OSHA rule

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charlie b

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I do not know the answer, but I can offer this. The resistance of a human body varies from person to person and from moment to moment. It is lower when the person is tired or when the person has been sweating. But it is not unreasonable, for the purposes of discussions of electrical safety, to assign a value of 300 ohms. At some point in everyone's life, their body's resistance to electrical current can get that low.

An electrical current of 0.1 amps passing through a human body is sufficient to cause death. Multiply that value by a resistance of 300 ohms (using Ohm's Law, E = IR), and you get a result of 30 volts. Therefore, it is possible that a voltage as low as 30 volts can inflict a fatal shock.

So I wonder why OSHA uses 50 volts, and not something lower.
 

H.L.

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It is my understanding that the 50 volt rule comes from the telephone industry. The POTS system runs at less than 50 volts
 

petersonra

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Northern illinois
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engineer
I think it may have been that there has to be a line in the sand and they just arbitrarily picked that voltage. It is not a bad choice, and is supportable. One could argue that under certain conditions even 1.5V batteries could produce enough current to kill. OSHA is known for badly thought out rules that do not enhance safety while increasing costs and making compliance a nightmare. In the area of electrical safety, they seem to have avoided that to some degree.
 

bphgravity

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Florida
In my opinion, hazardous current starts at 6mA, hazardous voltage starts at 15V, and typical human resistance is 1,000 ohms.
 
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bthielen

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This issue has come up in a conversation I have been involved in. Does anyone know of any known cases of someone being seriously injured through electric shock by voltages less than 30?

I could use the support.

Thanks, Bob
 

bphgravity

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Location
Florida
There must be a reason for the 15 volt line in Section 680.33 for pool lights. I would start there and find out why that particular voltage level was selected.
 

hardworkingstiff

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Location
Wilmington, NC
bthielen said:
This issue has come up in a conversation I have been involved in. Does anyone know of any known cases of someone being seriously injured through electric shock by voltages less than 30?

I could use the support.

Thanks, Bob

Did you see Lethal Weapon 1? Mel really got it from that car battery. (just trying to have fun here).

I don't know of any cases, but a short circuit on a charged car battery can make a heck of a flash. A lot of amperage behind it too.
 
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bthielen

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This issue was raised on another forum I frequent regarding the outdoors. The topic in question was related to the 12 and 24 volt dc power in boats. There have been some comments that were down-playing the potential hazards of these systems. My concern is that the comments being made could give someone a false sense of security and they could get careless. Asside from the potential hazards associated with the use of the batteries and possible explosion, I am looking for information to support that there could be a definite potential for deadly current with only 12 or 24 volt dc supply.

Charlie's comments here regarding the potential for serious injury from as little as 30vdc peaked my curiousity and I am looking for more information to back this up.

Thanks,

Bob
 

rbalex

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bthielen said:
Charlie's comments here regarding the potential for serious injury from as little as 30vdc peaked my curiousity and I am looking for more information to back this up.
You'll have a tough time finding much more than opinion.

Remember, the 50 Volt limitation is based on contact electrocutions (fatalities by definition) of "qualified" workers, not battery short-circuit explosions or burns. OSHA has no documented cases of electrocutions or serious shock injuries below 60V. In fact, electrocutions themselves are relatively few annualized and those below 300V represent about 15% of the total. See Tables 2 and 3 of Section 3 - III. Summary and Explanation of The Final Rule for Electric Power Generation, Transmission, and Distribution;Electrical Protective Equipment

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=PREAMBLES&p_id=873

I’ve been trying to dig up the referenced “Exhibit 9.2.” I have seen it and recall the 18 “unspecified” fatalities were at voltages obviously above 300V.

I do not want to imply battery explosions and shocks from low voltage contact are not serious. They just aren't the basis for the 50V rule.

Note in III. Summary and Explanation of The Final Rule for Electric Power Generation, Transmission, and Distribution;Electrical Protective Equipment there are several cases where OSHA disagrees with EEI on where to draw the line. EEI wanted it at 300V.
 

dlhoule

Senior Member
Location
Michigan
bphgravity said:
I also don't think systems with voltages of under 50V can produce arc-flash energies
.

Perhaps not, but I've seen enough of a flash from 18 Volts, where it was about the same as looking at an arc welder's flash. I don't want to mislead anyone about this: this was off a generator operating at anywhere between 12 V and 18 V DC. Average current was between 18,000A and 32,000A. Every time someone dropped a pry bar onto the bus while it was energized, we would have to replace sections of bus.
 

muskiedog

Senior Member
Location
Minnesota
Battery and jewelry

Battery and jewelry

I had a maintenance staff arc his ring on a battery terminal and had server burns and melted part of the ring.

Hard way to learn to take of the jewelry. He had no idea of that the battery could cause so much damage.
 

realolman

Senior Member
dlhoule said:
... this was off a generator operating at anywhere between 12 V and 18 V DC. Average current was between 18,000A and 32,000A. Every time someone dropped a pry bar onto the bus while it was energized, we would have to replace sections of bus.

What kind of application is this?

prybars being dropped routinely onto a 32000 a 18v buss?
 
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