Nylon-11 Bag
Definition
Specialised fire-debris bag (Tinius Olsen pouch) that does not leak light hydrocarbons. Polyethylene bags are forbidden because they let pentane, hexane and other light cuts diffuse out.
- Also called
- Tinius Olsen pouch
- Purpose
- Fire-debris evidence packaging
- Key property
- Does not let light hydrocarbons diffuse out
- Forbidden alternative
- Polyethylene bags
Common questions
Why are polyethylene bags specifically forbidden for fire-debris evidence?+
Polyethylene is permeable to light hydrocarbons such as pentane and hexane, which are common ignitable-liquid components. Volatiles diffuse out through the bag wall over hours to days, so by the time the sample reaches the lab the very compounds needed to identify an accelerant may have escaped.
What are the accepted alternatives to a nylon-11 bag for fire-debris packaging?+
Unlined new paint cans with friction lids and glass jars with PTFE-lined lids are the other standard containers, since both are impermeable to hydrocarbon vapours. The choice usually comes down to sample bulk and lab preference, not a difference in vapour retention.
Does the bag material affect how the lab later extracts volatiles from the sample?+
No, the packaging choice is independent of the extraction method used at the lab, such as passive headspace adsorption onto activated charcoal strips or solvent extraction. The bag's only job is to hold the volatiles in until that extraction step happens.
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