You didn’t define what n and r represent.

Regardless, the formula does not look familiar with respect to confidence intervals or level.
For some information related to confidence intervals and level, see the following link

http://theriac.org/DeskReference/viewDocument.php?id=214

n = no of tests and r = number of failures.

This formula is quoted in several text books and papers and I realize that no confidence level is associated with the equation. My question relates to one-shot devices.