Thermobaric weapons
Simon Morden
sweat...
http://call.army.mil/call/spc_prod/mout/docs/thermodoc.htm
Simon Morden
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George William Herbert
>For those who want to lie awake at night in a cold
>sweat...
>http://call.army.mil/call/spc_prod/mout/docs/thermodoc.htm
Ahh, the fear of the ignorant...
Thermobaric weapons are just a slight variant on fuel-air explosives.
FAEs have been around since Vietnam and earlier.
All of these weapons increase explosive yield per warhead mass somewhat
by only bringing along fuel and using atmospheric oxygen as the other
half of the detonation chemistry. Depending on what the fuel used is,
and other details, you can get from a 1.5 to roughly 3.0 multiplier of
effective explosive yield compared to conventional HE weapons.
The "overpressure effects" and such are a misnomer: any explosion
produces overpressure. Thermobarics produce more overpressure since
they have higher explosive yield per unit mass, but not more than say
a large mortar round or artillery shell.
The actual killing effect on the battlefield is usually not the
blast and overpressure of an explosion (you rarely get the projectile
that close to the target), but fragmentation. The explosive energy in
a mortar round or artillery shell fragments the metal casing and throws
those fragments out at high velocities. Beyond a few meters to low tens
of meters from the explosion, most or all of the damage is in the fragments.
FAE and thermobaric weapons have no fragmentation, and therefore a more
limited danger space compared to conventional artillery or mortar or
other explosive rounds. They are useful in enclosed spaces, such as
firing into buildings and such. But not much more useful than the same
sized round with conventional high explosives.
Amateurs keep seeing this and thinking "my god, these are new terrible
weapons which kill people!". The reality is, for a long long time there
have been weapons which kill about this efficiently. There have been
explosive filled cannon shells for centuries. Artillery rockets for
a hundred fifty years. Handheld rocket launchers and recoilless rifles
for over fifty years. Grenade launchers for a century. Thermobaric
warheads are at best a very very slight improvement, useful primarily in
a very limited situation (urban combat) and less effective on the average
battlefield than their predecessors.
-george william herbert
gher...@retro.com
Cue42
>Amateurs keep seeing this and thinking
>"my god, these are new terrible
>weapons which kill people!". The reality
>is, for a long long time there
>have been weapons which kill about this
> efficiently.
I suspect that rather than efficiency
the purpose for such weapons is to
demoralize opposing forces. The
innate fear of fire is a deep and abiding
human trait and weapons that make
use of it create the "horror-fication"
you previously mentioned.
The efficient delivery of death is only
one segment of strategy.
Standard disclaimers apply.
-Carl-
George William Herbert
Except that "thermobarics" aren't really a fire weapon.
Flamethrowers are; napalm is; white phosphorous is.
Thermobarics are a variant of fuel-air explosives,
which are explosives (short preparatory period and
then an instantaneous detonation, as opposed to burning
over a period of time with flame weapons).
Humans have been afraid of, and then learned to cope with,
every weapon invented so far. In cases where there is a
huge technical advance in lethality that usually takes
a great deal of tactical or technical advance. In cases
where it's minor, comperable to existing weapons, then it
is just a matter of familiarization. If you're familiarized
with explosive artillery rounds, then mortars aren't that
unfamiliar or frightening. If you're used to mortars,
grenade launchers aren't that unfamiliar or frightening.
If you're used to mortars and grenade launchers, then antipersonel
warheads on infantry rockets aren't that frightening.
If you're used to antipersonel warheads on rockets, then
thermobaric antipersonel warheads on rockets are not much
different. And this entire chain of events starts with
explosive cannon shells introduced 300 years ago now.
Napoleon's troops might not understand the RPG launchers
firing thermobarics, but they'd understand the explosions
and their significance and be able to deal with them.
Of course, there's a lot of good fiction material available
in theoretical or future weapons outside the box, or the
reactions of people *not* familiar with any of them to
them (as with any unfamiliar technology... flashlights
can terrify and delight stone age natives...).
-george william herbert
gher...@retro.com
Simon Morden
I'm sure that the author of the article will be delighted to know he's
over-reacting.
After all, he only works for the Marines and posts the article on a .mil site,
then
casually throws in phrases like 'highly dangerous', 'extremely lethal',
'circumvents
current blast and fragmentation protection', etc.
I'm not going to engage in a slanging match, but 'fear of the ignorant' is going
to get
anyone's back up. I'm relatively certain that article expresses the sum of a
good deal
of research.
JamesBWard
>Simon Morden <simon....@blueyonder.co.uk> wrote:
>>For those who want to lie awake at night in a cold
>>sweat...
>>http://call.army.mil/call/spc_prod/mout/docs/thermodoc.htm
>
>Ahh, the fear of the ignorant...
>
>Thermobaric weapons are just a slight variant on fuel-air explosives.
>FAEs have been around since Vietnam and earlier.
>
Correct me if I'm wrong, but IIRC troops in Vietnam didn't have FAE grenades -
the Russian weapon is an RPG with a thermobaric/FAE warhead, which I am
assuming is a more recent development. Which is a ilttle worse than what was
available before.
Christopher M. Jones
> gherbert wrote:
> >Ahh, the fear of the ignorant...
> >
> >Thermobaric weapons are just a slight variant on fuel-air explosives.
> >FAEs have been around since Vietnam and earlier.
> >
>
> Correct me if I'm wrong, but IIRC troops in Vietnam didn't have FAE
grenades -
> the Russian weapon is an RPG with a thermobaric/FAE warhead, which I am
> assuming is a more recent development. Which is a ilttle worse than what
was
> available before.
"A little worse" than the previous types of RPGs perhaps (though
not likely actually) but not in any way worse than the worst (or
even much less than the worst) that is commonly seen on the
battlefield. Mr. Herbert knows his stuff, by far the most lethal
(and hurtful) weapons on the battlefield damage through
fragmentation (aka "shrapnel"). Fragmentation grenades, anti-
personnel mines, etc. have been around for a very long time.
Tripping a "bouncing betty" anti-personnel mine is a seriously
bad day, much worse than encountering any "thermobaric weapon".
--
Cause it's time to bring the fire down
Bridle all this indiscretion
Long enough to edify
And permanently fill this hollow
Christopher M. Jones
> I'm sure that the author of the article will be delighted to
> know he's over-reacting. After all, he only works for the
> Marines and posts the article on a .mil site, then casually
> throws in phrases like 'highly dangerous', 'extremely lethal',
> 'circumvents current blast and fragmentation protection', etc.
>
> I'm not going to engage in a slanging match, but 'fear of the
> ignorant' is going to get anyone's back up. I'm relatively
> certain that article expresses the sum of a good deal of
> research.
Neither working for the marines nor posting to a .mil site
makes someone an authority in a subject. Nor does being an
authority make what one says automatically the unassailable
truth.
--
Take the red pill.
Charles R Martin
Simon, believe it or not, the Marines sometimes over-react.
Especially if they're getting set up for a grant proposal.
(I can say this for sure. I've seen it, singly and in groups.)
George William Herbert
>George William Herbert wrote:
>> Simon Morden <simon....@blueyonder.co.uk> wrote:
>> >For those who want to lie awake at night in a cold
>> >sweat...
>> >http://call.army.mil/call/spc_prod/mout/docs/thermodoc.htm
>>
>> Ahh, the fear of the ignorant...
>
>I'm sure that the author of the article will be delighted to know he's
>over-reacting.
>After all, he only works for the Marines and posts the article on a .mil site,
>then
>casually throws in phrases like 'highly dangerous', 'extremely lethal',
>'circumvents
>current blast and fragmentation protection', etc.
Simon, I think you've misinterpreted me.
I wasn't calling the author ignorant or overreacting.
I was stating that about *you*, regarding:
"For those who want to lie awake at night in a cold sweat..."
>I'm not going to engage in a slanging match, but 'fear of the ignorant'
>is going to get anyone's back up. I'm relatively certain that article
>expresses the sum of a good deal of research.
That article, various articles in _Armor_, the _Marine Corps Gazette_
various Janes' publications, etc. I'm familiar with the research
and their effects, though not enough to build one myself.
To quote from the source article:
::TARGET EFFECTS
::
::The RPO-A kills by causing massive damage to the lungs and other soft
::tissue. The explosive event produced by RPO-A is characterized by
::higher temperatures and pressures of a longer duration than is normally
::associated with conventional high explosives. Like FAE, the RPO-A
::delivers its damage primarily through blast effects. The thermobaric
::RPO-A munition is a good general purpose blast round, and a somewhat
::less effective incendiary round. It performs reasonably well over a
::broad range of applications but is particularly effective when
::detonated within an enclosed space (a building, trench or a bunker).
::Relying primarily on blast effects to kill personnel, instead of
::fragmenting shrapnel, is a unique concept in contemporary antipersonnel
::weaponry. Western protective equipment is designed chiefly to protect
::soldiers from bullets and fragments, and not blast effects.
::Consequently, helmets and ballistic armor will provide relatively
::little protection from the RPO-A.
::
::The flash intensity and duration of the RPO-A detonation can
::also cause temporary blindness.
The key here is the sentence:
::The thermobaric RPO-A munition is a good general purpose blast round,
::and a somewhat less effective incendiary round.
With it's roughly two kilo thermobaric powder warhead it has blast
effects similar to (but not identical to) four to five kilos
(around ten pounds) of TNT. Using the formulas in Ch 28 of Cooper's
_Explosives Engineering_:
P0 = overpressure peak (bars)
Pa = ambient pressure (bars)
W = TNT equivalent weight of charge (kg)
Ta = ambient temperature (kelvin)
R = radius from center of charge (meters)
(P0/Pa) = f[R / (WTa/Pa)^1/3]
Note that the function f is not simple, so they suggest using
the plot of the more complex scaling curve in Fig 28.2 rather than
trying to work it out in detail.
Scaled Distance Z is given by:
Z = R/[(WTa/Pa)^1/3]
For our case:
W = 5 kg (worst case)
Ta = 300 K (80 degree F day, for simplicity's sake and round numbers)
Pa = 1.0
thus:
Z = R/[(5x300/1.0)^1/3]
Z = R/11.4
Interesting values are going to be 60 PSI (~4 bar) and 5 PSI (~0.3 bar),
corresponding to the 50th percentile lethal blast overpressure at average
pulse durations and body orientations (ignoring about five pages of detailed
variants on the above in the interest of time and space) and the pressure
which will destroy moderately well built buildings respectively.
For 4 bar, from Fig 28.2 we find Z ~= 0.3
For 0.3 bar, from Fig 28.2 we find Z ~= 0.8
For Z = 0.3, 0.3 = R / 11.4, R ~= 3.42 meters
For Z = 0.8, 0.8 = R / 11.4, R ~= 9.1 meters
Thus this will kill people with blast effect within about 11 feet of
the detonation point and collapse walls and structures out to about
30 feet from the detonation point, similarly to the blast effects
of a mid-caliber HE mortar or artillery round but without the fragmentation.
This is, again, not too dissimilar to the effects of large explosive
cannon shell (say, the "heavy" 42-pounder cannon) dating back 250 years
and more. It's more man portable, but nothing terribly new in terms of
terminal effects on those unfortunate enough to be targeted.
-george william herbert
gher...@retro.com
Simon Morden
Okay, okay, I know when I'm beat :)
One parting (conventional) shot, though. I thought the point of the thermobaric and
the associated FAE weapons was that the zone of effect was that whatever was in the
gas cloud at the moment of ignition got incinerated. I'm willing to plead ignorance
here, fearful or otherwise, but wouldn't the equations you quote for the blast
effect of a point source HE explosive be redundant for the ignition of a large
volume of gas, especially when contained in a structure like a building? As far as
I understand it I can be upstairs sitting on the toilet when one of these rounds
sails through the lounge window - as long as the gas expands sufficiently to fill
most of the house, I'm (quite literally) toast.
Any gas fitters on line?
George William Herbert
>One parting (conventional) shot, though. I thought the point of the
>thermobaric and the associated FAE weapons was that the zone of effect
>was that whatever was in the gas cloud at the moment of ignition got
>incinerated. I'm willing to plead ignorance here, fearful or
>otherwise, but wouldn't the equations you quote for the blast effect
>of a point source HE explosive be redundant for the ignition of a large
>volume of gas, especially when contained in a structure like a
>building? As far as I understand it I can be upstairs sitting on the
>toilet when one of these rounds sails through the lounge window - as
>long as the gas expands sufficiently to fill most of the house, I'm
>(quite literally) toast.
No, the volume detonation effect changes pulse duration but
doesn't limit the effects to the volume of the detonation.
For gaseous FAE, say you're talking about a kilogram of fuel
gas of molecular weight 44 (propane). That's 22 moles, or
about a half cubic meter of gas at STP. The man portable
and light artillery FAE and thermobarics have a few kilos
of warhead; the 2 kilo RPO-A warhead would be the equivalent
of about a cubic meter of gas volume etc.
That's "fill a room" at best, more realistically a fraction
of a room, prior to detonation. And the time from release
to detonation is just enough to ensure adequate mixing with
the environmental oxygen... tens to hundreds of milliseconds,
depending on the FAE or thermobaric materials and quantity
and bursting charge.
Even if you wanted to fill a whole house, it would take a lot
more fuel and would be incredibly difficult to mix the fuel
with the atmospheric oxygen to get detonating conditions.
That's the real advantage of FAE and thermobarics; if blast
effects alone are what you're looking for, you get to use
atmospheric oxygen (free, and already present in quantity)
rather than carrying oxidizer along in the projectile, usually
figuratively in the form of energetic bond detonating compounds
rather than say sprengel explosives (mixtures of oxidizing and
reducing chemicals). The atmospheric oxygen typically is half
to two thirds of the mass going in to the explosion reaction
and the reactions between oxygen and good FAE and thermobaric
fuels are typically at least as overall mass effective as
conventional high explosives on a pound-for-pound basis.
Liquid oxygen plus various fuels is a great blasting agent
if you can use it safely in particular conditions.
-george william herbert
gher...@retro.com
Luke Campbell
> That's the real advantage of FAE and thermobarics; if blast
> effects alone are what you're looking for, you get to use
> atmospheric oxygen (free, and already present in quantity)
> rather than carrying oxidizer along in the projectile, usually
> figuratively in the form of energetic bond detonating compounds
> rather than say sprengel explosives (mixtures of oxidizing and
> reducing chemicals). The atmospheric oxygen typically is half
> to two thirds of the mass going in to the explosion reaction
> and the reactions between oxygen and good FAE and thermobaric
> fuels are typically at least as overall mass effective as
> conventional high explosives on a pound-for-pound basis.
> Liquid oxygen plus various fuels is a great blasting agent
> if you can use it safely in particular conditions.
There is something I must be missing here. Motor fuels store about an
order of magnitude more energy than high explosives (neglecting the oxygen
to burn the motor fuel). The specific energies I've heard quoted for
TNT are generally about 4 MJ/kg, while gasoline is about 40 MJ/kg. Is
there some reason why the more energetic fuels cannot be used in fuel-air
explosives? Is the blast highly inefficient at using the energy of the
fuel to create a blast wave?
Luke
Marc Lombart
<lwc...@u.washington.edu> wrote:
> Is
>there some reason why the more energetic fuels cannot be used in fuel-air
>explosives?
Good question, I thought the very name fuel-air explosive
implied the use of fuels for the explosives.
This is what I found.
<<Fuel-air weapons work by initially detonating a scattering
charge within a bomb, rocket or grenade warhead. The warheadcontents,
which are composed of either volatile gases, liquids or finely
powdered explosives, form an aerosol cloud. This cloud is then ignited
and the subsequent fireball sears the surrounding area while consuming
the oxygen in this area. The lack of oxygen creates an enormous
overpressure>>
From what I see, explosive energy is not what is needed in
FAEs, but rather high combustion.
Oh, more little tidbits.
<<Thermobaric is another term for fuel-air.>>
<<They were initially developed in the late 1960s. Russian thermobaric
weapons are now third-generation>>
--
Marc el Kato
mailto:master...@netzero.net
ICQ UIN: 3337155
Please, reply either to the group or via eMail, not both.
George William Herbert
More energetic fuels are used. Liquids aren't commonly used
as they're damnably hard to disperse properly; it's usually either
pre-formed particulate solids or gases.
For the energy balance, now...
If we approximate gasoline as Octane (C8H18) then you burn it as:
C8H18 + 12.5 O2 = 8 CO2 + 9 H2O
By weight, the inputs break down into:
144g Octane + 400g Oxygen => ...
So there's a nearly 3:1 mass leverage there.
On top of which, the energy density per mass input is higher
for that combined mass than for TNT.
The problem is that gasoline (even gasoline vapors) are a poor fuel
choice from a weapons standpoint. Too hard to get dispersed in the
right quantities, though you do see accidents where someone blows up
their house or garage that way from time to time.
But since the weapons need to use gases, they have to hold them
under pressure (propane is the classic example, at tens to low
hundreds of PSI depending on conditions) needing a robust storage
tank and dispersal mechanism, which reduces the payload mass fraction.
Propane's C3H8, 44g/mole, reacts with 8 O2 (256g) to form 3 CO2 and 4 H2O.
The most common US FAE fuel now is ethylene oxide; it's slightly better
oxygen balanced internally for robust reliable ignition at moderate
mixing fractions, which leads to consistent if slightly lower yields
per unit fuel mass.
-george william herbert
gher...@retro.com
Brian Davis
> Motor fuels store about an order of magnitude more energy than
> high explosives (neglecting the oxygen to burn the motor fuel).
> The specific energies I've heard quoted for TNT are generally
> about 4 MJ/kg, while gasoline is about 40 MJ/kg.
Part of the reason is that you're comparing apples & oranges (heat of
detonation vs. heat of combustion). The heat of combustion of TNT is
around 15 MJ/kg, at least closer to gasoline for instance.
--
Brian Davis
John Schilling
>George William Herbert wrote:
Fuels like gasoline are very efficient *if* you can get them to mix with
the surrounding air properly before setting them off. But that turns out
to be rather hard, because they are very finicky about what "properly"
mixing with air really means. An FAE weapon using gasoline might be made
to work in a laboratory, but in the real world environmental uncertainties
would probably mean that most of the gasoline mixes with air at a ratio
outside the explosive range and so does not contribute to the detonation.
Propane or methane would be somewhat better by virtue of being gaseous. No
droplet size effect to worry about. Even so, getting the mixture ratio right
would be problematic. And as an aside, nightmare scenarios about terrorists
using propane tank cars or LNG tankers as super-bombs tend to assume that if
you crack open the storage container the contents will fully mix with the
surrounding air at just the right ratio before any of it ignites. Not going
to happen.
What you really want, and what the military uses, are gaseous or highly
volatile liquid hydrocarbons which have been partially oxidated or nitrated.
This cuts down on the enery content quite a bit, maybe a factor of two, but
it opens up the allowable mixture ratio even more and so ensures that the
device will actually work.
--
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