What happened on January 27th, 1967?

Although it is impossible to eliminate all risks from such a complex and experiment project as the American space program, every precaution is taken to reduce the possibility of injury. Nevertheless, accidents do happen.  The first major casualties occurred when, despite every precaution, fire broke out on the Apollo 5 capsule on January 27, 1967, in spite of every effort to save them, 3 men died in this terrible accident.
     The program continued without pause, however, and there were no more serious injuries until 1981. Then the engines having been successfully tested on an earlier occasion, a rehearsal for the actual launching was held.  Not knowing that an engine-chamber was full of nitrogen gas, used to clean the motor, six technicians entered for routine work after the final rehearsal had been declared successfully. They collapsed as soon as the gas entered their lungs. One man died and the others were very ill.
     Though every one involved was shocked and grieved by this apparently unnecessary accident, preparations continued for the actual launching later that year.  However hard we try, accidents are hound to happen whenever a new and challenging project is undertaken. It seems to be the price of progress.