As millions watched in horror across the globe, a massive explosion ripped through downtown Beirut on August 4th, 2020. The explosion was massive and it took place at the Beirut port. The place of the explosion was submerged underwater after the incident. The explosion was so loud that it was heard more than 100 kilometres away in Cyprus. Buildings were shattered, dozens of people were killed, thousands were injured and the internet was littered with videos of wedding festivities being disrupted by the blast. There were also many pictures of Beirut citizens standing over a pile of rubble which once used to be their home/workspace. The world is rife with speculation about what might have caused the blast but the most widely agreed reason is an accidental ignition. There are explosions in history that resembled the massive fireball of Beirut. The more mundane explosions are rarely this size, but the same principles of physics and chemistry apply. In this post, we will take a look at the physics and chemistry behind the massive explosion and compare it to previous massive explosions in cities (which were not caused by some kind of wartime bombardment. Let’s get started.
Beirut Explosion 2020: The Explosive Facts Behind the Fireball That Ravaged the City
Did an explosion like Beirut happen before?
In 1917, an accidental detonation of 6 million pounds of a mix of explosives in the harbor of Halifax, Nova Scotia, left a swath of wreckage that, at least until August 4th, 2020, was the largest non-nuclear explosion ever created by humanity. As we learn more about Beirut, which could possibly challenge that record, the story of Halifax tells us what we might expect to learn about the ensuing trauma, and the modern cell phone videos, along with the blast physics gleaned by scientists in the intervening century, tell us why those patterns of trauma occurred in quite the way they did.
What makes Ammonium Nitrate so explosive?
Every fire is a rearrangement of molecules, and an explosion is basically a fire turbocharged into a hyper-energy-fueled frenzy. Unstable structures barter and swap atoms with one another until all of them, happy with their trades, blissfully settle into more relaxed, lower-energy states, like rocks reaching the bottom of a hill. But their excess energy has to go somewhere. In a campfire, where the chemical reactions are facilitated in a leisurely way by the oxygen in the air alone, energy is released slowly as enjoyable levels of heat and light. In an explosion, however, the devilish little instigator that is oxygen shoves the process into overdrive.
Preliminary blast reports hinted at the fact that the building that ignited the explosion was storing massive quantities of ammonium nitrate. It’s a highly flammable chemical that is generally used as a fertilizer. However, experiments have also been conducted to use it as rocket fuel. Oxygen is the key to ammonium nitrate’s deadly habit of exploding, and given that 47 known, major, accidental ammonium nitrate explosions have occurred in the last century, it is undeniably a habit. “Ammonium” is a nitrogen atom with four hydrogens, written NH4+, whereas the “nitrate” part of the mix is nitrogen with three oxygens, NO3-. Under boring everyday conditions, the + of the ammonium and the – of the nitrate pull the two molecules into a harmless hug, but when you add a spark—or a firework—the molecules realize that their very atoms can get a little friskier and convert into something completely new.
When ammonium nitrate is manufactured as fertilizer, it is mixed with other chemicals that usually stop this reaction from happening, though as the 2013 explosion at the West Fertilizer Company proved, those chemicals are not always successful. The first reports out of Beirut suggested fertilizer may have once again been the culprit. However, photos shared on social media showed bags marked “Nitroprill HD” supposedly being stored at the Beirut pier, and some have speculated that if those photos are accurate, Nitroprill may be a knockoff of the name-brand blasting agent Nitropril. Nitropril is designed for use in coal mines, so this particular breed of ammonium nitrate would not have been mixed with quieting chemicals like a fertilizer would be; rather, it would have been mixed to blow.
And nitrate, when mixed to blow, wants to ditch those little Os. It’s chemically unstable, meaning the bonds between the Ns and the Os vibrate with an unhappy level of physical tension. Overloaded with three oxygens, NO3- is eager to shove some onto any neighbor, and with a little bit of heat to get things moving, it will do so willingly. NH4+ is all too happy to accept.
What gave the Beirut explosion its colour?
The chemical rearrangement of ammonium nitrate answers a lot of the public questions about the videos, including the source of the startling red color of the plume. One of the byproducts of NO3- as it sheds all that oxygen is nitrogen dioxide, which has a logically obvious chemical structure of NO2 and looks deep, blood red. Many explosive materials give off tints and hues during a blast that suggest their chemical composition—chemical additives to color both smoke and explosions have been around since before the 1920s and are how we get different-colored fireworks and signaling flares—and it’s nitrogen dioxide that gives an ammonium nitrate explosion its signature, ominous blood-like tone. A small blast can look subtle and orange-ish, but on a large scale like at Beirut, the sunlight helps deepen its hue.
According to Brad Wojtylak, a special agent bomb technician and certified explosive specialist with the Bureau of Alcohol, Tobacco, Firearms, and Explosives, when smoke plumes are large enough, they begin to catch the sunlight, and refraction will darken the normal colors produced by any explosion. Wojtylak is not directly involved in the Beirut investigation but has 16 years of experience investigating blast accidents. He says as sunlight bounces around within the cloud of contaminants, other, less determined wavelengths get refracted off in different directions. When a smoke plume happens on such a large scale, only the longest wavelengths, the red shades, persevere all the way through to the viewer on the other side. So, the natural reddish color becomes even deeper, richer, darker than it would be for a small blast.
What does the smoke indicate?
An explosive with a pure burn, like any explosive used in military-grade weaponry, will produce smoke that looks equally pure: snowy, billowy white, or sometimes a pale grey. But accidental explosions are far less tidy, and their sloppy combustion also produces ash, particulates, and gross black charred contaminated matter. This black gunk billows into the sky along with the other byproducts, coloring the smoke plume, like the charcoal residue left behind after the more efficient parts of the campfire wood have burned away. To a blast expert, the videos, with their roiling cloud of black and red curling over the pier of Beirut, scream “ammonium nitrate.”
Did the Beirut Explosion produce a shock wave?
The videos also show an unnervingly uniform hemisphere of white propagating outward from the blast site, a dome of vicious vapor that eventually hurtles toward every person filming and announces its arrival in the audio with a crash. This hemisphere is the pressure wave produced by the explosion.
No, it’s not a shock wave. It’s a pressure wave, and that key difference affects the number of casualties expected. A shock wave goes from zero pressure to its absolute maximum pressure in almost no time at all. The impact of a pressure wave is like hitting the ground after rolling down a steep cliff; the force of a shock wave is like hitting the ground after falling through the air and reaching terminal velocity. High explosives produce shock waves; low explosives, like ammonium nitrate, produce pressure waves, which have a bit of slope to their shape, a period of time over which the pressure increases more gradually.
Shocks, because of their fascinating and complex physics, travel faster than the speed of sound, and they cause far more damage than pressure waves. Thankfully, we know this blast did not produce a shock because the speed of the water-vapor-filled white dome can be measured.
Sound travels through air at a speed of 343 meters per second. By measuring the times at which the pressure wave reaches these landmarks on the video, we know that, as it blazed down the pier, its rampage occurred at a speed of only 312 meters per second. That’s slow for a bomb. Then by the time the audible crash and mayhem reached the formerly peaceful and picturesque outdoor bar, it had slowed to at most 289 meters per second. The pressure wave, slower than the 343 meters per second speed of sound, caused destruction, horror, confusion, shattered glass, torn-apart flat surfaces, and disorientation for onlookers as their ears were subjected to the rapid pressure fluctuations. But a shock wave could have caused them to drop dead from lung trauma as they watched. The journalist in this video would probably not have survived if it were a shock wave.
What have the survivors said about the Beirut Explosion 2020?
Here are the accounts of some of the survivors of the Beirut Explosion 2020:
Hasan Homsi, 55, food cart owner
“I was at my sister’s house in the Ras El Nabeh neighbourhood, drinking coffee. We heard the explosion; the sound was crazy loud. The glass broke immediately and we saw the dead and wounded on the ground. I’ve been through the entire Lebanese war so it was normal; it felt like I was back. The smell of blood is still in my clothes from helping the wounded. I’m so sad, so sorry for these poor people.”
Miriam Shami, 27, dance teacher and fashion designer
“I had finished practice and was driving out of Beirut with three friends. I told them to put their face masks on because I thought there was a checkpoint checking for masks. Then we got to a traffic light at the exit of Beirut. We saw smoke. I was sending a voice note to my friend Raymond, the first blast hit and I said ‘Oh Mary!’ The second blast knocked the phone from my hand, I closed my ears and saw a car fly over from the other side. I panicked and tried to keep driving because I thought we were being shelled, but then my brain recalibrated and I knew it was from the fire. Thank god I was fine, though emotionally … I already knew I didn’t want to live here and of course now I don’t have a single percent of hope.”
Ali Sheikh, 20, works at a family cafe
“I was at the cafe with my dad and brother, but there was no one there due to the economic situation. There was a quake and we said, ‘Fine, that’s a quake, it will pass.’ Then suddenly the glass fell on us, the TV flew and all our cups broke. And my dad was hurt. I thought the explosion was right in front of my cafe – all of us did, it was so powerful. We went home to a house full of broken glass.”
Beirut Explosion 2020: The Aftermath
It’s important to remember that even before the deadly explosion happened, Lebanon was struggling badly. The country’s corrupt government had reduced the once prosperous country into a lawless land of chaos. Beirut, which was once known as “Paris of the East” had become a shell of its former shelf. People had major restrictions when it came to simple things such as withdrawing money from the ATM. Add the COVID-19 crisis and it points to a really sad state of affairs in the country. While the country was dealing with all of that, this massive explosion damaged the place in an almost unthinkable fashion. Almost 80% of the country’s food grain reserves have been wiped away. The infrastructural damage is still being calculated but it’s expected to be massive. The Lebanese people decided that they have had enough and started protesting. When French President Emmanuel Macron visited Beirut, locals urged him to rescue the country as they didn’t trust their own corrupt government. As of this article’s publication, The Lebanese Government, led by Prime Minister Hassan Diab has resigned from its position. While many Lebanese people might be thrilled to see these people go, it makes the future of the country even more uncertain. Let’s just hope for the best.