The first gas that we will be discussing in detail is hydrogen fluoride (HF). HF is a colourless gas which readily dissolves in water to form hydrofluoric acid (HFA) (Marx et al., 2005; Gad & Sullivan, 2014). HF is an extremely toxic gas and HFA is one of the strongest existing acids (Marx et al., 2005). 

Ingestions of more than 20 mg/kg body weight are considered a lethal dose. – Marx et al., 2005

Adverse health impacts will arise when exposed to it either in gaseous or liquid form (Centers for Disease Control and Prevention, 2018). 

Immediate signs and symptoms of exposure to HF/HFA:

• Exposure to HFA: severe pain on exposed skin immediately or more often several hours after exposure despite no physical burns observed.
• Ingestion of HFA: small amount of highly concentrated HF can severely damage internal organs and may even be fatal.
• Exposure to HF gas: at low concentrations will result in eye, nose and respiratory irritation. At high concentrations, it may be fatal due to the accumulation of fluid in the lungs or cardiac arrhythmia.

Long-term impacts of short contact with HF/HFA: 

• Survivors of inhalation of HF often suffer from chronic lung disease.
• Survivors may suffer from permanent visual problems and damage.

(Centers for Disease Control and Prevention, 2018)

Immediate intensive care treatment is required when exposed to HF/HFA. The damage of HF/HFA to the body can continue for weeks and will have lasting impacts on the person’s health (Centers for Disease Control and Prevention, 2018; Gad & Sullivan, 2014). 

HF is one of the main toxic gas released from the combustion of batteries (refer to chemical equations in the previous blog). Although many studies about the combustion of batteries and toxic gas release have been done, few have released exact amounts of HF gases produced when a battery burns (Larsson et al., 2017). Additionally, as the different battery manufacturers and battery types contain different variations of chemical compositions, it is difficult to specify the exact amount of HF gas released for a battery with a certain capacity (Larsson et al., 2017) (Figure 1). Generally, pouch cells tend to produce the highest concentrations of HF (Larsson et al., 2017). 

[A] possible explanation would be that hard prismatic and cylindrical cells can build a higher pressure before bursting, rapidly releasing a high amount of gases/vapours from the electrolyte. Due to the high velocity of the release and thus the short reaction time, combustion reactions might be incomplete and less reaction products might be produced. – Larsson et al., 2017

Figure 1: HF released during the burning of 7 different types of batteries at different SOC (Larsson et al., 2017)

From the experiments conducted by Larsson et al. (2017), they also found that the state of charge (SOC) of a battery will also affect the rate of HF released when the battery burns. Batteries at 100% SOC tend to have more extreme heat release and flames (Larsson et al., 2017). Experiments conducted on the same type of battery also found a clear correlation between the SOC of the battery and the rate of HF produced over time (Larsson et al., 2017; Zhang et al., 2022) (Figure 2). Similar experiments on different types of cells conducted showed similar results (Larsson et al., 2017). 

Figure 2: Correlation between the rate of heat release and concentration of HF over time at different SOC (Larsson et al., 2017)

 

Reference List

Centers for Disease Control and Prevention. (2018, April 4). CDC | Facts About Hydrogen Fluoride (Hydrofluoric Acid). CDC. https://emergency.cdc.gov/agent/hydrofluoricacid/basics/facts.asp 

Gad, S., & Sullivan, D. (2014). Hydrofluoric Acid. Encyclopedia of Toxicology, 964–966. https://doi.org/10.1016/b978-0-12-386454-3.00853-8 

Larsson, F., Andersson, P., Blomqvist, P., & Mellander, B. E. (2017). Toxic fluoride gas emissions from lithium-ion battery fires. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-09784-z 

Marx, C., Trautmann, S., Halank, M., & Weise, M. (2005). Lethal intoxication with hydrofluoric acid. Critical Care, 9(Suppl 1), P407 (2005). https://doi.org/10.1186/cc3470 

Zhang, L., Duan, Q., Meng, X., Jin, K., Xu, J., Sun, J., & Wang, Q. (2022). Experimental investigation on intermittent spray cooling and toxic hazards of lithium-ion battery thermal runaway. Energy Conversion and Management, 252, 115091. https://doi.org/10.1016/j.enconman.2021.115091