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Re: Enough to stop your heart [Re: LarryC] #177704
05/10/08 01:30 PM
05/10/08 01:30 PM
A
ameterguy  Offline
Member
Joined: May 2002
Posts: 30
Mass
Our Safety Trainer has always stated that the number is close to 50 milliamps to stop your heart. The path thru your body definitely matters as to if your heart is affected by the shock. A shock from hand to hand, is alot worse than from the fingers to the forearm of an arm. Also, if the skin is wet or dry affects the severity of a shock. As wet skin conducts much better than dry skin.

I found the following on the OSHA website.
http://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

Current level (in milliamperes) Probable effect on human body
1 mA Perception level. Slight tingling sensation. Still dangerous under certain conditions.

5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.

6-30 mA Painful shock, muscular control is lost. This is called the freezing current or "let-go" range.

50-150 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.

1000-4300 mA Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.

10,000 mA Cardiac arrest, severe burns and probable death.

Bob

Last edited by electure; 05/10/08 07:44 PM. Reason: To fix link
Arc Flash PPE Clothing, LOTO & Insulated Tools
Re: Enough to stop your heart [Re: ameterguy] #177708
05/10/08 03:57 PM
05/10/08 03:57 PM
W
wiking  Offline OP
Junior Member
Joined: Dec 2002
Posts: 32
Florida, USA
Coincidently regarding the 9 volt battery. I was very surprised yesterday when I took a 9 volt battery off the truck because I was going to change out the old one in my tracer. I put it in my pocket and then locked up the truck and put my keys in the pocket. I went upstairs and all of a sudden my pocket started feeling real hot. I reached in and pulled out my keys and evidently the clip that holds them together had crossed the terminals on the battery and it was very hot. Never had that happen before.

Re: Enough to stop your heart [Re: wiking] #177712
05/10/08 04:36 PM
05/10/08 04:36 PM
S
sparkyinak  Offline
Member
Joined: Jul 2007
Posts: 1,335
Alaska
That happend to me once. It scared the poo-poo out of me.


"Live Awesome!" - Kevin Carosa
Re: Enough to stop your heart [Re: LarryC] #177739
05/11/08 09:16 AM
05/11/08 09:16 AM
Z
Zog  Offline
Member
Joined: Sep 2005
Posts: 120
Charlotte, NC
Originally Posted by LarryC
I believe it was a USN sailor in electricians Mate "A" school. I think it was after learning about "internal resistance" with respect to batteries.

Larry C


Yes it was, I was in the Navy when this happened and we all had to read about the incident.


MV/HV Testing Specialist, "BKRMAN"
Re: Enough to stop your heart [Re: Zog] #177740
05/11/08 09:31 AM
05/11/08 09:31 AM
Z
Zog  Offline
Member
Joined: Sep 2005
Posts: 120
Charlotte, NC
If you want to talk about the effects of current flow through the human body you need to define all of the other factors.

AC or DC
Hz?
Path
Time
Voltage
Male or Female
Body weight
Body resistance (Determined by moisture level, contact area, and pressure)

The IEC did some resaerch at the U of IL back in the late 60's, they had volunteers willing to take electric shocks. From that some basic values were published.

A LV AC(60hZ) shock of an average weight (Was 140lbs in 1968) male for 1/2 second will cause

1mA - Sensation of shock (Like a 9V Battery on your tounge)
2-10mA - Mild shock not painful, still maintain muscle control
10-20mA - Loss of muscle control, AC causes muscles to contract, can cause you to clench down on the conductor and not be able to let go, the increased pressure causes body resistance to go down, so current goes up, time becomes a factor because fibrilation can occur at these levels if the duration is long enough, if not removed from circuit this can be a fatal shock. this is why most electricians are taught to touch things with the back of thier hand. (DC no let go currents are closer to 75mA)
20-50mA - Lungs collapse - causing victim to pass out due to lack of O2 many times
50-100mA - 5% chance to go into Ventricular Fibrilation
100-200mA - 95% chance to go into Ventricular Fibrilation
(Someone earlier said 100mA is the fatal current, if I had to pick 1 value to answer this question, it would be 100mA, however there are several other factors, it is not really a question that can be answered with a simple current level)
>200mA - I2R heating of the conductive parts of the body (circ and nervous system) are damaged, there are no degrees of electrical burns, all electrical burns are 3rd degree because the cook you from the inside out, nerves are also damaged causing permanant damage.


MV/HV Testing Specialist, "BKRMAN"
Re: Enough to stop your heart [Re: LarryC] #177874
05/14/08 09:53 AM
05/14/08 09:53 AM
S
sabrown  Offline
Member
Joined: Dec 2002
Posts: 305
Ogden, Utah, USA
5ma is considered a safe level for adults, but infants and toddlers can be killed at this level. I do not know the reasons.

Re: Enough to stop your heart [Re: LarryC] #179599
07/23/08 07:56 AM
07/23/08 07:56 AM
Z
Zapped  Offline
Member
Joined: Oct 2002
Posts: 482
Huntington Beach, CA, USA
On this subject, does anybody know if AC or DC is more dangerous, or is there a difference at all. It seems that, just by having been hit by AC so many times, that AC is the kicker.

The body uses AC as its internal nervous signaling system and muscle actuation. This would include the heart. It also seems to me that the difference in frequency and added voltage of AC would throw the body into much more distress than the same voltage in DC.

Any thoughts? Any facts?

Re: Enough to stop your heart [Re: Zapped] #179604
07/23/08 02:30 PM
07/23/08 02:30 PM
G
gfretwell  Offline

Member
Joined: Jul 2004
Posts: 9,373
Estero,Fl,usa
AC is dangerous at lower currents than DC


Greg Fretwell
Re: Enough to stop your heart [Re: Zapped] #180160
08/15/08 07:19 AM
08/15/08 07:19 AM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,261
SI,New Zealand
Originally Posted by Zapped
On this subject, does anybody know if AC or DC is more dangerous

AC has the "advantage" of having a current zero at every 2 sine wave "crossings" per cycle, as if that will help, but with DC, you don't have a chance to let go!.
DC will make all of your muscles tense and I mean ALL of them.
DC is what is used to tenderise cattle in slaughter-houses.

Re: Enough to stop your heart [Re: Trumpy] #180187
08/16/08 10:06 AM
08/16/08 10:06 AM
Z
Zog  Offline
Member
Joined: Sep 2005
Posts: 120
Charlotte, NC
There are a few things to consider here.

1st, the #1 cause of death from electric shocks is ventricular fibrilation, around 100mA or so (Depending on several factors) of 60hZ AC will cause the heart to go into fibrilation, to survive usually the victim will need, drum roll.... a DE-fibrilator, which uses DC to stop the heart, after the heart has stopped CPR is more effective and many times the heart starts beating normally again. This makes SC more dangerous.

2nd- AC has a skin effect, meaning the center of the conductor is not used, think of the curretnt flow cross section looking like a donut. DC uses the entire cross section of the conductor, now when that conductor is an arm or a leg the center of the "conductor" is bone (Poor conductor) which increases the effective resistance of the limb for DC compared to AC that flows around the bone and through the circulatory system and nervous systems, both of which are excellent conductors. Another reason AC is more dangerous.

3rd - the biggest factor in determining how much damage is done by a current flow is duration. For AC it takes about 10-20mA to cause a loss of muscle control, and AC causes the muscles to contract (Hence the time honored practice of using the back of your hand), so with AC, at around 15mA or so you can become stuck on the circuit and then duration increases, many times you will be stuck until someone kills the power. DC is very different, it takes around 75mA of DC to cause a loss of muscle control, and it causes your muscles to stiffen, rather than contract like AC does, so it is very hard to get hung up on a DC circuit. The 3rd and last reason AC is more dangerous than DC.

However, speaking from experience, DC hurts more.


MV/HV Testing Specialist, "BKRMAN"
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