Trying to figure out how Dr. Loomis was able to survive the explosion?

Hence why he's still alive and well (albeit with noticeable scars on his face and hands and walking with a limp) come Halloween 4: The Return of Michael Myers:

https://screenrant.com/halloween-2-movie-dr-loomis-hospital-fire-survive/

While there isn't an explicit canonical explanation for his survival, the original Halloween 4 script written by Alan B. McElroy actually opened with a scene attempting to explain how Loomis survived. The scene was never shot, as director Dwight H. Little decided it would be better to not get bogged down in explanations. It would've seen the force of the explosion blow Loomis out into an adjacent hospital corridor, and away from the bulk of the fire. Sure, that explanation is a bit weak, but it's more than Halloween 4's theatrical cut offers. The more cynical reasoning is money. Halloween 3 tanked, and producer Moustapha Akkad really wanted to bring Michael and Loomis back. Halloween creator John Carpenter fully intended Halloween 2 to be the demise of both characters, but the only thing more powerful than Michael Myers is Hollywood's desire for cash.