Permeability (Packaging)
Definition
The rate at which molecules of a gas or vapour pass through a solid membrane. Polyethylene has significant permeability to volatile organic compounds (C8-C12 hydrocarbons), making it unsuitable for fire debris samples. Nylon and metal are substantially less permeable to these compounds.
- Definition
- Rate of gas or vapour passage through a membrane
- Unsuitable material
- Polyethylene
- Reason
- Permeable to C8 to C12 hydrocarbons
- Better-performing materials
- Nylon and metal
- Application
- Fire debris sample packaging
Common questions
Why does polyethylene's permeability matter specifically for fire debris cases?+
Ignitable liquid residues sit in the mid-range hydrocarbon fraction that polyethylene lets escape or cross-contaminate between samples, so evidence can lose accelerant traces or pick up contamination before it ever reaches the laboratory.
What packaging is typically recommended instead for fire debris evidence?+
Unlined metal cans and certain nylon or specialised polymer bags are commonly used because they resist permeation by volatile hydrocarbons far better than ordinary plastic bags, preserving the sample's chemical profile.
Does low permeability alone make a container suitable for all chemical evidence?+
No, packaging choice also depends on chemical compatibility, avoiding reaction with the sample, and preventing cross-contamination from residues left in reused containers, not permeability to volatiles alone.
Related terms
- ASTM E1492
- Standard Practice for Receiving, Documenting, Storing, and Retrieving Evidence in a Forensic Science Laboratory: establishes container requirements for fire debris (metal can...
- BSA 2023 (Bharatiya Sakshya Adhiniyam 2023)
- India's evidence law that replaced the Indian Evidence Act 1872, governing the admissibility of documents and expert opinions in Indian courts; together...
- Chain of Custody (CoC)
- The documented sequence of individuals who had possession of, access to, or control over a physical exhibit from the moment of its...
- Court Sample
- In India under the NDPS (Seizure, Storage, Sampling and Disposal) Rules 2014, a duplicate sealed sample drawn at the time of seizure...
- DEA Form DEA-7
- The US Drug Enforcement Administration's Report of Drug Property Collected, Purchased or Seized: the primary chain-of-custody document that records every custodian, transfer...
- FSR Codes of Practice and Conduct
- Mandatory requirements issued by the UK Forensic Science Regulator under the Forensic Science Regulator Act 2021, governing exhibit management, method validation, contamination...
- Mahazar (Panchnama)
- In Indian criminal procedure, a document drawn at the time of search and seizure in the presence of independent witnesses (Panchas), recording...
- Tamper-Evident Sealing
- Packaging closure that makes any opening of the package visible: heat-sealed bags, security adhesive tape with a void pattern that transfers on...
- TWGFEX / SWGMAT
- Technical Working Group for Fire and Explosion Investigation (now the OSAC Ignitable Liquids, Explosives, and Gunshot Residue Subcommittee): the US body that...