Members and staff of the Chemical Safety & Hazard Investigation Board were blocked from examining evidence at the West Fertilizer Co. fatal accident site by state and other federal investigators, CSB Chairman Rafael Moure-Eraso wrote in a letter to Sen. Barbara Boxer (D-Calif.) last week. Boxer had asked CSB for an update. For a month after the April 17 accident, CSB investigators were restricted by the federal Bureau of Alcohol, Tobacco, Firearms & Explosives and the Texas State Fire Marshal’s Office, which were conducting a criminal investigation. The non-CSB investigators altered and removed nearly all relevant evidence, CSB said, but were unable to learn how the accident occurred. CSB’s root cause investigation will take 12 to 18 months, the board said, but preliminary findings may be released sooner. Last week, CSB released a video showing damage from the accident.