Original post by Mark Cotter at: https://community.fireengineering.com/profiles/blog/show?id=1219672:BlogPost:647493
Contrary to the action-oriented, fix-it, can-do attitude of firefighters that make us so effective in most fire suppression and rescue situations, sometimes the best thing we can do to protect the lives and property of those we are sworn to serve is let some things alone. What makes this “hands-off” approach even more difficult is that the tactic I am here addressing – Ventilation – is one that we had been taught and believed was not only helpful and necessary, but a priority for accomplishment. In fact, many fire departments have “hard-wired” this activity as a standard assignment for early-arriving resources, usually Ladder/Truck companies.
One of the surprising facts that has been brought to light by recent fire dynamics research is that increasing the air flow to a fire inside a structure, as by breaking windows, cutting holes in roofs, or even just opening doors, results in an increase in interior temperatures, regardless of any visible smoke and flame exhausting from the newly-created opening. Exceptions to this worsening are when it occurs after water has been applied to the fire in a volume sufficient to transition the blaze to the fuel-limited state, or by using the air flow from a fan to propel products of combustion from the interior to the exterior (Positive Pressure Attack [PPA]). Absent these actions, though, the processes we in the North American fire service had been taught would “improve” interior conditions by removing heated gases – vertical and horizontal ventilation – have been shown to create quite the opposite effects.
Oh well. At least we now know better, and can make adjustments to our practices with this new insight in mind, right? Also, since ventilation tactics were some of the more difficult and dangerous of the activities performed on the fireground, shouldn’t their elimination result in improvements to both our safety and efficiency? The value of embracing this new knowledge, and the dangers of ignoring it, are obvious, aren’t they? (Long, tired, sigh.) If only changing attitudes, beliefs, and practices were that simple.
Unfortunately, while the research has been clear and consistent in its findings that tactical ventilation should be delayed until after water application, proponents of its early performance remain loud and enthusiastic, and confusion and misinformation regarding the research findings abound. This is not surprising, given that the new approach is in many aspects the opposite of the way firefighters have been taught, trained, and deployed for generations. Reversing the practices of any group is a daunting prospect, especially one as large and diverse as the fire service. So, here begins another attempt at increasing our understanding about this controversial topic, about which so many of us are so passionate. My hope is that by providing a somewhat different perspective on this subject, we might be able to view it somewhat more clearly.
Ventilation can be generally defined as a noun that describes “The provision of fresh air to a room or building.” As air – specifically its Oxygen component – is a required leg in the fire triangle, any fire we are called to control already is being affected by this phenomena, whether it be encouraging or restricting growth. To the fire service, on the other hand, this term had generally been used as a verb that includes ”Any action that allows smoke out and air into the structure”, indicating that it consisted of operations that increased air flow. When a fire company was assigned to “ventilation”, it usually meant creating more openings and accelerating the exchange of air in the involved compartment(s). Our new knowledge of the effects of ventilation, be it noun or verb, on the process of combustion, suggests that it is something that we need to manage more comprehensively, instead of always augmenting, to now include its stabilization or reduction. Furthermore, since changes in ventilation can occur incidentally to other fireground activities, such as the use of hose streams, or opening a door or window for entry, it becomes a factor that must be considered by almost everyone involved in fire control operations, not just a team with that as its stated responsibility.
The title of this post comes from the SLICE-RS acronym, a menu for applying Modern Fire Attack (MFA) concepts to structure fires, where “I” stands for “Identify and control flow paths”. Flow Path is defined by Underwriters Laboratories (UL) as “The area(s) within a structure where heat, smoke and air flows from an area of higher pressure to lower pressure. It is composed of at least one intake vent, one exhaust vent and the connecting volume between…”. In other words, it’s the space(s) through which the ventilation process occurs. Determining those locations accurately is vital because, although a fire will eventually spread throughout a combustible structure even in the absence of a specific flow path, that extension and growth will primarily and most quickly occur along the route that the heated products of combustion – flame and hot gases – can most easily travel. Plotting the current or projected course of the fire is also key for staying out of its way, as the temperatures within typically exceed the upper limits of our Personal Protective Equipment (PPE).
With flow paths serving as the primary conduit for the process of ventilation, they are the logical area to focus efforts towards its management. Our options for their control, in a general sense (and sticking with the “I”-theme), are limited to just three: Isolate, Inhibit, or Increase.
Our tools include the creation or elimination of openings – usually regarding doors, windows, or roofs; and the manipulation of air movement, using hose streams, fans, and the occasional opportune wind direction.
The first intervention – Isolate – refers to avoiding any action that changes a flow path, and should be our default approach until fire control is accomplished. It involves limiting the creation of new flow paths and any increases to those already established, and includes closing doors after entry, avoiding breaking windows, and using appropriate external nozzle technique (straight/solid streams, aimed steeply upward, and kept still [immobile] – SSS). In fact, I am not the first to propose such a focus, as the “I” in VEIS stands for just that maneuver, acting as a cue to close the door after entering a room from a window, and before beginning the search. In that way, the room being searched, which would potentially become part of a flow path due to the open window left by the searching firefighter, is isolated by closing its door to the interior corridor. Diligence towards isolation will lead to the situation at least remaining more stable pending extinguishment efforts, while carelessness with the management of flow paths can create a rapid deterioration of conditions, leading to larger and more extensive involvement.
Firefighters have long acted to Inhibit flow paths, as by closing the door of an involved room, or even removing a door from an uninvolved room to then place over an open doorway, to limit fire spread when a charged hoseline was not yet in position. Furthermore, recent research has shown that reducing the ventilation to a fire does not just “hold the fire in check”, but actually reduces the rate of combustion, and thus the temperatures, in the burning room(s). (Adminttedly, this improvement is relative, and does not compare in speed or tenability to that created by the application of water, but it does make things “better”, nonetheless.) Also, we now have available smoke curtains – fire resistant fabric with integrated hangers – that can be quickly placed over broken windows or open corridors to block air flow, and thereby control flow paths.
Finally, and despite my introductory statement that sometimes we need to leave things be, there are times when an Increase in the velocity and/or volume of air flow will be beneficial to firefighting operations. Most commonly, this will occur after water has been applied to the fire, so that enhanced air flow will not cause an immediate increase in the rate of combustion. PPA is the primary method for increasing a flow path prior to fire control, as the heat thus created will also be exhausted, although interior hose streams have been shown to have a similar, if more localized, effect. Once the fire has been cooled, and convection is no longer powering the flow path, pressure differentials will need to be created by fans or hose streams to push and/or pull smoke and heat out of the structure.
This limited list of three control options is not intended to suggest that our actions to manage flow paths can be neatly categorized into one or the other. Closing a door may serve to both isolate and inhibit a flow path, while some or all effects may be brought to bear in the same structure, whether simultaneously, in different areas; or sequentially, as conditions change. Furthermore, just as Size-up is a continuous process, requiring constant reassessment of the effects of the fire and our efforts towards its control, flow path identification is not limited to a single point in time, and instead must be ongoing, and even predictive. That is, it is not sufficient to merely determine the locations of the fire and its flow path(s), but we also need to know what will happen to them, or where new ones will be created, in response to our various tactics. Avoiding the performance of a wrong action that affects a flow path, such as opening a door to the fire compartment without a ready hoseline, can have as much impact as performing a correct action, like closing a door to the fire compartment that’s already open.
While we may be using new terminology to explain our actions, tactical ventilation has always involved the control of flow paths. The new twist is that our options should no longer be limited to merely increasing the exhaust of products of combustion. Instead, we must be constantly vigilant and careful to prevent dangerous increases in, and ready and able to close off, flow paths, whether active or potential. This comprehensive approach, which operationalizes new insights from fire dynamics research, enhances our abilities to perform our job and benefit our citizens. Any less is not enough.
The author can be reached at firstname.lastname@example.org