Forensic Investigation of Battery Failures
Source: Brad Davis, PE, Assistant Technical Director Electrical/Mechanical, Envista Forensics
With the ever-increasing use of batteries and battery-powered devices, it is becoming inevitable that a fire area of origin will include some sort of battery. The question then becomes, did the battery or battery powered device cause the fire, and how do forensic investigators approach these fires where a battery is involved? In common situations like this, there are specific steps and approaches that assist investigators in the determination of whether batteries were involved in the ignition of a fire.
The Steps to a Successful Investigation
Step 1: Determining the Correct Area of Origin
Ensuring the fire area of origin is correct is the first key component in a fire investigation and requires the involvement of a knowledgeable and experienced fire investigator. A crucial component of this step is an accurate interview of the insured and insured parties in the space for additional information that will help in the examination. This would need to include the identification of the fire’s area of origin, if known, as well as any information the insured may have on the items in the area, modifications to those items, changes in operation, and their last known condition. This could include receipts, photographs of the items, and documents on the make and model or serial number.
The early identification of all electronic components and manufactures ensures the proper parties can be place on notice. If the area of origin is incorrect or items are misidentified, pieces of evidence critical to the determination of the cause of fire may be missed.
Step 2: Collecting Sufficient Evidence
During a fire investigation, it is important to ensure that a sufficient amount of evidence is collected. Often times, when Lithium-Ion cells vent due to overcharging or overheating of the battery, they can explode and expel their contents a surprisingly long distance. If the area of origin is constrained and collection is too tight, those contents, and the evidence needed to determine if the battery cell was the cause of the fire or just a victim of a fire started elsewhere, may be missed.
The other issue is those ejected contents can sometimes appear to be the origin of the fire since the contents are hot and can ignite materials in the area that they land. In some instances, there are multiple apparent areas of origin and can be areas even over 12-feet from the battery powered device. At that point, interviews with personnel in the area at the initiation of the event are crucial to the identification of the device that caused the fire.
Step 3: Collecting the Right Evidence
When collecting evidence, investigators must be sure they are collecting the correct items. One suitable method is to grid and collect all debris in a preselected area. This will lead to a higher degree of recovery of the ejected materials and cell components but will also lead to the collection, moving, and sifting of large amounts of debris. In some cases, debris is sifted through on scene, which allows for less material and debris to be collected but generates risk of leaving small critical pieces behind.
The Make Up of Battery Cells
Now that the evidence is collected, sifted, and the battery pack and cell components are recovered and identified, how do those pieces of evidence indicate whether the battery pack, battery powered device, or cell caused the fire? To better understand and answer this common question forensic investigators have to ask themselves, let’s talk about cell construction, chemistry, and what happens when these components start operating outside of their desired design.
Battery Cell
The basic component of a battery pack is a cell – the assembly of foil, electrodes, separators, electrolytes, and containers that allows the storage of electrical energy in a chemical form. Each battery chemistry is slightly different, and the individual components may be of a different chemical composition, but each cell will have these components.
In some cases, such as with Lithium-Polymer (Li-Po), the battery cells are a subset of a more general family of Lithium-Ion. Li-Po batteries will have a polymer separator and often have a square, rectangular, or prismatic case construction, rather than a metal canister of the typical Lithium-Ion cells. A very common Lithium-Ion cell is referred to as an 18650, which refers to a cylindrical canister with a diameter of 18mm and a length of 65mm. This metal canister will have some added protective devices built into the top of the cylindrical canister.
Battery Pack
An assembly of cells is referred to as a battery pack. The common battery chemistry that forensic engineers investigate, Lithium-Ion, requires the cells to operate in a very tight set of parameters. The voltage cannot be too high or too low, the current cannot be too great, and the temperature must be controlled. All of these parameters are critical, as battery packs or cells can suffer from a thermal runaway event and start a fire if they start operating outside their safe parameters. In order to prevent this, battery management systems are put in place to ensure that a cell or collection of cells operate in their design parameters.
Battery management systems need to be designed such that all the cells are within the desired parameters. Some manufacturers put battery management systems within the battery pack, some within the device using power from the battery, some within the device charging the battery, and some in both the battery and the device.
When shortcuts are made within a system, the state of individual cells cannot be accurately determined. Thus, it is important to determine if the failure occurred within the cell, the management system on the battery, or the management system in the device. This information is critical because it is possible that all of these components are made by different manufacturers or suppliers and the appropriate parties should be put on notice. For example, a major name brand notebook computer may have an off-brand battery purchased by the insured. This information should be known before the destructive examination.
In many cases, a battery failure is a brief event and by itself won’t cause a fire to spread. There needs to be a fuel nearby that can be ignited by the temperatures and duration of the heat from a battery failure. This nearby fuel can be almost anything and can be identified through good analysis, good interviews of the insured, and chemical analysis. In some cases, the fire’s fuel can be relatively obvious, such as a couch, but in others, a material is suspected but not necessarily known. Nearby materials suspected of being fuel to the fire can be identified using methods like FTIR. Once the material is identified, the properties of that material can be determined whether is it a sufficient fuel source to have caused the fire to spread. |
