I mentioned in a previous post that fire does not burn any differently than it ever has. This statement is based on the fact that fire is a science. With that being said, I’m about to emphasize that fires do burn differently today than they have in the past. This statement is based on the fact that the built environment has changed, thus impacting the fire dynamics we are now facing. Notice the significant difference the placement of the letter “s” in fires has on the meaning of the two, italicized statements.
The evolution of the built environment includes the increasingly common use of lightweight, low-mass, engineered wood structural components; petroleum-based fuel loads; and, open floor plans. The evolution of these three aspects of the built environment has combined to form the perfect storm of fire dynamics impacting both occupants and firefighters.
Changes in modern structural components stem from architects and engineers attempting and succeeding at increasing the load-carrying capacity and cost-efficiency related to those components. These changes began to impact the fire service in the 1970s. It started with truss construction of roof assemblies and truss construction of floor assemblies, both held together with gusset plates, followed by OSB I-beams and other engineered lumber structural components held together with glue. (I once heard a speaker suggest we stop using the term “lightweight construction” and start utilizing the term “low-mass construction.” His reasoning was that anyone who was ever buried under a truss roof collapse knows there is nothing lightweight about them. More so, it is the “low-mass” aspect of these components that creates the problem of reduced fire resistiveness, and therefore should be our focus. I’m not sure why this logic never caught on, but I have always agreed.)
While lightweight, low-mass construction was evolving, so were the development, marketing, and use of petroleum-based furnishings and finishes placed in homes. Cost, comfort, convenience, appearance, and a consumer demand for “bigger” all seemed to drive the change. The volume of natural products within the built environment decreased as the volume of petroleum-based products increased. Chicago Battalion Chief Peter Van Dorpe was the first I heard refer to these new furnishings as “comfortable gasoline,” a term that focuses on the true potential hazard when discussing fire suppression.
The third aspect of the modern built environment impacting fire dynamics is the increased oxygen supply available in the ever-popular open floor plan. During the plethora of home-improvement TV shows my lovely bride insists on watching, contractors and renovators are always taking out walls, vaulting ceilings, and opening up spaces. (Only one such show I ever saw included the installation of home fire sprinklers during renovation.)
While the impact of these open floor plans are now being stressed through the latest scientific research, the concept has been long understood by some. Lloyd Layman wrote in his book, Attacking and Extinguishing Interior Fires:
“The period of intense flame production within the confined atmosphere is of short duration, ranging from a few seconds to a few minutes, depending on the net atmospheric volume of the space and the rate of oxygen consumption.
“The term ‘atmospheric area’ is that part of the building where interior atmosphere can circulate freely. An atmospheric area may be confined to a room or may include several rooms or the entire building depending on the openings between various rooms or sections.”
It is not fire itself that has changed. It is the built environment in which fires are occurring that has changed. More volatile fuel loads surrounded by more voluminous amounts of oxygen within lightweight, lower-mass structural components are the culprits. So, why aren’t we focusing more on incorporating the fire suppression process into the built environment to address the problems that that environment has created?
This post was written by Rick Ennis, fire chief for the City of Cape Girardeau in Missouri and chair of the Missouri Fire Sprinkler Coalition.