Battery Energy Storage Systems (BESS)

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Battery Energy Storage Systems (BESS) are rapidly becoming essential infrastructure as New York City accelerates the transition to clean energy. They stabilize the grid, support renewable power generation, and provide critical resiliency for buildings and utilities. But they also introduce new engineering and fire-safety challenges and community concerns, specifically in a dense urban environment highlighted recently in a Gothamist article. NYC has one of the most complex regulatory environments nationally where the design, approval, and operation of BESS require rigorous compliance with the NYC Fire Code, Department of Buildings (DOB) rules, and FDNY’s detailed ESS review process.

EP Engineering provides fire protection engineering, hazard analysis, plan preparation, and authority-having-jurisdiction (AHJ) coordination for some of the city’s largest BESS deployments illustrates how engineering, testing, and FDNY review combine to ensure these systems can be safely deployed in close proximity to sidewalks, businesses, and industrial buildings.

1. What Makes BESS Projects Unique in NYC?

NYC applies the most stringent BESS regulations in the country. The 2022 NYC Fire Code Section 608, FDNY Rule 3 RCNY 608-01, and related DOB rules set the framework for:

  • Battery technology safety
  • System siting and separations
  • Fire detection and suppression
  • Heat flux & smoke plume analysis
  • Emergency response & shutdown requirements
  • Remote monitoring & operations
  • Annual inspection and permitting requirements

According to the FDNY Equipment Approval and Installation Guide, all stationary ESS must go through a four-step approval pathway:

  1. Product Approval – Certificate of Approval (COA)
  2. Site-specific Plan Review
  3. FDNY and DOB Filings
  4. Installation Inspection & Operating Permit

2. Understanding the Technology: What’s Inside a typical NYC outdoor BESS system.

Example System: Tesla Megapack 2XL

  • 24 Lithium Iron Phosphate (LFP) battery modules
  • Battery Management System (BMS)
  • Thermal Management System (TMS) (glycol loop & refrigerant cooling)
  • Tesla Site Controller (TSC) with remote monitoring
  • Deflagration control system with vents and sparkers
  • Non-occupiable sealed enclosure

These safety systems detect and mitigate thermal anomalies before they become hazardous, an essential requirement under UL 9540/9540A.

3. The Role of UL 9540A & Destructive Testing

Under FDNY requirements, all BESS units must undergo UL 9540A thermal runaway testing.
The Hazard Mitigation Analysis (HMA) includes extensive analysis of:

  • Cell, module, and unit-level UL 9540A test results
  • Tesla’s additional full-scale destructive testing (beyond UL requirements)
  • Heat flux modeling at 5 – 100 feet
  • Smoke plume behavior and exposure risks

This data is essential for FDNY engineering judgments.

4. Critical Engineering Requirements in NYC

Based on FDNY’s ESS Approval Guide, NYC imposes strict requirements on:

  1. Fire Alarm Systems
    1. FDNY requires:
      1. UV/IR flame detection
      1. Manual pull stations at entrances
      1. Remote annunciation
      1. Flame/smoke detection tied to the FACP
  2. Water Spray (NFPA 15) Systems
    1. For outdoor large BESS systems, FDNY requires manual NFPA-15 spray systems fed entirely from FDNY Fire Department Connections (FDCs).

5. Hazard Mitigation Analysis (HMA): A Required Deliverable

The NYC Fire Code requires a site-specific HMA prepared and sealed by a NYS Professional Engineer including;

  • Heat Flux Analysis (100-ft radius)
  • Smoke Plume Analysis (250-ft radius)
  • Exposure identification
  • Fire department access & FDC evaluation
  • Mitigation recommendations
  • Compliance with FDNY Rule 3 RCNY 608-01(g)(1)(c)

6. Inspections & Operational Permits

FDNY requires several staged inspections:

  • Fire alarm inspection (FAIU)
  • Rangehood Unit inspection for water spray systems
  • BFSU inspections for commissioning, shutdown testing, and annual permit renewal

Only after passing these can a BESS receive:

  • Letter of Approval (LOA)
  • One-year FDNY operating permit (renewed annually)

FDNY also requires familiarization drills with the local fire company and HazMat Operations before activation.

EP’s responsibilities on a typical project include:

  • Fire Alarm design (UV/IR detection, FA control, annunciation)
  • Fire Protection design w/ hydraulic calcs
  • Hazard Mitigation Analysis (HMA)
  • Heat flux & smoke plume modeling
  • FDNY TM-1 and Fire Alarm filings
  • Coordination with OTCR for DOB reviews
  • Responses to FDNY deficiency letters
  • Construction documents and revisions
  • Support during inspections and commissioning

Key Takeaways for Developers & Owners

1. Engage engineering teams before finalizing the site layout

2. Understand FDNY’s expectations:

The approval process is thorough and detailed. Every drawing, note, and device must align with code and FDNY rules.

3. Confirm COA status of selected BESS equipment

4. Testing data matters

UL 9540A and destructive test data are the basis for engineering judgments and mitigation measures.

5. Expect multiple review cycles

FDNY deficiency letters are normal and often extensive.

6. Safety systems are non-negotiable

BMS, TMS, deflagration vents, flame detection, and water spray systems must be designed and documented precisely.

7. Every site is unique

Urban environments require careful evaluation of:

  • Building adjacencies
  • Egress routes
  • Vehicle traffic
  • Public sidewalks
  • Nearby critical infrastructure
  • Firefighter access

8. Annual maintenance is mandatory

Inspections, drills, and permit renewals are core parts of operating a BESS in NYC.

For additional information, visit:

https://www.nyc.gov/assets/fdny/downloads/pdf/business/ess-equipment-approval-installation-guide.pdf