Laptop vs. Bathtub

[StarHalo]

My wife would like to set her laptop on a small side table in the bathroom to watch movies while she bathes, but she worries that if there were an earthquake, the computer could fall into the water and electrocute her.

If it did happen, it's a given the PC would be a loss, but would a person in the bathtub be harmed? Is there enough charge in a laptop Li-Ion pack to harm someone if it's shorted in a body of water they're sitting in?

 

[AnAppleSnail]

My wife would like to set her laptop on a small side table in the bathroom to watch movies while she bathes, but she worries that if there were an earthquake, the computer could fall into the water and electrocute her.

If it did happen, it's a given the PC would be a loss, but would a person in the bathtub be harmed? Is there enough charge in a laptop Li-Ion pack to harm someone if it's shorted in a body of water they're sitting in?

Let's hope that those have short-protection in them, and that she won't leave it sitting long enough for the battery to leak anyway. Get her one of those non-slip grip things, then as long as the table doesn't loom over the tub the laptop won't go swimming.

 

[Lynx_Arc]

just get some trim and attach it to make a ledge around the top of the table so it cannot slide off.

 

[spencer]

I don't know what earthquakes are like down there but the probability of the situation happening seems incredibly low to me. The battery should have short circuit protection in the unlikely event of it happening.

 

[StarHalo]

Well I know how to secure the laptop so it won't fall in

I'm more interested in the scientific question; what would happen if you put a fully-charged laptop in a bathtub you were sitting in?

 

[kingofwylietx]

This sounds like a good episode for Mythbusters.

 

[StarHalo]

This sounds like a good episode for Mythbusters.

lol, that's exactly what I pictured as I was mulling over it; Adam and Jamie with a whole stack of laptops and a tub with the gelatin electrode-heart dummy..

 

[Lynx_Arc]

Well I know how to secure the laptop so it won't fall in

I'm more interested in the scientific question; what would happen if you put a fully-charged laptop in a bathtub you were sitting in?

It would depend on the voltage delivered to the laptop and the conductivity of the water. At lower voltages it takes a lot lower resistance in the water for electricity to conduct well... you drop a hairdryer in a tub and could kill someone but drop a 6v lantern battery in a tub chances are you just get it wet unless you sit on it.

 

[StarHalo]

It's 19 volts at 3.42 amps..

 

[Popsiclestix]

There was a story of some guy who stuck probes from a 9V battery into each of his thumbs and then the resultant current traveling across his heart killed him.

That being said, as long as the skin is not broken, it still offers several hundred Ohms of resistance to electric flow and it is probably more likely that the currents will just flow through the water itself instead of through a person.

Most Li-ion battery packs will survive quick water immersion (couple of seconds to minutes) pretty well. Obviously, after that, you should probably throw them away, but there's no immediate danger. Just don't let them sit in the water.

 

[Lynx_Arc]

It's 19 volts at 3.42 amps..

it only takes about 100ma across the heart to kill someone, the biggest problem is higher voltage makes current flow beyond the internal resistance of skin. wet skin conducts better and in a tub you are all wet but for electricity to flow the water has to conduct to you, then through you. 19v could be dangerous it is enough that if there is some ions in the water like bath salts you could get zapped and wether the electricity would either pass through and mess your heart up or paralyze your nervous system I couldn't tell. I would just keep the laptop far enough away that if there was an earthquake it could fall on the floor and break instead of in the tub... or simpler thing to do is put the laptop on a platform that is lower than the bathtub so there is no way it can fall in at all.

 

[65535]

The path of least resistance for a laptop in a bathtub does not include your body at all. You have likely .5" maximum between positive and ground on the battery pack, and it's not over 20 volts. A current across the heart is pretty much impossible unless you ran leads into your body directly from the contact. Short circuit protection wouldn't matter, and current flow through water isn't terribly high at 20VDC anyways.

It would be an expensive wash for the laptop, pretty devastating.

 

[zipplet]

Make sure she runs the laptop on battery. If she runs it on mains and the charger PSU brick gets pulled into the bath that could be game over...

 

[jamesmtl514]

I'd be much more worried about the humidity in the bathroom destroying your laptop than the unlikely even it decides to play submarine.

 

[mattheww50]

My wife would like to set her laptop on a small side table in the bathroom to watch movies while she bathes, but she worries that if there were an earthquake, the computer could fall into the water and electrocute her.

If it did happen, it's a given the PC would be a loss, but would a person in the bathtub be harmed? Is there enough charge in a laptop Li-Ion pack to harm someone if it's shorted in a body of water they're sitting in?

It is unusual for the battery pack in a laptop to be much more than 12 volts. The PSU is another matter entirely, although if the building in question is less than 40 years old, the outlets in the bathroom should be on GFCI's. UL doesn't regard anything below 24 volts as a potential shock hazard (however depending upon the amperage available, it can be a serious energy hazard). The battery pack just doesn't present a serious shock hazard, even in a bathtub.

There is one source of high voltage in most laptops. The lcd display is usually illuminated by a pair of cold cathode fluorescent tubes, and they run at several hundred volts. The current is fairly low, but more than enough to be very unpleasant.

 

[Popsiclestix]

This problem can be modeled using a battery, a tub of water, and the worst-case scenario that a person connected in parallel with that tub of water. (ie. that person is directly touching the leads of the battery in the tub of water).

First of all let's assume the battery is 20V DC.

The conductivity of tap water is typically around 0.5 mS/cm. This translates into 2kOhm/cm. The leads are about 1 cm apart, so in effect there's about 2k Ohm between the two leads. 20V / 20 kOhms = ~10mA. This is your tub of water.

Now the person. Typical measurements suggests that a hand immersed in liquid is about 200 Ohms. Since we're dealing with whole body conductance here, the electric flow path is through one hand and out the other, doubling the resistance resulting in 400 Ohms of resistance. This is actually somewhat conservative, Wikipedia has it listed at 1 kOhms. Since the resistance is about 5 times lower than the tub, then 5 times the current flows through the person. This results in a current of about 50 mA; causing a tingling feeling at best. Nowhere near 300-500mA of DC current needed to cause a fibrillation.

Make sure she runs the laptop on battery. If she runs it on mains and the charger PSU brick gets pulled into the bath that could be game over...

Most bathroom outlets since at least the 80s have been equipped with GFCI to preclude against this possibility (except they had hairdryers in mind). It is not likely to be a GG, although she might feel a nasty shock.

 

[fyrstormer]

It is unusual for the battery pack in a laptop to be much more than 12 volts. The PSU is another matter entirely, although if the building in question is less than 40 years old, the outlets in the bathroom should be on GFCI's. UL doesn't regard anything below 24 volts as a potential shock hazard (however depending upon the amperage available, it can be a serious energy hazard). The battery pack just doesn't present a serious shock hazard, even in a bathtub.

There is one source of high voltage in most laptops. The lcd display is usually illuminated by a pair of cold cathode fluorescent tubes, and they run at several hundred volts. The current is fairly low, but more than enough to be very unpleasant.

Actually it's very usual for laptop batteries to be more than 12V. Most of them are 14-19V nowadays.

Anyway, it takes 6 amps to stop your heart, and it takes more than 14-19V to shove 6 amps through your chest, so there's nothing to worry about. Besides, the vast majority of any current would take the shortest possible path to ground and just jump from one battery terminal to another.

The reason AC is dangerous despite this fact is because AC relies on the ground around your house as a reservoir to "bounce" into and out of as the voltage changes polarity, and a bathtub full of water works just as well for that purpose. If you put 110V of DC into a bathtub, with a negative wire right there next to the positive wire, it would be tingly but harmless. It's the fact that AC works around the limited capacitance of the ground by changing polarity that makes it dangerous even when you're not actually touching the ground, because it can push/pull a large amount of amperage for a sustained period of time. With DC, the bathtub (and the person in it) would become fully-charged within a few thousandths of a second, and then the current would stop flowing.

 

[Lynx_Arc]

Anyway, it takes 6 amps to stop your heart, and it takes more than 14-19V to shove 6 amps through your chest, so there's nothing to worry about. Besides, the vast majority of any current would take the shortest possible path to ground and just jump from one battery terminal to another.

Death can occur from any shock that carries enough current. Small currents (40 mA - 700 mA) usually trigger fibrillation in the heart which is reversible via defibrillator, but large currents (> 1 A) cause permanent damage via burns, and cellular damage. The heart is most devastated by foreign electricity, next is the brain.[citation needed] Women are more susceptible to macroshock electrocution than men, but men are equally susceptible to microshock electrocution.[citation needed]

http://en.wikipedia.org/wiki/Electrocution

 

[Illum]

gee...talk about long baths

B@rt used to moderate the forum with his pepperpad in his bathtub...maybe you could ask him:duh2:

 

[Mr Happy]

I'm more interested in the scientific question; what would happen if you put a fully-charged laptop in a bathtub you were sitting in?

Basically, nothing...to you. The laptop would die, however. It is well known that immersion in bathtubs is fatal to laptops. Most laptops come with a warning in the instructions: "do not use in bathtubs, showers or swimming pools".

Nothing would happen to you because, assuming the laptop is running on batteries, all electric potentials are contained with the laptop. There is no potential difference for electric current to follow beyond the perimeter of the laptop case.