09 March 2012

Explosives 101: RE Factor

I’ve been busy lately: writing a synopsis for my current novel so I can shop it to agents, working on three short stories that won’t let me alone (drives me crazy in the middle of the night!), writing and assembling a “Parents Packet” for the folks at my church who want to send their kids to summer camp (that took 4 solid days!), and watching my kids (which also means driving them all over creation) this week because they’re home on Spring Break.

This is by way of apology for not having time to post comments on very many SS articles over the past couple of weeks. They’ve all been great; I’ve truly enjoyed reading every single one—but when it comes to posting comments, I’m really sorry. Too often, time management problems have reached out to snag me by the throat!

I wrote this post on Thursday morning in Scottsdale, Arizona. SS posts go up at midnight eastern time, which is 10:00 pm local time, and I’m scheduled at the cigar store from 4:00 pm to 9:30 pm. Which means: I need to put something together that folks will find worth reading, and that I’ll find quick to write. My solution?

A quick rundown on Explosives & How to Use Them.

I got the idea from what Deborah wrote yesterday, in her wonderful article examining the double-edge sword we all call Technology, about needing information concerning “how a weapon would work under certain situations.”

Now, I’ve fired all sorts of weapons — M-16’s, M-14’s, M-21 system (sniper rifle), M-60 Machine Gun (7.62 mm, I can dance with one of these pretty well), M1911 (commonly called a .45 automatic), M-9 (Army issue Barretta 9mm semi-auto sidearm), Ma-Deuce (M2, .50 cal. machine gun – not too good with this one, operator headspace & timing problems lol), M-79 “Blooper” (40 mm grenade launcher), M-203 (M-16 w/ 40 mm grenade launcher attached beneath upper receiver), AK 47 & other AK series, H&K MP5 & MP5SD (an automatic rifle—SD version is suppressed [has what Hollywood calls a “silencer”), suppressed Ruger .22 semi-auto target pistol, Light Anti-Tank Weapons (similar to a collapsible Bazooka – but NOT re-loadable, no matter what you saw in that Dirty Harry movie where they use them at Alcatraz), SAW’s, Glocks and other stuff — and, I’ve used them in the desert, the jungle, the African bush, while riding Zodiac rubber assault boats over the ocean, on the beach (while the weapon’s still wrapped in plastic) after swimming in as a member of a Scout Swim Team, in rain, snow and ice storms, and probably in more places than I care to remember! So, Deborah, feel free to call 24/7; I’m happy to answer any such questions I can. But, she also got me thinking about explosives . . .

Too often in fiction (print, television, films, on-line) I find myself turned off by writing that would have been a joy to read . . . except that the author didn’t know his/her “4th Point of Contact” (That’s paratrooper talk for: rear end) from a hole in the ground! So, I thought I’d post some pointers here that might help. Unfortunately, there’s a lot to explosives (I spent nearly 6 months studying them in the SF qualification course), so I’m going to post it in parts.

On the other hand, I’ve decided to label all the parts. And, if I remember, I’ll add the flags that will help you find the info you want when you need it (like in the dead of night, for instance).

Today’s Subject: RE Factor

Explosives are rated, and charge calculations are based on, what is called the “Relative Effectiveness Factor” (R.E. Factor, or just RE [“are-eee”] for short). I’m sure you’re familiar with the standard number line you learned in grade school, which has “0” (zero) as the baseline. An easy way to envision explosives that are listed by RE is to imagine them hanging from a spot on the number line.

On this number line, however, our base is TNT (Tri-Nitro Toluene C7H5N3O6) instead of zero. And, because charge calculations require multiplication, we’re going to assign TNT an RE Factor of “1” (one) instead of zero, because 1 is the multiplicative identity factor (don’t worry, there’s no test, and I’m not going to make you do math – I just want you to understand what RE is).

Explosive charge size is calculated based on the number of pounds of TNT required to do the job, then you multiply by the RE Factor of whatever explosive you plan to use, in order to convert “pounds of TNT” into the number of “pounds of the explosive you have on hand”.

For example: if we want to cut through a solid steel rod (maybe that rod is part of the support structure for a suspension bridge, for instance), we might use the formula P=3/8A. This means “Pounds of TNT needed to do the job” equals three-eighths of the “Area of the cross-section of the steel rod we plan to cut.” If it’s a rod with an area of one square inch, then we’d need 3/8 of a pound of TNT to cut the rod.

If we are using C-4 (plastic explosive) to cut the rod, then we’d divide our answer in the paragraph above by 1.34, because C-4’s RE is 1.34 (I know I said we were multiplying, but division is just inverted multiplication – it’s the same thing – Trust me!). In other words, C-4 is considered to have 1.34 times the relative effectiveness factor that TNT is calculated to have. And that’s why it’s called a Relative
Effectiveness Factor, because C-4 has an explosive factor of 1.34 Relative to TNT’s explosive factor of 1.0.

Thus: if TNT sits at the baseline of 1 on our number line, C-4 sits at a spot that is labeled 1.34. Dynamite would be sitting just below TNT, at 0.98 and ANFO (Ammonium Nitrate and Fuel Oil – the explosive used by Timothy McVeigh to destroy the Murrah Federal Building in Oklahoma City) is farther down, because it has an RE of only 0.47 (if I recall correctly; I don’t have any of my FM’s at hand, so I’m just working off memory here; it might be 0.42 or 43, but I think it’s 0.47).

A few things to note:

(1) TNT has an RE of 1 in the military explosive charge calculation system. HOWEVER: I’ve worked with civilian blasters who calculated their charges based on an RE system that used Dynamite as the baseline (i.e. in some civilian blasters’ calculation systems, charges are formulated calculating against Dynamite with an RE of 1). This would mean that TNT would have an RE of something around 1. 02 in this system. I thought you might need to know this, incase you write a story about a civilian blaster who’s planted a bomb, or something. His calculations might be a little different than mine, because he’d be using Dynamite as his baseline, instead of TNT.

(2) Don’t be fooled into thinking that a low RE factor means an explosive isn’t potent. Remember what a low RE explosive like ANFO did to the Murrah Building!

3) A good way to think of RE is to compare it to gears on a vehicle. When you need the heavy push of a low gear — to get a heavy load moving — go with a low RE such as ANFO or something. So, use low RE to move dirt, blow out bridge abutments, or push-in the side of a building. BUT: If you wanted to drive your car through a wall, you wouldn’t do it by inching your car up to the wall and then trying to slowly nose through. Instead, you’d get going as fast as you could — in a high gear! — and slam through that wall. So, for breaching a wall or obstacle (or cutting through steel girders, maybe), you want an explosive with a high RE factor, such C-4. High RE explosives go off with a sharp, higher-pitched CRACK! than lower RE explosives that tend to explode with a WHUMP! that you can feel, and which makes the ground jump under your feet (or chest and legs, if you’re lying prone hugging mother earth for dear life as hot lead shreds the air overhead, while you’re counting down and praying your charge goes off on “Zero!” LOL).

(4) For you guys in law enforcement who are sitting there saying, “What’s he talking about? That’s not breaching!” don’t sweat it. The specialized breaching charges you guys use, such as WB, detcord wraps, FLS, etc. are just that — Specialized breaching charges, designed to lower the amount of spalling that occurs. Spalling is the breaking off of fractured concrete, steel or wood from whatever you were breaching; this stuff shoots out from the explosion area in the form of shrapnel and hurts or kills people on the other side of the door or wall you’re going through. The breaching charges you’re familiar with for CQB are designed to reduce that hazard, and are therefore much different than what I’ve described above. (Though Det Cord is filled with PETN, which has a very high RE).

(5) The fireball explosions Hollywood loves, such as the explosion on the ground floor in DieHard is created using gasoline or dust. If you don’t think airborne dust can create a tremendous explosion, talk to somebody who owns a grain elevator; s/he’ll tell you stories that will scare your pants off!

OH! And, one more thing about machine guns . . .

I recently read a story in which a character fired a “60-caliber machine gun” from a helicopter. I’ve never heard of a .60 Cal. I think the author heard of an M-60 machine gun, which fires 7.62 mm rounds (about .30 cal.) and thought the “60” in M-60 referred to the caliber of the round. Please don’t make the same mistake.

I think that about covers it for a “Quick Down & Dirty” about RE Factors. And, your eyes are probably glazing over in boredom about now. So, I’ll call a halt to proceedings. Next time, I’ll cover Blasting Caps and how to Prime A Block of Explosives. And, I promise: Absolutely NO MATH. Lol

Until then . . . Take it easy, and Have a BLAST! (Sorry, couldn’t help it.)


  1. Fascinating, Dix,all clear as mud now. And honestly even though I don't totally understand most of what you said, I understand the frustration when something is terribly wrong with what you're reading. Mine was always anatomy/medical errors since I worked x-ray/radiation for years. My late husband worked commercial construction for 35 yrs and he was aggravated when writers substituted cement when they meant concrete. You mix water & cement to get concrete. Cement is the powdered stuff. Details, details, details.

  2. Fascinating, Dix,all clear as mud now. And honestly even though I don't totally understand most of what you said, I understand the frustration when something is terribly wrong with what you're reading. Mine was always anatomy/medical errors since I worked x-ray/radiation for years. My late husband worked commercial construction for 35 yrs and he was aggravated when writers substituted cement when they meant concrete. You mix water & cement to get concrete. Cement is the powdered stuff. Details, details, details.

  3. LOL Jan! I hear ya, when you say clear as mud. The reason I started with RE factor is because it gives a person a taste for the differences that exist between types of explosives--something not always realized.

    And, I commiserate with your husband when it comes to concrete vs. cement. 


  4. Also: Re-reading Number 4, I think it might come off looking as if I’m being a bit high-handed. I was just trying to clarify the difference between specialized and standard breaching – not trying to make it look as if someone who practiced CQB or dynamic entry might not understand what specialized charges are, or why they’re used.

    Hope the tone didn’t inadvertently offend anyone. And I apologize if it did.


  5. Terrific info and it makes me glad I do psychological mysteries!

  6. Dix, your intriguing column prompted me to glance over my copy of The Anarchist Cookbook (17th Printing, July 1978). Sure enough, it included the P = 3/8A formula along with several others. My favorite part is their Warning: Do not attempt to investigate a misfire too soon. AND. If you are using an electrical circuit, be sure you have disconnected it.

  7. “Do not attempt to investigate a misfire too soon. AND. If you are using an electrical circuit, be sure you have disconnected it.”
    ROFL!! You just pegged the reason for the rule: "He who set the charge must investigate his own misfire." lol
    And, Janice: I feel the same trepidation you mention—but vice-versa: when I try to do psychological mysteries, because I'm quite lost. In fact, I go to a couple guys I know who are counselors to try to get at least some idea if what I'm writing in that realm holds any water.
    My column in two weeks, though, should hopefully alleviate any such concerns for you. I plan to have information that's directly applicable to writing a story with a bomb or explosive device in it. My goal is to provide enough info that you could write something in which a person sets an explosive in place and it reads as if you have some experience doing such a thing.
    Just a shame I can’t get us all out on a demo range to launch a pickup in the air or something. . LOL Maybe some year we can all meet at Boucheron and arrange such an outing. Who knows.

  8. Great column, Dix. I love finding out about this kind of thing. Many thanks!

  9. Interesting stuff. The Anarchist Cookbook advice reminded me of Murphy's Laws of Combats, which I am sure Dic and R.T. are familiar with.

    Example: "Incoming fire has the right of way."

  10. A Broad Abroad09 March, 2012 23:03

    This is one way of getting SleuthSayers noticed!

    Introducing Dixon, our very own 'person of interest'.

    Great stuff, DH - I so enjoy behind-the-scenes information from someone truly in the know.

  11. This is one way of getting SleuthSayers noticed!

    Introducing Dixon, our very own 'person of interest'.

    LOL Not worried; I keep the classified stuff to myself. Consequently, I'm afraid I won't be covering much about booby traps or how to make explosives from common household or industrial products. And -- while the Anarchist's Cookbook can be useful as a writing reference tool -- please don't try to assemble any of the items described within, as some of the formulas in that text are improperly presented.

    I'm glad to hear some folks found this worth reading. I was a little concerned as RE Factor seems a little esoteric, but is actually an important thing to know about.

  12. Chiming in late, but I have to tell Jan about the time my stepdaughter came home from day camp and told us she'd been doing "cement poetry."

  13. Not trying to sharpshoot you here. But just FYI AN/FO has an RE of 0.80. You were thinking of just Ammonium Nitrate which I just looked up which is 0.42. damn close from memory though.

  14. That's interesting Zclif. 0.80 sounds a bit high to me, but . . . Could be; as I said I was winging it. Gonna have to try to dig out my old FM's and tighten up my shot group. LOL

    And, thanks for the input. I honestly appreciate it, and hope you enjoy reading my posts, buddy.


  15. Very good.. however.. the formula is too specific for the casual user.. the grunts or scouts or jarheads or whoever... except maybe an engineer. .. so you know we use a much easier calculation of P = Plenty.. of whatever is on hand... remember. . Keep it simple stupid .. A Scout. .

  16. Greg, I spent several years running around the Third World with a Girl Scout hat on my head, and ten other guys (the eleventh being another engineer sergeant) who constantly harped about why we couldn't just go with P=Plenty ... right up until it came time to hump all that demo into the target area on our backs! THEN, they decided cutting the load down to only the size we needed (plus that "little dab'll do ya'" that you always need to include) made a heck of a lot of sense. LOL

    "Scouts Out!"


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