A researcher was attempting to change the acetylene pressure on an atomic absorption spectrometer by adjusting the pressure regulator. He inadvertently set the pressure well above 15psig, despite the signs (and the red markings on the regulator) warning not to do so. When acetylene pressure exceeds 15psi, the gas can liquefy; in this state, acetylene can suddenly and explosively polymerize. Fortunately, this did not occur, although the regulator was ruined from overpressurization.
Learn more about this incident and its implications in Incident Ames Feb2014.