Looking into the forces that drive wildfires

Pioneer Fire northeast of Boise, Idaho, August, 2016. USFS photo.

High Country News has an excellent article written by Douglas Fox that looks under the hood, so to speak, at the science that causes wildfires to burn the way they do. There are forces, unknown until the last decade or two, that are major influences on the spread of a fire, such as the 100 mph flamethrower-like jets of flame that may have contributed to the deaths on the 1994 South Canyon fire near Glenwood Springs, Colorado.

Mr. Fox writes in illuminating detail about state-of-the-art research being conducted by Janice Coen, David Kingsmill, Craig Clements, Mark Finney, Michael Reeder, and Brian Potter, as well as legacy research done by the the U.S. military in the 1940s that provided data on how to design incendiary bombs to burn down many of the buildings in Hamburg, Germany on July 27, 1943 in order to demoralize the workers in Germany’s critical U-boat industry.

Most of the article is about recent research on wildfires, but here is an excerpt about the military’s work in the 1940s in northwest Utah that facilitated the attack on Hamburg by the British that killed at least 42,000 people.

…The U.S. Army’s Chemical Warfare Service had commissioned Standard Oil Development Company to construct a row of steep-roofed European-style apartment buildings. Erich Mendelsohn, an architect who had fled Nazi Germany, specified every detail: 1 1/4-by-2-inch wood battens, spaced 5 7/8 inches apart, to hold the roof tiles; 1-inch wood flooring underlain by 3 1/2-inch cinderblocks, and so on — all to replicate the dwellings of German industrial workers. The wood was maintained at 10 percent moisture to mimic the German climate. Rooms were outfitted with authentic German curtains, cabinets, dressers, beds and cribs — complete with bedding — laid out in traditional floor plans.

Then, military planes dropped various combinations of charges on the buildings, seeking the most efficient way to penetrate the roofs and lace the structures with flame.

Those experiments offered clues on what factors could cause firestorms. And in the years following World War II, scientists would study Hamburg and other bombing raids to derive basic numbers for predicting when a firestorm might form: the tons of munitions dropped per square mile, the number of fires ignited per square mile, and the minimum area that must burn. They concluded that Hamburg’s unusually hot weather set the stage for the firestorm, by making the atmospheric layers above the city more unstable and thus easier for a smoke plume to punch through. Scientists theorized that this powerful rise had drawn in the winds that whipped the flames into even greater fury.