Asphalt is a brown, brownish-black petroleum substance, which is a viscous liquid or glassy solid. Its main components are hydrocarbons and a small amount of nitrogen, oxygen and sulfur. Natural asphalt is formed in the initial stage of the decomposition of seabed sediments into oil, or after the oil is exposed to the surface, its light fraction is volatilized. Large natural asphalt deposits exposed to the ground form asphalt lakes. For example, Guanoco Lake in Venezuela covers an area of more than 4.45 million square meters and is estimated to contain more than 6 million tons of asphalt. Asphalt can also be the product of dry distillation of petroleum, coal tar, wood tar and oil shale. Asphalt is easy to process and can be used as waterproof layer of building materials, which is widely used in pavement. As early as the third century BC, asphalt was used in the brick wall of Yinghao Reservoir in Mohenjo, Pakistan to prevent water leakage.

Bitumen often contains carcinogens, especially benzopyrene, which is an important carcinogen and can induce skin cancer, lung cancer and digestive tract cancer, with the content as high as 2.5% ~ 3.5%. When asphalt is heated or treated at high temperature, it will produce yellow asphalt smoke, including common air pollutants such as carbon monoxide, sulfur dioxide and nitrogen oxides, with a diameter of 0. 1 ~ 1. According to the determination, the content of 3,4-benzopyrene in asphalt flue gas can reach 1.3 ~ 2mg/m3.

Smoke and particulate dust in asphalt can enter human body through respiratory tract and skin. Excessive intake can cause poisoning, dermatitis, blurred vision, conjunctivitis, chest tightness, headache and other symptoms. Long-term exposure to asphalt and asphalt smoke is easy to induce cancer.

Flue gas produced during the processing of oil and oil shale can be sent to boilers. At 600 ~ 800℃, the flue gas retention rate of asphalt is 0.3 ~ 0.5 m/s, so that asphalt can be burned. Electrostatic dust removal can also be used, that is, under the action of high pressure, asphalt flue gas is ionized, separated from airflow and adsorbed by electrodes. Workers working in asphalt smoke environment should use personal protective equipment.