BREN Tower is a guyed steel framework mast, 1,527 ft (465 m) high, on the Nevada Test Site in Nevada, USA. "BREN" stands for "Bare Reactor Experiment, Nevada." Despite its immense size, the tower has actually been moved from its original location. Built by the Dresser-Ideco Company for the U.S. Atomic Energy Commission, it was first erected in 1962 in the atomic bomb test area at Yucca Flat, where it was used for an experiment intended to improve understanding the effects of radiation in the atomic bombing of Hiroshima. A bare (unshielded) nuclear reactor on a hoist car could be moved to different heights on the tower; Japanese-type houses were built near the base of the tower and were bombarded with various intensities of radiation. After the Nuclear Test Ban Treaty banned open-air nuclear testing, the tower was dismantled and moved to Jackass Flats in Area 25 of the Nevada Test Site, where it was used for Operation HENRE (High Energy Neutron Reactions Experiment), a series of radiation measurement experiments using a small linear accelerator to provide neutrons. It still stands at Jackass Flats. Constructed of 51 30 ft (9.1 m) sections of high tensile steel, the structure is higher than the 1,472 ft (449 m) Empire State Building. It is supported by 5.5 mi (8.9 km) of guy wires designed to withstand winds exceeding 120 mph (190 km/h). The tower is equipped with an outside hoist to lift scientific equipment, and a two-person elevator inside the tower moves at 100 ft (30 m) per minute. The tower weighs 345 tons (313 tonnes). The structure is now owned by the Department of Energy and maintained by National Security Technologies, LLC. Access to the tower area has been closed since July 2006. No reason for the closure has been given. As part of the Nevada Test Site, it is also located in restricted airspace (R-4808N).