Detecting and Confirming the Presence of Road Flare Residue in Fire Investigations

Scott Nesvold, M.S., M.Eng., P.E.
Crane Engineering Building Science, USA
Kerri Pacholke, MFS, F-ABC
Crane Engineering, USA

Presented at International Symposium on Fire Investigation, 2012


In a recent fire investigation, a vehicle owner claimed an accidental fire had destroyed his vehicle. An observant fire investigator, who suspected arson based on the facts of the case, found a small pile of “white residue” and some other parts in the debris and sent the residue to a lab to be analyzed. Fourier Transform Infrared Spectroscopy (FT-IR) was conducted as a presumptive test and revealed the presence of Strontium, a common chemical found in road flares. The presence of a high concentration of Strontium was confirmed using a Scanning Electron Microscope (SEM) combined with an Energy Dispersive X-ray Spectroscopy (EDS) unit. Based on the evidence and this analysis, the residue was confirmed to be from a road flare. The vehicle fire was determined to be incendiary based on this analysis.

A test burn was conducted in a furnished condemned house. The house was burned room by room for fire investigator training. One fire was ignited in a furnished living room with a red road flare placed at the leg of a couch. The room was allowed to burn post-flashover for several minutes. Normal suppression and overhaul was performed by the firefighters on the scene. On the following day, a team of fire investigators was asked to determine the source of ignition. The flare residue remained and was visible in the area of origin, but was not discovered or identified by the team of investigators assigned to that particular room.

The testing required to identify flare residue is not included during standard ignitable liquid residue (ILR) tests. Traditional analysis performed on fire debris is for the presence of ILRs which are organic and volatile. Road flare residues are solid and inorganic and therefore, are not detectible using these standard examination techniques.

The residue that remains after burning a road flare is a whitish-grey solidified pool. The color and texture of the white material blends well with gypsum wallboard or plaster fragments typically found after post-flashover fires or fire department overhaul procedures and is therefore easily overlooked. Other components of a road flare may also be present including a cap, wooden plug, metal nail, wire legs, a base or possibly the remains of the cardboard tube.

Road flares are widely available for purchase, and are often included in a typical roadside safety kit. This widespread availability, high burn temperature (1450 °C, 2650 °F) and high heat release rate lends itself as a ready ignition source for incendiary fires. Due to the extended burn times of some road flares, they can be used to delay the start of an incendiary fire which may allow an alibi to be established.

Historically, minimal research has been performed on the role of road flares in incendiary fires. This research investigates the chemical signatures present following a fire that positively identifies the presence of road flare residue. It will also evaluate the remaining components and residue and visual burn patterns that occur when road flares are placed in proximity to common construction materials (such as gypsum wall board, carpet, plywood subfloors, etc.). Finally, it examines the remaining components and residue following vehicle fires.

NFPA 921 requires that the source of ignition, first fuel and the circumstances or conditions which brought them together be identified. The purpose of this research is to assist fire investigators in identifying the possible remains of a road flare during a fire investigation and explain the methods used to confirm the presence of a road flare through FT-IR and SEM-EDS analysis.

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