EMT Terrorism Response and Disaster Management Practice Test

Persistence in a chemical agent means it stays hazardous in the environment for a long time after release. A brownish-yellow oily substance that is highly persistent points to sulfur mustard. This vesicant has a viscous, oily, yellow-brown appearance and a very low vapor pressure, so it clings to surfaces, clothing, and soil and remains hazardous for days to weeks. In contrast, chlorine and phosgene are gases that dissipate quickly (chlorine is a greenish-yellow gas and phosgene is colorless), so they don’t match the description of an oily, long-lasting substance.