The Chernobyl nuclear disaster was the worst in history. Here are 4 things you didn't know.

At the end of April 1986, a safety test at the Chernobyl power plant in Ukraine went very wrong.

While the town slept, a sudden power surge led to a series of explosions at 1:24 am – killing two instantly.

The first people knew of it was likely when a fireball erupted into the sky – described by some onlookers as not unlike fireworks.

“There was a heavy thud,” recalls Sasha Yuvchenko, who was on the night shift at the Chernobyl power plant at the time.

“A couple of seconds later, I felt a wave come through the room.”

“The thick concrete walls were bent like rubber. I thought war had broken out… Steam wrapped around everything; it was dark and there was a horrible hissing noise,” he told The Guardian.

The heat emitted from the power plant was so intense that firefighters called to the scene watched as their boots melted.

Though Yuvchenko didn’t feel anything at the time, within an hour he began vomiting uncontrollably. His throat hurt.

He was transported to Moscow, where the men either side of him died an excruciating death; burning from the inside out.

Over the next several days, a cloud of radioactive dust travelled across northern and western Europe, extending as far as the United States. Nuclear rain fell as far as Ireland.

An evacuation zone was established, 36 hours too late, with more than 68,000 people evacuated from a 30 kilometre radius.

Potentially deadly rain poured for the next eight days, as the power plant continued to burn.

Yuvchenko, along with hundreds of others, suffered acute radiation sickness, which begins with symptoms like nausea, vomiting and headaches.

While some recovered, over the next weeks and months, many died a slow and painful death.

Now a new documentary, Inside Chernobyl with Ben Fogle, which airs tonight on Channel Seven, will explore one of the worst man-made disasters in history.

Watch a sneak peek for Inside Chernobyl. Post continues below.

Here are four things that you might not know about the Chernobyl nuclear disaster.

The Chernobyl necklace

A Chernobyl necklace is a scar left at the base of the neck after the removal of the thyroid.

Rates of thyroid cancer increased tenfold after the Chernobyl disaster in Ukraine, and also skyrocketed in Belarus, Russia and Poland.

Radioactive iodine is accumulated in the thyroid gland, causing cancer and in some cases, death.

The Red Forest is one of the most contaminated sites in the world today

The Red Forest sits within the Chernobyl Exclusion Zone and radiation remains dangerously high.

Its name comes from the red-brown colour of the pine trees after they died following the Chernobyl accident.

Much of the fallout from the explosion was buried in the Red Forest, and therefore a great deal of the radioactivity exists within the soil.

Interestingly, the trees themselves never decayed, and now free from any human interaction, many species of wildlife, including wild boars and birds, occupy the forest.

The land in which the forest sits, including the old town, with schools, hospitals and amusement parks, is estimated to be unlivable for the next 150 years.

The death toll

Following two immediate deaths, and 29 deaths due to acute radiation sickness over the ensuing three months, researchers are divided on how lethal the Chernobyl disaster was long term.

The Chernobyl Union of Ukraine, a non-government organisation, estimates that the present death toll sits at approximate 734,000, with most due to related cancers.

Conversely, the World Health Organisation estimates that 30,000 deaths can be attributed to Chernobyl.

It is understood that more than seven million people were exposed to radiation as a result of the accident

The Elephant's Foot

The Elephant's Foot formed during the Chernobyl incident, and is a lava-like material created during a nuclear meltdown incident.

Its name is derived from its appearance, large and wrinkly, resembling the foot of an elephant.

It is extremely radioactive, and immediately following the explosion, just 60 seconds of exposure would kill someone.

Now, if an individual is exposed to the material for 500 seconds, or just over eight minutes, it is lethal.

The mass will be radioactive for the next 100,000 years.

Inside Chernobyl airs at 7.30pm tonight on Channel 7 and 7plus.

This article was originally published on May 6, 2019, and was updated on March 22, 2021.