This webpage is maintained by the Centers for Disease Control and Prevention (CDC). The webpage provides information and resources on Chlorine. "Chlorine is an element used in industry and found in some household products. [...] Chlorine is sometimes in the form of a poisonous gas. Chlorine gas can be pressurized and cooled to change it into a liquid so that it can be shipped and stored. When liquid chlorine is released, it quickly turns into a gas that stays close to the ground and spreads rapidly. [...] Chlorine gas can be recognized by its pungent, irritating odor, which is like the odor of bleach. The strong smell may provide an adequate warning to people that they have been exposed. [...] Chlorine gas appears to be yellow-green in color. [...] Chlorine itself is not flammable, but it can react explosively or form explosive compounds with other chemicals such as turpentine and ammonia."
Centers for Disease Control and Prevention: http://www.cdc.gov/