Background Nowadays, calcium carbide craft is one of the most widely used method in China's vinyl chloride factories. Nevertheless, the acute or chronic poisoning induced either by small amount of vinyl chloride monomer (VCM) effusion during high-temperature processes or by inadequate protection in specific operation positions like patrolling, maintenance, and kettle clearing have contributed to a large fraction of VCM related occupational health problems.

Objective The study is conducted to recognize major exposure positions of VCM manufacturing, and understand the occupational health risk levels through the application and comparison of three recommended risk assessment methods.

Methods A total of 35 VCM workers from 19 major positions in 2 polyvinyl chloride (PVC) factories (factory B and factory G) in Tianjin City were investigated through field investigation and individual sampling. The occupational health risk levels were subsequently evaluated by semi-quantitative comprehensive index method, semi-quantitative exposure ratio method, and quantitative risk assessment method for carcinogens. Also, methodological differences among the three methods above were tested by Kappa conformance test.

Results All the 35 workers were male and aged (40.04±1.03) years, with an average working age of 6.0 (4.0, 9.5) years. They were assigned to positions such as VCM synthesis, polymerization, analysis, kettle clearance, material cutting, and machine maintenance. The time-weighted average concentrations (C_TWA) in positions like compressor operation, polymerization, VCM recycling, and paste resin in factory B reached very high levels (60.90-71.30mg·m^-3) that were 6-7 folds of the national occupational exposure limits (C_OEL=10mg·m^-3); the C_TWA in positions of preparation operation, internal polymerization, and synthesis controlling were 1-2 folds of the occupational exposure limits. Meanwhile, the C_TWA in factory G was not high, except the concentration in kettle monitoring and clearance position which was as high as 438.3 mg·m^-3, over 40 folds of the occupational exposure limit. The results of semi-quantitative comprehensive index method demonstrated that all positions were at medium to high risk levels; the results of semi-quantitative exposure ratio method presented low to extremely high risk levels; the results of quantitative risk assessment method for carcinogens showed positions in factory B were at high to very high risk levels, and positions in factory G were at negligible to very high risk levels. The results of quantitative risk assessment for carcinogens and semi-quantitative exposure ratio method were in a good conformance (K=0.632, P=0.002) when C_TWA ≥ C_OEL.

Conclusion Positions involved in processes such as VCM synthesis, compression, polymerization, recycling, kettle cleaning, paste resin, and maintenance are major exposure positions in PVC production enterprises. Their risk ranks are from medium to extreme high risks according to differences in exposure level and workplace environment. Application of the three different risk assessments in a combined way will certainly play to their strengths as limitations and advantages coexist.