This glass has an extremely high blast resistance and cannot be broken by any explosive weaker than a Nuke. 2 layers of this glass will resist any explosion in the game, including a full Nuclear Reactor.
To remove placed hardened glass, use any BuildCraft compatible Wrench (or the OmniWrench) and shift right click it. The glass will drop on the ground as an item. Note that this is the only way to retrieve placed glass.