NASA's poor maintenance practices have caused a fire in a mission control room, falling concrete in a space shuttle building and a steam line explosion, according to a government report issued today. The General Accounting Office report says the National Aeronautics and Space Administration is working to correct the shortcomings. Congress appropriated $141 million for maintenance in 1990 and more has been asked for future years. The GAO recommends that the space agency develop a comprehensive maintenance strategy, spend more money on upkeep and do annual surveys to determine which of its centers most need repairs. ``People and facilities are critical to mission success,'' said Sen. Barbara Mikulski, D-Md., who released a summary of the report today. ``We can't afford breakdowns on the ground if we're going to have spectaculars in space.'' The report said launch pads and the space shuttle processing facilities are generally well-maintained. But it said that eight NASA centers visited by GAO inspectors all have deteriorating facilities such as leaking roofs, peeling paint and leaking steam lines. Many of NASA's buildings are 30 to 50 years old. The report said NASA rated its own facilities as marginal. ``An example of deterioration is concrete falling from the roof of the 52-story building where the shuttle is joined with the external fuel tank and solid rocket boosters. ``NASA installed netting beneath the roof deck to catch the concrete,'' the summary said. Other incidents included a cooling tower that partially collapsed under the weight of ice that formed because water valves malfunctioned, the report said. Experts at the National Research Council recommend that agencies spend at least 2 percent to 4 percent of their facilities' replacement value on maintenance, the report said. The percentage for most of NASA's facilities between 1985 and 1989 was between 0.9 percent and 1.5 percent, it said. Mikulski said this year's federal budget includes a special $20 million fund to start rehabilitation and major maintenance at NASA's field centers. The space agency's facilities include 2,700 buildings and 3,200 other major structures encompassing 36 million square feet.