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Thread: Laptop vs. Bathtub

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    *Flashaholic* StarHalo's Avatar
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    Default Laptop vs. Bathtub

    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?

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    Flashaholic* AnAppleSnail's Avatar
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by StarHalo View Post
    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.
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    Default Re: Laptop vs. Bathtub

    just get some trim and attach it to make a ledge around the top of the table so it cannot slide off.
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    Default Re: Laptop vs. Bathtub

    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.

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    *Flashaholic* StarHalo's Avatar
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    Default Re: Laptop vs. Bathtub

    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?

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    Default Re: Laptop vs. Bathtub

    This sounds like a good episode for Mythbusters.

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    *Flashaholic* StarHalo's Avatar
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by kingofwylietx View Post
    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..

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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by StarHalo View Post
    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.
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    *Flashaholic* StarHalo's Avatar
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    Default Re: Laptop vs. Bathtub

    It's 19 volts at 3.42 amps..

  10. #10

    Default Re: Laptop vs. Bathtub

    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.

  11. #11

    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by StarHalo View Post
    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.
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    Flashaholic* 65535's Avatar
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    Default Re: Laptop vs. Bathtub

    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.
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    Default Re: Laptop vs. Bathtub

    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...

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    Default Re: Laptop vs. Bathtub

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

    Quote Originally Posted by StarHalo View Post
    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.

  16. #16

    Default Re: Laptop vs. Bathtub

    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.

    Quote Originally Posted by zipplet View Post
    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.

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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by mattheww50 View Post
    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.
    Last edited by fyrstormer; 06-12-2010 at 07:08 PM.

  18. #18

    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by fyrstormer View Post
    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
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    Thread Killer Illum's Avatar
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    Default Re: Laptop vs. Bathtub

    gee...talk about long baths

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

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    *Flashaholic* Mr Happy's Avatar
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by StarHalo View Post
    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.

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    Moderator Kestrel's Avatar
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by StarHalo View Post
    My wife would like to set her laptop on a small side table in the bathroom to watch movies while she bathes [...]
    Quote Originally Posted by Illum View Post
    B@rt used to moderate the forum with his pepperpad in his bathtub
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by Kestrel View Post
    LOL! First though, how much does she weigh?

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    Default Re: Laptop vs. Bathtub

    Rather that worry about electrocution, I'd be more concerned about the results of dead-shorting half a dozen 18650's in a body of water. If just one of them reaches thermal runaway (read the Li-Ion safety threads in regards to dead-shorting), your wife may find herself missing a limb, rather than feeling the tingles of electrocution.

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    Default Re: Laptop vs. Bathtub

    Tell her to read a book..... Its way cheaper to replace and a lot safer when it falls in the tub.

  25. #25

    Default Re: Laptop vs. Bathtub

    I'm amazed that this was so worrisome that it warranted a thread on CPF.

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    *Flashaholic* StarHalo's Avatar
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    Default Re: Laptop vs. Bathtub

    Quote Originally Posted by LuxLuthor View Post
    LOL! First though, how much does she weigh?
    It's a jet tub, so it's probably pretty heavy

    Quote Originally Posted by kito109654 View Post
    I'm amazed that this was so worrisome that it warranted a thread on CPF.
    Not worrisome to me, I'd be more worried about my wife's disposition without Facebook. I'm more interested in just the science behind dropping a laptop in a tub, it's not really something you hear about happening, so you have to wonder what would happen, particularly knowing how much energy is in those Li-Ion cells..

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    Default Re: Laptop vs. Bathtub

    Well, you probably have a 18650 just laying around collecting dust.... Just throw that in a bucket of water waaay back in your garden and see what happens. The effect you see there times 6 will be rouglhy what you'd expect from a laptop battery (with quite a big delay, those packs are semi-watertight).

    As far as the laptop's electronics go i dont really think anything will keep working long enough to be dangerous, laptops are built to be economical on power and light so they burn out/break relatively easy.

    All in all i think the worst part would be if the power brick dropped in the tub....

  28. #28

    Default Re: Laptop vs. Bathtub

    You can always try to 'simulate' an earthquake by shaking the side table to see how much the laptop would move off the table. Anything more than a moderate amount of force would be a major quake.

    I would think that even if you ran the laptop off the main and charger, the special circuit in the bathroom outlets (if your place is up to spec) would prevent anything serious. At the same time, I wouldn't say she would be unharmed for the second it takes for the circuit to trip.

  29. #29
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    Default Re: Laptop vs. Bathtub

    You should get her a portable DVD player with a remote, and secure it to the wall.
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    Default Re: Laptop vs. Bathtub

    There is no way that it would harm a human or child. There is only 19v@3.5A going into the laptop. The battery would not be of enough potential to harm or kill a human. It would at least take 10A to 20A DC to get you to wake up, but again there is the temporary paralysis which could lead to a drowning.

    It takes at least 100A AC to harm a human but again in water there is the drowning aspect in a tub of water.

    With 100% confidence i can say that the plug after the power brick is safe for 19v@3.5A and could not harm anyone. It might feel like an fire ant bit you or a bee sting and nothing more.Then for the power before the brick is still wall voltage so this is going to kill you. Anything after the power brick is going to be safe. Then for the battery only, you would only kill the laptop, which is not always a bad thing since it gives the excuse to buy a new one. A netbook is only $200 shipped these days.

    Almost slipped my mind too, I stand to correct myself is that there is two aspects of this:

    The stuff still applies above but there is a component that would definitely end a humans life.

    The question is: Does the laptop have the standard compact fluorescent lighting or the new led lighting for the back light of the screen.

    1)If it has the compact fluorescent then your a dead man. It has a transformer that would cook anything in a bathtub. I have seen all the way up to 1kV in these babies and this is AC so this is the game ender so please be advised that this is going to kill you.

    2) then for the led backlight screens, you are completely safe. The stuff that i stated above still applies but this is for the leds.

    Disclaimer: Led backlight = SAFE Compact Fluorescent = DEAD
    Last edited by ama230; 06-17-2010 at 06:57 PM. Reason: grammar
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