Here are the top fire‑protection systems and approaches for data centers in 2025, with the key pros/cons and where they fit in a layered protection strategy. I’ve ranked them by how commonly they’re recommended today for protecting uptime, equipment and people.

1. Very‑Early (Aspirating) Smoke Detection — VESDA / ASD

• What: Active air‑sampling detectors that continuously draw air to a central laser chamber (VESDA is the market example).
• Why top choice: Detects trace smoke long before flaming, enabling intervention (isolation, shutdowns, targeted suppression) and reducing false trips in high‑airflow rooms. Ideal as the “first line” in any mission‑critical facility. (Honeywell.com)
• Downsides: Higher up‑front cost and needs careful design/commissioning to avoid nuisance alarms.

2. Clean‑Agent Gaseous Suppression (Novec 1230, Inergen/IG‑541; FM‑200 in decline)

• What: Stored gaseous agents discharge to extinguish fires without leaving residue — commonly Novec 1230 and Inergen (IG‑541). (FM‑200 has been widely used but has higher GWP and is losing favor.)
• Why useful: Fast, effective, little to no cleanup; suitable where water would cause unacceptable damage to IT. Novec is favored for low‑GWP profile and safety margin; Inergen is effective and uses inert gases. (linkedin.com)
• Downsides: Requires room integrity (sealing), safe discharge protocols for occupied spaces, cylinder room footprint and periodic inspections. Note: some suppliers and insurers are shifting away from some halocarbon agents for environmental/regulatory reasons.

3. Water‑Mist (Low‑flow / High‑pressure) — FM‑approved options

• What: Fine‑droplet mist that cools and displaces oxygen locally; can be low‑flow or high‑pressure designs.
• Why now: Increasingly accepted for data centers (FM and other bodies have approved water‑mist system designs for data center use). Water‑mist greatly reduces total water used vs. conventional sprinklers and can limit damage while providing robust suppression. Good option where water damage penalties are acceptable or where clean agents aren’t feasible. (fire-techinfo.com)
• Downsides: Still involves water exposure (though far less than sprinklers); design/approval must match FM/NFPA guidance.

4. Pre‑action / Double‑Knock Sprinkler Systems (with rack‑level zoning)

• What: Sprinkler piping remains dry until a two‑step trigger (detection + heat) — minimizes accidental water discharge. Often used in conjunction with room and building sprinkler systems.
• Why useful: Reliable, code‑based last resort for full‑room fires; widely understood by AHJs and insurers. NFPA guidance expects sprinkler consideration depending on risk. (techtarget.com)
• Downsides: Water damage risk if activated; slower than clean agents/water mist to prevent early smoldering damage unless paired with early detection.

5. Rack‑Level / Local Pre‑Engineered Suppression (e.g., tubing systems, aerosol or small clean‑agent cylinders)

• What: Small, fast‑acting systems installed in or on racks (e.g., Firetrace, Ansul, rack‑mounted clean agents or aerosols).
• Why useful: Detects and suppresses at the rack level before fire spreads; minimizes collateral impact and downtime for other racks. NFPA now recognizes rack‑level approaches as part of a layered defense. (techtarget.com)
• Downsides: Adds complexity and maintenance per rack; needs careful integration with room systems and IT procedures.

6. Off‑gas / Battery‑specific Detection (for rooms with Li‑ion UPS / ESS)

• What: Sensors that detect decomposition/off‑gas from battery failures (early indicator of thermal runaway).
• Why useful: NFPA and standards now emphasize off‑gas detection for rooms with batteries/energy storage — a critical addition as more data centers add Li‑ion UPS and ESS. (fire-police-ems.com)
• Downsides: Must be tailored to battery chemistry and layout; not a substitute for thermal/voltage battery management.

7. Integrated Monitoring, Controls & Procedural Layers

• What: Alarm management, building automation integration, acoustic/noise mitigation on agent discharge, remote monitoring, emergency procedures and regular fire drills.
• Why essential: Detection + suppression only work if tied to procedures (isolate zones, safe shutdowns, coordinated responses with AHJ/ops). Standards (NFPA 75) and insurers expect documented emergency/recovery plans and testing. (fire-police-ems.com)

How to choose (practical guidance)

• Use a layered approach: Very‑early detection (ASD/VESDA) + one of (clean‑agent OR water‑mist OR pre‑action sprinklers) + rack‑level protection + off‑gas for battery rooms + solid procedures. Early detection greatly reduces the need for full‑room suppression and false discharges. (Honeywell.com)
• Follow NFPA 75 (2024 edition) and coordinate with your Authority Having Jurisdiction (AHJ) and insurer — code requirements and insurer preferences materially affect accepted solutions. (fire-police-ems.com)
• Consider lifecycle factors: environmental policy (GWP), availability of agents (supply chain & manufacturer support), maintenance costs, space for cylinder rooms, and retrofit complexity. Recent industry movement has increased interest in water‑mist and inert/low‑GWP agents. (fire-techinfo.com)

Vendors & technologies to evaluate (examples)

• Early detection: Honeywell VESDA (Xtralis), other ASD vendors. (Honeywell.com)
• Clean agents and rack systems: Kidde (Carrier), Johnson Controls/Ansul, Fike, Victaulic (pre‑action hardware) and local rack system vendors (Firetrace, others). (firetron.com)
• Water mist suppliers: SEM‑SAFE, other FM‑approved manufacturers. (sem-safe.com)

If you want, I can:

• Draft a short comparison matrix (cost/benefit/typical use) of the top 4 solutions above for your facility size/type, or
• Summarize NFPA 75 key clauses relevant to choosing detection vs suppression for your specific configuration (room vs modular vs rack).