Blasts don't necessarily leave scorch marks.
https://www.dvidshub.net/image/1266511/engineers-blast-back-basics
DVIDS
Lance Cpl. Nickolaus D. Lopez examines a crater made by the explosion of a 40-pound ammonium nitrate crater charge April 15 at Camp Schwab during a four-day basic demolition course. The enormous power generated by the explosive did not allow for a safe viewing of the detonation by the Marines. Lopez is a combat engineer with Marine Wing Support ...

, defer that to people who know what they're talkin about.)