BY CHRISTIAN EMRICH
This article describes the outcome of research in Germany concerning the different technical and tactical possibilities of positive pressure ventilation (PPV). A variety of opinions exist globally on the best strategy to fight fire and address the production of heat and toxic smoke. A research project at the University of Applied Sciences in Cologne, Germany, in 2008 and 2009 analyzed the three fan technologies (conventional, turbo, and straight-stream airflow) to determine the highest efficiency. Based on the results of tests performed in hot and cold conditions, the research group developed the recommended tactic: rescue ventilation. This tactic makes the use of the fans at fires much easier and much more efficient. In addition, it enhances firefighter safety, expedites victim search, and reduces structural damage.
The use of fans is one of the most controversial topics in firefighting. There are different opinions and different tactical designations [e.g., positive pressure ventilation (PPV), positive pressure attack (PPA)]. Often, fans are only used to ventilate a structure after a fire is extinguished and are not used with the maximum possible efficiency. We often hear, “Using the fan could push smoke into smoke-free areas.” Tactics such as PPV and PPA emphasize the exaggerated importance of the pressure fans create. But how can firefighters pressurize a structure if several windows are open or have been broken? We will answer this question later in the article.
First, we will analyze the characteristics of the three fan technologies to better understand the rescue ventilation tactic.
VENTILATION FANS
Firefighters ventilate a building to reduce heat, enhance visibility, and prevent smoke contamination of uninvolved areas. They can only achieve these goals if they know how to use their fans properly. Let’s look at each of the three fan technologies.
Conventional. The conventional fan produces a cone-shaped airflow and was the first fan to be used against smoke and fire. In training photos, such fans produce a wide cone of air that should cover the structure opening used to pressurize the structure. The test measurement results demonstrated that covering the entire inlet was less important than getting the maximum air volume into the structure. This is only possible when the entire volume can flow into the building. The theory of “pressurizing a building” and working with “positive pressure” works only as long as the structure has no other openings. But we cannot ventilate without a ventilation opening because there is no airflow through the structure. If several windows are opened, there is almost no pressure inside, but there is a good ventilation. So the most important thing is to position the fan at the correct distance to get the maximum air volume into the structure. Conventional technology fans must be positioned between five and six feet (1.5 to two meters) in front of the inlet (photo 1).
 |
| (1) Photos courtesy of author. |
Turbo fans. They must also be positioned very precisely. With the benefit of the injector principle (Venturi effect), they produce their maximum air volume, but only if they are positioned between seven and eight feet (2.5 to three meters) from the inlet. At a longer distance, the air flow loses volume on the way to the entrance. If the distance to the entrance is too short, the injector principle cannot produce the maximum air volume (photo 2).
 |
| (2) |
The angle is the second important adjustment for conventional and turbo ventilators. Firefighters must choose an optimal angle manually. The incorrect angle could cause as much as a 30-percent loss of air volume. The goal is to get maximum air flow through the center of the inlet, so it is important to set the fan at the proper angle.
Straight-stream airflow. This technology has been on the market since 2008. The prototype was tested in the research project too. This completely new fan technology with only a 16-inch diameter and the same engine power of conventional 16-inch fans produces an air volume equal to or greater than that of 24- and 27-inch conventional fans. Paralleling the positioning is much easier. Firefighters should not adjust the angle manually since this new technology automatically adjusts to the ideal angle. The air flow produced is not a wide cone as with conventional and turbo fans. The photos demonstrate the different flow characteristics; it is easy to see the difference. The straight stream has a very strong, concentrated air stream. This allows two new possibilities: (1) to position the fan between nine and 20 feet in front of an inlet—a distance of up to 20 feet allows firefighters much more room for themselves and their materials for the attack; and (2) to overcome stairs in front of a structure (photo 3). Photo 4 shows the optimum distance for a conventional (left) and a straight-stream airflow fan (right) from a structure opening if both technologies are used together.
 |
| (3) |
 |
| (4) |
Automatic systems in buildings such as hospitals, high-rises, and universities are immediately activated when an automatic smoke-detection system alarms and pressurizes routes to emergency exits with a pressure of 50 Pascals (per National Fire Protection Association 92A, Standard for Smoke-Control Systems Utilizing Barriers and Pressure Differences). With one open door, they obtain 25 Pascals in the emergency stairways. Fire protection engineers calculate the precise pressure these systems produce for each building. The pressurizing is much higher than the pressure produced by fans positioned perfectly with the exhaust inlets in the structure. An important difference between fire department fans and these automatic systems is that the positive pressure systems start working before the smoke expands. Their main function is to keep smoke out of the emergency stairways. When firefighters start working 10 minutes or more after an alarm, they are working against the heat and smoke that have already developed. They need to ventilate this dangerous environment to quickly extinguish the fire. These are two completely different conditions with the same description, “positive pressure.” In the future, we must differentiate between “ventilate a structure with an exhaust” (i.e., rescue ventilation) and “protect a structure against smoke and heat with only a little or no exhaust” (i.e., positive pressure ventilation). But in most cases, firefighters already have a vent when they arrive, so they don’t create pressure; they use air volume. In structures with ventilation in the fire room, only a pressure of less than 5 Pascals is possible. This is hardly a pressurization.
We performed the tests in Germany under realistic conditions—e.g., different weather conditions, cold and hot smoke, in high- and low-rise buildings for more than a year. The fans were positioned in front of the first-floor entrance at different distances and angles. All fans had gasoline-powered engines with 5.5 or 6 horsepower and a diameter of between 16 and 24 inches.
RESCUE VENTILATION
The key advantages of the rescue ventilation tactic are that it enables firefighters to work with the greatest safety, to find victims much more quickly, and to reduce damage to the structure. How is this possible? The rescue ventilation tactic includes the following simple but important steps, which can be easily taught. First, determine the correct distance at which to position the fan (each fan technology has its own optimal distance). The officer or battalion chief analyzes the environment and determines the situation (size-up).
Start the fan at low power and turn at a 90° angle from the inlet to confirm that the fan is ready and works properly. After a vent has been opened in the fire room, the officer will order the start of fan ventilation. At this point, the fan is turned 90° toward the inlet, and the power is increased to the needed level, which can be done in seconds. The maximum power level is not needed every time. The power level is adjusted to provide the needed airflow to overcome turbulences or a backflow of smoke against the direction of the ventilation channel. However, if the airflow is greater than needed, it creates dangers, such as contaminating clean areas with smoke. For maximum safety, always break windows from outside with a pike pole; no firefighter should be in dangerous no-visibility conditions with heat, smoke, and pyrolyzed gases.
The first attack crew stages at the smoke frontier until the vent is created. After this, the fan ventilation should begin, which will increase visibility within seconds so the crew can search for and rescue missing persons (photos 5, 6).
 |
| (5) |
 |
| (6) |
The biggest danger for the victims is carbon monoxide (CO), which prevents the transport of oxygen in the blood by the hemoglobin. According to the German ORBIT study, resuscitation of a person with CO poisoning must be started within 17 minutes. A later resuscitation will have no positive effect. When does the first engine arrive? Depending on the region, the first engine arrives approximately 10 to 15 minutes after the first emergency call. That means there are only two to seven minutes to size up the fire and determine the firefighting tactics.
If an attack crew starts search and rescue without ventilation, it works under very dangerous conditions with little or no visibility and smoke and heat. They need much more time for this, and most firefighters would die in these conditions.
When they have finished the first search and rescue, they can’t guarantee that there is definitely no victim. Although this is a significant amount of time, the visibility and gas concentrations don’t change. So the victims and firefighters are exposed to CO. The most important task is to replace the smoke, heat, and toxic gases with cooler fresh air before or while personnel are entering the fire room. That’s rescue ventilation.
If conditions are not improved and the first attack crew starts extinguishment, the sauna effect can occur and the probability of a Mayday and danger to life is extremely high. The sauna effect occurs when steam causes dry heat to change into high humid heat. While attacking the fire, firefighters experience the sauna effect such as the change from cold to hot, but the temperature remains constant.
As a training lesson, firefighters can experience this effect in a sauna. In the first session, have members experience the dry heat of the sauna; do not put water on the stones. In the second session, after some time, put five or six spoons of water on the stones. Immediately the heart rate of everyone inside will increase rapidly and the firefighters will want to leave. In the third session, do the same as in the second session, but this time, keep the sauna door open. Everyone will appreciate the great difference ventilation makes.
Rescue ventilation provides firefighters maximum safety and allows them to find and rescue victims more quickly. Because smoke and fire are more quickly brought under control, structural damage could be reduced. As a result of the rescue ventilation tactic, the smoke and its toxic components are more quickly removed without the dangers of positive pressure ventilation (photos 7, 8).
 |
| (7) |
 |
| (8) |
The officers/battalion chiefs must focus on the ventilation channel—the distance between inlet and ventilation opening. Open windows only in the fire room, so the fresh air is forced to go through the ventilation channel into the fire room and out the vent opening there. Fresh air coming out of the vent means that most of the toxic smoke and gases have already vented.
FLASHOVER AND BACKDRAFT
Flashover is a fuel-controlled fire that with enough oxygen produces much smoke and intense heat. This phenomenon needs temperatures of a minimum of 1,110°F for ignition. If the gases are cooler, they cannot burn, so no flashover occurs. Our problem is the heat: How can we control it? Search for the fire room windows [if possible, with the help of a thermal imaging camera (TIC)—photo 9], and open them with a pike pole or another tool so there is an initial vent opening. As in the rescue ventilation tactic, the fan is already positioned in front of the entrance with low power and turned 90° to the side. After the windows are opened, the ventilation can begin, which quickly reduces the temperature and optimizes the visibility. The interior attack crew moves forward with the smoke frontier and cools the smoke with water—the steam produced disappears through the vent. Now the flashover situation is under control.
 |
| (9) |
Backdraft is a ventilation-controlled fire with no oxygen that produces much combustible smoke. A backdraft situation evolves in closed spaces. After some time, the fire does not have enough oxygen and produces more and more pyrolyzed gases. The temperature is not the critical factor. In a prebackdraft situation, the oxygen determines whether there is ignition or not. The officer/battalion chief identify the signs of a prebackdraft situation: pulsing high dynamic gray/white/brown smoke that changes color or, if there is no smoke coming out of the building, the windows will be warm and black because of smoke and carbon. Here, an explosive mixture could exist, which only needs oxygen to ignite. In such a situation, don’t start ventilation immediatly. Open from a safe distance (e. g., using a pike pole) the window where the fire is believed to be behind and wait for the possible explosion or cool down the smoke. If there is no explosion, you can turn the fan and adjust its power level accordingly. Visibility will quickly increase.
Using rescue ventilation, the dangers of flashover and backdraft are reduced and under control with one tactic.
Every time you use ventilation, consider the weather. In higher floors, there often are winds that can produce the “blow-torch effect” when the wind is stronger than the fan’s airflow. If you have such a situation, open the vent carefully. Break only one window from outside with a pike pole. The other windows, if possible and necessary, can be opened from inside and safeguarded by a special door/window block or wedge. Generally, the results of tests in Germany indicated that the exhaust opening in the fire room should be as large as possible so that the natural wind from outside is no problem.
The final step of the research project was to create a card that could be used as a guideline at an incident (Figure 1). On the front are the different recommended positioning distances for each of the three fan technologies and questions that the officer/battalion chief must answer in his size-up. On the back is a flowchart that helps the officer determine when ideally to begin the ventilation.
|
Figure 1. Rescue Ventilation Card |
 |
| Figure courtesy of author. |
With the rescue ventilation tactic, all fire service personnel should be able to do their work in the future much more safely. That’s the highest goal we can have. Not only should firefighter safety is optimized, so too should the time for search and rescue of victims. Firefighters should be able to check a standard apartment and perform rescue ventilation within only a few minutes. That’s possible because they can work safely and quickly with visibility and without heat and smoke. The instruction is simple but very important because every intervention is a special situation for each firefighter. In such stressful situations, the only things that work are those on which you have trained intensively. The team has to know who has which job and what is important. Only a qualified early and coordinated commitment can upgrade the safety of firefighters, reduce the search and rescue time for victims, and minimize the structural damage.
CHRISTIAN EMRICH is in the two-year study program for junior fire chiefs in the Munich (Germany) Fire Department. He initiated the tactical ventilation research project in 2007 and coauthored with Ulrich Cimolino and Stefan Svensson Tactical Ventilation (2012). With Group Leader, he was the ventilation products product manager. Emrich has a bachelor’s degree in engineering and a master’s degree in rescue engineering from the University of Applied Sciences in Cologne and conducts classes on ventilation and fire attack internationally.
Fire Engineering Archives
