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Can you safely heat people with microwaves?

Sometimes, when I’m really cold, it can take over an hour to warm me up, even with a heating blanket. The quickest solution, a hot shower, feels really inefficient with all the heat going down the drain.

That got me thinking about microwaves. They heat food (partly) from the inside, contrary to simple infrared radiation.

Could we safely do that with people?

I found a Reddit thread where a non-lethal weapon and people getting eye damage because they stayed too long in front of a radar dish.

Could some sort of device be made that would warm specific areas (say, a hand or a leg) without endangering sensitive areas like the eyes?

Would it actually warm someone up from the inside? Would it be possible to make it safe?

Would it present advantages in cases of hypothermia, compared to heated IV fluids?

CaliforniaSober , (edited )

Look up neutron bombs.

Admetus ,

Microwave ovens work on resonance, so I’d be worried about heating up parts of the body more than others. Without resonance you wouldn’t have effective heating so it would be a bit complex to warm all parts of the body equally.

dsilverz ,
@dsilverz@thelemmy.club avatar

Raytheon, Epirus and other manufacturers already have “human microwave heaters” and they’re mobile, except that they’re called “Active Denial System”.

Hawke ,

Short answer: yes.

Eiri OP ,

Holy crap that looks satisfying

Doolbs ,

The Human Heater from Silicon Valley.

CountVon ,
@CountVon@sh.itjust.works avatar

One of my grandfathers used to work for Nortel. One of the projects he worked on was the Trans Canada Microwave, which was a microwave relay system built in the '50s to carry television and telephone signals across Canada. The towers were installed all over Canada in remote locations and high elevations. Maintenance on the system could be required even when the weather was bad. My grandfather told me that the engineers who worked on the towers would sometimes stick their hands in front of the microwave emitters to warm them up. It’s anecdotal, but I’m relatively confident that it’s theoretically possible to warm people with microwaves.

Big caveat, though. Those engineers knew how powerful the emitters were, they knew that microwaves are not ionizing radiation and thus posed no cancer risk, they knew roughly what percentage of their hands was composed of water, and thus how much heat energy their hands would absorb from the emitters at a given power level. That’s the only reason they were willing to do it, well that and they were probably the kind of people who got a kick out of doing something that would appear insane to most of the populace.

It seems very unlikely to me that a microwave system could be turned into a safe people-heating system for at least the following reasons:

  • Feedback loops. All modern HVAC works on feedback loops. Your thermostat detects that the temperate is cold, it fires up your furnace / heat pump / electric baseboard / whatever and produces more heat. When the thermostat detects that the temperature has reached the set-point, it shuts off the heat. Current thermostats would not be able to detect the effect of microwave heating, which prevent the establishment of a feedback control loop.
  • Uneven heating. Things with more water will heat up a lot faster than things with little water. This is usually fine when microwaving food since most of our food is water, in varying concentrations. If you’re heating up a burger in the microwave, you can put the patty in by itself for a minute, then put the bun in for 15 seconds, then reassemble a burger that doesn’t have a cold patty or a stiff overcooked bun. If you’re heating up a person, you can’t ask them to take out their almost-entirely-water eyeballs to ensure they don’t overheat.
  • Failure conditions. If your heat gets stuck in the on setting, the maximum result is probably that your house will get sweltering hot but not hot enough to kill you in a moderate timeframe. Depending on power levels, a microwave heating system could internally cook people in their sleep if it entered a failure mode where the heating got stuck in the on setting.
  • Efficiency. It takes a considerable amount of power to run even a small microwave, and that’s blasting microwaves into a relatively tiny cubic area. Trying to heat people would require microwaving a much larger volume, and said volume would also be moving around. Trying to emit microwaves in even a house-sized volume would probably be prohibitively costly.
  • Interactions with metal and other objects. Microwaves can create intense electrical fields around metal objects, and those can become intense enough to create plasma and electrical arcs. Hell, you can create plasma in your microwave with two grapes. Blasting microwaves into a large volume with unknown contents would be a great way to create an unexpected fire.
Eiri OP ,

Holy crap, i was imagining some sort of microwave bag or belt you could put the freezing body part in.

Your thing about metal objects made me think about what would happen to a hand full of rings stuck in there. Yeesh.

dual_sport_dork ,
@dual_sport_dork@lemmy.world avatar

TL;DR: Yes, but the ways in which it could go wrong if done incorrectly mean it is essentially guaranteed to be deemed never worth the risk.

Microwaves don’t heat food “from the inside” necessarily, but from a depth that the microwaves manage to penetrate into it. In the cases of the microwave frequencies used in domestic appliances, that translates to around 4cm, give or take a small amount. So you would theoretically be able to heat your subject subcutaneously down to that depth. Note that the surface would also get heated in the process. There are fancy formulae to determine what the graph looks like of energy imparted to water (for sake of argument) in what proportion at what depth, but I won’t get into that here. This may or may not be useful for some manner of non-supervillian related purpose, but I can’t think of what that might be off the top of my head.

If the question is, “does exposure to microwaves cause any kind of freaky health effects, cause cancer, or induce mutant superpowers over and above just heating up the subject,” the answer insofar as we can determine is no.

However, it is absolutely possible to cause a wide array of boring old regular injuries up to an including death by, not to put too fine a point on it, cooking people. It’s very easy to bring water and other liquids to a boil by heating via microwave, for instance, and doing that inside the subject’s skin is probably a recipe for disaster. You would have to be able to accurately control the amount of energy imparted on the subject, and you would need some compelling reason why you’d have to do that via microwave versus innumerable more traditional methods many of which are inherently fail-safe, like just immersing them in warm water.

Brokkr ,

Have you seen the Tom Scott video?

If it works for hamsters may be a properly built one could work for people, but there’s absolutely no ethical way to test that.

Tylerdurdon ,

Would you feel warmer if you were cooked? I’m not sure you’d feel much of anything, myself.

BearOfaTime ,

Infrared heaters already exist. They’re used in spaces where you want to only heat people and not the air, like shops.

They’re very effective. You know when you walk under them.

nobleshift ,
@nobleshift@lemmy.world avatar

Keep us posted …

spittingimage ,
@spittingimage@lemmy.world avatar

I once did three weeks of IT work in a forensic pathology lab.

Spoilered for disturbing detailsThey had a microwave - a regular microwave oven designed for use in the kitchen. They used it for degloving hands. That means they put the severed hand in the microwave and heated it until the fatty layer under the skin softened. That way the skin could be slid off mostly intact. I absolutely would not do this to a living person. It doesn’t seem healthy.

CaptDust ,

Welp, that’s enough internet for today. Imma head out.

The_Picard_Maneuver ,
@The_Picard_Maneuver@lemmy.world avatar

I’m choosing not to open the spoiler tag because of this comment. Thanks for taking one for the team.

PlasticExistence ,

Well your loss, my friend! That was a heartwarming anecdote about coworkers coming together to support each other in hard times and how their their microwave enabled that. I don’t know why it was hidden.

The_Picard_Maneuver ,
@The_Picard_Maneuver@lemmy.world avatar

https://c.tenor.com/s1wnF2DiWA0AAAAC/tenor.gif

PlasticExistence ,

https://lemmy.world/pictrs/image/7c124be5-3638-40f2-9c22-024dc96cb821.gif

bhamlin ,

Lucky you; spoiler tag was broken when I got to it. I have seen a thing I wish to unsee.

Uli ,

Copy that, see you later. Anyway, here’s some more internet for you:

www.youtube.com/watch?v=3hBRxwQXmCQ

18_24_61_b_17_17_4 ,
@18_24_61_b_17_17_4@lemmy.world avatar

What’d that smell like?

bane_killgrind ,

What if I wanna undress

Kolanaki ,
@Kolanaki@yiffit.net avatar

Yes. Kinda? There are microwave guns designed for crowd control. I don’t know how commonly they’re used if they are even out of an experimental stage though. They’re not gonna kill you, but they will make you uncomfortable.

slazer2au ,

Safely? Not likely. We have rules for Electromagnetic radiation for a reason.

givesomefucks ,

Microwaves work by exciting water molecules.

Put an empty bowl in and it comes out cool to the touch.

A bowl of soup and the bowl is crazy hot, because the soup warmed the bowl.

Heating a person with a microwave would make us pop as the water inside heats up faster than everything else. And blood is pretty fucking similar to water…

You could try it with an incredibly low dose, but you’d have to do it in carefully measured bursts. Even for hypothermia, warm baths are dangerous because the increase in body temp is too sudden and can fuck up the heart.

So there’s a whole bunch of risks and you’re still limited to what won’t freak out your heart. Warming just one part warms up the blood that’s there and send it through the cold parts. Like how you’re not supposed to immediately add water to a radiator after a car overheats. The thermic shock can cause massive problems.

So we could…

It just wouldn’t make any sense to do it

explore_broaden ,

Microwaves don’t just heat water molecules, although due to density they absorb a large amount relative to many other substances. Also since humans are mostly water, the heating should be even enough to not be quite as problematic as you describe. Some sensitive areas like eyes are an issue, but otherwise it’s possible a low enough dose could warm someone a couple of degrees without causing any harm.

givesomefucks ,

Bruh, it’s the heart that’s the issue…

The thermal stress is too great. Microwaves would heat the blood up, which within seconds would go into a cold heart

It’s why they won’t use a warm bath to hear someone up who’s dangerously cold.

Slow and steady is how you do it. So even if you used microwaves, it would be limited to pretty much the same delta temp as other methods.

It’s all risk no reward

explore_broaden ,

But wouldn’t the microwaves also warm the heart? There’s no reason a microwave at the right power couldn’t slowly heat someone up. I don’t think the OP is asking about someone who is dangerously cold either, so the extreme care that needs to be taken when someone is in serious danger due to how cold they are might not be relevant in this case.

givesomefucks ,

But wouldn’t the microwaves also warm the heart?

If it’s pointed at it…

But you know what heats a cold heart faster than blood from another body part?

Direct exposure to microwave radiation…

That’s what I mean, there’s a safe temperature differential to warm the body, and even stuff as conventional as a warm bath or hut tub can be too much.

If we shoot microwaves at a heart, the heat increase is waaaaaaaay above the safe limits.

So if someone was in a situation where the only method was microwave radiation, it wouldn’t result in an increase in heating without running serious risks.

There’s just no benefit and it introduces insane risks if you tried to do it slow enough.

explore_broaden ,

My point is that the heat increase of the heart doesn’t have to be so insane. If someone was designing a microwave human heater they would have to make the power level such that it would always result in a safe rate of temperature increase. Obviously using an off the shelf food microwave wouldn’t work.

Is heating someone too quickly a concern if they don’t have hypothermia? Like if I’m sitting round in my house and start to feel cold, and I get in a hot bath, it’s not going to heat me up too fast, right?

Eiri OP ,

Thanks. Your comment is the one that helped me understand the limitations the most.

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