The hospital explosion occours at the 2013 season finale and the aftermath in 2014.
Events leading to explosion
When Jade Montgomery burnt down Mangrove River High, pinning the blame on Matt Page, she has the students transferred to Summer Bay High, hoping to take over the school, even framing Bianca's husband Heath for assault, but Tamara Kingsley told the police she was lying and Montgomery was fired as a result. While the students were at Phoebe Nicholson's concert, Jade purchased a cell phone bomb and placed it in Bianca's laptop while she was out. While heading to work, Bianca left her laptop at the diner, which was found by Jett. Irene gave it back to her, via Heath before they head to the hospital after hearing Ricky had suffered some contractions. But just as Ricky was given the all clear, Bianca heard a phone ring and the bomb exploded, knocking them all back, including Hannah and Ethan, who told her she doesn't have to worry about his kids anymore.
The hospital was closed down and rebuilt by the time Chris Harrington's death cap mushroom risotto caused a lot of victims, including Leah and Alf. Ricky lost her baby and Montgomery was arrested for the explosion and Ethan's murder.
Heath Braxton (Knocked back by explosion, survived)
Bianca Scott (Knocked unconscious by explosion, suffered temporary memory loss)
Ricky Sharpe (Knocked back by explosion while in bed, survived but suffered a miscarrage days later)
Nate Cooper (Knocked back by explosion, survived)
Irene Roberts (Knocked back by explosion, survived)
Hannah Wilson (No known injuries)
Ethan MacGuire (Wounded by shrapnel, later died)