Or, here is what goes up hundreds of feet in the air in a BESS fire plume, to be distributed by the wind for days before the fire burns itself out: 

Hydrofluoric Acid

“Both types of battery  produce extremely toxic HF (hydrogen fluoride) gas which, in moist air or when doused  with water, turns into hydrofluoric acid — the most insidious acid known to science. “ Source: https://bessnot.info/lfp-battery-failures 

- Hydrofluoric acid, a solution of hydrogen fluoride gas (HF) in water, is one of the most corrosive and dangerous chemicals encountered in the laboratory. Exposure to HF can cause severe tissue damage and even death.

Another significant difference between LFP and NMC batteries is that the latter eject  micro and nano particulates of nickel, manganese, and cobalt oxides, as has been  demonstrated at the ongoing Moss Landing BESS fire. These heavy metal oxides are  carcinogenic to humans and animals, and are toxic to the soil.

Since LFP batteries use a lithium/iron cathode, they would not  eject these toxic heavy metal oxides in a thermal runaway event.  Nonetheless, LFP  batteries, like NMC batteries in thermal runaway, eject much more than simply toxic HF  (hydrogen fluoride gas and acid); both types of batteries eject a bizarre cocktail of toxic and carcinogenic organic compounds from the combustion of the various battery components and organic solvents added to the electrolyte to enhance electron transfer between cathode and anode…

Ethylene Carbonate: 

Harmful if swallowed, causes serious eye and respiratory irritation. 

Dimethyl  Carbonate: 

Considered less toxic than traditional methylating agents, though its metabolites (methanol, formaldehyde) are toxic.

Phospho Fluoride:  Or, the “P” in LFP…

Phosphorus fluorides are a group of highly reactive, toxic inorganic compounds, primarily Phosphorus Trifluoride 

Hazards & Safety 

• Extreme      Toxicity: Inhalation can cause severe lung damage (pulmonary edema) and be      fatal. 
• Corrosive:      Causes severe burns to skin, eyes, and mucous membranes. 
• Moisture      Reactive: Reacts with water/steam to produce highly corrosive and toxic      Hydrogen Fluoride (HF) and phosphoric acid. 
• Handling:      Requires strict ventilation, protective gear (respirators, gloves, eye      protection), and careful storage to prevent rupture or release. 

A LFP [lithium iron phosphate] battery includes  a LiFePO4 cathode, a graphite anode, a separator, and electrolyte. The  electrolyte is usually made of lithium salt (LiPF6) dissolved in carbonate  solvents. Common carbonate solvents have multiple compositions, including  ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC),  diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). These flammable  carbonate solvents are the primary fuel in battery fire during TR [thermal  runaway]. The TR [thermal runaway] of LFP [lithium iron phosphate]  batteries is caused by various abuse conditions in BESS [Battery Energy  Storage System], which can be mainly divided into: thermal abuse, electrical. Sources: AI and https://bessnot.info/lfp-battery-failures