Fire Dynamics: Small Scale Modeling Burns


CarolinaFireJournal - Trey Smith
Trey Smith
01/31/2017 -

With so many environmental and regulatory restrictions concerning live fire training within many communities these days, fire behavior instructors from across the globe are discovering a low-cost solution towards training students in today’s fire dynamics, air control and flow path management. The implementation of small-scale wooden plywood-type boxes — doll houses — now brings the “fire geek” laboratory to your backyard.

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Today’s firefighter must possess a working knowledge of air inlets and outlets and what the negative impact of creating structural openings will have upon fire growth. In our modern fuel environments, recognizing and predicting the potential for extraordinary fire growth and development is a key towards one’s survival.

After learning about using “doll house fire training” from several of my own mentors, I decided this would be a great aspect towards progressively introducing my students in understanding fire physics by recognizing and mitigating the factors that cause events like flashovers or backdrafts. I have used this form of training with great feedback and results for five years now with remarkable results.

As an instructor of 25 years, finally having the capability to create real backdrafts, flashovers, and watch how fireground tactics, once believed to be creditable and reliable methods, are now being questioned through thermal imaging and validated data. New nozzle and hoseline techniques designed to provide a safer fire attack and reducing the threat of thermal exposure is now becoming more popular in using this “out of the box” training method.

Trainees from my era were only able to experience backdrafts and flashovers by watching videos or stories from crusty old firefighters. Today we can create these events on a much smaller scale with better understanding of the “whys of fire fighting.” Today’s firefighters are much more educated and trained but with much less experience than our predecessors. Using small-scale modeling, live fire training provides us with the ability to “read the fire” like we never have before through thermal imaging and comprehensive fire dynamics studies. It’s fun to watch my student’s faces when they hear and feel the “whoosh” from a backdraft. It really grabs their attention and gives them the experience side of learning. Regardless of rank, reading the fireground is not a chief’s job, but everyone’s job! If a tailboard firefighter or line officer can recognize a changing fireground and alert others we all benefit!  

 

 

 

 

The implementation of doll house fire fighting has been instrumental in demonstrating the ideal fuel-to-air mixture that not only exist in hazmat events but structural fire events, as well. We must accept structural fire gases (smoke) is potential ignitable fuel as seen during ventilation-limited fires and how by simply opening up without cooling can become a firefighter killer.

Trainees are now able to see and re-create a variety of fireground scenarios on a smaller scale that can explain fire behavior through a basic understanding of fire dynamics and how flow paths are created and travel.

In using doll house fire training since 2012, I have been able to safely demonstrate to large groups of seasoned firefighters and officers from across the U.S. the behavior of hot buoyant gases and how it can overwhelm a crew operating within the flow path.   Sometimes this is seen as fire gases flowing from one compartment into another compartment horizontally or vertically. The prop also allows for the creation of holes in attic spaces with wooden covers that are periodically removed to reveal the increased flow path velocities along a vertical track from the fuel source ventilation openings.

Most doll house fire training props are disposal wooden boxes constructed of one, two, or multiple compartment boxes that enable the instructor to discuss various types of flow paths. The design also includes removable doors that show the efficiency of controlling the airflow in order to reduce the efficiency of the fire and result in decaying of the fire. The use of small garden sprayers or garden hoses can show the efficiency of a transitional attack with minimal staffing situations.

Types of Doll House Burn Boxes

Some companies provide flash fire training systems that have LPG fueled boxes that enable trainees to see the flammability range by creating backdrafts, flashovers and gas explosions. These systems show trainees the conditions that lead to these dangerous situations and open a discussion on the tactics used to reduce the risk. It also demonstrates what can happen in a worst-case scenario. These systems are usually a scaled version of a residential structure, with a door, roof vents and interior props. Using a handheld controller, an instructor has a wide range of flexibility and can choose from pre-programmed scenarios, or manually introduce smoke, fuel and ignition sources, and can even control the amount of air flow and ventilation to create conditions found at a fire scene. Trainees can view the events in real time and gain a true understanding of some of the most dangerous fire risks.

Wooden Box Material MDF vs. OSB

(MDF) is denser than plywood and particle board so it tends to survive several more burns than particle board. MDF has an even thickness all throughout and is smooth on both sides and provides good fuel. It is a type of hardboard made from wood fiber that has been glued and heated under pressure. Particleboard (chipboard) is an engineered wood product manufactured from wood chips, sawmill shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded.

Single Compartment Boxes

Single compartment boxes are not new to the fire service. They have been typically used in discussing the fire sciences but have limited capabilities when demonstrating the various types of flow paths. Typically, most boxes used for fire dynamics small scale burns are disposable, however, the Max Fire Box is a re-usable box that allows prefabricated panels to be removed and replaced as they are consumed. The use of ceramic/fireplace glass also provides a unique perspective into the development of fire gases so the trainee can see a side profile of fire dynamics.

Two-Compartment

The two-compartment plan (two rooms) enables the trainee to visually watch as fire gases travel throughout compartments towards a doorway or via a window or roof opening. This design also allows the instructor to alter the scenario by removing wooden windows or door covers over the openings thus changing flow paths by simulating the failure of the window or opening of a doorway. The use of a positive pressure blower and an anemometer to gauge wind speed can also be used to mimic a wind-driven fire condition, as well.

Multi-Compartment

The use of a multi-compartment doll house provides the instructor with a variety of fire scenarios that can simulate basement fires, attic space fires, vertical flow path events, and the effects of vertical ventilation. The design specs and schematics for openings are flexible and can be customized to suit the instructor’s preference and scenarios to be demonstrated.

Resources

If you are looking to build your own doll house for training, here are two great resources available online.

  • Fire Chief Ed Hartin of the Central Whidbey Island Fire and Rescue (WA) provides a series of schematics from his website, along with, an abundance of information on compartment fire behavior training. Chief Hartin’s schematics provide a series of single, and multi-compartment designs. Chief Hartin’s schematics can be found at the following link: http://www.cfbt-us.com/pdfs/revised_dh_plans_v3.pdf.
  • East Haven (CT) Deputy Fire Chief P.J. Norwood has expanded upon the plans from Chief Hartin by incorporating an attic space and roof openings that allow the instructor to create partial or fully opened vertical ventilation openings that demonstrate how the influence of roof operations can contribute towards fire growth. The schematics can be obtained by visiting his site at https://www.dropbox.com/s/0a1xj8u7yet8u6o/Palmers%20Dollhouse.pdf?dl=0.

Trey Smith is the Founder of Flow Path Management (http://flowpathmanagement.com) He is a 29-year veteran of the Charlotte Fire Dept. Captain Smith also serves as an active member of the Kill the Flashover Research Project and International Society of Fire Service Instructors assisting in the delivery of the Principles of Modern Fire Attack and several other custom live fire training courses. Captain Smith is also the owner of Rescue North Carolina LLC. ( Trey Smith is the Founder of Flow Path Management (http://flowpathmanagement.com) He is a 29-year veteran of the Charlotte Fire Dept. Captain Smith also serves as an active member of the Kill the Flashover Research Project and International Society of Fire Service Instructors assisting in the delivery of the Principles of Modern Fire Attack and several other custom live fire training courses. Captain Smith is also the owner of Rescue North Carolina LLC. ( http://rescuenc.com ) where he specializes in delivering Swiftwater and other technical rescue programs through the N.C. Office of the State Fire Marshall, Rescue 3 International, as well as, his customized industrial safety and rescue courses.
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Issue 32.2 | Fall 2017

Keeping First Responders Safe
Ideas to improve safety on the job, leadership, serving our community and keeping the desire to serve others...