Some Mechanical and Structural Aspects of the Smolensk Crash
By Dr. Gregory Szuladzinski, Ph.D., MSME
SCND2014GS

Appendix IV. Mechanics of HE Explosion and Aircraft Fire

Landing aircraft normally has a substantial fuel load. If, during an emergency landing the fuel ignites, it often results in a great fire which would burn, or at least scorch the whole craft.

It is different scenario when a bomb detonates. (The word "bomb" is only a mental shortcut of 'explosive, which is subject to detonate.’) If a bomb is suspended in the air, for experimental purposes, there is a blast simultaneous with the appearing fireball. (If the weight of the charge is known one can calculate the size of the fireball). The surface of this fiery sphere is the shock wave. When the diameter of the sphere reaches a certain multiple of the diameter of the bomb, then the wave separates from the ball and continues its rapid outward movement, attacking all the obstacles on the road. In short, the fire is limited in its reach.

If an explosion occurs inside the structure, the ball deforms according to the shape of the interior, unless the structure broken in some area. If the bomb separates the structure into parts, the flying fragments will be swept by fire. After contact with the ground, those parts will burn for some time. Elements located farther from the source or sheltered from the explosion remain unlit.

The ripping of the hull in this case suggests an internal explosion. The “selectivity” of fire in this event was very well illustrated by the available video clips.Therefore, one should look to the nature of fire as supporting evidence for the explosion inside the airplane.

An explosion of this nature leaves a signature that is difficult to remove. The surfaces are directly affected by persistent traces that can be detected by metallurgical analysis.

People near the source of the blast may be affected by the shock wave and the fire, or just by the latter. The shock wave action is the more likely farther from the center of fire. But secondary fires are possible and that may complicate the investigation.