Buildings which are physical structures are sometimes subjected to fire hazards that could burn the whole or part of the building thereby posing risks to occupants of the building and the building/physical structure itself.

But of concern is the largely ignored risks that inhabiting a burnt building without a structural integrity test being done pose to the human population and the environment.

Most people erroneously believe that only the parts of the building exposed to the fire should be avoided and go ahead to inhabit such buildings after merely cleaning up assuming that the only damage done is the visible damage.

Apart from structural elements like the roofing materials, blockwork and interiors that usually get weakened and damaged beyond re-use, the concrete structure support members also get affected by the fire but due to their reinforced nature, they manage to stay intact physically but would have suffered thermal capable of making changes that could lead to an imminent failure of the building.

It is a fact that concrete forms the critical mass and bulk of a building/physical structure and if such structure is exposed to a fire, the concrete would be affected by the action of fire on the building with the resultant effect not being the most desired.

Reinforcement concrete in buildings (pillars, columns, beams) should typically have a fire resistant covering in the form of a partial impregnated concrete with a suitable monomer or some other expensive means to reduce the concrete exposure to fire hazards but it does not totally eliminate the possibility of the concrete structure being acted upon by fire.

The behaviour of concrete in fire depends on its mix proportions and constituents and is determined by complex physicochemical transformations during heating. Normal-strength concretes and high-performance concretes micro structurally follow similar trends when heated, but ultra-high-performance concrete behaves differently.

A key property unique to concrete amongst structural materials is transient creep. Any structural analysis of heated concrete that ignores transient creep will yield erroneous results, particularly for columns exposed to fire.

Failure of structural concrete in fire varies according to the nature of the fire; the loading system and the type of structure. Failure could occur from loss of bending or tensile strength; loss of bond strength; loss of shear or torsional strength; loss of compressive strength; and spalling of the concrete.

The above stated facts reveal that the exposure of concrete structures to fire definitely causes a change in the characteristics of the concrete structure which indicates that failure of the structure becomes imminent, the time of eventual failure depending on the duration and intensity of the the fire the concrete was exposed to.

According to Mr. Abdur-Rahman Agbede, a civil engineer based in Lagos, inhabiting a building that had been exposed to fires is not safe and should be discouraged as such buildings have to be certified fit for habitation or use by a qualified structural engineer after the fire.

Agbede said a typical fire destroys the interior, roofing materials and weakens blockwork that it encounters but leaves the building reinforcement structure (pillars, columns, beams, etc) intact, even though it would have suffered internal stress that requires its ability to bear the design load and other applied forces after the fire.

The proper way to go after a fire according to Mr. Agbede is to invite a qualified structural engineer after the removal of other structural material and debris to conduct a Concrete Strength Test to determine the strength of the concrete and advice accordingly on the result of the concrete strength test that will be determined in the lab.

He said that in very mild fires, the fire resistant covering in the structure could protect the concrete from the hazards of the fire but it was only in the place of a qualified structural engineer to pronounce such buildings safe for habitation.

He generally advised that in the case of any fire incident in a building, it is advisable for house owners or inhabitants to seek the services of a structural engineer to do the right check on the building and not make any unscientific assumptions that could further endanger their lives and the environment.

From all of the above stated, it is proper to say that any building exposed to fire or close enough to a burning building as could impact on the concrete structures of the building should be examined and certified fit for human habitation by qualified professionals and the concerned authorities.

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