“It’s not hard to make sarin. You could mix it in the backyard. Two chemicals melded together.” — Seymour Hersh interviewed on CNN, December 9, 2013.

The idea that the chemical warfare agent, sarin, is easy to make is central to Seymour Hersh’s claim that the August 21 attacks killing hundreds of Syrians could have been carried out by the rebel group, the Al Nusra Front. (With unquestioning confidence in the reliability of his source(s), Hersh rests this claim on classified intelligence reports none of which he claims to have seen.)

Hersh’s backyard sarin production appears to be concocted from fiction. The only non-state actor known to have engaged in large-scale sarin production was the Japanese cult, Aum Shinrikyo. They invested $30 million in this endeavor which included the creation of a production facility.

The plant was a free-standing three-story building, staffed by workers with chemistry and chemical-engineering expertise who designed and built proper process controls. It was a complex, expensive operation, and its production capacity was approximately 2 gallons of sarin per batch.

Dan Kaszeta, a former officer in the U.S. Army Chemical Corps and former member of the U.S. Secret Service, estimates that the August attack would have required one ton of sarin — far more than Aum Shinrikyo was able to produce even with their dedicated facility.

Hersh says “there’s two inert substances” used for producing sarin. But Kaszeta points out that the precursors are neither easy to obtain nor inert. Methylphosphonyl difluoride is both reactive and corrosive and as a Schedule 1 substance under the Chemical Weapons Convention, is tightly controlled.

Even if the precursors are obtainable, anyone trying to make sarin in an at-home lab would face a challenge because, in many ways, the ingredients are more dangerous than the final product. An intermediate step in the production, for example, requires the use of hydrogen fluoride gas at a high temperature. Hydrogen fluoride is nasty stuff, and a lot of it is needed to make sarin. Even in its more stable liquid form, the smallest leak would destroy all the chemistry equipment and almost everything else in a modern kitchen. Anyone trying to combine these ingredients may kill or seriously harm himself and anyone nearby.

Amy E. Smithson, a researcher on chemical and biological weapons at the Henry L. Stimson Center in Washington, who investigated the Aum Shinrikyo attacks in Japan emphasized that in assessing the capacity of non-state actors to use chemical weapons there is a huge gulf between the “theoretical possibility” and the “operational reality.” And keep in mind that Aum Shinrikyo was operating in the tranquility of peacetime Japan — it’s obstacles were all technical with none from the battlefield.

“By almost any standard, Aum was a terrorist nightmare – a cult flush with money and technical skills led by a con-man guru with an apocalyptic vision, an obsession with chemical and biological weaponry, and no qualms about killing,” Smithson writes.

But by almost any standard, Aum Shinrikyo’s chemical weapons program, and an earlier attempt to develop biological agents, failed to produce anything close to the killing power the group desired.

The cult started off by trying to simply acquire chemical weapons from a rogue U.S. operation peddling nerve gas on the black market – but found itself dealing with a front for the U.S. Customs Service.

For terrorists, the lesson here is plain: Worldwide law enforcement and intelligence agencies represent no small obstacle.

When Aum Shinrikyo then turned to producing its own stockpiles of chemicals in 1993, it soon ran into complex problems involved in dispersing nerve gas in ways that kill lots of people.

“Weaponizing” chemical agents requires munitions that disperse the substances in droplets, which can kill on skin contact, or vapor, which can be lethal if inhaled. But most explosive devices within the technological reach of terrorists would either destroy most of the chemical agents upon detonation or fail to effectively disperse them.

Spraying also can effectively disperse chemical agents. But most experts believe that 90 percent of any agent sprayed outdoors will not reach its intended targets in lethal form, given the vagaries of temperature, sunlight, wind and rain. Pumping chemical or biological agents into a building’s indoor ventilation system is no easy task either, requiring detailed knowledge of how air is distributed from floor to floor.

In Aum Shinrikyo’s first attempt to attack a rival group by spraying sarin gas from a moving van, Smithson notes, “the sprayer completely malfunctioned and sprayed backwards.” The second attempt ended up exposing the group’s security chief to the toxic nerve agent.

When the cult finally executed its climactic subway attack, its dispersal method of choice was poking holes in plastic bags with sharpened umbrella points. Noxious fumes then seeped from the bags into the subway cars.

The resulting chaos and death shocked the world. “Rescue crews found pandemonium, with scores of commuters stumbling about, vision-impaired and struggling to breathe,” Smithson writes. “Casualties littered the sidewalks and subway station exits. Some foaming at the mouth, some vomiting and others prone and convulsing.”

But in the final analysis, she notes, 85 percent of the 5,510 people treated at Tokyo hospitals and clinics were simply worried, not harmed. Twelve ultimately died from sarin exposure, about 40 others were seriously injured, and slightly less than 1,000 were “moderately ill.”

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