Why Can't Arson Evidence Be Collected In Bags

Why Arson Evidence Can't Be Collected in Bags: The Crucial Role of Proper Containment

Arson investigations are complex and delicate, demanding meticulous attention to detail at every stage. One seemingly simple aspect, the collection of evidence, holds significant weight in determining the success or failure of the case. A critical mistake often made, and one that can irrevocably compromise the integrity of crucial evidence, is the use of plastic bags for storing arson debris. This article will delve into the scientific reasons why plastic bags are unsuitable for collecting fire scene evidence, exploring the crucial role of proper containment and the potentially devastating consequences of improper storage.

The Volatile Nature of Fire Debris

The aftermath of a fire is a scene of volatile and reactive materials. The very nature of combustion leaves behind a complex mixture of substances that are prone to change, even subtly, with exposure to various environmental factors. This includes:

Accelerants and their Residues:

Arson investigations often focus on identifying accelerants – substances used to start or spread a fire more quickly than normal. These can range from readily available fuels like gasoline and kerosene to more specialized chemicals. The residues of these accelerants are often volatile and easily evaporate. Furthermore, the chemicals themselves can react with other materials at the fire scene, leading to further changes. Confining them in an airtight bag can lead to:

• Evaporation: Volatile accelerants will evaporate from the sample, reducing the concentration and making identification difficult or impossible.
• Chemical Reactions: Confining the sample can create an environment promoting chemical reactions between the accelerant residue and other materials, altering the composition and obscuring the original evidence.
• Contamination: The bags themselves might release volatile organic compounds (VOCs) that contaminate the sample, leading to false positives or obscuring the true accelerant.

Other Ignitable Materials:

Besides accelerants, other ignitable materials are present at the scene. These could be materials that ignited easily or played a part in the spread of the fire. Their interaction within a confined space like a plastic bag can also lead to unwanted changes.

Biological Materials:

Fire scenes may also contain biological evidence, such as blood or other bodily fluids. These could be relevant to determining the cause or the perpetrators of the fire. Enclosing these materials in a plastic bag would create a warm, moist environment, promoting bacterial growth and degradation of the evidence.

The Importance of Proper Containment: Preventing Contamination and Degradation

The preservation of arson evidence hinges on preventing both contamination and degradation. Improper containment using plastic bags facilitates both:

Contamination:

Plastic bags, particularly those made of low-density polyethylene (LDPE), can outgas VOCs. These gases can easily contaminate samples, introducing substances not originally present at the fire scene. This can lead to inaccurate analysis and misleading conclusions about the presence or nature of accelerants. Furthermore, the transfer of contaminants from the bag itself, or from other samples stored nearby in the same bag, can compromise the sample’s integrity.

Degradation:

The volatile components of the fire debris are crucial for identification. However, enclosing these substances within an airtight bag will not allow for proper aeration, leading to evaporation of these volatile components, rendering the sample useless for analysis. The lack of oxygen circulation further facilitates the degradation of evidentiary materials through chemical reactions.

Alternative Methods for Collecting Arson Evidence

Proper collection of fire debris requires careful consideration of the evidence’s volatile nature. Several techniques are employed to ensure that the evidence's integrity remains intact for analysis:

Metal Cans:

Airtight metal cans with appropriate seals are commonly used for storing fire debris. The inert nature of metal prevents contamination from the container itself. Metal also provides a more durable and tamper-evident container than plastic bags.

Glass Jars:

Similar to metal cans, glass jars offer a non-reactive and inert environment, which is crucial for preserving the integrity of the evidence. The sealing mechanism helps prevent loss of volatile components.

Specialized Evidence Bags:

While plastic bags are generally unsuitable, specialized evidence bags designed for forensic purposes are sometimes used. These bags often have enhanced features such as a low outgassing rate and tamper-evident seals, but these are only suitable for certain items and should be handled with caution.

Chain of Custody:

Beyond the type of container, meticulous documentation of the chain of custody is crucial. This ensures that the evidence is handled properly and its integrity maintained from the point of collection to the point of analysis.

The Legal Implications of Improper Evidence Collection

The use of plastic bags for collecting arson evidence can have severe legal consequences. If the evidence is deemed compromised due to improper storage, it could be deemed inadmissible in court. This could lead to the dismissal of charges, hindering justice and allowing arsonists to go unpunished. The reliability of forensic findings relies heavily on the proper preservation of the evidentiary materials. Anything that compromises that reliability compromises the strength of the prosecution's case.

Conclusion: The Importance of Proper Training and Protocol

The proper collection and preservation of arson evidence is of paramount importance to successful prosecutions and accurate determination of the fire's cause. The use of plastic bags is a common mistake with potentially severe ramifications. Thorough training of investigators and adherence to strict protocols are essential to ensure that arson evidence is collected and handled correctly, maintaining its integrity for analysis and ultimately contributing to justice. By understanding the volatile nature of fire debris and employing appropriate containment methods, investigators can significantly improve the chances of a successful investigation and prosecution. The use of inappropriate containers such as plastic bags represents a serious lapse in this process that can have far-reaching and potentially devastating consequences. The meticulous care taken in the collection, handling and analysis of arson evidence directly impacts the efficacy and fairness of the justice system, underscoring the critical importance of prioritizing correct methodologies and adhering to best practices.