Wikipedia:Reference desk/Archives/Science/2018 March 5

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March 5

Shocking... positively shocking

In case of electric shock through water (e.g. an electric heater thrown into a bathtub), by what factor does the current through the body increase compared to an electric shock through dry skin (e.g. from touching some electrified steel bars in a bank vault), assuming that the voltage is the same in both cases? 2601:646:8E01:7E0B:59E2:B6:A6B8:FAC7 (talk) 03:54, 5 March 2018 (UTC)

this source gives a value of 300 ohms "total body resistance" during immersion in water. But note, this is not a trivial thing to measure, will vary between situations, and it's not trivial to predict the consequence of being exposed to current while immersed in water. But that aside, there's a figure for you. In that same article, resistance for dry callused skin on the hand is given as up to 100,000 ohms. Naively you'd take that information and predict that in dry conditions, you take 333 times less current through your body. That's probably true given the right conditions. The same article also goes into detail however, how the naive assumptions are wrong. The resistance of human skin to current is actually a pretty weird thing to measure, for multiple reasons. Firstly, human skin acts like a capacitor in some circumstances, with the result that current can actually flow nicely through skin when exposed to a source of rapidly changing voltage. Secondly, high voltage can cause biological structures in the skin to break down, which actually changes the skin's conductance. So long story short, assuming the dry person and the wet person are exposed to the same voltage, the electric shock could be anything from orders of magnitude different, to basically the same, depending on the particulars. Someguy1221 (talk) 06:23, 5 March 2018 (UTC)

Well, for me a ballpark figure would do -- the reason why I'm asking is that, among my many other projects, I'm doing some initial concept work for a James Bond-themed FPS computer game, and I want to have a general idea of how much more damage should electricity cause in water vs. in dry conditions. So, given the figure above, I guess I should make any electrocution while in water instantly fatal, given that I've already decided that touching 750 1000 volts or higher will be instantly fatal (lower voltages causing proportionately lower damage, 220 volts causing 32 22 points of damage for example) -- am I right? 2601:646:8E01:7E0B:71B8:6856:E929:5E71 (talk) 09:18, 5 March 2018 (UTC)

• Like so many fatal electric shock circumstances, the situations you describe are such a hazard not because of the live conductor, but because of the unusually low impedance of the earth path.

It's common to think "Don't touch the live conductor", but in fact we do often do this, and survive. It is very common in fatal accidents for someone connected with it to say, "Yes, we always used to get a bit of a tingle from that switch, but we didn't think about it." Then one day, someone touches it with bare or wet feet (and so a better contact to the floor) and they receive a serious or fatal shock. The involvement of water in particular is why there is so much additional care taken (UK regulations at least) for electrical work around bathrooms and kitchens (as a Brit looking at US wiring, I'm just amazed they aren't all dead yet).

A "typical human" is an a moderate-resistance insulating bag of conductive salt water. In a safe condition, we touch properly insulated things. In a fault condition those manufactured insulators have failed and we're relying on the resistance of our skin (the insides are very conductive and nothing will stop that). Anything we do to reduce the skin resistance is what makes a shock into a death. So wet hands, or a piercing of the skin, and especially wet feet (the earth path is usually the more difficult path to make conductive) is bad news.

Bathtubs are earthed (through the pipes, if nothing else) and a body in such a large skin area of water has a low impedance to earth - so, fatal shocks. In some cases though, people have survived the "toaster in the bathtub" scenario simply because the bath is so conductive - if the tub is a large copper one, with the toaster at one end, close to the tub and the body some distance away from it, the current flowing directly from toaster to bath is so high that it trips some further safety device (look into "RCD" devices) before serious injury takes place. Many bathtubs are insulators and although the plughole fittings are enough to give them the same low impedance, a toaster at the tap end might be survivable when the same toaster at the far end of the bath would not be - current flow through slightly conductive water is complicated and the risk depends on just where the body is in relation to the path.

Most electric security fences, for this reason, use a bipole system, not a dipole. Alternate wires are electrified at opposite polarities - so the hazard current is between wires, down a low impedance metallic path. In contrast, animal control fences use a single conductor (for cost) and rely on an earth return through hooves and the ground. As those are high voltage, but restricted current (and pulsed too), the earth return is workable - although most of the shocking voltage is across the earth, not the animal. It's only too noticeable that a shock from such a fence is startling more than painful, but not if you're close to the ground electrode (where the earth impedance is low and most of the voltage would then be across you).

For the harm aspects of electrocution, it's important to understand the relationships between voltage, current and time - also AC vs DC circuits. A really high voltage will cause arcing and burning. A middling voltage will, if the circuit impedance is low, give a large current that can be damaging ("It's the Volts that jolts, it's the Mills (Milliamperes) that kills") - particularly for a cross-body or through-the-heart shock. Especially as the heart is normally electrically self-controlled and applying a voltage across it may cause fibrillation (if used properly, the de-fibrillation effect can be medically useful). A low voltage, especially DC, can also kill, if it's sustained for long enough and the effect is to contract enough muscles to stop you breathing. DC is bad because it tends to make muscles tense in one direction and stay there, whilst AC does the Ian Curtis dance and although you might be injured in the resultant stage diving, at least you don't hang onto the conductor like a dead sloth. There's also the rare example of super-low voltage electrocution, which is only found in submariners, electroplaters and telephone exchange engineers. Even a 2V lead-acid battery can, if big enough, deliver a fatal current. Andy Dingley (talk) 10:35, 5 March 2018 (UTC)

I assume that in a real-life scenario, if you throw an electric heater into a bathtub, the circuit breakers would trip or fuses blow. And wouldn't be a "fatal electric shock circumstance." I wouldn't test this although. Hofhof (talk) 13:42, 5 March 2018 (UTC)

The circuit breaker might take a long time to trip or might not trip at all, since tap water is not all that conductive and a. 15 amp breaker takes way more than 15 amps to trip quickly. Caution:Don’t try this at home! A utility I worked at used a salt bucket as a current limiting device a galvanized steel bucket was connected to the system electrical ground connection and filled with water. A copper paddle with a wooden handle was connected to 120 v ac and held with a hand clad with an approved rubber glove and leather outer glove. Some table salt had to be dissolved in the water to get significant current to flow when the copper rectangle ( perhaps 5 inches by 7 inches ) was lowered into the water. With some salt in the water the current was enough to boil the water near the paddle and trip an overcurrent relay ( several amps). This chancy device was retired in favor of safer resistive load boxes (akin to electric toaster).Edison (talk) 17:54, 5 March 2018 (UTC)

See liquid rheostat. The scary ones were the ones used on early electric locomotives! Andy Dingley (talk) 23:35, 5 March 2018 (UTC)

The fuses are unlikely to blow. This is an electric heater, which is a high power device, usually designed for the limit of practical use. In the UK, it would be fused at 13A and would be a 2kW or 3kW device. The situation is also an earth fault, which is of higher impedance than the normal connection. The over-current fuse might blow if you stuck a fork into the heater and touched the case, but a conduction path through water is unlikely to do it.

What's a "circuit breaker"? Again, like the fuse, an over-current breaker is unlikely to trip. Instead if it's a specific type of circuit breaker, an RCD, then it might trip in time to save you. However the fault current an RCD can pass by design (to avoid nuisance tripping) is generally higher than a safe current limit - especially on a general supply circuit. If you do have equipment in a bathroom (UK practice seriously discourages this), it's usual to provide a lower tripping current and faster acting RCD for such a situation. Andy Dingley (talk) 23:43, 5 March 2018 (UTC)

I’m surprised you are unfamiliar with “circuit breakers” but fortunately we have an article about them. Edison (talk) 22:41, 7 March 2018 (UTC)

It seems clear that Andy Dingley knows what about circuit breakers, their point is the term is imprecise since it can mean different things. Nil Einne (talk) 02:00, 8 March 2018 (UTC)

• One minor point. "Bathtubs are earthed (through the pipes, if nothing else)" is not necessarily true. The faucets are normally above the tubs, and at least where I live, drain pipes are now commonly made of plastic. --69.159.62.113 (talk) 08:37, 7 March 2018 (UTC)

The requirements and practice for deliberately earthing bathtubs have changed over the years, and for the last forty (at least) there has been a strong requirement that this is done by added protective conductors (wires clamped on). Before this, tubs were metal and so were water supply pipes, so there was a fairly good, although accidental, earth connection.

In the '60s and '70s, there was a shift to plastic tubs and plastic wastepipes. The taps were still strongly earthed and there was a period when these "toaster in the bath" accidents were caused by this. Once again, the bather was already in contact with the live supply (usually a radio near the edge of the bath), yet unharmed, and it was when they reached out and touched the earthed tap to run a bit more water that they received a serious shock. The increasing use of plastic meant that a specific earth conductor and equipotential bonding was needed in baths and kitchens - especially kitchens, as sinks are still largely stainless steel. Equipotential bonding is not the same as earthing (although it can be part of it), as it has conductive things connected together, but not necessarily earthed. However it does mean that there won't be a dangerous condition where one metal thing becomes accidentally live, then there's a dangerous shock on touching another which was accidentally earthed.

Plastic supply pipes are now coming into common use, rather than copper, but water is still enough of a conductor that it could be a shock hazard as an earth return. Andy Dingley (talk) 10:37, 7 March 2018 (UTC)

Winds and fire

While fueling a fire by bringing fresh oxygen, a strong wind would also tend to extinguish it, by analogy of birthday candles. How one can measure the associated balance of oxygen vs extinguishing, possibly in terms of wind speed required to offset the oxygen intake and extinguish the fire? 212.180.235.46 (talk) —Preceding undated comment added 16:08, 5 March 2018 (UTC)

In the real-world scenarios, wind generally serves to spread fire. Here's [1] a nice research paper that describes how wind velocity and other variables affect fire spread. One situation where wind can help extinguish fires is when the fuel load is light and there is not much mass burning. E.g. this[2] research paper on grass fire modeling indicates that they can sometimes be put out by very high winds. Fire modeling is a very complicated and complex field; there are few (if any) general laws, and much is still not well understood. A lot of the research is still confined to very specific questions and applications: e.g. here [3] is an interesting study of the effectiveness of using vortex rings to extinguish fires in oil and gas wells. This is all about fires much larger than a birthday candle. I am not aware of any work regarding calculation of wind speed necessary to extinguish such small fire, but perhaps someone else can shed some light on that! SemanticMantis (talk) 16:34, 5 March 2018 (UTC)

Read Firestorm. There is no typical balance since fires are very different depending on energy source and scenario. Almost all firefighting strategies aim at cutting off the supply of Oxygen. The few situations where its better to extinglish the fire by cutting off the flame manually its usually done with explosives. For that read our article about Red Adair. --Kharon (talk) 17:02, 5 March 2018 (UTC)

Note that if you don't blow hard enough, the candles won't go out. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:12, 6 March 2018 (UTC)

Or even if they do, they might not stay out. DMacks (talk) 21:26, 6 March 2018 (UTC)

From what kind of soda glass was made in the ancient time?

I looked for the way the glass was made in the ancient time and I found this site which states "Glass is produced from a mixture of silica-sand, lime and soda". What kind of soda it was? and how did they make it? 93.126.116.89 (talk) 17:20, 5 March 2018 (UTC)

"Roman glass was made from the melting of sand and natron – mineral soda – from the Wadi Natron in Egypt", from Ancient_glass_trade. More info at History_of_glass, which says "The alkali of Syrian and Egyptian glass was soda ash, sodium carbonate, which can be extracted from the ashes of many plants, notably halophile seashore plants: (see saltwort)." See also Sodium_carbonate#Occurrence_as_natural_mineral. It would seem some ancient glass was made with mined mineral soda ash, while other ancient glass was made using plant-derived soda ash. SemanticMantis (talk) 17:34, 5 March 2018 (UTC)

What is the reason that it's not recommended to "mix" different alcohol drinks?

Always I've been told that it's forbidden to mix different types of alcohol (for example vodka and beer or wine). What is the reason for that? 93.126.116.89 (talk) 18:06, 5 March 2018 (UTC)

Old saying I learned as a kid: Hard before beer, you are in the clear. Bear before hard, you are in the yard. 209.149.113.5 (talk) 18:46, 5 March 2018 (UTC)

"Alcohol myth buster: 7) Switching between beer, wine, and spirits will make you more drunk. FALSE: Your blood alcohol content is what determines how drunk you are. Mixing drinks may make you sicker by upsetting your stomach, but not more intoxicated". UK National Health Service Alansplodge (talk) 19:07, 5 March 2018 (UTC)

Old British saying: "Cider on [i.e. after] beer makes you feel queer, beer on cider, nothing finer." Note that in Britain, "cider" is always alcoholic, so we don't use the term "hard cider" (in 45 years of drinking I've never seen a so-called "soft cider"), and is often stronger than the average beer. {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 19:49, 5 March 2018 (UTC)

I'm pretty sure Alanspoldge has provided a reasonable reference to read indicating it is likely false. Continuing to insist that it is true, absent a competing reliable source, isn't useful. --Jayron32 20:58, 5 March 2018 (UTC)

I don't see anyone insisting on anything Jayron. DuncanHill (talk) 23:44, 5 March 2018 (UTC)

NHS (via AlanSplodge): ". . . Mixing drinks may make you sicker by upsetting your stomach, but not more intoxicated."

British saying I quoted: ". . . makes you feel queer . . . ". "Feel queer" means feel ill, not "be drunker." {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 12:37, 6 March 2018 (UTC)

• But then again, "Whisky on beer, never fear; beer on whisky, very risky." (common in the UK)

Much depends on the relative strengths of the two, and on the habits of the drinker. In UK drinking practice, whisky after beer is more commonly the habit of a fairly moderate drinker. Beer on whisky though is unusual, unless you're seeking to get drunk in a serious manner. Also "drinking beer" in the UK would be seen as drinking several pints of British beer, quite possibly double figures, which is an alcohol content comparable to the whole of Milwaukee. Andy Dingley (talk) 23:54, 5 March 2018 (UTC)

Drinking whisky with beer (i.e. alternating sips) is a common practice in Scotland, where the combination is known as a "hof an' hof" (i.e. a half and half). Note however that Scotch whisky is essentially distilled beer, so this is not really mixing in the same way that combining beer with wine or cider is. {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 12:37, 6 March 2018 (UTC)

There are lots of cocktails made by mixing hard liquor with beer or wine, see for example the famous boilermaker (beer cocktail). Looie496 (talk) 20:04, 5 March 2018 (UTC)

My favourite is the Dog's nose, where a single or double gin is added to a pint of porter or stout. For historical authenticity (as drunk by the 18th-century Bow Street Runners), one should first mull the porter (a microwave can substitute for a red-hot poker), then sprinkle some finely grated nutmeg on top, then add the gin. It's a wonderful 'winter warmer', but I'd never drink more than one. {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 12:37, 6 March 2018 (UTC)

Could it be that taking two types of alcohol is harder on the liver too, even if you don't get more intoxicated? Hofhof (talk) 22:34, 5 March 2018 (UTC)

I suppose it could be. The body is pretty complicated and all sorts of weird things can happen. But I can't think of any reason to think it is harder on the liver. Do you have a reason to think that? --Trovatore (talk) 22:56, 5 March 2018 (UTC)

• If you're drinking "two types" of alcohol (such that your liver cares) then the second is likely to be methanol, which is well known for making you sick, blind, mad and dead in that order.

There are many other things in an "alcoholic drink", some of which are well known for causing various upsets. Not many of them involve the liver. Andy Dingley (talk) 23:54, 5 March 2018 (UTC)

If you have a variety of drinks, you are likely to have more in total, than if you just had one kind. Graeme Bartlett (talk) 23:52, 5 March 2018 (UTC)

Bingo! I think you nailed it. --Stephan Schulz (talk) 09:35, 6 March 2018 (UTC)

Only problem is that the claim is that the order of the drinks matters. Hofhof (talk) 13:32, 6 March 2018 (UTC)

• The question, as stated, is anecdotal evidence with poor experimental design. It's inconclusive either way.

There are two hypotheses put forward here, which aren't contradictory, and both of which fit the claim and the observed data.

1. Total alcohol content, not order of consumption, is what matters.

2. There are other social effects, such that the order of consumption is also correlated (but not physiologically causative) with quantity.

Andy Dingley (talk) 14:11, 6 March 2018 (UTC)

One thing that may be relevant in some circumstances is that the human digestive tract absorbs alcohol fastest at 20% alcohol + 80% water mixture. So if you consume a mix of a low alcohol drink (or even water) and hard liquor it can give a steeper path to intoxication than just hard liquor. 91.155.192.188 (talk) 14:27, 6 March 2018 (UTC)

I heard it as "liquor before beer, you're in the clear; beer before liquor, never been sicker." The explanation I've heard is based on rate of consumption. If one first establishes the pace of drinking hard alcohol, one is sipping a relatively small volume over time or is drinking a quick shot but only occasionally. Keeping up that pace switching to something with less alcohol content means you slow down the rate of alcohol consumtion. But if instead you start by drinking a lower-alcohol beer, you're drinking at a faster volume pace. Switching to a higher alcohol content means you need to suddently slow down the volum pace to keep from suddenly jumping to a higher alcohol pace, and need to do so at a time when your judgement might already be impaired. Though chasing a sipped mixed drink with a power hour sure confounds things. DMacks (talk) 14:49, 6 March 2018 (UTC)

Somebody (not me, because that would be original research) feels that mixing wine with almost any other alcoholic beverage can upset my (I mean, their) tummy more than just the other alcoholic beverage. That person assures me that alternating tequila and beer is refreshing and benign.Hayttom (talk) 20:30, 6 March 2018 (UTC)

I had always heard this in relation to nausea rather than drunkenness per se; if we're only talking about biological triggers for emesis, there is room for unexpected biology. But searching up some refs: [4] [5] [6] all I see are guesses no matter which perspective it is taken from. Wnt (talk) 08:49, 7 March 2018 (UTC)