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Fire behavior's threat to firefighter safety

Advancing firefighter safety means exploring the science of the past, and the likely future


Long before recorded history, we have been fascinated by fire. Whether concluding its origins lie in magic, mystery or molecules, firefighters throughout the ages have wondered about the space between the fuel and the flame.

While the history of fire's mystery is intriguing, working firefighters' concerns are a little more pragmatic. How big and how hot are the rudimentary questions for those standing in its glow — and for many generations, this was enough to begin any fire attack intelligently and safely.

Early strategy and tactics were focused on putting the wet stuff on the red stuff. If that wasn't enough, you could pull down the walls and hope for the best.

Just getting water close to burning fuels was enough of a challenge and anything short of a foundation in the morning was met with celebration and fresh grain for the horses.

The call to action from the fire tetrahedron is to remove or cool the fuel, exclude the oxygen or interfere with the chain reaction. Any of these actions are appropriate to firefighting and how we accomplish any one or more of these directives are up to us.

If you remove the fuel, the fire stops. Removing the air or smothering it is also a good plan. A tarp, a chemical extinguisher, foam and certain aspirated compounds such as Halon hold a place in the rules of extinguishment. Of course there is always water, when available and at the right speed and volume.

To the naked eye
When it comes to fire, at least size wise, we have learned the flame seen is a third less in dimension. While our eyes cannot see it, infrared and sometimes ultraviolet light is evident. The amount unseen depends on the material vapors burning.

Regardless of what you see or don't see or your terminology, fires ignite, grow, sustain and wane. Each segment has its own characteristics and clues for determining a successful extinguishment.

Currently, for a responding firefighter it is still about color and intensity of flame. Are flames a bright yellow and lapping at the walls or are they a deep red and blowing out the window like a jet engine? Is there a constant sound or the quiet crackling of radiant red embers?

Success has always been judged by where you are in the fire's timeline and applying extinguishing agents accordingly.

Up until now we've believed the clues have been evident and the characteristics predictable. But for firefighters today, there are cutting-edge fuels and fires requiring new information as to how to suppress their energy.

As an example we now know that these new fire loads are producing hydrogen chloride and cyanide in copious amounts. We now realize that HCl and HCN is ever-present and more importantly, it lingers throughout overhaul after the flames have been extinguished.

New science
These new combustible environments are being studied, written about and applied directly to fire suppression theory by some of the best minds in our profession. Scientists have documented these critical advancements in fire science for years and tried valiantly to explain their relevance to fire behavior and subsequently, suppression actions and firefighter safety.

During the 1600s, scientists said phlogiston was a substance leaving all burning matter and when it depleted itself, the fire went out. Of course, once mass was interpreted into the chemical equation in the 1780s, phlogiston ceased being an element and was demoted to the library's science fiction isle.

Yesterday it was flashover and latent heat of vaporization as it relates to thermal ballast. Today it is free radicals, neutral molecules and exothermic reactions.

Tomorrow the conversation will turn to converting combustion energy resources and sonic extinguishers. All of this viable progress is driven by science.

The difficulty for scientists is not their quest for truthful explanations, but that their conclusions are pragmatically obscure when attempting to apply them to the fireground. Without definitive solutions, firefighters find no relevance for the minutia of mathematical and molecular answers, especially when they are in the thick of them.

Unfortunately, some current strategies are falling short in the wake of such complex chemistry and the flames they produce. Such a spectral locomotive comes with incandescent particles, photon emissions and even small amounts of radiation.

As one captain put it: "It isn't just fire anymore, but what it is we aren't exactly sure."

Regrettably, outside academia, the cost of misunderstanding is not a poor grade but a life-threatening situation made faster and hotter than ever before. China's port tragedies are a textbook example of this level of penalty.

New rules
Today, fire behavior has an entirely new set of parameters. Big is not always discernable through visual perception and hot has so many layers of intensity that it can literally change the fireground as it changes the science.

There are fuels now with molecular formulas not even imagined years ago. These "space-age" fuels create temperature levels that PPE can tolerate initially but can liquefy adjacent material within seconds of its continuing incipiency.

What is burning is just the beginning for these 21st century products. Respect for fuel load — quality as well as quantity — takes on a whole new meaning.

Rollover and flashover move across this temperature spectrum so quickly their first warning signs are often seen too late or they react so fast as to not be predictable other than by direct exposure. Regardless of the science, these are not safe environments for firefighters.

There is geometry, weather and alchemy lingering just outside the general curiosity of textbook fire science. For firefighters, this means study, observe and practice what you think you know.

Learn about heat transfer, rate of release, heat flux and temperature. Study the equations until you begin to see them in the fire. Examine thermal conductivity from the convective heat transfer coefficient. Then explain it.

Fire's future
Firefighters should learn to interpret MSDSs and SDSs and apply product names and hazard recommendations toward an honest interpretation of their risk and potential for harm. They should seek out the information first responders are entitled to.

If chemical companies can describe the behavior of their molecules, it stands to reason that with a little prodding they could extent their testing into areas appropriate to the fire service.

Being able to document and classify fire behavior according to useable standards worked out by engineers, scientists and firefighters would bring this information into practical, on-scene realm, much like the incident command system and hazmat dispersion programs have for their participants.

Since the first fire we have stared into the flames. Ironically with all of the advancements in science and technology shrinking the in-between space, we still do not have all the answers.

This is what makes fire science so thick and rich. Deep down inside, at the core of it all, there is still a magnificent mystery.

Now this mystery is endangering firefighters more than ever before with increased heat and light intensities, phenomenal movement and deadly by-products. Fire has reached a whole new level in theory and practice, and the function of the fire service is to know these new forms and respond appropriately.

The key to safely suppressing these new incarnations of a legendary force is to recognize enough of the scientific principles to be able to apply them effectively to extinguishment or evacuation, whichever is response relevant. 

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