Fires occur when indoor or outdoor areas that contain or are constructed from flammable materials are exposed to flame and catch fire. As the blaze spreads, creatures in the nearby area are subject to the deadly effects of fire and smoke inhalation. GMs running a fire encounter might refer to the rules for forest fires found on page 426 of the Core Rulebook. The fires detailed here suggest fire are more easily combatable fires, such as those newly sparked or spreading within an urban setting.

The Spread of Fire

Unchecked, fire tends to spread both rapidly and unpredictably. Minor factors, such as the dryness of the burning material, the presence of wind or breeze, flammable finish on flooring, dry vegetation in an area, and countless other factors can all contribute to the spread of a fire. Once a fire has burned an area, it will not return to that area. Likewise, once an area has been doused with water or covered with a non-flammable substance, such as dirt, that area is safe from further effects of the blaze for the immediate future.

Every round that a fire burns, regardless of whether characters are attempting to control it, roll 1d20 and consult the following table to determine the activity of the fire for that round and how many (if any) 5-foot squares the fire spreads to. The GM chooses which squares a fire spreads into if multiple possibilities exist. Fire cannot spread into areas where it has already been extinguished (unless noted otherwise), nor can it spread into squares where flammable materials are not present. Characters who are inside of a square when it catches fire are subject to damage, as per the rules for catching on fire on page 444 of the Core Rulebook.

Progress of Spreading Fire

Burning Buildings

Buildings that catch fire are quickly engulfed and are often a complete loss. If there are no characters or NPCs attempting to put a fire out, a building becomes unsalvageable in a space of time dependent on the size of the building. Ultimately how fast a building burns is left up to the GM to decide and depends on a variety of factors, but a rough guideline is as follows: small one-floor buildings (as occupied by many commoners) are consumed in 6d8 minutes; larger homes (like town houses and the homes of merchants) are totally consumed 4d20 minutes after catching fire; and major structures (like villas, castles, or cathedrals) are consumed in 2d4 hours. Buildings built entirely of flammable materials burn in half the time, while structures consisting mainly of non-flammable materials take half again as much time to burn. While burning, most structures begin collapsing. See the previous section for details on how to deal with such dangers.

Dense Smoke Inhalation

Dense smoke, as might fill a burning building, can prove even more dangerous than the flames that create it. In addition to the rules for smoke inhalation presented on page 426 of the Core Rulebook, a character in dense smoke must make a DC 10 Fortitude save every round that she is subject to these conditions. A character may fail this save a number of times equal to her Constitution modifier. After failing to save for the last time, the character falls unconscious and is subject to suffocation (see page 445 of the Core Rulebook).

Dousing a Fire

Dousing a fire requires a large amount of water or other non-flammable material, such as dirt, to be deposited on the burning area. One effective strategy for extinguishing a fire quickly is to surround the burning area with nonflammable material. PCs doing this must make a ranged touch attack against an AC of 10 to deliver their payload to the intended square. The following indicates how many 5-foot squares of fire a number of the listed containers can extinguish with successful delivery.

Back-drafts

Fuel-starved flames bursting into freshly opened chambers pose a lethal threat to fire fighters. Such hazards typically arise from rooms no larger than 40 square feet and sealed from ample air-flows. When these rooms catch fire, they deplete the supply of oxygen in 2d6 × 5 minutes. After such a point, the fire continues to burn, but the combustion is a slow smolder. When a door or obstruction is opened or removed, the air from outside the room rushes in and instantly restarts the flames, resulting in a fiery eruption. Any characters that are either already in the room or are within 15 feet of the newly opened entryway take 5d6 points of fire damage (DC 15 Reflex save for half ). The area opened to must be oxygen-rich for a back-draft to happen, and does not occur if one oxygen-starved room opens into another.

Firefighting Magic

A number of spells have the potential to affect areas that have caught fire and can serve to reduce the seriousness of a blaze. While these are by no means all the spells that might aid a fire-fighting spell-caster, these account for the majority of the magical effects that can be brought to bear against flames. Other obvious spells, such as control water, rely on the specifics of a situation and are left to the GM to determine the effects.

• Control Weather
  In general, weather conjured by this spell has a 40% chance to extinguish an uncovered square full of flame every round. This does not prevent flames from spreading, but those left exposed are quenched with relative swiftness. Fires burning within a structure are unaffected by this spell unless it has some obvious point of entry (such as through an open roof or large window).
  
• Gust of Wind
  This powerful wind blows out 10 feet of fire in its path. Flames blown out can be reignited by nearby flames.
  
• Ice Storm
  An ice storm extinguishes fire in the area it affects. The hail from the spell melts and leaves an area soaked, preventing it from catching fire again.
  
• Polar Ray
  This spell extinguishes the fire along the ray’s path. The ice from the spell melts due to the heat and leaves an area soaked, preventing it from catching fire again.
  
• Pyrotechnics
  Upon affecting a fire, a pyrotechnics spell extinguishes up to four squares of fire. Affecting flames with this spell can backfire upon a caster, though, potentially hindering those nearby with even more light and smoke.
  
• Summon Monster
  Several summoned creatures might possess qualities allowing them to aid in putting out fires, whether special abilities or the power to cast any of the spells noted here. Water elementals especially can put out flames in any square they cross, though burning squares count a difficult terrain for them while purposefully trying to extinguish flames. Even water elementals take damage from fire, and can be destroyed by entering a blaze.