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In an upcoming game, a conflict will be held in a massive underground cavern. One of the options to the PCs will be to collapse the cavern to prevent the enemy from advancing. My question is if there are any rules in the books that handle underground collapses, particulalry damage and survivability? I remember seeing it somewhere in a Rifts book, but an SDC source will be fine (it's an SDC world we're playing in)

Any help would be appreciated. Thanks

If you're talking about truly collapsing a "massive underground cavern" on somebody, damage and survivability consist of "More than you can take" and "You die" respectively. Dropping the ceiling on yourself is a nice dramatic way to go, but is the sort of thing that is an auto-kill.

If you're just talking about collapsing the ceiling next to yourself, so you're trapped in a cave like the victim of a coal mine accident or something, it's not really a matter of damage so much as a save versus unconsciousness each hour as the air thins out and oxygen levels drop, with standard coma survival rules if you are miraculously rescued.

If you're just worried about a loose piece or two of rock falling and hitting people, not a true collapse, go with the 1D6 per 10 pounds rule. A piece of granite roughly 1 cubic foot in size will weigh in at around 166 pounds, and would hit from a 30 foot ceiling at approximately 20 mph. Take 16D6 damage, and roll on the critical injury table. A bigger chunk, say 1 cubic yard, will weigh in near 4500 pounds... see above re: auto-kill.

Rocks fall, everyone dies.

I don't know who said it first but it has become a cliche and a trope within the RPG community.

Thinking about, the only place I saw something similar in any Palladium book was in the RDF Accelerated Training Manual. There was a holographic simulation where firing missiles in an under water cavern had a percentage chance of causing a cave in. It gave damage (in MDC) and I believe also caused the mecha to be pinned. I don't have access to that book at the moment however. If I had to guess, I think it was 2D4X10.

If you want a precedent, you can look at telekinesis and use the damage values given in there as a guideline for falling rock damage.

While realistically anyone caught in a complete cave in is likely to be dead, people do sometimes survive such things although they usually require rescuing. For cinimatic effect I would have all important people (PC's and important NPC's) caught in such a collapse to survive by being caught in a relatively stable air pocket. I would grant them 10% of their base hitpoints and let them try and figure out how to get out.

Not sure if it was the first person to say it but my first experience with that trop was in the webcomic Foxtrot. Where Jason convinces his sister to play D&D. She spends several hours making a character which dies 2 minutes into the game.