The tragic news of a huge explosion in Beirut, which took the first lines of news resources, raises natural questions: how could this have happened, what exploded there, due to what factors are such incidents possible? To understand, let's take a closer look at the properties of ammonium nitrate and the hazards associated with it.
A huge number of houses were damaged to varying degrees, destruction affected half of Beirut's buildings, about 300 thousand residents were left homeless. According to the governor of the Lebanese capital, Marwan Abboud, the damage from the explosion is estimated at between three and five billion dollars. Pictures from space of the port of Beirut, taken before and after the tragedy, show an area of continuous destruction around the entire port area. Three days of mourning has been declared in Lebanon.
What is ammonium nitrate
Ammonium nitrate, or ammonium nitrate, is an ammonium salt of nitric acid, has the chemical formula NH₄NO₃ and consists of three chemical elements - nitrogen, hydrogen and oxygen. The high nitrogen content (about a third by weight) in a form readily assimilable by plants makes it possible to widely use ammonium nitrate as an effective nitrogen fertilizer in agriculture. In this capacity, ammonium nitrate is used both in pure form and as part of other complex fertilizers. The bulk of the saltpeter produced in the world is used precisely in this capacity. Physically, ammonium nitrate is a white crystalline substance, in industrial form in the form of granules of various sizes. It is hygroscopic, that is, it absorbs moisture well from the atmosphere; during storage has a tendency to caking, the formation of large dense masses. Therefore, it is stored and transported not in the form of a solid bulk mass, but in dense and durable bags that do not allow the formation of large caked masses that are difficult to loosen.
Ammonium nitrate is a strong oxidizing agent. The three oxygen atoms that make up its molecule make up 60 percent of the mass. In other words, ammonium nitrate is more than half oxygen, which is easily released from its molecule when heated. Thermal decomposition of nitrate occurs in two main forms: at temperatures below 200 degrees, it decomposes into nitrogen oxide and water, and at temperatures of about 350 degrees and above, free nitrogen and free oxygen are formed simultaneously with water. This separates ammonium nitrate into the category of strong oxidants and predetermined its use in the production of various explosives, which require an oxidizing agent.
Ammonium nitrate - a component of industrial explosives
Ammonium nitrate is included in many types of industrial explosives and is widely used in this, mainly in the mining industry. Man has not yet invented anything more effective than an explosion to destroy rocks. Therefore, almost any work with them is based on an explosion: from mining in mines to open cuts and quarrying. The mining industry consumes a huge amount of explosives, and every mining enterprise or coal mine always has its own plant for the production of explosives, which are consumed in large quantities. The relative cheapness of ammonium nitrate makes it possible to use it for the mass production of various industrial explosives.
And here we can note the amazing breadth of the formation of explosive systems by ammonium nitrate. By mixing nitrate with literally any combustible substance, you can get an explosive system. Mixtures of nitrate with ordinary aluminum powder form ammonals, which are therefore called - AMMONIUM nitrate - ALUMINUM. 80% of the mass of ammonal is ammonium nitrate. Ammonals are very effective, they are good at blasting rocks, certain varieties are called rock ammonals.
If you impregnate nitrate with diesel fuel, you get another class of industrial explosives - igdanites, named after the Institute of Mining, the Institute of Mining of the Academy of Sciences of the USSR. Saltpeter is capable of forming explosive mixtures when impregnated with practically any flammable liquid, from vegetable oil to fuel oil. Other classes of nitrate-based explosives use additives of various explosives: for example, ammonites (these are not only fossil cephalopods) contain TNT or RDX. In its pure form, ammonium nitrate is also explosive and can detonate. But its detonation is different from the detonation of industrial or military explosives. What exactly? Let us briefly recall what detonation is and how it differs from ordinary combustion.
What is detonation
In order for combustion reactions to begin in combustible substances, the atoms of the fuel and oxidizer must be made free and brought closer together until chemical bonds are formed between them. To release them from the molecules in which they are contained means to destroy these molecules: this does the heating of the molecules to the temperature of their decomposition. And the same heating brings together the atoms of the fuel and the oxidizer to the formation of a chemical bond between them - to a chemical reaction.
In normal combustion - called deflagration - the reactants are heated by normal heat transfer from the flame front. The flame heats the layers of the combustible substance, and under the influence of this heating, the substances decompose before the chemical reactions of combustion begin. The detonation mechanism is different. In it, the substance is heated before the start of chemical reactions due to mechanical compression of a high degree - as you know, under strong compression, a substance heats up. Such compression gives a shock wave passing through the detonating piece of explosive (or simply volume, if a liquid, gas mixture or multiphase system detonates: for example, a suspension of coal in air). The shock wave compresses and heats the substance, causes chemical reactions in it with the release of a large amount of heat and is itself fed by this reaction energy released directly into it.
And here the detonation velocity is very important - that is, the velocity of the shock wave passing through the substance. The larger it is, the more powerful the explosive, the explosive action. For industrial and military explosives, the detonation speed is several kilometers per second - from about 5 km / sec for ammonals and ammonites and 6-7 km / sec for TNT to 8 km / sec for RDX and 9 km / sec for HMX. The faster the detonation, the higher the energy density in the shock wave, the stronger its destructive effect when it leaves the boundaries of the piece of explosive. If the shock wave exceeds the speed of sound in the material, it crushes it into pieces - this is called blasting action. It is it that breaks the body of a grenade, a projectile and a bomb into fragments, crushes rocks around a borehole or borehole filled with explosives. With distance from a piece of explosives, the power and speed of the shock wave decrease, and from a certain short distance it can no longer crush the surrounding substance, but can act on it with its pressure, push, crumple, disperse, throw, throw. Such pressing, crushing and throwing action is called high-explosive.
Features of detonation of nitrate
Industrial ammonium nitrate without any additives that form explosives, as we have already noted above, can also detonate.Its detonation speed, in contrast to industrial explosives, is relatively low: about 1.5-2.5 km / sec. The spread of detonation velocity depends on many factors: in the form of which granules the saltpeter is, how tightly they are compressed, what is the current moisture content of the saltpeter and many others. Therefore, saltpeter does not form a blasting action - it does not crush surrounding materials. But the high-explosive effect of detonation of nitrate produces quite tangible. And the power of a particular detonation depends on its quantity. With large explosive masses, the high-explosive effect of the explosion can reach destructiveness of any level.
Speaking about detonation, we note another important point - how it starts. Indeed, in order for a shock wave of compression to go through the explosives, it must be launched somehow, created with something. Simply igniting a piece of explosive does not provide the mechanical compression required to initiate detonation. So, on small pieces of TNT, set on fire with a match, it is quite possible to boil tea in a mug - they burn with a characteristic hiss, sometimes smoke, but burn quietly and without an explosion. (The description is not a recommendation for making tea! It is still dangerous if the pieces are large or contaminated.) To trigger the detonation, you need a detonator - a small device with a special explosive charge inserted into the main body of explosives. The explosion of the detonator, tightly inserted into the main charge, launches a shock wave and detonation in it.
What could have caused the detonation
Can detonation occur spontaneously? Maybe: ordinary combustion can turn into detonation when it is accelerated, with an increase in the intensity of this combustion. If you ignite a mixture of oxygen with hydrogen - an explosive gas - then it will start to burn quietly, but as the flame front accelerates, the combustion will turn into detonation. Combustion of multiphase gas systems such as all sorts of suspensions and aerosols, which is used in ammunition for a volumetric explosion, quickly turns into detonation. Combustion of propellant can also turn into detonation if the pressure in the engine begins to rise rapidly, in an off-design manner. An increase in pressure, acceleration of combustion - these are the prerequisites for the transition from ordinary combustion to detonation.
Also, combustion catalysts can be various additives, contaminants, impurities - more precisely, they or their components, which will contribute to the local transition to detonation. Oxidized, rusty ammunition is more likely to detonate if the explosive is adjacent to the oxidized section of the hull. There are many nuances and points in the initiation of detonation that we will omit, so let's return to the question: how could the saltpeter detonate in the warehouse?
And here it is obvious that pyrotechnics could perfectly play the role of a detonator. No, just a hissing powder racket hardly caused the detonation of saltpeter with its force of smoke with sparks. But the video captures numerous massive flares, sparkling in the smoke of the fire before the saltpeter explosion. These are small explosions of a scatter of fireworks pyrotechnic components. They served as an obvious detonating start. No, they were not industrial detonators. But in the conditions of a fire, heating of large surfaces of nitrate with a flame and the massiveness of thousands of pyrotechnic operations that occur, these pyrotechnic missiles were probably introduced into the heated surface of nitrate with further explosions in hot nitrate. At some point, its detonation under such an impact occurred - and spread to the entire array of stored saltpeter.
It is difficult to analyze further events in detail without detailed information and study of the explosion site. It is not known how fully all 2750 tons were detonated. Detonation is not some kind of absolute beginning that always happens as it is written on paper. It happens that the TNT briquettes stacked together do not detonate all: some of them simply scatter to the sides, if reliable measures are not taken to transfer the detonation between them.After massive explosions of rocks, when hundreds and thousands of wells filled with explosives are blown up (they can be equipped with explosives for a whole month), after a cloud of dust settles, only specialists first always enter the explosion zone and inspect what exploded and what did not explode. They also collect unexploded explosives. So it is with saltpeter in a warehouse in the port of Beirut: the completeness of detonation of the explosion of the entire mass of nitrate is difficult to determine, but it is clear that it was quite large.
Features of the explosion in Beirut
The very picture of the explosion corresponds well to the detonation of saltpeter. A large column of reddish-brown smoke after the explosion is a typical color of the cloud with red nitrogen oxides, which are released in large quantities during the decomposition of nitrate in the explosion. Due to the low detonation velocity of nitrate, there was no massive crushing action. Therefore, a large crater did not form at the site of the explosion: the materials of the piers and the concrete ground cover of the warehouses were not detailed, therefore they were not thrown away. Due to this, there was no bombardment of the city with pieces flying out from the area of the explosion, and the high sultan of flying pieces and fragments formed by the explosion did not rise above the place of the explosion.
At the same time, the abundant release of gaseous combustion products - water vapor, nitrogen oxides - gave the picture of the explosion the features of a volumetric explosion. In addition to a rapidly passing shock wave, powerful enough and visible as a fast foggy wall, the shooting shows an approaching wall of expanding explosion gases mixed with dust and billowing up from the surface of the earth at a rapid approach. This is typical for explosions of large volumes with a low detonation velocity. The nature of the damage to buildings with a high probability will show that they were affected not only by the shock wave itself - powerful, but short-term - but also a longer exposure to the expanding gas-air flow scattered from the explosion area.
Nitrate explosions to Beirut
Explosions of fertilizers based on nitric acid salts have occurred before, they are well known, there are a lot of such cases in history. So, on September 1, 2001 in Toulouse, at the fertilizer plant of the Grande Paroisse company, a hangar exploded, in which 300 tons of ammonium nitrate were detonated. About 30 people died, thousands were injured. Many buildings in Toulouse were damaged.
Earlier, on April 16, 1947, there was an explosion of 2,100 tons of ammonium nitrate aboard the ship "Grancan" in the port of Texas City, USA. It was preceded by a fire on the ship - a similar situation and sequence of events. The explosion caused fires and explosions on ships and oil storage facilities nearby. About 600 people were killed, hundreds were missing, more than five thousand were injured.
On September 21, 1921, 12 thousand tons of a mixture of ammonium sulfate and ammonium nitrate exploded at the BASF chemical plant near the town of Oppau in Bavaria. An explosion of such power formed a huge crater, two nearest villages were wiped off the face of the earth, and the city of Oppau was destroyed.
Catastrophic explosions of ammonium nitrate with great destruction and numerous victims occurred in 2004 in the North Korean city of Ryongcheon; in 2013 in the city of West in Texas, USA; in 2015 in the port city of Tianjin in China. And the list goes on. Unfortunately, ammonium nitrate, with all the huge advantages that it brings to a person, remains a dangerous object that requires compliance with a number of safety requirements in handling. And carelessness or negligence can cause new tragedies, the prevention of which requires both toughening the rules for handling saltpeter and increasing responsibility for their observance and implementation.