Thermal Runaway Gas Analysis
Thermal Runaway Gas Analysis typically refers to the identification and quantification of gaseous products generated during a thermal runaway event—common in batteries (especially Li-ion), chemical reactors, or energetic materials. It’s an important safety assessment because the released gases can be flammable, toxic, or reactive, and they directly influence explosion severity, fire propagation, and venting system design.
Thermal Runaway Test Procedure:
- The thermal runaway experiment is conducted either in Accelerating Rate Calorimeter (ARC®) or in a high-pressure vessel. Based on size of cells and expected volume of gas generated, vessels are selected. Belmont Scientific has multiple vessels fully equipped with cell temperature & voltage, vessel pressure and heating systems (3.765L with 1900psi, 0.25L with 3000psi and 60L with 110psi).
- Thermal runaway is initiated by heating the cell at a defined heating rate from room temperature to a defined end temperature (commonly 200 ⁰C or until cell goes to thermal runaway.
- Once the pressure vessel has cooled down to room temperature, the pressure vessel is attached to the gas transfer assembly to transfer gas mixture to gas analysis cylinder. Gas samples are collected in an appropriate sample container (pouch, gas analysis cylinder etc.) and analyzed
Data collected during the test includes
- Pressure
- Cell temperature
- Cell holder temperature (if applicable)
- Outside vessel temperature
- Heater current (if applicable)
- Heater voltage (if applicable)
- Cell voltage
- Sample Gas
Standards:
Gas analysis done by GC-MS according to ASTM D1945 “Standard Test Method for Analysis of Natural Gas by Gas Chromatography”
Equipment used:
- High-pressure vessels are fully equipped with heating, temperatures and measurement capabilities as shown in Picture 1.
- Accelerating Rate Calorimeter (ARC) equipped with closed holder and cylinder with pressure transducer.
- Inhouse BSI’s gas sampling setup as shown in Picture 2.
Picture 1: High pressure vessels
Picture 2: BSI Thermal runaway test and gas sampling setup
Example Test:
A sample test was conducted in triplicate for a lithium Ion 21700 cell but inside a high-pressure vessel (Picture 2) to measure the volume of spent gas generated and collected for gas analysis. The gas analysis is done using GC-MS according to ASTM D1945 “Standard Test Method for Analysis of Natural Gas by Gas Chromatography” and exemplar gas volume measured are summarized in Tabel 1 and gas composition summarize in Table 2 below:
Table 1: Thermal Runaway Vent Gas Volume Test Results
| Sample: INR21700, 4.5Ah | Weight loss(%) | Peak Vessel P (Psia) | Peak Cell T (C) | End Vessel P (Psia) | Total Volume (L) |
|---|---|---|---|---|---|
| Average | 61.4 | 179.1 | 543.5 | 54.1 | 9.4 |
| Average Deviation | 4.1 | 14.4 | 68.9 | 2.2 | 0.5 |
Table 2. Thermal Runaway Vent Gas Analysis Summary
| Component | Average | Mean Deviation | D.L |
|---|---|---|---|
| Gas Volume (L) | 9.4 | 0.5 | % v/v |
| Non-Hydrocarbon Gases | |||
| Nitrogen | 19.37 | 3.378 | 0.01 |
| Oxygen | 0.125 | 0.005 | 0.01 |
| Argon | 0.29 | 0.007 | 0.01 |
| Carbon Dioxide | 10.5 | 0.578 | 0.05 |
| Carbon Monoxide | 46 | 1.667 | 0.05 |
| Hydrogen | 19.6 | 0.978 | 0.05 |
| Hydrocarbon Gases | |||
| Methane | 3.587 | 0.309 | 0.001 |
| Ethylene | 0.17 | 0.043 | 0.001 |
| Acetylene | 0.01 | 0.002 | 0.001 |
| Ethane | 0.15 | 0.018 | 0.001 |
| Propylene | 0.044 | 0.016 | 0.001 |
| Propane | 0.007 | 0.002 | 0.001 |
| Isobutane | 0.001 | 0.0004 | 0.001 |
| n-Butane | 0.022 | 0.004 | 0.001 |
| Butene | 0.023 | 0.003 | 0.001 |
| Isopentane | nd | nd | 0.001 |
| n-Pentane | 0.003 | 0.000 | 0.001 |
| Pentenes | 0.009 | 0.003 | 0.001 |
| Hexanes + | 0.157 | 0.031 | 0.001 |
FAQ:
1. What is the purpose of Thermal Runaway gas Analysis?
Characterize Hazards
- Identify flammability of vent gas mixture (H₂, CH₄, CO, hydrocarbons).
- Detect toxic gases (HF, HCl, CO, NOₓ).
- Quantify gas release (self-sustaining combustion risk).
Safety Design Inputs
- Explosion risk (Lower/Upper Flammability Limits, detonation potential).
- Sizing of venting systems (pressure relief design).
- Fire suppression strategies (e.g., water vs. inert gas effectiveness).
Root Cause Analysis
- Trace decomposition pathways of electrolytes, solvents, polymers, or active materials.
- Assess severity at different states of charge or temperatures.
2. What typical gases are released from Li-ion cells?
These are the possible gases which might get released during a thermal runaway
• Flammable: H₂, CO, CH₄, C₂H₄, C₂H₆ and higher saturated and unsaturated hydrocarbons
• Toxic/corrosive: HF, CO
• CO₂ and O₂
3. Can gas analysis help prevent thermal runaway?
Indirectly—by understanding decomposition pathways and identifying high-risk chemistries, engineers can design safer cells, better cooling, and stronger enclosures.
4. What standards or guidelines exist regarding vent gas analysis?
UL 9540A for battery energy storage safety testing.