VX (vē´ĕks), nerve gas several times more toxic than sarin but less volatile. It kills within minutes if inhaled or deposited on the skin; protection from VX would require both protective suits and masks. The compound was first prepared in the 1950s during research for new insecticides; its chemical formula is classified by the U.S. government as secret. VX contaminates for several days ground on which it is released. Accidental release of VX in Utah in 1968 caused the death of thousands of sheep, some of them as far as 40 mi (64 km) from where the gas escaped.