Forensic lab: VOCs trap toxins after fire

PFFPD_Forensics said in a May 23 post on X that volatile organic compounds, or VOCs, can migrate into fire-damaged materials and become trapped during what it called a “chemical partitioning event.” The account said that process can embed contaminants into porous surfaces and complicate evidence collection after a fire. The post described a problem familiar to fire-debris analysts: chemicals released during combustion do not remain only in air or soot, but can move into carpets, wood, drywall and other materials. Research from NIST, the National Institute of Justice and other forensic sources shows that partitioning and adsorption can alter what investigators recover later from a scene. ### How do VOCs get trapped after a fire? NIST said in a 2023 study that many smoke VOCs persisted for days after smoke entered a test house, creating a longer-term exposure pathway and a surface reservoir of contamination. The agency said two timescales controlled that partitioning: a faster one of 1.0 to 5.2 hours for equilibrium between adsorption and desorption, and a slower one of 4.8 to 21.2 hours before ventilation overtook those exchanges in controlling air concentrations. (nist.gov) The American Society of Trace Evidence Examiners said fire debris often includes porous material in which an ignitable liquid can penetrate and remain even after an intense fire. That is one reason investigators collect flooring, furnishings and other absorbent debris from suspected origin areas when they are testing for ignitable liquid residues. ### Why does that matter to a forensic lab? The National Institute of Justice said a 2014 fire-debris study examined the effects of “competitive adsorption” by substrates typically found in fire debris on classification under ASTM E1618. (nist.gov) The study said charred yellow pine could affect the distribution and abundance of ignitable-liquid components, especially normal hydrocarbons in petroleum distillates. (asteetrace.org) NIST said fire-debris analysis typically relies on gas chromatography-mass spectrometry, or GC-MS, and that one of the field’s challenges is understanding how compounds persist and should be preserved. The agency said its work includes determining how storage conditions affect preservation of ignitable liquid residues, including solvent choice, evaporation, storage temperature and vial cap type. ### Does trapped contamination create a risk of misleading results? (nij.ojp.gov) The National Center for Forensic Science at the University of Central Florida said combustion and pyrolysis products from flooring, furnishings and construction materials can interfere with determining whether an ignitable liquid residue is present in fire debris. That means analysts must distinguish between chemicals produced by the fire itself and chemicals introduced before or during ignition. (nist.gov) The NIJ study said porous materials sampled near the center of a pour pattern had higher recovery of ignitable liquid residues than samples taken at the edges. That finding points to why scene selection matters before the laboratory work begins. ### What does this mean for investigators working the scene? A 2021 study in the Journal of Occupational and Environmental Hygiene found that fire investigators can be exposed to airborne contaminants for hours to days after suppression. (ncfs.ucf.edu) The researchers reported median PM2.5 levels above 100 micrograms per cubic meter during early investigation periods and said peak formaldehyde concentrations exceeded NIOSH ceiling limits shortly after fires and sometimes one day later in boarded structures. (nij.ojp.gov) ASTEE said volatile residues can evaporate easily, so samples should be collected in airtight containers for laboratory submission. The group said analysts then extract vapors from the container, concentrate them and analyze them by gas chromatography and mass spectrometry against known standards. ### Is this only a house-fire issue, or also a smoke-contamination problem? The U.S. Environmental Protection Agency said smoke from wildland-urban interface fires can contain greater amounts of hazardous air pollutants because structures and human-made materials are burning. (ncbi.nlm.nih.gov) EPA said those fires can have a distinct chemical profile, including elevated trace metals such as copper, lead and zinc. NIST said surface cleaning removed smoke VOC reservoirs more effectively than portable air cleaners in its test-house study, but forensic investigators are not cleaning for remediation when they first enter a scene. (asteetrace.org) Their next step is preservation: collecting debris from relevant locations, sealing it properly and submitting it for GC-MS analysis under ASTM-based fire-debris methods. (nist.gov) (epa.gov)