The phrase "oh blast" is correct and usable in written English.
You can use it as an expression of dismay or frustration. For example, "Oh blast! I left my keys at home."
At noon, to the reverberating wail of "Oh, Hussein," blasting from a loudspeaker and rhythmic drumming, the battle is reenacted.
Junya Watanabe's show was right after Balenciaga — and, oh, what a blast of fresh air.
Obviously it weren't going back weeks, but instead of that, you would start like a bull at a gate every night yes, but you would quickly change to, oh I will blast this all in one go.
Oh, and soundsystems blasting jungle, soca and dancehall of course.
Then he gathers his thoughts and says all the nice regulation stuff about how much fun it was making X-Men – "Oh, and Prometheus was a blast" – and what great friends he made with his co-stars.
JG: Oh man, it was a blast.
"Oh, this ought to be a blast," Mr. Boehner sighed as he opened a news conference for questions.
Campaign is a blast and multiplayer is oh so much fun, a few matchmaking delays excepted (hopefully this will settle down soon).
