The existence of pyrolysis compounds from hardener of sand in working environment air at a foundry was investigated by quantitative analysis. Also, the concentrations and dilution ratio required until single component threshold of 72 volatile organic compounds (VOCs), 7 aldehydes and 2 ketones were analyzed. Additionally, the changes in air quality via the casting process are discussed in this study. As a result, numerous components such as VOCs and/or pyrolysis compounds were detected. Especially, acetaldehydes and xylene were dominated in the air. They also highly contributed to the dilution ratio required until single component threshold of the air.