Abstract: Objective To explore the application of semi-quantitative risk assessment contact index method in the pre-assessment of occupational hazards by identifying the occupational hazard factors in the production process of the delayed closed decoking technology transformation project of a petrochemical company in Karamay City. Methods In December 2023,a semi-quantitative risk assessment model was established with reference to the Technical guidelines for occupational health risk assessment of chemical harmful factors in the workplace（GBZ/T 298-2017） and the Catalogue of highly toxic substances. Combined with the toxicity of chemical harmful factors in GBZ/T 298-2017 appendix Table F.1 and Table F.2,the hazard characteristics were evaluated and graded respectively,and the exposure index method was used to determine the risk level. Results The test results of the main occupational hazard factors of the existing delayed coking decoking equipment showed that the concentration of coke dust was 0.2-1.36 mg/m³,the concentration of hydrogen sulfide was <0.53 mg/m³,the concentration of solvent gasoline was <0.44-0.20 mg/m³,and the noise intensity of each position was 76.0-83.1 dB（A）. The occupational hazards caused by coke dust,hydrogen sulfide,solvent gasoline,benzene,toluene,xylene,liquefied petroleum gas,and sodium hydroxide used in the process of exhaust gas desulfurization in the proposed project were all at low risk level（risk index R=2）. The risk of occupational hazards caused by hydrogen sulfide exposed to non-coke and non-coke operation is moderate（risk index R=3）. Conclusion The semi-quantitative risk assessment contact index method can be used in the pre-assessment of occupational hazards in the absence of analog detection data,and can better predict and assess the occupational hazards risk level in the production process,so it has been applied in the closed de-coking pre-assessment in the petrochemical industry,making up for the shortcomings of the analogue assessment method.

Key words: Closed decoking, Pre-evaluation, Semi-quantitative, Risk assessment