Battery Energy Storage Systems (BESS)

Battery energy storage systems store electricity for later use. They range from a home battery next to a garage panel to containers of batteries at a solar farm or an industrial site. They help keep power on and make solar more useful, but large amounts of stored energy bring fire, shock and arc flash hazards that need careful design, installation and maintenance.

• Electrical
• Solar
• Utilities

What a BESS is

• A battery energy storage system has battery modules, a battery management system (BMS), an inverter or power conversion system, controls, protection devices and often cooling, ventilation and fire protection.
• Residential systems are wall-mounted or floor-standing units, often added to rooftop solar. See rooftop solar and Solar Installers.
• Commercial and utility systems use cabinets, rooms or shipping-container-sized enclosures holding hundreds of kilowatt-hours or more.
• Battery chemistries: lithium-ion is the most common, in several types (such as lithium iron phosphate and nickel manganese cobalt). Others include lead-acid, nickel-based, and flow batteries. Each has its own hazards. See Battery Safety.

Main hazards

• Thermal runaway and fire: if a lithium-ion cell is damaged, overheated, overcharged, defective or short-circuited, it can heat itself uncontrollably, burn, vent flammable gas and spread to nearby cells. Fires can be intense, hard to put out and can reignite hours or days later.
• Toxic and flammable gases: burning or overheated batteries release gases, including hydrogen fluoride, carbon monoxide and flammable vapors that can explode when they gather in enclosed spaces. Lead-acid batteries can release hydrogen during charging.
• DC shock and arc flash: batteries are always live. A battery bank can deliver enormous fault current, and direct current arcs are hard to interrupt. You can’t simply shut off the source. See Arc Flash & NFPA 70E.
• High voltage: large systems may run at hundreds or thousands of volts DC, plus the AC side.
• Chemical hazards: electrolyte leaks, acid in lead-acid batteries, and corrosive materials.
• Mechanical hazards: batteries are heavy, and lifting and moving them causes injuries. See Lifting & Ergonomics.
• Backfeed and islanding: a BESS can feed power back to the grid or to a building during an outage. See Transformers and Standby Generators & Transfer Switches.
• Emergency response: firefighters face special hazards from stranded energy and gas.

Codes and standards

• NFPA 855 (Standard for the Installation of Stationary Energy Storage Systems) covers location, spacing, maximum quantities, fire protection, ventilation, detection and signage, and the model fire codes and many local rules adopt it. See International Fire Code.
• The National Electrical Code (NEC) has rules for energy storage systems (Article 706), including disconnects, overcurrent protection, labeling and wiring. See National Electrical Code.
• UL 9540 is a safety standard for energy storage systems, and UL 9540A is a test method to evaluate thermal runaway fire propagation. Look for listed equipment, installed per instructions. See Listed & Labeled Equipment.
• Local building and fire departments may require permits, plans, inspections and special rules, especially for residential use and commercial installations. See Building Permits & Inspections.

Codes and local rules change, and differ widely, so check what applies in your area.

Installation safety

• Use qualified, trained installers, with experience in energy storage and the product. Follow the manufacturer’s instructions exactly. In many places, electricians and licensed solar contractors must do the work, and permits are required.
• Choose the location carefully. Codes limit where batteries can go. Residential rules often restrict locations such as living spaces and bedrooms, and may prefer garages, outdoor walls or utility rooms, with spacing from exits, windows and other equipment. Keep batteries out of flood zones and away from direct sun and heat, and protect them from vehicle impact with bollards.
• Keep required clearances, and keep combustible materials away. Don’t store items on or around the unit.
• Make sure of ventilation and temperature control as the maker requires. Overheating and cold both affect safety and life.
• Install fire and gas detection and fire protection where required, such as smoke and heat alarms and a way to alert people and responders. For larger systems this may include suppression, explosion control and thermal monitoring.
• Label and mark the system, disconnects and hazards. Provide a clear emergency shutdown method and info for first responders.
• Use correct wire sizing, overcurrent protection, disconnects and grounding, with proper torque on terminals. See Grounding & Bonding and Breakers & Fuses.
• Commission and test the system, including the BMS and shutdown, and train the owner.

Working on or near batteries

• Batteries can’t be de-energized by flipping a breaker. Even with the system disconnected, the battery pack itself remains live. Follow the maker’s procedure for isolating, such as disconnect switches, and use lockout/tagout. See Lockout/Tagout and Testing for Absence of Voltage.
• Wear arc-rated clothing, insulated gloves, eye and face protection as the hazard analysis requires, and use insulated tools. See Arc Flash PPE Categories and Rubber Insulating Gloves.
• Remove metal jewelry, keep tools off the battery tops, and cover exposed terminals so nothing can short them.
• Use meters rated for the voltage. See Test Meters.
• Only qualified persons work on energized systems, with a permit if live work is justified. See Energized Work Permits and Electrical Safety Programs.
• Handle battery modules with proper lifting, as they’re heavy, and inspect for swelling, leaks, corrosion, damage or odors before work.
• Don’t use or charge a damaged battery. Damaged lithium-ion batteries can ignite later.

Signs of trouble

• Swelling or bulging, leaking fluid, hissing or popping sounds, strange smells (sweet, chemical or burning), smoke, unusual heat, discoloration, or error and fault warnings on the system display.
• If you see warning signs: stop, move people away, shut the system down if it’s safe and allowed, and call the installer, the utility or the fire department. Don’t try to move or open a failing battery.

Fire and emergency response

• If a battery system is burning or smoking, evacuate everyone, call 911 and tell them it involves a battery energy storage system, and keep away. Don’t try to fight a lithium-ion battery fire with a normal extinguisher, other than a very small fire at its start, since it can reignite.
• Firefighters need information on the system’s location, shutoff and hazards, so provide a site plan and contact numbers. Many codes require placards and emergency response plans for larger systems. See Emergency Action Plans and hazardous gas releases.
• After a fire or damage, have the system inspected by qualified people before it is used. Reignition is possible.
• Fires release toxic smoke. Stay upwind and keep clear. See Carbon Monoxide.

Homeowners and building owners

• Hire a licensed, experienced installer, get permits and inspections, and ask about listings (UL 9540), warranty and the manufacturer’s support.
• Keep smoke and CO alarms working. See Smoke & CO Alarms.
• Keep the area around the battery clear, and don’t modify the system or add loads without the installer’s approval.
• Tell your insurer and the fire department as required. Know where the shutoff is.
• Use the manufacturer’s app and alerts, and keep software up to date.
• Don’t DIY battery work, and don’t open battery enclosures. See DIY Electrical Work: Permits.

BESS safety checklist

• System is listed (UL 9540), permitted and installed by qualified installers per the maker’s instructions
• Location, clearances, ventilation and fire protection follow NFPA 855, the NEC and local rules
• Disconnects, labels and emergency shutdown are clear, and responders have the information
• Workers treat batteries as always live, with lockout, insulated tools and arc-rated PPE
• Damaged, swollen or leaking batteries are not used; warning signs are acted on at once
• Everyone knows to evacuate and call 911 in a battery fire

Last updated: October 4, 2026