Explosion speed for calculations

[DontTalk]

There exist some amount of calculations that rely on the speed at which an explosion, from a chemical explosive, expands. Dodging or reacting to those can be a good feat after all.

To this point we used this table of detonation velocitys and thought that the detonation velocity of an explosive is how fast the shockwave/fireball expands.

Well, curious as I am I was reading up a bit on that yesterday and got that detonation velocity is not that at all. As you can read in this article the detonation velocity is the velocity at which the chemical reaction traverses the explosive. That is not at all the value we want here.


So I thought about what do do instead and after a view hours of trying to figure out how to properly use certain formulas for blast waves I decided to just recommend the easy method I stumbled upon first.

This calculator can calculate which speed a shockwave has and after how long it will have crossed a certain distance, if the amount and type of explosive is known (how estimations on whieght and type will be made I will not discuss now). Given that it comes from the United nations (who would have thought I would find such a calculator there of all places) I would expect it to be accurate.

Since the shockwave does the most damage if it comes to dodging this can be used and for short distances I would believe the assumption that fireball spread equals shockwave spread is acceptable.

Leaves one possible question open: The calculator states that it is made for hemispherical blasts while many of the blasts we want to calculate are spherical. Well, this artcile states that it is a good approximation to half the amount of explosive to convert surface explosion data (hemispherical) to air explosion data (spherical). That makes sense as the energy that spreads in any direction in the air is halfed since no energy is reflected from the surface. So for spherical/in the air explosions we just use half the amount of explosives.


So that would be what I think is a problem and how it should be solved. What do you think, everyone?

 

[Alakabamm]

Looks good, we can maybe stick it on the calc page as well

 

[Antvasima]

Yes. It would be appreciated if you could add a section about this to either the Calculations page, or the Calculation Guide page.

 

[CrossverseCrisis]

Looks interesting,

 

[SunWukong1986]

Interesting. I haven't seen something like that one before. Thanks for enlightening me.

 

[LordXcano]

Wouldn't a hemispherical blast just be a blast that isn't detonated mid-air? Also, what would we use as the standard assumption for weight of various explosives and range?

EDIT: Yeah it says hemispherical is just a surface blast.

 

[DontTalk]

Well, the standard assumption question comes up.

For range you just take your scaling results.

To take your scarlet witch calc as example you would use 96.52 cm = 0.9652 m as range for the calculator. The arrival time would then be your timeframe.

For weight we have three options:

1. We actually try to scale the volume of explosives present and just use the density of the explosive we assume it to be in order to figure out the weight.

2. For things like bombs and C4 packages there are standard sizes I believe, so one can make a case for those being used even without scaling.

3. One could try to figure it out by the destruction the explosion caused. This method needs a bit work. If one can figure out how much destruction an explosive causes at a certain distance or how large of a fireball an explosive is supposed to cause one can try to backwards calculate values from there. But in detail I am currently not sure how this can work. (There are some articles on the topic of shockwaves and effects, but as I mentioned on the top I found them quite difficult)

Edit: Dont know if it helps in some cases, but let me just say that there are some other calculators for other explosion data avaiable as well.

Edit2: See here for standard size of C4 packages.

Edit3: Here a approximation for fireball size to explosive weight is mentioned. Not certain if reliable.

 

[Antoniofer]

This is interesting, should we make a section of "explosion speed" or something? however, it sound like a attack speed combined with range...

 

[DontTalk]

Hmm...? nah that is only relevant for calculation purposes. For example

 

[LordXcano]

The explosion size was actually waaay larger but I can see this being useful.

 

[DontTalk]

Hmm.. yes in cases like yours where the explosion gets restricted backwards calculating from the size of the explosion might not work all too well. But since you have visuals the option of outright scaling the volume directly still is an option here.

 

[DontTalk]

Ok, I will bump this once again to make sure everyone that wanted to complain about the suggestion gets to it now.

Can I take it that everyone that wrote here to this point is in agreement with changing the priorly used method with the new suggestion for all calcs?

 

[TheMightyRegulator]

Seems fine on this end.

 

[Antvasima]

I am also fine with this.

Somebody might need to recalculate the Black Panther's and Scarlet Witch (Marvel Cinematic Universe) speed feats with your new method afterwards.

 

[ThePerpetual]

I suppose this is fine, though I may need some help learning to use it properly.

 

[Antvasima]

So, is somebody from the calculation group (preferably DontTalk or Alakabamm) willing to write a special page for explosion speed, or to add a section to our calculation pages?

 

[LordXcano]

I suppose this is fine, though I may need some help learning to use it properly.

Basically, unless the material is stated assume one of the more common explosive materials (TNT, C4) and scale the volume of the explosive. Then get the charge weight from the explosive density. Afterwards, scale the size of the explosion.

Input weight and range and then you'll have the explosion's speed.

 

[DontTalk]

Article which gives explanation on use has been created.

 

[Antvasima]

Okay. Thank you very much for the help.