Large, reliable energy storage systems are central to the quest for renewable energy resources such as wind and solar. Those found in standby power applications such as fire alarm systems and UPS applications are the most familiar. Battery storage systems have also been used for electrical load balancing to stabilize supply and demand fluctuations on the electrical grid.

In the past, these systems used traditional lead-acid or nickel-cadmium batteries. However, with the need for more effective storage systems for renewable energy resources, lithium-ion battery energy storage systems have proven to be the most effective. The demand for such systems has grown fast and continues to increase rapidly.

Lithium-ion storage facilities have high-energy batteries that contain flammable electrolytes. They are prone to quick ignition and potentially violent explosions.

The fire protection challenge with lithium­-ion battery energy storage systems is met primarily with early-warning smoke detection devices, also called aspirating smoke detectors (ASD), and the release of extinguishing agents to suppress the fires. The extinguishing agent is nitrogen gas, but the focus here will be on the detection portion of the fire protection problem.

NFPA 72, National Fire Alarm and Signaling Code, defines an air-sampling-type detector as “a detector that consists of a piping or tubing distribution network that runs from the detector to the area(s) to be protected. An aspiration fan in the detector housing draws air from the protected area back to the detector through air sampling ports, piping, or tubing. At the detector, the air is analyzed for fire products.” 

Active air sampling

This is called an active air-sampling detector. Conversely, a typical duct detector is a passive air-sampling detector, and it requires the HVAC system to be operating.

NFPA 72 Chapter 17, Detection Devices, contains the requirements for ASDs or air-sampling smoke detectors. The 2022 edition assumes that a specific performance­-based design will be developed. Absent that criteria, the code requires each sampling port of an air-sampling-type smoke detector be treated as a spot-type smoke detector for the purpose of location and spacing.

NFPA 72 states that “for an air sampling-­type smoke detector, the sensitivity at the detector is not equal to sensitivity at the sampling port. Sampling port sensitivity is dependent on two main factors: the number of sampling ports in the piping network and the set alarm sensitivity of the detector.”

Again, in the absence of performance-­based criteria, NFPA 72 suggests the sensitivity at each sampling port of an air-sampling-type smoke detector should not exceed the 4%-per-foot obscuration criteria of a spot-type smoke detector.

The sampling pipe networks are normally designed using computer-based fluid dynamics design calculations to ensure the detector meets the required performance. The code also requires that the sampling pipe network design calculations include pressure, volumetric flow and alarm sensitivity at each sampling port. Many large lithium battery storage cabinets resemble an electrical cabinet, and for design purposes can be treated as such.

Cabinet protection

For the protection of cabinets containing electrical equipment, the code requires the air sampling ports be in the main airflow at the exhaust vents and installed downstream of the airflow distribution path, or in accordance with the manufacturer’s published instructions. 

Annex A provides additional guidance stating that “electrical equipment cabinets are commonly ventilated vertically (bottom to top passive cooling) or horizontally (front to back passive cooling) or are fully enclosed with active internal cooling. 

“For passively cooled applications, the sampling pipe can be located externally with sampling ports directly in the main airflow of the exhaust vents or in the cabinet with the sampling port(s) located within 1 inch to 2 inch of the cabinet top. For fully enclosed cabinets, the sampling port is in the cabinet within 1 inch to 2 inch from the cabinet top. In either case, the manufacturer’s published installation instructions should be followed.”

Additionally, the code also requires sampling system piping be conspicuously identified as “SMOKE DETECTOR SAMPLING TUBE—DO NOT DISTURB” at changes in direction for branches of piping; at each side of penetrations of walls, floors or other barriers; and at intervals on piping that provide visibility within the space, but no greater than 20 feet. All sampling ports shall be identified as such.

Piping network materials, sizing, installation, capillary tubing and supports for sampling pipes must be in accordance with the air-sampling-type smoke detector manufacturer’s published instructions.

Currently, only one manufacturer offers an ASD designed to detect normal fire particle sizes and the byproducts of overheated lithium-ion electrolytes. It is important to determine the fire protection needs of a lithium battery energy storage system early in the bidding process, and understand the required detection systems.

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