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My PHD Focus's specifically on the interaction of Blast shock waves and Skeletal Muscle. I've spent some time looking at the pictures and videos coming out of Beirut. Here is a few thoughts on why that explosion is particularly devastating.
Ammonium Nitrate - A high nitrogen fertiliser - accounts of 80% of explosive used in North America - and is used commonly in Improvised Explosive Devices.
Why is it so explosive?
At low temperatures (<200Degrees), the compound decomposes to Nitrous Oxide and water.
Why is it so explosive?
At low temperatures (<200Degrees), the compound decomposes to Nitrous Oxide and water.
However. At Higher temperatures you get a runaway reaction - where an increase temperature leads to further increased in temperature in a spiral fashion. The ammonium nitrate decomposes into nitrogen, oxygen and water.
On its own its not an explosive - you need to mix it with...
On its own its not an explosive - you need to mix it with...
An Azide or Fuel Oil (Hence ANFO). These are the detonation component in order to get it to .. Explode. Ammonium Nitrate is cheap, hence its popularity as an Explosive. It is a major fire risk as it supports oxidation.
2750 Tonnes of Ammonium Nitrate is a LOT. Scientists/People/Ordnance Experts (Ordnance is there term used to describe explosive material) often describe explosive quantity in TNT (Trinitrotoluene) eqiuvelant.
Its around 1,500 tonnes of TNT.
As a comparison..
Its around 1,500 tonnes of TNT.
As a comparison..
On 5 April 1958, an underwater mountain was levelled by the explosion of 1,375 tonnes of Nitramex2H, an ammonium nitrate-based explosive. This was the first live broadcast of an explosive event also!
Shock to detonation is not the only way you can ignite Ammonium nitrate though. If you have a well contained fire - deflagration to detonation can occur.
what's Deflagration I hear you cry? That is when you heat a substance until it burns away rapidly i.e Low order explosives.
what's Deflagration I hear you cry? That is when you heat a substance until it burns away rapidly i.e Low order explosives.
detonation on the other hand is when combustion occurs very rapidly and induces a shock wave. Thats what was seen in Beirut. Whether it deflagrated first and THEN detonated will remain to be seen from forensic fire experts.
On a wide note - Low Order Explosives are those that have a subsonic explosion - and thus deflagrate .
High Order Explosives on the other hand Detonate with a shock wave...
High Order Explosives on the other hand Detonate with a shock wave...
But why is this so devastating? Those who have done any reading on Blast will come across the Primary/Secondary/Tertiary/Quaternary blast injury terminology coined in the 1960's. This refers to whether you were injured by the explosion itself (Primary), the blast wind...
Primary Blast - This refers to injury from the explosion itself, and the shock wave.
Secondary Blast - Refers to injury from debris picked up by the Blast Wind (more on that in a second)
Tertiary Blast Injury - From being picked up by the blast and thrown against something
Secondary Blast - Refers to injury from debris picked up by the Blast Wind (more on that in a second)
Tertiary Blast Injury - From being picked up by the blast and thrown against something
Quaternary - As a result of thermal injury/ burns from the explosion
The Blast wind results from the pressure difference at the shock wave front, the change from a high pressure zone to a low pressure area behind the shock front results in the production of a wind.
The Blast wind results from the pressure difference at the shock wave front, the change from a high pressure zone to a low pressure area behind the shock front results in the production of a wind.
This picks stuff up and turns it into a projectile. Dust, Stones, Glass for instance.
This is one of the problems with Blast.
The Other is the Shock Wave which is produced when High Order Explosives Detonate.
This is one of the problems with Blast.
The Other is the Shock Wave which is produced when High Order Explosives Detonate.
Shock Waves are strong pressure wavs in elastic medium travelling faster than the speed of sound (300m/s). They are used therapeutically to break kidney stones for instance.
They have interesting properties...
They have interesting properties...
Where the explosion happens - in the air, in the ground, and thus what medium the shock wave travels through - affect its energy and how it interacts with structures. The majority of research on blast concentrates on air blast shock waves. - as those are the most straightforward
In the case of an air shock wave produced from a detonation just above the ground - the shock wave will travel outwards through the air, and may hit the ground relatively quickly. When it does so it will reflect on itself. Such reflections..
can result in an increase in the shock wave energy - up to 8x. Furthermore reflected shock waves travel faster when reflected in themselves than in air. So you can imagine some interesting phenomenon when shock waves start reflecting in built up areas. One such phenomenon is
Mach Stem ( mach being the speed relative to the speed of sound - so Mach 2 is 2 x speed of sound). So in an 'open field' (no buildings), the shock wave will move equally outwards in a uniform fashion. In a closed field - with buildings - wave reflection will take place...
If the shock wave is now reflecting off buildings, with net energy increases, the potential damage to tissue can be significant. Combined with the debris in the blast wind (Glass for example), the injury complexity will be significant. I haven't even begun to discuss...
The potential for blast neurotrauma (brain injury) or the effects on structures such as the Gut, or the lungs. Hence these patients will have Soft tissue, Bone as well as respiratory, gut and brain sequelae. These patients will need multidisciplinary care....
Papers from experience in Afghanistan and Iraq - published by learned colleagues @PlasticSurg_DE @MilOrthoTrauma @DMS_MilMed to name but a few, highlight how these injuries are often deeply contaminated by debris (sand etc), unstable,
That require numerous trips to theatre for debridement, before you can event start on closing their wounds. So the dressing requirements and nursing care is also big. They need joined up co-ordination between specialist nurses, intensivists, surgeons etc
@markfoster182 demonstrated in his Phd that these patients have a significant Systemic inflammatory response, and thus find it difficult to fight infection. He also showed that their care requirements in terms of cost are ENORMOUS.
So in summary, a significant amount of High Order explosive that detonates in a built up area produces a large shock wave that reflects off buildings - produces a lot of debris and will result in a large number of complex casualties in an over stretched healthcare system...