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How real is the threat? -

Given the tense and seemingly intractable situation in the Middle East and Ukraine, the specter of a nuclear conflict has once again reared its ugly head. The world knows very well the consequences of an atomic bomb. And ironically, it was in Soviet Ukraine in 1986 that the world's worst nuclear accident occurred, at Chernobyl. The fallout was catastrophic, not least the dreadful effects caused by acute radiation syndrome. But what exactly is this sinister-sounding condition?

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What is acute radiation syndrome? -

Acute radiation syndrome (ARS)— often called radiation sickness—is an overwhelming illness caused by irradiation of the entire body (or most of the body) by a high dose of radiation in a short period of time.

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Ionizing radiation -

More specifically, ARS is a complex of syndromes developed in humans due to short-duration whole body exposure to ionizing radiation. It is a life-threatening condition.

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Lethal dosage -

Ionizing radiation exposure that results in radiation sickness is usually measured in a unit called the gray (Gy). ARS involves a total dose of greater than 0.7 Gy, or 70 rad (a rad being a unit of absorbed radiation dose).

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Other required conditions -

Other required conditions for ARS are the dose usually has to be external, the radiation must be penetrating, and the entire body affected. The dose must also be delivered within a matter of minutes.

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What causes ARS? -

Although radiation sickness is serious and often fatal, it's rare. Besides the detonation of a nuclear weapon, possible sources of high-dosage radiation include an attack or accident at a nuclear industrial facility. Another alarming scenario is the detonation of a conventional explosive device that disperses radioactive material (dirty bomb).  Pictured: a nuclear test in Nevada.

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The WWII atomic bombs -

The atomic bombing of Hiroshima and Nagasaki during the Second World War killed tens of thousands in the initial explosions. But many more would later succumb to radiation poisoning.

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Atomic aftermath -

In fact, within a few months of the attacks, between 90,000 and 166,000 people died in Hiroshima, while another 60,000 to 80,000 died in Nagasaki.

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Burns and radiation -

Sixty percent of immediate fatalities at Hiroshima were a result of burns. At Nagasaki, 95% of the population succumbed to burns. Additionally, exposure to radiation caused acute, near-immediate deaths by killing cells and directly damaging tissue. Longer-term effects of exposure included numerous cases of cancer, which caused mutations in the DNA of living cells.

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Chernobyl disaster -

The Chernobyl disaster in 1986 saw a catastrophic explosion throw clouds of radioactive material over the surrounding area. The official internationally recognized death toll was 31 people.

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Worrying predictions -

This figure was later revised by the United Nations, noting that 50 emergency workers died of acute radiation syndrome. Nine children later died of thyroid cancer. In 2005, the UN predicted a further 4,000 might eventually die as a result of radiation exposure.

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High death toll -

The UN's estimate proved accurate: a total of 3,940 deaths from radiation-induced cancer and leukemia were recorded among the 200,000 emergency workers who were at or near the scene over 1986-87.

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Classic ARS Syndromes -

So, what medical disorders develop as a result of radiation sickness? Hematopoietic syndrome, also known as bone marrow syndrome, will usually occur with a dose between 0.7 and 10 Gy (70–1,000 rads).

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Bone marrow syndrome -

The survival rate of patients with bone marrow syndrome decreases with increasing dosage. Cause of death is the destruction of the bone marrow, resulting in infection and hemorrhage.

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Gastrointestinal syndrome -

Typically, patients exposed to a radiation dose greater 10 Gy (1,000 rads) will develop gastrointestinal (GI) syndrome.

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Gastrointestinal syndrome -

GI syndrome is nearly always fatal. Destructive and irreparable changes in the gastrointestinal tract and bone marrow usually cause infection, dehydration, and electrolyte imbalance. Death is commonplace within two weeks.

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Cardiovascular/central nervous system syndrome -

A radiation dose greater than approximately 50 Gy (5,000 rads) will induce cardiovascular (CV)/central nervous system (SNS) syndrome.

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Cardiovascular/central nervous system syndrome -

All patients are expected to die from this syndrome, likely within three days of exposure due to collapse of the circulatory system and pressure buildup up in the cranial vault as a result of excess fluid content caused by edema, vasculitis, and meningitis.

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What are the symptoms? -

If you've had a mild exposure to ionizing radiation, it may take hours to weeks before any signs and symptoms begin. However, with severe exposure, symptoms manifest themselves within minutes to days after the event.

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Clinical stages -

ARS progresses through four clinical phases. The prodromal stage (N-V-D stage) occurs within hours of exposure. Nausea, vomiting, as well as anorexia and possibly diarrhea, are classic symptoms.

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Latent asymptomatic phase -

The latent asymptomatic phase can lull the subject into a false sense of security in that the patient looks and feels generally healthy for a few hours or even up to a few weeks. This phase generally begins hours to 21 days after exposure.

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Overt systemic illness phase -

In this stage, hours to fewer than 60 days after exposure, symptoms depend on the specific syndrome previously listed. At their worst, for example as a result of CV/CNS syndrome, patient symptoms will likely include extreme nervousness and confusion, nausea, vomiting, and diarrhea, hair loss, and burning sensations of the skin.

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Death or recovery phase -

Generally speaking, patients who do not recover die within several months of exposure. For those fortunate enough to survive exposure to ionizing radiation, the recovery process lasts from several weeks to up to two years.

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Treatment of ARS -

Treatment of acute radiation syndrome varies depending on its severity, but is generally about supportive care in a clean environment.

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Triage -

Treatment focuses on reducing and treating infections, maintaining hydration, and treating injuries and burns. Additional procedures may include blood transfusions, use of antibiotics, or stem cell transplant.

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Is radiation sickness contagious? -

If someone who has been exposed to a high dose of radiation is decontaminated—their clothes are removed and their body is washed— they’re not "contagious." And because it's internalized, you can't "catch" ARS.

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Contamination risk -

Beware, however. If someone who has been exposed to a high dose of radiation isn't decontaminated and you're near them, you're at risk for radiation exposure.

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What to do in an emergency -

While there's little you can do to prevent situations that lead to significant radiation exposure and radiation sickness, there are measures you can take in the event of an emergency. These include staying tuned to your radio, television, or smart device to be updated on what protective actions local, state, and federal authorities recommend.

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Preventative measures -

If you're at home, close all doors and windows, and shut off any fans, air conditioners, and heating units— anything that brings air in from the outside. Then move to an inner room or basement.

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Evacuation -

In the event of an evacuation order, follow the instructions provided by your local authorities. Travel lightly but consider packing sealed or canned food, plenty of bottled water, and necessary medicines.

See also: The minutes following a nuclear blast are vital to your survival

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