Chlorine is yellowish-green gas with a distinct odour.
Chlorine is a severe nose, throat and upper respiratory tract irritant. In general, people experienced irritation of the nose, a weak cough, and increased dryness of the throat at concentrations ranging from 0.02 to 2 ppm.
Concentrations of 1 to 2 ppm produce significant irritation and coughing, minor difficulty breathing and headache. Concentrations of 1 to 4 ppm are considered unbearable. Severe respiratory tract damage including bronchitis and pulmonary edema (a potentially fatal accumulation of fluid in the lungs) has been observed after even relatively low brief exposures.
No long term exposure limits are safe. Short term exposure limit (15 minutes) 0.5-1.5ppm.