USB charger outlet in Bathroom Zone2

Peter69 said:

I've been asked to add a USB charging port into a bedroom with a bath in it.

mapj1 said:

It must be said, very few modern bathrooms have that much free space

gkenyon said:

electrocution in the bath

I suppose that in the days before fixed plumbing, one might have taken a bath in a bedroom, but my mind boggles nowadays. Who is going to spend so long in a bath that the 'phone's battery will run out? 

Presumably, there would already be sockets in the bedroom.

I am bound to wonder what completed the circuit in Graham's link. Could it be that supplementary bonding contributed?

The user might not have any charge at the commencement of the soak?

In terms of "completing the circuit", the newspaper report points to the expert believing contact with the shower, so something might have come through the charger?

I agree it's not clear, and certainly things would be a little safer if there were no path the Earth available.

However, there have also been electrocutions in the bath from mains products, where there was no path to Earth involved, and of course in these cases RCDs won't operate either !

Connections to Earth (or bonding) aside, when someone is immersed, current thinking is that there isn't an agreed limit of voltage below which things can be considered "safe" - so the device itself might be bad enough in some cases ... but that is not clear.

The problem in the case of Ann-Marie O'Gorman above, and indeed the ten or so others in the last decade, is not the 5V of the USB - its the full- fat mains, presumably appearing on the charger output due to either damp or other fault bridging primary to secondary in the power supply - she had mains electrocution style  entry and exit burns according to the autopsy, and yes, the path was completed to earth.

Consultant forensic engineer Paul Collins also told the court that it was likely that Ann-Marie’s phone fell into the water and in an attempt to grab it, her right finger touched an earthed  shower attachment, causing her body to be electrocuted.

Also in at least one other case, (and there have been at least ten in the last decade) the mains extension lead complete with charger ended up in the bath tub, though the official reports are not always clear on this. 

Note that there are some immediately  dangerous USB power supplies on sale on the web, and most folk dont realize that when you order something to be posted to your house from abroad, there is no particular guarantee that the UKCA, CE or other safety marks are anything more than decoration - the importer, in this case also the purchaser, is ultimately responsible for checking. (and quite a lot of real importers dont seem to realize their responsibilities either.)

Example of a particularly bad mains powered  rechargeable torch with a dangerous USB output for charging your phone.... Long vid but the first 5 mins is probably enough.

Mike

gkenyon said:

Connections to Earth (or bonding) aside, when someone is immersed, current thinking is that there isn't an agreed limit of voltage below which things can be considered "safe" - so the device itself might be bad enough in some cases ... but that is not clear.

It makes you wonder how they can put the electrode right inside the heart (for ablation purposes) and get away with it.

The interested may find 

https://www.researchgate.net/profile/G-Cargill-Iii/publication/335250921_Electric_Shock_Drowning_Causes_and_Prevention/links/5d5b416b45851521025227f1/Electric-Shock-Drowning-Causes-and-Prevention.pdf 

informative. The problem is current in the body, and that in turn depends a lot what sort of wet - fresh water, tap water and sea water are very different terms of currents in the body, and the 2 cases,

1) where a body is part immersed in water that is one of the 2 contacts, where low resistance water as a series element makes it worse,

2) Where the body is  fully immersed in water carrying a current to and from elsewhere, and it might be better if the liquid was a lower resistance parallel path to reduce the current through the body.

In practice voltages as low as 28 have been reported as lethal but the circumstances that achieved that have been very unlucky coincidences of all the unfortunate factors.

The most reliable safety measure is to have current and time limiting, rather than voltage, which is where RCDs have an advantage.

Mike.

Other factors include:

 - Skin resistance when substantially immersed is unknown ... and may drop to very low (nearly zero) values. This factor means that very low voltages, perhaps into single figures, might actually be very bad to someone who is substantially immersed in a bath.

 - the passage of electricity through water is complicated by the fact we are looking at electric fields emanating from the 'electrodes' in the water, and the passage of current is through the path of least resistance ... which might not be where you think it is because of things like concentration of salts increasing near the body, and also the points of entry/exit to tbe body seem to concentrate around the lowest impedance path through it ... usually the chest/trunk, where they can cause a lot of damage.

 - in electric shock drowning, the direction of current flow without the person in the water comes into play, due to the distances involved.

gkenyon said:

Skin resistance when substantially immersed is unknown ... and may drop to very low (nearly zero) values. This factor means that very low voltages, perhaps into single figures, might actually be very bad to someone who is substantially immersed in a bath.

I assume that most of us have licked a PP3 battery  so it cannot just be voltage.

If 30 mA is the safe limit, 9 V across 300 Ω could be risky.

Worth noting my cardiologist doesnt recommend this as teeth have a nerve pathway to the heart and pp3 have cause arrhythmia.

Frequency voltage/ current and time, all finely tuned. The bodies nerve do not react to higher frequencies and the 'burn' is the desired result. There are no pain receptors in the heart but it does make you cough?

Chris Pearson The pathway is important here. As others have pointed out, there are routes to severe damage ... but not, in otherwise healthy people, the heart.

Chris Pearson The pathway is important here. As others have pointed out, there are routes to severe damage ... but not, in otherwise healthy people, the heart.