Fire risk assessment of battery home storage compared to general house fires

Original Article ↗ Hacker News Discussion ↗

New research on fire risk from home battery storage systems finds they are statistically less likely to ignite than typical house fires or internal combustion engine (ICE) vehicles, with risk levels likened to that of a clothes dryer. Commenters broadly welcome the finding but point out important caveats: lithium battery fires are harder to extinguish and more toxic, data for home storage is sparse and skewed toward newer, safer chemistries like LFP, and national codes and installation quality vary widely. The conversation widens to practical issues such as where batteries should be sited, evolving safety regulations, the dangers of cheap uncertified lithium products (especially e-bike packs), and questions about long-term and systemic risks, including cybersecurity of internet-connected storage systems.

Overall risk comparisons

  • Thread highlights that, per the paper, home storage systems (HSS) and EVs ignite less often than general house fires and ICE vehicles.
  • HSS fire likelihood is likened to clothes dryers/tumble dryers, but commenters stress that fire severity and toxicity can be worse for batteries than for many other causes.

Data and methodology concerns

  • Several comments question robustness:
    • HSS incidents in Germany were collected via web crawling for a single year (2023) due to lack of official data.
    • EVs and HSS are new; failure rates may change as systems age.
    • Battery chemistries and system designs are lumped together.
    • The paper is a preprint, not yet peer-reviewed.
  • Some see the results as directionally reassuring but statistically fragile.

Battery chemistry and design

  • Strong emphasis on differences between lithium iron phosphate (LFP) and other lithium-ion chemistries (e.g., NMC):
    • LFP is repeatedly described as much more fire-resistant and less prone to thermal runaway.
    • Many newer EVs and home batteries (including newer Powerwalls) reportedly use LFP; older systems often did not.
  • Commenters criticize the paper for barely differentiating chemistries.

Fire behavior and firefighting

  • Multiple posts stress that Li‑ion fires are self-sustaining, extremely hot, produce toxic gases, and may re‑ignite.
  • Firefighting strategies discussed: cooling/flooding, isolating packs in sand or water, and sometimes simply letting an EV burn while protecting surroundings.
  • Risk in enclosed spaces (garages, basements, elevators) is seen as particularly concerning.

Codes, installation quality, and placement

  • Germany is portrayed as stricter by default; US enforcement is uneven, with many poor or DIY installations and patchy NEC adoption.
  • Real-world example: a 15 kWh system required a fire-rated “room” and door, adding ~5–10% to battery cost (DIY).
  • Several standards (e.g., AU/NZ) restrict installing batteries in habitable spaces or near egress.
  • Many commenters prefer batteries outside, behind fire-rated barriers, or in standalone structures, but note climate and cost constraints.

Comparisons with other risks

  • Numerical translation: expected intervals (very approximate) like ~360 years between general house fires vs ~20,000 years for HSS in a single dwelling.
  • Some argue battery focus is overblown relative to ICE vehicle fires, gas explosions, and kitchen fires; others counter that even rare lithium fires can be uniquely destructive.

Regulation, standards, and cheap batteries

  • Strong concern about low-quality e‑bike/scooter batteries and chargers, especially in NYC, where they are a leading fire cause.
  • Calls for mandatory UL-equivalent certification and better enforcement, especially on online marketplaces, which are accused of tolerating fake safety markings.
  • Note that UL alone doesn’t guarantee cell quality; pack-level design and prevention of cascading failures matter.

Cyber and IoT concerns

  • Some worry that internet-connected HSS with closed-source firmware could be mass-compromised, inducing simultaneous overcharge/overheat events.
  • Others respond that core protection is typically handled by dedicated hardware/analog ICs, limiting what malicious firmware can do, though it might still increase wear.

User attitudes and practical mitigations

  • Enthusiasts remain interested in solar + storage despite cost and code hassles, often citing climate and resilience.
  • Skeptics are wary of unclear long-term risks, code immaturity, and cleanup/toxicity after a fire.
  • Practical mitigations mentioned: placing batteries in fire-rated closets or outdoors; using fire-rated boxes or even ovens for charging e‑bike packs; avoiding overnight charging; keeping sand nearby for small battery fires.