Learn German: Die Explosion hätte mich fast erwischt.

This is the core of expressing a near miss in German. Because the explosion didn't actually hit you, it is an unfulfilled past event. German uses the past Subjunctive II (hätte ... erwischt) together with fast to show that this was a hypothetical outcome that narrowly did not happen.

I usually translate 'to hit' as schlagen or treffen. Why use erwischt here?

erwischen literally means to catch or to get. It is very commonly used in everyday German for things that catch you by surprise or just manage to reach you, like a storm, an illness, a departing train, or an explosion. The verb treffen would also work here (hätte mich fast getroffen), but erwischt sounds a bit more colloquial and dramatic.

Could I put fast earlier in the sentence, like Die Explosion hätte fast mich erwischt?

That would sound unnatural to a native speaker. In German sentence structure, pronouns like mich usually want to be as early as possible after the conjugated verb (hätte). Adverbs like fast usually sit right in front of the specific thing they are modifying, which here is the past participle erwischt at the end of the sentence.

The lesson also mentions beinahe. Can I swap fast for beinahe in this sentence?