Technical Article
BESS Maximum Allowable Quantities at the C&I scale
When installing a battery energy storage system (BESS) in a behind-the-meter project, what is the maximum size allowed in a single fire area?
For the vast majority of commercial and industrial (C&I) BESS projects, say 100 kWh to 10 MW nameplate power, we’re given rules by local, state, or other authorities having jurisdiction about the maximum allowable quantities (MAQ). These local rules can be traced back to the International Fire Code (IFC), Section 1207, Electrical Energy Storage Systems. In this article, we’ll examine the MAQ guidelines established in the 2024 IFC and explore avenues for exceeding MAQ if necessary.
Why the IFC?
The International Fire Code is the model fire code intended for adoption by state and local authorities responsible for regulating, among many activities, the installation of battery energy storage systems (BESS). Some 40+ states adopt the IFC wholesale or without amendments.
Within Chapter 12, Section 1207 of the 2024 IFC, there are two subsections we’ll focus on in this article:
Before discussing MAQ, it is important to gather context and understand how the IFC distinguishes outdoor BESS installations in 1207.8 Outdoor Installations.
Outdoor Installations Near Exposures
Outdoor BESS installations have different classifications and treatments within 1207.8 Outdoor installations. Most BESS installations in C&I spaces are appropriately classified as “installations near exposures.” BESS in suburban and urban areas, community centers, and campuses will, in most cases, be close to human activity, lot lines, public ways, and buildings. Few C&I BESS projects will meet the requirements of 1207 for “remote installations” or “installations in dedicated use buildings.” In addition, BESS installed on exterior walls of buildings is possible (consult Section 1207.8.4), though of limited interest to most C&I use cases.
Table 1207.8 gives us the proverbial ‘compliance checklist’ and each related section. Notice that for “installations near exposures,” all sections require compliance.
Outdoor installations near exposures must follow the rules itemized in Sections 1207.8.1 through 1207.8.3. Many sections, like “Clearance to exposures,” “Vegetation control,” and “Means of Egress,” establish a 10 ft. minimum setback from a long list of exposures. For more information on these, check out our 3-hour online course on NFPA 855 and Fire Codes for Energy Storage Systems.
Maximum Allowable Quantity
Beyond the setbacks from a BESS to nearby exposures, we also must consider the maximum allowable BESS energy capacity that the IFC allows inside the site boundary. For this, we turn to the language in IFC 1270.5.2:
1207.5.2 Maximum Allowable Quantities. Fire areas within rooms, areas, and walk-in units containing electrochemical ESS shall not exceed the maximum allowable quantities in Table 1207.5
As the vast majority of the BESS installations in the C&I markets to date use lithium-ion storage technology, here, IFC sets the upper limit of aggregate storage capacity within a fire area at 600 kWh.
A fire area is defined in Section 202 of the 2024 IFC as:
“The aggregate floor area enclosed and bounded by fire walls, fire barriers, exterior walls or horizontal assemblies of a building. Areas of the building not provided with surrounding walls shall not be included in the fire area if such areas are included within the horizontal projection of the roof or floor next above.”
For an outdoor pad-mounted BESS installation, we can charitably read this definition as “a fire area within… (outdoor) areas containing (lithium-ion based) BESS shall not exceed (600 kWh)”. While this leaves some room for interpretation, Mayfield generally recommends deferring to local fire professionals as a best practice.
Consultation with the local fire chief or response team representative about a new BESS installation is highly recommended for numerous reasons, including confirmation of fire area(s) demarcation in relation to BESS location.
This threshold of 600 kWh might appear to be an unwelcome one, especially in the C&I markets. However, IFC does provide a path to exceeding this MAQ limit on lithium-ion-based BESS later in Section 1207.5.2.
Exceeding 600 kWh per IFC 1207.5.2
The 2024 IFC provides three paths to exceed the MAQ thresholds:
1207.5.2 Maximum Allowable Quantities. Fire areas within rooms, areas, and walk-in units containing electrochemical ESS shall not exceed the maximum allowable quantities in Table 1207.5
Exceptions:
- Where approved by the fire code official, rooms, areas, and walk-in units containing electrochemical ESS that exceed the amounts in Table 1207.5 shall be permitted based on a hazardous mitigation analysis in accordance with Section 1207.1.6 and large-scale fire testing complying with Section 1207.1.7.
- Lead-acid and nickel-cadmium battery systems installed in facilities under the exclusive control of communications utilities, and operating at less than 50 VAC and 60 VDC in accordance with NFPA 76.
- Dedicated-use buildings in compliance with Section 1207.7.1.
In accordance with exception (1), any lithium-ion-based BESS installation with greater than 600 kWh aggregate capacity may be approved, provided the party or parties responsible have ready both a hazard mitigation analysis and a large-scale fire test.
Section 1207.1.6 defines requirements for a hazard mitigation analysis (HMA). An HMA examines potential BESS failure modes and their respective consequences. IFC 1207.1.6.1 addressed these fault conditions. For example, since lithium-ion BESS in failures are known for potential release of vent gases at varying concentrations and varying risks, an HMA for lithium-ion BESS will most often include an assessment of deflagration hazards.
An HMA can take a long time to create, and will be subject to review from a fire professional. Installers and or developers may not have the exact BESS product specified at the time of submittal, but one HMA can be written for multiple BESS products, allowing the decision makers adequate time to specify at a later date.
IFC has a definitional section in 1207.1 for a large-scale fire test as well. Though the landscape of possible testing methods that adequately meet the large-scale fire testing requirements in Section 1207.1.7 may or may not be expanding, at the time of writing, Section 1207.1.7 calls out only one explicitly, UL 9540A:
1207.1.7 Large-scale fire test. Where required elsewhere in Section 1207, large-scale fire testing shall be conducted on a representative ESS in accordance with UL 9540A. The testing shall be conducted or witnessed and reported by an approved testing laboratory and show that a fire involving one ESS will not propagate to an adjacent ESS…
Recap
The IFC helps any installer, developer, or designer understand the maximum allowable quantity (kWh) for a given BESS installation in Section 1207.5.2. Any lithium-ion-based BESS installation with greater than 600 kWh aggregate capacity per fire area will require a hazard mitigation analysis and a large-scale fire test. Ensuring proper compliance with IFC 1207 helps align any BESS project’s electrical design and construction with the jurisdictional expectations to streamline permitting and improve overall project safety.
Mayfield Renewables provides design and engineering services for solar-plus-storage systems, including systems that require BESS above and below a 600 kWh nameplate. Contact us today for a consultation.
