Simulation Of Positive Pressure Ventilation (ppv) For Research And Training

Abstract

Using simple fans, a structure can be slightly pressurized to provide rapid and effective removal of heat, smoke and toxic gases this technique is known as positive pressure ventilation (PPV). Both laboratory and live fire tests clearly demonstrate the possible benefits of using PPV during fire attack to include saving lives, reducing property damage and minimizing long-term adverse health effects for firefighters. Training and practice are required in order to use PPV techniques effectively. Unfortunately, live fire PPV training and practice is dangerous, expensive and not environmentally benign. As positive pressure ventilation becomes more widely used in the fire service, creative techniques for research and training in PPV are desirable. A simulation method for PPV has been under development at the University of Central Florida's Two-Phase Flow and Heat Transfer Laboratories. This method is an inexpensive, non-destructive means of educating and training firefighters to use PPV and has been shown, under certain conditions, to be an accurate reproduction of the events occurring during actual live fires. INTRODUCTION During most structural fires intense heat, dense smoke and large quantities of flammable and toxic gases are released into the building. Proper ventilation can remove many of the mechanisms supporting the combustion process including high heat and flammable gases. FIRE SAFETY SCIENCE-PROCEEDINGS OF THE FOURTH INTERN4TIONAL SYMPOSIUM, pp. 1029-1039 1029 Copyright © International Association for Fire Safety Science Ventilation also creates a more survivable environment by increasing visibility and oxygen levels while removing toxic gases and it allows for better execution of the primary objectives of fire service personnel including rescue of trapped victims and location and suppression of the fire. In the United States, ventilation is a common practice and many different techniques exist to facilitate the removal of heat and smoke from a building. One such technique is Positive Pressure Ventilation or PPV. PPV is a technique where fans with high volumetric flow rates are used to create a slight positive gage pressure within a structure to force heat and gaseous products of combustion out strategically selected exhaust points as conceptually illustrated in Figure 1. (a) BEFORE PPV (b) PPV IN OPERATION FIGURE 1 Smoke Removal Using PPV When properly implemented, PPV can reduce temperatures, improve visibility, introduce cool fresh air and remove toxic gases quicker and more efficiently than most other traditional ventilation techniques. Research activities at the University of Central Florida (UCF) in conjunction with the Orange County Fire Rescue Division (OCFRD) have focused on evaluating the potential merits of PPV including implementation, live fire measurements, fan characteristics and simulation. PPV has been used as a smoke removal procedure in post-fire salvage and overhaul for nearly three decades by a few fire service agencies but has only recently seen use in the initial stages of fire attack. Table 1 provides a chronological overview of the published work on PPV. Included in the table are a corresponding reference and a summary showing if the work involved PPV for fire attack, overhaul or both, any experimental research to quantify PPV and some general comments on what was contained in the article or book. In virtually all cases, investigators have concluded that PPV is an effective fire attack tool that can be of significant vdue for the reduction of smoke, carbon monoxide and heat when properly used. In addition, it is universally accepted that PPV should not be used on all fires and that the proper implementation of PPV requires training. Training for PPV can be dangerous, expensive and destructive. Live fire training is typically conducted in burn buildings, donated residences or during actual emergency responses. An additional training scenario involves cold PPV where smoke generators provide a controlled environment for training exercises. Each of these techniques have inherent benefits and disadvantages. Burn buildings have the advantage of training repeatability, however they are not readily accessible to all fire departments and are limited in structural layout. Fires in donated structures can provide realistic training but recent EPA and OSHA guidelines (asbestos, escape routes, etc.) make such training expensive and difficult. Since fires destroy the structure, training is risky and may unnecessarily jeopardize life and property. Cold PPV is an effective technique for learning the fundamentals of PPV implementation, but does not simulate the phenomena produced by the release of heat during a fire. 1989 Hughes [I21 1989 Mittendod I131 I I TABLE 1: PPV Research Activities and Literature Listing