Phosgene. Molecular model of the chemical warfare agent Phosgene (carbonic dichloride, chemical formula C.0.Cl2). Phosgene (also known as CG) was first used during World War I in 1915. The odour, likened to mouldy hay, made it difficult to detect and hence a very effective weapon. It is highly toxic with the ability to cause fatal respiratory damage. It severely corrodes all bodily tissues. Phosgene is also used as a building block for synthetic polymers such as polycarbonate. Atoms are colour-coded: carbon (grey), oxygen (red) and chlorine (green).