Firefighting tactics to beat 21st century fires
Modern fuel loads have changed fire behavior, making it imperative that the fire service adapt its tactics
For many fire departments, the standard operating procedure for attacking a single-family dwelling fire has been to pull lines, force entry and set up a PPV fan to support interior operations. While this approach has been successful in years past, resent test data being developed by UL and the National Institute of Standards and Technology indicate today's residential fire has changed dramatically.
Using the routine (sometimes non-thinking) approach can prove lethal for firefighters who fail to consider the changing dynamics of today's residential structure fire. Far too often first-arriving firefighters feel the overriding need to take immediate action by quickly entering the structure and automatically beginning operations.
If the first arriving fire officer fails to take that extra minute or two to conduct a competent 360-degree size-up of some critical factors before entering, the lives of their firefighters can be seriously jeopardized. Fire officers must understand the nature of today's risk in order to effectively manage it.
It is well known that today's lightweight wood-frame structure burns faster and fails sooner than wood-frame structures built in years past. The full-dimension lumber used in home construction up to the 1970s yielded more mass for structural support during a fire.
Floors and roofs were typically built using a minimum dimension of 2 x 8 and 2 x 6 inch solid wood. However, in the 1970s a significant shift occurred with the introduction of smaller 2 x 4 inch lumber used in floor and roof truss support systems. With the use of smaller dimension lumber in structural supporting members, lightweight (disposable) construction was born and has continued to evolve into lighter, cheaper materials with less mass for structural support. Less mass means quicker failure.
The combustibility of lightweight building components has also greatly increased from those used in traditional wood-frame construction. This includes engineered truss-joist I-beams, metal plate connected wood trusses, and finger-jointed wood trusses. Metal C-joists, also used in a lightweight wood-frame structure, have a rapid failure rate when exposed to fire.
The vast majority of homes and apartments, fast-food restaurants, hotels and commercial buildings constructed in the past 20 years are built of lightweight wood frame. Structural failure times of four to six minutes are well documented.
The bottom line is that you'd better have a compelling reason, such as a savable life, before allowing firefighters on or under this type of construction once it has been involved in a fire.
The open-air or atrium design used in many homes today contributes to rapid fire development due to the lack of compartmentation, synthetic fuel loading and the abundance of air available to feed the fire.
Fire loads have changed dramatically in the past 20 years. And synthetic fuel loads are one of the most significant factors impacting firefighter safety and survival.
Sofas, home furnishings, and mattresses in past years were largely made of natural fiber materials such as cotton, jute, and wool. They burned much slower and off-gassed less toxic byproducts. Just look around the room and take note of everything that is either made of plastic or synthetic material.
This has contributed significantly to faster-developing fires, with less time to flashover, and less time for escape for both the occupants and firefighters. In addition, carcinogenic byproducts of combustion are much more prevalent.
In newer built homes this hastens structural failure time.
In addition, most newer wood-frame structures are wrapped in various synthetic insulating materials, and then often covered with vinyl siding and vinyl soffits. When vinyl siding is burning, it behaves like solid gasoline. An exterior fire can spread up the vinyl siding, breach the soffit, and involve the attic within several minutes.
Critical information is being gathered by UL, NIST, and FDNY through live structure fire research at Governors Island, N.Y. Past findings by UL strongly suggest that increased use of synthetic materials in our homes has resulted in a greater amount of fuel to burn.
Residential fires appear to be using up much of the available oxygen before the fuel is consumed. This is resulting in fuel rich, smoky, oxygen-deprived fire environment that seems to be going out. However, once oxygen is introduced through ventilation, or perhaps through window failure, extreme and often deadly fire conditions can result.
This is especially true if the fire becomes wind-driven, which has been well documented during NIOSH firefighter fatality investigations. FDNY Battalion Chief George K. Healy said, "Now we're learning when you vent that window or the door, the fire is developing in, say, a minute with the available oxygen."
In years past fire development occurred within several minutes or perhaps tens of minutes.
Ventilation is not the only tactic being scrutinized. Some chief officers have come to believe, that quickly dousing a hot smoky room to cool it off near the ceiling might be more important than preserving the visibility near the floor. This has long been considered taboo in the American fire service.
However, research is yielding facts that prove much of what we once believed about fire behavior is not necessarily accurate any longer. For example, a quick application of water via a straight or solid stream through a window can significantly cool an involved room just prior to entry, without pushing the fire or heat through the structure, which has long been believed to occur.
Ventilation has been shown to be primarily responsible for this by creating a flow path through the structure. The prompt application of water in a compartment involved in fire is critical in reducing the incidence of exposure to extreme temperatures.
Traditional theories associated with the application of water in spreading fire have been found to be factually inaccurate. Firefighters should apply water immediately into a compartment when the compartment is accessible, particularly from outside an IDLH environment.
This represents a significant departure from the accepted practice of attacking through the unburned compartment. Yet recent scientific research demonstrates unequivocally that the prompt application of water to a compartment on fire from outside the IDLH is not only appropriate, but preferred in safeguarding firefighter lives.
Given the reality and negative impact of reduced staffing levels in many departments, this tactic is a good option to consider.
The fire service has been taught for years that ventilation cools the fire environment. However, UL research indicates that ventilation is actually allowing today's fire environment to become much hotter and much more dangerous, according to UL fire researcher and retired Deputy Fire Chief Stephen Kerber, who says this is being proven time and again.
For additional information on current fire research, UL offers a free online training program through its fire service outreach web site.
The fire service has always focused on search and rescue of trapped occupants, and getting water on the fire as secondary. But with fires now developing so quickly, getting water on the fire first now needs to be a top priority, in order to perform search and rescue.
The risk posed by today's wood frame structure demands firefighters take a different tactical approach. The American fire service culture has been hard-wired for many decades to extend a fast and aggressive interior fire attack, from the unburned side whenever possible.
But with today's modern residential fire, firefighters must be intelligent first and aggressive second. If we fail to stay current and well informed and rely on yesterday's tactics or luck, we will continue to experience preventable LODDs and injuries.
And that's just not acceptable.