Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds formed during the incomplete combustion of organic materials, and they represent one of the most significant chemical hazards in fire-damaged buildings. PAH testing after a fire involves collecting surface wipe samples, bulk material samples, and soil samples for analysis by gas chromatography-mass spectrometry (GC-MS) at independent NATA-accredited laboratories, with results compared against Australian NEPM (2013) health investigation levels to determine whether the property is safe for reoccupation.

What Are PAHs and Why Do Fires Produce Them?

Polycyclic aromatic hydrocarbons are a family of over 100 organic compounds, each consisting of two or more fused aromatic (benzene) rings. They are formed whenever organic material — wood, plastics, textiles, food, petroleum products — undergoes incomplete combustion. In a building fire, the conditions for PAH formation are ideal: high temperatures, limited oxygen supply, and abundant organic fuel sources.

The US EPA has identified 16 priority PAHs that are routinely analysed in environmental assessments due to their prevalence, persistence, and toxicity. In our fire damage assessments, we consistently detect elevated levels of the following compounds:

• Benzo[a]pyrene (B[a]P) — the benchmark PAH compound, classified as IARC Group 1 (carcinogenic to humans). Used as the reference compound for PAH toxicity because it is the most extensively studied.
• Naphthalene — the lightest PAH, semi-volatile, with a distinctive mothball odour. Classified as IARC Group 2B (possibly carcinogenic). Often the most abundant PAH in fire residues by mass.
• Pyrene and fluoranthene — abundant in soot from fires. While not individually classified as carcinogenic, they contribute to the total PAH burden and serve as indicators of combustion contamination.
• Benz[a]anthracene and chrysene — IARC Group 2B compounds frequently detected in fire soot at concentrations that contribute meaningfully to the total carcinogenic PAH load.

Health Risks of PAH Exposure After Fire

The health significance of PAH contamination after fires cannot be overstated. Benzo[a]pyrene is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC), placing it in the same category as asbestos and benzene. Several other PAHs — including dibenz[a,h]anthracene, benzo[b]fluoranthene, and benzo[k]fluoranthene — are classified as Group 2A (probably carcinogenic) or Group 2B (possibly carcinogenic).

Exposure to PAHs in fire-damaged buildings occurs through three primary pathways:

• Inhalation — PAHs adsorbed onto fine particulate matter (soot) become airborne when disturbed by foot traffic, cleaning, or air movement. Volatile PAHs like naphthalene can off-gas directly into indoor air.
• Dermal absorption — direct skin contact with soot-contaminated surfaces allows PAH absorption through the skin. This is particularly relevant for occupants handling fire-damaged belongings or children crawling on contaminated floors.
• Ingestion — young children are at highest risk through hand-to-mouth behaviour on contaminated surfaces. PAH-contaminated soil around fire-damaged structures is also an ingestion risk.

Long-term PAH exposure at elevated concentrations is associated with increased cancer risk (particularly lung, skin, and bladder cancers), respiratory disease, immune system suppression, and reproductive effects. The NEPM (2013) health investigation level for benzo[a]pyrene in residential soil is 3 mg/kg — a threshold that reflects the significant risk these compounds pose even at relatively low concentrations.

How PAH Sampling Is Performed After a Fire

In our fire damage assessments, PAH sampling follows a structured methodology designed to characterise both the extent and severity of contamination:

Surface wipe samples are the primary method for assessing PAH contamination on hard, non-porous surfaces (benchtops, glass, tiles, metal fixtures). We use standardised wipe sampling techniques based on NIOSH methods, collecting samples from measured surface areas (typically 100 cm2) using solvent-moistened wipes. This allows results to be expressed as mass per unit area (e.g., micrograms per 100 cm2), enabling comparison with health-based guidelines.

Bulk material samples are collected from porous materials such as carpet, underlay, insulation, plasterboard, and soft furnishings. These materials act as sinks for PAHs, absorbing compounds from smoke and soot. Bulk sampling determines whether contamination has penetrated to levels requiring material removal rather than surface cleaning.

Soil samples are collected around the perimeter of fire-damaged structures and from adjacent garden beds. Ash, soot, and contaminated water runoff deposit PAHs into surrounding soil, which is particularly important to assess where children play or food is grown. Results are compared directly against NEPM (2013) health investigation levels for the 16 priority PAHs.

Laboratory Analysis: Gas Chromatography-Mass Spectrometry

All PAH samples are submitted to independent NATA-accredited laboratories for analysis by gas chromatography-mass spectrometry (GC-MS). This analytical technique separates individual PAH compounds chromatographically and then identifies each one by its unique mass fragmentation pattern, providing both qualitative identification and quantitative measurement at concentrations as low as parts per billion (ppb).

The standard analytical suite reports on all 16 US EPA priority PAHs individually, as well as total PAHs. Individual compound quantification is essential because the toxicity varies enormously between compounds — benzo[a]pyrene is approximately 1,000 times more potent as a carcinogen than some other PAHs. A total PAH result alone is insufficient for health risk assessment.

We use independent NATA-accredited laboratories because NATA accreditation ensures the laboratory operates to ISO 17025 quality standards, with validated methods, regular proficiency testing, and documented quality assurance procedures. The independence of the laboratory from both the assessor and any remediation contractor ensures results are unbiased and defensible.

Interpreting PAH Results Against Australian Guidelines

Interpreting PAH results requires comparison against health-based investigation levels established under the NEPM (2013) and enHealth guidelines. The key reference values for residential settings include:

• Benzo[a]pyrene — NEPM (2013) health investigation level: 3 mg/kg in residential soil (HIL-A). This is the most conservative benchmark and typically the limiting value in PAH assessments.
• Total PAHs (as B[a]P equivalents) — calculated using toxic equivalency factors (TEFs) that weight each PAH compound according to its carcinogenic potency relative to benzo[a]pyrene.
• Naphthalene — NEPM (2013) HIL-A: 3 mg/kg (residential), with additional consideration for vapour intrusion given its semi-volatile nature.

For surface wipe samples, there are no formal Australian regulatory limits for PAHs on indoor surfaces. In our practice, we apply health-based risk assessment principles using the methodology described in the NEPM (2013) Schedule B4, considering exposure frequency, duration, and pathway-specific factors to determine whether measured concentrations pose unacceptable risks.

Results interpretation is where the expertise of a qualified assessor becomes critical. A Chartered Chemist can contextualise laboratory data within the specific circumstances of each property — considering building use, occupant demographics (presence of children, elderly, immunocompromised individuals), exposure duration, and the full contaminant profile rather than PAHs in isolation.

What Happens After PAH Testing

If PAH testing reveals contamination above health investigation levels, the assessment report will recommend remediation measures proportional to the contamination severity. For surface contamination on non-porous materials, professional cleaning using appropriate solvents and methods may be sufficient. For porous materials with embedded PAH contamination, removal and replacement is typically required.

After remediation, clearance testing should be conducted by an independent assessor to verify that PAH levels have been reduced to acceptable concentrations before the property is reoccupied. This clearance testing must be performed by a party independent of the remediation contractor to avoid conflicts of interest.

If you need PAH testing after a fire event, contact Test Australia for an independent assessment. Our Chartered Chemist qualifications and forensic science expertise ensure your PAH results are accurately interpreted within the context of Australian health guidelines and your specific property circumstances.