Thursday, December 2, 2010

From Kelli - Water and Power


OK, here’s a scenario. Murderer holds the victim’s head down in a rather large, deep porcelain sink with a bit of water in it. How much water would have to be in the sink for the victim to drown? Would the entire head have to be submerged?
An addendum: how much does water amplify a fatal electric jolt? (assuming the victim is in or touching water). If the victim is later removed, how would the ME determine the presence of the water?


Simple: enough water to obscure the airways and keep the victim from inhaling any air. So it entirely depends on the size of the sink and the size of the victim’s head. Of course more is better, depending on how effectively the person can struggle. The less water, the easier it will be for them to rise above it, thereby extending the process. All you need is enough water to cover their mouth and nose.

Diagnosing death by drowning is a little more difficult. There’s no hard and fast way to do it. A pathologist’s determination of ‘drowning’ is always partly assumption based on the condition and circumstances of the body. A characteristic like pulmonary edema can also occur because of overdose or heart failure. Some drowning victims suffer a laryngeal spasm so that the lungs close off and remain dry. So the pathologist must do whatever they can. Both sea and lake water should contain diatoms, which will get into other tissues and organs during the process of drowning. The doctor can look in places other than just the lungs, since water could get into the lungs even if the person was already dead when they hit the water.

As for adding in electricity: I do not have a physicist on my ‘people to email when I have a question.’ Chemist, yes, not physicist. But from what I have been able to determine, water conducts more or less depending on the amount of dissolved minerals in it. Completely pure water should not conduct at all. Salt water can conduct quite well. This does not necessarily amplify the charge, simply moves it.
However, I asked my Otis field engineer husband, and he reminded me of Ohm’s law: current equals voltage over resistance. He (my husband, not Ohm) says that water lowers the skin’s resistance. I’m not sure how lowering resistance across the skin surface translates to resistance to the jolt entering the body, but we’ll go with him for the moment. Average household electricity is 120 volts and about 15-20 amps of current. 30 amps can kill you. If water lowers the resistance while household voltage remains constant at 120 volts, then the current increases. So in that sense, the water could increase the current.
Now, assuming you are speaking of a household situation, you’re going to have to take GFI—ground fault interrupter—outlets into consideration. I’m not going to call him back and ask him about those, or I’ll be on the phone all night.








Lisa Black is a full time latent print examiner/CSI and the NYT bestselling author of the Theresa MacLean series, including Takeover, Evidence of Murder and the recently released Trail of Blood. Please visit her website at http://www.lisa-black.com/.

4 comments:

Meredith Cole said...

Thanks for the information, Lisa--and the great question, Kelli! I was curious about water and electricity, too, and why we all live in fear of dropping our hair dryers into the bath.

Rebecca Cantrell said...

Thanks, Lisa, and also please thank your husband for us! We have the whole family working for 7criminalminds now.

Great question, Kelli! I'll be very careful around the sinks and tubs at your house from now on. Of course, if it's for a Miranda book, it's probably a bar sink.

Kelli Stanley said...

This is fascinating, Lisa!! Thank you so much, and please thank your hubby for us, too!! The conversation around your house must be pretty darn scintillating! :)

Becks, dear, at least I give my victims a chance to fight back, Ms. shoot-him-in-the-gut-and-watch-him-writhe-in-pain! ;)

And no, not a bar sink, Smarty Pants ... not sure if this is for the Miranda series or a stand-alone I'm plotting. :)

xoxo

Rebecca Cantrell said...

hey, the gut shot guy LIVES. Maybe.

Still, you are right. You're giving 'em a fighting chance.

What a nice killer you are! :)