Diphosgene (DP), trichloromethyl chloroformate, is a clear, colorless liquid with an odor similar to phosgene. It is noncombustible, a strong irritant to the eyes and tissue, and is toxic by inhalation and ingestion. DP has a boiling point of 127ºC-128ºC (263ºF) and a vapor pressure of 4.2 at 68ºF (20ºC). The liquid density is 1.65, which is heavier than water, and a melting / freezing point of 314ºF (157ºC). Inhalation LC50 is 3600 mg/m³ for 10 min. Effects of exposure are quite similar to phosgene gas. Its molecular formula is ClCOOCCl3, and the structure and molecular formula are shown in Figure 8.38. The DOT lists diphosgene as a 6.1 poison liquid. The NFPA 704 designation for CG is estimated to be health 4, flammability 0, reactivity 1, It has a four-digit UN identification number of 2972.