 The open-air third floor held large inflatable gas bags which could store the sulfur hexafluoride (SF6) gas from the Marx generator enclosures when they needed to be opened for maintenance.The ATLAS-I program was shut down after the end of the Cold War in 1991, which brought an end to destructive EMP testing of aircraft, being replaced by far cheaper computer simulations as technology improved.Despite going without maintenance 20 years, the wooden trestle structures were all still standing in 2011, and the structure remained the biggest metal-free wood laminate structure in the world.