The term ventilation is constantly used by fire fighters and the fire marshals department. In simple terms, ventilation is the process through which toxic gases, smoke and heat is removed from a burning building and consequently replaced with cleaner, cooler and air rich in oxygen. This is part of the rehabilitation process of a burning building. The process has two distinct components. The first component involves the removal of hot air, smoke and toxic gases. The second component of the ventilation process is pumping in cleaner, cooler and air rich in oxygen. While performing this process, it is important to exercise caution because sudden addition of air rich in oxygen, in a building filled with smoke and fuel can lead to a back draft or an abrupt flash over. Modern techniques of construction encompass materials that are very flammable. This phenomenon is very contrasting in that while some of the materials like oil based paints and furniture supply fuel for any fire, modern buildings also have limited supplies of oxygen because of the tightly shut doors and windows. In case there was an incident of fire in such a building, it would be very under ventilated.
This calls for caution of the part of fire fighters because uncoordinated ventilation can transform under ventilated fires into infernos because of the sudden supply of air rich in oxygen. To avoid this, it is important to coordinate ventilation with other activities like attacking fire with other appliances in addition to the application to water. It is also important to understand different ventilation techniques. In this regard, this paper will highlight the differences between horizontal ventilation, vertical ventilation and positive pressure ventilation.
Horizontal ventilation utilizes existing features in order to increase the flow of air rich in oxygen into the gutted building. Some of the features that horizontal ventilation utilizes include windows, doors and other openings that are at the same level with the fire. In some instances, when the fire threatens to get out of hand, fire fighters use their discretion and make additional openings on the building’s walls. This is in a feat to increase horizontal ventilation to the building. Horizontal ventilation is very efficient in fires reported in residential buildings, fires that are reported in rooms and those fires that the fire attack team can control with relative ease.
In horizontal ventilation, just like the name suggests, the toxic gases, heat and smoke escape the gutted building in a horizontal direction. As espoused earlier, this is because any openings that are used and those that are added at the discretion of the fire fighters are made at the same level with the fire. These additional openings and the use of existing openings at the same level with the fire utilizes the convection currents to carry superheated gases and smoke to other areas in the building that are not involved in the fire.
Unlike horizontal ventilation, vertical ventilation uses a different approach altogether. While horizontal ventilation uses existing openings or creates additional openings at the same level with the fire, vertical ventilation uses openings in the roof or floor of the building. Unlike horizontal ventilation where the smoke hot air and toxic gases escape in a horizontal direction, smoke hot air and toxic gases escape in a vertical direction, in vertical ventilation (Kleane & Russell 267).
More often than not, fire fighters used pathways such as exhaust vents, openings on the roof such as monitors, scuttles and skylights, stairwells and ceilings for vertical ventilation. Fire fighters can also exercise their discretion and create additional openings on the floor and roof. It is important for fire fighters to ensure that any additional openings should extend through and past all layers of the floor and roof. When using vertical ventilation, fire fighters have to be wary of certain risks. As espoused earlier, additional openings can be created in the roof and floor in order to increase the vertical flow of smoke hot air and toxic gases. This poses the biggest risk of the ventilation process (Schottke 467).
As part of the preparations necessary, fire fighters must evaluate the design and construction of the roof and floor of the building. The biggest risk of the vertical ventilation process is the potential for collapse of the roof. In this regard, and in order to prevent this, fire fighters must carry out an assessment of the roof to determine whether there are heat vents, roof scuttles, louver ventilation, fan shafts and plumbing vents in order to avoid tripping or collapse of the building’s roof (Schottke 467).
Positive pressure ventilation is often categorized under mechanical ventilation as opposed to natural ventilation. The difference between positive pressure ventilation and natural ventilation is that natural ventilation uses convectional forces to get the smoke hot air and toxic gases out of a building while positive pressure ventilation actively forces the smoke hot air and toxic gases out of the building. Positive pressure ventilation is commonly used in both horizontal and vertical ventilation. Positive pressure ventilation is used for various purposes during and after the fire is contained.
The ventilation process utilizes fans in order to actively introduce cooler, clean and air rich in oxygen into the building. The fans pump air from outside and direct it into the building through vents and other passages. Additionally, positive pressure ventilation can be used to mitigate the interior temperatures in addition to reducing smoke coordination. This is used when fire fighters are coordinating a fire attack. Positive pressure ventilation is also used when fire fighters want to clear smoke hot air and toxic gases out of the building after the fire in the building has been extinguished. It is important to note that positive pressure ventilation is used in recognition of the fact that horizontal ventilation and vertical ventilation may not be sufficient enough to properly ventilate the building during a coordinated fire fight or after the fire has been extinguished.
Of note here is the efficiency of positive pressure ventilation in ensuring the flow of air rich in oxygen into a building. Positive pressure ventilation unlike horizontal ventilation and vertical ventilation that uses convectional forces to ventilate the building, actively pumps air into a building or rid a building of smoke hot air and toxic gases during a coordinated fire attack or after a fire in the building has been extinguished. Positive pressure ventilation uses powerful fans that are placed in openings on the roof and floor. Positive pressure ventilation can use existing fans in the building. Modern buildings are constructed in a manner that not only encourages natural ventilation but also augments it using mechanical ventilation.
This means that buildings feature large vents on the roofs that are fitted with huge fans. These fans work throughout the day to pump in fresh air filled with oxygen. The fans also remove hot air from the building. Positive pressure ventilation also employs heating, ventilation and air conditioning (HVAC) systems installed in buildings.
These systems incorporate technology that is based on scientific principles of heat transfer, thermodynamics and fluid mechanics. Heating, ventilation and air conditioning systems are important systems in buildings because their regulate humidity and temperatures in the building using fresh air from outside. Positive pressure ventilation takes advantage of these pre- existing systems to ventilate the building during and after the fire attack is over and the fire has been extinguished. In buildings where these systems do not exist, fire fighters can install fans in vents on the roof.
Positive pressure ventilation is unlike vertical ventilation and horizontal ventilation in one fundamental difference. Vertical ventilation and horizontal ventilation both use natural, conventional forces. Under conventional forces, hot air rises because it is less dense when compared to cooler air. As such, when hot air rises, cooler air comes down to take its place. This is how hot air from inside a building is exchanged for cooler air from outside the building. It is for this reason that openings are made on the roof in the case of vertical ventilation. It is noteworthy that the fire fighters prefer to make one larger opening, as opposed to many small openings.
While the biggest concern here is the surface area, small openings on the roof might compromise the structural integrity of the roof and cause potential collapse of the roof. In the same breadth, openings on the walls of the building on fire are opened at the same level with the fire. Additional openings can be made on the wall in case fire fighters deem it necessary. All this is to enhance conventional exchange of hot contaminated air from inside the burning building with cooler cleaner air from outside the building.
Unlike vertical ventilation and horizontal ventilation, positive pressure ventilation does not rely on natural, conventional forces. Instead, positive pressure ventilation, like the name suggests creates a positive pressure inside the building. This effectively increases the rate at which air flows from inside the building to the outside. In this manner, the smoke hot air and toxic gases are removed from the building at a higher rate when compared to vertical ventilation and horizontal ventilation (Schottke 450)
Positive pressure ventilation can be used with either vertical ventilation or horizontal ventilation. This increases the speed of ventilation for either of these mechanisms. This is because positive pressure ventilation in this manner is used alongside other openings in the building like windows, doors and other additional openings in horizontal ventilation and heat vents, roof scuttles, louver ventilation, and fan shafts in the case of vertical ventilation. Positive pressure fastens up the convention flow of the smoke hot air and toxic gases because of the positive pressure created in the building, hence making the ventilation process faster than either horizontal ventilation or vertical ventilation.
As highlighted in this paper, ventilation is very vital in the rehabilitation of a building after it has been gutted down by a fire. The choice of the method of ventilation is dependent on many factors, among them being the type of building and its design and architecture. Horizontal ventilation is a type of ventilation where the smoke hot air and toxic gases are evacuated from the building using the horizontal direction. This method is appropriate for fires reported in residential buildings, fires that are reported in rooms and those fires that the attack team can control with relative ease.
This method uses openings in the walls of the buildings that are on the same level with the fire. Additional openings can be made at the discretion of the fire fighters. Unlike the horizontal ventilation, vertical ventilation expels the smoke hot air and toxic gases from the building in a vertical direction. This method uses openings in the roof and floor of the building. The caveat with this method is that it carries viable risk of roof collapse. The openings in this method include heat vents, roof scuttles, louver ventilation, and fan shafts. Additional openings can also be made on the roof in order to augment the already existing openings.
The positive pressure ventilation method applies positive pressure inside the building in order to speed the rate of evacuation of smoke hot air and toxic gases from the building. This is achieved mechanically through the use of fans placed appropriately on the building depending on the location of the fire on the building. These fans can be erected on the roof tops of high rise buildings or on the walls in case the location of the fire is on a floor in a building. The positive pressure ventilation can be used to augment both vertical ventilation and horizontal ventilation.
Garcia, Kriss, Reinhard Kauffmann, and Raymond Schelble. Positive Pressure Attack for Ventilation & Firefighting. Tulsa, Okla: Penwell, 2006. Print.
Kleane, Bernard J, and Russell E. Sanders. Structural Firefighting: Strategy and Tactics. Sudbury, Mass: Jones and Bartlett Publishers, 2008. Print.
Schottke, David. Fundamentals of Fire Fighter Skills. Burlington, MA. Jones & Barlett Learning. 2014. Print.