Wikipedia:Reference desk/Archives/Science/2018 February 15

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February 15

Nature (journal) still British?

Moved to talk:Nature (journal). --Trovatore (talk) 22:01, 15 February 2018 (UTC)

DIY automatic fire suppression with a CO2 bottle attached to a line

I would like one of these automatic line fire extinguishers for inside my computer but they're crazy expensive. I figure I can make something myself by attaching a disposable (60 Litre gas) Ar/CO2 welding gas canister to a suitable regulator with a sealed tube. I'm not sure what the tube will be made of or how to plug it though. The volume of gas in the canister (60 L) compared to the room (75 000 L) is negligible so I'm not concerned about risk of asphyixiation. Is this a workable idea? I'm not sure what tubing to use or how to plug it (clamping seems obvious) — Preceding unsigned comment added by 185.216.51.87 (talk) 07:46, 15 February 2018 (UTC)

Computers aren't noted for fires. They're also fairly self-extinguishing. More important than an extinguisher would be a means to automatically isolate the mains power. You can do this with standard modules, detecting the fire with either an ionisation sensor, optical smoke sensor, heat rise sensor (measures the rate of heat rise, not just the temperature of hard-working electronics) or even a UV sensor. It's fairly common for fire-risk electronics to use a 'trace wire' sensor, which uses a thermistor material as insulation in wire, and can detect heat rises electronically.

The seal and release valve for simple automatic gas release extinguishers is usually a sprung-loaded pin against a bursting disc. This is leakproof in storage. The seal around the pin, on the downstream side, doesn't have to be perfect. You'll need at least a lathe to make one though, or else some lucky finds in the scrap bins. Andy Dingley (talk) 11:41, 15 February 2018 (UTC)

I've had a few computers go up in smoke - lots of smoke from the burned insulation on the wires but no flames. The one on my desk at work as gone twice, each time it was the power cable to the dvd. It was a faulty connector and the replacement supplied under warranty was faulty too. Open the window and it's all good! I've never thought a computer needed a built in fire extinguishers. When I worked on main frames, the computer rooms had halon suppression systems, but I never saw one in use in the 20 years I worked on Big Iron --TrogWoolley (talk) 15:36, 15 February 2018 (UTC)

• The volume of gas in the canister (60 L) compared to the room (75 000 L) is negligible so I'm not concerned about risk of asphyixiation - well, that's a bit careless. First of all, symptoms (or rather, the absence of obvious symptoms, which makes it extremely nasty) of inert gas asphyxiation occur well above 0% O2 (see [1], table 1). Second, your canister will not be at atmospheric pressure, so the expended gas volume will be larger than the canister's. Third, you cannot assume the gas concentration will be spread uniformly (CO2 and Ar are both heavier than air).

Maybe your intended design will actually be safe, but the argument you presented here does not prove it. Tigraan^{Click here to contact me} 15:15, 15 February 2018 (UTC)

Well suppose it was concentrated in the lowest 6.7% of the room (5000 L); that would be a 1.2% drop in oxygen concentration and still not hazardous to work in. Impaired cognitive function could occur from a >2% reduction (like if it was restricted to 3.3%). But air is not that still; I know this from seeing dust floating around when the light hits it right or experiencing diffusion of odour. 129.215.47.59 (talk) 17:32, 15 February 2018 (UTC)

" that would be a 1.2% drop in oxygen concentration and still not hazardous to work in."

That is not true. This is CO₂ we're talking about, which is not simply biologically inert. As a result, risk assessment for CO₂ exposure in a confined space is complex. Andy Dingley (talk) 17:53, 15 February 2018 (UTC)

Okay, that's a good point; my actual bottle of choice is 14% CO2 and 86% Argon which might be a bit better. 185.216.51.87 (talk) 09:58, 16 February 2018 (UTC)

This publication suggests adverse effects from spending days at 0.85 or 1.2% CO2 but it would be hard to accidentally spend more than a few minutes at 1.2% CO2 if the tank is only 14% CO2 (8.4 L). 129.215.47.59 (talk) 14:37, 16 February 2018 (UTC)

From the ebay link we can assume that the bottle contains 390g of gaseous mixture, which translates into about 220L (390g / 1.78g/L for Ar) when spilled at atmospheric pressure; a 4bar bottle does not seem unrealistic either. Another possibility though is that the "60L" refers to the atmospheric-pressure content (giving the "volume" at atmospheric pressure is a common marketing ploy for gas suppliers) and the added weight is simply the casing. In either case, the orders of magnitude seem OK-ish for your use case, though I would never approve such a device were I in charge of H&S. Tigraan^{Click here to contact me} 20:24, 16 February 2018 (UTC)

CO2 will not prevent or stop a Short circuit and since most circuit boards are flame resistant because they contain Flame retardants it seems unlikely computers can burn enough to become a thread. --Kharon (talk) 17:09, 15 February 2018 (UTC)

I can make something like this to cut the power as soon as smoke is detected. The gas would only come into play if the fire had taken hold despite the power cut (which is needed anyway to stop the fans from simply venting the gas) 185.216.51.87 (talk) 10:01, 16 February 2018 (UTC)

This would be very dangerous. If I'm not mistaken a full CO2 cylinder contains liquid CO2. According to [2] 1 litre of liquid CO2 will expand to 19.5 litres of CO2 gas at room temperature at a pressure of 1 atmosphere, so your cylinder will produce almost 1,200 litres of CO2 gas. The other problem, as has already been said, is that when CO2 is released into an enclosed space, as it is heavier than air it sinks to the floor displacing the air above and forms a layer of pure CO2. One method that used to be used for killing laboratory rats and mice was to fill an open topped bin with CO2 to displace the air and then place the cageful of animals in the bin - they would be dead wihin minutes. As it says here "In high concentrations may cause asphyxiation. Symptoms may include loss of mobility/consciousness. Victim may not be aware of asphyxiation. Low concentrations of CO2 cause increased respiration and headache"' Richerman (talk) 21:44, 15 February 2018 (UTC)

My proposed bottle contains 60 L of gas; you misread my post/my post was unclear. 185.216.51.87 (talk) 09:54, 16 February 2018 (UTC)

This is a slight digression, but I think it's worth pointing out (because a lot of people don't know it) that CO₂ is not just an asphyxiant (something that kills you by displacing oxygen). Low concentrations are harmless and normal, but high concentrations are actively toxic, and will kill you quite dead even if there's plenty of O₂ around. There is some information at hypercapnia, though I think the point needs further elaboration there. --Trovatore (talk) 22:08, 15 February 2018 (UTC)

Which is why this procedure was necessary after the explosion aboard Apollo 13. --69.159.62.113 (talk) 22:52, 15 February 2018 (UTC)

• CO₂ in these amounts is very commonly used in carbonated beverage dispensers, both for restaurant and home use, and there is a whole infrastructure of suppliers of the tanks, fittings, and refill services. There is probably a store or service in your town. These tanks are much more suitable for this than are the big welding gas tanks. You really will need to ensure that you are not going to kill yourself, but if you use a correctly-sized container, your approach should be workable. You want to aim for a system that will displace most of the air inside the computer but not displace much of the volume of the room as a whole. The earlier comment about shutting off the mains current makes a really good point. If you do not do this, the fire will likely restart once the gas dissipates. If you are going for a whole-room solution, don't do it. Use a commercial system. See Halomethane. -Arch dude (talk) 04:37, 16 February 2018 (UTC)

Removing bogus unsigned "hat" with text "Please don't kill yourself, unregistered and unsigned IP user asking about "do not try this at home" speculation." Note there is no Wikipedia or Refdesk policy against unregistered users asking questions nor about "do not try this at home" processes. Perhaps it is a radical position at the moment, but I doubt that a Sodastream gas refill is too dangerous for civilians to be allowed to handle. I should note however that we are here to provide references and information, not give advice about what is the right way for you to do things, and we will probably never know if you kill yourself.

To veer nearly on topic a moment, I wonder if such a fire extinguisher can reduce the small risk of fire sufficiently to make up for the risk it might accidentally deploy or get deployed and perhaps crack circuit boards while unattended potentially causing a fire. Designing products to avoid all risk seems like a fraught process (just ask Samsung...) Wnt (talk) 12:20, 18 February 2018 (UTC)

• Please don't ask us to speculate on potentially deadly home projects, consult with a professional. μηδείς (talk) 22:43, 18 February 2018 (UTC)

WP:NOTHOWTO (cited in another hat I also removed) is a guideline on how to write articles in terms of style, i.e. "the bullets are loaded into the top of the magazine" not "you put the bullets in the top of the magazine". We should not provide advice i.e. "you should do this..." but we can provide information. Wnt (talk) 14:01, 20 February 2018 (UTC)

In pregnancy, women should have deacrese or increse blood pressure, physiologicaly?

In pregnancy, women should have deacrese or increse blood pressure physiologicaly? Normally for pregnant women there are physiological expectations during their pregnancy and it's expressed in many medical values, but I don't remember if while having pregnancy it's increase or decrease in BP. One of them should be in normal. Their BP is not as non pregnant women. 185.191.178.183 (talk) 19:52, 15 February 2018 (UTC)

We don't do medical advice. Ian.thomson (talk) 20:01, 15 February 2018 (UTC)

This isn't a request for medical advice, it's a request for information about the physiology of pregnancy. - Nunh-huh 22:53, 15 February 2018 (UTC)

Our article on pregnancy indicates possible complications, but if you are in any doubt, consult a medical expert. Dbfirs 20:06, 15 February 2018 (UTC)

I don't try get any medical consultation. No doubt. I'm nt talking about specific case but general. I simply want to know the general physiology. Thank you 185.191.178.183 (talk) 21:17, 15 February 2018 (UTC)

In the meantime I found this article which states: "During the first few months of pregnancy your blood pressure actually generally tends to drop, as your blood volume increases and your body starts working long hours to get that baby-making factory up to speed...". Now for me it is a big question or paradox, since the blood volume is one of the component of Hypertension (That's why when having low blood pressure -hypotension- one of the treatments it to supply the patient with liquids, or alternatively when having hypertension - high blood pressure, then the treatment is with diuretics in order to decrease the blood volume.) and here is a play role in hypotension? it seems to be a paradox. Isn't it? — Preceding unsigned comment added by 185.191.178.183 (talk) 21:27, 15 February 2018 (UTC)

Physiological changes in pregnancy is a more scholarly discussion of the physiology of normal pregnancy, where the factors other than blood volume are also discussed. "Blood pressure decreases in the first and second trimesters but increases to non-pregnant levels in the third trimester." Suffice it to say that volume isn't the only factor involved. There are complex changes in cardiac, renal, and hormonal physiology. - Nunh-huh 23:01, 15 February 2018 (UTC)

The volume paradox is really pretty straightforward: increasing your blood volume within a fixed system of blood vessels will increase blood pressure. Venous capacitance in a non-pregnant person can only hold so much blood. But if you add in a brand new organ (the placenta) that is full of spaces for blood to go, then the blood volume has to increase just to stay topped up in what has become a larger container. Wnt (talk) 12:27, 18 February 2018 (UTC)

Eclampsia μηδείς (talk) 20:58, 16 February 2018 (UTC)

See Maternal physiological changes in pregnancy#Cardiovascular which decribes the normal rise in cardiac output but fall in blood pressure. Klbrain (talk) 17:19, 17 February 2018 (UTC)

Effect on circulation, extremity in cold water

If we immerse our hands or feet in cold water the body will reduce the blood flow. If we keep our extremities as long as needed to cause damage, would the body increase blood circulation to avoid it? --Hofhof (talk) 20:24, 15 February 2018 (UTC)

No. This is what causes frostbite and related conditions. LongHairedFop (talk) 21:06, 15 February 2018 (UTC)

Sure, at some point your finger is toast. But I just find it strange that the body can't warm up a specific member when it perceives it's almost frozen (provided the rest is OK). --Hofhof (talk) 00:51, 16 February 2018 (UTC)

See Thermoregulation. Your body produces heat, and cold air absorbs that heat. Your fingers and toes (also ears an nose) have a higher surface area to volume, so in very cold conditions they're liable to lose heat faster than most of the rest of you, and faster than your body can generate more heat. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:56, 16 February 2018 (UTC)

Evolution is a blind watchmaker. If there isn't enough selection pressure in favor of a trait, it won't develop. In humans, limb damage due to cold isn't common or harmful enough for a strong selection pressure. Natural selection cares more about keeping the person alive and capable of reproduction, which is why the body's response to cold is to shunt blood away from the extremities and to the body core. Recall that humans evolved in tropical and subtropical Africa. We're adapted to warm climates. The reason we can survive in other climates is because of our intelligence, which allows us to create technology such as clothing. --47.146.60.177 (talk) 08:22, 16 February 2018 (UTC)

What 47 said. μηδείς (talk) 20:55, 16 February 2018 (UTC)

• The responses above are actually not correct. When the body temperature begins to drop, the initial response is vasoconstriction (shrinkage of blood vessels) that withdraws blood from the extremities and causes their temperature to drop. However, if your hand temperature drops below a certain point, a reverse response known as cold-induced vasodilation sets in, causing increased blood flow to the hands and consequent rewarming. The physiological factors that control this response are rather complex. If your body is thermally challenged, there may a cycle of alternation between vasoconstriction and vasodilation. For a recent review, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4843861/ (freely accessible). I have experienced this effect many times. Looie496 (talk) 21:25, 16 February 2018 (UTC)

Looie, you might just castigate the OP for a vague question, rather than the respondents. For example, it has been recently published that the increase in heart-attack deaths due to snow shoveling are not caused by the increased exertion, but due to vasoconstriction due to the cold, presumably felt mainly on the exposed face and maybe hands. The bottom line is that humans don't have countercurrent exchanges in their extremities like dolphins and sharks or reduced blood flow to their feet like snowbirds because we haven't had the need to evolve them within evolutionary time. Basically, Allen's Rule explains why we have more African than Eskimo basketball players. But any mechanisms more body-area specific than that are undocumented. The OP is asking why we don't have a superpower, and 47's answer of Blind Watchmaker is the proper response. μηδείς (talk) 22:30, 16 February 2018 (UTC)

It wasn't a vague question. 47's answer is philosophically valid, but in this case it is irrelevant. Incidentally, in the meantime I have located some relevant material on WP: Vasodilation#Cold-induced vasodilation and Hunting reaction. Looie496 (talk) 23:43, 16 February 2018 (UTC)

Looie496's answer is the one worth reading here, and includes a MEDRS-grade review link for this precise scenario. Good question, great answer! Wnt (talk) 17:36, 17 February 2018 (UTC)

Perhaps the confusion is on my part, but are we talking about a whole-body reaction, or a reaction limited to, say, just one digit? Given the Hunting reaction is hormonal, would it not effect the entire body through the bloodstream? In other words, if a person has one hand exposed to the cold and the other in a glove, will not bloodflow be affected in all the extremities, even though the exposed hand will obviously suffer the most due to lack of insulation? Or is it observed that blood flow only to the exposed limb is affected? μηδείς (talk) 17:44, 18 February 2018 (UTC)

@Medeis: I read down a bit in that article Louee496 posted, and it says that it is a very local reaction - cold induced vasodilation (CIVD) in the fingertips didn't affect muscle performance more proximally in the same finger, and nerve blockade did not inhibit it though local anaesthesia did. So it is apparently a local reflex, in which nitric oxide plays a role, triggered by I would presume some temperature threshold, which opens arteriovenous anastomosis (-es) to increase blood flow and warm the fingers. Wnt (talk) 12:44, 20 February 2018 (UTC)

I'll have to ctrl f for nitrous oxide. Assuming your are correct, it would seem my understanding above is incorrect. μηδείς (talk) 15:30, 20 February 2018 (UTC)

How is blood pressure is measured in a person without extremities at all?

Normally blood pressure is measured by application of sphygmomanometer on the upper extremities or in the lower in case that the upper are absent. But in case that a person doesn't have extremities when his BP is measured? 185.191.178.183 (talk) 21:15, 15 February 2018 (UTC)

Blood pressure measurement#Invasive. DMacks (talk) 22:50, 15 February 2018 (UTC)

Relative Density

I tried to solve a question from a textbook which went thus: A block of material of volume 2×〖10〗^(-5)m3 and density 2.5×〖10〗^(-3)kg/m3 is suspended from a spring balance with half the volume of the block immersed in water. What is the reading of the spring balance? Now, I know that the reading of the spring balance is the weight in water and that in the formula for upthrust, the volume immersed is half the volume of the block but when I substituted the figures, I didn't get it right. Please, what do I do? 41.58.233.194 (talk) 22:39, 15 February 2018 (UTC)

It sounds as if you had the right method if you included the density of water. The reading will be the original weight minus the weight of water displaced as long as this difference is positive. (Most spring balances don't register negatives.) What answer did you get? Is the block made of expanded polystyrene? Are you sure that there is a minus sign in front of the three? Dbfirs 22:54, 15 February 2018 (UTC)

The density of fresh water is about 1 x 10³ kg/m³ so a material with density of 2.5 x 10^—3 kg/m³ would not sink. In fact, such a material is much lighter even than air so is not credible. We can assume the minus sign in front of the three is incorrect. Dolphin (t) 06:13, 16 February 2018 (UTC)

A +3 brings it into possibility as a real material. Graeme Bartlett (talk) 06:58, 16 February 2018 (UTC)

I agree. Aluminum has a density of about 2.7 x 10³ kg/m³. Dolphin (t) 08:46, 16 February 2018 (UTC)

• Assuming the +3/-3 thing did not solve your problem, you would do well to present what calculations you have performed, instead of saying "I did not get it right when I substituted the figures". For an obvious example, if you said the textbook asked to multiply two numbers and when you did so the answer did not match the solution, how can we know whether the book or you made a mistake? Same thing here, with book wrong / calculus wrong / physics wrong as possible answers. Tigraan^{Click here to contact me} 20:07, 16 February 2018 (UTC)

To read about it see Archimedes' principle Graeme Bartlett (talk) 06:02, 17 February 2018 (UTC)

The first thing I'd do would be to get everything into grams and milliliters, simply because density in g/ml is easily comparable to water (which is 1 almost by definition at a certain temperature) for a sanity check, rarely going below 0.5 and never much above 20. And 1 ml = 1 cc (cubic centimeter); there are 10^6 ml in a cubic meter. That gives us 20 ml of a substance with a density of 2.5 g/ml*, which is easier on the eyes. Multiply those two out and you have 50 g of mass. Balance that against 10 ml of water (remember, 1 g/ml) and it should be clear you have 40 g net "weight" (i.e. mass of comparable weight). Which had better be the answer. Wnt (talk) 17:27, 17 February 2018 (UTC) *(assuming +3 - the original option gives a density a bit over 1/1000 that of air at sea level, which is 1.225 x10^−3 g/cm^3!)