Archives > 2007 > September 2007 > Tool Time - Big Building Big Ventilation

September 2007

Tool Time

by Raul A. Angulo

Big Building Big Ventilation

We all know the quick, rule-of-thumb hydraulics formula – big fire means big water. The same applies to ventilation – big building means big ventilation. The Tempest 60-inch MVU (mobile ventilation unit) packs a walloping 150,000 cfm at 78 miles per hour.

It seems to be the nature of man to want to build things better and bigger. Take a look at guns, tanks, cars, trucks, tractors, rockets, planes, tunnels, buildings and even hamburgers. Accordingly, skyscrapers and big-box warehouses are here to stay, and the fire service has had to adapt.

The job of ventilating large structures has become an enormous challenge. Enormous jobs require enormous tools.

The city of Seattle, like most major cities, is struggling to solve the increasing traffic problems that create gridlock nightmares for daily commuters and roadway commerce. Sound Transit is the new light rail system being introduced into the city. With that comes a huge tunnel system that will allow the trains smooth traverse through the hilly terrain that surrounds downtown Seattle.

Tunnel fires pose numerous problems for firefighters. Access and ventilation top the list. There is only one strategy for tunnel ventilation – horizontal. Initial planning permits and negotiations called for the purchase of a Tempest Technology 60-inch MVU for the Seattle Fire Department. Ventilation can happen anywhere in the list of incident priorities, but it may be that ventilation becomes the first priority before rescue and life safety can even be initiated.

Tempest Technology

The Tempest Technology Corporation was founded in 1987 and is now a leading manufacturer of engine and electric powered blowers for the fire service in the tactical technique known as positive pressure ventilation or PPV. Tempest blowers and PPV fans are also used by construction contractors to control hostile environments they encounter such as dust, fumes and poisonous gases like carbon monoxide, greatly improving the safety environment in confined spaces. Tempest blowers are even used on golf courses to dry out wet greens.

PPV blowers are sometimes called PPV fans (in Seattle, we just call them fans), but they are not smoke ejectors. Positive pressure ventilation is a different smoke removal principle and was first developed in the United States in the 1960s. There are 60 MVUs in service worldwide.

Today, PPV is an accepted firefighting tactic used by fire departments all over the country and around the world. PPV works on the principle that air flows from high pressure to low pressure, taking the path of least resistance. More on that later.

The MVU is a giant, 60-inch PPV blower skid-mounted to the PALIFT Palfinger PLT-10 Hook-Lift system. The PALIFT Hooklift is an all hydraulic piece of equipment that is installed on a two or multiple axle chassis or semi-trailer. The PALIFT Hooklift system allows loading, unloading and dumping of various heavy commercial bodies like flatbeds, open top containers, dump bodies, water tanks and storage containers.

Its diesel engine comes equipped with a Murphy display and diagnostic module, which displays the following information – engine hours, engine RPM, system voltage, percent engine load at the current RPM, coolant temperature, oil pressure, fuel economy, throttle position, manifold air temperature and current fuel consumption.

The MVU has remote control capability via a portable control box with a 20-foot cable which controls engine/fan RPMs, fan start/stop, tilt up/down, rotation left/right, scissors up/down, lowering system raise/lower and an emergency shut down switch.

In addition to this emergency shut down switch that controls the entire system, safety features also include a steel fence running along both sides and the end of the platform and an audible warning signal during the lowering of the fan unit.

One of the best systems on the MVU is the water mist system. The MVU misting system is used for knocking down suspended gases, providing additional cooling during ventilation operations – a water mist flow following the path of pressurized air – and protecting exposures.

The misting system can also be used for mass decontamination at a hazmat or a bio-chemical terrorist incident, as well as a water misting corridor to cool and rehab firefighters in extreme hot weather conditions.

The MVU has a rear storage cabinet for hose, couplings, traffic cones, wheel chocks, golf clubs, and related equipment. There is also a clinometer, which is like a level that indicates the degree of slope of the surface that the MVU is sitting on. The clinometer reads both lateral and longitudinal slope.

People cannot truly appreciate the power and strategic advantage the MVU provides to an incident commander unless they are sold on the principles of the effectiveness and advantages of positive pressure ventilation.

“PPV has been strenuously put to the test by agencies that have attempted to make it fail under all kinds of fire scenarios,” to quote from The Power of Positive Pressure, Garcia and Kauffman, Fire Chief, Sept. 2005. “The positive outcomes and advantages achieved by PPV have been researched and confirmed using empirical and practical methods by international fire engineering groups, fire professionals and fire departments. Despite numerous successful tests of blowers’ effectiveness during initial fire attack, many fire departments use them only for post-knockdown operations.”

Concerns About PPV

Many opponents of PPV claim that setting up a blower will fan and spread the fire throughout the structure. They also claim that if victims are in the pathway between the fire and the exit point, the PPV fan will push the fire toward the victims and incinerate them. Unfortunately, many of their false concerns are due to a lack of hands-on training and experimentation with PPV during live fire burns. There are just as many, if not more, “what if ” concerns and problems with traditional vertical roof top ventilation and vent, enter, search (VES) tactics.

The primary objectives of effective ventilation are to remove heat, smoke and fire gases from a burning structure, prevent flashover and/or backdraft and to channel or change the direction of the fire.

Fire within a confined area can be channeled in a vertical direction, reducing the interior temperatures of the involved area and preventing the horizontal spread of smoke and fire. Redirecting smoke and fire reduces extension, thereby enhancing property conservation.

PPV works on the principle that air flows from high pressure to low pressure by taking the path of least resistance. If you had a tiny hole in a balloon and filled it with air, the air would leak out of the hole because the pressure inside the balloon is greater than atmospheric pressure.

If you slowly rotated the balloon 360 degrees, you could aim the direction of the leaking air. PPV blowers create a high speed, cone-shaped pattern of air that “seals” the entrance opening, forcing air into the fire building. By placing a PPV fan outside of the structure blowing inward, a “positive pressure” is created inside structure that is equally distributed at all points.

An exhaust point is created near the seat of the fire. According to John Mittendorf in his book Truck Company Operations (Fire Engineering, 2000), the ideal exhaust point, which is typically a window or door, should be three quarters to two times the size of the entrance opening. The exhaust opening creates an exit point that releases the interior pressure, drawing heat and smoke to this point of low pressure. Contaminants and soot are drawn from the ceiling, the floor and around obstructions.

Benefits Of PPV

There are many benefits to PPV:

• -Directing the removal of heat, smoke, gases, soot and other products of combustion.

• Reducing interior temperatures.

• Creating a safer interior environment.

• Reducing the chance of a flashover.

PPV introduces fresh air with the fire attack, pushing carbon monoxide and other lethal gases away from firefighters and victims, increasing their chances for survival.

It also improves visibility, making it easier for firefighters to find victims and locate the seat of the fire.

Firefighters can move more freely within the structure once PPV has been established, allowing them to quickly search for and rescue multiple occupants. Further, it controls fire extensions, reduces fire loss, enhances property conservation and increases firefighter safety.

Ideally, these benefits occur simultaneously when the PPV blower is set into position 10 to 15 seconds before the initial attack line is advanced. For this to occur, PPV blowers need to be on every engine company because they are typically first to arrive on scene. This task is usually assigned to the first-in truck company or later arriving fire units.

Controlling The PPV Path

Consider an engine crew of three firefighters at a typical one-story house fire with a room fire on the C-D corner. The driver can quickly lay an attack line to the front door and return to the rig, the firefighter assigned to the nozzle can set and start the PPV fan. The officer can run to the back with a pike pole while doing a quick 360-degree size-up, create an exhaust point after determining the location of the fire, and return to the front of the house. Both members, with self-contained breathing apparatus (SCBAs), can initiate an aggressive interior attack. With practice, it is amazing how quick and simple this evolution is.

It is important that the path of pressurized air between the entrance opening and the exhaust opening be controlled to achieve effective ventilation. The most common Tempest blower in service is the 21-inch fan. It flows at 15,000 to 20,000 cfm at approximately 25-30 mph. To ventilate large area structures, multiple PPV fans need to be stacked or run in series. Sequential ventilation becomes necessary when venting basements, multi-story occupancies, high-rise buildings, large commercial buildings, warehouses (big box buildings), malls, airport terminals and tunnels. Sequential ventilation is dividing larger structures up into smaller areas so they can be ventilated using 21-inch fans.

With all conditions being optimal, two 21-inch PPV blowers in series can ventilate a 20-story high-rise building in approximately 30 minutes. Compare that to a MVU at 150,000 cfm at 78 mph. This is where the MVU comes into play. The same building can be ventilated in approximately 3 minutes.

A Few Case Studies

To illustrate the value of the MVU, here are a few case studies.

In Chicago on July 13, 2006, a Blue Line train derailed and caught fire. There were 1,000 riders with 152 transported to area hospitals. The incident was 400 feet into a tunnel. Chicago’s MVU was successfully deployed, assisting in tunnel evacuation for the riders.

In Fresno, Calif., a Target store caught fire from a welder who was cutting out a trash compactor. The retail area was 130,000 square feet and the warehouse was 12,600 square feet. The fire was extinguished, but smoke became the primary problem. Firefighters attempted sequential PPV using tarps and 21-inch blowers. After realizing the space was too large for the portable units, the MVU was brought and ventilated the entire structure in 3 minutes. Even small pockets of space areas were completely ventilated. Firefighters described the MVU’s performance as “amazing.”

On June 27, 2002, a training exercise in the CRN Memorial Tunnel, W.Va., showed the value of the MVU. The tunnel is 2,785 feet long, 28 feet high and 28 feet wide. Smoke generators were positioned at the midpoint of the tunnel. The MVU was positioned 40 feet outside the north portal. The tunnel cleared in 23 minutes and obstructions in the tunnel did not affect the PPV.

In Seattle, Wash., a test was conducted in the BNSF Railway. The tunnel carries two tracks and is 5,141 feet long, 28 feet high and 35 feet wide. One 48-inch MVU was positioned at the south portal, flowing 130,000 cfm. Two smoke generators were positioned at midpoint in the tunnel. The locomotive and train cars were 200 feet inside the south portal. The smoke cleared to midpoint in 5 minutes and the tunnel was completely cleared in 10 minutes, and the train did not affect the PPV.

Many major cities have tunnels. Tunnel firefighting presents unique challenges to firefighters. Because the fire cannot vent itself, access is quickly limited by heat and smoke, and vehicle engines may not operate due to insufficient oxygen levels. Time to access scene – hiking in – is limited by SCBA air supply. Victims may be required to self-rescue, and the tunnel can be blocked by fire.

A Logical Solution

A PPV MVU is the only logical solution to this logistical nightmare. The same principles of PPV apply to tunnel fires. Smoke and heat will take the path of least resistance. Air will travel from higher pressures to lower pressures.

Vertical roof top ventilation is labor intensive and time consuming. Older roofs can have layers and layers of “roof repairs” that can produce a lot of smoke and eat up chainsaw blades. Add this to a sunny 85-90 degree day, and the heat will physically wear out your firefighters.

Opening A Roof

High-pitched roofs require firefighters to operate from a roof ladder or aerial ladder. Only one, or two firefighters at best, can operate from an unsupported aerial or a roof ladder. Many fire departments don’t even have aerial apparatus. The interior hose line attack is well underway before “truckies” can effectively ventilate a roof.

Lightweight trusses, both wooden and steel, add to the hazards of roof-top vertical ventilation. They are prone to early collapse. Have you ever timed how long it takes for your firefighters to open a roof? That seems like an important baseline to establish for personal self-assessment as well as departmental self-assessment. And if the fire isn’t directly below the roof, you have no other choice but to use some form of horizontal ventilation.

The household combustibles of today are primarily plastics. They burn faster and hotter than combustibles of 30 years ago. They produce more toxic smoke and more British Thermal Units (BTUs). The traditional 4-foot-by-4-foot roof cut is often insufficient to effectively vent today’s fires. If a vent hole is too small, the truck company needs to cut another hole. That’s takes more time. That means collapse time is closer, and you have less firefighters to re-deploy for other critical tasks.

Convincing Skeptics

The study of PPV is intensive. It requires live-fire, hands-on training in acquired structures to convince skeptics. We have only scratched the surface. Perhaps I have opened a can of worms for your department. If so, good.

The U.S. is one of the only, if not the only fire service, worldwide that routinely sends firefighters to the roof to ventilate. The use of blowers has been studied and evaluated for decades, both in the United States and in Europe. It has been proven to be an effective tool for ventilation in a variety of structures. Lightweight truss construction and future changes in the roof construction industry will force the fire service to use alternatives to vertical ventilation.

Type I Fire Resistive construction offers no practical means of ventilation other than using the existing building systems and designs supported by controlled horizontal and vertical ventilation.

Simply breaking out windows of a high rise for horizontal ventilation creates a whole new set of problems. The National Institute of Standards and Technology, (NIST) is performing tests with the Chicago and New York City fire departments. They are using positive pressure MVUs as a way of ventilating high-rise fires.

PPV greatly enhances firefighter safety by creating a safer interior environment, which also increases the chances for the survival of trapped victims. Better visibility allows for quicker search and rescue operations to accomplish our primary objective – life safety.

Positive pressure mobile ventilation units offer a unique solution for emergency ventilation of tunnels and large structures.

Remember, “Big building – Big ventilation.”

Editor’s Note: Raul A. Angulo is a 27-year veteran of the Seattle Fire Department and captain of Ladder Company 6. He is on the Educational Advisory Board for the Fire Department Instructors Conference and is on the Board of Directors for the Fellowship of Christian Firefighters. He lectures on fire service leadership, company officer development and fireground strategy and accountability throughout the U.S., Canada and Mexico.