Guide

Game HE grenade and high-explosive blast damage systems explained

Harbor Breach, a 5v5 tactical shooter, launched ranked with a single high-explosive (HE) grenade profile: flat 120 HP damage inside a 6 m sphere, no armor interaction, and no material-aware penetration. Post-plant retakes on cramped sites like B Vault became a lottery: defenders hugging corners behind thin plywood took lethal damage through geometry that looked solid, while players in open doorways sometimes survived at 4 m because the client showed a different blast VFX radius than the server applied. Telemetry tagged 58% of HE kills as “unfair nade death” — victims could not predict whether a cooked nade would one-shot, chip, or whiff.

The refactor replaced the flat sphere with a server-authoritative blast resolution pipeline: detonation FSM, radial falloff curves, line-of-sight occlusion rays, armor and helmet modifiers from the armor system, and wallbang coupling through the penetration material table. Audio and minimap tag telegraphs give defenders a readable wind-up. Unfair nade deaths on post-plant retakes fell from 58% to 14%; HE utility purchase rate rose 22% once players trusted the math. This guide explains what HE grenade systems do, how detonation and falloff work, armor and penetration coupling, friendly fire policy, the Harbor Breach refactor, a decision table, pitfalls, and a production checklist.

What HE grenade systems do

An HE grenade (also called a frag or explosive grenade in competitive shooters) is a damage utility distinct from vision denial (flash, smoke) and area denial (molotov). Its job is to convert positioning mistakes into chip or lethal damage — clearing corners, punishing stacks, and finishing wounded targets after rifle exchanges.

Core responsibilities

Detonation authority — server owns fuse expiry, impact detonation, and cook timing inherited from throwable physics.
Blast sampling — for each player in radius, compute distance falloff, LOS occlusion, and penetration attenuation.
Damage application — apply base blast damage through armor, helmet, and ability shields; emit kill feed and assist credit.
Feedback telegraphs — pre-detonation audio pin, ground decal, tag pulse on minimap, and post-blast ringing for survivors.
Policy gates — friendly fire tier, self-damage cap, and round-phase restrictions (buy phase, warmup).

HE systems sit downstream of throw arc and fuse logic. If those are wrong, perfect blast math still feels random. Treat HE as a damage resolver, not a separate grenade codebase.

Server detonation FSM

Model each live grenade entity as a finite state machine on the authoritative simulation tick:

THROWN — entity spawned with thrower ID, fuse deadline, cook offset, and team affiliation.
IN_FLIGHT — physics integration for arc, bounce, and sticky attachment; optional beep cadence in last 500 ms.
ARMED — fuse reached zero or impact trigger fired; freeze position; broadcast pre-blast telegraph (audio + decal).
DETONATING — sample blast volume; enqueue damage events per target; spawn VFX and debris (client cosmetic only).
RESOLVED — emit analytics row; despawn entity; apply post-blast tag debuff if configured.

Detonation must be idempotent: laggy clients may request impact twice; only the first ARMED transition executes DETONATING. Replays and kill cams read the resolved damage list, not client-side particle radius.

Falloff curve profiles

Profile	Max damage	Lethal radius	Chip radius	Use case
Ranked standard	95 HP	2.2 m	5.5 m	Tactical shooters; rewards spacing without full-map chip
Ranked light	70 HP	1.8 m	4.5 m	Lower TTK titles; HE finishes, rarely solos
Hardcore	150 HP	3.0 m	6.0 m	One-life modes; HE is primary area weapon
Training	40 HP	1.0 m	8.0 m	Practice range drills with wide chip for feedback

Use smooth falloff (e.g. quadratic or inverse-square clamped) rather than step bands. Step bands create invisible “damage cliffs” one footstep wide that players learn only by dying.

Line-of-sight occlusion and penetration

Raw radial distance is not enough. Competitive integrity requires two more gates before applying damage:

Direct LOS ray — from blast center to target capsule; any opaque collision mesh blocks full damage unless penetration applies.
Penetration attenuation — thin materials (wood, drywall) reduce damage per the material table shared with wallbang hitscan; thick steel blocks entirely.
Cover hint volume — optional designer-placed volumes tagged HARD_COVER apply a flat 50% reduction even when LOS is technically open (represents partial entrenchment).

Harbor Breach's pre-refactor bug was applying full damage when any ray from blast to target intersected a penetrable surface — even when the player was behind three layers of concrete. The fix requires shortest-path penetration budgeting: sum material thickness along the ray; stop when budget exceeds grenade penetration class.

Penetration class table (example)

Material tag	Thickness budget cost	Max stacks
Wood / plywood	0.4 m eq	3
Thin metal	0.8 m eq	2
Concrete	2.0 m eq	1
Steel / vault	Blocks	0

Armor, helmet, and chip damage

HE damage should flow through the same armor resolver as bullet hits, with grenade-specific modifiers:

Armor body multiplier — typically 0.65–0.80 for kevlar; HE ignores some armor in hardcore modes only.
Helmet gate — if blast center is above target waist and helmet equipped, apply helmet reduction to headshot-class portion (often 20–40% of total blast when crouched behind low cover).
Chip floor — minimum 5–12 HP chip at max radius so HE always “does something” when it lands near you.
Overkill suppression — damage beyond lethal HP does not roll into overkill stats; keeps assist attribution clean.

Self-damage uses a separate multiplier (often 0.5×) so aggressive cooks are possible without instant self-elimination. Team damage follows friendly-fire tier policy.

Tag, audio, and minimap telegraphs

Unfair nade deaths often trace to missing wind-up, not wrong numbers. Minimum telegraph stack:

Pin pull audio — audible at 8–12 m; distinct from flash or smoke pin if those share animations.
Ground impact clack — confirms landing position for defenders; sync with server entity position, not client prediction.
Pre-detonation beep — last 300–500 ms at fixed cadence; hearing-impaired accessibility via screen-edge pulse.
Tag debuff — optional 2 s minimap ping on damaged survivors; decays faster than rifle tag to avoid permanent tracking.
Post-blast tinnitus — short audio muffling for survivors only; do not stack with flash tinnitus at full intensity.

Spectator and broadcast modes should show blast center decal without revealing pre-throw trajectory ghosts that spoil attacker intent in clutch 1vX.

Harbor Breach refactor

Before the blast pipeline, Harbor Breach HE kills drove support tickets about “random nades through walls.” Post-refactor changes:

Quadratic falloff: 95 HP at 0 m, 40 HP at 2.2 m, 12 HP chip at 5.5 m.
Penetration budgeting shared with wallbang material table; steel blocks.
Armor multiplier 0.72 body; helmet reduces elevated blast component.
Pre-detonation beep + ground decal synced to server ARMED state.
Analytics: unfair_nade_death_rate per map site and rank tier.

Post-plant retake success rate (attackers reclaim site within fuse window) rose from 41% to 49% — not because nades got stronger, but because attackers learned readable chip lines. Unfair nade deaths fell from 58% to 14%.

Decision table: HE blast resolver vs alternatives

Approach	Strength	Weakness	When to use
Full blast pipeline (this guide)	Predictable; armor-aware; wallbang-consistent	CPU cost per detonation; tuning surface	Ranked tactical shooters with HE utility
Flat damage sphere	Trivial to implement	58% unfair deaths in Harbor Breach playtest	Avoid in ranked
Client-only VFX radius	Looks impressive	Desync kills trust; exploit bait	Never for damage authority
Instant ray-only (no falloff)	Easy LOS check	No skill in spacing; binary live/die	Arcade modes only
No HE utility	Zero balance risk	Retake meta stagnates; role homogenization	Only if utility budget is zero-sum elsewhere

Pitfalls

VFX radius larger than server radius — players dodge damage they think they escaped; classic unfair-death source.
Penetration ignores thickness — one plywood sheet equals three; vault walls feel inconsistent.
Armor bypass accidentally — HE one-shots full-buy players; eco nades dominate rifle duels.
No self-damage cap — cooked nades become suicide only; entry fraggers stop using HE offensively.
Tag debuff permanent — minimap tracking for 10 s after 5 HP chip; defenders feel punished for surviving.
Double damage on multi-tick detonation — idempotency bug applies blast twice on high packet loss.
FF tier mismatch — ranked blocks rifle FF but HE team damage still on; griefing vector.
Warmup HE kills counted — practice lobbies inflate nade-death analytics used for balance patches.

Production checklist

Define max damage, falloff curve, lethal radius, and chip floor per playlist.
Implement THROWN through RESOLVED detonation FSM with idempotent ARMED.
Sample damage with LOS rays and penetration budget from material table.
Route damage through armor, helmet, and ability shield resolver.
Apply self-damage and friendly-fire multipliers per policy tier.
Sync pre-detonation audio, ground decal, and beep to server ARMED state.
Emit kill feed, assist credit, and tag debuff events to analytics bus.
Match client VFX outer radius to server chip radius within 5% tolerance.
Dashboard unfair_nade_death_rate by site, rank tier, and material tag.
Playtest post-plant retakes, stack clears, and self-cook entry lines.
Document HE damage numbers in competitive rulebook and buy-menu tooltip.
Re-QA after armor, penetration, or throwable fuse system changes.

Key takeaways

HE grenades are damage resolvers — not independent VFX toys.
Smooth radial falloff plus LOS and penetration gates make nade deaths readable.
Armor coupling prevents eco nades from invalidating rifle investment.
Pre-detonation telegraphs reduce tilt as much as tuning max damage.
Harbor Breach cut unfair nade deaths from 58% to 14% with falloff, penetration budgeting, and synced telegraphs — not by removing HE utility.