In what circumstances should you avoid using plastic bags for evidence collection?

Avoiding the use of plastic bags for the collection of wet, damp, or bloody clothing is crucial because plastic can trap moisture. This moisture creates an environment conducive to mold and bacterial growth, which can degrade delicate biological evidence, such as DNA. When fabric is sealed in a plastic bag without adequate airflow, the potential for contamination and deterioration increases significantly.

Collecting evidence in the right manner is essential to preserve it for analysis. In contrast, other circumstances such as collecting items with no potential for DNA evidence, using bags for dry paperwork, or packaging hard surfaces like metal do not present those same risks. These materials do not require the same level of consideration regarding moisture and biological integrity, making the use of plastic bags less problematic in those contexts.