Risks quantified at NASA

How were the identified risks quantified at NASA? Is the quantification system truly quantitative or is it a qualitative system?
Were probabilities assigned to any of the risks? Why or why not?
What methods of risk response were used at NASA?
Did it appear that the risk response method selected was dependent on the risk or on other factors?
Should someone have stopped the Challenger launch, and, if so, how could this have been accomplished without risking one’s job and career?
How might an engineer deal with pressure from above to follow a course of action that the engineer knows to be wrong?