By THOMAS J. RINOLDO
Scenario: You are the on-duty deputy chief when the station tones sound. The dispatcher reports a possible house fire at 14 South Street. South Street is downtown, and it will take a few minutes to get there. Engine 3 arrives and reports smoke showing from the second floor of a 2½-story wood-frame structure. Command is passed to Ladder 3 while Engine 3 begins to stretch a handline to the second floor. The remaining ladder firefighters begin setting up the aerial to the roof. Engine 5 arrives and lays a supply line into Engine 3, then takes in a backup line. Rescue 1 arrives and starts up to the second floor for a primary search. You arrive at the scene, do a quick 360° size-up of the structure, and consider strategies and tactics with the incident commander (IC). You reassign the ladder officer back to his company, and you assume command.
As you observe the structure and the conditions, you radio Engine 3 to get a progress report. The officer answers that they are with Rescue and are trying to advance to the second floor but cannot because of the tremendous heat. Walking around the structure again, you see fire from inside the window at the B/C corner, but it has not yet broken out. You quickly look for the ladder company and see the members just getting to the roof.
Does this scenario sound familiar? Does your department send the ladder company only to the roof at every fire? Does your department routinely stretch handlines into the fire building without coordinated ventilation? Do you use fans only for overhaul? If yes, then it may be time to revisit your ventilation practices.
| (1) Photos 1-3 by David Studley. |
Ventilation is the planned and systemic removal of heat, smoke, and fire gases from a structure and replacing them with fresh, cooler air. As a fire grows and consumes fuel, it begins to change the environment within the structure (the building and contents) and generates heat, smoke, and gases that rise and begin to increase the internal pressure within the structure. The heat, smoke, and gases confined within that structure bank back down into the structure, creating the mushroom effect and a flashover condition. As the fire grows, it generates more heat and consumes more fuel, making occupant survival impossible and conditions more dangerous for interior companies. Good, proven ventilation practices can help stretch the line easier and buy time for any victims still trapped. Poor practices can be disastrous.
There are two basic ways to ventilate a structure—vertically and horizontally. The methods used to accomplish these vary, usually by cutting, breaking, or opening the structure’s exterior to create an opening and give the heat, smoke, and combustion products an avenue to exit.
The fire’s location and size; location of victims and interior crews; building construction and, if present, features such as skylights, scuttles, or rooftop bulkheads; available equipment; and available personnel are all factors to consider when choosing which type of ventilation to use.
VERTICAL VENTILATION
Vertical ventilation is the process of creating an overhead opening as high up and as close to the seat of the fire as possible. This allows the heat, smoke, and combustion products to travel up and out of the structure—much like a chimney—following the path of least resistance (lower pressure). Unless the fire is in the space directly under the roof or a backdraft condition is present, ventilating the roof may not be the best first choice. If you are battling a first-floor fire in a multistory structure, this would cause all of the heat, smoke, and combustion products to travel up through the remaining floors and expose them and anyone high in the structure to the fire’s effects.
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A basement fire in a balloon-frame structure does require the roof to be opened, so vertical ventilation will be needed early in the attack. However, this venting must be coordinated with the interior companies. Additionally, the hoselines must be ready to, or be in a position to, apply water; and the walls and ceilings need to be opened up to access the void spaces. This minimizes horizontal travel within the void spaces. Use the natural features of the building such as skylights, scuttle openings, or vent shafts whenever possible to facilitate rapid movement of the heat, smoke, and combustion products from the structure. Give careful consideration when using natural features; this may lead these products to travel through unaffected areas of the structure and create a potential for autoexposure, especially in air or light shafts. Also, vertical ventilation is sometimes problematic if the attic space is finished. Your crews may do a great job of opening the roof only to find it impossible to punch down the ceiling below because of the flooring.
HORIZONTAL VENTILATION
Horizontal ventilation is the process of creating an opening on the fire floor to allow heat, smoke, and combustion products to travel horizontally out of the building without affecting or, at least, minimizing the effect, to the uninvolved areas of the structure. For most fires, horizontal ventilation is the best first option.
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Create this opening as close to the seat of the fire as possible. Taking out a window on the Bravo side for a fire on the Delta side allows products to travel horizontally through the structure and could create larger problems. Ideally, this would mean opening or taking out windows in the involved area. Having good ventilation ahead of the interior hose crew to push the heat, smoke, and combustion products out allows advancement from the uninvolved area of the structure. It is imperative that any ventilation is communicated and coordinated among the IC, the ventilation crews, and the interior attack crews to ensure that they—and any fire victims—are not placed between the fire and the exit path. Do not take out windows until water is at the nozzle, the hoseline has been bled and the pattern checked, and the interior crew is ready to put water on the fire. Ventilating too soon allows the fire to increase in size and intensity. Heavy wind conditions must be accounted for as well. Ventilating against heavy winds will create wind-driven fires that will endanger the crews trying to advance. Although both methods work very well by themselves, using them in conjunction with each other will make ventilation more efficient.
MECHANICAL VENTILATION
If used properly, mechanical ventilation can assist with and make ventilation more efficient. Once the fire’s main body is knocked down, the interior crew can use the water stream to vent the area. This method is called hydraulic ventilation or “power venting.” It is achieved by directing the hosestream out a window opening from inside the structure. The line is moved back a few feet from the window opening and a narrow fog pattern is adjusted to cover as much of the window opening as possible to create a lower pressure at the window than that within the structure. The heat, smoke and products of combustion will be drawn past the stream following the path of least resistance (lower pressure) and be drawn out of the area through the window. This method rapidly clears the immediate area to make overhaul easier. If the fire is still burning in other areas, it will be drawn toward the power vent and the firefighters on the line. While performing this tactic, firefighters should be in full personal protective equipment, prepared for the fire lighting up behind them or being drawn to them. Self-contained breathing apparatus should also be used because all the by-products of combustion (heat, smoke and gases) will be pulled toward this opening. Do not use power venting as the primary means of ventilation.
Negative-pressure ventilation is similar to power venting because it creates a lower pressure condition at an opening, which gives air flow a path in and out of the structure. However, the method used to create that lower pressure is different. Instead of using water from the hose, an electric fan is placed in the opening, blowing out. This creates lower pressure in the immediate area around the fan and allows for the heat, smoke, and combustion products to be drawn past the fan, following the path of least resistance out of the building. For greater efficiency, place the fan high into the opening; seal any empty space with some type of covering, usually a salvage cover, to prevent recirculation. If fire is still burning within the structure, this method will also draw it toward the exit. Again, do not use this method as the primary means of ventilation. It also requires more setup time and staffing because you must place a hanger in the opening, establish a power source for and stretch electrical cords to the fan, and cover the remaining opening with the salvage cover. In most cases, you just hang the fan and turn it on, making it less efficient.
| (4) Photo 4 by Doug Dow. |
Another method of mechanical ventilation is positive pressure ventilation (PPV). This involves placing one large or several small fans in a series outside of the structure, blowing in. These fans are usually gasoline powered, which creates the needed air flow. The theory of PPV is based on introducing a large volume of air into the structure to increase the pressure within, above the exterior pressure of 14.7 pounds per square inch atmospheric. This may sound radical, but note that the active fire conditions within the structure also slightly increase the pressure. To prevent recirculation of the air, the fan (or fans) is placed several feet from the entrance opening to allow a cone of air to seal the opening. Carefully choosing and controlling the exit opening allows the heat, smoke, and combustion products to follow the path of least resistance (lower pressure) out of the structure.
As with horizontal ventilation, the exit opening should be at or as close to the area of origin as possible to minimize air traveling to uninvolved areas. For greatest efficiency, the exit opening should be no larger than 1½ to two times the size of the entrance opening. Personnel must be trained to limit the amount of openings created as the incident progresses for pressurization to occur. If conditions are such that you encounter tremendous heat, your people must be prepared to open up the building to release the heat. Do not try to keep the building “closed up” to use PPV later on. If multiple openings have been created, the structure can still be pressurized by using interior doors and ventilated room by room.
You must also consider that, when using an internal combustion engine, carbon monoxide (CO) will be introduced into the structure. Although some fans now have or can be retrofitted with an exhaust extension to direct it away from the opening, use atmospheric monitoring, especially during the overhaul phase, to ensure that personnel are not exposed to increased CO levels. PPV has been used very effectively for years in many parts of the country in all types of structures for overhaul and early ventilation during the fire attack, also called positive pressure attack (PPA). However, it is still considered off limits in many parts of the country, except during the overhaul phase, for a variety of reasons.
There is no substitute for good ventilation practices. Ventilation is critical to fire control, second only to the application of water. Vertical ventilation works when the fire is in the space directly below or in the walls of a balloon-frame constructed structure. However, aggressive interior operations are critical for opening up and cutting off the fire. Horizontal ventilation allows for rapid fire removal in the affected area. Both allow for the removal ahead of the advancing hose team.
Mechanical ventilation will help make ventilation more effective. If PPA is used, an aggressive interior attack must be established and coordinated with the interior crew, and the entrance and exit openings must be controlled. The large volume of air created and the rapid removal of the heat, smoke, and combustion products will increase the safety of the interior crew and allow for a faster advance on the seat of the fire. Used improperly, this and other techniques can contribute to fire growth, extension, and great danger to trapped occupants.
The obstacles encountered will differ from structure to structure. However, you must establish standard operating guidelines to address ventilation practices and give your personnel direction in its proper application. Training on sound, proven ventilation practices provides personnel the skills necessary to apply them on the fireground and to understand the importance of early, coordinated ventilation for a fire attack.
THOMAS J. RINOLDO is a 16-year fire service veteran and a lieutenant with the Framingham (MA) Fire Department, assigned to Platform Company 1, Group 1. He is a nationally certified firefighter I/II, fire officer II, fire instructor II, and rope rescue technician. Rinoldo is an instructor at the Massachusetts Firefighting Academy working for the Recruit Firefighter Training program and is a lead instructor for the Technical Rescue Training program. He is also an examiner for the Massachusetts Fire Training Council, which oversees all firefighter training and firefighter certifications in the Commonwealth of Massachusetts. Rinoldo is also a member of the International Society of Fire Service Instructors.
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