A Comparison of Photoacoustic and Grayscale Measurements of Soot Deposition on Surfaces

Published

March 25, 2026

Author(s)

Amy Mensch, Ryan Falkenstein-Smith, Shine Park

Abstract

This study investigates the effectiveness of non-invasive soot deposition measurement techniques as a practical tool for fire investigators to quantify burn patterns in a fire scene. A novel technique relying on the photoacoustic effect of soot is compared to an established grayscale method. Soot was deposited on gypsum wallboard (drywall) and metal substrates mounted 97 cm, 128 cm, and 158 cm above a 13 kW propene diffusion flame burner, and the mass deposited was measured gravimetrically. Digital photographs were taken of the soot-coated substrates next to an optical density calibration target. The image grayscale values for the substrate were converted to optical density. Then the substrates were perturbed with a camera flash, and the photoacoustic response of the soot was measured by a microphone as the peak sound pressure. The best-fit curve for the optical density data versus soot mass loading was linear, while the photoacoustic response and was log-based, with the photoacoustic method producing a higher correlation coefficient. The photoacoustic correlation was dependent on the flash intensity, with similar photoacoustic responses for both drywall and metal substrates.

Citation

Fire Safety Journal

Volume

162

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.firesaf.2026.104767

Local Download

Keywords

photoacoustic, grayscale, soot deposition, fire forensics

Citation

Mensch, A. , Falkenstein-Smith, R. and Park, S. (2026), A Comparison of Photoacoustic and Grayscale Measurements of Soot Deposition on Surfaces, Fire Safety Journal, [online], https://doi.org/10.1016/j.firesaf.2026.104767, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=959825 (Accessed March 31, 2026)