Combustion By-Product
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Combustion By-Product

What are combustion by-products and where do they come from?

Fire, either wildfire or structure burning, happens often in our world. It can impact property, the environment and public health. The residues of the fire, or combustion by-products, are gases and small particles that are emitted through the incomplete burning of fuels such as oil, gas, kerosene, wood, coal, and propane.  The particulate matter components will include drops of condensed soot, char, ash, metal oxides and inorganic solids. These materials can be acutely hazardous to human since they can contain heavy metals, polycyclic aromatic hydrocarbons (PAHs).

Therefore, an investigation of any fire damage should include the combustion-by-products evaluation. It also becomes part of insurance companies’ requirement in a typical fire damage restoration.  Testing can be done after a fire event in order to determine what areas might have been impacted, or the testing can be used during or after a cleaning or remediation in order to guide professionals in their remediation efforts.

Sampling for Combustion-by-Products

The value of sample data is dependent on the quality of and reliability of the collection method and sampling procedure used. There are currently no standards for combustion-by-products sample collections. However, investigators should use the most recent professional guides such as 2019 AIHA ” Technical Guide for Wildfire Impact Assessments for the OEHS Professional” and 2012 ANSI/IESO/RIA-6001 “Evaluation of Heating, Ventilation and Air Conditioning (HVAC) Interior Surfaces to Determine the Presence of Fire-Related Particulates as a Result of a Fire in a Structure.

There are a few commonly used methods for the sampling of Combustion-by-Products, including Tape Lifts, Wipes, MicroVac, and Air. Each method has its own advantages and disadvantages. For detailed description, please refer to AIHA publication mentioned earlier. Below is a brief summary of the methods:

Sampling Method Advantages Disadvantages Comment
Tape Lifts

Good collection efficiency for particles with typical dust loading;

Defined sample area for analysis;

Maintains particle integrity during collection;

Little to no damage to captured particles

Low collection efficiency for rough surfaces;

Extremely fine particles (e.g., soot) can be obscured by the tape adhesive;

TEM confirmation of soot cannot be applied;

Limited sampling area per tape lift

Use clear Scotch Tape;

Do not fold the tape;

Put the tape loosely in a heavy duty ziploc bag with one end of the tape slightly folded;


Able to sample relatively large area;

Efficient for relatively smooth nonporous surfaces with low or heavy loading;

Can be used for TEM soot confirmation analysis and chemical analysis (e.g., PAHs)

Not appropriate for porous surface;

Physical separation of particles collected as agglomerates often results;

Liquid agents may degrade or solubilize the particles;

Can remove finishes (e.g., paint), affecting analytical results

Both dry and wet wipes can be used;

Wet wipe is recommended due to higher collection efficiency;

Easy sample preparation in the lab;

Effective for collecting particles from porous and uneven surfaces;

Permits the confirmatory identification of soot by TEM;

Permits chemical analysis of collected material

Ineffective for collecting particles from relative sooth, nonporous surfaces with low loading;

Does not preserve positions of particles on the original surface;

Can induce damage to delicate structures or agglomerates such as char and ash

Collect at least visible amount of debris;

25 mm 0.45 um pore size MCE cassettes are recommended

Easy sample preparation in the lab;

Can determine if combustion-by-products is airborne;

Can have direct respiratory health implication;

Can be used for soot confirmation by TEM

Limited to airborne particles only;

Can be significantly reduced if sampling is done after extensive period from the fire damage;

Use 0.45 um pore size MCE filter;

Collect at least 600 liters of air (e.g., 1 hour sampling at 10 L/min)

Analyzing Combustion-by-Products

Eurofins EMLab P&K offers a comprehensive suite of testing services for combustion- by- products particulates, from simple presence or absence analysis through potential sourcing analysis using advanced chemical and microscopic techniques.  At Eurofins EMLab P&K, we can accept samples collected on tape lifts, wipes, micro vacuuming, or air cassettes.  Our analytical techniques include but are not limited to,

  • Polarized Light Microscopy (PLM)
  • Epi-Reflected Light Microscopy (RLM)
  • Transmission Electron Microscopy (TEM)

The analytical method Eurofins EMLab P&K employs is ASTM D6602-13: Standard Practice for Sampling and Testing of Possible Carbon Black Fugitive Emissions or Other Environmental Particles, or Both. This is a semi-quantitative analytical method. The relative percentage of combustion-by-products such as char, ash, and soot is visually estimated and reported as a percentage using direct microscopy technique. The reporting limit of the method for each component is 1%. Other opaque particles such as paint, rubber, metal oxides, etc. are also reported as a combined percentage with a description of the major constituents. The soot identification by PLM is presumptive. A confirmatory analysis of the presumptive soot can be achieved by preparing the suitable samples for TEM analysis. The TEM confirmatory analysis will be based primarily on grape-like morphology and the primary carbon peak using EDS attached to a TEM.

Interpretation of Results

There are currently no regulatory limits established for the presence of airborne contaminants for the combustion-by-products, with an exception for soot which has a limit of 15µg/m3 by the US EPA.

There are also currently no regulatory limits established for the presence of surface contaminants associated with fire loss (smoke or soot residue). Therefore, the results of combustion-by-product testing are predominantly used as a “qualitative” measure of assessing areas of potential impact rather than a “quantitative” assessment of the severity of impact.

Based on our experience, the background level for common combustion-by-products in a typical building is 1-2%. Therefore, fire damage contamination is considered likely if the reported concentration of combustion-by-products is significantly higher than the background level.  To better interpreting the analytical results, Eurofins EMLab P&K recommends collecting control samples from non-fire impacted areas for comparison.