This story was updated at 7:26 p.m. EST.
California safety inspectors have cited the private spaceflight company Scaled Composites in connection with an explosion that killed three of the firm's workers last July.
The citations, issued Thursday, faulted the Mojave, Calif.-based firm for failing to provide "effective information and training of the health and physical hazards associated with nitrous oxide," a compound used during a July 26 test that ended in an explosion, killing three employees and injured three others at the Mojave Air and Space Port.
"Scaled Composites regrets that this accident occurred, and we have expressed our condolences to the victims and their families and provided support during this difficult time," said Doug Shane, Scaled Composites executive vice president, adding that the firm cooperated fully with California's Division of Occupational Safety and Health Administration (Cal/OSHA) during the investigation.
"And we continue to work with the agency so that the enhanced procedures already implemented promote the safest workplace conditions possible," Shane told SPACE.com.
Led by aerospace visionary Burt Rutan, Scaled built and flew the piloted, air-launched SpaceShipOne suborbital spacecraft three times in 2004, two of which launched within two weeks to win the $10 million Ansari X Prize.
The firm was conducting tests as part of the development for SpaceShipTwo, a larger spaceliner designed to carry space tourists to suborbital space for Virgin Galactic, when the deadly accident occurred last summer. According to Friday's report, Scaled faces up to $25,870 in fines for the citations.
"The company has 15 working days from date of issuance to pay the assessed fines or appeal them," Kate McGuire, a spokesperson with Cal/OSHA, told SPACE.com in a statement.
Like SpaceShipOne, the new SpaceShipTwo will be air-launched by a carrier craft. But the new craft is expected to carry up to eight people - two pilots and six passengers - at a time to an altitude of 68 miles (110 kilometers), where they would experience several minutes of weightlessness before returning to Earth. Scaled and Virgin Galactic officials were working toward a planned rollout of SpaceShipTwo later this year and operational flights in 2009 when the accident occurred.
Virgin Galactic plans to stage its space tourist flights out of a central terminal at Spaceport America in New Mexico.
Editor's note: This story was corrected to reflect the fine amount. The citations included $25,870 in fines, not $25,310 as initially reported.