Ventilation Practices and Evidence-Based Research. By: John Paul Jones, Fire Chief KCKFD

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1 Ventilation Practices and Evidence-Based Research By: John Paul Jones, Fire Chief KCKFD In the world of fire suppression, I believe one can say that on the fire ground, ventilation is everything. Especially considering that the fires we experience today can be more of a challenge based on the high-energy producing materials inherent with modern construction, household goods, furniture, appliances and furnishings. The purpose here is to provoke discussion. Should we be doing it differently? Let us begin by considering some of the principles of physics associated with ventilation that we will encounter on the fire scene. When we ventilate and let the heat and products of combustion out of the structure (container), isn t there a corresponding decrease in both pressure and temperature? If we apply a hose stream to introduce the heat-absorbing capabilities of water into the environment, don t we want the resulting steam to have an avenue to exit as it carries heat out of the structure by utilizing the existing pressure differential? According to Amontons' Law or Gay Lussac s Law of physics concerning pressure and temperature, it basically tells us that if you have an increase in heat, you have a corresponding increase in pressure and vice versa. According to the laws of physics, any fire of significance within a structure will pressurize the structure (vessel or container) because of the pressure differential caused by the increase in temperature. Should the most effective way to ventilate at the most critical time on the fire ground be termed pressure differential ventilation instead of positive pressure ventilation? Shouldn t we be thinking in terms of pressure differential ventilation techniques where the goal is to let the heat, smoke, toxic gases and steam out of the structure (container)? Should we strive to release the products of combustion instead of purposely confining them? Don t we have an understanding of fire behavior that tells us that if the products of combustion are confined and exposed to high enough temperatures, they may indeed become a fuel that can ignite in the presence of adequate amounts of oxygen to produce conditions of backdraft, flashover, or rollover? Are the laws of physics telling us that the current philosophies associated with positive pressure ventilation as applied to fire attack have serious if not dangerous flaws? Page 1 of 7

2 The answer to all of these questions is yes, but with caution. Think about this, why would we want to, as a common practice, confine or contain heat and fuel together as we expose both of them to available oxygen? The fundamental approach to each fire we encounter should be to read the situation, to have the ability to understand and to know the relationship between temperature, pressure and heat flow. Therefore, the tactics you use in order to deal with these physical laws will determine the most favorable outcome. But if the only outcome you desire is for the fire at some point to be extinguished, then best practices can become foggy at best. Again, fundamentally, we need to ask ourselves this question: Why are we, at times, applying a one size fits all mentality for ventilation applications in regard to fire attack? For example, on a standard bread and butter residential fire, a common practice may be where one would put a fan out in front of the front door and tell the firefighters not to make any openings except for one that is smaller (preferably in the room of fire origin) than the opening where we are introducing air from the PPV fan without consideration of fire flow? Should our goal be to increase pressure? Absolutely not, it must be understood that according to the laws of physics, we will definitely have pressure when we experience a real fire event, and without a negative pressure intervention, the products of combustion will be produced faster than they can exit the structure. Let s consider the science behind the fact that the products of combustion want to be released from the structure. Why? Because of the difference in pressure and the fact that pressure will flow from a high pressure to a low pressure environment. The fire will comply with the laws of physics every time. Why do we at times subscribe to blanket methods of ventilation that confine heat and toxic gases? (fuel + heat + fuel being produced faster than it can be expelled + continued temperature increase = backdraft, flashover, rollover, etc.) Or consider, why do we at times, subscribe to the process of creating openings without regard to the consequences of the introduction of oxygen? Shouldn t we be subscribing to specific measures and practices that recognize the need to reduce internal pressures by letting the products of combustion out of the structure while experiencing a corresponding decrease in flashover potential? If we create a negative pressure differential, won t the dangerous levels of fuel and heat automatically exit the structure because of a difference in pressure as Page 2 of 7

3 we make openings in the structure (container)? And if we don t, what happens then? Now as the new NIST research is revealing to us all, a major consideration with pressure differential ventilation or positive pressure ventilation, for that matter, is the introduction of oxygen into the equation. So, how do we look at this introduction of oxygen, using the evidence-based solutions of applying ventilation techniques for specifically timed circumstances? We have to understand that the fuels of today burn hotter, faster and react with more veracity when exposed to oxygen at a point when the fire needs it the most in order to burn with the greatest efficiency. Shouldn t our goals include efforts to achieve greater understanding of ventilation from the standpoint that gives consideration to strategy of let it out or as we have termed, pressure differential ventilation? If your only goal was to apply pressure differential ventilation (negative pressure ventilation) without the introduction of water, then yes, you will have the possibility of an initial temperature reduction followed by a dramatic increase in temperature. In regard to the concept of heat transfer, if you introduce water (simultaneous to ventilation and in sufficient quantities) into the equation you will have heat transfer occur where the heat of the gases will be transferred to the water and have a very positive effect. So, why not apply water into the structure before entering? If you are simultaneously applying pressure differential ventilation strategies, then you will have the heat absorbing water as steam, carrying the heat away from the structure, as it contracts the fire gases and exits through prescribed openings large enough to cause a rapid decrease in pressure within the structure. My question to you now in regard to a scientific approach is, why? We need to know the why? behind our actions. The NIST studies are important because they will tell us why we should do things differently. The NIST studies are providing us with answers. Why would we want to adhere to some of our current prescribed methods that we cannot, through scientific methods and evidence-based reasoning, verify as best practices? Back to what I had mentioned before about physics, the relationship between temperature and pressure is the most important principle of physics for us to understand. Now this is what brings us to the why question as related to our Page 3 of 7

4 actions. If we are to take advantage of pressure differential ventilation, we must consider heat transfer, heat flow, the understanding of the role of fuel, the timing of making openings, and the application of water. Remember Gay Lussac s Law, if you increase heat you increase pressure, so in a fire of significance, you will have a pressurized interior environment that wants to equalize with the outside air pressure. If you introduce water you will experience heat transfer and the creation of steam. If you continue to apply water and apply pressure differential ventilation techniques that entail making enough of an opening or openings to allow for a rapid reduction in pressure and temperature, then this will produce a simultaneous, rapid deceleration and interruption in the production of fire, heat and fuel. An understanding of the thermal flow path is important because the use of pressure differential ventilation techniques again, without regard to understanding the introduction of oxygen, can be catastrophic. It may be that sometimes, the timing of our tactics directs us to limit the use of pressure differential ventilation until it is warranted and does not pose an immediate threat or hazard to victims or firefighters. But we must also consider what we truly know best, how the heat absorbing capacity of water interrupts the process of combustion, and manipulates the thermal flow path of fire gases and use it to our best advantage. When applying pressure differential ventilation ( letting it out ) we may create a thermal flow path that can be used to our advantage as the products of combustion exit the structure (container) along with the steam from the effective timing of the application of water. Remember Gay Lussac s law, if you reduce pressure you will reduce heat. The thermal flow path of fire is a result of a situation where continued combustion creates heat that increases pressure and air will be drawn in as heat and smoke exits in an attempt to create equilibrium. The introduction of water with the right stream application (straight stream or solid stream) interrupts the process of combustion creating steam which causes a reduction in temperature and a reduction in overall pressure. As the temperature and pressures are reduced, as heat, smoke and steam leave the structure, an explosive combustion potential will be reduced to the point where flashover conditions are eliminated and the thermal flow path is weakened or cooled to a point where firefighters can operate safely at lower levels within the structure (container). Page 4 of 7

5 Our goal should be effective heat transfer that reduces the temperature as a decrease in pressure is achieved (through ventilation) simultaneous to the introduction of water into the environment. But we must consider how the environment is effected overall and consider whether or not the thermal stratification of heat will be compromised. Why would we not want to introduce water into this environment prior to entry? The answer is that, we should. In doing so, we can reduce temperature and interrupt the thermal flow path, which is how the fire breathes. This interruption can be of tremendous help to us because the effects of the introduction of oxygen in intensifying the fire will be countered by the reduction of temperature caused by the introduction of water. So again, the introduction of water (straight stream or solid stream) reduces temperature and releases the fuel, steam and pressure within the structure. The contraction of hot gases caused by heat transfer or energy absorption and their release to the outside environment (pressure differential ventilation) increases survivability of firefighters and victims within the structure. This is food for thought in an attempt to get you to think about ventilation differently in relation to the process of combustion that is confined to a structure (container). As we have discussed, physics does show us a direct relationship between heat and pressure, if you increase heat, you have a corresponding increase in pressure. As a fire progresses, this pressure differential when confined, will draw in air (as openings are allowed) from the outside of the structure (container), feeding the fire oxygen. The increase in temperature will have a corresponding increase in pressure and the heat (temperature) unless interrupted, will continue to rise to dangerous levels. The purpose of my writing about this is to challenge you as leaders in the fire service to consider an immediate and aggressive examination of a new way of looking at strategy and tactics in the fire service as it relates to ventilation. With an evidence-based approach, the NIST studies will challenge us to use this new evidence-based reasoning in an effort to ask why we apply one technique over another. The evidence based consideration for the: who, what, when, where, why and how for ventilation. Again, we need to understand the relationship between our coordinated activities that have a cause and effect relationship to the resulting positive or negative consequences in order for us to extinguish fires safely and effectively. Page 5 of 7

6 The science behind the fire must be understood, and the physics behind the processes involved with this combustion must be understood. Fire is dynamic and subject to change based on the interrelationship between temperature, pressure, and the flow of heat. We must rely on the research being done because we can t conduct experiments on the fire ground where we can change variables to examine cause and affect relationships. Instead we can become victims of our experiences in that our understanding of fire behavior may be skewed unrealistically because of the limiting effects of these experiences as they may not be providing for a scientific approach. The laws of physics governing the relationship between temperature, pressure and heat transfer must be understood in relation to what we do in the fire service. It is very important for all of us as leaders within the fire service, to read, to study, and to understand the information being developed by the real scientific research taking place within the NIST studies. We in the fire service must visualize and see the laws of physics in action as we take action and use these physical laws to our advantage. We must understand and know heat transfer on the fire ground from a scientific, evidenced based point of view, in real time. We must understand the thermal flow of heat in relation to the actions we are taking on the fire ground. Maybe, as a result of creating a new understanding of pressure-differential ventilation, we will always consider the proper timing of the application of water before we make entry. The interrelationship between heat, pressure, ventilation, thermal flow path, and the application of water can be considered interdependent within the dynamics of combustion taking place within a structure (container). Our ability to be effective is directly related to understanding these evidence-based scientific studies. I believe as we continue to look at our best practices through the prism of this evidence-based scientific research, we will increase our effectiveness tremendously and systematically reduce the probability of injury and death for firefighters and civilians alike. Once again, I challenge you to read the NIST information, to explore these new ideas, and the resulting application of new techniques and best practices. Why? Because it would be irresponsible not to, because we owe it to those who trust that we are going to do everything in our power to reduce the risk inherent with fighting fire. Page 6 of 7

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