Explosives as Movie Star: 10th Anniversary of Vertical Limit

December is the tenth anniversary of Vertical Limit. There are rescues, avalanches, blasts, leaps, and crevasse plunges every few minutes, high up on K-2. Emotions run high as recriminations and treachery abound.

It's not my favorite movie, but it's fun to watch, because it counts as one of the sillier portrayals of high explosives. Apparently inspired by The Wages of Fear and the excellent remake Sorcerer, the writers ladled a generous amount of nitroglycerin into the plot.

In the movie, the explosive is portrayed as a glowing liquid inside glass containers, which are packed conveniently in cases. When sunlight falls on it, run for the hills!

In reality nitroglycerin doesn't blow up when sunlight falls across it (though it is ultra-sensitive when thawed, after having been frozen), and it's not a garish fluorescent color. It's clear to slightly amber, and has the consistency of a light syrup. Miners used the liquid long ago in hard-rock tunnel jobs and mines, but it was so unsafe that dynamite took its place. Nitroglycerin and its close relatives are still used in manufacturing a limited number of explosives, propellants for cannon and rifle ammunition, and heart medicine. Anscanio Sabrero first mixed up a batch in 1847.

Back in 2000, when visiting Dyno Nobel's dynamite plant near Carthage, MO, I learned that Dyno Nobel had ceased using nitroglycerin there in favor of metriol trinitrate, aka nitropentaglycerin. It's abbreviated MTN. MTN is less likely to cause headaches and is somewhat more stable than nitroglycerin when heated, but equally prone to exploding under shock.

I had the chance to accompany a Dyno Nobel employee inside some of the buildings while the dynamite manufacturing process was underway, and found it quite interesting. The smell of MTN reminded me of a blend of two familiar odors: the chemicals used to disinfect swimming pools, and the disinfectant once used in hospitals.

An “aha” moment for me was seeing a stream of MTN flow from an upper pipe to a lower one with a bigger diameter. The clear liquid gurgled peacefully across an air gap, so it was in plain view. (This precaution is for a good reason; it avoids shock waves -- see below). Later I went to the wooden building where MTN is mixed with absorbent and loaded into casings to make the familiar “dynamite sticks.” The packaging structure was decades old and had a peaceful, timeless quality, and reminded me of an old mining building of the kind I've seen out west because it was built into a hillside. There were no radios and every nail head was covered, to prevent sparks.

But even when experts take much care there is still a residual risk when dealing with nitroglycerin and MTN, which are extremely powerful, pound for pound. In fact, two months before I visited, the Carthage plant had suffered a good-sized explosion while processing a batch of MTN. But there were no injuries that time, thanks to many precautions: intense training, sirens, a generous distance between buildings, doors that open easily when a man is running for his life, stuff like that. See Chapter 9 of Inviting Disaster.

One no-no for visitors to a dynamite factory is dropping stuff: say knocking a coffee mug onto a hard surface with one's elbow. That's because of the slim chance that MTN could have leaked onto a floor. My guide on the tour made sure I left behind my cell phone, coins, and car keys. Even though the plant was doing everything it could to prevent such a puddle, the precaution was mandatory.

Back to the adorably bad movie Vertical Limit: I can't think of any reason that even half-sane mountain climbers would load up their backpacks with nitroglycerin. When I visited Dyno Nobel wasn't shipping any MTN as a liquid to quarries and mines; it blended the liquid with absorbent and packed it into dynamite casings first.

(Yes, there was a time in oilfield work when quantities of nitroglycerin would be made locally and delivered by truck; it helped cleanse aging oil wells of paraffin build-up downhole. Readers with access to Ebsco Host databases can read all about it in a Saturday Evening Post article, "The Most Dangerous Job in the World," January 27, 1951.)

I first read about the history of nitroglycerin when writing an article on the history of vault-breaking and safecracking. In the late 1800s, itinerant criminals called yeggs would steal dynamite from quarries, boil it with water in kettles (very bad idea, that one), skim the "soup" off and store it in rubber flasks. Once on the job, they'd funnel it into tight-fitting safe doors before detonating it.

One reason that nitroglycerin and MTN can be so dangerous when transported in liquid form is that they slosh. They have the consistency of a light syrup, so they trap air bubbles. Explosions have been triggered by sudden shifts of the liquid, although it's not inevitable. (Old hands in the oil field industry tell stories of cans of nitroglycerin falling off a truck and bouncing down a hillside, without incident.) Sloshing caused the entrapped air bubbles to compress rapidly; this made the air in the bubbles heat up; this made the container explode. It's called adiabatic heating. According to Dyno Nobel, adiabatic heating is not a problem if plumbing is adapted to MTN's special demands. Hence the air gap I mentioned above.

Spontaneous explosions are most likely if MTN hasn't been thoroughly cleansed of all unused ingredients and unwanted reactants. Tainted batches can blow up promptly, or months later if the explosive has been stored (unwisely) as a liquid.

Strangely, I found while researching Inviting Disaster that a great many more people have been killed by accidental explosions of the “safer,” modern explosives based on ammonium nitrate than by accidental explosions of nitroglycerin. The most common reasons for ammonium-nitrate disasters -- such as the two ships that blew up at Texas City in 1947 -- were carelessness and lack of knowledge.