NFPA 855 Guide: Complying with the Battery Fire Code for Safer Energy Storage Systems

Investors love growth stories—but they also read incident reports.

In New York City alone, lithium-ion battery fires surged nearly ninefold – from 30 in 2019 to 268 in 2023 – illustrating how quickly these incidents can escalate (New York Post).  

One Moss Landing-scale event can stall a funding round or force a product recall. NFPA 855—the “Standard for the Installation of Stationary Energy Storage Systems”—spells out how to design, site, and maintain battery systems without courting those headlines.

This guide unpacks the code, aligns it with typical startup milestones, and offers practical next steps so you can de-risk certification, compress sales cycles, and maintain investor confidence.

Key Points

• NFPA 855 is the leading fire-safety standard for stationary energy-storage systems. It is increasingly being adopted in model fire codes and by authorities having jurisdiction (AHJs), making early compliance important for approvals, insurance, and market access.
• Core requirements include rack separation limits, a Hazard Mitigation Analysis to prevent thermal-runaway cascades, early-acting fire suppression and gas detection, stored-energy caps for occupied buildings, and detailed safety documentation (UL).
• UL 9540A thermal-runaway testing is the evidence base for NFPA 855 decisions on spacing, vent sizing, and suppression; bring these test summaries to AHJ pre-application meetings to streamline approvals (NFPA).
• Embed NFPA 855 checkpoints into each development sprint—prototype Hazard Mitigation Analysis (HMA), pilot-site emergency plans, and final commissioning reports—to avoid late-stage redesigns and accelerate EPC, PPA, and insurance negotiations (UL).
• Post-deployment, NFPA 855 mandates commissioning, periodic inspections, and thorough record-keeping (e.g., UL 9540A test reports and HMA documentation). NFPA 70B provides maintenance interval recommendations; however, NFPA 855 does not set quarterly or annual requirements or address O&M cost implications (UL).  

Understanding NFPA 855

NFPA 855 is the flagship fire-protection code for stationary energy storage systems (ESS), covering everything from coin-cell pilot rigs to multi-megawatt battery energy storage systems (BESS). Its scope spans siting, construction, ventilation, detection, suppression, and emergency response planning.

How it Harmonizes

• NFPA 70 (National Electrical Code): Governs wiring methods inside the ESS enclosure.
• NFPA 72 (Fire Alarm and Signaling): Dictates detection and notification requirements.
• UL 9540A: Provides thermal-runaway testing data that the AHJ uses to verify NFPA 855 mitigation strategies.

“NFPA 855 aims to mitigate risk and ensure that all installations are done in a way that takes fire and life safety into consideration,” notes Brian O’Connor, P.E., NFPA staff liaison (Utility Dive).

Key NFPA 855 Requirements

NFPA 855 converts abstract risk into measurable design targets. Below are the clauses most likely to trigger redesigns if discovered late.

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Values represent common jurisdictional thresholds—always confirm local amendments.

1. Siting & Separation

Battery racks exceeding the thresholds above must be separated by fire-rated walls or additional spacing. Outdoor containerized units may qualify for reduced distances if UL 9540A test reports demonstrate limited thermal-runaway propagation.

2. Thermal Runaway Mitigation

Thermal runaway remains the primary cause of BESS fires (Jensen Hughes). NFPA 855 now requires a Hazard Mitigation Analysis (HMA) to prove that single-cell failure will not trigger cascading events. “The HMA is step number one,” stresses Deputy Fire Marshal Brian Scholl, NFPA 855 committee member (Fire Suppression Systems Association).

Firefighters assess a lithium-ion BESS fire—exactly the hazard NFPA 855’s thermal-runaway provisions seek to prevent.

3. Fire Suppression & Detection

• Clean-agent or water-mist systems must activate before cell venting escalates.
• Off-gas detection and remotely monitored gas sensors are now recommended practice (UL FSRI).

4. Stored-Energy Caps

Systems exceeding 600 kWh in occupied buildings typically require dedicated battery rooms, explosion-venting, and emergency power-off circuits (ZincFive).

5. Documentation

Safety Data Sheets (SDS), commissioning plans, and maintenance manuals are enforceable deliverables. Failure to provide them can halt an AHJ plan review.

Navigating Battery Fire Code Intersections

NFPA 855 is rarely applied in a vacuum. The 2024 International Fire Code (IFC) Chapter 12 incorporates many NFPA 855 tables but may differ on separation language (ICC Digital Codes).  IFC is adopted statewide in 42 states (plus PR & VI), indicating broad reliance on IFC for fire-code enforcement; local ESS provisions typically flow from the IFC chapter on Energy Systems (Sandia).

Startup-Friendly Checklist for Zoning & AHJ Approvals

• Bring UL 9540A summary tables to pre-application meetings.
• Verify if your municipality has adopted the 2019 or 2023 edition.
• Ask for written clarification on containerized systems; some AHJs classify them as “mobile,” excluding them from NFPA 855.
• Document any local amendments (e.g., Phoenix HMA mandate) to avoid mid-construction redesigns.

Being proactive here prevents the “double jeopardy” of redesigning for both NFPA 855 and IFC after prototypes ship.

Designing for Energy Storage Fire Safety: Engineering Controls and Best Practices

Turning code clauses into CAD models and bill-of-materials decisions is where startups win or lose runway.

Cell Spacing & Pack Architecture

Evidence supports that increasing cell spacing inhibits or can prevent propagation; e.g., tests found ≥ 2 mm horizontal spacing (open environment) made propagation “hardly occur,” and > 4 mm horizontal (closed environment) prevented propagation (Springer).

Off-Gas Detection

UL Fire Safety Research Institute (FSRI) identifies off-gas sensing (HF, CO, H₂, hydrocarbons) as an early-warning method for Li-ion thermal-runaway/deflagration hazards; NFPA 855 does not prescribe specific detection setpoints. Use low-ppm, early-warning sensors tied to remote monitoring so operators can act before first responders (ScienceDirect).

Deflagration Venting

Use UL 9540A installation-level gas data to determine the mixture’s percentage of Lower Flammable Limit (LFL) ; if a deflagration hazard is credible, design and verify explosion relief per NFPA 68, setting vent area and panel set pressures (Pstat/Pred) by calculation and manufacturer data (Jensen Hughes).  The Arizona 2019 incident injured four firefighters when accumulated gases ignited upon door opening (Fire Protection Research Foundation).

Thermal Barriers & Insulation

Use high-temperature ceramics or intumescent coatings between modules; published tests show these barriers can delay or suppress thermal-runaway propagation.

“The technology's overall safety record is strong and improving—there were about the same number of fires in 2023 as in 2019, even as global battery storage deployments have increased 20-fold,” notes the Electric Power Research Institute (EPRI).

Expert Tip

Run computational fluid-dynamics (CFD) plume modeling to visualize worst-case off-gas flow within enclosures. Early CFD finds vent-placement issues before metal is cut.

Compliance Roadmap from Prototype to Field Deployment

Aligning NFPA 855 checkpoints with product-development sprints avoids late-stage backtracking.

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Document as you go. Retrofitting paperwork costs multiples of doing it contemporaneously—and VCs will notice.

Documentation, Testing, and Ongoing Maintenance Obligations Under NFPA 855

Compliance does not stop at COD (commercial operation date).

Commissioning Tests

• Fire-suppression acceptance test per the applicable NFPA standard (e.g., NFPA 13 for sprinklers; NFPA 2001 room-integrity for clean agents) (GJFD).
• Verification that gas sensors alarm at calibrated setpoints
• End-to-end shutdown simulation with utility interconnect

Periodic Inspections

Use NFPA 70B to establish a risk-based Electrical Maintenance Program (EMP) with intervals set per Table 9.2.2 (e.g., periodic infrared inspections and torque verification per manufacturer). Intervals follow an NFPA 70B risk-based program instead of preset quarterly/annual schedules (Expanse Electrical).  

Plan fixed O&M at ~2.5% of CAPEX per year (per NREL’s 2023 Annual Technology Baseline for utility-scale battery storage, which estimates fixed O&M at 2.5% of capital cost).

Record-Keeping Essentials

Keep records per the applicable standard/AHJ (e.g., NFPA 72/25 retention rules):

• Maintain BMS health logs per OEM and your NFPA 70B maintenance program (frequency is program-based) (US DOE).
• Follow the ITM standard for your system (e.g., NFPA 2001 often semi-annual; NFPA 25 uses monthly/quarterly/annual for sprinklers).
• Keep module replacement/maintenance records per OEM and your maintenance program (commonly reviewed by the AHJ).

Paper or electronic records are generally acceptable if they meet content/format the AHJ requires.

Obtaining NFPA 855: About This Product, Related Products, and Digital Resources

NFPA sells the standard in three formats:

• PDF Download: Instant access, search-friendly.
• Hardcopy Handbook: Includes commentary and visuals—handy for whiteboard sessions.
• NFPA LiNK Subscription: Bundles NFPA 855 with cross-referenced codes and in-app bookmarking.

Related documents worth budgeting for:

• NFPA 70E (arc-flash and electrical safety)
• UL 9540A Test Method
• NFPA 1 Fire Code (if your AHJ references it)

Annual NFPA LiNK subscriptions are priced by license tier – Individual, Team, or Enterprise – so costs vary based on your organizational needs. Engage procurement early to avoid delays.

Frequently Asked Questions

Does NFPA 855 apply to mobile or containerized battery energy storage systems?
NFPA 855 applies to stationary ESS, including containerized units, and also to mobile/portable ESS when installed in a stationary situation; AHJs may classify truly mobile units differently.

How does UL 9540A testing data support NFPA 855 compliance?
UL 9540A fire testing data on thermal runaway is used by NFPA 855 to justify reduced spacing, larger system sizes, and explosion-control design (NFPA).

What documentation does an Authority Having Jurisdiction typically request during plan review?
AHJs typically require a Hazard Mitigation Analysis, UL 9540A test report, electrical one-lines/site plans, fire protection system design, and an emergency response plan with training provisions (NFPA).

Are there exemptions for small-scale residential energy storage under NFPA 855?
NFPA 855 Chapter 15 limits units to 20 kWh in one- and two-family dwellings, with aggregate limits (40 kWh in closets/storage, 80 kWh in garages/outdoors), plus 3-ft separation unless UL 9540A supports less.(Mayfield)

How often should thermal runaway mitigation systems be tested according to NFPA 855?
NFPA 855 requires commissioning/acceptance tests and ongoing inspection, testing, and maintenance per referenced NFPA standards and manufacturer instructions (e.g., NFPA 72, NFPA 25), many of which call for annual testing (NFPA).

Conclusion

Early alignment with NFPA 855 can save months of redesign, unlock insurance coverage, and reassure risk-averse investors. Integrate code checks into each sprint, involve the AHJ before steel hits the ground, and document everything.