The key is the airtight room. We know it was airtight because the homeowner felt pressure when he tried to open the door.
The explosion is because the pressure kept building up until it reached the breaking point of the container (the airtight room).
This would not have happened in a room with normal ventilation.
OK I viewed the ENTIRE video and re-read the article.
So this was a secure room UNDER his house. Implies lockable/ sealable. WHOLE different scenario in place.
Ever seen “Backdraft”? Know what one really is?
slow burning fire, low O2 levels, explosive mixture at high end of limits.
somehow O2 is introduced — door opens, window breaks dunno. BOOM!
Explosion happens, small fire (if any) burns.
OK, I can let this go ;-)
the “concrete that moved” part is kinda impressive. His wife was OUTSIDE on the patio. Implies considerable explosive force under the patio.