Is the word "blast" an onomatopoeia?
Not really, I think.
An onomatopoeia is when the would has (about) the same sound as that made by the thing it describes.
The word "cuckoo" is a good example, as that is (about) the sound this bird makes. In other languages the cuckoo is named in similar ways (the Dutch word "koekoek" is pronounced like coo-cook).
So you decide if "blast" sounds like a blast, but I beg to disagree.