On August 6, 1945, at 8:15 a.m., a thirteen-kiloton uranium bomb detonated 600 meters above the Shima Hospital in Hiroshima. One second later, the fireball reached its maximum diameter of 274 meters and the ground temperature beneath it exceeded 3,800 degrees Celsius. Within that single second, the fundamental architecture of the human body, every atom, every molecule, every cell, every tissue and every organ of thousands of people was subjected to forces that no biological structure was designed to survive.

In previous articles published on this blog, I have described the geopolitical conditions under which a nuclear detonation in the Middle East is not only possible but increasingly plausible. I have analyzed Iran’s nuclear trajectory, the vulnerability of the Dimona reactor, and the medical consequences that would befall both Israeli and Palestinian populations given their geographic proximity. But those articles described the effects of nuclear weapons in broad strokes. This series narrows the lens. It asks a different question. Not whether a nuclear bomb could detonate in the region, but what exactly it would do to the human beings standing beneath it.

This is Part I. Ground zero. The zone within 800 meters of the hypocenter of a 10 to 15-kiloton detonation, where the Severe Damage (SD) zone begins and ends according to the classification established by the U.S. Federal Emergency Management Agency (FEMA) and the Radiation Emergency Medical Management (REMM) program of the Department of Health and Human Services. The zone where almost no one survives. The zone where medicine has almost nothing to offer except documentation.

Before the blast wave arrives, before the radiation penetrates tissue, the first assault on the human body at ground zero is light.

The nuclear fireball emits a thermal pulse that travels at the speed of light and delivers its energy in less than three seconds for a weapon in the Hiroshima range. At distances under 500 meters from the hypocenter, the thermal fluence exceeds 100 calories per square centimeter. To put that in clinical perspective, a thermal exposure of 10 cal/cm² is sufficient to cause third-degree burns on exposed skin. At ground zero, the energy delivered is ten times that threshold.

The thermal radiation strikes the body before the conscious brain can register any sensation. The speed of light does not negotiate with human reflexes. The skin, the largest organ of the body, receives the full impact first. The epidermis, which is only 0.1 millimeters thick in most regions, is instantaneously carbonized. The dermis beneath it, containing the nerve endings, blood vessels, hair follicles and sweat glands, is destroyed before it can transmit a pain signal. At these energy levels, the destruction passes through the full thickness of the skin and penetrates into the subcutaneous fat and superficial muscle. These are not burns in any conventional clinical sense. There is no blister formation, no inflammatory response, no reddening. The tissue is charred before inflammation can begin.

The eyes are catastrophically vulnerable. The lens of the human eye focuses incoming light onto the retina with an amplification factor of approximately 100,000. A person looking in the direction of the fireball would receive a focused thermal beam onto the macula, the area of the retina responsible for central vision, producing an instantaneous and irreversible retinal burn. But at ground zero, retinal burns are an academic concern. The entire globe of the eye would be destroyed by the thermal pulse before the retinal burn could form a scar.

One of the most persistent myths about ground zero is that victims were “vaporized.” Scientifically, this is almost certainly inaccurate. Vaporizing a 70-kilogram human body (which is approximately 60% water) would require energy far exceeding what is delivered even at the hypocenter of a Hiroshima-class weapon in the fractions of a second available. What happened instead was massive carbonization. The body did not disappear into gas. It was charred, reduced in volume, and in some cases fused with surrounding materials. The famous “Human Shadow Etched in Stone” at the Sumitomo Bank in Hiroshima, located just 260 meters from the hypocenter, is not the silhouette of a vaporized person. It is the thermal imprint left by a body that absorbed enough radiant heat to shield the stone beneath it from bleaching while the person suffered lethal flash burns.

Approximately one third of a second after the thermal flash at ground zero, the blast wave arrives.

The shockwave from a nuclear detonation is qualitatively identical to that of a conventional explosion but exponentially more powerful. At 500 meters from the hypocenter of a 15-kiloton airburst, the peak overpressure exceeds 10 psi (pounds per square inch) with wind speeds exceeding 500 kilometers per hour. These are forces that reduce reinforced concrete buildings to rubble. The human body, despite its remarkable resilience, is caught between two realities at this distance.

The first reality is that the human body can theoretically survive overpressures of up to 30 psi (approximately 2 bar) in an open field. The lungs, which are the organs most vulnerable to blast overpressure, can withstand more than most people assume. The lethal threshold for pulmonary blast injury in humans is estimated between 40 and 60 psi. By this measure alone, some individuals at ground zero could technically survive the direct pressure wave.

The second reality eliminates the first. No one at ground zero stands in an open field. They stand inside buildings. And buildings are far more fragile than human bodies. At 5 psi, most residential structures collapse. At 10 psi, reinforced concrete frames are severely damaged. At 20 psi, virtually nothing remains standing. The human body does not die from the overpressure itself. It dies from the building falling on it. From the wall slamming into it at 500 km/h. From the body being hurled 30 meters against a concrete surface. From the glass fragments that penetrate the torso like shrapnel at supersonic speed. The mechanism of death at ground zero is, in most cases, blunt polytrauma compounded by thermal injury. Not the elegant physics of pressure waves, but the brutal mechanics of flying concrete.

The blast wave also affects the air-filled organs of the body directly. The eardrums rupture at overpressures as low as 5 psi. At ground zero, tympanic membrane rupture is universal and bilateral. The lungs, as mentioned, can suffer blast lung injury: hemorrhage into the alveoli, air embolism from ruptured pulmonary vasculature, and pneumothorax. The gastrointestinal tract, particularly the large intestine, is also vulnerable to blast overpressure, with perforation possible at the ileocecal junction and at the rectosigmoid, the areas where gas accumulates. But again, at ground zero, these injuries are largely theoretical because the individuals suffering them are simultaneously being crushed by collapsing structures and burned by the thermal pulse. The clinical picture, if one could somehow examine it, would be that of combined injury: a patient with fourth-degree burns over 90% of the body, multiple long bone fractures, a flail chest, bilateral hemopneumothoraces, a ruptured spleen, and perforated bowel. There is no trauma center on Earth equipped to save this patient.

The initial radiation

The third mechanism of destruction at ground zero is the most invisible and, at this distance, the most biologically redundant.

A nuclear detonation produces a burst of ionizing radiation consisting primarily of gamma rays and neutrons. This radiation is emitted within the first minute of the explosion, with the most intense pulse occurring in the first second. At the hypocenter of a 15-kiloton airburst, the radiation dose received by an unshielded individual can exceed 100 Gray (Gy) at very close range, declining steeply with distance to approximately 5 to 15 Gy at 500 meters ground distance. Even at these lower doses, the radiation remains supralethal.

To understand what these doses do to the human body, consider the following clinical scale. A whole-body dose of 1 Gy produces mild nausea and a transient decrease in lymphocytes. At 4 to 6 Gy, approximately 50% of exposed individuals die within 60 days without medical treatment, primarily from bone marrow failure. This is the LD50/60. At 10 to 20 Gy, the gastrointestinal epithelium is destroyed and death occurs within 7 to 14 days from sepsis, dehydration and hemorrhage as the intestinal lining sloughs off. At 50 Gy, the central nervous system is directly damaged, and death occurs within 24 to 48 hours from cerebral edema and cardiovascular collapse.

At 100 Gy, every organ system fails simultaneously. The bone marrow, which produces the red blood cells, white blood cells and platelets that sustain life, is obliterated. The stem cells in the intestinal crypts, which regenerate the gut lining every three to five days, are destroyed in a single moment. The endothelial cells lining every blood vessel in the body suffer irreparable DNA damage. The lymphocytes, the most radiosensitive cells in the human body, are killed almost instantaneously. The brain, normally considered radioresistant, suffers direct neuronal death at these doses.

At the molecular level, gamma rays and neutrons interact with the water molecules that constitute 60% of the human body, generating hydroxyl radicals (OH·) and other reactive oxygen species through a process called radiolysis. These free radicals attack the DNA molecule, producing single-strand breaks, double-strand breaks, and base modifications at a rate that overwhelms the cell’s repair mechanisms. A single Gray of low-LET radiation produces approximately 1,000 single-strand breaks and 40 double-strand breaks per cell. At 100 Gy, the DNA of every cell in the body is shattered beyond any possibility of repair. The cellular machinery that reads genetic instructions, synthesizes proteins, and maintains the organized architecture of tissues ceases to function.

But at ground zero, this radiation damage is delivered to a body that is already burning and already being crushed. The radiation dose is supralethal by a factor of twenty, but the individual receiving it has already sustained injuries incompatible with life from the thermal pulse and the blast wave. This is the cruel arithmetic of ground zero: three lethal mechanisms delivered almost simultaneously, each alone sufficient to kill, together constituting a form of biological destruction for which clinical medicine has no vocabulary.

The Hiroshima evidence

What we know about ground zero comes almost entirely from the reconstruction of events at Hiroshima and Nagasaki. No living witness survived unshielded at distances under 500 meters from the hypocenter. The evidence is forensic: the position of charred remains, the angle of flash burns on surfaces, the structural analysis of collapsed buildings, and the shadow patterns etched into stone and concrete.

The Radiation Effects Research Foundation (RERF), successor to the Atomic Bomb Casualty Commission established by the United States and Japan in 1947, has spent nearly eight decades studying the survivors of Hiroshima and Nagasaki. But its data is drawn from those who survived, meaning those who were at greater distances, those who were shielded by concrete, those who by accident of geography were not in the direct line of sight of the fireball. Ground zero itself left almost no survivors to study.

The one remarkable exception was the Nagasaki University Medical School Hospital, located just 600 meters from the hypocenter of the Fat Man bomb. Its reinforced concrete walls, built to withstand earthquakes, absorbed enough of the thermal pulse and blast wave to protect some of the people inside. Even so, 43% of the occupants, patients and medical staff alike, perished. The survivors suffered severe combined injuries: burns, fractures, lacerations from flying glass, and acute radiation syndrome. The hospital became both a casualty ward and a research site, the first and only empirical evidence of what happens to human beings at the boundary of ground zero when some form of shelter intervenes.

What this means today

A nuclear weapon detonated in the Middle East would not be a 15-kiloton bomb from 1945. Modern nuclear warheads range from sub-kiloton tactical devices to multi-megaton strategic weapons. Iran’s suspected nuclear capability, based on its enrichment of uranium to 60% and its stockpile of fissile material, suggests a first-generation device in the range of 10 to 20 kilotons, comparable to the Hiroshima and Nagasaki weapons. The ground zero effects described in this article would apply directly.

But even for a Hiroshima-class weapon, the ground zero zone in a modern Middle Eastern city would encompass hospitals, schools, residential buildings and mosques within an 800-meter radius. In a city like Tel Aviv, that radius covers approximately 2 square kilometers of some of the most densely populated urban terrain on Earth. In Tehran, the density is comparable. The number of human bodies subjected to the triple assault described above, thermal pulse, blast wave and supralethal radiation, would be measured in the tens of thousands.

There is no medical response for ground zero. No triage protocol applies. No field hospital can be deployed. The physicians, nurses and paramedics who would normally respond are, if they were within 800 meters, among the dead. This is the fundamental reality that distinguishes nuclear weapons from every other instrument of war: at ground zero, medicine does not arrive late. It does not arrive at all.

The next article in this series moves outward, to the zone at one mile from the hypocenter, where the injuries are survivable but the medical system is not.

© The Times of Israel (Blogs)