Chlorine gas has a characteristic pungent odor with a detectability threshold of a few parts per million in air. Liquid chlorine in contact with eyes, skin, or clothing may cause severe burns; as soon as it is released in the atmosphere, it vaporizes with irritating effects and a suffocating action, which were exploited in World War I by using it as a war gas. Although it is only detectable by smell at 3,5 ppm, it causes severe irritation of the throat at 15 ppm. It is extremely dangerous to bread in a 40 ppm atmosphere. A dosage of 1000 ppm is lethal. Due to these effects, chlorine is considered a dangerous substance so special care should be taken in its manipulation.