Vapourization with Phasers

The Dude · Post by **The Dude** » 2003-11-03 05:31pm

After reading the AJT section on the hate mail page, I got to thinking about the implications of vapourizing a person with a hand weapon, and the similarities this situation should have with real-life examples of rapidly transforming solids or liquids into vapour - namely, explosives. So I decided to do some rough calculations on resulting overpressures, for shits and giggles.

Some assumptions:
- vapourization is fast (<1s)
- human being is 100% water
- open space (i.e. no ceiling)

We can calculate the number of moles of vapour produced by the simple equation n = 1000 m/M where n is number of moles, m is the mass (in kilograms) and M is the molecular mass (in g/mol) - this case 18g/mol.

The volume of the expanding vapour is given by V = 2/3 * pi * r^3 (a hemishpere centered on the floor where the victim was standing).

By gas law, P = nRT/V (R = 8.314J/mol/K; T=temp in Kelvins, assume T=330K, about halfway between room temp and boiling point)

Therefore P = 1500 * m * R* T / M / pi / r^3

If you vapourize a 75-kg man from 3 meters (10 feet) away, you will be hit by an overpressure of nearly 200 kPa (~30psi) - almost 2 atmospheres! This sort of blast would be quite lethal out to at least 5 meters, and will knock people on their asses out to about 15-20 meters!
Gradual vapourization will be less violent (inversely proportional to the rate of vapourization) - but it will nonetheless produce lethal explosions at Trek small-arms range.

Luke Starkiller · Post by **Luke Starkiller** » 2003-11-03 06:00pm

A 2 atmosphere overpressure is lethal? I thought that unarmoured humans could stand up to a 5 atmosphere overpressure, for very short periods.

The Dude · Post by **The Dude** » 2003-11-03 06:19pm

Luke Starkiller wrote:A 2 atmosphere overpressure is lethal? I thought that unarmoured humans could stand up to a 5 atmosphere overpressure, for very short periods.

You're right, my bad.

I found this:

here.

This means that the lethal radius will be about 2.5 meters. That same site also mentions that the threshold overpressure for lung damage is 0.7atm and for ruptured eardrums 0.2atm.

This is all minor details, though, since the point is that we never observe such explosions in ST, therefore phasers can NOT operate on this principle.

neoolong · Post by **neoolong** » 2003-11-03 06:20pm

Uh, human beings aren't 100% water. Can you make that assumption without skewing the results?

The Dude · Post by **The Dude** » 2003-11-03 06:30pm

neoolong wrote:Uh, human beings aren't 100% water. Can you make that assumption without skewing the results?

It's not going to skew the results to a degree relevant to the scale of the analysis. The human body is 50%-70% water, depending on the person. Most of the rest is carbohydrates (in the chemical sense, not the nutritional sense). So the real number of moles of vapour produced can't be much less than estimated above, and may well be more.

Post by **Sea Skimmer** » 2003-11-03 07:06pm

Luke Starkiller wrote:A 2 atmosphere overpressure is lethal? I thought that unarmoured humans could stand up to a 5 atmosphere overpressure, for very short periods.

The human body can withstand significantly more then that actually, its debris that accompany those overpressures that are going to kill you.

The Dude · Post by **The Dude** » 2003-11-03 07:18pm

Sea Skimmer wrote:The human body can withstand significantly more then that actually, its debris that accompany those overpressures that are going to kill you.

You are correct insofar as the presence of debris does increase the kill factor. However, the source above indicates that direct exposure to a 400kPa (4 atm) peak overpressure blast wave is ~100% lethal, even in the absence of missiles.

YT300000 · Post by **YT300000** » 2003-11-03 07:47pm

The Dude wrote:This is all minor details, though, since the point is that we never observe such explosions in ST, therefore phasers can NOT operate on this principle.

They work on the NDF (Nuclear Disruption Force) principle. It says that somehow, in a technobablic way, nuclear forces rip things apart.

Grand Admiral Thrawn · Post by **Grand Admiral Thrawn** » 2003-11-03 08:01pm

neoolong wrote:Uh, human beings aren't 100% water. Can you make that assumption without skewing the results?

However he used a figure of 75kg. Since we've seen phasers vaporize people that could be 100+kg and the human body is roughly 70% water...

The Dude · Post by **The Dude** » 2003-11-03 08:15pm

Indeed. I just used 100% water as a simplification since most of the non-water materials on the body (particularly carbon) do not have gaseous forms.

Anyway, the point here was to show that you can't apply the thermodynamics of vapourization to phasers. In fact, since phasers seemingly annihilate organic matter, a thermodynamic analysis would result in a negative yield, as the final energy state is lower than the initial.

The Dude · Post by **The Dude** » 2003-11-03 08:17pm

YT300000 wrote:They work on the NDF (Nuclear Disruption Force) principle. It says that somehow, in a technobablic way, nuclear forces rip things apart.

I realize that's the standard explanation, but I fail to see how disrupting nuclear forces somehow causes a quantity of mass and energy to wink out of existence.

YT300000 · Post by **YT300000** » 2003-11-03 09:28pm

The Dude wrote:
YT300000 wrote:They work on the NDF (Nuclear Disruption Force) principle. It says that somehow, in a technobablic way, nuclear forces rip things apart.
I realize that's the standard explanation, but I fail to see how disrupting nuclear forces somehow causes a quantity of mass and energy to wink out of existence.

But the writers of the TM sure didn't.

Post by **The Yosemite Bear** » 2003-11-04 07:12pm

I thought we were 70% to 90% water..

The Dude · Post by **The Dude** » 2003-11-04 09:02pm

The Yosemite Bear wrote:I thought we were 70% to 90% water..

Carbon makes up about 20% of bodymass and nitrogen about 3%; Ca, K and P make up another 3%, other minor elements about 1%. That leaves only low-70s percent for oxygen and hydrogen, much of which is tied up in organic molecules.

Ender · Post by **Ender** » 2003-11-05 02:56am

Out of curiosity, how much noise should that make?

The Silence and I · Post by **The Silence and I** » 2003-11-06 07:17pm

A heck of a lot, I would think! It would likely smell bad too, really bad

Phasers clearly cannot be merely DET weapons. Why so many people don't get that is perhaps a better question.

Kamakazie Sith · Post by **Kamakazie Sith** » 2003-11-07 03:41am

The Silence and I wrote:A heck of a lot, I would think! It would likely smell bad too, really bad Phasers clearly cannot be merely DET weapons. Why so many people don't get that is perhaps a better question.

Because most people don't think past what they see on screen.

The Nomad · Post by **The Nomad** » 2003-11-08 08:49am

Kamakazie Sith wrote:
The Silence and I wrote:A heck of a lot, I would think! It would likely smell bad too, really bad Phasers clearly cannot be merely DET weapons. Why so many people don't get that is perhaps a better question.
Because most people don't think past what they see on screen.

Another example of this at TrekBBS :Ships, Planets and the Nature of Warfare with some "SW weapons are lasers !" morons.