Under standard conditions, pure carbon monoxide (CO) is a colorless, odorless, non-irritating gas. The relative molecular mass is 28.01, the density is 1.250 g / l, the freezing point is -207 ° C, and the boiling point is -190 ° C. Its solubility in water is very low and it is not easily soluble in water. The air mixed explosion limit is 12.5% ～ 74%. After entering the human body, carbon monoxide will combine with hemoglobin in the blood to produce carboxyhemoglobin, which will prevent hemoglobin from binding with oxygen, which will cause hypoxia in the tissues of the body and cause the body to suffocate to death. Therefore, carbon monoxide is toxic. Carbon monoxide is a colorless, odorless, and odorless gas, so it is easy to ignore and cause poisoning.