1
$\begingroup$

It's been said in many places that it's not voltage that kills you but the source's current (or more so a combination of the two), but take a current of 0.1A which can be considered fatal. Would a 0.1A current for 10 seconds be worse than a 0.1A current for 1 second?

$\endgroup$
2
$\begingroup$

The current applied for the longer time could potentially (pun always intended) be worse than the shorter time. This is because currents flowing through your heart causes the it to not work properly as well as serious damage. Your heart depends on correlated currents of specific ions, so external currents can mess this all up. Therefore, the longer the current it's applied, the more time you have a malfunctioning heart and the more damage that will be caused.

Of course if you're past the time for it to be lethal than there is no difference in any two times, unless you want to compare damages in spite of lethality.

To bring some more physics in, you can consider the power (energy/time) delivered to your body while the current is applied. Treating the human body as an ohmic resistor with resistance $R$, the power delivered to the body is $$P=I/R^2=E/\Delta t$$

So, if the current is on longer, more energy ($E=P\Delta t$) is supplied to your body and more damage can occur just through ohmic heating without even considering messing with heart function.

$\endgroup$
2
$\begingroup$

Duration affects how "powerful" the electricity is due to a greater number of amp hours.

The lethality is far more complicated. As little as 10 milliamps can exceed the "let go threshold", meaning that you would be unable to voluntarily break contact with the source, but that little current isn't necessarily fatal. The lethality depends on the course that the current takes through the body, much like lightning can take various courses through the air; and people have survived lightning strikes.

As explained in the Wikipedia link above:

The current may, if it is high enough and is delivered at sufficient voltage, cause tissue damage or fibrillation which can cause cardiac arrest; more than 30 mA $[5]$ of AC (rms, 60 Hz) or 300 – 500 mA of DC at high voltage can cause fibrillation. $[6][12]$ A sustained electric shock from AC at 120 V, 60 Hz is an especially dangerous source of ventricular fibrillation because it usually exceeds the let-go threshold, while not delivering enough initial energy to propel the person away from the source. However, the potential seriousness of the shock depends on paths through the body that the currents take. $[6]$ If the voltage is less than 200 V, then the human skin, more precisely the stratum corneum, is the main contributor to the impedance of the body in the case of a macroshock—the passing of current between two contact points on the skin. The characteristics of the skin are non-linear however. If the voltage is above 450–600 V, then dielectric breakdown of the skin occurs. $[13]$ The protection offered by the skin is lowered by perspiration, and this is accelerated if electricity causes muscles to contract above the let-go threshold for a sustained period of time. $[6]$

If an electrical circuit is established by electrodes introduced in the body, bypassing the skin, then the potential for lethality is much higher if a circuit through the heart is established. This is known as a microshock. Currents of only 10 µA can be sufficient to cause fibrillation in this case with a probability of 0.2%. $[14]$

$[5]$ ucsb.edu - Electrical Safety Information - Physics Department, UCSB Archived 2013-10-23 at the Wayback Machine., 2012-01-09

$[6]$ Clifford D. Ferris, Electric Shock, chapter 22.1 in Jerry C. Whitaker (ed.) The Electronics Handbook, CRC Press, 2005, ISBN 0-8493-1889-0, pp. 2317-2324

$[12]$ Jack Hsu (2000). "Electric Current Needed to Kill a Human". The Physics Factbook. Archived from the original on 2013-10-23. Retrieved January 14, 2018.

$[13]$ Reilly 1998, p. 30

$[14]$ Norbert Leitgeb (6 May 2010). Safety of Electromedical Devices: Law - Risks - Opportunities. Springer Science & Business Media. p. 122. ISBN 978-3-211-99683-6. Archived from the original on 1 April 2017.

Your question is: "Would a 0.1A current for 10 seconds be worse than a 0.1A current for 1 second?" - Since it is presumed that one would prefer to have none, more is worse than less.

Electricity can not be measured by amperage or voltage alone it is a combination of the two that determines the amount.

For example you are bombarded by water constantly but do not drown from the moisture in the air. Similarly people go for New Year's Eve polar bear swims and do not freeze, or stay in long.

A welding machine will have a relatively high amperage and relatively low voltage, conversely a Van de Graff generator will have a relatively high voltage and a relatively low amperage - neither is especially dangerous as a source of electrocution.

Welding and risk of electric shock

Why doesn't a Van de Graaff generator harm you?

That doesn't imply that it is impossible to injure yourself with a welding machine or Van de Graaff generator, the purpose of that explanation is to explain that the combination of voltage and amperage produced by those devices isn't as optimal (for electrocution) as wall socket current (or that of a defibrillator).

In the old style Lown type monophasic waveform defibrillators the first shock is applied at 200 joules, next 300j, to a maximum of 360j, with the subsequent shocks at 360j. Modern truncated exponential biphasic waveform defibrillators use a much lower 130 + 20j biphasic waveform to produce comparable results to the Lown waveform.

Unlike monophasic devices, biphasic defibrillators use different waveform technologies: either a biphasic truncated exponential (BTE) wave or a rectilinear biphasic wave.

The rectilinear biphasic waveform was developed specifically for external defibrillation and takes into account high and varied patient impedance levels (the blocking of current flow caused by chest hair, large chest size, and poor electrode-to-chest contact). The rectilinear waveform maintains a stable shape in response to impedance, and the constant current in the first phase reduces potentially harmful peak currents. The rectilinear waveform is delivered at 200 joules, as little as 130 joules could be used but it is less effective when transthoracic impedance is high.

The reason that, when medically necessary, the use of lower energy is preferred is that studies have shown that initially there is significant ST segment changes associated with high-energy defibrillation, which can last up to several months (if the patient survives).

Studies by the Journal of the American College of Cardiology (JACC) show "Triphasic waveforms are superior to biphasic waveforms for transthoracic defibrillation".

Monophasic, Biphasic and Triphasic Waveforms

The purpose of the prior few paragraphs is not to provide medical advice but to explain that the shape of the waveform along with the amount of energy has an effect on the electrocution potential that is not thoroughly understood and that certain waveforms are less affected by impedance or efficiency of contact.

Thus it is best to avoid any contact with electricity (unless medically indicated) and shorter durations and intensities are less damaging.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.