Nov. 1950: Sorry, Margaret—Boom Nears End #ThrowbackThursday

This article was originally published in the November 1950 edition of Mayovox.

The little man,
With dynamite,
Shakes the walls,
Fills me with fright.

Blasting, blasting
All the day.
I’ll miss him when
He goes away.

We hate to have to break this to Margaret Hurn, creator of the above plaintive verse, but—

boom“General blasting should be finished by the time your story comes out. Blasting for column footings and elevator pits should be finished about two or three weeks after that,” says Gus Olson (of Stocke and Olson, building contractors for the new diagnostic unit). Agreeing with Olson are Bill Degroot and Jack Ostern, as dependable a pair of “powder men” as ever fired a charge.

Bill and Jack liked to laugh themselves to death when we relayed a question about was there any possible danger, blasting that close to the ’29 building.

To prove how ridiculous it was, they invited us to stand right up close and shoot a picture as a charge went off. We explained how it’s better to focus a camera from a long way back, but they insisted, and so we stood up close with a couple of bored truck drivers. And Bill and Jack were right—when you're ready, there is nothing to it: just a tiny tremor and a light “poof.”

(The picture didn’t turn out very well, unfortunately. Something shook the camera.)

The two powder men had a theory. They figured that when you’re down in the pit (even when you’re not actually working with dynamite), you’re unconsciously set for the blast when it comes. But if you’re concentrating on shorthand or answering a question or typing a letter, why it will catch you off guard, every time.

It sounds reasonable, and Jack and Bill are sorry if they upset anybody. Anyway, they’re just about finished.

As long as we were down in the pit, we thought we might as well get a story.

That strata of rock being blasted to make way for the foundation of the new Clinic building runs under the Kahler, First National Bank, and other buildings. This, we all agreed, was probably why a light charge could sometimes be felt sharply in any of the three buildings.

On this job, there are two kinds of blasting—“general shooting” and “shooting for the footings.” The principle difference from the layman’s point of view, we gathered, is in the distance between the holes drilled for the dynamite.

When the holes have been drilled—they vary in depth from four to ten feet, depending on the result wanted—the powder men take over. First, they inspect the holes, which on this job are always set in the form of a square. Satisfied, they jab lengthy poles into the holes to clear out any loose obstructions.

Into each hole, they drop from one and one-half to four one-pound sticks of dynamite, depending on whether it’s to be a “shallow” or a “deep” shot. Chatting cheerfully, they attach an electric detonator, poke away with their sticks until they have the dynamite where they want it. They pound earth down the holes. Then, trailing the wires attached to the detonators, they walk back a number of yards and shove down on a plunger.

A yards-square piece of rock mushrooms upward, ready to be trucked away. Then, Bill and Jack do it all over again. They act like it’s fun.

(In the bedrock where they were working the other day, each charge produced from three to four yards of rock broken into manageable sizes; occasionally, a single rock will be a full load for a truck. All told, about 6,000 yards of rock will be excavated before they are finished, Olson estimates. Most of it goes for fill at Soldiers Field; the rest went to the new bridge site adjoining Mayo Park.)

Watching Bill and Jack work, we found that—as with any skilled men, working with tools they know and respect—there is a pattern, almost a ritual.

Take the business of covering the holes before firing the charge. To prevent debris from flying, powder men on a job like this use two massive three-quarter-inch woven steel cable pads; each of these protective “mats” weighs 2,200 pounds. Tucked in the way they tuck them in, these huge pads would contain bigger “shots” than any Bill and Jack figure to fire around here.

The pattern of safety carries over from day to day—no “loaded” hole is ever left overnight; all dynamite and caps are carried away nightly, stored in a place of safety.

How do you know how much dynamite you can use, with safety, on a given job? Gus Olson referred us to the job engineer, Joe Ostrander for the final word on this.

Joe, a lean, sinewy young guy with a nice grin and much patience, said that there is a rule of thumb for deciding how much dynamite you can use and still be sure of having a “safe” charge. Take this job, where the hardest blast makes a barely perceptible vibration at the Clinic. Well, the margin of safety is five times the faintest vibration you can feel at the point in question.

A conscientious young man, Joe gave us a textbook formula for determining blasting safety:

_              (ER)  D____       
C equals V (50 squared) K

That’s where K equals .001 for hard rock and .008 for swamp, he elaborated.

With this cleared up, we checked the Encyclopedia Britannica for some background on explosives in general. Among other interesting things, we found that the "father of explosives" was Friar Roger Bacon who discovered (some 700 years ago) the process for purifying a salt by crystallization from an aqueous solution. This led to gunpowder, and everybody knows where that led.

Bacon died a natural death at 80, so why worry?

Alyssa Frank

Alyssa Frank

Alyssa Frank is a Marketing Segment Manager at Mayo Clinic Laboratories. She leads marketing strategies for product management and specialty testing. Alyssa has worked at Mayo Clinic since 2015.