Many scientists, including Ballard, are concerned that visits by tourists in submersibles and the recovery of artefacts are causing the wreck to decay faster. Underwater bacteria have been eating away at Titanic's steel and transformed it into rust since the ship sank, but because of the extra damage caused by visitors, the National Oceanic and Atmospheric Administration estimates that "the hull and structure of the ship may collapse to the ocean floor within the next 50 years."[122] The promenade deck has deteriorated significantly in recent years, partly because of damage caused by submersibles landing on the ship. The mast has almost completely deteriorated and has been stripped of its bell and brass light.