Produced liquid sulfur contains approximately 350 parts per million (ppm) of dissolved H2S and hydrogen polysulfides. Spontaneous degassing results in accumulation of these gases in the head space. If the sweep gas is interrupted, H2S can reach the lower explosive limit (LEL) (approximately 3.25%) creating a hazardous condition. In addition, a smoldering pyrophoric fire can be a source of ignition and monitoring SO2 in the head space warns of this condition.