Fire investigation, post-fire assessment and forensic engineering
Domain 7 tests systematic, evidence-based determination of where a fire started, how it developed, and whether a structure or a system failed. Conclusions must follow the data, not precede it.
Method before opinion
The recognised discipline is the NFPA 921 systematic approach: define the problem, collect data, analyse including all reasonable hypotheses, test each hypothesis against the evidence, and select the one that best explains all of it. Origin and cause are separate findings: origin is a location, cause is a mechanism. Multiple origins must be positively evidenced, never inferred from the extent of damage.
Reading fire patterns
Useful indicators include V and U patterns, char depth mapping, calcination of gypsum, concrete spalling, melting points of metals (aluminium about 660 °C, copper about 1083 °C), glass crazing versus melting, and the smoke-staining boundary marking the hot layer. Ventilation reshapes patterns dramatically: an under-ventilated compartment fire can leave a low-burn pattern near an air inlet that mimics an origin. Arc mapping and identified arc beads support an electrical hypothesis but do not by themselves prove it.
Flashover and origin
Flashover produces widespread, near-uniform damage and can consume the true origin. Floor-level burning and inverted-cone patterns in a post-flashover room must be interpreted against the pre-flashover geometry. Clean burn on protected surfaces and soot shadowing usually record the layer, not the seat of the fire.
Post-fire structural assessment
For concrete, record spalling depth, cracking, colour change, rebar exposure and cover. For steel, record deformation and connection condition, remembering structural steel loses strength rapidly above roughly 550 °C. Repair specifications should follow a documented assessment process (for concrete, the TR 68 approach) with cores and a residual capacity check rather than cosmetic patching.
Worked example
One room shows deep charring at a socket outlet, a V pattern above it, and arc beads at the spur; a second, shallower burn area is found at the door. Hypothesis A: electrical fault at the socket. Hypothesis B: fire spread from the door. Test the char depth and the bead morphology: beads showing half-cycle features consistent with a fault under load support hypothesis A, and the door burn is then explained as a ventilation-driven secondary pattern.
Traps
Attributing flashover damage to the origin; claiming alligatoring proves an accelerant; ignoring ventilation effects; presenting an expert conclusion without the underlying data; breaking the chain of custody for samples.