Re: [Phys-l] Electrocution in Bathtub - Hollywood style

[John Denker <jsd@av8n.com>]

On 10/17/2007 09:41 AM, Fakhruddin, Hasan wrote:

> I have seen this in at least three Hollywood movies; electrocuting 
> someone in a bathtub or in a similar situation by throwing a
> powered-on electric appliance such a toaster in the water.  I don't
> believe this would ordinarily electrocute the person in the bathtub;
> will it?

It depends on what you mean by "ordinarily".
 -- I wouldn't recommend this as a reliable way of killing
  somebody.
 -- But I certainly wouldn't recommend it as a safe & healthy
  situation for the bather, either.


I assume this is (at least partly) a question about the physics.

My first advice, as usual, is _draw the circuit diagram_.
  http://www.av8n.com/physics/img48/bathtub.png

I'm not going to discuss the details unless somebody asks, but
it's clear that fatal scenarios are possible in this situation.

  For starters, assuming that the victim hasn't thought very much
  about this threat, one very human reaction might be to grab the
  toaster -- in order to throw it out of the water -- which would
  be a Very Bad Move.  

  Also, even if the initial posture (as shown) makes it hard to
  get an immediately-fatal shock to the chest, you have to ask
  what happens next.  A non-fatal shock to the lower body might
  cause the victim to lose control of posture, leading eventually
  to fatal consequences.  And unless the victim is very clever, 
  it is hard to stand up from the initial posture without using 
  the hands, and touching things with the hands greatly increases 
  the risk of fatal shock to the upper body.

  Dry skin is a pretty good insulator, but wet skin is not.

Draw the circuit diagram!

Some facts:

> From the US Consumer Product Safety Commission:
> > In May 2002, a 14-year-old girl from Arlington, Texas, was
> > electrocuted when wiring problems in an apartment swimming pool's
> > underwater lights charged the water with electricity. A 16-year-old
> > boy was seriously shocked when he jumped in the pool to try to save
> > the young girl. Another teenager used a fiberglass shepherd's hook (a
> > non-conductive device) to pull both victims from the water.

This goes to show that the conductivity of real water is in the range
where R2 is small enough to be lethal, while R1 is large enough to not
blow the CB.

Many people are afraid of snakes, but in fact there are two orders of
magnitude more fatal at-home electrocutions than fatal snake bites.
Large appliances figure more prominently than small appliances for
some reason, and "installed household wiring" figures prominently,
for some reason that I definitely haven't figured out:
  http://www.cpsc.gov/library/foia/foia05/os/electrocutions2001.pdf


On 10/17/2007 10:59 AM, Edmiston, Mike wrote:

> If your house is up to code, and the product is designed correctly, you
> won't, because GFCIs (ground-fault-circuit-interrupters) are required in
> the bathroom. 

True if the product is a hair dryer, but not true for toasters,
which is what the OP asked about.  I've often wondered why
toasters don't have built-in GFCIs, but they generally don't.

Also, I've seen lots of houses that are not up to code.  And 
in my experience, bringing them up to code is not always easy.
Sometimes it's a 5-minute installation job, but sometimes it
isn't.  For example, if the outlet in the bathroom is part of 
the lamp fixture (as it often is), where are you going to put 
the GFCI?  
 -- The kind that you substitute for a wall outlet won't work.
 -- The kind that you put in the main breaker panel might not
  work, because they are generally bigger and there might not
  be room enough.

I'm not saying it takes a PhD in experimental physics to solve 
this problem, but I am saying the average Hollywood victim-to-be 
might plausibly face unsolved problems in this area.

===================

The implausible part of the story is how the toaster gets into 
the bathroom, and/or why the victim-to-be continues bathing while 
the attacker rigs up the toaster and a sufficiently-long extension 
cord.

An electric /fan/ in the bathroom makes more sense.