1. Volatile organic compounds (VOC) such as benzene, toluene and xylene. Waste oil liquid contains a lot of volatile organic compounds, which may cause harm to the environment and human health after volatilization.

2. Hydrogen sulfide: Hydrogen sulfide is one of the common harmful gases in waste oil liquid, with strong smell and great toxicity. Long-term exposure or inhalation of hydrogen sulfide will cause harm to respiratory system, digestive system and nervous system.

3. Ammonia and nitrogen oxides: There may be compounds such as ammonia and nitrogen oxides in waste oil liquid, which may easily cause irritation and damage to eyes, nasal cavity and respiratory system.

4. Carbon monoxide: Waste oil liquid contains toxic gases such as carbon monoxide, which is harmful to human body. Long-term contact and inhalation may lead to poisoning.

These harmful gases are harmful to the environment and human health, so safe treatment technology and equipment must be adopted in the process of waste oil liquid treatment to minimize the impact of these harmful gases on the environment and human health.