瞬间之美 | 摄影师捕捉爆炸的惊艳瞬间

来自摄影师

Christian Weber

曾经他还给我们分享过

大火之后……黑线 Blackline

。

爆炸：在极短时间内，释放出大量能量，产生高温，并放出大量气体，在周围介质中造成高压的化学反应或状态变化，同时破坏性极强。当然，也拥有极大速度。

摄影师Christian Weber捕捉了各种爆炸绽放的决定性瞬间。这些瞬间是如此的纯粹又如此吸引人。拍摄的这些爆破物具有超音速的速度，低爆破波的冲击波达到每秒1126英尺，高爆破波的冲击速度达到每秒27000英尺—该速度是步枪子弹的10倍。没有两个爆炸时相同的，因此，这些照片均独一无二，举世无双。

What is an explosion?

In its simplest definition, it is things moving apart from each other very rapidly. In a more scientific context, an explosion is the conversion of chemical energy to kinetic energy, which is often associated with the generation of heat, light, and a loud noise. The initial volume of an explosive, whether in solid or liquid form, undergoes an exponential increase in mass as it is converted to simpler compounds in a gaseous state. These gases are not content to linger close to the seat of the blast, but instead seek new quarters further away from the explosion with amazing speed. The precise rate at which the gases travel depends upon the type of explosion, which is characterized by the chemical nature of the energetic compounds present, the quantity of those compounds, and the extent of their confinement.

Some technical terms have been applied to the rate at which an explosive wave front propagates through its given reactants. These terms afford analysts a way of broadly characterizing just how fast an explosive decomposition is taking place. If the shock wave is traveling below the speed of sound, the term “deflagration” is applied to that reaction, and it can simply be thought of as very rapid burning.  Energetic compounds that deflagrate are typically called “low explosives.”  If the shock wave is traveling faster than the speed of sound, the term “detonation” is applied to that reaction, and those compounds that behave in this manner are called “high explosives.” (A word of caution may be appropriate here: the reader should not be disrespectful to explosives prefaced with the word “low,” as they can be quite powerful.) The significant energy release of the high explosives and their concurrent supersonic wave fronts afford them a great capacity to do work for us. It would be naïve, however, not to respect the low explosives, which have been around for centuries and have been responsible for, or instrumental in, hundreds of successful engineering projects.

During the phase change that a solid or liquid explosive compound undergoes when it transitions to the gaseous state, the entropy of the thermodynamic system increases in a random way, which is difficult to predict and leads to the generation of dramatically impressive light, sound, and color. Of course, secondary to the explosion itself are the materials surrounding or nearby the blast, which can also be relocated in a fraction of a second by the expanding gases and shockwave, contributing further to the overall spectacle.

The amount of potential energy that is stored in the molecule of an explosive can be determined using various applications of mathematical formulae, including bomb calorimetry, the Trauzl lead block test, and the ballistic pendulum. The resultant conversion of potential to kinetic energy is what performs the desired work, such as rock blasting, mining, ground ejection, etc.  It is wasteful of the product to employ too much explosive and wasteful of time to employ too little. Hence the application of these formulae.

Prior to the much more recent discovery and development of high explosives, one of the raw materials necessary for the manufacture of the widely used low explosive, black powder, became a deciding factor in trade agreements between those countries rich in nitrates and those without such resources. Some might even compare the lucrative nitrate trade of the seventeenth, eighteenth, and nineteenth centuries with the complexity and intrigue of the ancient spice trade.  Nitrates were “farmed” in India and shipped to England, but they were of mediocre quality. A product higher in nitrogen existed in bird droppings, which accumulated in the very dry climates of a few islands faraway from the British Empire. For years, the Dutch East India Company held a monopoly in the nitrate-rich guano trade from these islands. America, in an effort to circumvent the monopoly and its inherent high prices, explored and laid claim to several islands in the vast expanse of the Pacific. Without the key inclusion of chemically bonded nitrogen, the remaining ingredients of explosives (black powder, sulfur, and charcoal) would not explode. Chemically bonded nitrogen, a gas in its elemental state and a major component of the Earth’s atmosphere, was the oxidizing agent lacking in the explosive mixture. Thus the chemical compound potassium nitrate became a central ingredient to the process and a source of great wealth to those who were able to harness its potential.

The proper and constructive use of explosives requires considerable knowledge and skill to direct a tremendous amount of energy toward the goal of its user. Early usage of explosive mixtures consisted merely of placing an amount of the powder directly against the item or object to be moved or broken and then quickly ducking for cover. Not surprisingly, much of the energy of the blast was not efficiently directed towards its target, but instead was wasted on the surrounding area. To “tamp” an explosive was to use inert materials, like sand bags (although any convenient material such as logs or rocks would do) to direct more of the resultant energy toward the target. If, for example, black powder was being used in a hole drilled in rock for mining or quarrying, then the explosive rigger would use clay as a tamping material to fully occupy and seal the borehole. Because of this focus, tamping, done properly, was able to reduce the amount of explosive materials necessary to perform a task that had previously wasted energy on the surrounding area.

Unlike today, igniting any kind of explosive mixture over a century ago was risky business.  A reliable and predictable method to ignite explosive devices eluded blasters until the advent of the “safety fuse” developed by William Bickford in 1831. It may appear to be a logical and even easy device to conceive of now, but prior to its development explosions were quite unpredictable due to the numerous unreliable methods used to ignite them. These included the use of a loose, thin line of black powder merely poured on the ground as a trail for ignition, a quill filled with the explosive powder, and other improvised methods devised to put distance between the blaster and the blast. These approaches tended to burn at irregular rates and were easily damaged and prone to water infiltration.  Consider this nightmare: a long trail of loose black powder concludes at several large kegs of the same material. You have lit the trail, but after waiting a minute or so, the kegs have still not exploded. What do you do? Who would dare to venture closer to determine what has gone wrong with the ignition? The invention and development of the safety fuse made such decisions much less frequent and thus made blasting much safer, as ignitions became more reliable. The safety fuse was merely a small amount of black powder tightly wrapped in jute and sealed with shellac to prevent water infiltration.  An additional benefit of Bickford’s safety fuse was its predictable burning rate of about thirty seconds per foot.  Predictable fusing was a huge step forward in mining safety and in the constructive use of explosives.

Alfred Nobel, who endowed the prizes that bear his name, was responsible for significant breakthroughs in the world of explosives, including mixing nitroglycerine with a type of clay to form what he called dynamite.  Due to the success of Nobel’s dynamite, several other models of it were subsequently developed using different fillers, each with various specific properties, used in place of clay to absorb the nitroglycerine. Energetic fillers, for example, provide an additional blast effect. Between the earlier use of black powder and subsequent use of dynamite, work that originally had to be done by hand, such as mining and tunneling through mountains for expanding the railroad network, could now be done much more quickly and efficiently.

It might be interesting to note that in the historic context of the artful use of explosive material, one of the most well known explosives, TNT (trinitrotoluene), was used as a textile dye well before its widespread use as an explosive.  Developed in Germany in the early eighteen-sixties, TNT’s yellow color and relative insensitivity (to exploding) allowed its safe usage as a dyestuff. (It does ultimately, however, have toxic properties and is therefore no longer used for this purpose.)

The color of the light and smoke emitted by an explosive is determined by the chemistry of its ingredients.  This is a twofold proposition: the colors are determined either intrinsically by the molecules present in the base materials themselves, or from additives chosen by the chemist or pyrotechnician.  An explosive containing too much carbon in the key molecules is said to have poor oxygen balance. When an explosive with a poor oxygen balance is detonated, excess carbon results in black smoke. TNT is an explosive with more carbon than oxygen in its molecules, which means that detonation is accompanied by black smoke. In some instances, carbon is deliberately added in order to produce such an effect. Other effects and colors are also possible depending on the elements chosen – yellow can be obtained by the addition of sodium salts, red by adding strontium salts, green by the addition of barium salts, blue with copper salts, and mixtures of each to create other colors.

Today’s engineers still apply the focused application of explosive devices on a host of new products and innovative technologies. Reliable and almost instant automotive airbag deployment is accomplished by the use of a small explosive charge. Early experimentation with aircraft ejection seats included the use of explosives to jettison pilots clear of their planes. Explosive reactive armor (essentially sandwiches of steel plates with an explosive filler) has saved the lives of countless soilders, who would otherwise have been wounded or killed when their tanks were hit by incoming penetrator projectiles. Energetic compounds have been known for centuries. Harnessing their power, first by trial and error and more recently with mathematical calculations and computer modeling, has been a largely fruitful endeavor.

Christian Weber’s photographs of explosions freeze decisive moments to capture the colorful emission of light and incandescent particles of various explosive combustions. These moments are incredibly brief, which makes their photographic representation all the more compelling. Low explosives by definition may have a shock wave as fast as the speed of sound, which is 767 miles per hour (in dry air at twenty degrees celsius), or 1,126 feet per second.  High explosive wave fronts may reach an astonishing 27,000 feet per second, or about ten times the speed of a rifle bullet. Of course it is safe to conclude that no two explosions are identical due to the stochastic nature of these events.  Thus the events recorded in Weber’s images are truly unique and impossible to replicate.

Peter Diaczuk

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