Nerve agents are a deadly poison, one that has until now been mostly considered to be a weapon of mass destruction. They are, according to one expert, "possibly some of the most dangerous things that humans have ever made, after the atom bomb". 

The science behind them demonstrates just how dangerous they can be for anyone who comes into contact with them, and difficult for the emergency services who treat them.

Nerve agents are the mark of a sophisticated attack. Really a name for a family of different chemical weapons, nerve agents are incredibly difficult to produce and to use, and if they have been intentionally used during the incident in Salisbury then it would mark an unexpected and profound change in the kind of deadly weapons on the streets of the UK.

They specifically attack the body's nervous system, forcing it into a painful and intense shutdown. They do so in a way that requires complicated processes, and the poison as a result must be created in highly specialised laboratories.

There is a huge variety of nerve agents, though some of them are more well-known, such as the banned VX nerve agent was used to kill the estranged half-brother of North Korea's leader last year in Malaysia. The police and government haven't said which of them was used in this attack.

But they all work on much the same principles.

They get their name from the fact that the chemicals involved block the mechanisms through which nerves usually transfer messages to organs. As such, it can cause profound and deadly effects in the people exposed to them, and symptoms can begin with strange behaviour and convulsions but can run all the way to death.

“All these chemicals work in much the same way by inhibiting an enzyme called acetylcholinesterase at the nerve junction (synapse)," said David Caldicott, a clinical senior lecturer in the Faculty of Medicine at Australian National University. "Under normal circumstances, acetylcholinesterase regulates the amount of the neurotransmitter acetylcholine crossing nerve synapses — so it effectively works as an off-switch.  Acetylcholine acts mainly on the body’s autonomic nervous system — the body’s involuntary nervous system — which controls things such as heart rate, respiratory rate, salivation, digestion, pupil dilation, and urination.

“You can imagine that if you block one of the major ‘off-switches’ of the body, and are left with all the lights turned ‘on’ all of the time, the body might run into trouble.  With an extremely rapid build up of acetylcholine in the synapse, things like secretions, respiratory problems, and muscular dysfunction can go on unattenuated.

“There are some commonly-used chemicals of this type – we use them in agriculture as organophosphate pesticides, but obviously these are designed to attack the nervous system of agricultural pests, not people.  The Germans invented a weaponised version in the form of tabun in the Second World War.  Sarin, in dilute form, was deployed in the Tokyo gas attacks, and VX on Kim Jong Nam in Korea.  That last example showed that with some ingenuity, versions of these chemicals can be used as personalised weapons and not just weapons of mass destruction.”

If someone is exposed to such an attack, it will become very clear very quickly.

"Nerve agents will act within seconds or minutes if inhaled and slightly slower if exposure is the result of skin contamination," said Hilary Walker, a former radiation scientist and health emergency planner. "Nerve agents affect the nerve junctions in the body and acute exposure leads to the symptoms that have been described such as apparent white eyes as the pupils are constricted, convulsions, drooling and in the worse cases – coma, respiratory failure and death."

Because of the power of such poisons, it is important that emergency services are careful and precise in the ways that they respond. There are systems in place to deal with such attacks, both to ensure the survival of anyone affected by them and to minimise the spread of the deadly chemicals.

"There are well rehearsed emergency procedures for dealing with such contamination and the emergency services obviously activated these to prevent spread – hence the decontamination activity with hoses," said Dr Walker. "There are antidotes to help reverse the effect of the gas which the emergency services hold but they need to be administered rapidly and by this time, I expect that the hospitalised patients might only be receiving symptomatic treatment."

Any possible recovery depends entirely on the kind of nerve agent used, and how quick the response is.

"It would depend on the severity of exposure but typically if the symptoms can be controlled until the agent is removed then recovery is good," said Chris Morris from the Medical Toxicology Centre, Newcastle University. "With the type of supportive care given in these cases, then there may be minimal long term effects if treatment was rapid and effective. There are some possible long term symptoms such as anxiety and depression but these are relatively non-specific."

The Independent 

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