Didion Mills Damage Analysis

U.S. Chemical Safety Board (CSB) | Cambria, Wisconsin


The Didion Milling complex was destroyed by a series of combustible dust explosions. The blasts collapsed four large buildings, severely damaged four others, and killed five mill workers. Federal investigators with the Chemical Safety Board retained Atlas Engineering to analyze the structural performance of the buildings under the blast loads.

Our firm has special expertise in structural systems, their behavior, and their vulnerabilities. We observed the collapsed and damaged buildings on the ground, reviewed their designs, and calculated failure loads for critical connections. Based on the pattern of the post-blast debris and review of witness accounts, we were able to estimate the sequence of collapses among these interconnection structures.

Our analysis and report to the Board showed that the mill buildings were especially vulnerable to the overpressure loads typically generated by dust explosions, due to their reliance on precast construction, and deficiencies in design and construction. The buildings were multi-story and structurally connected, and structural failures cascaded from one building to the next. We found clear evidence of disproportionate damage and progressive collapse. Our analysis of the mill buildings' structural response to the explosions was incorporated into the Board's final report on the disaster.