Donors and Acceptors: Physical distancing lessons from the explosives industry

Since I'm an analogy guy the notion of masks "to protect you from me, and me from you" reminded me of what I learned about an explosives-safety principle called donors and acceptors.

This was during a visit to the DynoNobel dynamite plant near Carthage, MO. It's what chemists call a nitrating plant, meaning that nitrogen compounds are mixed with other ingredients. The result is blended with an absorbent to fill tubes and make sticks of dynamite. 

When I visited in 2000 this was the last dynamite factory still operating in North America. That's because dynamite has mostly been replaced by less sensitive blasting agents relying on ammonium nitrate. 

The blasting agent our crew used on a construction project in Missouri was one of those ammonium-nitrate explosives, called Tovex, a product of DuPont. It came in tubes and we used Primacord and electric caps to set it off. 

The key ingredient at the Carthage plant, ethylene glycol dinitrate, is an updated version of nitroglycerin, made from glycerol and white fuming nitric acid. EGDN flows like a light vegetable oil. 

Nitroglycerin will explode if shocked or overheated, and the Carthage plant was dealing with thousands of pounds in a single batch, so special precautions were in order. Before our tour, Rick Fethers, the DynoNobel safety officer who served as my escort, went over the plant map. The plant was divided into four zones and people working around the plant had to know which zone they occupied at all times. That way, after hearing a specific set of honks from the alert system, they'd know how to run from danger rather than into it. 

I asked why the buildings were so far apart. Rick explained the risk-management principle of  keeping separation between "donor" and "acceptor" buildings. These are minimum distances required in case of explosion, so that one blast doesn't throw explosives or missiles into nearby storage magazines, potentially triggering a plantwide chain reaction. 

Here's a table from the 2017 "Table of Distances" guide from the Institute of Makers of Explosives. 

Reading down the first column to find a quantity between four and five tons of high explosives (that's the "donor"), reading across the row shows the minimum permissible distance to a barricaded "acceptor" magazine full of blasting agent is 47 feet. And that protective barricade has to be at least twenty inches thick. 

And the publication goes on to explain that if the "acceptor" magazine of blasting agent lacks a barricade, the minimum safe distance is six times greater, or about 300 feet. 

Here's a photo from a 2008 Department of Defense test at China Lake using a one-ton TNT donor charge. This was followed by a careful search for all debris, which reached out two-thirds of a mile. 

So there's the analogy from a hundred years of hard experience with explosives: Today's anti-COVID rules about keeping a six-foot (or more!) separation and using face masks are like the regulated safe distances and barricades between explosives: precautions now can stop a chain reaction later.