[en] In order to prevent loss of SF₆ gas in the event of SF₆leakage into the column vacuum system, the Holifield facility tandem accelerator is equipped with two all-metal pancake valves which serve as primary gas-containment valves. While these valves have never failed to function when required, there has been some concern that they might not close reliably with the high-velocity flow that could occur in the unlikely event of a large leak in the column vacuum system. Thus, it was decided to supplement these valves with auxiliary gas-containment valves which would reliably close, even with a high-velocity flow. This paper discusses the auxiliary valves system. 5 figs