A sharp-eyed space worker helped NASA avoid what might have been a serious fire hazard aboard the international space station, space agency officials have told MSNBC.com.
In an exclusive interview late last week, space station manager Michael Suffredini detailed how an explosive fire might have been broken out in an oxygen line, potentially injuring spacewalking astronauts. “It could have been a very bad day,” he said. “It would have been ugly.”
Responding to the concern, engineers kicked off a test program as well as an in-depth analysis of the potential threat. NASA officials said the analysis so far indicates that the equipment aboard the space station should pose no hazard, as long as the astronauts in orbit follow stringent operating procedures. One said an extra "procedural fix" would be put in place.
NASA's response illustrates how seriously the space agency is taking safety concerns in the wake of the 2003 Columbia tragedy — which led to the loss of the shuttle and its crew, and raised alarms about a "broken safety culture."
Concerns about ‘ignition event’
The potential trouble spot was a high-pressure gas line running from oxygen tanks mounted on the space station's exterior into the U.S.-built Quest air lock. NASA's concerns first came to light last week when an internal memo that was posted on NASASpaceflight.com, an independent, British-based Web site.
The memo said that preliminary testing had turned up "a potential for velocities in the ISS Oxygen System to exceed the 100 ft/s maximum limit," and that a NASA team was "working options, including procedure updates, to mitigate the concern."
Kirk Shireman, a NASA space station official, elaborated on the concern during a Houston news conference on Thursday. Shireman said it had to do with the potential for an "ignition event" aboard the space station — in plain English, a spark. Such a spark could be dangerous, summoning up the specter of the fatal fire aboard Apollo 1 in 1967 and a series of fires on Russia's Mir space station, including the near-fatal one in 1997. One big difference: None of those fires involved oxygen under high pressure.
Shireman said the concern was elevated because "lots of things you don’t usually think of as fuels will burn" — including the metal used in the walls of high-pressure gas lines.
Raising the alarm
The investigation was sparked by a sharp-eyed inspector who was looking over a similar oxygen line on a station module being prepared for launch later this year. Like the air lock currently in orbit, the Italian-built Harmony module (previously known as Node 2) contains high-pressure lines designed to distribute oxygen from storage tanks to other locations on the station.
While eyeballing one of the fittings on a valve on the line, the engineer noticed a tiny metal shaving, probably left over from the fabrication or assembly process but not caught in the cleanup activity that followed. Such contamination is like spotting a termite in your house: If you see one, you should assume there are lots more you haven't seen.
The concern was that in the presence of pure oxygen under high pressure, metal can burn as readily as more common fuels such as wood, plastic or food particles. The particle could be ignited by striking or scraping along the interior of the line at high speed. The flash of heat would be enough to ignite other nearby particles, setting off an explosion.
“It didn’t occur to us until we looked at it,” Suffredini admitted. That slight hint of trouble was all it took to mobilize a response: “We haven’t gotten over the scars of the Apollo fire,” he continued, “so when people say ‘oxygen’ we perk up our ears and pay special attention.”
How hazardous could it be?
This hazard was a significant one, Suffredini said. “It could blow the line open,” he explained. As the same type of line already on the air lock in orbit runs along the external surface of the station, “it could damage the shell [the pressure hull] and injure the crew inside the airlock,” he said. If it punched a big enough hole in the side of the airlock, it could lead to rapid depressurization of that portion of the station.
Engineers determined that if the air flow inside such lines could be kept below about 100 feet per second, any particle being blown along the line would not have enough energy to ignite itself on wall contact. But in places where hoses are plugged together and then pressurized, there could be a brief surge of air that approached the speed of sound — far in excess of the speed limit.
At a NASA laboratory near White Sands, N.M., technicians rigged up a high-pressure line and test valves containing metal dust. On one of the first runs, as soon as the oxygen was turned on, a belch of flame whooshed out from the test apparatus, Suffredini said. The stainless steel in the fitting caught fire and burned along its inner surface until the oxygen flow was cut off manually.
That got the attention of top-level NASA managers. However, engineers determined that the initial test rig was built to a lower standard than the actual flight hardware. When a smoother line was tested, there was no ignition. Furthermore, the lines on flight hardware are cleaned to much finer levels than the test rig. Any remaining contaminants would be flushed out more easily in zero gravity than on Earth.
As a result, NASA concluded that the lines on the space station itself were safe. "For the kinds of potential contamination we have in these lines, it's not an issue," Suffredini said.
Shireman said he expected the addition of an extra "procedural fix": not operating the valves abruptly enough to create a surge of oxygen in the first place. He said more tests are being conducted to verify that the fix would be sufficient.
Speaking on condition of anonymity, a source in the space program told MSNBC.com that the White Sands lab was the perfect place for checking the safety of the oxygen system. "The lesson to me is that we tend to be complacent about oxygen on the ground," the source said in an e-mail. "Any high-pressure gas oxygen system can ignite; only stringent procedures avoid this."
In the wake of the Columbia tragedy of 2003, that stringency seems to have manifested itself properly. The space workers and managers followed the dictates of NASA's heightened "safety culture." They tested, analyzed and debated the implications of contamination first spotted by a single inspector. As a consequence, there almost certainly will be no fire or explosion from this cause.
James Oberg, space analyst for NBC News, spent 22 years at NASA's Johnson Space Center as a Mission Control operator and an orbital designer.