Andrew Draper talks to energy consultant Jim McDowall about dealing with fire risks in energy storage and the US standard NFPA 855. It governs installation of stationary energy storage systems and is under review, with an update due in 2026. Efforts are underway to get it adopted more widely, and more quickly.
Putting a fire out is not necessarily the best way to deal with a fire in an energy storage system (ESS), said McDowall. Letting it burn out in a controlled manner is an approach supported by many. And designing ESS to stop fires happening in the first place is the point of the NFPA 855 standard from the National Fire Protection Association in the US.
The Standard for the Installation of Stationary Energy Storage Systems first came into existence in 2020, and efforts are underway to have it adopted as the de facto standard. The NFPA states the standard provides the minimum requirements for mitigating the hazards associated with ESS. It defines the design, construction, installation, commissioning, operation, maintenance and decommissioning of stationary ESS.
McDowall, battery energy storage consultant with decades of experience in the industry (including 45 years at Saft), is a member of three task groups at the NFPA: fire suppression, explosions and toxic emissions.
He told BEST that if a state had adopted a model fire code from either the NFPA or International Code Council (ICC) before 2020 (some states are still following 2012 fire codes), there is nothing at state level on energy storage, unless it has been updated in any way. The codes are updated periodically to reflect advances in technology, design and so on.
He said the US is further ahead code-wise than most other countries. The ICC’s International Fire Code has a sort of harmonised content from NFPA 855, though not quite the same, he added. It contains regulations to safeguard life and property from fires and explosion hazards. They include general precautions, emergency planning and preparedness, fire service access and water supplies, automatic sprinkler systems, fire alarm systems, special hazards, and the storage and use of hazardous materials.
“So you had these different requirements and sometimes there would be a ‘gotcha’ there where something slipped through on the International Fire Code that was out of step with 855. So in fact, in the 2027 International Fire Code, they’re going to do the same thing that NFPA1 is doing and just have those high level requirements that point to 855,” McDowall said.
Going straight to state legislatures
The American Clean Power Association, for whom McDowall works as a consultant, is taking this further. “They’re addressing this delay in adopting the model codes, which in turn delays adopting NFPA 855. They’re going straight to state legislatures and saying ‘you should be adopting the latest version of NFPA 855 and just say, energy storage facilities shall comply with this standard’. And sometimes there’s a bit of a quid pro quo in terms of more streamlined permitting,” he said. This would bypass the years it takes for jurisdictions to update their fire codes, he added.
California near 10GW ESS capacity
In February, the California Energy Commission and California Public Utilities Commission held a workshop to study safety concerns for large-scale lithium-ion ESS in development, permitting, construction or in operation.
Although there have been fires in New York and California, the Energy Commission Chair, David Hochschild, reportedly said the state’s ESS have been performing well and reliably. He told S&P Global the state was on the verge of hitting 10GW of energy storage.
David Erne, deputy director of the California Energy Commission’s energy assessments division, said California has twice as much battery storage capacity as any other state. The California Independent System Operator has battery storage capacity of 7GW or 47% of total US capacity, according to S&P Global in a briefing note of 14 November.
Public worry about ESS safety
The Electric Power Research Institute (EPRI), of Palo Alto, California, in the US, maintains a database on BESS failures, the BESS Failure Event Database. In a paper issued last November (Lithium Ion Battery Fires in the News), it said the failure rate for grid-scale BESS has decreased due to safety improvements, driven in part by increased regulation.
“Over the last four years, there have been on average 10 such failure events annually, even as global battery deployments have increased 20-fold,” it said. Grid-scale storage is subject to a large family of codes and standards such as NFPA 855 and UL 9540. They impose clearance and separation distances, fire suppression and venting or explosion control for BESS, among other requirements intended to reduce risk, it noted. Lessons learned from failures have been incorporated into newer BESS deployments.
McDowall said in the long term, as BESS installations become more common, there will be more events, even if they are few and far between. “But the rate of safety events is going down as a percentage of gigawatt hours deployed. If you look at it on that basis of the number of fires versus the number of gigawatt hours deployed, the rate is plummeting.”
Michigan adopts NFPA 855
The State of Michigan passed bill 233 last November on renewable energy, which specifically stipulates that new energy storage facilities must comply with NFPA 855. The act, which takes effect in November, sets out that ESS must be:
- 300 feet away from occupied buildings and dwellings
- 50 feet away from public roads and shared property
- quieter than 55 decibels (using the A-weighted scale designed by the American National Standards Institute)
- using dark sky-friendly lighting
- built within five years of a certificate being issued, otherwise it becomes invalid.
McDowall said the American Clean Power Association is dealing with delays in adopting the model codes, which in turn delays adopting NFPA 855. “They’re going straight to state legislatures and saying ‘you should be adopting the latest version of NFPA 855 and just say, energy storage facilities shall comply with this standard’.”
A toxic stew
One of the NFPA’s working groups studies toxic gases. McDowall points to a dichotomy. “If you look at testing that people like DNV GL have done, there’s this toxic stew of emissions when you have a highly instrumented lab test, of hydrogen fluoride, hydrogen cyanide, hydrogen chloride, all being given off by burning lithium-ion cells.
“But whenever there’s a fire, the state environmental protection group…will come along and they will do air sampling around the facility, and they never find dangerous levels of contaminants,” he said.
Many of them are consumed by the heat of the fire and they also disperse rapidly. Adequate insulation and spacing between containers prevents fire spreading so a ‘let it burn’ approach is favoured unless the fire is close to buildings etc., he said.
Let it burn
McDowall points to events where this approach would be right. “With the event in Surprise, Arizona, the fire suppression worked, it knocked out the fire, but it didn’t stop cell-to-cell propagation. So there was ongoing venting of all these flammable gases, they built up above the upper flammable limit. So they couldn’t burn. It was too concentrated,” he said.
That condition remained entirely stable for many hours until the firefighters opened the door after much consideration, which allowed oxygen to get in. A spark is thought to have caused an explosion and two of the firefighters were blown some 75 feet into a fence and were quite badly injured. Several firefighters and a police officer were hospitalised.
The fire and subsequent explosion occurred in April 2019 at the McMicken facility operated by the Arizona Public Service utility.
The 2023 version of NFPA 855 allows either explosion prevention by emergency ventilation, or deflagration venting, said McDowall. “That means you allow an explosion to occur and you make sure it comes out of the roof of the container rather than out of the sides at firefighters who might be standing nearby.
“And the problem with deflagration venting is that the same thing could occur if you get enough cell venting without flame, you could build up those flammable gases above the upper flammable limit. And then you can’t have an explosion.”
Explosion prevention
That means no explosion protection whatsoever, he said. In the first draft of the 2026 standard update, which is subject to change, deflagration venting is deleted and there must instead be explosion prevention and secure powering for the fans.
“If you had fire suppression by anything other than sprinklers – if you had clean agent, if you had aerosol, you’re just going to ventilate it out of the container and it’s going to be completely useless,” he said. “And in fact, there’s some text in there saying that ventilation has to take precedence over fire suppression by any means other than sprinklers.” And sprinklers are only effective if you can direct the water at the cells in thermal runaway, which is often not possible.
Another drawback with fire suppression is stranded energy. A fire that is extinguished, but not burned to completion, may reignite. “So if you allow the fire to burn out, okay, you’ve got this nasty crap left at the end, but you haven’t got any toxic runoff, you haven’t got any stranded energy and you don’t have any possibility of reignition,” McDowall said.
“And quite honestly, I think NFPA 855 should be adopted worldwide. You know, it’s not geographically sensitive in its requirements and it represents the best safety practices that are out there.” That in turn may lead to a revision of the UL 9540A test method, which shows how to conduct testing to ensure compliance with NFPA 855, McDowall said.
Updates to NFPA 855
The NFPA is undertaking a public consultation on its proposed changes to NFPA 855. This will close on 30 May. Other proposed changes include ensuring complete combustion of one energy storage unit will not result in fire or thermal runaway in adjacent units.
Chris Groves, product manager, Wärtsilä ES&O, confirmed his company follows industry guidance ‘let-it-burn’ approach with its battery energy storage systems. “Suppressions should generally only be utilised if there is an immediate risk to nearby exposures. If water is to be used, a fire water mitigation plan should be in place,” he said.
