Trail of Cthulhu contains some rudimentary guidelines for the use of explosives. They can be found on my system cheat cheet, but I’ll briefly summarize them here for easy reference.
SETTING EXPLOSIVE DEVICES: Requires an Explosives test. A Sense Trouble test (difficulty 4 or the result of the Explosives test) can be made to dive out of the way our pull comrade to Close range.
THROWN EXPLOSIVE: Make an Athletics test (difficulty 2 for point blank range, 3 for close range, or 5 for near). If aiming for for a very specific spot the difficultyies are 3 for point-blank, 4 for close, or 7 for near. If the explosive is not balanced for throwing, add +1 difficulty.
OTHER EXPLOSIVES: Artillery/mortars use a Mechanical Repair test. Rifle-Grenade uses a Firearms test.
TRANSPORTING EXPLOSIVES
These basic guidelines are quite useful. However, at the, let’s say, “prompting” of my players, I’ve found the not-so-occasional need to figure out what might be involved in the transportation and use of truly prodigious amounts of explosives. In the case of globetrotting campaigns like Eternal Lies or Masks of Nyarlathotep, this has often included hauling explosives on lengthy wilderness expeditions. (You’ll probably have similar experiences with the scenarios in Pelgrane’s Mythos Expeditions, although I don’t own that book personally yet.)
DEDICATED PORTER: An additional porter is required per 1 large gun or 1-3 charges of dynamite.
CARRIED BY INVESTIGATOR: If explosives are carried by an Investigator, they will suffer damage per day and an increased difficulty to physical tasks (as shown on the table below). A maximum of 6 charges can be carried by a single Investigator.
URBAN AREAS: Transporting large amounts of explosives through metropolitan regions usually requires a Stealth test (or similar precautions). The difficulty of this test is increased based on the number of charges (as indicated on the table below).
