Guide

Game incendiary and molotov fire zone systems explained

Harbor Market shipped with two incendiary grenades per attacker and objective sites barely larger than a shipping container. Defenders learned to blanket every plant volume with overlapping molotovs: each throw spawned a permanent fire decal with no fuel limit, no spread cap, and tick damage that stacked from three independent sources. Attackers crossing into site took 45 damage per second with no readable warning beyond orange particles. Rounds where the site was physically uncrossable without a full heal rotation accounted for 71% of post-plant defenses. The refactor replaced infinite decals with fuel pools that propagate along floor meshes, cap total burn area per zone, show a red floor outline one second before damage ticks begin, and allow smoke plus a one-use extinguish canister to clear lanes. Site camps fell to 24%; successful retakes rose from 29% to 61%. Incendiary and molotov fire zone systems are the authored rules for thrown area-denial fire: ignition footprints, burn damage over time, spread and dissipation, and counterplay that keeps denial tactical rather than absolute. They complement vision utilities in our smoke grenade guide and instant sensory effects in our flash and stun guide, while sharing throw mechanics with our grenade systems guide.

This guide covers fuel pool anatomy, burn tick scheduling, spread propagation, extinguish and counterplay, friendly fire policy, readability, interaction with smoke and cover, server authority, the Harbor Market refactor, a technique decision table, pitfalls, and a designer checklist.

What fire zone systems do

An incendiary grenade or molotov cocktail is a spatial damage utility whose payload is sustained area denial, not burst explosion (though some designs combine both). Good fire design creates temporary no-go zones that force repositioning, punish clustering, and reward map knowledge — without making objectives permanently sealed.

Core channels every fire zone must define:

Ignition footprint — initial splash radius on detonation; usually floor-aligned, not a full sphere.
Burn tick damage — damage per second or per tick while an actor's hit volume overlaps fuel; ties into DoT scheduling.
Fuel duration — how long the pool persists before self-extinguishing; distinct from tick interval.
Spread rules — whether fire propagates along flammable surfaces, up stairs, or stops at material boundaries.
Stacking policy — multiple pools overlapping: additive damage, max-of-sources, or diminishing returns.
Counterplay — smoke suffocation, extinguish tools, water volumes, jump-over height bands, or ability clears.

Fire zones pair with cover systems: standing cover blocks line of fire but not floor denial; players on crates may be safe if the burn volume is ground-hugging.

Ignition footprint and surface binding

Molotovs break on impact; incendiary grenades may airburst or stick. The gameplay volume should bind to navigable floor geometry, not float at the detonation centroid:

Impact normal snap — raycast down from break point; pool center projects onto walkable mesh.
Initial radius — typical PvP values: 2.5–4 m for molotov, 3–5 m for military incendiary; tune to doorway width.
Height band — damage applies from floor to 0.5–1.2 m so jumping clears low pools but not ceiling-hugging thermals.
Material tags — metal and water extinguish on contact; wood and carpet extend spread; document in level style guide.
Slope limits — fire does not climb slopes above 35° unless you explicitly author “flammable ramp” tags.

Harbor Market's bug was binding fire to the grenade's world position including Z — pools spawned mid-air on stair lips and painted infinite decals on invisible collision. Floor-only binding fixed 80% of “invisible fire” reports in the first patch.

Burn tick damage and readability

Fire damage is almost always implemented as damage over time with a short tick period (0.25–0.5 s). Players must read three signals before taking damage:

Telegraph phase — 0.5–1.0 s where the floor outline glows but ticks are zero; gives reaction time.
Active burn — ticks apply; HUD shows burn icon with DPS estimate or remaining fuel time.
Exit grace — optional 0.2 s after leaving volume before last tick; prevents edge flicker frustration.

Typical competitive tuning bands:

Phase	Duration	Damage
Telegraph	0.8 s	0
Peak burn	6–8 s	12–18 DPS
Ember fade	2 s	4–6 DPS taper

Total damage if standing center should threaten but not auto-kill a full-health player without heals — roughly 60–90 HP over full duration forces a decision, not a death sentence from one utility. Pair with health systems that expose recoverable vs permanent HP if your title uses them.

Spread propagation and area caps

Spread is what separates molotovs from static AoE circles. Production approaches:

Edge propagation — each tick, fire attempts to grow 0.3–0.5 m along adjacent walkable cells tagged flammable.
Fuel budget — pool carries N liters; spread consumes budget; when empty, fire dies regardless of time remaining.
Zone cap — max 12–18 m² per throw; prevents hallway painting from site to spawn.
Overlap merge — second molotov in same 4 m cell adds +30% duration, not a second full DPS stack.
Vertical rules — no upward spread through open stairwells unless thermobaric variant is authored separately.

Harbor Market added a per-site fuel budget of 22 m² combined — defenders could still deny a plant angle but not the entire site plus both entries. Third molotov in the same site only refreshed ember fade on existing cells, adding zero DPS.

Extinguish and counterplay

Area denial without counterplay becomes passive defense camping. Standard counterplay menu:

Smoke suffocation — dense smoke volume reduces oxygen; fire in overlapping cell extinguishes over 2–3 s. Document density threshold so players learn the combo.
Extinguish canister — limited tactical item; clears 5 m radius instantly; 45 s cooldown in Harbor Market.
Water volumes — map-authored pools and sprinklers are hard counters; use sparingly on competitive maps.
Jump and mantle — if burn height is low, skilled movement bypasses without consuming utility.
Thermobaric trade — some titles let frag grenades blow out fire cells; high risk, high skill expression.

Counterplay should be discoverable in tutorial and visible in kill feed tags (“burned,” “extinguished”).

Friendly fire and self-damage policy

Fire is the utility most likely to grief teammates. Publish explicit rules:

Self-damage — full, half, or zero on own molotov; zero encourages spam; full punishes careless throws.
Team damage — ranked often uses 50% team burn or none; casual may allow full to teach spacing.
Carrier damage — if bomb plant overlaps fire, define whether defuse is interrupted, slowed, or unaffected.
Economy cost — incendiaries priced between flash and smoke in buy-phase economy so spam has opportunity cost.

Interaction with smoke, flash, and audio

Utility composition rules prevent opaque interactions:

Smoke + fire — smoke does not extinguish unless density exceeds threshold; burning smoke needs high-contrast orange rim lighting so players see both effects.
Flash + fire — flash detonation inside fire cell does not clear fuel; blinded players still take burn ticks.
Audio — crackle loop with distance falloff; distinct from frag explosion. Increase volume 20% when local player enters telegraph zone.
Recon abilities — thermal vision may highlight fire cells through smoke; define as intentional counter-intel.

Server authority and replication

Fire state is server-owned like smoke volumes:

Server validates throw impact; spawns pool id, cell bitmask or polygon, fuel remaining, and end time.
Clients render particles and decals; damage queries use server cells only.
Spread ticks run server-side at 0.5–1.0 s intervals, not per frame.
Cap active pools per player (2–3) and per zone to protect CPU.
Replay and spectator modes show pool outlines for casters.

Desync bugs appear when client flame VFX extends beyond server cell grid. QA overlay must match damage query each build.

Harbor Market refactor

Harbor Market replaced infinite decals with a tuned fire stack:

Floor-bound pools — 3.2 m initial radius, 0.9 m height band, impact normal snap.
Telegraph outline — red floor ring 0.8 s before first damage tick.
14 DPS peak — 7 s active, 2 s ember fade at 5 DPS.
Spread cap — 8 m² per throw, 22 m² per objective site combined.
Overlap rule — second pool in 4 m: +40% duration, no DPS stack.
Smoke extinguish — density > 0.5 clears cells in 2.5 s; extinguish canister added to buy menu at 200 credits.

Metrics after eight weeks of ranked play: post-plant site camps dropped 71% to 24%; successful retakes rose 29% to 61%; molotov team-damage reports fell 58%; average round time decreased 11 s (fewer heal-stall timeouts).

Technique decision table

Approach	Best for	Weak when
Static circular pool	Arcade modes, fast iteration, mobile	Competitive site denial needs spread nuance
Cell propagation with fuel budget	Tactical shooters, lane denial, readable caps	Large open maps need big cell size for CPU
Physics fluid splash (rare)	Simulation showcases, single-player	Multiplayer determinism and net cost
Combo burst + fire (thermobaric)	Anti-camp frag alternative	Overlaps frag grenade role; tune carefully
Permanent map fire hazards	Environmental storytelling, PvE	Ranked fairness without telegraph

Common pitfalls

Invisible floor fire — VFX on wrong layer; damage on navmesh only.
Infinite stack — three molotovs = instant death; use overlap merge and site caps.
No telegraph — players blame netcode for tick deaths they could not see coming.
Airborne pools — missing floor snap on stairs and ledges.
Smoke ambiguity — unclear whether smoke extinguishes; publish threshold in patch notes.
Plant denial — fire blocks objective interaction without defuse interrupt rule; becomes hard stalemate.
Particle bigger than hitbox — classic fairness ticket generator in PvP.

Designer checklist

Define initial radius, height band, DPS, duration, and telegraph time.
Bind pools to floor geometry with material spread tags.
Cap spread area per throw and per objective zone.
Document overlap stacking: additive, max, or duration-only.
Ship smoke extinguish and/or canister counterplay.
Publish self-damage and team-damage percentages.
Show floor outline before first damage tick.
Replicate pool state server-side; clients render only.
Tag burn deaths in kill feed and death recap.
Telemetry: site camp rate, team burn incidents, extinguish usage.

Key takeaways

Fire is area denial, not a second frag — tune for repositioning, not instant kills.
Floor binding and telegraphs prevent “invisible burn” fairness issues.
Spread caps stopped Harbor Market site camps from 71% to 24%.
Counterplay is mandatory — smoke, extinguish, or movement bypass.
Server owns the fuel grid — client flames are presentation only.