Workers at a pioneering space tourism company were watching a rocket propellent test through a chain-link fence in the Mojave Desert when some were killed by an explosion, according to a state investigation released Thursday.
The report comes nearly a month after Mojave-based Scaled Composites LLC was cited for five workplace violations and fined $28,870 in connection with the July blast that killed three technicians and critically injured three others.
Scaled, which put the first privately funded manned rocket into space in 2004, was conducting a so-called cold-flow test of nitrous oxide when the accident occurred. The routine test was part of the development of a new hybrid rocket motor for a commercial spaceship Scaled is building for Virgin Galactic.
State occupational safety inspectors faulted Scaled for failing to train workers and supervisors about the potential hazards of nitrous oxide.
"Nitrous oxide is a volatile substance, and it blew up," said Kate McGuire, a spokesman for the California Department of Industrial Relations, known as Cal-OSHA.
Seventeen Scaled employees and contract workers were inside a fenced-in yard at the Mojave Air & Space Port, in the desert north of Los Angeles, at the time of the accident. During preparation, they transferred the chemical from a stainless steel tank into a propellent system mounted on a test stand, according to the inspectors.
Shortly before the test, six workers took shelter in a mobile command center that was protected by an earthen berm about 430 feet away from the test stand and telephoned the rest of the crew that the test was about to begin. The remaining 11 workers gathered near a chain-link fence to watch.
The explosion occurred three seconds into the test, the report said.
Two workers were killed instantly. A third died while being flown to a hospital. Three others were hospitalized with burns to their chests. A seventh person was treated at an offsite clinic. All were standing near the fence.
Inspectors noted about 10,000 pounds of nitrous oxide was being held in the testing area under 390 pounds of pressure at 70 degrees Fahrenheit.
Doug Shane, executive vice president at Scaled, said the company had no comment on the latest report. Shane previously said the company has cooperated with the state investigation and made changes to its work force training and procedures.
McGuire said Scaled has filed a notice appealing the citations and fine.
The explosion is the only fatal on-the-job accident in the history of Scaled, which was bought by Northrop Grumman Corp. last year.
Scaled and Virgin Galactic last month in New York City unveiled models of their commercial rocket, SpaceShipTwo, and the aircraft that will launch it into space.
Scaled founder Burt Rutan said then that the accident had delayed the spaceship engine's development as the company tried to find out what went wrong.