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What's the proper method to calculate fictional explosions from non detonative fuels?

AguilaR101

AguilaR101

1,673
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I've come across a few different calcs that have some contradictory standards regarding on how they've been measured.

Here the energy density of fuels was used as means to dismiss the destructivity of a weapon claiming that the gasoline would result in building level explosions by chain reaction

Here the energy density of fuels was dismissed and the feat was only rated based on how much heat the flames can transmit to a character

[here the use of the explosion formula was denied on the basis that the explosion originates from gas]

[this was accepted using the fireball formula despite kepkley suggesting how fuel was involved in it, and the use of energy density seems to have been rejected as well]

While it's not pretty evident at a first glance, there seems to be some disconnect between calcers as to how interpret and measure these explosions.

So I ask, how exactly are we supposed to measure these types of explosions if neither the fireball formula nor the energy density can be used?

I would argue that we should measure them using the fireball formula on the basis that fiction very blatantly portrays them as detonations regardless of how detonative the fuel is in real life and doesn't lead to inflation unlike using the energy density as the values usually line up with the actual AoE/DC of the explosion, it's also not impossible for fuels to cause an actual detonation in real life when subjected to extreme conditions
 
Ultimately it depends on if it's actually an explosion that generates pressure, I'd think.

As per energy density, it shouldn't be applicable since most of the energy isn't going onto something taking the blast
 
If you mean something like a plane crashing into a building and generating a big fireball, then using the fuel's energy density and chemical energy wouldn't be accurate for finding the durability of someone inside the plane who survives the resulting fireball.

I did vouch for that initially, but it's inaccurate, since the character only tanks the heat of the fireball itself.
 
I've been asking me: where do we draw the line between AoE attack and explosion? I mean, some times we rate the first ones as explosions despite not sharing similar properties.
 
@DMUA The thing is that whenever these explosions happen in fiction they're portrayed as detonations, which is evidenced by the fact they destroy objects in the vicinity (as opposed to simply lightning them on fire), and cause a loud boom that is uncharacteristic of the simple ignition of fuel in the open.

@Kep So would the fireball/explosion formula be more accurate in that case for the calc?


I didn't make a good job bringing up more clear cut examples but my main questions are:

  • Can we use energy density of fuels under any context?
  • Should we dismiss explosion feats (and the use of the fireball formula) by attending to the fact they were caused by non-detonative fuels regarless of whether or not they behave exactly like any normal explosion would?
 
Well, if it's portrayed as a detonation, I suppose it would make sense to treat it as such. Otherwise it should be avoided.
 
Everything has pretty much already been said. However, my personal belief is that if the detonation causes pressure, destroying objects and knocking them back, then it can be treated as an explosion.

If the detonation merely sets objects in the vicinity on fire (Molotov cocktails are a good example of a detonation that wouldn't count), then it cannot be considered as an explosion. Calculating the character tanking being set on fire would probably be more appropriate there.
 
I agree with what Crimson said, plus, we tend to calculate shockwaves as explosions basically because they behave like that.
 
So basically

-Energy density of fuels shouldn't be used to measure durability

-Fuel based explosions can utilize the explosion formula as long as they behave like one (shockwaves, destruction, moving objects) and aren't just setting things on fire

Is this correct?
 
Eh, even then the durability of characters who tank fuel-based "explosions" (not actual explosions) is only 9-B maximum. They only tank heat.

There is no reason to arbitrarily utilize a wrong result.
 
If a shockwave is generated and it's shown as an actual explosion it's bound to be higher
 
If it's something like:

  • A plane crashes and "explodes" into a big fireball
  • A car crashes and "explodes" into a big fireball
The character who survives it is only 9-B.

If it is something like:

  • The character is inside a room, the engine is shown leaking and getting on fire, and then it bursts and explodes, throwing everyone back
Maaaybe.

Gasoline doesn't explode. It burns. It looks like an explosion, but it isn't one.
 
Yeah, but fiction can often treat it like an explosion, giving off pressure and such
 
It treats it like an explosion visually, but unless it is outright shown blowing people back via a shockwave, compressing the air around it, and etc. then we should only assume 9-B for the character's durability via tanking the air being heated up.

In fact, even actual explosions aren't scalable to the full durability, since characters only tank a portion of it. If they tanked the entire yield, there wouldn't even be an actual explosion to begin with - after hitting the character in question it would dissipate.
 
If the scene is something like:

  • The characters are inside a car workshop, and one of the gas canisters is leaking. Everyone runs for cover and it bursts, throwing everyone several meters back.
Probably.
 
That can happen actually

For example this shows people flying back from the blast, and even real gas explosions are actual explosions as shown in the OP

If you tank something point blank you'll get nearly the entire yield, otherwise inverse square law would definitely put a damper on it.
 
@Kep But not if it just makes a transparent ring expand out from the point of explosion?
 
Andytrenom said:
@Kep But not if it just makes a transparent ring expand out from the point of explosion?
Click to expand...
You mean this?

https://en.wikipedia.org/wiki/Condensation_cloud

That would be pretty explicit evidence of the explosion generating overpressure from what I can see.

I also think that just the presence of damage in the sorrounding area ie: buildings crumbling, cracked walls, bent metal objects, broken windows, etc as an immediate result of the explosion (as opposed to it happening after prolonged exposure to heat) would be good indicators of whether or not an explosion has pressure as well. Kepekleys suggestion of using humans being blown back as a frame of reference for example, would not work in instances where the only characters around are superhumans who can just withstand the pressure without being blown away, so I think making clear that there are other ways to figure out whether or not an explosion has overpressure would be best.
 
Bump.

I just want to confirm, would the following be good indicators of the explosion generating pressure?:

  • Crumbled buildings
  • cracked walls
  • bent metal objects
  • broken windows
Provided they're the caused immediately by the explosion (as opposed to this happening after prolonged exposure to heat).
 
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