RCW 9A.76.110: Escape in the first degree.

(1) A person is guilty of escape in the first degree if he or she knowingly escapes from custody or a detention facility while being detained pursuant to a conviction of a felony or an equivalent juvenile offense.

(2) It is an affirmative defense to a prosecution under this section that uncontrollable circumstances prevented the person from remaining in custody or in the detention facility or from returning to custody or to the detention facility, and that the person did not contribute to the creation of such circumstances in reckless disregard of the requirement to remain or return, and that the person returned to custody or the detention facility as soon as such circumstances ceased to exist.

(3) Escape in the first degree is a class B felony.