Ammonium nitrate is a fertilizer. Under the wrong conditions, heat, confinement, contamination, it is also one of the most powerful industrial explosives there is. When it goes, it injures the body in four distinct ways, and the deadliest of them leaves almost no mark.
The wave you cannot see
A detonation is not a fast fire. It is a pressure wave that slams outward through the air faster than sound. That wave is the primary blast injury, and it does its worst where air meets tissue: the ears, the gut, and above all the lungs.
Blast lung
The lungs are built of millions of tiny air sacs. The overpressure wave tears the fine boundary between air and blood, and the lungs begin to fill and to bleed. It is called blast lung, and it is a leading cause of death among people who survive the first instant of a large explosion. The cruel part is that it can be silent at first. A person can walk away, talk, seem fine, and fail hours later as the lungs flood.
The other three
Around that invisible wave come the injuries everyone can see. Flying debris and fragments that cut and pierce, the secondary injury. The body itself thrown against the ground or a wall, the tertiary. And then the burns, the smoke, the crush of a collapsing building, the quaternary. One explosion, four mechanisms, often all at once in the same person.
Why this matters
Because blast lung hides, the early medical record can look deceptively mild, and a defense can point to it and say the person was barely hurt. The science says the opposite. In a real detonation, the absence of an obvious wound is not the absence of injury. It may be the most dangerous injury of all, still unfolding.
The lesson
An explosion is not one event. It is four injuries riding the same wave, and the one that kills is the one you cannot see. Read the whole body, and read the clock.
On primary blast injury and the mechanism of blast lung, see Primary Blast Lung Injury, a review in the British Journal of Anaesthesia, and the general blast-injury literature (StatPearls). This is general information, not medical or legal advice.
