Ventilation is a necessary process of almost any firefighting operation. The ability to remove smoke, heat and fire gases from a structure can greatly assist with the ability to find victims. It creates an environment more survivable for those victims, reduces the environmental impact your firefighters have to operate in and will accelerate your ability to facilitate fire control and extinguishment. However, improper ventilation or proper ventilation delivered at an inappropriate time can greatly increase the amount of work required to complete fireground tasks by spreading fire and increasing heat, and could contribute to the injury or death of firefighters. As we all know, smoke, heat and gases from an incipient fire will rise and when it meets a vertical restraint, will flow laterally and mushroom down along walls. This process is somewhat like water, with the products of combustion following the path of least resistance. Windows or other openings will allow for natural ventilation to occur, while active ventilation forces or allows for the removal of heat, smoke and gases from a structure and exchanges these with fresh air. Ventilation methods utilized by the fire service consist of mechanical ventilation, vertical ventilation and hydraulic ventilation. All of these processes allow for the removal of hazardous fire products and the replacement of these with fresh air. Before we discuss the processes of fire service ventilation tactics, it is imperative that we discuss the importance of the timing of ventilation. Remember, we are attempting to remove the hazardous by-products of fire from within a confined area. When we do that, fresh air will move in to fill the vacuum caused by the removal of the smoke. This alters the dynamics of the fire by increasing the amount of oxygen being utilized by it and will increase the size of the fire we are trying to find/extinguish. Ensure that prior to initiating the ventilation process, all impacts have been analyzed. Is the ventilation going to push the fire products onto victims or increase the stress currently impacting interior crews? Will the ventilation force the fire into the egress paths of victims or firefighters? Will the ventilation create a backdraft or cause a flashover? Are interior crews in place and ready for the change in the fire presentation? Is incident command aware of the changes being introduced to their action plan? You must always ensure all of the players are ready for the impacts you are getting ready to change with the initiation of ventilation. Natural ventilation This style of ventilation is not considered a mechanical ventilation technique — we don't need anything to direct the flow of air into or out of a structure — yet it is an excellent method to remove fire products. Remember that taking out windows and doors is a great way to allow for an exit of the fire products from the structure, but you still need to coordinate this with interior crews. In addition, if positive pressure is the method your crews may be utilizing in the future, are you removing your ability to control the interior air flow? This process must still be coordinated with incident command to ensure only the windows necessary are being removed; needlessly destroying windows that are not necessary to extinguish the fire is poor customer service. Natural ventilation can be accomplished when time and conditions permit. Windows should be opened rather than broken out, and it may be better to remove a window to relieve heat and smoke rather than leave them in place for positive pressure ventilation, especially when there is a known rescue. Double hung windows should be opened one-half down from the top and one-third up from the bottom. Textbooks say two-thirds, but there are only two sections in most double hung windows and they will only open half way. Open other types of windows as much as possible. Storm windows must also be opened or removed. Shades, blinds, drapes, curtains and other window coverings must be moved away or removed to avoid obstructing air flow. When wind is a factor, windows on the leeward side should be opened first. In addition, when roof or roof features must be opened for venting, windows on the top floor should also be opened. If windows on several floors must be opened, begin on top and work down as opening windows from below first may cause fire and smoke spread. Mechanical ventilation Smoke ejectors — or ventilation fans — should not be considered as a good substitute for natural ventilation techniques. They are rarely able to move the volume of air that Mother Nature can. However, they are good selections when considering partially or completely confined spaces where fire has been knocked down. They are also good boosters for positive pressure tactics in large square footage structures and can be of great assistance in stairwell ventilation when used in conjunction with positive pressure tactics as well. When considering where to place a smoke ejector for good ventilation remember that these style fans are most effective when placed to improve natural air flow. When using in windows or doorways, you need to remove all shades, drapes, blinds, curtains and screens. If possible, the open space around the fan housing should be closed to ensure you are not recycling your fire products back into the structure. Also, the exhaust path of the fan should not push smoke into congested areas, HVAC systems or cooling intakes. Remember to utilize your fan jacks when hanging in windows or doors, while ladder rungs can be utilized as an alternative mounting method. If you must use fans in pairs, remember that one fan used to assist in bringing fresh air in and one to remove the products of fire works best. Try to mount your exhaust fan high in the vent opening to allow for the hotter products to be ejected. The fan bringing in fresh air should be placed lower to allow for the intake of cooler air. Positive pressure ventilation Positive pressure ventilation is one of the primary methods utilized by the fire service today. When utilized appropriately, it is a great problem solver. The process underlying the concept of positive pressure is based on the "Venturi Principle." Effectively, when air is forced into a structure through an opening, it will seek the path of least resistance to find its way out of a structure. If the opening it utilizes as an exit is three quarters or less the size of the initial opening, there remains a residual positive pressure in the compartment where the air is being forced in to. This positive pressure pulls the smoke and heat inside a compartment and moves it out of the controlled ventilation exit with the air being forced through the front ventilation opening. It is critical that there be only one entrance for the ventilation unit and only one exit for the removal of smoke and heat. This exit must be smaller than the opening or there will be no build-up of positive pressure to pull the by-products of the fire. Positive pressure tactics have the ability to move fire and fire gases, which is the ventilation part. This also can cause a rapid increase in fire development. You should attempt to place the ventilation opening between your firefighters and the fire or between the fire and trapped victims. It is critical to know where the fire is and where it is going to move once this tactic is selected. If you initiate positive pressure in conjunction with your attack crews, know what this method is going to do to them. Positive pressure is a tool to be utilized when a size-up confirms this ventilation tactic will assist with a rapid fire suppression, quick location of victims and will not increase the risk/benefit profile for interior crews. Don't simply utilize this tactic because "we have always done it this way." Positive pressure will work effectively in all areas, but may need assistance in high rises if using it as your only means of ventilation. Remember, smoke ejectors placed at the doorway of floors being ventilated into a positively pressured stairwell ventilation system will greatly increase the time this evolution can be completed. When placing the positive pressure fan, it must be set up in a fresh air environment with its ventilation stream aimed at the opening, generally a doorway. Ensure the cone (circular pattern of air) at the opening completely covers the door. If utilizing multiple positive pressure fans, stacking the fans helps to increase the input volume. When dealing with oversized or double doors, consider placing tandem fans side by side. Utilization of one positive pressure fan requires the fan to be placed about 6-10 feet from the doorway. For a multiple fan process, it is best to place the first positive pressure fan 3-5 feet from the doorway and the second fan 6-10 feet from the doorway, attempting to place the larger volume fan in front. Finally, remember most positive pressure fans are gasoline powered. If the exhaust from your ventilation fan may entrain the carbon monoxide from your fan, ensure the environment is checked with an atmospheric monitor to ensure personnel can enter safely. It's vital to bear in mind that ventilation to a structure does not always mean it is a safe environment. Recent studies show that gases we are not monitoring for on a regular basis — such as cyanide — can kill us. Fog streams Fog streams are an effective ventilation tactic that is enabled through the use of hydraulic principles. This, in conjunction with the Venturi Principle, makes for a rapid, effective method to ventilate an area. This process works best if started as quickly as possible after extinguishment. The most effective use of the fog ventilation works when the stream is positioned so the fog pattern covers most of the window opening. First, ensure the glass has been removed completely from the window opening. Then place the nozzle about 2 feet from the window frame and open the nozzle in a wide fog pattern. Observe the movement of smoke in the immediate area and adjust the distance of the fog nozzle from the window until the most movement of smoke from the area has been achieved. Fog streams should not be used for venting if they damage items requiring protection, damage items outside of the fire building or enter adjoining buildings. They should not be used in freezing weather due to ice formation, and remember fog stream ventilation is a short-term ventilation tactic. Longer-term ventilation tactics should utilize other options. Vertical ventilation Vertical ventilation is one of the most hazardous tasks accomplished on the fireground and should only be used when it is necessary and can be completed safely. Don't loiter to admire your work when complete! The keys to success in delivering this tactic are to: Have two means of egress Limit the total time of work on roof Not let the ventilation hole get between you and your means of egress Vertical ventilation can be accomplished by utilizing existing openings in the roofing deck or making our own. Natural openings are those structural items that require a hole to exist in the roof of a structure. The size of the opening should be selected based on availability and the largest possible. Multiple floor structures should have a number of options available. Vertical shafts that run the height of the building will work the best, such as stairways, elevators and large utility shafts. Remember that skylights, scuttles, monitors, attic vents and swamp coolers can all be removed to assist with ventilation. (Note: Ladders should be used to provide safer footing for any pitched roof operation and to spread the load on any flat room. There should always be two means of escape for any roof operation and a protection hoseline should be in place on the roof. Roofs should also be checked to make sure they are safe to work on. Spongy material, bubbling tar, melted snow or dry spots, on the roof — or smoke or heat emitting from it — are some of the signs that its integrity may be compromised.) When accessing your ventilation spot, select your ventilation site based on the closest area over the seat of the fire as well as an area where a sufficient sized hole can be cut. Crews accessing the roof should have, as a minimum, a gas-powered saw (chain or circular), an axe to louver the decking after the cut (and in case the saw quits) and a pike pole/trash hook to punch the ceiling when necessary. Some crews will say always take a roof ladder with you. If your roof pitch is such that you don't feel comfortable working without one, take one. In addition, recent rain or snow, or standard pitches on concrete or tile roofs, may warrant the addition of a roof ladder. Ensure the primary firefighter to access the roof is able to sound it for stability. Sound your rafters all the way to where your cut will be. Locate and mark the position of the rafters for the individual utilizing the saw. Remember that a 4-by-4 hole will be considered a minimum sized hole. Don't cut the roof rafters -- in a truss system that may be weakened by fire, this could be an initiator of a collapse of the roof support system. When cutting your ventilation hole, consider making your farthest cuts first to ensure your last cut places you closest to your egress point. Louver the roof deck and prepare to punch the ceiling on the ceiling of the floor under your cut. Do not proceed without checking with command – interior crews must be ready! Once given the go ahead by command, punch the ceiling. Again, consider making the farthest holes and work toward your egress. All personnel should be in full SCBA for this event. Once the ventilation task is complete, get off the roof. A trench cut is a useful variant of the vertical ventilation technique. This task is an option when fighting fires in a long, narrow structure. This hole is cut from one exterior wall to the other and 4 feet wide. The key to success is to plan the position of the trench cut so that you are far enough ahead of the fire to be able to complete the task before the fire gets to your crew. To sum up, this article addressed in a rapid fashion one of the hallmarks of our profession. This skill of ventilation is an art and can make or break the direction of numerous activities on a fireground. We owe it to ourselves to be practiced at this process so that we can create an environment that will allow for safe, rapid victim location and rescue, fire location and extinguishment and the creation of the safest possible environment for our brothers and sisters to work in. If it's been a while since your crews walked through a ventilation process, take the time to practice. If nothing else, walk through how your team will perform a vertical ventilation scenario as a crew. Perfect practice makes for safer, effective crews. Next month we will look at the best ventilation tactics based on the type of occupancy/building construction style structure fires. About the author Michael Lee has 25 years experience in pre-hospital paramedic experience and about 20 years experience in the fire service. He started as a FF/Paramedic and worked up through the ranks, including training officer, to his current position as battalion chief. He currently serves as battalion chief at Mountain View Fire Protection District in Colorado. He is currently filling the role of safety officer for FEMA USAR Colorado Task Force One and has military service in the U.S. Navy. To contact Michael, email [email protected].