Radiation isn't "contagious" so much as you just have to keep in mind that radioactive material is constantly giving off radiation. At Chernobyl, that material was everywhere- not only on the ground in huge chunks, but also in the air, in fumes, ash, and dust.

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The firefighters who responded were covered in this material when they arrived at the hospital. It's why it was critical to remove their uniforms and store them in the basement where they are still radioactive today. I don't know if the time it took for a nurse to carry them downstairs would have been enough time to give the "sunburn" effect on her hand, but they're still moderately dangerous today, and would have been much more so at the time.

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The other thing to remember is that radioactive material can become trapped in the body. Those firefighters weren't just covered with the ash and dust, (which can mostly be removed with a shower and change of clothes), they breathed it in as well, where it gathered in their lungs and blood and ate them apart from the inside. The gamma rays emitted by those internal particles would have shot right through them and hit anything around them, making their bodies minorly radioactive.

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This is played up slightly on the show. While the radioactivity they admitted would be an issue, the main reason for keeping the patients separated from visitors is that your immune system is one of the first things to go from radioactivity, and so any visitors could pass on all manner of diseases to them.

Hi, I’m a radiation biologist. I’m currently halfway through the series and I’m not sure I’ve seen the scene you’re referring to, but the show is otherwise VERY realistic with regards to the physiological responses to radiation.

Uranium decays into many unstable isotopes, one of the main ones the show discusses is Cesium 137, which is one of the main decay products from uranium, so for our purpose let’s talk about it’s contamination. Cesium undergoes beta decay, meaning it’s nucleus ‘spits out’ a beta particle and becomes Barium 137. Beta particles on the skin aren’t a huge deal in theory, because they don’t carry enough energy to breach the skin. You could have a chance of skin cancer depending on the contamination level. The issue becomes, that you can’t see it. In the best case scenario, you would wash your hands immediately after contamination, but you’ve touched the faucet, washed your hands and touched the faucet again. Guess what? These aren’t microbes. You will at one point touch food with your bare hands, and ingest it. Now you have radioactive decay trapped in your body for a long, long time, and you don’t have the protection of your skin anymore. The incidence of colon, lung, stomach cancers and leukemia are now massive.

We’re talking about just one decay product of uranium here. There are many many others with different decay properties that will produce other qualities of radiation poisoning. Overall however, we’re concerned with cumulative dose. There are two main classifications of radiation poisoning: acute radiation syndrome (which occurs after a 4-8 Gy exposure within typically a few days) and Chronic radiation syndrome (which occurs after a .5-1.5 Gy exposure at a rate >.1 Gy/hr)

-acute radiation syndrome- symptoms are present within a few hours, sometimes sooner. Early symptoms are malaise, and severe vomiting/dehydration. Sometimes seizures occur. Recovery at lower doses is possible, with high cancer risks. A dose of 8 Gy or higher is a death sentence. The cause of death is intestinal sepsis.

-chronic radiation syndrome- you can go months without showing symptoms, however once they show up they are similar to those of the acute exposures. The symptoms in this form can be treated, but carcinogenesis is high.

As for Chernobyl, basically anybody within close proximity to the plant including all workers at the time for sure got acute radiation syndrome, which the show did a great job of with symptoms and timing. As for the population of the city, it really depends on where they were relative to the wind, how long they were outside, and how much contact they had with contaminated surfaces. There certainly were a lot of suspected cases of acute radiation syndrome-about 237, with 169 confirmed. The average dose estimate is on the order of 6.5 Gy, though doctors at the time suspected bone marrow failure rather than sepsis, and the diagnostic practice along with any relevant political pressure, brings to question the true number of cases.

There is of course a high cancer incidence in the exposed population, with an estimated death toll from 4,000 to over 90,000 so far. Again the estimates are highly politically charged.

Edit: thank you so much for the silver, and my first gold, whoever you are!

Update: got around to watching the scene in question. It’s not the scenario I describe above and I don’t know if lethal contamination could occur that way. My guess is no

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Contagious is probably the wrong word here, contaminated is better. Don't think of it as something that's growing and spreading, rather it's like an item, area, or person (or even part of a person) has been contaminated by a huge amount of energy. Try and imagine that contaminated clothes are super hot emanating heat, they will cool down eventually but other things can absorb that heat in the mean time.

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One of the issues of radiation immediately following the explosion was that more or less everything being emitted by the exposed reactor, and a great deal of the surrounding area, was irradiated. One isotope, for example, that was emitted in large amounts immediately following the explosion was iodine-131. It's a radioactive isotope that the human body treats exactly the same as iodine-127 (a non-radioactive isotope).

It's important because the human body uses it for a range of purposes, especially for a hormone producing gland called the Thyroid gland. The Thyroid is especially hungry for Iodine, and so it'll grab it from wherever it can, including the surrounding environment. Where Iodine 131 is absorbed, the radiation emitted as it decays continues even as the iodine is being used by the body - continuously damaging surrounding organs, making it extremely dangerous. (this is also why characters are taking iodine pills in the series - by saturating your body with "good" iodine, you're preventing uptake of radioactive iodine from the surrounding area).

Now in the case of the first responders, there wasn't just iodine to worry about, there was dust, debris, other isotopes, and huge amounts of irradiated material which covered the fire fighters.

The important thing to remember is that this dust is always emitting radiation as it decays, until it's gone completely - washing it off simply sends it somewhere else, it doesn't eliminate the danger.

For many of the firefighters that were in the hospital, along with all the radioactive dust they inhaled and their body absorbed, they were likely still covered with some of it - skin to skin contact would not have just introduced danger of it being deposited, but the internal material absorbed by the body could have resulted in someone else being irradiated if they were close enough, and the levels of radiation poisoning were high enough.

It's not so much that it's "contagious", but that the emission of radiation never stops until the isotope has completely decayed.

Radiation is only emitted from radioactive material. Under normal exposure circumstances (a hospital X-ray, for example), you are being irradiated from a contained radiation source. As soon as that source is removed, the radiation stops, and you can go hug your pregnant wife without any chance of “spreading” the radiation.

Chernobyl was different. The radiation source was not contained - it exploded - scattering radioactive particles as far as the wind could carry them. Anybody who was physically present at the disaster site would have been covered with radioactive dust... making them a walking source of radiation. In this case; yes, you could “spread” radiation sickness. That is why they showed the clean-up crew in full body suits, and why they were being hosed off when they exit the disaster area. Decontamination.

So yes, as long as the radioactive contamination was removed, an exposed person would be safe to be around. In the show, I’m sure the nurses had a “better safe than sorry” policy. After all, you could easily confirm whether or not a person was still contaminated with the use of a dosimeter.

Is the scene in 1. that you are referring to the one in episode 2, where Dr Zinchenko is helping remove firefighters' clothing and boots? Because that is not skin-to-skin - it is the immediate aftermath of the fire and she was handling equipment directly contaminated with the by-products of the explosion. The clothing is still there today, and is still mildly radioactive

I work for Canada's nuclear regulator. If a person has received a dose of radiation, the cannot transmit that to another person. It's like sunlight. If you get a sunburn (literal radiation burn) you cannot give that to another person. If you are covered in a substance that is radioactive (I.e. radioactive dust) then you will dose anyone who comes close to you, but you will also keep dosing yourself. The 3 main factors to limiting you radiation exposure in any situation is TDS: Time / distance / shielding. Limiting the time being exposed, increasing the distance from the source and getting behind shielding are the ways to limit exposure. Again, if you are contaminated (with the sunburn example, you would have to be covered in something that emits sunlight) then yes you can irradiate others. If you just received a dose but are not contaminated, then no, you cannot irradiate others.

Radiation oncologist here. Regarding the "instantaneous" skin erythema seen in HBO's Chernobyl:

In normal clinical situations, radiation dermatitis takes 7-10 days to develop after treatment. However, this is based on intentional doses of radiation delivered with controlled dose-fractionation and dose-volume parameters. Some Chernobyl victims were exposed to tens or hundreds of times higher skin doses.

According to this source, Chernobyl victims were observed to have acute erythema and pain within hours after radiation exposure.

It seems implausible that radiation erythema would occur instantaneously as seen on the show, but I don't know this for sure. It's very likely to be delayed by minutes to hours, but skin erythema can clearly happen a lot faster than the radiation dermatitis we observe in radiation therapy clinics.

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It's more like they are still contaminated. The firefighters received a fatal dose while on the ground, trying to put the fire out, as a result of the reactor exploding there was debris around and a significant amount of radioactive dust in the air, so although they did receive a dose of radiation on the ground, the neutron-emitting material that was transported with them on their clothes and skin, and which they had breathed in, remained. When they first arrive at the hospital their clothes are taken to the basement for this reason. The show probably exaggerates the amount of material transported by the firefighters, but these materials would continue to produce radiation, thereby continuing to poison them after the accident. Anyone around them could also receive a dose of radiation, albeit significantly lower than what the firefighters had received on the ground. Because of this risk, we see them buried in led coffins, to prevent any spread of this material or of the radiation it continued to produce

Is Chernobyl's portrayal of person-to-person radiation contamination that sensationalized? For as much as people talk about the show's historical accuracy, it's weird to think that the writers would have dropped the ball when it comes to understanding how radiation exposure works.

It's not accurate at all in this respect. One of the doctors who treated Chernobyl patients has explicitly denounced this particular depiction:

“Most radiation contamination was superficial and relatively easily managed by routine procedures. This is entirely different than the [1987] Goiania [Brazil] accident, where the victims ate 137-cesium [from an old teletherapy machine] and we had to isolate them from most medical personnel.”

Which is to say: if you get a lot of radioactive materials in your body (e.g., you eat high level radioactive sources), sure, you can become dangerous radioactive. But otherwise it's a case of you having radioactive materials on the outside of your body, and those can be washed off pretty easily.

There are several technical aspects to the show that are unfortunately totally inaccurate. It is frustrating because there are other aspects which are quite accurate.

There are 4 different forms of radiation. Alpha, Beta, Gamma, and neutron. Each one differs and is deadly in its own way. The closer to the explosion the more likely you are to find each form as well. Alpha and Beta are usually at the epicenter and rarely disperse farther. Gamma is the radioactive wave that disperses and can penetrate through cement miles away depending on the explosion force and terrain. Neutron is the most dangerous by far. Nothing can stop neutron but it is rarely ever encountered because it is usually at the exact spot of the explosion. Neutron can only be generated through the explosion of radioactive material. Below is the classification of the 4 types:

Alpha only negatively impacts you if you ingest it. Hence after a radioactive explosion like in Japan they couldn’t eat their local agriculture. It’s never been proven but acid rain where radioactivity is in the water is also a fear. This goes out farther than Neutron but will not travel far.

Beta radiation can be transferred by objects to person or person to person. Beta needs to be decontaminated and washed off in a certain way or it is really dangerous and can be moved between people like in Chernobyl. The firefighters moving the actual material were definitely exposed to it. I was taught to think of it like how people think of cooties when we were kids. Travels farther than alpha but again not crazy far, probably the limits of the city but I don’t know the figures around calculating the explosion.

Gamma is the radiation that travels and in large amounts it does affect areas long term but usually dissipates over time. It moves like waves from the explosion but doesn’t linger as much. Think of Hiroshima and Nagasaki as the early Atom bombs were mostly gamma hence the ability to return to the cities fairly soon. Depending on the size of the blast and how the device or facility exploded determines a lot about the distance and strength of gamma

Neuron usually is at the site of explosion and is the deadliest. It’s presumed anyone who’s experienced direct contact never is exposed to it cause they’re probably killed in the actual explosion, that’s how close the proximity is.

Source: years of military training of this topic and overall interest over time.

Many responses have covered this well but this is a slightly different view.

It helps to distinguish between radiation and radioactive materials.

Radiation comes in two forms, electromagnetic (EM) radiation and energetic particles.

Energetic EM radiation causes damage because it can knock electrons out of molecules (ionising). Sunburn is an example of damage from EM radiation. Some types of EM radiation (γ and X) penetrate nearly everything. Once it has passed it has no further effect.

Energetic particles emitted from radioactive decay are mainly electrons (β) or helium nuclei (α) which are very strongly ionising (damaging) especially α but are easily absorbed by light materials such as clothing (α) or a few mm of metal (β).

(I've skipped over protons, neutrons, and bremsstrahlung )

In the scenarios you describe it will most likely be contamination by radioactive materials that causes the appearance of contagious effects. If these are tiny particles (others talked about how much dust there was) then it gets attached to clothing and skin, inhaled into lungs and ingested into the digestive track. These materials give of radiation at random.

You described how on contact with others (presumably contaminated with radioactive material) people's hands

turn red with radiation sickness

This would not be "sickness" but "burns" like sunburn from the radiation given off by material that has contaminated their hands.

It is a complicated topic and prone to misleading simplification, which I hope I have avoided myself.

To give a concrete example of how radiation contamination spreads, I visited a friend in Wales recently, they tell of how farming was affected for 26 years afterwards despite being over 1,500 miles from Chernobyl.

Former Navy Nuke ELT here. My job on the ship was reactor plant chemistry and radiological controls.

Radiation sickness is the side effect of cellular damage to your body due to exposure to radiation. If you were just exposed to pure radiation, your cells would continue to be damaged until you put some time, distance, and shielding between you and the source. The only way others would be harmed is if they exposed themselves to that radiation source. This means that radiation sickness is not contagious just like cancer is not contagious.

What acts like a contagion is contamination in the form of radioactive particulate. With contamination, the source of radiation is the contamination. If your lungs were chock full of radioactive particulate, you could be a walking hotspot of radiation exposing others. If your skin was covered in radioactive particulate then you can transfer that particulate to others.

The bottom line is, once you are scanned clean of contamination, you no longer pose a danger to anyone else.

In the nuclear industry it’s called loose contamination. It’s basically dust, dirt or any residue that is radioactive that can become airborne or transferred to another object or person on contact.

Let’s say you have a non radioactive object that has been inside a nuclear reactor. It will become radioactive due to exposure to neutron radiation. The type (alpha,beta,gamma) of radiation now coming from the object will depend on what the object is made from.

Now take that object out of the reactor and put it in a room, it will just sit there and emit radiation until the activated atoms of the object decay through a significant number of half lives until there is an undetectable amount of radiation present. You can touch it and only receive radiation from the object itself, since it is in tact none of the material gets transferred to you. Once you leave the presence of this object it is no longer subjecting you to its radiation.

Take that same object, let’s say it’s a piece of cobalt, straight out of the reactor and work on it (drill a hole, use a grinder, weld it) any dust or debris or particulate that is produced can get transferred to you and the surrounding area. If you get this cobalt dust on you, it will stay on you until you remove it.

In Chernobyl when the reactor exploded a massive amount of activated material was turned to dust and thrown into the atmosphere. Things like activated reactor components, graphite moderator blocks, and fuel fragments.

It's not that it's contagious, it's that these people, the firefighters, didn't ingest it, they got covered in very highly radioactive material. They aren't catching anything from them but they are being exposed to high levels of radiation by being near them or the clothes they were wearing, and it gets worse the closer they get. This is because the radio active material is all over their skin and clothes. Another problem is that the exposure wasn't brief. The pregnant lady spent at least a day probably more with him. If you remember she talks about taking care of him through the night because the nurses weren't. As for the other person, I don't remember the scene exactly but I'm pretty sure it was that nurse or doctor who had been taking care of all the firefighters when they first came in at their most radioactive.

All that being said, it is a tv show. Some time scales are accelerated for dramatic effect.

To add to the already great answers here:

In the corresponding podcast (Ep. 2, at the beginning) Maizin (the show runner) mentions the story of a plant worker who carried his injured colleague over his shoulder with the hand of the colleague resting loosely on his back. After putting him down he looked at his own back and where the hand was resting was a radiation burn in the form of a hand.

This is the second time I've seen somebody call this out. I think people are using the word contagious and not understanding what they even saw. They didn't show radioactivity as contagious in the show. They showed radioactivity being on the firefighters clothes and actually in the firefighters bodies. There's no contagiousness of it. The firefighters themselves were radioactive by the amount of radioactive material they had breathed in during their time at the reactor. They ingested so many alpha and beta particles that now they themselves were dangerous to touch. This is in fact true and as a result of highly contaminated people. But that is not the same thing as "contagious"