NERVE agents are some of the most toxic substances unknown – even tiny doses can prove lethal.
What is a nerve agent and how do they work?
Nerve agents are a class of chemicals called organophosphates – meaning they contain phosphorous – that are extremely poisonous.
They attack the nervous system of the human body, which passes messages from the brain to other parts of the body, telling it what to do.
In order for those chemical messages to reach different parts of the body, they jump from one nerve to another.
Nerve agents interfere with those chemical messages, in such a way that just a short exposure will stop the messages being transmitted properly.
They do this by stopping the enzyme acetylcholinesterase functioning, which prevents muscles from relaxing.
It's one of the oldest nerve man-made agents and was originally produced as an insecticide in Germany in 1938.
However, it has gained notoriety through its use in warfare and was outlawed in 1997 by the Chemical Weapons Convention.
Witnesses to the deadliest nerve-gas attack in Syria in four years, last April, described seeing victims foaming at the mouth and suffering fits.
The highly toxic substance is lethal, even in the smallest of doses – and even more dangerous for children.
THE IMMEDIATE SIGNS A PERSON HAS BEEN EXPOSED TO SARIN GAS
Those exposed to a low or medium dose of sarin gas by breathing contaminated air, eating contaminated food, drinking contaminated water or touching a contaminated surface may experience symptoms within seconds, according to the Centers for disease Control and Prevention in the US (CDC).
In others it may take hours for symptoms to appear.
Those who have been exposed may experience:
- runny nose
- watery eyes
- small pupils
- eye pain
- blurred vision
- drooling and excessive sweating
- a cough
- tightness in the chest
- rapid breathing
- nausea and vomiting
- weeing more often
- slow or fast heart rate
- low or high blood pressure
Exposure to larger amounts of the nerve agent can have much more harmful, if not fatal, effects.
People may experience:
- loss of consciousness
- respiratory failure leading to death
Who is Sergei Skripal?
Sergei Skripal was born on June 23, 1951.
He was a Russian officer who was convicted in 2006 of spying for the United Kingdom.
Skripal was accused by Russian prosecutors of working for MI6 in the late 1990s and passing secrets to the British using a James Bond-style spy rock.
At the time, he was serving in the Russian Ground Forces and was nicknamed "the Spy with the Louis Vuitton bag".
What is the latest diplomatic situation around the Skripal 'poisoning'?
Wiltshire county's acting police chief Kier Pritchard said "around 21 people" including the Skripals have received medical treatment as a result of the nerve gas attack.
British Home Secretary Amber Rudd said enormous resources are being devoted to determining who poisoned Skripal, 66, and his 33-year-old daughter Yulia.
They were found unconscious on a bench, triggering a police inquiry headed by counter-terrorism detectives.
"The use of a nerve agent on British soil is a brazen and reckless act," Rudd told Parliament. "This was attempted murder in the most cruel and public way."
Rudd said Britain would respond strongly when it is clear who is to blame.
The Russian Embassy in London, which has mocked other British politicians for suggesting Russian involvement, tweeted that it agreed with Rudd: "First evidence then conclusions on Mr Skripal's case. Responsible political approach."
Prime Minister Theresa May said on March 14 the UK will expel 23 Russian diplomats after Moscow failed to explained how a Russian-made nerve agent was on British Soil.
On March 17 Russia announced they would also expel 23 British diplomats in retaliation.
Russia has also said it will close the British Council in Russia, which promotes cultural ties between the countries as well as the British Consulate in St Petersburg.
The British Council, the UK's international organisation for cultural relations and educational opportunities, said it was "profoundly disappointed" at being told to cease operations in Russia.
Russia said it was responding to "provocative actions" and "unproven accusations" by Britain.
Foreign Secretary Boris Johnson said on March 18 Britain had proof the Kremlin had been developing chemical weapons to assassinate its enemies.
He told the BBC's Andrew Marr Show: "We actually have evidence within the last ten years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination, but has also been creating and stockpiling novichok."
Was a nerve agent used in the Sergei Skripal poisoning?
The ex-KGB spy and his daughter were found slumped on a bench in a "catatonic state" while out in Salisbury on Sunday March 5.
They were "targeted specifically" when they were dosed by a deadly nerve agent, Assistant Commissioner Mark Rowley confirmed – it is now believed the nerve agent used was Novichoks.
Police also revealed that the first cop on the scene was also seriously ill following the incident and was taken into intensive care.
Are we on the cusp of WW3?
He was named three days after the incident as Sergeant Nick Bailey.
Russia's UK embassy have denied that their special services were involved.
Security sources told The Sun that the poison could only have been produced in a handful of labs worldwide - including the Russian government's notorious Yasenevo complex.
What advice is there for those affected?
Hundreds of people may have come into contact with the nerve agent.
Salisbury residents have been advised to take action to protect themselves.
Anyone who visited the pub or restaurant the pair visited last Sunday have been told to wash their clothes immediately and clean all jewellery, mobile phones, glasses and other items with antiseptic wipes.
People are then advised to wash their hands after cleaning any items.
Staff at Zizzi’s restaurant were told to destroy any clothes they had been wearing at the time and to visit their doctor for a health check.
Drinkers in the Mill pub were urged to take similar steps.
England's chief medical officer, Dame Sally Davies, estimated that around 500 people could have been affected in the time window.