I add to this answer ongoingly, either as new information comes to my attention, or when the subject is raised elsewhere on SEEE, or when 'pushback' occurs to what seems to be to be a very well established and very important fact. That is
- "12V and even substantially higher DC voltages are extremely unlikely to kill you.
But, it has happened, and can happen in exceptional circumstances.
Do not be scared of such voltages, but do be aware of the unlikely but potential dangers."
FACT:
12 VDC CAN kill and has killed people.
While 12 V is almost always safe, worst-case situations can and have led to death.
Mechanism may be ventricular fibrillation BUT paralysis of the respiratory muscles occurs at about 20% of the current needed to introduce fibrillation.
See the discussion and solid references at the end of this answer.
12 VDC applied across the chest has killed volunteers despite medical experts standing by !!!
(From memory - volunteer prisoners participating in medical research).
Carry a car battery with exposed terminals on a hot day when you are sweating and press the terminals to your body (as could happen worst case when lifting the battery, etc.), and you may end up repeating the experiment.
Once conduction into the body starts, you get a very low impedance/resistance circuit into what is essentially a large bag of dilute saline solution.
The references, especially A review of hazards associated with exposure to low voltages make it very clear that a number of reputable peer reviewed sources substantiate this fact.
Added - February 2023:
I have received a substantial amount of "pushback" in the 11+ years since I posted this answer.
A summary of my answer is: "12V sources can cause death in very unusual worst case circumstances. While this is exceptionally unusual the possibility exists. The most likely situation would be application either across the chest or from chest to one limb in conditions where the chest was wet. Death could be from ventricular fibrillation or paralysis of respiratry muscles. Voltage would usually need to be applied for a prolonged period. In exceptional circumstances muscle lockup in conjunction with a secondary effect such as drowning may occur.
This paper A review of hazards associated with exposure to low voltages summarises a range of peer reviewed literature. It makes it clear that electrocution at 12V would be very very rare indeed, and that conditions to make this possible in some cases are 'easily enough' arrived at.
I suggest that people who wish to comment on plausibility first read the relevant parts of this paper.
At the end I've added EXTRACTS FROM PAPER A review of hazards associated with exposure to low voltages.
There are two main "what kills" issues.
One is general trauma - burns, etc., and that is obviously very situation and person-dependent. I've had shocks from 1200 VDC, 230 VAC, 50 VDC, RF, and miscellaneous other sources. No major burns. I'm still alive
Enough current for long enough to stop your natural heart rhythm and throw it into fibrillation.
Also possible are respiratory muscle paralysis and muscle lockup followed by death by a secondary cause.
At typical domestic voltage levels, you are USUALLY safe if the current flows for well less than one ventricular heart valve cycle and at "low enough" current.
Earth leak circuit breakers (ELCB), also called ground fault interrupters (GFI) and other names, aim to trip at currents somewhere under 20 mA and in about 20 ms = well short of a heart cycle.
See graph below.
This article provides useful detail on GFCI operation.
Image from above article:
A shock from a circuit protected with an ELCB / GFI device will be felt but will USUALLY not be fatal.
A 9 V battery on the tongue almost certainly won't kill.
A 9 V battery across the chest with saline solution (or sweat) just might - probably not.
A 12 V "car battery" or any high current source from a few volts up MAY kill in the very worst case. Hand to hand, I have never heard of shock occurring or being felt.
110 VDC (not AC) routinely killed Edison's linesmen.
50 VDC MAY not be felt with dry hands on a dry day. On a high humidity day, brushing the back of the hand with terminal strips with 50 VDC causes annoying minor shocks (as experienced in e.g., Telecom wiring frame jumper running -- based on my long-ago experience)
75 VAC imposed on 50 VDC gives a very nasty shock sometimes. Worst case, this could kill.
High current 1200 VDC hand to the body somewhere may not kill - I'm still alive.
Can 12 Volts kill?
Yes.
Probable? - no.
Possible? - yes.
Data point: Note that this is a completely true and non-fabricated account. I have a friend (still alive) who built a lamp to take flounder fishing. It used a 12 V SLA battery and an Aluminum pole with the light at the top. Flounder fishing involves wading through shallow salt water. In the course of fishing, he discovered that an electrical fault existed - in some manner, he was exposed to 12 VDC between his hand holding the pole and the water he was standing in. He was completely unable to release his grip - the current flow exceeded his "let go" threshold. regardless of how "worst case" this may have been and what various tables and standards say, it was clearly possible to reach his personal can't-release level. The literature states that respiratory paralysis can occur at currents not significantly greater than the can't release level. If he'd been by himself (never a wise idea with such activities), he may have found himself floundering :-). Note that this was a hand-to-leg current path. Chest to chest worst case can be reasonably expected to be potentially higher.
The table below is from this page -
A Summary of Surveillance Findings and Investigative Case Reports - Part I. Electrocution-Related Fatalities.
this is not a primary reference source but the figures used have been obtained from an "official" source. See above page.
Note that for 60 Hz AC ventricular fibrillation is stated as occurring at 100 mA, but paralysis of respiratory muscles occurs at 20 mA. These limits are very much user and situation dependent but give an order of magnitude indication.
With very informal equipment, I measured 1500 ohms resistance across two areas on my abdomen. I decided not to measure across my chest in the vicinity of the heart. I used flat contacts with no skin penetration. At 12 V, if resistance did not change with the current flow (and I'd expect it to probably drop), a current of 8 mA would be produced. Measurement with skin penetrating electrodes may reasonably be expected to increase this significantly.
A superb discussion of electrical safety, current levels in various situations, and consequences can be found here. The writer's competence and bona fides are above reproach*. The discussion relates to the provisions of standard IEC60990 'Measurement of touch current and protective conductor current'. This is a "for money" standard that I do not have access to, but excerpts from it are provided in the above reference and elsewhere.
- '*' P E Perkins PE.
[email protected]
Convenor IEC TC108/WG5,
IEC 60990 'Measurement of touch current and protective conductor current"
A careful but less than an exhaustive examination of the above document and other related web material makes it very clear that
"Electrocution" from a 12 Volt DC source would be extremely unlikely
In worst-case situations, it could happen.
Related:
Full copy of standard ECMA287 - Safety of electronic equipment
Touch current comparison data paper - P Perkins
NIOSH - worker deaths by electrocution
Accounts of two deaths by electrocution. One at 12V. One at 24V. Note that BOTH these are unsupported hearsay reports and actual cause of death may not have been electrocution.
Table 1. Estimated Effects of 60 Hz AC Currents
| Amps |
Effect |
| 1 mA |
Barely perceptible |
| 16 mA |
Maximum current an average man can grasp and "let go" |
| 20 mA |
Paralysis of respiratory muscles |
| 100 mA |
Ventricular fibrillation threshold |
| 2 Amps |
Cardiac standstill and internal organ damage |
| 15/20 Amps |
Common fuse or breaker opens circuit* |
- Contact with 20 milliamps of current can be fatal.
As a frame of reference, a common household circuit breaker may be rated at 15, 20, or 30 amps.
February 2023:
This paper cited by Nick Bolton provides much useful material
A review of hazards associated with exposure to low voltages - 18 pages. Published ~= 2004.
Interestingly - this answer has 2 downvotes* - which is interesting considering the undoubted truth it tells. Maybe the downvoters and anyone who doesn't think it is a good answer would like to tell me why? The aim is to be balanced and objective, and as factual as possible. If it falls short, please advise.
- And a 3rd on August 11 2022
EXTRACTS FROM PAPER A review of hazards associated with exposure to low voltages.
The letters at the start of each extract indicate where the extract may be found within the paper. These are of the form
Page number, column (l or r), n = 10ths of a way down the column.
So eg 13 l.8 = page 13, left column, 8/10th way down column.
Below some extracts I indicate the current drawn with 12V applied for the lowest resistance mentioned.
Note that I have consciously "cherry picked" these extracts, and in some cases not included conclusions from the information provider. This does not make them less valid - read and see.
12 r.5 The 1988 European Organization for
Nuclear Research, (CERN) “Dangers due to
electricity” safety Instruction (IS-28) is “essentially
based on IEC publication 479-1” (see above)
including statistical resistance values (Table 1). In
addition the IS-28 report specifies a total body
resistance of >650 Ohms under moist/wet conditions and
325 Ohms for ‘immersed skin’. Presumably based on
minimal ‘let-go’ thresholds, the IS-28 report
specifies “as a rough guide to complete safety, the
current limit should be considered as 10 mA” for
<20 ms.
Noting that 12v and 325 Ohms gives 37 mA
5 l.4: DiMaio and DiMaio
(2001) concluded that for 120 V, dry skin may have
a resistance of 100 kOhm; dry and calloused skin up to
1000 kOhm; moist skin 1 k or less; and moist, thin
skin as low as 100 Ohms
100 Ohm = 120 mA at 12V
5 r.8: Hart (1985) reported an internal resistance
of 400-500 (hand-to-hand) and 450-500 (handto-foot). He found internal body resistance from hand-to-forearm was 140 Ohm and from finger-to forearm 700-800 Ohm
140 Ohm = 85 mA at 12V
5 r.9 - 6l.1: Statistical impedance data was developed
by Underwriters Laboratories (12 VDC, relatively
large electrodes, ‘wet’ conditions; Whitaker 1939)
Low Voltage Electrocution - 6 - M Bikson
for children (3-15 years; 14-58 kg) and for adults
(18-58 years; 45-95 kg).
- For children they found a
resistance variation from the 5% to 95% rank of 1.7
to 4.47 k (hand-to-hand) and 0.9 to 2.04 k (two
hand-to-two feet).
- For adults they found a
resistance variation from the 5% to 95% rank of 1.28
to 2.45 k (hand-to-hand) and 0.63 to 1.16 k (two
hand-to-two feet).
- 60 Hz AC resistance values can
be 60-90% of these DC resistance values (Reilly
1998).
6 l.2: Thus the majority of research reports
consider worst-case (large contact area, wet
conditions) total body resistance (limb-to-limb) to be
slightly greater than 500 Ohm. Worst-case resistance
across the chest can be less than 100 Ohm. Under nonworst-case conditions (e.g. small contact size, dry
skin) total body resistance values quickly increase to
greater than 2 kOhm.
100 Ohm = 120 mA at 12V
"Let-go" limits are well below those usually needed for electrocution. However, an inability to release grip can and has lead to injury and death. My flounder-fishing friend could have drowned worst case.
9 r.8: Let-go comments: Gilbert (1939) used the release-grip
endpoint in determining an average let go current of
21 mA. Whitaker (1939) using the release-grip
endpoint current found a range of 8.4 mA to 14 mA,
average 11 mA. Thompson using a rotate-handle
endpoint reported an average ‘let-go’ current of 11.7
mA, maximum 28 mA. In the commonly referenced
initial report of Dalziel (1938), using the release-grip
criteria, the average endpoint was 17.7 mA,
maximum 25 mA (male subjects). These reports
were reviewed by Reilly (1998; Table 2). Dalziel
and Lee (1969, 1972) summarized results from 124
males and 28 females; the average ‘let-go’ currents
were 22.3 mAPEAK male and 14.8 mAPEAK female
Low Voltage Electrocution - 10 - M Bikson
while the lower 0.5 percentile values were 12.7
mAPEAK male and 8.5 mAPEAK female. Thus across
studies 8.5 mAPEAK appears a safe ‘let-go’ threshold
13 l.4: Based on the reports summarized above,
respiratory paralysis can lead to death but requires
several minutes of contact; currents as low as 30
mA PEAK across the chest may induce paralysis.
13 l.8: Based on the reports reviewed above, for
less than 1 min duration electrical contact, currents
40 mA may be necessary to cause ventricular
fibrillation,
Added September 2023:
This answer of mine
THIS MACHINE (ONLY VERY VERY OCCASIONALLY) KILLS.
BE SENSIBLE - DON'T LET IT
to SEEE Jan 2020 question Can a switching power supply kill you? adds usefully (imho) to this discussion.
This image from that answer (and another) provide information on IEC claimed limits. From here with my annotations. Th AC3 area is probably of most interest in the current (unintended pun noted) context. While the B boundary suggests 5 MA at 10 seconds, it is not clear why, if 5 mA will cause ANY result, why there is a 10 second period during which it is not relevant.
My above recorded account of a friend's muscle lockup experience at 12 volts (while standing in salt water & holding a metal fish spear) is very much an extreme case - and could easily prove fatal for others in similar circumstances if experienced when assistance was not available.
