Newsgroups: sci.military.moderated
Subject: Re: FAE
From: .@postoffice.utas.edu.au, (R Fleming)
Date: Wed, 15 Jan 1997 03:32:17 GMT

Andrew Boulton <aboulton@cix.compulink.co.uk> wrote:

> raj@alumnae.caltech.edu said:
> << A bigger question that I have WRT very small FAE's is their potential 
> effectiveness.  My general impression is that FAE's are primarily 
> intended for doing damage to unhardened structures.  They trade off peak 
> overpressure and fragment generation[...]
> 
> I thought (normal) FAEs generated humongous overpressure. I assumed that 
> the lack of FAE grenades was due to technical problems (difficult and/or 
> expensive to scale down).

FAEs generate _tiny_ pressures, by comparison to conventional explosives.
Some back-of-the-envelope calculations I did suggest that their peak
pressures would definitely be under 100 atmospheres, possibly less. Some
types of shaped charges, with conventional explosives, approach ten
_million_ atmospheres peak pressure (this is exceptional, but 100, 000 atm
is nothing special).

However the FAE pressure is fairly uniform over a largeish area, while the
HE pressure drops quite quickly outside the bulk HE. Furthermore, HE
pressure pulses are measured in micro- to milliseconds, FAE pressure
pulses are much longer.

This makes FAE good for detonating mines and demolishing (relatively)
flimsy structures, while conventional HE are better at shattering tough
materials and accelerating fragments. As Raj points out, all else being
equal, fragments are much more deadly than blast.

Newsgroups: sci.military.moderated
From: greenla@umich.edu (Lee Green MD MPH)
Subject: Re: FAE
Date: Thu, 23 Jan 1997 17:54:29 GMT

From greenla@umich.edu (Lee Green MD MPH)

In article <E4DotA.1J1@ranger.daytonoh.ncr.com>, snikki@josie.abo.fi (Sami
Nikki INF) wrote:
> Most people can take pressures up to 25 atm for the brief moments 
> that we're talking about here. 
> (I read this in the Finnish governments report on various weapon types)
> To kill a person using an FAE outdoors one needs to generate about 30-40 a
> atm. Lung damage is a factor down to 15 atm. After that we're mostly
> talking about busted ears and headaches.

Hmm, I must beg to differ.  I don't recall the exact threshhold
overpressure for the effects I describe below, but it's much lower than 15
atm.  I seem to recall it being under 8 atm.

The air-filled spaces in the human body aren't engineered to tolerate
pressure differentials.  They collapse inward rapidly, and that's the
genesis of the injury produced by FAEs.  Sudden application of 200-300 psi
overpressure to the chest compresses it and the lungs it contains inward
at high velocity.  It then rebounds equally rapidly.  This action causes
shearing of the entire network of pulmonary vessels, and the lungs fill
instantly with blood as they reexpand.  Pulmonary venous return to the
left ventricle drops to zero, thus cardiac output drops to zero, so blood
pressure does too.  This produces a state of no systemic perfusion, aka
death.  At the same time, the other major air-filled space in the body,
the nasal cavity and sinuses, undergoes a similar process.  Essentially,
the face implodes.  That ruptures the cribiform plate upward into the base
of the brain, an injury which would be fatal by itself even if the victim
still had lungs.

Being within the 300 psi blast radius of a BLU-73 FAE gives one a zero
percent probability of survival.

-- 
Lee Green MD MPH          Disclaimer: My postings are my doing, not
Family Practice           a service of nor in any way the
University of Michigan    responsibility of the University of
greenla@umich.edu         Michigan.
KF8MO@W8PGW.#SEMICH.MI.USA.NA

PGP public key on MIT keyserver at
http://www-swiss.ai.mit.edu/~bal/pks-toplev.html

Newsgroups: sci.military.moderated
From: greenla@umich.edu (Lee Green MD MPH)
Subject: Re: FAE
Date: Sun, 19 Jan 1997 00:30:17 GMT

From greenla@umich.edu (Lee Green MD MPH)

In article <E415tt.CLo@ranger.daytonoh.ncr.com>, .@postoffice.utas.edu.au,
(R Fleming) wrote:

> FAEs generate _tiny_ pressures, by comparison to conventional explosives.
> Some back-of-the-envelope calculations I did suggest that their peak
> pressures would definitely be under 100 atmospheres, possibly less. Some

Typical FAE overpressures are (e.g., the BLU-73) 300 psi, or around 20
atmospheres.  That is quite more than enough to kill troops, and
unhardened vehicles and buildings as well.  Of course, it's not intended
to pierce armor or bunkers.  That pressure is present over an area of a
bit over 10,000 sq m (60m radius).

-- 
Lee Green MD MPH          Disclaimer: My postings are my doing, not
Family Practice           a service of nor in any way the
University of Michigan    responsibility of the University of
greenla@umich.edu         Michigan.
KF8MO@W8PGW.#SEMICH.MI.USA.NA

PGP public key on MIT keyserver at
http://www-swiss.ai.mit.edu/~bal/pks-toplev.html

Newsgroups: sci.military.moderated
Subject: Re: FAE
From: .@postoffice.utas.edu.au, (R Fleming)
Date: Fri, 24 Jan 1997 17:35:14 GMT

greenla@umich.edu (Lee Green MD MPH) wrote:

.@postoffice.utas.edu.au, (R Fleming) wrote:

> > FAEs generate _tiny_ pressures, by comparison to conventional explosives.
> > Some back-of-the-envelope calculations I did suggest that their peak
> > pressures would definitely be under 100 atmospheres, possibly less. Some
> 
> Typical FAE overpressures are (e.g., the BLU-73) 300 psi, or around 20
> atmospheres.  That is quite more than enough to kill troops, and
> unhardened vehicles and buildings as well.  Of course, it's not intended
> to pierce armor or bunkers.  That pressure is present over an area of a
> bit over 10,000 sq m (60m radius).

For comparison, a frag bomb of the same weight (500lb?) has a high
probability of killing unprotected personnel to about 150m, and
significant hazard out to over 1000m.