The Physics of the Fireball

The Physics of the Fireball

Let me start off by saying that these questions are purely hypothetical. I am asking the questions “why” and “what if” not as if I’m saying the rules and descriptions provided by the game are wrong. D&D (as well as all RPGs) is set in a fictional world of magic and the real world rules of physics do not apply. The physics of the D&D world is magic. It is based on a set of rules written by a team of developers, not science.

The RAW are just that, rules as written. If you don’t like them, you can change them. Almost every game has house rules, as the DM and the players decide they want to do something a little different that what the rules dictate… and there is nothing wrong with that.

Art Credit - PHB, 5th Edition, WotC

Art Credit - PHB, 5th Edition, WotC

These musings are just random things I think about when reading something in one of the hardcovers. They are meant to stimulate debate, not argument. I am surely not saying there is a right or wrong answer, because one person’s answer may not be the same as someone else’s. And guess what… they are both right.

The Fireball

We all know the fireball, also known as the wizard’s favorite spell of all time. I understand that it is magical fire and doesn’t have to conform to any of the rules of fire in the real world. That said, it sure seems like they go out of the way to make the fire as ‘real’ as it could be. It goes around corners, ignites flammable objects, and hurts a whole hell of a lot. This magic fire sure does look and feel like plain old regular fire to me.

The 5th edition spell description is as follows:

A bright streak flashes from your pointing finger to a point you choose within range and then blossoms with a low roar into an explosion of flame. Each creature in a 20-foot-radius sphere centered on that point must make a Dexterity saving throw. A target takes 8d6 fire damage on a failed save, or half as much damage on a successful one. The fire spreads around corners. It ignites flammable objects in the area that aren’t being worn or carried.

The description has been modified throughout the editions, but the basics remain the same. A big ball of fire explodes in a spot of your choosing. But the wording got me thinking about some things…

Bat Shit

Why do we still have bat guano as a material component? They’ve had over five chances between all the editions to change the material components into something else, and yet here we are in 5th edition still having to have a little piece of poo in your component bag. Sulfur makes total sense when you want to make things go boom, so I looked up bat guano to see if I could find out why it’s still a material component.

Turns out that bat poo is rich in nitrogen and can be used as gunpowder in its dried form. So now we have two material components that are used in the real world and the fantasy world to produce an explosion since bat guano and sulfur together would make an even bigger boom than one by itself. Still not sure why we don’t just use gunpowder, but at least now I understand how guano plays a role in the creation of a fireball.

Going BOOM - Explosions

I started by looking up the word fireball for a real world definition.

Fire Ball: Unconfined accidental fuel gas releases often result in a fireball once ignited. However, if the gas mixture is unconfined or if confinement is breached, the burning gas expands as a fireball at normal atmospheric pressure, and the maximum fireball volume is approximately ten times the initial volume of the mixture.
"Fire Protection Handbook’, 18th Edition (1997), p. 1-75, National Fire Protection Association, Quincy, MA.

Fireball: A large mass of fire caused by a large explosion, as of inflammable liquids or a nuclear device. The larger fireballs, as of nuclear explosions, rise seemingly intact into the air and may reach high altitudes while still glowing.
Gcide, Online Definintion.

Fireball: A bright ball of fire, especially one at the centre of an explosion.
Oxford Advanced Learner’s Dictionary.

No gas involved in the D&D fireball so that’s out. Nuclear explosions are fairly rare in D&D, much to the disappointment of players. The dictionary definition doesn’t provide us with anything useful. It’s the word explosion, which is in all three definitions and the 5e description that caught my eye. The word explosion then leads me to my biggest question - If a fireball involves an explosion, why is there no concussive wave blast?

Next, I researched with the word explodes (or explosion). The definition of explosion varies, but here are a couple of the examples I found:

Explosion: A large-scale, rapid, or spectacular expansion or bursting out or forth
Merriam Webster Dictionary

Explosion: The sudden conversion of potential energy (chemical or mechanical) into kinetic energy with the production and release of gases under pressure, or the release of gas under pressure. These high-pressure gases then do mechanical work such as moving, changing, or shattering nearby materials.
NFPA-921, 1998 Edition

Explosion: An explosion may be defined as a phenomenon where a blast (pressure or shock) wave is generated in air by a rapid release of energy. This energy may have originally been stored in the system in a variety of forms (e.g., nuclear, chemical, electrical, or pressure energy). To be considered explosive, the release of energy must be rapid enough and concentrated enough to produce a pressure wave that can be heard. The resulting blast wave is largely responsible for the damage that was caused (Ref. 84). Buildings may be damaged and people may be injured by the blast wave, with additional indirect effects from missile generation, crater formation, ground shock, and fire.
Center for Chemical Process Safety Copyright © 1996 American Institute of Chemical Engineers

Explosion: A loud boom and then things suddenly go away quickly from where they had just been.

Every definition above involves things being pushed, knocked or blown back very quickly from the center of the explosion. Since we’ve determined that the fireball involves “chemical” components (the bat poo and the sulfur), the spell-caster is using them to create an explosive device that they can shoot from their person using magic. (I can’t stress enough that I know this is a fantasy world, and the laws of magic don’t have to line up with the laws of physics as we know them.)

We all have our own mental image of what a fireball would look like, but I’m pretty sure the general image is the same… a streak of light that, when it reaches its destination, expands (or one could say explodes) into a giant ball of fire. So why isn’t there a force wave that knocks players back?

Blast Waves - Why am I still standing when I get hit in the face by a Fireball?

From Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs by Center for Chemical Process Safety Copyright © 1994 American Institute of Chemical Engineers:

Direct, Primary Effects
The main direct, primary effect to humans from an explosion is the sudden increase in pressure that occurs as a blast wave passes. It can cause injury to pressure sensitive human organs, such as ears and lungs.

Indirect Effect
The explosion wind following a blast can carry persons away, causing injury as a result of their falling, tumbling over, or colliding with obstacles. This effect is referred to as a tertiary effect. Effects are described, together with criteria to calculate the probable degree of lethality.

Tertiary Effects
Air particles in a blast wave have a certain velocity which, in general, flow in the same direction as the propagation of the blast wave. This explosion wind can sweep people away, carry them for some distance, and throw them against obstacles. Upright people are most vulnerable (Figure C-2B). No lethal injuries are likely to be incurred as a person tumbles and slides along the surface, but upon collision with an obstacle, consequences may be deadly. Such consequences depend upon velocity at impact, the hardness and shape of the obstacle, and the portion of the body involved in the collision. Table C-2 gives injury criteria. (references Bowen, J. G., E. R. Fletcher, and D. R. Richmond. 1968. Estimate of man’s tolerance to the direct effects of air blast. Lovelace Foundation for Medical Education and Research. Albuquerque, NM.)

The simplest picture regarding a Blast Wave

The simplest picture regarding a Blast Wave

When researching how an explosion generates a concussive blast or blast wave, my head started to hurt. The physics behind how it works is beyond my high school physics understanding (I got a D+ by the way). In Fluid dynamics, a blast wave is the increased pressure and flow resulting from deposition of a large amount of energy in a small very localized volume.

Ummm… ok then.

Basically what that means is an explosion will generate a really fast and powerful wave of energy that will fuck up everything caught in it. It will cause damage to objects and people by the blast wind. The closer you are to the center of the blast, the more damage will be inflicted. The blast wave decreases in force the farther away from the center it moves.

Since we determined that the fireball is an explosion, and that the fireball starts as a streak of light that blossoms outward, it should have a blast wave along with it.

Now What?

Let’s say you are in the blast radius. What effects from the blast wave created from a fireball might one need to figure out?

  • If a player takes a direct hit if they are disintegrated or not.

  • Character conditions based on distance from the center.

  • Force damage from the blast, again, based on distance from center.

  • Effects on nature and surrounding structures.

I may have started to attempt all of the above (and more). I also have made someone else at Dump Stat, that shall remain nameless, very angry when I tried to write out those rules for just the character conditions. Stepping back and looking at it from the DM perspective as he was (again, not naming names), it was a total clusterfuck and he has very reason to want to strangle me. One fireball could take half a session to figure out. I had stripped away the fun of a fireball by adding physics, forgetting that we were in a fictional world of magic.

Instead, I created some fun force damage spells based on the fireball. Take a look and let me know your thoughts. In the end, I am going to go with the simple answer that a fireball is simply “a ball of fire”. That works for me.

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