In the special case when the likelihood of failure remains constant with respect to time ( for example , in some product like a brick or protected steel beam ) , and ignoring the time to recover from failure , failure rate is simply the inverse of the Mean Time Between Failures ( MTBF ) .
In special processes called renewal processes , where the time to recover from failure can be neglected and the likelihood of failure remains constant with respect to time , the failure rate is simply the multiplicative inverse of the MTBF ( 1 \/ Î '' ) .