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Also known as gatecrashers, petards are incendiaries designed to blow open doors or other small fortifications. Petards are second level concoctions, and thus cost 1000 GP in components in addition to special ingredients, given a functional recipe. One recipe involves ash that was used in the ritual to summon a fire elemental.
Petards are designed to be more targeted than firebombs, and also use slow fuses, so they are not as effective in direct combat (though they can make excellent diversions or surprise attacks, if used tactically). The standard, and safest, use of a petard uses a full slow fuse and takes one turn. The fuse may also be trimmed for faster detonation (within 1d6 combat rounds; on a roll of 1 the detonation is premature and the petardier is caught in the blast). Any standard (even reinforced) door will be blown open by a petard charge. Solid metal doors will be blown on 3 in 6 and stone doors on 1 in 6. Anyone within 10′ of a petard detonation takes 2 dice of damage (save for half).
Longer fuses may be used, but for each turn worth of extension there is a 1 in 6 chance the fuse will go out before it reaches the petard. For example, a petard with a 4 turn fuse has a 3 in 6 chance of not detonating. Stacked petards will blow each other, but will never do more than one extra die of damage (so 10 petards results in 10 chances to blow a door but only 3 dice of damage).