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The World of Iniquus - Action Adventure Romance

Wednesday, January 7, 2015

The Big Bang Theory: Explosives Info for Writers with New York Times Bestselling Author John Gilstrap

ADR labels for dangerous goods, class 1 - Expl...
 (Photo credit: Wikipedia)

Today, we are visiting with New York Times Bestselling Author, John Gilstrap.

I asked him over to ThrillWriting because of his expertise in things that are hazardous to our heroes and heroines and also make for lovely volatility in our plotlines.
Fiona - 
Well John, you went and did it. You hung up your hat from your "big-boy" job; and now, you are leading a life of leisure. Firstly, congratulations and much good fortune in your retirement.

Can you tell folks what you did when you whistled off to work? Why are you a hazmat expert?

John - 
John GIlstrap
In my "other" life--my non-writing life--I was a safety engineer. I got my masters degree in that field a while ago, and have been a safety professional for 35 years. My expertise, starting way back at the beginning of me career, deals with explosives, hazardous materials and hazardous waste. During my 15 years in the fire and rescue service, I was a member of the HazMat team.

Fiona - 
Okay - so John, you are reading right along. The novel has reached its boiling point. All hell's breaking loose. You're at the edge of your seat and then...the author blows it (figuratively) because they didn't know enough about explosions to make things work.

Do you run into this often? And if so - what are some of the most common errors? 

John -
The most common errors that frost my flakes are huge explosions from little devices, or tiny explosions from huge devices. There's a general underappreciation for the effects of the overpressure. 

A detonation is defined as a pressure wave that travels at supersonic speed. We're talking ruptured ear drums, crushed sinuses, really bad stuff. There's likewise an under appreciation for shrapnel. a tiny piece of steel going very fast does lots of harm.

Def. insert: Overpressure, according to the free dictionary is  - A transient air pressure, such as the shock wave from an explosion, that is greater than the surrounding atmospheric pressure.

Fiona - 
In your Digger Graves novels, things blow up a lot. His team's explosions don't really subscribe to the laws. So we have good guys doing technically bad things for the greater good. What are the assessment steps that he will go through to choose the right size BOOM.

John - 
People in the door-crashing business come prepared with specialized charges pre-made. Delta Force calls one type of such charge a GPC--general purpose charge. It's essentially a lump of C4 with tail of det cord (PETN) and a cap. That's great for opening pretty much any door.


In the Grave books, Boxers is the explosives guy, and he's been known to daisy chain GPCs for a really, really big boom.

Jonathan's big concern is often collateral damage. You don't want to kill other good guys while trying to help the good guys. Sometimes, though, there's no choice.

Fiona -
Big Guy does like to make some noise.

John -
It's like his favorite thing.

Fiona -
With the GPC, how dangerous is it to carry (volatile)? What could make it go off unexpectedly, anything? What are the things that would make it not work properly and leave Johnathan and Boxers standing there looking for a plan B?

John -
The cool thing about C4-which a lot of people all "plastic explosives" is the fact that it's really hard to set off. In fact, a lot of soldiers use a chunk of it to start a fire. To get it to go bang, you have to hit it with another detonation. Under most circumstances, even shooting it with a bullet will not make it go high-order (detonate). Maybe it's time to go a little into the science here.

Fiona -
Yes, please! 

John - 
In broad terms, there are two types of explosives--primary and secondary. (And that pie can be sliced in many more ways.)

Remember that most of this stuff is designed for use in battle, so you don't want the good guys blowing themselves up. 

A primary explosive -  is one that is VERY sensitive to heat, friction or impact. I used to deal with azides that would go high order if you looked at them cross-eyed. Nitroglycerine is like that. You don't handle NG in glass because the energy of breaking glass crystals will make it blow up. Primary explosives -  are the materials inside of "detonators" or "initiators." Primer caps in bullets are also primary explosives. They're used in small amounts, but are easily set off.

So. . . to get a secondary explosive to go bang, you "prime" it with a primary explosive/detonator. The energy of the smaller detonation will trigger a detonation in the secondary, which generally is a KFB kind of explosion (Ka-effing-boom)

Most munitions have a safe/arm device built into it that will keep an accidental initiation of the primer from hitting the secondary.

Fiona -
So I'm imagining that from the secondary standpoint things could go wrong if 
  • It got wet? 
  • That the connector wasn't connected? 
And I suppose the main problem with the primary would be it going off before we wanted it to?

John - 
Well, a solid connection is certainly important. That's why a lot of operators will use two detonators in a charge. The chances of screwing up both of them is pretty small. 

As for the effects of getting wet, that really varies from explosive to explosive. It also depends on the definition of "wet." For example, the explosive that brought down the Murrah Building in Oklahoma City was a combination of ammonium nitrate (fertilizer) mixed with fuel oil. It's called ANFO, and as the world saw, that's a very effective combination. But ammonium nitrate on its own won't detonate. Neither will fuel oil. The wetness is important.

I think writers get into really dangerous territory credibility-wise when they get into more exotic applications of explosives.

Now, as far as danger from initiators going off prematurely, there are some pretty simple steps to keep that from happening. For example:
  • The wires to a detonator should always remain twisted together before they're used. By shorting out the wires, there's no possibility for an errant circuit setting them off in your bag.
  • Never carry primaries and secondaries in the same container.
  • And the last thing to be put into an explosive charge is the detonator. In a perfect world, that job is done by a single person. (I used to call that person "the most expendable employee." I served in that role for some time.) 

Fiona -
I just read a Michael Connelly book where a molotov cocktail was thrown down a trash chute. What are a few common homemade bomb types that would be good choices for writers to use in a plotline?

John -
I haven't read that one of Mike's books, so I can't speak to that, but Molotov cocktails kill as many throwers as they do throwees. When dealing with flammable liquids (gasoline) as opposed to explosives, there is no pressure wave, so the only damage is done by setting things or people on fire. Very inefficient.

You'd do way more damage by packing strike-anywhere matches into a PVC pipe, sealing it, and throwing it. The fire inside the tube will burn without venting until the pipe bursts. (By the way, don't do that. It's one of the most sensitive, easily-ignited bomb that's ever been made.)

Fiona - 
Not that we are trying to hand out bomb making recipes, but let's say our heroine is running from the bad guy and finds herself in a janitors' closet. She has to make that shed over there go boom to distract the bad guy so she can save the day. What components would she look for and what might she come up with?

John -
Hmm. I think it would be really hard to make something go boom. Setting a fire would be simple, but with explosives, the ignition train is a problem. Even the ANFO I referred to above needs a detonator to get it to go.

Breaking gas lines is effective, but it's hard not to be part of the fireball.

Remember that scene in Bourne Identity where Jason Bourne shoots the Diesel tank out back and it blows up? Can't happen. Not only is diesel fuel hard to set afire (particularly in winter), it won't go bang. Gasoline won't go bang. It would just dribble out and catch fire.

Oh! I have the explosive for your heroine!

She finds a propane tank (or acetylene or any other flammable gas). Open the valve and sets the stream on fire. The place the flame up against another tank of flammable gas. As the second tank heats, it will increase internal pressure and leak. The flame contact on the outside of the steel will cause the pressure to rise. When the tank finally fails, there'll be a huge explosion. It's called a BLEVE--boiling liquid expanding vapor explosion.

Fiona -
Nice! LOL. 

Lets talk about the boom. Earlier you mentioned shrapnel -- that hits good guys as well as bad guys. Along those lines, how far/how fast would they need to run to stay safe? Any truth to the people who dive through the air in the movies as the concussion hits, and they can roll out of it? 

John - 
The detonation velocity of TNT is roughly 4.3 miles per second. That's how fast you would have to run to out-run the blast wave. Now, the rules of physics mandate that the farther you are from the source of the blast, the lower the pressure wave.

The overpressure of TNT at the surface approaches 1 million pounds per square inch. People don't fly through the air from that kind of pressure. They vaporize. They become humidity. 

Now, consider that it takes roughly five pounds per square inch to bring down a concrete block wall, and you get a sense of how big a deal these things can be.

Sound is merely perceived pressure changes that make the ear drum vibrate. Imagine a five psi (pounds per square inch) hit on that tiny membrane. Hearing loss is a real problem with explosives.

More science...

Fiona - 

John - 
Remember that nature abhors imbalance. Behind every pressure wave is a rarefaction wave (a vacuum) that is much longer in duration.

So, after the blast wave shatters things, the rarefaction wave sucks on the shattered things. All the while, that blast is propelling hunks of stuff at high velocity--and then, on the outer reaches, it sucks them back.

It's a pressure storm that you just can't survive. The only defense against an explosion is distance or shielding.

Fiona - 
How cool is that? (Unless you're in the middle of it.)

If the good guys sets a detonator and needs to protect themselves - don't hide behind a car right? Where should they go? What should they do to stay close to the scene safely? What with all of that blasting and sucking going on...

John - 
Well, we're talking about making the best of a bad situation, right? People with the longest careers move back a couple thousand feet before they detonate the bomb.
But if that's a luxury your character doesn't have, then a good makeshift foxhole will do. 

Fiona -
So laying in a ditch, not so much

John - 
Laying in a ditch could help a lot, actually. Assuming you're a decent distance away. Remember that an explosion is omnidirectional (although they can be directed). If you're below grade, the pressure wave will be absorbed by the ground, and the shrapnel won't have a line to get you.

But remember that gravity is a bitch. The stuff that flies up will indeed come back down--and sometimes ten or fifteen seconds later. You don't want to be hit by that.

I always tell people that if you're around to say, "Oh,shit!" after the explosion, you're halfway to survival. Then you just keep your head down.

Here's a good photo of what I'm explaining:

This picture shows the first milliseconds of a very large detonation. Note how far the pressure wave is ahead of the flame front. Also, note that the pressure actually creates weather by condensing the moisture out of the air.

Fiona - 

Suddenly shifting gears on you, would you tell us your favorite scar or harrowing story?

John - 
Inexplicably, I have relatively few scars. 

My fire service career provided some scary encounters with people who were clearly not sharing the same reality as the rest of us--that became particularly problematic when they were armed and I was not--but probably the scariest single moment for me was when I fell through the floor while fighting a fire. 

It was in the wee hours, and the building on fire was a daycare center, meaning that there really was no life hazard to worry about. The structure was a converted one-story home with a basement, and at zero-dark-early, the visibility inside was south of zero, and it was very, very hot. But we couldn't find the seat of the fire. I told my crew to stay near the wall, and I moved out into the center of the room--among a forest of chairs and desks--hoping to find some sign of flames. 

The floor went spongy under me, and then it went away, and I dropped through. It turned out that I was directly over the seat of the fire. As I fell, I was able to get my arms out to the side, cruciform, and that's what saved me from falling all the way through and burning to death. My teammates pulled me out, and I was okay, but that was unnerving.

Fiona - 
YIPES! And it's just such storytelling that makes your Johnathan Graves books some of my favorite reads. Can you tell us about the series?

John - 
I write thrillers about Jonathan Grave--a freelance hostage rescue specialist. The books are based on research I did for SIX MINUTES TO FREEDOM, the only book that Delta Force has ever cooperated with.

Fiona - 
Thanks so much for stopping by and helping us fellow writers and other curious folk learn about things that go boom. Just so my readers know, John has promised a return visit later in the year where we will learn about liquids and gases and other ways to be dangerous in our writing. So we'll all look forward to that.

In the meantime, here is how to keep up with John:

Thank you so much for stopping by. And thank you for your support. When you buy my books, you make it possible for me to continue to bring you helpful articles and keep ThrillWriting free and accessible to all.


  1. I love this post! I failed chemistry in high school, but was able to understand every one of John's explanations! And now, I feel like I should go blow something up. In one of my books, I mean. :)

  2. That is insane that soilders set c4 on fire and it doesn't blow!