Comparing the Biggest Explosions - Conventional vs Nuclear vs Accidents Transcript, AI Summary & Key Points

00:04 Hello, it's Scott Manley here. On May 28th, Blue Origin's New Glenn rocket was sitting on the pad fully fueled with methane and liquid oxygen running a static fire test. Almost immediately in, something went catastrophically wrong. The whole vehicle vanished inside an enormous bright orange multi-lobed fireball that lit up the Florida sky. A powerful pressure wave rolled out, shook houses, shattered windows, and one of the lightning towers collapsed.

00:30 The pad took a beating, but thankfully, no one was hurt because they were following proper range safety rules. Now, early on in the analysis of this, we made a rough estimate that this explosion was probably equivalent to about a kiloton of TNT. That wasn't hugely scientific. We knew that the fuel load likely had the energy content of more than 3 kilotons, but the actual explosion physics doesn't really match the detonation of 3,000 tons of TNT.

00:56 It was more chill, if you can believe that. I even produced comparison built uh videos showing it scaled alongside a 200-ton and a 2-kiloton nuclear test explosion. When we talk about the energy of an event like this, it's a shorthand to give us an idea of the scale of the energies involved, but the exact mechanics and effects change depending upon whether it's a rapidly burning mass of rocket fuel, high explosives, or a nuclear device.

01:26 The number tells us how much chemical or nuclear or kinetic energy is released, but it doesn't tell you how that energy turns into the blast, heat, light, radiation, or flying debris. And that's what I want to talk about today. So, yeah, we hear the kiloton of TNT equivalent, right? And the chemical energy contained in TNT is about 4.184 megajoules per kilogram, which by the way, is also 1,000 kcal or about half the recommended day dietary calorie intake for an adult.

02:00 My mind is blown, literally, by the fact that 1 g of TNT has the same energy as one dietary calorie. Don't eat explosives, by the way. So, anyway, 1 ton of TNT is about 4.2 gigajoules, and a kiloton is 4.2 terajoules. Now, for most explosions, the damage is caused by the blast wave, the overpressure that pushes against structures, crushing or even shattering them, depending upon how the pressure is generated and how quickly it rises and falls.

02:30 The area of effect of a blast wave follows cube root scaling. It's a volume effect. You need eight times bomb yield to double the radius of effect with the same pressure. But, that assumes the same type of event. Change the source of the blast and the area and the type and the effects all change. A 1-kiloton chemical high-explosive bomb, a 1-kiloton nuclear airburst, and a 1-kiloton rocket propellant explosion, and, you know, a 1-kiloton airburst from an asteroid like Chelyabinsk or whatever, might produce or will

03:04 produce rap vastly different damage patterns. This is because the underlying mechanisms are fundamentally different and distinct. Now, no matter the source, when a huge amount of energy suddenly appears in the air, it creates a small, insanely hot, higher-pressure region. That region expands violently and drives a shock front outwards, a near discontinuous jump in pressure, density, temperature, and air velocity.

03:31 They all change at the same time. Ahead is normal air, right behind is the blast wave. Now, the blast wave can actually be quantified in different ways. First of all, there's the peak static overpressure or delta P. That's the maximum extra pressure above normal atmosphere. Increase the pressure by 20% and windows break, 30% and uh houses start falling over and eardrums get ruptured.

03:53 Rapid increases of two to three atmospheres is where your lungs get seriously injured. Very high increases cause crushing and shattering. Then there's the dynamic pressure, the wind pressure from the fast-moving air behind the shock. This is often what what what throws people, overturns cars, and snaps trees. Then you have the impulse. That is the total push, right?

04:16 The area under the pressure versus time curve. This is basically the integrated pressure during the positive phase. A short, sharp spike can shatter windows, whereas a longer, lower push can push over the whole building. And then you have the positive phase duration, how long the overpressure lasts. Short for small chemical charges that can you know of the order of milliseconds, whereas this will be longer for large fireballs or distributed sources.

04:44 Longer duration usually means more effective impulse applied to things than the same for the same peak pressure. So even if we have the same amount of energy in a blast wave, the shape and by extension the effects of the blast wave can vary. And the blast wave effects can also be modified depending upon where the blast occurs relative to the surface, for example.

05:06 In notably in nuclear air blasts, the pressure wave that hits the surface reflects off and then interacts with other parts of the blast wave, and it creates what's called a Mach stem where these are interacting. And that's where the blast is twice as powerful. So anyway, let's discuss the mechanisms by all which all these explosions proceed. In your classic bomb, what you have is a block of energetic chemicals that are just ready to react.

05:34 Usually a carefully constructed molecule which breaks down and releases energy and hot gas. You start the reaction, you need to give it enough energy to to it going. And in the old days, you would just have a fuse that you would light one end and it would burn down until it touched the explosive and then the fire would burn rapidly in an explosion. But, modern safe explosives require a harder kick from a detonator that generates a mini shockwave and that's what drives it.

06:04 Either way, the explosion starts at a point and it burns outwards from there. The energy that's released in one spot is enough to drive the reaction in the material next to it. In that way, that means you can imagine the reaction moving through the explosive rapidly with the unreacted material ahead of it and the hot gas being produced behind it. And the speed at which this reaction front moves is important.

06:25 Old style black powder merely burns fast, but in high explosives like TNT, the reaction front moves beyond the speed of sound in the explosive and this supersonic explosion is what's called a detonation. So, the chemicals decompose and they generate hot gas, nitrogen, water vapor, CO2, and this locally increases the pressure. These hot gases expand and they generate a pressure wave, which will cause the damage.

06:55 And with high explosives, there's a measure which is sometimes referred to called a brisance. It's the ability of an explosive to shatter or crush material, to break rock, concrete, or steel into small fragments rather than just like pushing or heaving them. The word comes from the French word briser meaning to break or to shatter and it sort of entered the technical use in the 19th century as chemists and military engineers needed a way to describe the local destructive characteristics of explosions beyond just the

07:24 total energy or how much rock they could move. So, brisance is not the same as the total explosive power. An explosive can release a lot of energy, but it could still have relatively low brisance if the pressure is building slowly. Whereas, a high pressure or high-brisance event means an extremely rapid pressure increase, which can shatter things. So, yeah, high-brisance explosives are true high explosives.

07:52 They have very high detonation velocities. For example, 7 to 9 km/s, an extremely high detonation pressure. So, you're talking explosives like RDX, HMX, composition B, and to a lesser extent, TNT is in this group. They produce a sharp pressure spike with microsecond rise times. And this is what you want for things like shape charges or armor-piercing warheads and fragmentation music munitions.

08:20 Now, low-brisance explosives are where the detonation velocity is slower. It means more like pushing and more heaving effect. And examples are, well, your classic old-school black powders and also things like ammonium nitrate. These will tend to break rocks into larger pieces and move it rather than pulverize it, which is actually desirable in many kinds of operations.

08:42 So, now, let's switch over and talk about something that isn't supposed to explode, the rocket. Right, a rocket exploding on the pad, it's going to have the fuel in one tank and the oxidizer, and they're kept separate ideally until they reach the engines. Of course, that breaks down when the rocket breaks down. But that means that there's no simple combustion front moving through the propellant mixture.

09:03 While there's a lot of energy in that rocket, it can't be released without the propellants being mixed, and that slows down the explosion a lot. During the event like this, the energy of the explosion can help to mix the propellants and keep them make them burn, or it could scatter the fuel into the air, where that then burns with the oxygen in the atmosphere in the large fireball.

09:23 This can actually exceed the amount of available oxygen, and it can take some time for the fuel and the air to mix, resulting a slow, hot fireball that can rise like a mushroom cloud while still burning, taking away energy from ground zero. Or in cases like the Amos 6 explosion of a Falcon 9, a lot of the fuel end up spilling spilling into the flame trench and it continued to burn there for a long time.

09:46 And while that's not explosive energy, the sustained fire caused a lot of further damage. Now, while we're talking about fuel mixing with the air and burning, it is actually possible to build a specialized bomb which uses atmospheric oxygen with fuel. This is called a fuel-air explosive and they contain most of their mass as combustible material which gets mixed in with the air in a cloud which is then ignited.

10:10 This way you can fit more bang in your bomb, babe. But the detonation sequence is a carefully orchestrated series of events that ensure mixing of the fuel at the correct mixture ratios before the ignition is triggered. It's possible for this to happen by sheer bad luck in some accidents, but it generally doesn't happen. It has happened, for example, in flour mills where a cloud of flour in the air gets ignited by a spark or something and that creates a powerful blast.

10:38 It's also possible that this happened during the Starship serial number four failure where the fuel leaked for some time before an ignition source was found and we saw a very obvious shockwave heading away. So, what's critical to understand is that the faster the things happen, the sharper the pressure increase. And the faster the pressure increase, the more damage is likely to be caused by the blast.

11:04 Think about a wall that is standing freely, right? If the pressure rises slowly, then the air just flows around to the backside and it balances the pressure coming from the front side. But a rapid rise of pressure will push this over. Now, imagine a building which is enclosed. Like the doors are closed, the windows are closed. It's much harder for the air to flow in and out.

11:24 And even a slow rise in pressure can lead to a pressure differential between uh the inside and the outside that could break windows first or blow open doors. So again, a slow increase to a high peak pressure can still cause damage to structures depending upon their shape, their geometry, and how they're sealed. Another effect that is important is that explosions can cause damage by accelerating shrapnel, and that can cause damage to things that are resilient to the blast.

11:51 For example, a thin support cable offers very little cross-section to pressure and blast wave, but could easily be severed by say a chunk of a propellant tank thrown out by a rocket disintegrating. If you look at the aftermath of the Blue Origin explosion, you'll notice that one of the vertical legs on the tower that is standing is bent and broken, but the rest nearby are relatively straight.

12:13 And that's likely the result of a piece of shrapnel hitting that one leg, but not the others. So things that might stand up to the blast wave might still be damaged by things thrown around by the blast wave. Anyway, let's uh to take a look at the thermal effects, because those giant fireballs are what people think explosions look like thanks to movies, because movies want to make explosions look spectacular rather than realistic.

12:41 A high explosive blast is generally hotter than a fuel-air deflagration, but the higher pressures and expansion velocities result in it cooling rapidly. For all the heat at the moment of detonation in high explosives, they aren't good at starting fires. In fact, a common method for stopping an oil well fire uses high explosives to blow out the flame and starve it of oxygen with the inert combustion products.

13:07 A rocket exploding can be a big, slow fireball, and it will start more secondary fires. But now, how about nuclear explosions? Those are completely different, and they're they're really the place where we first heard the notion of equivalent yield. A nuclear explosion starts as a reaction in the fissile material at the core of a compressed fissile pit.

13:29 And this is in a region which is maybe the size of a grape. And that reaction, it accelerates from nothing to its peak and it dissipates in under a microsecond. The energy is released in the form of gamma rays, neutrons and alpha particles. And sure, some of that highly penetrating radiation just escapes the pit, travels through the casing into the atmosphere, but most of those alpha particles heat the pit and it's converted to a high-energy hot plasma.

13:56 So hot that it radiates x-rays, which transfer the heat energy outwards. The entire device and its casing is converted to a ball of intensely hot plasma. And this shines brightly in the x-rays. That ionizes the air around the bomb creating a fireball which expands, driven by this blackbody radiation which further ionizes the air. But quickly, the radiation-driven expansion stops and what we're left with is a hot fireball, which then transitions into a hydrodynamic expansion with the high pressures generated by the high

14:29 temperatures. And so the key thing to understand here is about 1/3 of the energy of a nuclear bomb comes out in the form of thermal radiation. About half of it comes out as a blast wave and the remaining portion is radiation in some form, either prompt or as fallout. So the blast from a 20-kiloton nuclear weapon will be less powerful than 20 kilotons of actual TNT if you're measuring the blast wave.

14:54 Not that we've ever actually had that amount of high explosives in one large pile. But the US did do experiments with large conventional explosions at a test range. Minor Scale was the largest. They built a 4,300-ton ANFO bomb. That's short for ammonium nitrate fuel oil and it's a common recipe for making car bombs. Ammonium nitrate is a common fertilizer and it can be made to detonate on its own given a hard enough kick.

15:21 If you add about 6% oil, that helps to balance out the chemistry and increase the energy density. The Beirut explosion was a warehouse full of ammonium nitrate that burned for a long time before that fire finally transitioned from a slow burn into a highly energetic detonation. A normal small detonator is actually too puny to make the ANFO detonate.

15:43 You actually need a bigger kick. Typically, what you do is you have a detonator that starts an explosion in a brick of high explosives, and that is then enough to start the detonation of the ANFO. I learned all this, by the way, when I was living in Northern Ireland. By talking to people in pubs, of course, right? Anyway, yeah, the minor scale test involved a large steel dome that was built for the test, and then it was detonated, right?

16:10 The footage is absolutely stunning. It's about equivalent to 4 kilotons of TNT. But remember, the blast wave is only half the energy, and the other effects can actually be important. For small nuclear weapons, the ionizing radiation is actually the most important effect if you're a human, right? A human can be far enough away that they'll be unaffected by the blast wave, but you could still get a lethal dose of radiation.

16:36 An extreme example of this is the Davy Crockett warhead, right? The nuclear bazooka. It had a yield of maybe 10 or 20 tons, and I'm not saying kilotons, tons. It was designed to be used against masses of tanks, and it it would be lethal within about a quarter mile, almost exclusively due to the radiation, which would kill the tank crews. At the other end of the scale, for large devices, there's the Tsar Bomba.

17:01 In that case, the thermal radiation is the dominant effect. It'll start fires far beyond the point where the blast wave is destructive. This transition between the cause of death is because the radiation is extremely lethal. I mean, think about the demon core incidents where a tiny nuclear reaction killed a scientist without any blast or heat. But, the radiation gets blocked by the air, so it fades faster.

17:29 Similarly, the blast wave, it loses energy to the air, but it goes a lot further. But, of course, the blast wave, it follows the inverse cube law for its decay, right? The thermal radiation, on the other hand, it follows the inverse square law. So, it fades less quickly. Uh in the atmosphere, there is some attenuation due to clouds and other stuff, so it's not a perfect inverse square law, but it still fades slowly enough that for the big bombs, the thermal effects are most important.

17:56 And, of course, beyond that, there are other effects. The The main thing to get here, it's not a simple linear relationship between the TNT equivalent yield and the destruction that is caused. So, explosions are complicated, and while we can measure the energy released, it's only a rough estimate of the effects. The same is also true of asteroid impacts. But, well, at this point, I think this video is long enough already. I'm Scott Manley. Fly safe. >> [music] [music]