Lithium-ion (Li-ion) batteries are rechargeable and used worldwide to power a wide range of devices from cellphones and laptops to handheld tools.  Larger Li-ion batteries are used in energy storage systems, hospital equipment, and electric vehicles.  The rapid growth of Li-ion technology and its prolific use around the world has quickly outpaced the knowledge around storing and protecting this sought-after and very expensive commodity. While a lot of consumer research has been done on the safety of these batteries in individual devices while in use, little has been done on the potential fire hazards of these batteries when stored or used in large quantities.  Li-ion batteries may come with a higher risk of a fire or an explosion due to battery failure than other batteries.  The electrolyte in other batteries, including Nickel cadmium, Nickel metal hydride and Lead acid, is not ignitable. The electrolyte in Li-ion batteries is ignitable. The major cause for a Li-ion battery fire is thermal runaway.  If unmitigated, a thermal runaway can lead to cell rupture and the venting of toxic and highly flammable gases.  Those flammable gases can cause a fire or explosion if ignited.

Fortunately, Li-ion batteries are much safer than they were 10 to 20 years ago, and fires are a rare occurrence.  However, limited research has been done to understand the potential hazard associated with the storage and use of Li-ion batteries, and how to adequately mitigate against property loss as a result of this hazard.  Li-ion batteries burn at temperatures between 900-1500 °C (1652-2732 °F).  The Occupational Safety and Health Administration reports that the U.S. Consumer Product Safety Commission identified over 25,000 overheating or fire incidents involving more than 400 types of lithium-battery-powered consumer products over a 5-year period.

The major cause for catastrophic failure of Li-ion batteries is thermal runaway that occurs when heat generated from exothermic reactions inside the battery outpaces heat dissipated from the battery leading to a rapid increase in temperature and pressure that further increases the reaction rate.  If unmitigated, this self-accelerating process will lead to cell rupture and the venting of toxic and highly flammable gases, and the release of heat. Popping or white smoke may be an indication of thermal runaway.  An explosion scenario can be more severe for a large battery, where heat generated by one failed cell can heat up neighboring cells and lead to a thermal cascade throughout the battery.

Thermal runaway of Li-ion batteries can be caused by a variety of situations such as mechanical damage to the cell that can lead to internal shorts and heat generation, exposure to excessive temperatures, internal shorts due to cell defects, faulty wiring causing external shorts, or a surge in the charging or discharging current.

Fires involving lithium-ion batteries are also known to reignite long after they have been damaged in a fire – sometimes up to a week later.  After a fire, there is often stranded energy which requires the batteries to be removed from the area.  Stranded energy is any scenario where electrical energy remains in a battery without an effective means to remove it.

There is a growing trend to replace lead acid batteries, which need replaced every 3-4 years at a significant cost, with Li-ion batteries which need replacing every 20 years. Anywhere there is a critical power need such as utilities storing solar energy, data and telecommunication centers, hospital imaging equipment (CT scanners and X-ray machines), control systems for manufacturing and building systems (networking and phone systems), to electric vehicles the switch is being made to Li-ion batteries. For equipment with a critical power need, Li-ion battery pack size can range from about the size of a microwave to a 40-foot ISO shipping container.

Li-ion battery failure is characterized by four stages: initial abuse, off-gas generation, smoke generation, and fire propagation. 

Stage 1 – Initial abuse – can be thermal, electrical, or mechanical abuse such as physical battery damage, overcharging, overheating, and manufacturing defects

Stage 2 – Off-gas generation – an opportunity window of time in which fire or explosion can be prevented

Stage 3 – Smoke generation – at this point, thermal runaway has occurred, and a catastrophic event is imminent

Stage 4 – Fire generation – propagation occurrence takes place

The initial battery abuse and off-gas generation stages are where protection mechanisms utilized during these two stages is essential to help prevent battery failure.  Many current protection systems provide hazard detection at Stage 3, which occurs after battery failure is imminent.  A UL Firefighter Safety Research Institute report makes recommendations regarding monitoring for Li-ion battery failure that includes:

  • Li-ion battery ESS (Energy Storage Systems) should incorporate gas monitoring that can be monitored remotely.
  • Li-ion battery ESS should incorporate robust communications systems to ensure remote access to data from the Battery Management System, sensors throughout the ESS, and the fire alarm control panel remains uninterrupted.
  • Li-ion battery ESS should incorporate adequate explosion prevention protection (i.e., detection and mitigative action) as required in NFPA 855 or IFC (International Fire Code) Chapter 12, where applicable, in coordination with the emergency action plan.

NFPA 855 for Energy Storage Systems focuses on ways to mitigate the risk associated with Li-ion battery failures by specifying mandatory requirements for the overall management of ESS and for hazard mitigation analysis.  Besides mandating detection capabilities, the standard focuses on battery installations, which are typically an arrangement of tightly packed cells placed in modules that are stacked vertically in racks. Since these systems often consist of multiple racks, a main objective of the standard is to make sure, if a fire occurs, that it is contained to a single rack. Whenever possible, staging Li-ion batteries at a distance of at least 3 feet from other Li-ion batteries and walls can prevent cascading thermal runaway reaction to adjacent cells or objects.  Properly designed sprinkler protection with sufficient water supply is also key. If adequate sprinkler protection is not provided, it is expected that significant battery involvement will occur, which may result in thermal runaway which can propagate to adjacent cells. If the fire propagates from one rack to the next, it could last for a considerable length of time, potentially overwhelming the sprinkler system or taxing the water supply resulting in an uncontrolled fire.

For the occupational safety and health (OSH) professional, the future is now.  Li-ion batteries are being increasingly deployed in energy storage systems.  These battery energy storage systems may be a risk that is currently unidentified in an organization.  OSH professionals need to recognize where these Li-ion batteries and ESS are in our manufacturing facilities, warehouses, hospitals, shipping containers, and production sites, just to name a few, and take the necessary actions to manage the risk to life and property. 

For more information and/or assistance, contact:
Melissa Heike, M.S., CSP
Sr. Consultant
RJR Safety Inc.

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