What is sarin gas, how does the nerve agent kill you and when was it used in Tokyo?

THE nerve agent sarin is believed to have been used in the Assad government’s alleged chemical weapons attack on Douma.

It's claimed a helicopter dropped a huge barrel bomb containing the toxin on the Syrian town - leaving 70 dead and hundreds injured. But it's not the first time the nerve agent has been used in warfare - here's what we know...

What is sarin gas?

Sarin is a colourless and odourless agent that was outlawed as of April 1997 by the Chemical Weapons Convention.

It attacks the nervous system and causes incredibly painful and uncontrollable muscle contractions that make it impossible to breath, leading to death by asphyxiation.

In its purest form, sarin is estimated to be 26 times deadlier than cyanide.

Symptoms following exposure to sarin include a runny nose, tightness in the chest and constriction of the pupils.

Victims then continue to lose control of bodily functions and begin drooling, urinating, vomiting and defecating.

Muscle spasms then make breathing incredibly difficult before the victim becomes comatose and suffocates.

Antidotes like atropine and pralidoxime can help stop the deadly muscle convulsions if administered quickly after exposure.

In March 2018 former Russian spy Sergei Skripal and his daughter Yulia were poisoned in Salisbury, Wiltshire.

Counter-terror police believe the pair were "targeted specifically" when they were dosed with an unidentified nerve agent.

It has now been linked to an attack on the Syrian town of Douma leaving 70 people - including young children - dead.

Was sarin used by the Assad regime in Khan Sheikhoun?

Ruthless Syrian dictator Bashar al-Assad was accused of genocide after a sarin attack on the rebel town of Khan Sheikhoun on April 4, 2017.

Horrific footage and pictures showed dozens of victims — many of which were children — writhing in pain and frothing at the mouth, matching symptoms of sarin.

The Russian-backed regime was accused of massacring innocents in an attempt to drive out anti-Assad rebels from the north eastern town.

The health minister in Turkey, which treated many of the attack's victims and conducted autopsies on others, said test results conducted on victims confirmed sarin gas was used.

Recep Akdag was quoted by the as saying traces of sarin had been detected in the blood and urine of several victims.

French spooks have claimed to have proof that the Syrian government used chemical weapons in the deadly attack on its own people.

The country's foreign minister Jean-Marc Ayrault said on April 24 the chemical analysis of samples, compared to ones taken in alleged 2013 attack, "bears the signature" of President Bashar Assad's government and shows it was responsible.

French intelligence services found Syrian government forces could have launched such an attack by a bomber taking off from the Sharyat airbase.

"The regime's Air Force, is the only one with these aerial capabilities," Ayrault said.

Assad has repeatedly denied using chemical weapons.

In June the world's weapons watchdog confirmed the banned nerve agent was used in the attack.

What does footage of the Khan Sheikhoun gas attack show?

In May 2017, footage showed lifeless children piled in heaps in the aftermath of the gas attack in Syria.

Footage obtained by CNN showed dozens of children lying in pain – battling for life with every breath after allegedly being gassed by President Assad’s murderous regime.

In the clip, innocent youngsters struggle tbreatheth – some frothing at the mouth in the immediate aftermath of the gas attack.

Many victims can be seen lying motionless while others convulse as rescue workers desperately attempt to hose off the chemicals to stop their suffering.

In January 17, it was reported that Assad carried out a gas attack on the outskirts of Damascus which injured six people - including children.

People in the Eastern Ghouta region, which is under daily bombardment, reported a smell of gas after a missile strike.

How was sarin gas used by Aum Shinrikyo in Tokyo?

In 1995, doomsday cult Aum Shinrikyo carried out a brutal attack on commuters on the Tokyo subway.

Members of the cult inflicted injuries on over 6,000 people and killed 13.

The six members responsible for the attack were issued the death penalty and were placed on death row.

Their leader, Shoko Asahara, was hanged at the beginning of July 2018.

On Thursday, July 26, Justice Minister Yoko Kamikawa said the remaining six were hanged.