Battery Safety: What is Off-Gassing and Why Does it Occur​?

Batteries have become an integral part of our daily lives, powering everything from smartphones to electric vehicles. But have you ever considered the potential risks associated with the batteries that enable the seamless functioning of these devices? While advancements in battery technology have revolutionised the way we live, it’s crucial to explore the potential hazards these power sources pose.

Lithium-ion batteries are combustible and hazardous, with the potential of dangerous and explosive thermal runaway – which can not only have devastating consequences for the environment and property but can threaten human life. Therefore, it is important to understand the first signs of a possible disaster – off-gassing.

Understand Off-gassing: The Silent Emission

Off-gassing refers to the release of gases from lithium-ion batteries often as a result of abuse or misuse. When a battery is subjected to conditions such as overcharging, over-discharging, or physical damage, it can lead to the breakdown of internal components, causing the release of gases. These gases typically include carbon dioxide, carbon monoxide, and other volatile organic compounds – which can be toxic for anyone who may come in contact with them.

Explaining Off-gassing Dynamics:

Off-gassing dynamics differ based on battery setups. In enclosed setups like racks or small housings, off-gassing can accumulate within the confined space, increasing the risk of pressure buildup and ignition. In open setups, such as outdoor installations, off-gassing may dissipate more easily, but still poses risks in poorly ventilated areas.

How Off-gassing Occurs and the Timeline:

Although not always a guaranteed precursor to thermal runaway in lithium-ion batteries, off-gassing events typically occur early in their failure. Thermal runaway occurs when a battery undergoes uncontrolled heating, leading to a rapid increase in temperature and pressure within the cell. This escalation can ultimately result in the battery catching fire or exploding, posing significant safety hazards.

The timeline for off-gassing can vary depending on the severity of the abuse and the type of battery. In some cases, off-gassing may occur gradually over time as the battery undergoes repeated stress, while in other instances, it may occur suddenly due to a single event, such as overcharging.

Factors in which Off-gassing can occur:

  • Physical Damage: Any damage to the battery, such as punctures or crushing, can cause internal components to degrade, leading to off-gassing.
  • Overcharging: Excessive charging can cause the decomposition of electrolytes within the battery, leading to gas generation.
  • Overheating: Like off-gassing, excessive heat can trigger thermal runaway by destabilising the battery’s internal chemistry.
  • Over-discharging: Discharging a battery beyond its recommended limit can also result in the release of gases.
  • Internal Short Circuits: Any malfunction that causes a short circuit within the battery can initiate thermal runaway.
  • Manufacturing Defects: Faulty manufacturing processes can introduce weaknesses in the battery structure, making it more susceptible to thermal runaway.

What are the dangers of Off-gassing buildup?

Off-gassing buildup can lead to the battery storage container turning into a pressure vessel that is just waiting for a spark to ignite. To mitigate this risk, it’s crucial to have a monitored ventilation system in place. Additionally, compliance with FM standards is essential, as BESS should maintain lower than 25% LFL or have a container that can open to vent gas, ensuring safety in case of off-gassing.

Why Early Detection of Off-gassing is Critical:

Early detection plays a critical role in preventing catastrophic battery incidents. By identifying signs of off-gassing at the onset, operators can intervene before the situation escalates into thermal runaway. Here’s why early detection is crucial:

  1. Preventative Maintenance: Early detection allows for timely maintenance and corrective action to address battery issues before they worsen. Routine monitoring of off-gassing can help identify underlying problems in battery systems, such as overcharging or internal damage, enabling proactive maintenance to mitigate risks.
  2. Risk Mitigation: Off-gassing serves as an early warning sign of potential battery failures. By monitoring off-gassing levels, operators can implement risk mitigation measures, such as adjusting charging parameters or isolating malfunctioning batteries, to prevent thermal runaway and its associated hazards.
  3. Enhanced Safety: Timely detection of off-gassing enhances safety for both personnel and property. It provides an opportunity to evacuate affected areas, implement emergency protocols, and minimise the impact of battery-related incidents on surrounding environments. Additionally, early intervention reduces the likelihood of injuries and property damage resulting from thermal runaway events.
  4. Cost Savings: Detecting off-gassing early can help avoid costly repairs or replacements of damaged batteries and equipment. By addressing issues proactively, operators can extend the lifespan of batteries, optimise performance, and avoid unplanned downtime, resulting in significant cost savings over time.
  5. Regulatory Compliance: Many regulatory standards and guidelines mandate the monitoring of off-gassing as part of battery safety protocols. Early detection ensures compliance with regulatory requirements and demonstrates a commitment to maintaining safe battery operations in accordance with industry standards.

Incorporating robust gas detection systems and technologies for early detection of off-gassing is essential for proactive risk management and maintaining the integrity of battery systems. By prioritising early detection, stakeholders can safeguard against potential hazards, minimise disruptions, and promote the safe and sustainable use of battery technology across various applications.

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Industry Overview: Battery Power

Batteries are effective at reducing power outages since they can also store excess traditional grid energy. The energy stored within batteries can be released whenever a large volume of power is needed, such as during a power failure at a data centre to prevent data being lost, or as a back-up power supply to a hospital or military application to ensure the continuity of vital services. Large scale batteries can also be used to plug short-term gaps in demand from the grid. These battery compositions can also be used in smaller sizes to power electric cars and may be further scaled down to power commercial products, such as phones, tablets, laptops, speakers and – of course – personal gas detectors.

Applications include battery storage, transportation and welding and can be segregated into four main categories: Chemical – e.g., ammonia, hydrogen, methanol and synthetic fuel, electrochemical – lead acid, lithium ion, Na-Cd, Na-ion, electrical – supercapacitors, superconductive magnetic storage and Mechanical – compressed air, pumped hydro, gravity.

Gas Hazards

Li-ion battery fires

A major concern arises when static electricity or a faulty charger damages the battery protection circuit. This damage can result in fusing the solid-state switches into an ON position, without the user knowing. A battery with a faulty protection circuit may function normally, however, may not provide protection from short circuit. A gas detection system can establish if there is a fault and may be used in a feedback loop to shut off power, seal the space and release an inert gas (such as nitrogen) into the area to prevent any fire or explosion.

Leakage of toxic gases prior to thermal runaway

Thermal runaway of lithium-metal and lithium-ion cells has resulted in several fires. With research showing that fires fuelled by flammable gases are vented from the batteries during thermal runaway. The electrolyte in a lithium-ion battery is flammable and generally contains lithium hexafluorophosphate (LiPF6) or other Li-salts containing fluorine. In the event of overheating, the electrolyte will evaporate and eventually be vented out from the battery cells. Researchers have found that commercial lithium-ion batteries can emit considerable amounts of hydrogen fluoride (HF) during a fire, and that emission rates vary for different types of battery and state of-charge (SOC) levels. Hydrogen fluoride can penetrate skin to affect deep skin tissue and even bone and blood. Even with minimal exposure, pain and symptoms may not present for several hours, by which time damage is extreme.

Hydrogen and explosion risk

With hydrogen fuel cells gaining popularity as alternatives to fossil fuel, it is important to be aware of the dangers of hydrogen. Like all fuels, hydrogen is highly flammable and if it leaks there is real risk of fire. Traditional lead acid batteries produce hydrogen when they are being charged. These batteries are normally charged together, sometimes in the same room or area, which can generate an explosion risk, especially if the room is not properly ventilated. Most hydrogen applications cannot use odorants for safety, as hydrogen disperses faster than odorants do. There are applicable safety standards for hydrogen fuelling stations, whereby appropriate protective gear is required for all workers. This includes personal detectors, capable of detecting ppm level hydrogen as well as %LEL level. The default alarm levels are set at 20% and 40% LEL which is 4% volume, but some applications may wish to have a custom PPM range and alarm levels to pick up hydrogen accumulations quickly.

To find out more on the dangers of gas hazards in battery power visit our industry page for more information.