.
 

Ron H

Joined Apr 14, 2005
7,063
As strantor said, a 9 volt battery can not source nearly as much current as a lead acid car battery can. Licking a 9 volt battery won't cause more than a couple of milliamps to flow through your tongue. Licking a car battery could easily allow a lot more current to flow, and thus cause a lot more damage.
I think others may have commented on the inaccuracy of this, but I think this is lore. This paper, entitled 9 Volt Battery-SHORT CIRCUIT ANALYSIS, reports short circuit current of 4 to 5 amps for a short time. If the current is limited to a few milliamps, it is by the resistance of the wet tongue, and not by the battery's internal resistance.
 

WBahn

Joined Mar 31, 2012
29,976
Random thoughts on things in the thread:

If you take a new 9V battery and short across it with a 0.5mm pencil lead, you can produce a glowing demonstration of the basic principle of a carbon arc lamp. It takes some significant current to resistively heat a graphite rod to the point of glowing bright red. It also drains the battery very quickly, but I've had it going for up to about 15 seconds before the loaded voltage dropped enough to see the glow diminish.

The big thing to remember is that licking a 9V battery is resulting in current flowing for a short distance across a wet medium in the vicinity of cells that are very, very sensitive.

Leaning on an exposed wire in a 9V system leaves unanswered what the return path was. Was it also at the same forearm? Or was it the waste pipe that his other arm was touching? Or what? I would not expect a properly working 9V circuit to cause problems except in exceptional conditions, such as through two open wounds creating a path across the heart.

However, since it was disclosed that the 9V ultimately comes from a 240AC powered source, it is possible that the power source has failed (or was poorly designed in the first place) and the 9V between the terminals is riding on 240VAC relative to ground (and I do mean 'ground' in this case). If the thing powered by the 9V has no reasonably low path to ground, it may function just fine under these conditions. But when his forearm came in contact with it, he got a couple hundred volts from his forearm to whatever part(s) of his body offered decent return paths to ground, and the copper waste pipe almost certainly qualifies.

I used to test my car's ignition system by holding onto the suspect wire (unplugged from a plug) and crank the engine. Then I got bright and started just holding the wire end close to the block to observe the sparks across the gap.

Aside: Remember about, oh, a decade ago when Duracell and Eveready came out with their "high performance" alkaline batteries and really hyped them around Christmas time? I think the Duracell battery was the "titanium" and the Eveready battery was the "e2". They were selling the batteries for something like twice the normal price claiming that they were designed for "today's demanding applications". Well, I went and looked up the specs on the manufacturers pages and found that they were identical, even to the point of looking like the curves came from the same data sets. I just checked Eveready's site and their standard alkaline battery (522) and their industrial battery (EN522) still have identical specs, including little features in the curves that are telltale signs of being plots from the same data sets. Their "Gold" battery doesn't offer any curves at all on its data sheet.

I went and looked at their obsolete data sheet for their e2 9V and, guess what, it's identical (again, including the telltales) to their present standard battery. And, to top it off, their obsolete standard battery also had virtually identical curves, though they appears to be a different data set. To the slight degree that they were different, the old battery has slightly better performance. This might be due to the removal of the mercury from the process, but that's only a guess.
 
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