FREMONT, Nebraska — Confined and concentrated combustible dust can ignite and generate secondary dust explosions “powerful enough to destroy buildings,” the Chemical Safety Board warns. CSB issued the warning as part of its ongoing investigation into a fatal explosion and fire on July 29 at the Horizon Biofuels facility in Fremont, Nebraska. Preliminary findings show that the blast was triggered by a combustible wood dust explosion, “a well-known – and completely avoidable – hazard,” CSB Chair Steve Owens said. …CSB says combustible dust, when shaken loose and dispersed into an “explosive concentration in the confinement of a closed space” after a primary event, can explode when exposed to an ignition source. The agency says it’s continuing to: Examine the facility’s design, process flow, dust handling and dust control systems. …The agency said that “complete findings, analyses and recommendations, if appropriate,” will be part of a final investigation report.