Maybe American nuclear plants aren’t as safe as we thought they were. The emergency vents at nuclear plants in the U.S.—which officials said would prevent hydrogen explosions—are the same type that were unsuccessful in Japanese plants. When venting failed at the Fukushima Daiichi plant, the hydrogen gas fueled explosions and released radioactive materials into the atmosphere, which reached levels of about 10 percent of the emissions from Chernobyl. Details released this week show that mechanical failures and design flaws in the vents actually led to catastrophic delays in activating the emergency venting system. American officials have long said U.S. reactors would be safe from disasters because of newer, stronger venting systems, but the Tokyo Electric Power Company says Fukushima Daiichi had actually installed the same vents years ahead of the disaster.