The tickle of curiosity. The gasp of discovery. Fingers running across the keyboard.

The tickle of curiosity. The gasp of discovery. Fingers running across the keyboard.

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Showing posts with label John Gilstrap. Show all posts
Showing posts with label John Gilstrap. Show all posts

Sunday, June 28, 2015

DANGER ZONE: Liquid and Gas Explosions with John Gilstrap

Flammable Liquid
Flammable Liquid (Photo credit: Wikipedia)
We are chatting about things that go BOOM! in the night with New York Times bestselling author John Gilstrap.

John, will you tell my fellow Thrillwriters and readers why you're my go-to guy for all things explosive?


John- 
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- 

I am making making my way through all of your books and one of the things that I enjoy most is when you blow things to smithereens. We have discussed explosions before in THIS ARTICLE, but we decided to devote another article to gasses and liquids. Can you start with a primer on liquid and gas explosions? 

John Gilstrap
John - 
Let's start with some basic science. In reality, there really is no such thing as a flammable or combustible liquid. No liquids burn. Only gases and vapors burn. When gasoline burns, it's actually the vapors surrounding the gasoline that are burning. As the fire creates more heat, the rate of evaporation (vapor creation) increases, and the fire gets bigger. At the same time, because the liquid is evaporating, the volume of liquid decreases. When there’s no more liquid to produce vapor, the fire goes out. The difference between a flammable and combustible liquid, is the temperature at which the liquid creates

enough vapor to burn. That temperature is called the "flash point" (it has nothing to do with a "flash" like a lightbulb; “flash” is the chemistry term for the act of transforming from liquid to vapor).

A flammable liquid is defined by a liquid whose flash point is less than 100 degrees F. A combustible liquid has a flash point between 100 and 200 degrees F. Gasoline has a flash point of around -43 degrees F, so it is considered a flammable liquid. Diesel fuel’s flash point is around 123 degrees F, so it is considered a combustible liquid. 


Once they start to burn, the difference is purely academic. So, building on what we talked about in our last chat, it is difficult to get an explosions from flammable liquids. Depending on how much vapor as accumulated at the time of ignition, you can get a pretty good whump when they first ignite, but I can’t think of a way to get a really big bag. 

Gases, on the other hand (like propane) are gaseous at atmospheric temperature and pressure. To use them (say, in our gas grills), we compress the gases into tanks and convert their physical state to a liquid via condensation. If the pressure vessel is ruptured, that gas reconverts at a ratio of several hundred to one back to its gaseous form. If the gas is flammable (as opposed to, say, nitrogen, which is not), that big gas cloud will ignite all at once.

That rapid expansion and ignition can and often has caused low-order explosions. It's very difficult to get gases to detonate, however. Remember, a detonation is a flame front that travels at supersonic speed.

Fiona -
Could you define low order explosions? What would they look/feel like if present as one goes off? And as a follow up, is there medium and high order? If yes, how are they differentiated and experienced?

John -
Low order = a subsonic transmission of energy. 

High order = supersonic transmission of energy (i.e., a detonation) 

Up close, like standing on the surface, the difference is academic. As you move farther away, however, a low order explosion loses its destructive energy much sooner. With a detonation, the blast effects are much more widespread.

Fiona - 

So subsonic you don't hear a BOOM! ? 

John - 
Oh, there’ll be a boom. When an airliner crashes, the resulting fireball is a low-order explosion. There's still a boom, because sound and pressure are the same thing. What you won't get is a destructive shock wave.

Bursting a balloon is a very low order explosion.


Fiona -
The myth about exploding a gas tank by shooting it with a bullet. Why is this impossible?

John - 
An auto gas tank is not a pressure vessel. It just holds liquid. If a hole is poked, the liquid will leak out. If it's a flammable liquid, it will leak out burning. The fire will not propagate back into the tank through the hole for several reasons, probably the most important of which is because there won’t be enough oxygen among the vapors inside the tank to support combustion. You can get a *whump* and a fireball, but you won't get a *bang*. It's just physically not possible.

Fiona - 
What are some mistakes that you've either read in books or seen in movies that you would like us to avert? John - Remember that scene in Bourne Identity where Jason Bourne uses a shotgun to create an explosion when he shoots a diesel tank in the back yard? That. In movies in particular, where firefighters are working a fire, or where our heroes are trying to survive. All of that pretty fire along the floor is wrong. Heat rises. In fact, here's a video of what the inside of a fire really looks like.



Fiona - 
Thank you. I've been doing Citizens Fire Academy, and we got to see a flashover in their fire building. Very scary stuff. 

John - 
Yeah, I've been way too close to a couple of those over the years. You find out very quickly where your exposed skin is.

Fiona - 
Have you ever used gas or liquids in your novels? I know Big Guy is awfully fond of his C4 - have your characters ever needed to fabricate a bomb on the spot with found ingredients? 

John - 
Not in the Grave novels, no. But I think maybe in AT ALL COSTS, my second novel. That was my hazmat novel. Flammable liquids (FL) are very inefficient weapons. They are damaging only to the degree that people get splashed. Or, I guess, from the radiant heat. If you can create a BLEVE, though (boiling liquid expanding vapor explosion), you can do a lot of harm.

More science

Remember, I said before that liquified gas reconverts to its gaseous form instantaneously. Well, imagine a tank of propane that is exposed to fire. As the tank heats, the liquefied gas inside also heats, which causes vapor pressure to increase. The hotter the contents, the higher the pressure. 

Meanwhile, continuing flame impingement causes the steel of the tank to weaken. As the pressure inside increases. Sooner or later, the tank will weaken to the point where it can no longer contain the internal pressure, and it will unzip, at which point you get this instantaneous liquid-to-gas conversion that ignites all at once. The resulting (low order) explosion has been known to throw railroad tank cars over 600 feet. That can happen at the BBQ-bottle scale as well. 

Fiona - 
At what temperature does steel weaken and will this happen in a normal fire? I'm wondering about the construction of fire-proof safes/file cabinets. 

John - 
There are quite a few variables, but 1500 F is in the ballpark. At 2000 F you're talking imminent collapse in most cases.

But remember, that's the temp of the steel itself. These days, there are all kinds of ways to insulate the steel structure. Fiona - Going back to your last response, BBQ scale propane - could someone effect this by starting a small fire and setting the tank on top? Or is that not enough heat? John - Okay. More science . . . All liquid--even liquefied flammable gases--are heat sinks (a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium). That means flame impingement on the liquid space will never get the steel hot enough to weaken.

However, if you can direct a flame to the vapor space at the top of the container, you'll get an efficient transfer of heat and the tank will melt. Or, you could shoot a propane bottle for more or less the same effect. (Stand back a ways, though.) 

Fiona - 
How far back? 

John -
Hey, a quick plug: I'll be teaching a course on all of this at CraftFest in New York on July 8, 2015.

How far back is dependent on how full the tank is, but I'd be twitchy at much closer than 100 yards

Fiona - 
Directing a flame to the vapor space - how might that be done and conversely if someone was trying to protect a tank what could they do to protect it from exploding? 

John - 
I'll take that in two parts. 

One: How to make it happen. Imagine a welding cart, where two bottles of flammable gas are right next to each other. If you crack the valve of one and direct the burning gas stream to the vapor space of the bottle next to it, you've got a pretty good shot. Or, in your scenario of putting a five-gallon propane tank on a fire, as the pressure increases, the pressure relief valve will release and cause direct flame impingement on the vapor space of the bottle. 

Then the question is whether there’s enough time of impingement to cause the explosion. There’s no way to predict that.

Two: To protect it. Well, that's tougher. My SOP in the fire service was to pull back and drown the bottle with an indirect water stream. But for something bigger, we wouldn't even do that. We'd evacuate the area and put in earplugs. 

BLEVEs are extremely unpredictable. The only way to stop the inevitable once you have flame impingement is to keep the pressure vessel cooled to a temperature below its critical temp.

Fiona - 
What household/garage-held liquids/gases might serve a danger or conversely a MacGyver-type last ditch effort explosive? As an example I've seen hairspray used as a blow torch before (long story about a rat - don't ask). 

John - 
ANY compressed gas cylinder will work--including hair spray, but the magnitude of a household aerosol can is just not enough to do real harm. I've had them popping off all around me in fires. They scare the bejeebers out of you, but there's not enough potential energy to do much harm. 

Fiona - 
We've talked about solids as explosives in our last article and this one is about liquid/gas. I'm curious about the combination of the two. Are there particular products (not to teach people how to cook bombs for sure) but products that people should know not to store in the same place unless, for example, a bad guy shoots a hole in a container and all of a sudden product A leaks into product B - and if you would be so kind a science lesson? 

John - 
Okay . . . Fuels and oxidizers do not get along. Pretty much anything in your garage that ends with "nitrate" in its chemical name should be kept away from fuel sources because nitrates are very strong oxidizers. 

Petroleum products react spontaneously with strong oxidizers to create a fire. Medicinal O2 and fuels = bad stuff. 

Oddly, some of the most stable items to store are the things you'd think you'd have to worry about. Stuff like ammunition is very stable, and difficult to cook off. To shoot a box of ammo is to put a hole through the box and spill powder. Nothing dramatic. If you store gasoline in your house, you're not thinking things through. 

In Oklahoma City, the Murrah Building was brought down with a mixture of ammonium nitrate (fertilizer) and fuel oil. It's called ANFO, and it's a very useful and powerful explosive. It's the addition of the oxidizer that makes such a big boom. Very, very high order. Rocket propellant is essentially polymer and oxidizer, with a little magic and voodoo thrown in. 

Fiona -
Voodoo being the essential ingredient.

I have been to a house where my friend was on O2 as you come to her door there is a big sign "no smoking allowed" If a non-English speaking person was smoking and walked into the house what if anything would happen?

John - 
Oh, there's a great/horrifying story about this. Supposedly, there was an old lady in an oxygen tent back in the day who, when preparing for the arrival of her family, combed her hair. A tiny static spark immolated her. The astronauts of Apollo 1 were incinerated on the pad because of a tiny spark in a high-O2 atmosphere. Very, very dangerous.

Fiona - 
Carbon monoxide is lethal because it displaces oxygen in the bloodstream, is it also flammable?

John - 
It is. 

Fiona - 
What did I miss that you feel we should know? 

John - 
I encourage everyone to research this kind of stuff before you put it down on paper. Whether it's explosives or guns or knee surgery, there are SO MANY resources available through the Interwebs. And people should feel free to reach out to me if they want to bounce an idea or two. 

Fiona - Thank you kindly for sharing your expertise - as always it was fabulous learning from you. Now, you have a new book. Can you tell us what it's all about?

Read it Now


John - 
Jonathan Grave finds it hard to believe that a fellow combat vet has gone rogue, killing American agents and leaking sensitive intel to hostile foreign interests. With black ops assassins on the trail of his old friend, Grave sets out to get to him first. He finds far more than he bargained for. Not only the wily operative, but evidence of a conspiracy so dangerous, so far-reaching, that an unthinkable tragedy is in-motion. Grave and his elite team of specialists must expose a deadly high-level secret —and do it in time to avert a catastrophe of historic proportions…

You can stay in touch with John here:



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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.

Cheers,



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.


RELATED ARTICLE: Breach Entry

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.) 
RELATED ARTICLE Bomb Squad

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 - 
Yay!

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 - 
WOW!

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.