question
The people on Black Ridge scream but are unable to hear themselves over the vast, grinding,building roar as eighty pounds of plastic explosive and ten thousand gallons of propane undergo an explosive change. They cover their eyes and stagger backward, stepping on their sandwiches and spilling their drinks. Thurston snatches Alice and Aidan into his arms and for a moment Barbie sees his face against the blackening sky—the long and terrified face of a man observing the literal Gates of Hell swing open, and the ocean of fire waiting just beyond.

Q 1: In “building roar as eighty pounds”, "as" means “when”?

Q 2: "an explosive change" == "an exploding"?

Q 3: In “sees his face against the blackening sky”, his face means “Thurston’s face”?

Question

question
The people on Black Ridge scream but are unable to hear themselves over the vast, grinding,building roar as eighty pounds of plastic explosive and ten thousand gallons of propane undergo an explosive change. They cover their eyes and stagger backward, stepping on their sandwiches and spilling their drinks. Thurston snatches Alice and Aidan into his arms and for a moment Barbie sees his face against the blackening sky—the long and terrified face of a man observing the literal Gates of Hell swing open, and the ocean of fire waiting just beyond.

Q 1: In “building roar as eighty pounds”, "as" means “when”?

Q 2: "an explosive change" == "an exploding"?

Q 3: In “sees his face against the blackening sky”, his face means “Thurston’s face”?

Answer

1.Perhaps more "while" than "when". The latter describes a point in time whereas "while" and "as" talk about a duration, although in this case, I guess it's over so quickly it doesn't make much difference.
2. The guy must have needed to get his word count up. "Undergo an explosive change" = "explode".
3. Yes, just like "his arms".