I’ve found the DMG II to be a fairly frustrating supplement. It has rules for a lot of situations that I find it useful to have rules for, but I’ve found that essentially all of those rules are either needlessly complicated, unbalanced, incomplete, or some combination of the three.

Take the rules for burning buildings, for example: These rules have a marginal utility in designing an encounter with a building engulfed in flames. But they noticeably lack any rules for how such a fire might be started, prevented, or put out. The rules for how such a fire spreads are minimalistic almost to the point of non-existence (the fire spreads to a new 10′ by 10′ area every minute — which, paradoxically, means that the larger a fire is the longer it will take for it to spread outward). The rules also suggest reducing PC interactions with a burning building to a series of abstract skill checks encompassing several rounds at a time, oddly distancing them from what should be a fast-paced and dangerous encounter.

The rules I’ve devised for handling fires can be found below. They are being released under the OGL. Some of the material simply gathers existing rules for catching on fire, heat dangers, and the like from the DMG. The core of the rules are inspired from another source (check the Section 15 of the OGL), but I’ve significantly revised them with an eye towards streamlining them for easier use and reference.

ADVANCED RULES: FIRE

BASIC FIRES

A large fire is treated like a mindless construct with the following stats:

• Construct [fire]
• 1 HD (1d10) for every 5 ft. square it occupies (plus bonus hit points per a construct)
• Size determined by the number of squares it occupies
• No ability scores except for Dexterity 15
• BAB = ¾ HD (per cleric) (do not apply size modifier to attack bonus)
• Weapon Finesse (bonus feat)

A fire is immune to all attacks except water, cold, and smothering attacks.

• 1 gallon of water causes 1d6 points of damage
• Smothering a fire with a blanket causes 1d6 points of damage
• A quench spell destroys it completely

A fire can attack adjacent creatures, objects, or squares each round. It can make a number of attacks based on its size (see table).

SPREADING THE FIRE: When the fire attacks an adjacent square, it hits automatically and deals 1d6 points of damage. This is energy damage and is therefore halved against inanimate objects (although the DM can rule that certain materials are more vulnerable to fire and double this damage back to normal). The hit points of a square are determined by either its floor, wall, or ceiling (whichever is lowest).

Any items in the space being attacked are also struck by the fire and probably catch on fire. If an object in a space is on fire, the space it’s in also takes 1d6 points of damage each round.

As a special exception to the normal rule, accumulate all damage from a spreading fire into a single total for the round before applying the space’s hardness.

Once a square has lost half its hit points, the fire spreads to that square (increasing its size). However, once the square loses all of its hit points, the fire will burn out in that square (decreasing its size).

CHALLENGE RATING: A fire of size Large or smaller is CR 2. Larger fires are CR 4. Collapsing attacks or dangers increase the Challenge Rating by +1.

BUILDING COLLAPSE

Characters in a building with wooden ceilings and floors that have been burning at least 10 rounds may face collapse. There is a 20 percent chance each round in such a burning building that a character faces a +10 attack from a falling rafter or bit of ceiling; an attack that hits inflicts 2d6 points of damage.

If the fire has been burning for ten minutes or more, the entire ceiling might collapse instead (20 percent chance). In such a case, no attack roll is needed—all characters within suffer 8d6 points of damage (Reflex save, DC 15, for half damage).

CHARACTERS IN A FIRE

CATCHING ON FIRE: Creatures or objects struck by a fire suffer 1d6 points of damage. They are also at risk of catching on fire and must make a Reflex save (DC 15) to avoid this fate. If a character’s clothes or hair catch fire, they take an additional 1d6 points of damage immediately. In each subsequent round, the burning character must make another Reflex saving throw. Failure means they takes another 1d6 points of damage that round. Success means that the fire has gone out. (That is, once they succeed on their saving throw, they are no longer on fire.)

A character on fire can automatically extinguish the flames by jumping into enough water to douse themselves. If no body of water is at hand, rolling on the ground or smothering the fire with cloaks or the like as a full round action permits the character another save with a +4 bonus.

Those unlucky enough to have their clothes or equipment catch fire must make a Reflex save (DC 15) for each item. Flammable items that fail take the same amount of damage as the character.

Objects on fire do not benefit from their hardness.

IN A FIRE: Characters moving through a fire provoke an attack of opportunity from the fire (there is no limit to the number of attacks of opportunity a fire can take). Characters who end their turn in a fire are automatically hit by the fire.

HEAT DANGERS: Characters in a burning building are considered to be in severe heat. Those standing close enough to the fire are considered to be in extreme heat (see table for the danger distance, depending on the size of the fire). See Heat Dangers in the DMG for more information.

Severe Heat: In severe heat (above 110° F), a character must make a Fortitude save once every 10 minutes (DC 15, +1 for each previous check) or take 1d4 points of nonlethal damage. Characters wearing heavy clothing or armor of any sort take a –4 penalty on their saves. A character with the Survival skill may receive a bonus on this saving throw and may be able to apply this bonus to other characters as well. Characters reduced to unconsciousness begin taking lethal damage (1d4 points per each 10-minute period). A character who takes any nonlethal damage from heat exposure now suffers from heatstroke and is fatigued. These penalties end when the character recovers the nonlethal damage she took from the heat.

Extreme Heat: Extreme heat (air temperature over 140° F, fire, boiling water, lava) deals lethal damage. Breathing air in these temperatures deals 1d6 points of damage per minute (no save). In addition, a character must make a Fortitude save every 5 minutes (DC 15, +1 per previous check) or take 1d4 points of nonlethal damage. Those wearing heavy clothing or any sort of armor take a –4 penalty on their saves. In addition, those wearing metal armor or coming into contact with very hot metal are affected as if by a heat metal spell.

SMOKE INHALATION: Characters close enough to be suffering extreme heat from a fire are also close enough to be breathing heavy smoke. They must make a Fortitude save each round (DC 15 +1 per previous check) or spend that round choking and  coughing. A character who chokes for 2 consecutive rounds takes 1d6 points of nonlethal damage. Smoke obscures vision, giving concealment (20 percent miss chance) to characters within it.

Advanced Rules: Crowds – Design Notes Encumbrance by Stone – Design Notes Advanced D20 Rules: Extra Effort