Saturday, March 10, 2012

Why My Mother Wouldn’t Let Me Bake

I don’t want to alarm you, but there’s a bomb in your pantry, one that is likely to be powerful enough to destroy your home.  What’s worse is that it’s so well camouflaged that you’d never suspect its destructive properties until it was far too late.  Sure, the safety mechanism has to be removed, and it has to be properly armed and triggered, but make no mistake, it’s dangerous and lethal.

The bomb in your pantry
Let me stop you before you have your local explosive ordnance disposal (EOD) squad tear your kitchen apart, I suppose I should tell you that I’m talking about the five pound sack of flour you have in between the sugar and the baking powder.  

In its normal state – that is, tightly packed and sealed in the sack, the flour is completely inert.  No danger to anyone.  However, should the flour be forcefully expelled from the sack in such a way that it forms, for a brief time, a cloud of flour dust in your kitchen, the key ingredient for Aunt Faye’s strawberry shortcake transforms into a potentially lethal explosive.  All it takes is an ignition source, whether it be from an electrostatic discharge, friction, arcing from the wiring of a nearby appliance, hot appliance surfaces or fire from the burners on the stove, and you’d be lucky if all you had to do is remodel the kitchen.

The mechanism I’ve just described is a typical dust explosion.  A dust explosion is the rapid oxidation (think “burning” or “combustion”) of dust particles suspended in the air in an enclosed location.   Dust explosions occur due to the abnormally high surface area in relation to overall mass of particles suspended in a dust cloud.  Burning can only occur on the surface of a solid or a liquid, where it is free to react with atmospheric oxygen.  In the case of our five pound sack of flour, it has a surface area of about 2.2 square feet.  Disperse that flour into the air, and the dust particles (each with an approximate diameter of 50 micrometers) could have a surface area in excess of 34,000 square feet.  This huge increase in surface area allows the dispersed flour to burn much more rapidly, and the small size of the particles allows them to ignite with far less energy.
Washburn A Mill Explosion, May 2, 1878, Minneapolis, MN

When the mixture of flammable particles (the “fuel”) and air is ignited in a confined space, a tremendous overpressure is created, along with tremendous heat.  This overpressure, and the resulting blast and heat, is often enough to destroy a structure such as a house or a grain silo.

So why, in a blog about weapons and their uses in storylines and plots, am I telling you about flour? 

Mainly because the behavior of clouds of flour when ignited has been the principle behind the development of an entire class of weapon systems.  These systems, called thermobaric weapons, exploit the peculiar nature of the blast waves caused by fuel-air explosions to cause significantly more damage than conventional weapons using condensed explosives.

Thermobaric weapons get their name from the Greek words for "hot" (thermos)and "pressure" (baros).  Typically, they consist of a container packed with a powder or liquid fuel.  Materials chosen for the fuels are selected on the basis of the degree of heat given off when they burn (their “exothermicity”), with hotter fuels being better for the purpose.  Fuels range from powdered metals, such as magnesium or aluminum to boron, silicon, titanium, magnesium, zirconium, carbon or hydrocarbons such as ethylene oxide or propylene oxide.   In the center of the fuel mixture is a bursting charge, usually composed of a conventional explosive that disperses and ignites the fuel.

Courtesy of the BBC
At the time of detonation, the bursting charge disperses the fuel into an optimized vapor density and then ignites it.  Things start to happen rapidly at this point.  When a thermobaric weapon is detonated in a confined space, such as a house, a cave or a bunker, a series of shock waves that interact with each other are created.  These shock waves increase the duration of the fireball to between 10 and 50 milliseconds.  As the combustion gasses begin to cool, pressure drops sharply and a partial vacuum is created which is powerful enough to cause severe injury and structural damage.

How devastating is a thermobaric weapon?  The overpressure within the detonation can be within the order of 400 pounds per square inch (psi), and the temperature of the fireball may range from 4,500° to 5,500° Fahrenheit, followed by an expanding blast wave moving at more than two miles per second.  The effect is magnified between two and nine times when the weapon is detonated within a structure, cave or bunker as opposed to open space.  Those near the point of detonation are simply vaporized, and  injuries suffered by those further away from the epicenter include burst eardrums, crushed inner ear organs, severe concussions, ruptured lungs and internal organs and blindness.  This is in addition to severe burn injuries caused by the fireball.  Thermobaric weapons are a very effective, very nasty piece of kit.

Russian RPO-A Thermobaric Rocket Launcher
While the most famous thermobaric munitions are massive, air delivered bombs weighing many thousands of pounds, the technology is not limited by size.  Characteristics of thermobaric munitions that lend themselves nicely to plotlines and stories include small size, portability and proliferation.  Thermobaric munitions entered widespread use with the Soviet Army in Afghanistan in the mid-1980s.  The RPO-A rocket launcher is about three feet long, and when loaded with the “Bumblebee” rocket, weighs only 24 pounds.  The more modern (circa 2004) RSgH-1, which weighs about 17 pounds including launcher and rocket, is a thermobaric variant of the RPG-27, with a blast effect equivalent to thirteen pounds of TNT.

XM1060 40mm Thermobaric Grenade
The United States has fielded a number of weapons based on thermobaric technology, including the fist sized XM1060 40mm Thermobaric Grenade, the 17 pound Shoulder Launched Mulipurpose Assault Weapon – Novel Explosive (SMAW-NE; a derivation of the Israeli B-300 system), and the AGM-114N version of the 106 pound Hellfire guided missile.  The AGM-114N uses a layer of fluoridated aluminum layered between the outer casing and a conventional PBXN-112 explosive.
SMAW-NE Thermobaric Rocket Launcher
Flour, a fine mist of kerosene or finely powdered metals – all of them can be used by your characters, good and bad, to devastating effect, especially in scenes where transporting a large amount of conventional explosive is impractical or impossible.
Of course, I’d always thought that mom didn’t want to let me bake because she was concerned about my ability to create a mess in the kitchen.  Apparently, she was more worried about my ability to make a mess and destroy the house in the process!
My mom is a very wise woman.  You never know what danger lurks behind household staples...


  1. Hmm, and sugar can build up electrostatic charge. Should we really be storing them together? (JK!)Thanks for the weapons lesson!

  2. I absolutely love the article but you got to dumb it down for me. I had a scene where my protag is in the kitchen and antag is holding a gun on her. She is, in fact, messing in the cupboard. What can she do w/said flour beside try throw it in his eyes? Set it "innocently" on a burner that she "accidentally" turns on? Talking electric coil. Since I didn't want to blow up anyone, including protag, a bomb per se didn't occur to me but I did have her start a fire that came in handy later. What kind of time lapse are we talking here? Enlighten me, You of the Great and Sneaky Mind.

  3. Hiya!

    This sounds like a complete post on its own...perhaps you could email me offline and give me the full details on the scene? From that, I could put something together that might work for you, and take the idea of working thermobarics into a storyline one step further.

    All the best,


  4. Oh, man, that is great . . . I want to write a storyline in which my pastry cook heroine manages to trounce the bad guys with a homemade thermobaric weapon. How cool is that. A whole world of devious destructiveness is opening up before me . . .

  5. Wow. Super cool (or hot). Amazing plotline possibilities!