Picking up from the post about the Myth Dwarf class...
Dwarven grenades have a range of 40' (80' for Myth Dwarves, since their range increments are doubled for throwing weapons), and a blast size of 25' by 25'. Note that I use 5' squares/spaces for movement in my campaign. Small grenades do 3d6 damage when exploding, and large ones do 4d6. A Save vs. Breath will halve this damage. Being hit up an undetonated grenade does no damage.
Dwarven grenades, both small and large, are not used like regular throwing weapons. Instead, the thrower must make a Tinker check. If successful, the grenade goes exactly where the thrower intended (provided this place is within range) and explodes. If failed, the thrower rolls a d6. On 1-5, the grenade was not lit or thrown properly and becomes a dud. It is still thrown to the desired location, though, so another bomb or intense flame could set it off in the future. On a 6, the grenade blows up in the thrower's face - no saving throw for the thrower, but others within range get a Save vs. Breath for half damage. Exception: If a Dwarf fails a Tinker check to throw a grenade, no d6 is rolled. It is always a dud instead of a face-exploding disaster. Naturally, Dwarves can still find plenty of other ways to blow themselves up, like throwing grenades successfully at targets that are too close.
Yes, this means that as long as the grenade is thrown intact, it can never miss, but only fail to explode. Yes, I know this is completely unrealistic and not even very good at emulating the source fiction, since dwarves in the Myth games throw their bombs too near or far or off to the side all the time in the Myth games. I considered a bunch of different, more complex, and frankly better grenade rules before setting on this system because it is simple and easy to use and doesn't trip me up, and it possibly makes grenades more useful and far less likely to result in unintentional TPKs, which would probably make my players never want to play a dwarf again and thus make me sad because I love the dwarves in Myth. I'm thinking I should change these rules anyway, but I haven't gotten around to it yet.
Satchel charges do 6d6 damage, and have the same blast size as grenades. They are over-encumbering items. They are not thrown, but rather placed on the ground ahead of time. They can be detonated by another explosive, a thrown torch, flaming oil, a long fuse, etc. They are mainly used as traps, although they can also be put to use demolishing structures.
A Dwarven mortar is a big, over-encumbering, one-Dwarf artillery piece. Short range for a mortar is 100', medium is 200', and long is 600'. It costs 500sp and basically functions like a longer-range musket that does 6d6 damage. When attacking with a Dwarven mortar, a Dwarf does so with an attack bonus equal to a Fighter of the same level - this is only for Dwarven mortars, not other kinds of guns. If the attack hits, the target and anyone within a 25' by 25' square centered on the target take 6d6 damage, Save vs. Breath for half. It takes the same amount of time to reload a Dwarven mortar as it does to reload a musket. There is no misfire chance for a Dwarven mortar used by a Dwarf, and the normal misfire chance for a musket when used by anyone else. Firing the weapon does not require a Tinker check to avoid a dud.
Keep in mind that a player who dies by total immolation or some kind of powerful fire or heat attack while carrying dwarven explosives will, of course, explode in a chain-reaction, probably resulting in a TPK anyway as everyone caught in the blasts takes damage from every bomb the character was carrying. This kinda-sorta happened once - I'll provide the details if I ever get around to doing a write-up of our experience with the LotFP adventure Fuck for Satan.
Dwarven explosives are illegal to buy or sell, but legal to own, throughout the Cath Bruig Empire. Dwarves tend to be extremely protective of the secret alchemical formulas for their explosives, and it is illegal for Dwarves to teach these formulas to humans or other non-Dwarves without the express, written permission of the Dwarven government (or, in the rarest cases, the Cath Bruig Emperor himself). The penalty is exile from Dwarven lands, forfeiture of all dwarf-related property rights and inheritances, and a general pariah status among Dwarves everywhere. An exiled Dwarf who returns to Dwarven lands can be killed on sight. A human who is permitted to learn the formulas is sworn to abide by these same laws.
Human PCs who do learn these formulas can make Dwarven explosives if they are of the appropriate level (1 for small grenades, 4 for satchel charges, etc.), but it takes them 1d6 days each to make the first three of each type of bomb, since it takes some time to get the hang of the process.
I am considering adding more restrictions to the ability of other classes to make bombs.