When Fire Doesn’t Mean Failure: How Forensic Engineers Determine Survivability

Nels R. Peterson, P.E.

Nels R. Peterson, P.E., M.S.C.E.

“Total loss” isn’t a diagnosis—it’s a conclusion. In fire claims, I’m often asked to determine whether a building or system truly failed, or whether it can be safely repaired and returned to service. That determination hinges on survivability: did the structure or component experience heat, flame, and byproducts at a level and duration that compromised its function or capacity? Sometimes the answer is yes. Just as often, targeted investigation shows the damage is localized and repairable.

Below is how I approach survivability in the field.

What “survivability” really means

Survivability isn’t about whether something looks burned, it’s about whether it has lost enough material properties or integrity that it can’t do its job. For structures, that usually means asking:

  • Did the thermal exposure reduce strength or stiffness below safe levels?
  • Did connections, fasteners, or interfaces lose capacity or continuity?
  • Did heat, soot, or water introduce secondary risks (corrosion, hidden delamination, embrittled grout, moisture trapped in assemblies) that will shorten service life if left unaddressed?

With those questions in mind, we work from the outside in, mapping where the fire burned hottest and longest, and correlating that to the materials present.

Heat doesn’t distribute evenly, and that matters

In real fires, temperature is rarely uniform. Fuel loads (vegetation, stored goods, furnishings) create pockets of high heat that sit right next to areas that barely warmed up. One recent review involved a masonry retaining wall after a wildland–urban interface event. Portions of the wall shed bricks; other spans were intact. When we overlaid burn patterns from adjacent vegetation, the failures lined up with the heaviest fuels. Localized heating likely embrittled the grout there, allowing discrete sections to release. That pattern—damage concentrated where fuel loads were highest, with undamaged areas adjacent—pointed to a survivable system with targeted repair, not blanket replacement.

Field forensics: translating burn patterns into engineering decisions

To turn a charred scene into a defensible scope, I look for consistent relationships between burn evidence and performance:

  • Fuel and flame indicators. Continuous, darkened soot fields; melted or deformed plastics; and vegetation consumption help rank heat intensity and duration, zone by zone.
  • Material response.
    • Wood—char depth is a proxy for time–temperature exposure. Shallow, uniform char with solid substrate typically supports repair. Deep, uneven char, crushed fibers, or heat-split members suggest replacement.
    • Steel—temper colors, coating blisters, and distortion indicate peak temperatures. Minor discoloration without deformation often survives; visible yielding, connection slip, or loss of fireproofing points to higher scrutiny.
    • Masonry/concrete—spalling, surface “sugaring,” and friable mortar/grout can be localized to hot spots. Sound, tight mortar outside those zones is frequently serviceable.
  • Connections and continuity. Impacts to fasteners, anchors, and laps tell you more about survivability than broad surface staining does. If load paths remain continuous and connection capacity is intact, targeted repairs are viable.
  • Pre-existing vs. event-caused. Fresh fracture planes tend to be bright and clean; long-standing conditions often show dirt, corrosion byproducts, or paint bridging. Distinguishing the two prevents unrelated deficiencies from being misattributed to the fire.

Common misreads that inflate (or understate) scope

Fire scenes come with optical illusions. A few I see regularly:

  • “It’s all black, so it’s all bad.” Soot is an excellent traveler. It deposits far beyond heat-damaged zones. Cleaning and clearance testing can separate cosmetic contamination from thermal damage.
  • “If one section failed, the whole system did.” Localized high heat can knock out a small segment while adjacent segments remain within acceptable properties. Patterned damage aligned with fuels argues for sectional repair.
  • “New cracks = fire damage.” Some cracks predate the event; others result from rapid cooling during suppression. Fracture brightness, edges, and presence of paint or debris help time-stamp the distress.
  • “The structure survived, so we’re done.” Heat, soot, and suppression water can set up long-tail problems—corrosion in concealed steel, moisture in tight assemblies, or alkaline–silica reaction in overheated concrete. Survivability includes mitigating these secondary effects.

From scene to scope: building a repairable, defensible plan

A survivability assessment should lead naturally to a scope that is safe, practical, and justifiable. I organize it around:

  1. Zones of exposure. Map the site into high, moderate, and low thermal zones based on physical indicators and fuels.
  2. Component-by-component calls. For each zone, document whether framing, masonry, metals, and finishes are clean-and-restore, repair, or replace, with the evidence that drives each call.
  3. Connections and anchors. Verify or re-establish continuity where heat or suppression may have compromised it (e.g., re-anchoring, supplemental plates, repointing).
  4. Environmental remediation and clearance. Specify cleaning methods, encapsulation where appropriate, and post-cleaning testing criteria.
  5. Monitoring or testing, if needed. Moisture mapping in tight assemblies, pull tests on anchors, or concrete petrography in suspect areas provide the confidence to avoid unnecessary replacement while preserving safety.

Survivability in wildland–urban fires

Wildfire claims often feel binary—total loss or untouched, but many sites fall into a middle ground of smoke, radiant heat, and ember exposure. The same method applies:

  • Track fuel-driven heat (mulch beds against walls, wood piles, dense shrubs) to predict where materials saw meaningful temperature.
  • Expect discrete failures (embrittled mortar, warped siding) in those zones, not necessarily across the entire façade.
  • Use targeted repair—repointing, selective unit replacement, fastener upgrades—where the primary structure remains sound.
  • Validate indoor air quality and cleanability, which is often the real determinative factor for habitability when structural elements have survived.

Why this approach helps claims move

A careful survivability assessment cuts two ways. It prevents premature demolition when systems are serviceable, and it prevents under-scoping when heat really did take capacity out of a member or connection. For adjusters and counsel, the value is a scope that holds up: decisions tied to observable indicators, material science, and clear documentation, rather than to how dramatic the scene looks.

Takeaway

Fire doesn’t automatically equal structural failure. By reading burn patterns through the lens of fuel, heat, and material response—and by verifying connections and continuity—engineers can distinguish what must be replaced from what can be safely repaired. That difference saves time, preserves value, and keeps occupants safer over the long term.

 

About the Author

Nels R. Peterson, P.E., M.S.C.E. is a Consulting Engineer in our Seattle-Tacoma Office. Mr. Peterson provides consultation in the areas of structural analysis, scope of damage, cause of damage, and water intrusion investigation. You may contact Nels for your forensic engineering needs at npeterson@edtengineers.com or (253) 345-5187.

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