A medevac EC135 diverted to a nearby airport when the #1 engine failed.

Narrative

We arrived on station and landed behind another air ambulance. Fifteen minutes later we lifted with our patient for the hospital. About 4 NM from our destination; the aircraft suddenly yawed to the left accompanied by a very slight nose down tuck. The #1 engine had failed without any advanced warning.The #2 engine immediately went into OEI [One Engine Inoperative] high and remained there for approximately 15-20 seconds until I realized what had just happened. I reduced the collective until the #2 engine transitioned to OEI low and remained there until I climbed to a slightly higher altitude; which was for approximately 30 seconds. I then reduced the collective to maintain between 60-77% Q and placed the #1 engine start switch to idle.After informing the medical crew what had just occurred; we contacted Operations and informed them we were diverting to ZZZ. We made an uneventful landing on BRAVO Taxiway; sliding approx 20-25 FT. After placing the #1 engine switch to off; the #2 engine was shutdown and the patient was airlifted by another air ambulance to the hospital.