Explosion trauma is grouped by causal mechanism into four tiers. Tier one (primary) reflects the pure over-pressure wave damaging air-filled structures: tympanic rupture, pulmonary barotrauma, and hollow-viscus perforation. Tier two (secondary) is penetrating trauma from projectiles and shrapnel. Tier three (tertiary) is blunt trauma from the body being hurled by the blast wind.
The fourth tier (quaternary) is the catch-all for every remaining explosion effect - flame and flash burns, toxic-gas and dust inhalation, crush injury, and worsening of chronic disease.
Facial and chest burns produced by the fireball and radiant heat of the detonation match the quaternary definition precisely, since they arise neither from the pressure wave, nor fragments, nor displacement.
\[\boxed{\text{Burns from a blast} = \text{Quaternary blast injury}}\]