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Condensed Aerosol Fire Suppression for BESS / Battery Energy Storage Systems.

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Arizona battery fire’s lessons can be learned by industry to prevent further incidents, DNV GL says

By Andy Colthorpe

July 29, 2020


Investigators at the scene: DNV GL said utility APS took great care to preserve the site for examination, including constructing a tent around the badly damaged BESS facility. Image: APS.

An April 2019 fire and subsequent explosion which caused injuries to firefighters and destruction of a grid-scale battery storage system in Arizona likely started with an internal cell defect that caused the “preventable” incident, analysis has found.

Utility Arizona Public Service (APS) commissioned an investigation just three days after the incident, with experts performing an environmental assessment of the facility and site, a forensic analysis and inspection of evidentiary data to determine the origin of the blaze as well as the explosion, as well as the review the suitability of fire suppression equipment in place. Project partners AES, which developed the project, Fluence, which supplied the system and LG Chem which supplied the batteries, also took part in the investigation.

Further to that investigation, a team from DNV GL was asked by APS to perform technical analysis of the event at McMicken Battery Energy Storage System in West Valley, Arizona, characterized as thermal runaway leading to an explosion. The project featured a 2MW / 2MWh battery energy storage system (BESS). DNV GL has also made recommendations that would reduce the chances of another such event taking place at other storage facilities.

It took around two hours from the first report of a suspected fire at the facility, at 17:48 local time on 19 April 2019, to around 20:04 before an explosion happened from inside the BESS. The BESS and its container was “essentially destroyed” and the incident left several firefighters injured. All that was known at the time was that an equipment failure had taken place in the incident, which brought fire safety back to the top of the agenda for the energy storage industry.


DNV GL’s energy storage team leader, Davion Hill, wrote in his report that “an extensive cascading thermal runaway event” began through internal cell failure within one LG Chem 0.24kWh nickel manganese cobalt (NMC) pouch cell in the BESS – believed to a “reasonable degree of scientific certainty” to have been the product of an internal cell defect involving abnormal deposition of lithium metal and dendritic growth within the cell.

The report found that the fire suppression system onsite worked as designed to but was inadequate to prevent or stop the cascading thermal runaway. Heat transfer between every cell and module in one of the battery racks caused the thermal runaway to propagate – facilitated by the absence of “adequate thermal barrier protections between battery cells,” which could have stopped or slowed the propagation. ***

Some three hours after the thermal runaway was thought to have begun, firefighters opened up the BESS door, which agitated flammable gases that remained and brought the gases into contact with a spark or heat source – causing the explosion.

DNV GL said that standards today informing first responders on how to deal with incidents at such systems are already more advanced than they were when McMicken went online in 2017, but also recommended that hazard assessments and corresponding training should take place “before and during the commissioning of energy storage systems”. At this year’s Energy Storage Digital Series online conference, attendees heard from several industry representatives that storage stakeholders should work closely with and educate first responders in areas where systems are deployed.

The McMicken system was one of two 2MWh battery projects put in place by APS with AES as EPC contractor and installer to investigate the use of energy storage on its networks, including the ability for BESS to help integrate growing shares of rooftop solar PV in the utility’s service area.

On the day of the incident, the BESS was performing solar smoothing applications – charging during the daytime from local solar generation and discharging electricity to the grid during the evening peak load. Data collected by APS found that just before 5pm on 19 April, there was a sudden drop in voltage during one of the system’s charge cycles.

Thermal runaway began shortly after that. Smoke detection systems went into operation but off-gassing of battery cells as the thermal runaway cascaded through neighboring modules caused a “flammable atmosphere within the BESS,” the DNV GL report said. Then, when firefighters opened the side container door around three hours after thermal runaway began, an explosion occurred within 2-3 minutes, causing the side and rear doors of the BESS as well as other debris to be ejected by the explosion. 


16:54:30               Battery voltage drop of 0.24 V in rack 15, module 2, battery 7 (4.06 to 3.82 V)

16:54:38               Total voltage drop of 3.8 V in rack 15 (799.9 to 796.1 V); BMS loses module level data

16:54:40               Temperature readings begin to increase in the rear of rack 15

16:55:20               BESS smoke alarms 1 and 2 activate and the fire protection system triggers several 

                             circuit breakers to open (BMS DC breakers,inverter AC contactors, main AC breaker)  

16:55:45               Ground fault detected

16:55:50               Fire suppression system discharges Novec 1230 suppression agent (30 second delay

                             from alarm time, as per its design)

16:57                     APS contacts Fluence to verify the fire suppression system discharged

17:07                     Fluence advises APS that its Field Service Engineer is en route to the site for visual

                              confirmation of potential fire

17:12                     APS dispatches a Troubleman to the site

17:40                     Fluence field service engineer calls 911 to report suspected fire

17:44                     APS notifies 911 End of data collection and cessation of remote communications (end of

                              battery backup power for main servers and communications equipment)

17:48                     Fire department arrival time

20:02                     Front door of container opened by emergency responders

20:04                     Explosion occurs


In response to a number of fires at BESS projects in South Korea over a period of about a year, beginning in August 2017, DNV GL had said previously that it was important that minor defects or other issues did not lead to more catastrophic failure situations. The group noted in its report on the McMicken fire that those incidents were associated not only with NMC batteries but also happened in some cases with lithium iron phosphate (LFP) cells. Those fires were initially thought to have been primarily caused by inappropriate system integration practices but were later also found in many cases to have been the result of defective battery cells.

“The lessons the industry has learned from these incidents is that Li-ion batteries are inherently fragile, and any electrical, thermal, or mechanical abuse, along with internal defects, can potentially initiate cell failure and thermal runaway,” the DNV GL McMicken incident report said.

DNV GL concluded that certain best practices available to the industry could have prevented the tragic incident in Arizona, beginning first with addressing cell quality. Further to that, barriers to limit or prevent cascading could be put in place, both from cell-to-cell and module-to-module. Better means to safely ventilate the system would have meant dissipation of flammable gases before first responders gained access, while strategies for extinguishing fires inside systems including fire suppression, ventilation, and cooling “should be a requirement going forward,” the report said. DNV GL also noted that many standards are now in place that were not at the time of the system's commissioning, including relevant standards from the National Fire Protection Association (NFPA).

APS has made the DNV GL-authored report available online and it can be viewed here.


Sustainable Energy

Fire Suppression Agent Selection

June 26, 2018, Featured ArticlesTechnical Articles

Published in SPRINKLERAGE , An American Sprinkler Association Publication


Protection for a Mobile Power Generation Unit


Summary Jackson Associates, Inc. was approached by a government contractor to analyze protection of a power generating unit (PGU) which is part of a large trailer unit. The trailer is built to fit inside a large military aircraft for rapid deployment throughout the world. The unit was being designed and tested by a consortium of military manufacturers and contractors.

Jackson Associates, Inc. was assigned the portion of the project intended to explore potential types of extinguishing systems to protect the power generating unit for the program and identify the strengths and weaknesses of the various systems.  We do not have permission to provide any photographs or information regarding the purpose of the units.

Project Task the PGU module contains two diesel generators. The main fire hazard would be from a diesel fuel leak that could cause a pool fire or an atomized spray fire. The design parameters call for storage in a range from -40°F to 150°F and operating temperatures of 35°F to 125°F Because of the extreme congestion inside the PGU most systems would require locating the extinguishing storage vessels on the exterior of the PGU. The weight of the system is also a significant factor for air transportation. The lower extremes in temperature obviously eliminate any water-based extinguishants, without some type of freeze protection. The PGU also requires many openings to allow for cooling during operation. We chose to look at the following extinguishing systems:

1. Clean Agent Systems


  2. ECARO-25

  3. NOVEC-1230

  4. FM-200


2. Carbon Dioxide


3. Compressed Air Foam


4. Dry Chemical


5. Condensed Aerosol


6. Water Mist


We were unable to find an approved antifreeze presently available for water mist systems (although there is speculation that it may be in development). Therefore, water mist was eliminated from consideration. The following is a description of the qualities of the remaining five types of systems.

Clean Agent Systems “Clean agent fire extinguishing system” is a term that covers a wide variety of extinguishants which were developed as alternative replacements for Halon 1301 and other halons. The Montreal protocol of 1987 imposed severe international restrictions on production of halons, freons and other chlorofluorocarbons (CFCs) that were detrimental to the earth’s atmosphere. Design and installation of clean agent extinguishing systems are governed by NFPA 2001.


The most common halon replacements are:

1. Inergen (IG-541) N₂(52%) Ar(40%) CO₂(8%)


2. ECARO-25 (HFC-125) CF₃ CF₂H


3. NOVEC-1230 (FK-5-1-12) CF₃CF₂C(O)CF(CF₃)₂


4. FM-200 (HFC-227ea) CF₃ CHFCF₃




Inergen utilizes inert gasses and works by lowering oxygen levels below the level that will allow combustion while at the same time maintaining an oxygen level that would allow humans to continue to occupy the space. In this application, Inergen has three main drawbacks:

1. It requires maintaining a very accurate concentration level. In this application, with high ventilation rates and unclosable openings, this will be impractical.

2. The amount of gas is significant and is stored in heavy high-pressure cylinders that would add undesirable weight.

3. The refill stations are tightly controlled by the manufacturer, which greatly reduces availability for recharge after a discharge.


ECARO-25, NOVEC-1230 and FM-200


All of the above clean agents have an ozone depletion potential (ODP) of zero. Both FM-200 and ECARO-25 have a significant global warming potential (GWP), whereas NOVEC-1230 and Inergen have a GWP of 1. This makes NOVEC-1230 and Inergen preferable as extinguishing agents, from an environmental standpoint, since all four agents have similar extinguishing capabilities. Since Inergen was eliminated, as explained above, we consider Novec-1230 as the preferable clean agent.

A white paper by Mark L. Robin, PhD, of DuPont, which provides technical details of the various chemicals, can be found at


1. NOVEC-1230 is very effective and will quickly extinguish the fire without an adverse effect on personnel in the area.

2. The system size and weight are reasonable.

3. The equipment is durable.

4. Since NOVEC-1230 is a liquid at normal room temperature, for recharging it is easily transferred to the cylinder which is then pressurized with nitrogen.

5. There is no clean up and the generator can be restarted immediately.

6. NOVEC-1230 is environmentally friendly.

7. It is not corrosive to electronics.

8. NOVEC-1230 systems are UL listed and FM approved.


1. Industry standards are that an extinguishing concentration is to be maintained for 10 minutes. The system is required to discharge in no more than 10 seconds. However, the unclosable openings in the PGU make it likely that the extinguishing concentration will be maintained for less than one minute. Due to the heat from the diesels, re-ignition of the fire is a real concern once the gas concentration descends below the required level.

2. NOVEC-1230 can absorb moisture if not properly handled during recharge, causing it to become acidic. Acidity can cause reduced effectiveness and cause corrosion of the cylinder.

3. Clean agents function by chemically reacting with the fire and interfering with the fire chemical reaction. In order to do this, the clean agent breaks down into other chemicals when heated to extreme temperatures at the flame. The broken-down chemicals can be toxic. In order to minimize the toxic chemicals, clean agents are required to discharge totally in a maximum of 10 seconds. When the system discharges it could create a potential concern. The discharge would extinguish the fire but, after the NOVEC-1230 leaks out the unclosable openings, the lower concentration could allow the fire to restart. With the inadequate concentration, the fire could produce excessive amounts of toxic gasses from the breakdown of the clean agent. One of the reasons that clean agents are typically required to maintain extinguishing concentration for a minimum of 10 minutes is to assure that the fire cannot restart, creating toxic chemicals from the extinguishing agent.

4. Because of the size, the cylinder and actuator would need to be located in a weather-tight enclosure on the outside of the PGU.


Carbon Dioxide Carbon dioxide has been successfully utilized for fire suppression for more than 100 years. The NFPA standard for carbon dioxide is NFPA 12, Standard on Carbon Dioxide Extinguishing Systems. Carbon dioxide displaces oxygen to a percentage that will not support combustion. Following a discharge, the oxygen percentage is also below the level that would be necessary to support human life. Because of this safety issue, NFPA 12 now prohibits the use of carbon dioxide in occupiable areas (areas where it is possible for a person to enter) without several safety features. To install carbon dioxide in occupiable areas, various safety requirements are required, including:

1. Safety signs at all entrances.

2. An electrically monitored lock-out valve.

3. A pneumatic (CO₂-powered) pre-discharge siren.

4. Pneumatic time delay.

5. Audible/visual discharge alarm signals at each entrance to indicate that the system has discharged.

6. A distinctive and recognizable odor that must be added to the carbon dioxide. This is typically accomplished with a wintergreen odorizer provided by the equipment manufacturer.

The above safety devices add complexity and expense to the system.



1. It is very effective and will quickly extinguish the fire.

2. Carbon dioxide is an oxygen diluting agent and does not break down like clean agents. Therefore, the code allows it to take up to 2 minutes to achieve the design concentration. Because of this, we can easily extend the discharge and maintain the concentration with extra gas for several minutes.

3. The equipment is durable.

4. Carbon dioxide is readily available around the world.

5. There is no clean up and the generator can be restarted immediately.

6. Carbon dioxide is a greenhouse gas, but the quantities are negligible.

7. It is non-corrosive to electronics.

8. Carbon dioxide systems are UL listed and FM approved.


1. It displaces oxygen, so it is hazardous and potentially lethal to personnel inside the PGU.

2. In order to address safety concerns, additional safety equipment is required.

3. There is significant expense in training all personnel on the precautions and procedures for safety.

4. The carbon dioxide is stored in high pressure cylinders that are bulky and heavy.

5. Because of the size, the cylinder and actuator would need to be located in a weather-tight enclosure outside of the PGU.

3. Compressed Air Foam


Compressed air foam is a hybrid type foam system that incorporates a foam tank filled with a freeze-protected, premixed foam water solution. To discharge the foam, a compressed air tank pressurizes the tank and forces the solution into a mixing chamber. There, air is mixed with the solution, causing it to expand between 10 and 20 times and then flow through piping to discharge nozzles. It has been used extensively in portable extinguishing systems at military airports and in large engine compartments.


The following are advantages of compressed air foam:

1. The foam is very effective at extinguishing both pool fires and three-dimensional fires.

2. The foam will blanket the burning liquid and remain effective for an extended period.

3. The systems are fairly compact.

4. The equipment is durable.

5. Recharge is simple. Just pour in the new foam solution and refill the air cylinder.

6. The foam is widely available.

7. The foam is environmentally friendly.

8. The discharge nozzles are standard open sprinklers.

9. The foam is not corrosive to electronics although drying out any exposed electrical components could be necessary.

10. The foam solution is UL approved.



1. Clean-up may require vacuuming out the foam and drying out the PGU.

2. While it is non-corrosive, it is an aqueous solution and any critical exposed electrical is a concern.

3. There are no nationally recognized listings of the units as fixed systems.


Dry Chemical Dry chemical is one of the most widely used fire extinguishants. It is most commonly used in portable fire extinguishers. However, it is also available in larger industrial and vehicular systems. NFPA 17, Standard for Dry Chemical Extinguishing Systems, governs the installation of dry chemical systems. Dry chemical systems utilize a chemical powder which chemically reacts and interrupts the fire chain reaction.

The following are advantages of dry chemical:

1. It can effectively extinguish a fire and could continue to remain effective for several minutes.

2. The system size and weight are reasonable.

3. The equipment is durable.

4. Recharge is very simple, involving loading the powder and pressurizing with nitrogen.

5. The chemical is widely available.

6. It is environmentally friendly.

7. UL listed, and FM approved.


1. The systems are extremely messy (envision throwing 50 pounds of powdered sugar in the air).

2. The clean-up inside the PGU would be extensive.

3. Dry chemical can be corrosive to electronics and aluminum if not properly cleaned up. For example, dry chemical should not be used around aircraft because of potential damage. See the related Boeing Service letter at

4. Personnel must be trained. While there would probably be no lasting effects, if personnel were inside the PGU when it discharged, inhalation of the dry powder and/or getting it in the eyes would be very unpleasant.


5. Because of the size, the dry chemical cylinder and actuator would need to be located in a weather-tight enclosure outside of the PGU.


Aerosol fire suppression systems are a relatively new fire suppression product, in comparison to many of the other products. NFPA 2010, which was first issued in 2005, governs the design and installation of aerosol fire extinguishing systems. Systems are available that can operate automatically at a preset temperature, manually, or electrically from a listed fire alarm releasing panel.

The sealed aerosol generators, through an exothermic reaction, discharge extremely small aerosol particles between 2 and 10 microns. Because of the small size of the particles, they suspend in the air and will remain suspended for an extended amount of time in the enclosure. Since the particles are suspended in air, when the generator cooling air is stopped the aerosol particles are less prone to leaking out of enclosure openings than most gaseous extinguishing agents that are heavier than air.


1. Much smaller and lighter than other extinguishing systems. A single generator could be located inside the generator enclosure (the size of a large coffee can) that would weigh around 20 pounds. All other systems would need to be in weatherproof enclosures outside the PGU and would weigh many times 20 pounds.

2. The aerosol can effectively extinguish a fire and can remain effective for an extended period – often up to an hour.

3. Sealed generators require much less maintenance than the remotely mounted agent containers of other systems.

4. The equipment is very durable.

5. There is no piping into the PGU that could require removal for servicing of the PGU.

6. It is fairly economical to install a second generator as reserve in order to provide continued protection to restart the generator after a fire.

7. The enclosure is not pressurized, as it would be with discharging of gaseous systems. Therefore, the extinguishant is not ‘pushed’ out of the PGU during discharge.

8. The aerosol generators are sealed units so there is no recharging. The generator is simply replaced with a new unit.

9. The aerosol particles are not corrosive to electronics.

10. Cleanup is very minimal.

11. Generators are UL listed.


1. If discharged while personnel are working in the PGU, there could be temporary eye irritation.

2. The gasses discharging out of the unit can be up to 100°C, but temperatures decrease rapidly as you get away from the generator.

3. The units were tested by Underwriters Laboratories to a maximum of 130°F so the generators are listed for 130°F. The manufacturer stated that they typically will function well above that and have been extensively used in military vehicles in Afghanistan.


With the design requirement for this application, it became apparent that aerosol was the best fit. Some of the favorable factors were the compact equipment, lightweight, no piping, limited clean up and lack of corrosiveness to aircraft aluminum.




Wind Turbine Generators (turbines) experience failures that may lead to small, contained fires and, at times, devastating large fires that render the turbine a total loss. Causes such as loose glowing electrical connections, short circuits, arcing and component failures can cause direct and secondary damage throughout the equipment.

Secondary damage, also known corrosion, is caused by residual chemicals after a combustion event. When measured in remediation cost, secondary damage can be 10-15 times more severe than direct damage.

Flame Guard USA, an industry leader in aerosol fire suppression systems, released the X-Tinguish® XT-3000, a fixed condensed aerosol generator that is used in early stage and fully developed fires. Once the X-Tinguish®XT-3000 generator is triggered, an aerosol mist is generated. The mist expands volumetrically, engulfing the space and suppressing the flames within seconds. This tool successfully reduces the temperature by as much as 1,000°F in as little as 30 seconds, reducing the need for water by as much as 80 percent in applicable environments.

In an effort to quantify what, if any, adverse effects the aerosol mist may have on various metals and electronic circuitry, Flame Guard USA partnered with AREPA, a professional equipment reconditioning firm, to conduct an experiment.


Turbines contain metals such as copper, aluminum, stainless steel, galvanized steel, as well as both non-conformal coated and coated circuit boards. In an effort to simulate extreme field conditions, AREPA secured the noted metals and electronic circuitry, exposed them to the X-Tinguish® XT-3000 aerosol mist and placed them in a chamber with elevated moisture and heat. AREPA harvested analytical samples on the exposed components after seven days, 14 days and 30 days in order to properly understand the chemical reaction that was taking place on the sampled surfaces.


AREPA determined that nitrates (NO3-), magnesium (Mg++) and potassium (K+) were the ions present following the aerosol mist exposure. As noted in the tables below, prolonged exposure did affect a portion of the tested surfaces, although not in a uniform way. Following seven days of exposure, all the contaminated surfaces were restored back to their newly manufactured cleanliness levels. Following 14 days, stainless steel, and galvanized steel exhibited surface haziness while copper developed black patina (corrosion). Technical reconditioning successfully removed the hazing and the black patina. The circuit boards were not impacted. Following 30 days of exposure, the metals did not exhibit a significant difference from the 14-day mark. AREPA’s technical reconditioning processes were successful once again at restoring the metals back to their new cleanliness levels.

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Section 4


Condensed aerosol fire suppression systems do not differ in many areas when compared to other fire suppression systems. Condensed Aerosol fire suppression systems must adhere to the guidelines laid out by the NFPA according to NFPA 2010.

Condensed Aerosol Fixed Fire Suppression systems differ from other fire suppression systems in they do not require pressurized storage vessels, piping, valves, nozzles, nor the constant maintenance required by other fire suppression systems, such as Clean Agent, water, inert gases, and CO2.

Condensed Aerosol Fixed Fire Suppression systems do require ceiling, wall, or cabinet space for aerosol generator installation. The area required is out of way of any persons that may utilize the space. Each generator has very small footprint, are low-voltage electrical, and may utilize conduit if required by the local AHJ.


Condensed aerosol fire suppression systems are recognized Internationally as being extremely efficient in suppressing fires in seconds within enclosures, (even those with openings). Condensed aerosol can remain buoyant for up to an hour within closed systems. This Aerosol fire suppressant can remove heat quickly and efficiently (up to 1,000°F in 1 minute). X-Tinguish® Condensed Aerosol in non-toxic, non-corrosive , and non-conductive. Condensed Aerosol generators have an extremely small footprint, are easy to maintain, and require very little maintenance during their entire lifespans.

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