This shock wave envelops any object it encounters in a balloon of static pressure. During this fleeting stage—the primary blast effect—the individual does not move.
An abrupt fall in pressure follows, creating a vacuum. Then comes the secondary blast effect, a rush of supersonic wind that floods the vacuum, hurling and fragmenting objects it encounters, weaponizing debris as high-speed, penetrating projectiles.
Marines on patrol in Afghanistan in noticed a motorcyclist pass by, and moments later an IED exploded. Peter van Agtmael, Magnum Photos. The wind itself causes the tertiary blast effects, lifting human beings or even ton armored vehicles in the air, slamming them against walls, rocks, dusty roadsides.
The quaternary blast effects are everything else—fire that burns, chemicals that sear, dust that asphyxiates. The mystery lies in the effects of the primary blast. Or is external shock pressure on the chest channeled inside vasculature up through the neck and into the brain? Does the transmission of complex wave activity by the skull into the semiliquid brain cause an embolism? Does pressure deform the skull, causing it to squeeze the brain? Is the explosive noise damaging? The flash of light?
The majority of soldiers diagnosed with blast-induced neurotrauma have also been hurled or rattled by blast wind. Is military neurotrauma, then, simply an exotic form of concussion? The tests in Colorado arose from a landmark study by the military of breachers, those soldiers whose job is to set explosives and who for years had been reported to suffer a high incidence of neurological symptoms.
The study, conducted by the U. Marine Corps Weapons Training Battalion Dynamic Entry School, followed instructors and students over a two-week explosives training course. This suggested that repetitive exposure even to low-level blasts—even over just a two-week period—could be damaging. The breacher study went some way toward bringing blast-induced neurotrauma into focus. Previously, many in the military and medical communities had found it difficult to believe that a low-energy blast could inflict significant injury.
Christian Macedonia Ret. But today some researchers are floating a different theory: that mild TBI may increase vulnerability to certain psychological disorders, possibly accounting for the high rate of such disorders and even suicide among veterans. In the bunker we waited for the smoke to clear, then ventured into still-singed air. Pressure gauges at head and chest level had recorded the back-blast as it bounced off corners and walls.
The explosion itself had been preserved on video, which replayed events, at two to three frames a second, that had flashed by at a speed of 14, frames a second—the ignited fuse glowing red-gold in a long, snaking, elegant stem of light, then the gold-black bloom of the explosion: BOOM.
Shot 52 was one of a series intended to cast light on the phenomenon of back-blast, the reflection of blast pressure off a surface. Other studies are examining the length of blast exposure and the frequency and type of blast. On site to lead the analysis was Charles Needham, a world authority on blast physics. And in , the detonation of around tonnes of ammonium nitrate in the port of Tianjin, China, killed people.
Manufactured as little beads that resemble cooking salt, ammonium nitrate is cheap to buy and usually safe to handle, but storing it can be a problem. Over time, the compound absorbs moisture, which can make the beads stick together into a huge rock, says Sella. When such a large quantity of compacted ammonium nitrate is exposed to intense heat — if, say, an accidental fire breaks out — it can trigger an explosion. The shock wave following a such a blast can be deadly. The explosion produces an area of high pressure that travels faster than the speed of sound, shattering glass and injuring people.
In Beirut, the disaster has had such tragic consequences for reasons unrelated to the explosion itself. Only of the injuries were "penetrating," or the kind that leave visible wounds. The rest were from various forms of concussion caused by events such as explosives, falls and vehicle accidents. Most of those injuries—about 21,—were considered mild, which means that the person was confused, disoriented or suffered memory loss for less than 24 hours or was unconscious for 30 minutes or less.
Such patients don't usually get brain scans, and if they do, the images generally look normal. That's a problem, Franck says, because psychological problems arising from concussive head injuries can come from cell-level damage, since the brain "rewires" as it tries to heal. With blunt trauma we have a much bigger database. With explosions, it's mostly people in the armed services, and they're having a hard time because they'd like to access treatment and get help, but they don't know what to screen for.
Past experiments with rats have shown brain damage from explosive blasts, especially to the hippocampus, but did not look at the cellular level. And while previous studies in humans have examined brain cells in head injury cases, the tissue has only come from patients who were already dead. Since we can't peer inside a live human brain as it is being concussed, Franck grew cells from rat brains on biological scaffolding inside a gel-like substance.
The setup allows the cells to grow in clusters similar to how they would bunch up in a brain. The cells aren't as densely packed and are not doing all the things that brain cells would usually do, but they do provide a rough analogue.
It was an ugly car--a white s Cadillac, rescued from the junkyard. In the trunk, pounds of ammonium nitrate and fuel oil, the same lethal ingredients that the Oklahoma City Bomber used to destroy the Federal Building in Our car bomb, we were told, would vaporize sections of the Cadillac and level the modular building standing next to it. And our explosives were just one 15th the size of the bomb in Oklahoma City. This was one of our most anticipated shoots for our two-hour NOVA special, " Hunting the Elements "--and also one of the most horrifying.
We had stepped into a virtual terrorist's playground--the Energetic Materials Research and Testing Center at New Mexico Tech--and our morbid curiosity grew with each demonstration. Here, bomb experts and scientists spent their days teaching emergency personnel how to respond to nightmare scenarios, and the daily menu of demos was extensive. For an appetizer, a briefcase bomb that blew the torso off a wooden dummy and a pipe bomb that obliterated a watermelon and the table it was sitting on.
For the main course, a letter bomb that amputated and wedged a mannequin's foot in the ceiling and a wooden dummy suicide bomber whose improvised explosive device shot bolts through metal signs like bullets. Above: A wooden dummy "suicide bomber" wears a vest packed with C4 explosives a class of plastic explosives and bolts that double as projectiles. We filmed all four explosions with a special high-speed camera that played back the action in eerie slow-motion detail.
But it was the dessert course--the grand finale car bomb--that most horrified As we watched the playback of the slow-mo footage, a dome of super-heated gas--invisible in real time--appeared above the initial fiery blast, and with each frame, moved up and outwards, warping our view of the desert behind it into a wavy, trippy landscape. It's not just the heat and debris from the bomb that'll kill you, he told us. It's the shock wave that'll knock you dead.
Above: Watch the car bomb explode at frames per second.
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