is useful for detecting the recent deployment of sarin as a weapon). impa then degrades into methylphosphonic acid (mpa), which can also be produced by other organophosphates. sarin with residual acid degrades after a period of several weeks to several months. the shelf life can be shortened by impurities in precursor materials. according to the cia, some iraqi sarin had a shelf life of only a few weeks, owing mostly to impure precursors. along with nerve agents such as tabun and vx, sarin can have a short shelf life. therefore, it is usually stored as two separate precursors that produce sarin when combined. sarin's shelf life can be extended by increasing the purity of the precursor and intermediates and incorporating stabilizers such as tributylamine. in some formulations, tributylamine is replaced by diisopropylcarbodiimide (dic), allowing sarin to be stored in aluminium casings. in binary chemical weapons, the two precursors are stored separately in the same shell and mixed to form the agent immediately before or when the shell is in flight. this approach has the dual benefit of solving the stability issue and increasing the safety of sarin munitions. history sarin was discovered in 1938 in wuppertal-elberfeld in germany by scientists at ig farben who were attempting to create stronger pesticides; it is the most toxic of the four g-series nerve agents made by germany. the compound, which followed the discovery of the nerve agent tabun, was named in honor of its discoverers: chemist gerhard schrader, chemist otto ambros, chemist gerhard ritter, and from heereswaffenamt hans-jürgen von der linde. use as a weapon in mid-1939, the formula for the agent was passed to the chemical warfare section of the german army weapons office, which ordered that it be brought into mass production for wartime use. pilot plants were built, and a high-production facility was under construction (but was not finished) by the end of world war ii. estimates for total sarin production by nazi germany range from 500 kg to 10 tons. though sarin, tabun and soman were incorporated into artillery shells, germany did not use nerve agents against allied targets. adolf hitler refused to initiate the use of gases such as sarin as weapons. u.s. honest john missile warhead cutaway, showing m134 sarin bomblets (c. 1960) 1950s (early): nato adopted sarin as a standard chemical weapon, and both the ussr and the united states produced sarin for military purposes. 1953: 20-year-old ronald maddison, a royal air force engineer from consett, county durham, died in human testing of sarin at the porton down chemical warfare testing facility in wiltshire, england. ten days after his death an inquest was held in secret which returned a verdict of misadventure. in 2004, the inquest was reopened and, after a 64-day inquest hearing, the jury ruled that maddison had been unlawfully killed by the "application of a nerve agent in a non-therapeutic experiment". 1957: regular production of sarin chemical weapons ceased in the united states, though existing stocks of bulk sarin were re-distilled until 1970. 1976: chile's intelligence service, dina, assigned biochemist eugenio berríos to develop sarin gas within its program proyecto andrea, to be used as a weapon against its opponents. one of dina's goals was to package it in spray cans for easy use, which, according to testimony by former dina agent michael townley, was one of the planned procedures in the 1976 assassination of orlando letelier. berríos later testified that it was used in a number of assassinations and it was planned to be used to kill inhabitants, through poisoning the water supply of argentine capital buenos aires, in case operation soberanía took place. march 1988: halabja chemical attack; over two days in march, the ethnic kurdish city of halabja in northern iraq (population 70,000) was bombarded by saddam hussein's iraqi air force jets with chemical bombs including sarin. an estimated 5,000 people died, almost all civilians. april 1988: sarin was used four times against iranian soldiers at the end of the iran–iraq war, helping iraqi forces to retake control of the al-faw peninsula during the second battle of al-faw. 1993: the united nations chemical weapons convention was signed by 162 member countries, banning the production and stockpiling of many chemical weapons, including sarin. it went into effect on april 29, 1997, and called for the complete destruction of all specified stockpiles of chemical weapons by april 2007. when the convention entered force, the parties declared worldwide stockpiles of 15,047 tonnes of sarin. as of november 28th, 2019, 98% of the stockpiles have been destroyed. 1990: kosovo student poisoning in march 1990, several months after the unilateral move by the serbian government to segregate schools throughout kosovo, a mysterious illness – massive poisoning of mostly school children appeared. the first victims to suffer this disease were students, who seasoned the most terrific nightmare of their lives. schoolchildren could detect a "white powder" on their desks. if they poked it, they quickly developed symptoms: first froth around the mouth and then cramps and fainting. many schools from each corner of kosovo began to report such happenings and from the first day on the absence of pupils in schools started to increase. on 1 august 1990, french doctor bernard benedetti, in an interview for “the lacourse” newspaper, claimed that he secretly entered a hospital in pristina and obtained blood samples from 150 patients. the analyses were done in two laboratories in paris. according to dr. benedetti, those patients were poisoned. when mr. benedetti visited kosovo again in 2000, he confirmed the results of the 1990s tests. according to him, publication of the results was stopped by the french government in an attempt to preserve diplomatic relations with serbia. another group called the commission of geneva was sent in kosovo. this group was made up of charles graves, verena graf and jean-jacques kirkyacharian. they didn't take blood analyses but during their trip they interviewed health personnel, children and their parents. they also took detailed notes of the symptoms. they wrote that some doctors had noticed a smell from the students which was similar to "vinegar". according to them, it was possible that the disease was caused from poisoning which might have been in the form of organic phosphates (nerve gas). the suspicion of nerve gases was reinforced in february 1992 when aubin heyndrickx gave a press statement in which he claimed that he had studied all reports and analysis of blood and urine and that he concluded that an organic chemical nerve gas had been used such as sarin and tabun, both listed as warfare agents. 1994: matsumoto incident; the japanese religious sect aum shinrikyo released an impure form of sarin in matsumoto, nagano, killing eight people and harming over 500. the australian sheep station banjawarn was a testing ground. 1995: tokyo subway sarin attack; the aum shinrikyo sect released an impure form of sarin in the tokyo metro. twelve people died, and over 6,200 people received injuries. 2002: pro-chechen militant ibn al-khattab may have been assassinated with sarin by the russian government. may 2004: iraqi insurgents detonated a 155 mm shell containing binary precursors for sarin near a u.s. convoy in iraq. the shell was designed to mix the chemicals as it spun during flight. the detonated shell released only a small amount of sarin gas, either because the explosion failed to mix the binary agents properly or because the chemicals inside the shell had degraded with age. two united states soldiers were treated after displaying the early symptoms of exposure to sarin. march 2013: khan al-assal chemical attack; sarin was used in an attack on a town west of aleppo city in syria, killing 28 and wounding 124. august 2013: ghouta chemical attack; sarin was used in multiple simultaneous attacks in the ghouta region of the rif dimashq governorate of syria during the syrian civil war. varying sources gave a death toll of 322 to 1,729. april 2017: khan shaykhun chemical attack; sarin gas was released in rebel-held idlib province in syria by the syrian air force during an airstrike. april 2018: douma chemical attack victims reported to have symptoms consistent with exposure to sarin and other agents. on 6 july 2018, the fact-finding mission (ffm) of the opcw published their interim report. the report stated that, "the results show that no organophosphorous nerve agents or their degradation products were detected in the environmental samples or in the plasma samples taken from alleged casualties". the chemical agent used in the attack was later identified as elemental chlorine.