A UPS system using valve-regulated lead-acid batteries atop metal racks. The batteries are protected by a fixed, powdered aerosol fire extinguishing system. (Photo by author.)
Storage of energy involves converting energy from forms that are difficult to store to more economical storable forms. Electricity must be used as it is being generated or converted immediately into another form of energy. Some technologies provide only short-term electrical energy storage, while others can be very long term. An early solution to the problem of storing electrical energy was the development of the battery as an electrochemical storage device. In the past, batteries have been of limited use in electric-power systems because of their small capacity and high price tag.
Recently, new battery technologies have been developed that can now be incorporated into grid (network) utility applications. This article explains battery storage technology to fire service members to improve safety and efficiency on the fireground. It also aims to enhance site visits to facilities and buildings using this equipment for fire protection inspectors.
Uninterruptible power supply (UPS) battery technology provides small-scale, emergency alternating current (AC) electrical energy to a load for 10 to 20 seconds to several hours in the event the main power fails. It supplies energy for a defined purpose whereas grid batteries flow large-scale amounts of AC electrical energy through feeder lines to the general public. UPS provides near-instantaneous protection from input power interruptions. The on-battery runtime of most UPS sources is sufficient for building management to start a standby power source or properly shut down protected equipment. UPS is typically used to defend computers, telecommunications, and electrical equipment where an unexpected power disruption could cause equipment damage, product/data loss, business disruption, and security/safety hazards. UPS batteries are commonly placed inside large metal cabinets or charging racks located within a designated equipment room of a building.
Grid battery energy storage (BES) systems will facilitate the United States in meeting the challenge of projected energy consumption. It will also address environmental issues such as global warming and climate change by reducing the emission of carbon dioxide into the atmosphere when fossil fuels are burned to generate electrical power. It can help with the integration and broader use of renewable (solar, wind) energy as well as enhance the efficiency of nonrenewable (coal, oil, natural gas) energy. According to the United States Energy Information Administration (EIA), net electricity generation from all forms of renewable energies in America increased by more than 15 percent between 2005 and 2009. A BES integrated with a photovoltaic (PV) array, for example, can maximize consumption of solar energy by using electricity stored off-peak. BES also provides frequency regulation to maintain the balance between the power generated by the PV panels and the network’s load to achieve a more dependable power supply. The use of BES is well-established in off-grid PV installations, too. Moreover, it allows businesses to continue operating through intermittent power outages.
BES holds substantial promise for transforming the electric power industry. These systems store vast amounts of electricity during times when production from power plants as well as intermittent, renewable electricity sources exceeds consumption. One of the distinctive characteristics of the industry is the actual amount of electricity that can be generated is relatively fixed over short periods of time, although demand for electricity fluctuates throughout the day. Developing BES technology is used to ensure reliable electric power systems. BES is also employed to store electrical energy so it can be available to meet demand whenever needed (load leveling). Helping to try and meet this goal, BES can manage the amount of power required to supply customers at times when need is greatest (peak load hours). It represents a major breakthrough in electricity distribution.
This technology also enables end users to save money. During peak daytime hours, when electricity consumption is highest, energy costs more to produce. The cost of electricity is, therefore, moving from a standard flat rate charge to a time-of-use (TOU) price structure, where rates are dependent on when electricity is consumed. With TOU pricing, the cost of electricity during peak daytime hours is often many times higher than it would be for the same amount of electricity in the evening or at night. Energy fees are reduced when electricity stored during off-peak times is distributed during peak hours (peak shaving). Additional benefits of grid energy storage systems include reducing infrastructure investments and improving emergency preparedness. Grid BES systems can be installed inside an energy storage facility on charging racks or in big, trailer-like storage containers outdoors.
In 2013, the New York State Energy Research and Development Authority (NYSERDA) awarded a total of $1.4 million to six companies engaged in researching and developing energy storage systems. Under the terms of these awards, additional private investment capital was required. Funding recipients were all members of the NY Battery and Energy Storage Technology (NY-BEST) Consortium. The companies, located throughout New York State, used the funding to turn energy storage technologies with proven technical feasibility into working prototypes. The goal is to add resiliency to the electric grid or provide increased energy efficiency.
Additionally, as part of a contingency plan for the potential closure of Indian Point’s (Buchanan, NY) two remaining active nuclear reactors, Con Edison recently filed a proposal to provide 100 MW of load reduction measures including demand response, energy productivity, and energy storage. In New York State, Con Edison and NYSERDA started a program providing new incentive offerings for battery-storage systems that reduce on-peak demand. The goal of the program is to develop advanced energy storage technologies in collaboration with industry, academia, and government institutions that will increase the performance and competitiveness of electricity generation and transmission in the grid and in standalone systems. The proposed New York City incentive bears some resemblance to California’s Self-Generation Incentive Program, to support existing and emerging distributed energy resources. In California, qualifying technologies include wind turbines, fuel cells, and associated energy storage systems.
Batteries are a cost-effective way of storing energy using electrochemical technology. Charging a battery creates reactions in the compounds. This response then stores the energy in a chemical form. When needed, reverse chemical reactions generate electricity that flows out the battery and back to the electrical system of a building or the power grid. They deliver direct current (DC) electricity. An inverter electronic component is used to transform the DC electricity to AC electricity for consumer use.
Electrochemical batteries are devices that store energy in electrochemical form. The container, two electrodes (anode-negative and cathode-positive), and electrolyte fluid are the primary elements of a cell. This type of battery has two or more electrochemical cells used to generate a chemical reaction between its electrode plates and electrolyte to create an electrical current. Flow batteries, however, store their electrolyte in tanks situated outside their container. In flow-battery technology, electrode plates, typically consisting of chemically reactive materials, facilitate transfer of ions within the battery. The anode releases electrons during discharge via the oxidation part of the oxidation-reduction (redox) electrochemical process. These electrons flow through the electric load connected to the battery, giving up energy. Electrons are then transported to the cathode for storage. The most common battery technologies used today include lead-acid, nickel-based, sodium-sulfur, lithium-ion, and vanadium redox. This article will focus only on energy storage batteries for UPS system and grid BES system applications.
Types of Batteries
Lead-acid (LA) batteries: Until recently, the only BES technology economically feasible was the lead-acid type. Modification of the electrode structures enabled this battery to be used for large-scale energy storage applications. Improved valve regulated lead-acid (VRLA) batteries with sealed cells are now available. The valve opens to vent hydrogen gas from the battery whenever internal pressure exceeds the ambient pressure by a predetermined amount. This feature provides a longer battery cycle life by reducing the amount of electrolyte evaporation. In the charged state, the metallic lead negative electrode and the lead sulfate positive electrode are immersed in a dilute sulfuric acid (H2SO4) electrolyte. During the discharge process, electrons are pushed out of the cell as lead sulfate is formed at the negative electrode while the electrolyte is reduced to water.
Lead-acid batteries have low up-front costs, are robust, and are used in both UPS and grid battery arrangements without sophisticated battery monitoring systems. Disadvantages include relatively short lifetimes; significant maintenance requirements; waste-handling challenges; low energy-to-weight ratio; and the lead/sulfuric acid makeup being highly toxic and corrosive, creating both a human and environmental hazard. Additionally, valve regulated lead-acid batteries are prone to cell thermal runaway, leading to a potential fire or explosion.
Lead-acid batteries do not burn or burn with difficulty. Firefighters should cool the exterior of the battery with water spray if exposed to fire to prevent rupture and extinguish fire with agent suitable for surrounding combustible materials. Be careful not to apply water on sulfuric acid, as it will react violently. Commonly, dry chemical, carbon dioxide, and foam portable fire extinguishers are used for small, isolated fires.
Nickel-cadmium (NiCad) and nickel-metal hydride (NiMH) batteries: Nickel-based batteries are the second most popular electrochemical energy storage devices after lead-based batteries. They are economically priced and have a long shelf life. NiCad and alkaline batteries are the most common. Their alkaline cells can be connected in series as well as parallel to build up battery electrical systems with the desired power. These batteries are also robust and used where energy must be stored in low temperature environments. Cadmium, however, is a toxic element that was banned for most uses by the European Union in 2004. Portable fire extinguishers normally recommended for minor fires involving nickel-cadmium batteries include dry chemical, carbon dioxide, foam, and dry sand.
Nickel-metal hydride chemistry technology has a multitude of attributes that make it suitable for energy storage applications. These types of batteries have a much higher energy density than that of lead-acid alternatives. Nickel-metal hydride batteries have inherently long cycle lifes and little to no maintenance requirements. They have almost completely replaced nickel-cadmium batteries because of environmental issues. Incipient fires in nickel-metal hydride batteries require a Class D (combustible metal) smothering extinguishing agent that excludes the oxygen from the atmosphere such as METL-X, dry sand, dolomite, and soda ash. Water may not be effective on extinguishing a nickel-metal hydride battery fire and may evolve hydrogen gas.
Sodium-sulfur (NAS): Originally developed by the Ford Motor Company in the 1960s, this technology was sold to the Japanese company NKG. A sodium-sulfur battery is a metal battery made from molten sodium (negative electrode) and molten sulfur (positive electrode). The electrodes are separated by a solid ceramic sodium alumina, which serves as the electrolyte. The battery must be kept hot (more than 600°F) to facilitate the charging process. Independent heaters may be a component of the BES. It has a high energy density, high efficiency (90 percent), and long cycle life and is manufactured from inexpensive materials. Systems used exclusively for load leveling are common (approximately 50 percent). Sodium-sulfur battery systems having additional functions (emergency power) represent another 20 percent of the total. BES sodium-sulfur technology can be found at nearly 200 sites in Japan. United States’ utilities are also using sodium-sulfur systems for grid energy storage. Special sealing technologies are used to protect NAS battery cells from moisture since pure sodium spontaneously burns or explodes in contact with water. Firefighters should not use water to extinguish fires involving sodium-sulfur batteries. Effective portable fire extinguishers to use on diminutive sodium-sulfur battery fires include dry chemical, carbon dioxide, foam, and dry sand.
Lithium-ion (Li-ion): Li-ion battery technology for grid storage applications has been rapidly gaining headway since 2010. The energy density of the li-ion battery is typically twice that of the standard NiCad battery and can be up to six times that of LA batteries. Cells are manufactured in cylindrical or rectangular shapes and built into multicellular modules that are connected in series/parallel arrays to create a battery string. The electrical current is generated by li-ions embedded in a graphite or nickel metal-oxide substrate. This material is placed in a carbonate mixture or gelled polymer electrolyte. Li-ion batteries are low maintenance and have no battery memory, which precludes the need to cycle them on a scheduled basis to prolong battery life. Three types of li-ion batteries in commercial and industrial applications are cobalt, manganese, and phosphate.
Although it can occur with batteries of almost any chemistry, the major drawback of the li-ion battery is that it is especially prone to cell thermal runaway. This phenomenon can occur from overcharging, a manufacturing defect, or physical damage. Cell thermal runaway refers to rapid self-heating derived from a heat releasing redox chemical reaction. When a li-ion battery has a thermal runaway, physical expansion of the battery occurs, and electrical short circuits within the battery either start or continue. Subsequently, battery energy is violently released, causing adjacent battery cells to also heat up.
Li-ion cell thermal runaway reactions are powerful because they have high-energy densities and their cells contain flammable electrolyte. Thermal runaway can start when electrolyte reaches temperatures as low as 150°F to 200°F. It will accelerate quickly at higher temperatures, and the greater the charge in the battery, the faster thermal runaway occurs. Temperatures during a thermal runaway can reach 1,110°F. The battery cells will also experience increased pressure and the venting/possible ignition of cell gases. Flames emanating from the cells have been described as torch-like.
Extinguish incipient li-ion battery fires using Class D extinguishing agents, including LITH-X (powdered graphite), copper powder, dry sand, dolomite, and soda ash. Additional extinguishing agents of the nonsmothering type that have proved successful are dry chemical and carbon dioxide. You can use water to control li-ion battery fires; however, hydrogen gas may be evolved, which can form an explosive mixture with air.
Flow batteries: Flow batteries, especially vanadium redox batteries (VRB), are attractive because of their very long cycle life and their flexibility in managing power and storage capacity separately. They are ideally suited for grid energy storage having high-energy efficiencies. Drawbacks include substantial operational/maintenance costs and low energy density. A flow battery is an electrochemical device similar to a conventional battery, but it is technically analogous to a fuel cell. Use dry-chemical portable fire extinguishers for small fires and water spray or foam for larger fires.
Redox flow batteries (RFBs) store electrolyte in two containers that are separated from the cell stack. One container holds electrolytes for anode electrode reactions and another container has electrolytes for cathode electrode reactions. This design enables the two tanks to be sized according to the application. New technologies have been developed using electrolyte that is water-based rather than acidic. This electrolyte, therefore, is neither corrosive nor flammable. There are many kinds of RFB technologies including iron/chromium and zinc/bromide.
General: Hazards potentially awaiting firefighters include fire, water-reactive materials, electrical shock, corrosives, chemical burns, toxic fumes, flammable gases, and explosions. Firefighters must don all personal protective equipment (PPE), including positive-pressure, self-contained breathing apparatus (SCBA) for every incident involving battery-storage facilities. Be aware, however, that PPE will not protect against electrolyte that is corrosive in nature. Spilled corrosive electrolyte warrants the response of a hazardous-materials (haz-mat) unit. Electrolyte fluid observed within battery storage areas must be assumed to be corrosive until deemed otherwise through testing by a haz-mat technician or confirmed not to be via conversation with a knowledgeable/certified person on the premises. Sulfuric acid electrolyte from LA batteries will emit toxic fumes during evaporation. Although not inherently flammable, sulfuric acid can support combustion by reacting with other chemicals to liberate enough heat to ignite nearby combustibles as well as hydrogen gas. Li-ion batteries contain flammable liquid electrolyte that may vent and catch fire when high temperatures are introduced or when the batteries are mechanically damaged. Fires involving these type batteries burn rapidly threatening surrounding building contents.
Engine company operations: The first-arriving engine company should stretch a hoseline regardless of whether the incident is a fire or emergency. For emergencies, stretch an uncharged hoseline a safe distance away from the battery-storage area for possible use if conditions worsen and a fire should occur. I highly recommend that the initial hoseline be 2½ inches in diameter to ensure adequate flow for a worst-case scenario fire.
Good communication between the first-arriving engine company officer and ladder company officer will aid in coordinating hoseline operations and water application after power has been confirmed turned off. Note that residual energy may still be present in batteries and supplied equipment for some time after power shutdown.
Use a nozzle that can provide a long stream in a 30-degree spray pattern to protect firefighters and surroundings. The standoff distance and water configuration greatly reduce the likelihood of electrical shock to the firefighters at the nozzle. Do not directly apply water streams onto batteries. If possible, use the ceiling, walls, or floor to deflect water onto batteries that are on fire.
Ladder company operations: Ladder company firefighters should use portable, multifunctional flammable gas detectors with the ability to sense hydrogen gas. Keep in mind that most batteries (LA, VRLA, NiCad) produce flammable hydrogen gas during normal charging. Overcharging, excessive heat, and other factors can cause batteries to generate even more of this gas. As hydrogen builds up, the risk of fire and explosion increases. A spark can lead to a violent explosion with subsequent fire. Hydrogen has a very wide explosive range, with the lower explosive level (LEL) being approximately 4 percent by volume. Hydrogen is colorless, odorless, and the lightest of all gases.
The incident commander (IC) should order the officer of the first-arriving ladder company to shut down power to the batteries if firefighting operations warrant. The officer should designate a firefighter of his unit to perform this task and instruct the member to remain at the shutoff location for the remainder of the operation to ensure the system is not inadvertently placed back on.
Ladder company firefighters should also use their thermal imaging cameras (TICs) to detect heat buildup inside storage batteries which could lead to cell thermal runaway. Perform this assignment from a safe distance to avoid being injured should the batteries fail or explode. Ascertain heat propagation to adjacent batteries with the TIC as well. The IC may have to extend operational time or leave one or more fire companies at the scene to continue to monitor battery heat conditions. There are few worse feelings than coming back to the scene of an advanced rekindle fire that is beyond the extinguishment capabilities of responding resources.
Fire Safety Regulations
Facilities and buildings where battery energy systems are installed and operated should have a fire safety and protection plan detailing procedures of what actions responsible employees and occupants are to perform in the event of an emergency, fire, acid spill, gas leak, or other dangerous event. This information is vital for first responders to obtain to enhance their situational awareness of the incident. The plan should be readily available for review on the premises. Preplanning is essential for formulating strategy and tactics for both fires and emergencies.
Regulations should also include the following:
- Certified person: A certified person who is familiar with battery system emergency procedures should be at the premises during all hours of operation. This employee must be aware of system power capabilities, chemistry technology, and the locations of all shutdown switches. Knowledge concerning fire extinguishing equipment, the fire alarm system, and battery monitoring/control equipment is essential.
- System diagram: A system diagram in a conspicuous location denoting key components of the battery storage system is extremely important.
- Fire alarm system: Alarm notification appliances such as horns and strobe lights should be inside the battery room as well as outside each room entrance. Moreover, emergency response instructions will greatly enhance the notification process.
- Fire detection: Ideally, the installed smoke detection system will notify occupants by sounding an alarm and activating exhaust fans. It should also send a signal to both a manned, in-house fire alarm control unit (FACU) and a central station monitoring company. Air sampling smoke detection (ASSD) is especially helpful in providing rapid notification of a potential fire condition prior to active flaming.
- Fire suppression system: If a sprinkler system is installed, heads should be positioned in such a way that they do not directly release water onto the battery cells. This design is essential to circumvent a possible explosion. Normally, sprinkler systems protecting live, energized equipment are of the preaction (two step) type, whereby, a fire detection system, once activated, allows water to enter into the branch lines and flow to unfused heads. Alternatives to water-based fire suppression systems include total flooding methods that inundate a battery storage area enclosure with inert gas, carbon dioxide, powdered aerosols, or clean agents (halon replacements).
- Gas detection: Advancements in air sampling smoke detection technology leverage the air-sampling pipe network within the battery room to also detect harmful concentrations of flammable hydrogen gas. The gas detectors are installed inline with the sampling pipe downstream of the battery room. Any alarm for gas should send a signal to a gas-detection monitoring panel. If there is no hydrogen gas detection system in the battery storage room, the certified person for the premises should bring a portable hydrogen detector into the area when performing inspectional rounds.
- Haz-mat liaison: This person is designated to meet with first responders on their arrival in connection with any fire or emergency on the premises. He should inform firefighters as to the location of the haz-mat incident as well as provide safety data sheet (SDS) information.
- Portable fire extinguishers: A minimum 4-A: 20-B: C rating is recommended for portable fire extinguishers located inside battery-storage areas. Incipient fires involving batteries have been successfully extinguished using ABC dry chemical, carbon dioxide, foam, water, water mist, Class D smothering agents, and clean agents. It is imperative that ownership select portable fire extinguishers that are compatible with battery chemistry. Extinguishers should be within 20 feet of cabinets/battery charging racks.
- SDS: These documents provide workers and emergency personnel with procedures for working with hazardous substances in a safe manner. Information on SDS will normally include physical and chemical characteristics; health effects; first-aid actions; storage/disposal procedures; and proper protective equipment to wear during firefighting, mitigation, and spill handling.
- Seismic protection: Battery storage racks should be seismically braced according to the building code of the authority having jurisdiction.
- Signage and instructions: Caution/Warning/Danger signs where needed should be posted in and around battery rooms. They give both occupants and firefighters a heads-up to promote safety. These signs should be used to denote potential hazards (high voltage, hydrogen gas, corrosive electrolyte solution) as well as where smoking is prohibited. The NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response, diamond should also be posted according to standard guidelines. Cabinets, racks, and storage containers should have signage or markings identifying type of batteries, electrical rating, and applicable chemical and fire hazards.
- Spill control and neutralization: Approved capture, control, absorbent, and neutralization materials should be available onsite for mitigation of corrosive acid or caustic base electrolyte spills involving LA, NiCad, and select types of flow-battery liquid. Li-ion batteries will not require neutralization. Acid spill kits should also be available inside battery rooms to facilitate cleanup and neutralization. The kit consists of a container of acid/base neutralizer and protective clothing. Leaks can occur when replacing batteries or if a battery has a crack in the case and leaks acid out.
- System shutdown protocols: Emergency procedures denoting how to shut down the power from the battery system are critical for occupant and first responder safety. This information should be posted near the battery system or stored in a secure location on the premises. Procedures should include 24/7/365 telephone numbers to contact the owner, stakeholders, and building engineers for obtaining additional information regarding the battery system and to request their response to the scene.
- Thermal runaway detection (battery management): Devices should be installed to monitor, detect, and control cell thermal runaway during charging of batteries. A thermal runaway detection apparatus includes circuitry for determining an increase in internal battery conductance or a decrease in internal battery resistance. The circuitry can also be used to safely manage charging of the battery.
- Ventilation system: NFPA 70E, Standard for Electrical Safety in the Workplace, provides requirements for safely designing a battery-charging room. This standard requires a ventilation system to exhaust air from the room to the outdoors and maintain proper operational temperature. For systems that generate hydrogen gas (LA, VRLA, NiCad), the system should be arranged to exhaust air from high in the room. The design objective of the ventilation system should be to limit hydrogen gas in air to less than 1 percent concentration by volume. When the hydrogen concentration rises to levels above 4 percent, there is a considerable risk of an explosion. When batteries that emit hydrogen gas are installed inside a cabinet, the cabinet should be approved for use in occupied spaces and be mechanically or naturally vented.
Safety Through Preplanning
Consider all electrical equipment energized during fire and emergency operations, including battery storage systems. When working in and around batteries, firefighters should follow standard operational procedures developed during preplanning. Obtain valuable information by visiting buildings and facilities that have these storage systems. Training must stress to all members the potential dangers involved when exposed to this technology. This knowledge should guide strategy and tactics to ensure a successful and safe operation.
Special thanks to Dr. Daniel H. Doughty, president and founder of Battery Safety Consulting Inc., for his technical expertise on this article.
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