Editor’s Note: A Shared History is FireRescue1’s newest monthly column. In it, fire-service historian Bruce Hensler will explore the unique aspects of our history and provide perspective for today’s firefighters. This edition is the first of a three-part series that examines how fire-suppression knowledge was used for different means during World War II.
For individual fire departments and the entire fire service, it is necessary to know the chronology of facts that form the basis for our cultural identity. It identifies us as an important social group and tells others of our accomplishments.
But history is more than facts and timelines. We study history to further our understanding of the world and our place in the world. We study and document our work, past and present, to make our story known.
And sometimes that story takes unexpected twists. Such is the case with the history of the fire service — here’s one peculiar and little-known example.
Fire as a weapon
In the 1800s, American cities burned regularly and what we learned from fighting those fires shaped the modern fire service. In the Second World War, we applied that knowledge to starting fires using incendiary devices and high explosives dropped from airplanes over European and Japanese cities.
In contrast to firefighting, this is known as fire-raising and it became an effective tool for frightening the civilian population and destroying industrial capacity in enemy countries. It required the effort of experts in military aviation, explosives, target analysis, and aerial photogrammetry, as well as economists, historians, statisticians and fire protection engineers.
Early in the war, the air forces relied on trial and error to maximize efficiency of bombing. They bombed, evaluated the bomb damage by studying aerial photos and used the information for the next bombing run.
Trial and error is costly in terms of resources, especially the bomber crews flying in formation over enemy cities thousands of feet in the air facing hostile fire from anti-aircraft batteries and fighter planes.
The English learned quickly from studying their own cities after bombing raids by the Germans that weight for weight, incendiary devices were more effective than high explosives at creating very large destructive fires.
The United States recognized the inevitability of their involvement in the war and sent experts to England to study the use of fire in an air war. Their focus, however, was on the defense of urban and industrial centers from fire.
More effective than explosives
In 1943, the British Air Ministry began a focused effort to study the real potential of fire as a weapon. They knew that the right amount of incendiary devices when dropped on target were more effective than explosive weapons.
The problem was in knowing the right amount of fuel to drop for a given target and how to identify with accuracy the target areas from aerial photographs. To gather information, over two years, they indiscriminately dropped thermite sticks on German cities, without regard for the target city’s potential for flammability.
In order to analyze the data they gathered they requested assistance of fire experts from the United States. Under the auspices of the U.S. State Department, fire protection engineers from the staff of the National Fire Protection Association went to England and joined the effort to make fire-raising an effective weapon of war.
Using fire offensively against urban and industrial centers required knowledge of the flammability potential of a target, the composition of the buildings and contents, plus the physical arrangement of the target. To get a good fire going using incendiary bombs required that the devices be dropped in sufficient mass that they could burn uninhibited for eight to 30 minutes at the point of impact.
Experts in operations research, statisticians, mathematicians and fire protection engineers calculated flammability potential, analyzed targets, and calculated bomb loads to understand how fires could be made to grow, jump obstructions, cross open ground, and extend over a wide area.
They were also interested in the rate of fire spread because it was critical that fires develop quickly before firefighters could organize an attack. They learned that the best way to slow firefighting efforts was to drop explosives, but only after the fire was allowed to grow and extend.
Contained within these walls
From our knowledge (our history) of fighting great fires in the 19th century, the fire engineers knew that the combustibility of structures, the arrangement of structures, and the presence of parapeted fire walls were the most critical factors in predicting fire behavior in high-density urban areas.
Even cities of brick buildings could be destroyed if fire was allowed to grow in proportionate size and extend itself.
The NFPA fire engineers studied fire insurance maps of cities where bombing had created great fires. Where those maps identified high-risk fire zones, the NFPA engineers overlaid the perimeter of bombed areas and found coincidence: those high-risk areas were the areas where great fires might be started with incendiaries dropped from airplanes.
The NFPA engineers also predicted, quite accurately, that parapeted fire walls influenced whether a fire could be made to spread. By concentrating incendiary bombs in sufficient quantity within a target area confined by fire walls, that area could be made to burn violently.
They referred to these confined areas as fire cells.
Using aerial photographs of German cities, NFPA engineers identified individual fire cells having a high potential for flammability where air crews should concentrate their incendiary bombing along with the dropping of high-explosives to disrupt command and control of firefighting operations.
The next two articles of this series on fire and the air war will focus on the fire-bombing of the German cities of Hamburg and Dresden by U.S. and British air crews, as well as the firefighting efforts that saved London from the fires of the German Blitz.
