"All the double-shell tanks contain waste that continuously generates some flammable gas," the board said in a letter received by Wyden on Monday. "This gas will eventually reach flammable conditions if adequate ventilation is not provided."
The safety board had previously issued a warning about their concerns, which have not yet been addressed. In September, the board sent a letter to the Department of Energy, claiming that there were no adequate safeguards to protect against the buildup of flammable gasses inside Hanford’s waste storage tanks. The letter, which outlines the concerns shared with Sen. Wyden on Monday, was declassified on Tuesday.