One Size Never Fits All - Positive Pressure Attack

One size fits all, an iconic statement that the American fire service tends to apply to a very dynamic event. Unfortunately, the environment that we respond to and are expected to provide a service in does not fit into a “one size fits all” category. We as a fire service have become a utilitarian service that is expected to utilize a variety of task, tactical and strategic operations to accomplish our mission. Like all tactics, we as firefighters have an emotional connection to the effects of the tactic. That emotional connection can sometimes blind us on the true benefits or the appropriate use of a tactic. As the American Fire Service continues to evolve through technology, the complexity of the environment that we work in does not afford us the opportunity to have emotional connections to tactics, science and facts; thus the title of this article, “One Size Never Fits All” is a more accurate definition. Go to almost any fire station in America and you will find a gas powered positive pressure fan either on the engine or the truck. The evolution of the “fan” over the last twenty years has grown past the use of just a ventilation tool. Vent for life was our motto; the use of the fan was one functional tool in the vent for life motto. The challenge with vent for life is COORDINATION. Since the beginning, the application of water in a coordinated attack was critical for the vent process. Failure to have coordinated attack on the fire when venting causes rapid fire growth that jeopardizes the safety of the fire fighters and the victims still inside. We know for a fact that the failure to apply water along with ventilation creates a very dangerous environment. The first order of business is to identify and define Positive Pressure Attack (PPA) versus Positive Pressure Ventilation (PPV). PPA is defined as the use of the mechanical positive pressure fan in a coordinated initial attack into a compartment fire with the fan being used as an aid in the suppression process. PPV has an accepted definition of the use of the mechanical fan for the sole purpose in assisting in ventilation post knock down or fire control. Positive Pressure Attack originated as a means to ventilate a structure after the fire was knocked down. Over the years the use of a positive pressure fan has evolved into using the fan to assist in the extinguishment process. Experts like Kris Garcia and Reinhard Kauffmann and Ray Schelble developed tactical operations that include the use of a coordinated attack with the use of the positive pressure fan. The fan was placed in the intake (airflow) of the structure to provide pressure into the compartment with an exhaust created allowing the super-heated gasses to vent out the exhaust as the fire fighters in a coordinated effort stretched an attack line from the clean air side of the flow path advancing towards the seat of the fire. The concept was that properly used PPA allows firefighters great control over the interior environment of a fire building, and provides for increased ventilation (cool fresh air) for potential victims and better visibility for the firefighter to attack the fire. Positive Pressure Ventilation is the tactical use again of a mechanical fan to assist in venting the structure post fire control. The need for a single intake, flow path and then an exhaust are used in conjunction with the fan to aid in the removal of the super-heated gasses. Over the last twenty years, PPA has become a valuable tool that most organizations use consistently for residential structure fires. Over the last ten years some organizations have developed larger truck mounted and elevated fans for the use in commercial and multi-story buildings. Recently, Underwriters Laboratory conducted research and testing on the benefits and disadvantages of the use of PPA. I was fortunate enough to sit on that committee along with PPA experts from around the world. Kris Garcia, one of the most prominent PPA experts is also on the committee. Information listed in this article is documented tests through KTF and NIST. The Tactic: The use of a PPA fan positioned in the inlet of a structure, positioned to maximize the creation of a flow path from the unburned side of the structure to the fire compartment then vented out an exhaust. Crews are to identify the air intake; traditionally the front door, then an exhaust opening must be created. This is traditionally done by taking a window or opening a door closest to the fire. Once the exhaust is established crews will then move back to the inlet and make their initial attack with the fan blowing at their backs. The Goal: The goal of the fan blowing at your back is to clear a path through the structure to the seat of the fire and out the exhaust. The concept is the fan clears all the super-heated gasses out of the structure and out the exhaust providing for better visibility and patient survivability. In addition, the thought was it would provide for less thermal insult on fire fighters as the advance through the structure. The Challenge: One of the critical challenges of PPA is creating the appropriate and effective sized exhaust outlet; the “book” says 2 ½ times the inlet size. With the modern fuels high energy release and expansion rate we are finding that we struggle to create a large enough exhaust to move the volume of super-heated gasses out of the structure fast enough must be accomplished with a larger exhaust. Inaccurately identifying where the fire is located causing fire extension into non fire compartments causing more damage. The use of PPA is dependent on the following items: 1. The fire occupancy can be identified and is compartmentalized. 2. A large enough exhaust can be created. 3. The fire is compartmentalized and located near an exterior wall 4. Exhaust vent and fire are located on the same floor 5. The occupant and fan position are not impacted by wind speed or direction. The use of PPA is another tool for our tool box, Yes, I know that is cliché but it’s true we are a dynamic organization that must have multiple tactical options to safely provide the expected service to our community. Aggressive tactical operations that are performed by skilled firefighters under the direction of educated company officer that use tactical knowledge to best provide service is critical. In all cases tactical operations should not delay the application of water. Water in all cases provided for improved conditions for patient survivability and improved conditions for interior fire operations. The result from the UL PPA study will impact how and when PPA is applied, however it will not be eliminated it from our tool box. Bottom line is that it all depends; there are conditions and situations for each tactic.