My advice is to take advantage of Apple's generous offer and replace knock-off power supplies if possible. I certainly wouldn't advise anyone to run out and grab live wires.
At the same time, I don't want to be responsible for mass panic. Both of these incidents occurred in China, and I'm not aware of any reports of this occurring in the United States.
So please, don't run through your house unplugging all of your iOS devices, but please trade in any questionable USB power adapters ASAP.
The voltage is irrelevant and that section of the article should be removed. People can get severely injured by car batteries operating at 12V.
The reason these reports have started to come in from China is most likely an abundance of cheap knock-off power adapters. It has absolutely nothing to do with 120V vs. 220V.
Since current is proportional to voltage when resistance is fixed, it stands to reason that the same person touching a 120V wire would experience a lower current flow than when touching a 220V wire under the same circumstances, and thus would be less likely to suffer lethal effects. Lower voltage, lower current, less lethality.
But more to the point, the text clearly says that any electric shock under the right circumstances could be fatal. We're not trying to whitewash this.
That said, 120V shocks are generally not lethal - here's a discussion where people are trading shock stories. A few hundred people a year might die from electrocution, and while that's certainly terrible, I think it's safe to say that a vastly larger number of people suffer 120V shocks each year and survive.http://forums.anandtech.com/archive/index.php/t-2199635.html
Except that the trick in your opening statement is irrelevant - body resistance to applied voltage is NOT fixed. Body resistance changes based on humidity levels, biological stress, muscle state, posture, contact location, and more. Applied voltage can change muscle state, freezing out (say) sweat glands and increasing resistance with increasing voltage.
Sure, no argument there. But for voltage to be irrelevant, wouldn't you have to be saying that you would be no more scared to accidentally come into contact with a 220V wire than a 120V wire? That's what it comes down to in my mind, and personally, I know I'd be more worried about a shock from a 220V feed.
Adam, as a physicist I'm telling you guys what you are 'reporting' is factually wrong. You have definitely left your area of expertise. Take it or leave it.
As to your example, if the adapter would deliver at twice the voltage (it doesn't actually) it would drop the current by half (it doesn't do that either). So no, not "lower voltage, lower current, less lethality". It's actually quite the opposite. Plus, electrocution is far more complicated than a simple volt-amp figure. As Tom pointed out there's the actual flow to the body that depends on many different aspects, the state of your skin, muscles, etc. AC vs. DC injuries, etc. Bottom line, it's complicated and experts spend a lot of time trying to debunk silly myths and legends. All of their efforts are thwarted when a couple of I'm guessing well-meaning folks publish simplistic personal accounts despite a lack of thorough understanding of the matter.
But that's entirely beside the point. It's the same adapter you plug into 120V or 220V. You should be worried about its output, not the input. These adapters will take anything from 100V to 240V, 50 Hz and 60 Hz. It's the output that's regulated and with a faulty adapter there's no telling what's coming out of the adapter. But the type of socket you plug it into should definitely not be your concern.
And please remove this line "That said, 120V shocks are generally not lethal" for the sake of everybody's safety.
It's simply not true. Just because people survive 120V buzzes does not make it safe. People survive 240V buzzes too. But that's not because it's safe. It's because they simply get lucky.
As I already explained, people die from 12V shocks. Please stop repeating this myth that 120V is somehow below some magic threshold where you can fool around without getting hurt. It's not. This is serious business and you ought to treat it that way.
But if we're talking a faulty adapter, one of the faults could be a failure of the step-down, no? And then you could be touching the full input...
I guess I'm resisting this for a couple of reasons:
1) As a matter of policy, we don't edit articles for more than typos after they've gone into an email issues, because that's the primary readership. The train has left the station for tens of thousands of readers.
2) I'm just not seeing that we're promulgating any myths about safety. We state clearly that any electric shock can be fatal, and the statement that 120V shocks are "usually" not fatal is demonstrably true: in the set of people who receive 120V shocks, most of them do not die. Similarly, while any voltage can be problematic, it's similarly true that higher voltage is more likely to be bad, due to being proportional to current. Regardless, we're never recommending that you try to get shocked or fail to take precautions against getting shocked.
3) If anything, I think this discussion in the comment thread is far more valuable than pretending the text was never written - anyone who reads the article will see this back and forth and can tell that some people feel very strongly about it.
I was quite surprised to see that such an ignorant comment made it into a TidBITs article.
I don't think that the dozens of people electrocuted each year in the US would agree with your blanket assessment of the non-lethalness of 120Volts.
I actually rewrote the last two paragraphs for you guys. No nonsense, just the facts. Because I agree with the point you originally wanted to make, people shouldn't panic.
"While these stories are alarming, readers who use Apple certified adapters that are in good condition shouldn’t panic.
If you own an unauthorized and potentially dangerous USB power adapter, it’s worth $10 and a trip to an Apple Store to trade it in for an Apple power adapter."
Simple as that. :)
Thanks, Simon (and everyone else). While I'm uncomfortable changing the historical record of what was said after our set-in-stone mark of publishing the email issue, I've marked up the text along the lines of your suggestion.
I've now marked the offending text with strikethrough, which will clarify that we are essentially removing it from the article while leaving it readable so this comment thread makes sense. I do believe that the comment thread is far more valuable for shedding light on the topic than simply pretending the original point was never made.