1981: Five technicians are asphyxiated while setting up a ground test for the space shuttle Columbia, then in preparation for STS-1, the first operational shuttle mission. Two of them die.

The accident occurred during a nitrogen purge of the orbiter. John Bjornstad, 50, one of the five Rockwell International technicians who entered a rear section of the orbiter above the engine, died en route to the hospital. The second fatality, Forrest Cole, died two weeks later.

The nitrogen purge was a routine procedure that used nitrogen to flush all the oxygen out of the engine compartment prior to test-firing, when any errant spark could touch off a fire. No oxygen = no possible fire.

Following a successful simulated countdown, the technicians were cleared by NASA safety supervisors to enter the compartment. Believing the conditions inside Columbia to be safe, they entered not wearing air packs. Because nitrogen is both odorless and colorless, the five men lost consciousness before realizing anything was amiss.

A sixth technician discovered them and alerted a security guard, who donned an air pack and dragged the victims from the compartment. Rescue efforts were further complicated when the ambulance responding to the emergency call was stopped and searched for seven minutes by security guards near the launch-pad perimeter at the Kennedy Space Center.

The front gate was unaware that anything had gone wrong inside.

Following a three-month investigation, a NASA board of inquiry concluded that a last-minute change in testing procedures, coupled with a breakdown in communications at the space center, caused the accident.

The two deaths were the first fatalities for the U.S. space program since Jan. 27, 1967, when astronauts Virgil Grissom, Ed White and Roger Chaffee were killed when fire swept through their capsule during ground testing for the first Apollo mission.

The accident did not delay the scheduled launch of Columbia on April 12. The orbiter, commanded by Apollo veteran John Young and piloted by rookie Robert Crippen, returned Americans to space for the first time in nearly six years and kicked off the mostly successful space shuttle program.

But tragedy can bide its time – and often does in inherently risky ventures – and struck Columbia again on Feb. 1, 2003.

Source: Various