The impact of recirculating industrial air on aircraft painting operations

The 1990 Clean Air Act Amendments resulted in new environmental regulations for hazardous air pollutants. Industries such as painting facilities may have to treat large volumes of air, which increases the cost of an air control system. Recirculating a portion of the air back into the facility is an option to reduce the amount of air to be treated. The authors of this study developed a computer model written in Microsoft Excel 97 to analyze the impact of recirculation on worker safety and compliance costs. The model has a chemical database with over 1300 chemicals. The model will predict indoor air concentrations using mass balance calculations and results are compared to occupational exposure limits. A case study is performed on a C-130 aircraft painting facility at Hill Air Force Base, Utah. The model predicts strontium chromate concentrations found in primer paints will reach 1000 times the exposure limit. Strontium chromate and other solid particulates are nearly unaffected by recirculation because the air is filtered during recirculation. The next highest chemical, hexamethylene diisocyanate, increases from 2.6 to 10.5 times the exposure limit at 0 percent and 75 percent recirculation, respectively. Due to the level of respiratory protection required for the strontium chromate, workers are well protected from the modest increases in concentrations caused by recirculating 75 percent of the air. The initial cost of an air control system is $4.5 million with no recirculation and $1.8 million at 75 percent recirculation. The model is an excellent tool to evaluate air control options with a focus on worker safety. In the case study, the model highlights strontium chromate primers as good candidates for substitution. The model shows that recirculating 75 percent of the air at the Hill painting facility has a negligible impact on safety and could save $2.7 million on the initial expenses of a thermal treatment system.