Evaluating Structural Damage After a Wildfire

By: John Miller, P.E.

There’s a primary danger and fear experienced by property owners evacuated from the path of a raging wildfire – will my home or business be there when I return? Whether a structure emerges relatively unscathed by fire or with extensive damages, questions may arise about how to address damages. Let’s take a look at how fire damage affects common building materials and how these can be assessed for repair versus replacement.

Wood
Charring is evidence that wood has been fire damaged. The National Fire Protection Association (NFPA) defines char blisters as “convex segments of carbonized material separated by cracks;” this is often referred to as alligator charring. Structural damage to wood is measurable in section loss, and this reduction of the wood member reduces its structural strength. The burning of wood also produces soot, but soot staining does not affect the structural capacity or service life of wood.

Charred wood after a fire.

Concrete & Masonry
Structural fire damage to concrete and masonry typically occurs as a result of rapid differential thermal expansion/contraction (thermal shock), including rapid cooling. Visual evidence of fire damage includes a change in color, cracking (shallow progressing to deep), spalling, and softening of the concrete and mortar. Cracked or voided concrete can often be identified by tapping with a hammer. Fire-damaged mortar joints and concrete can be removed with a hard tool and samples can be taken and tested.

Testing hardness.

Steel
Structural fire damage to steel occurs when the fire is hot enough to change the metallurgical properties of steel, typically above 1200⁰F. Damage results in measurable deformation of the member, which may include buckling of columns or beam flanges. A visual inspection that shows the members are not deformed is sufficient to determine that steel is not structurally damaged. Samples from steel affected by fire can be taken and tested when necessary. Other metals, such as aluminum, will behave differently based on their metallurgical properties.

Buckled steel member after a fire.

Nearly any building material or component can be inspected to determine if it is fire damaged. This includes plumbing, shingles, drywall, and driveways – basically anything in or on a building. Many times, an evaluation of visual appearance may be sufficient to make a determination about the viability of materials, but when a visual inspection isn’t enough, testing of the materials may be an option. It’s important to utilize knowledge of the material properties and their response to heat when inspecting for damage, as well as collaterals around the component which can provide key indicators of the extent of fire and heat in that area.

   

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About the Expert

Mr. John Miller joined Donan in 2009 and currently serves as a forensic engineer and principal consultant based out of the firm’s Louisville, Kentucky office. He has 32 years of engineering experience and has completed approximately 1900 forensic investigations. Mr. Miller has worked in the following industries: bridge design and inspection, bridge and highway structure inspection, highway design and home construction and remodeling. His area of expertise is structural engineering with an emphasis on structural damage from impact, wind and flood. Mr. Miller’s project capabilities also include a wide range of civil and structural investigations including hail damage, foundation damage and the causes of water intrusion. Mr. Miller is a licensed professional engineer in Alabama, Colorado, Florida, Georgia, Kentucky, Mississippi, New Jersey, North Carolina, Oklahoma, South Carolina, Tennessee and Texas. He earned his Bachelors degree in Civil Engineering from the University of Kentucky. View John's full professional profile here.