Anthony puts the grenade's pin back in place. A second later, he kisses a grenade without the pin (Look at the big ring attached to the pin).
When Hal and Margaret open up the pipe when being trapped in the collapsed munition room and are almost suffocating, you can clearly hear fresh air coming in through the pipe when it opens. When breathing in an air-tight closed space, breathing doesn't create any vacuum or under-pressure at all, it just turns oxygen into carbon dioxide. Furthermore, collapsed rock and rubble can never close off a room air-tight.
Very close speaking of the air tight room how did Hal & Maggie get out of there before his dad got to the surface. In addition how did Tom Mason climb up a 20 foot wall with no hand holes without a ladder.