Marsec High Explosive
A high explosive system for breaking through barriers or impassable terrain. Extra care must be taken when throwing this device. Its increased size means that it can't be thrown the same distance as a conventional grenade. From: Apocalypse Ufopaedia
A strong but heavy,
demolition charge explosive grenade used to injure or kill stronge hostile forces, destroy building structures such as wall, ramps, fire escapes etc. and may form a crater in grassy terrain. An agent may not be strong enough to throw such a heavy device far enough to escape its blast radius, so using detonate-on-impact may not be suitable unless thrown from a high elevation, onto hostiles below. The timer should be set enough for agents to leave the immediate area.
It is possible to bring down entire buildings through proper placement and timing of enough High Explosives. As a example see: