The explosion was reported at 216 Brattle Street in Holden Saturday morning after the tank blew. The canister had been left in the car overnight with a small leak, the State Fire Marshal's Office said.
It's unclear what caused the spark to ignite the acetylene.
Neighbors pulled the man from beneath the car after the explosion and paramedics took him to an area hospital with serious injuries.
The man's name was not released.
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