flame spread

1. FLAME SPREAD DEFINITION: The movement of fire from one place to another. When an investigator first arrives at a fire scene, he begins observing fire damage around the perimeter of the scene. Mental notes and observations begin to materialize as to the direction the fire traveled from one place to another. Understanding the fire flow is critical to the investigator.

3. FLAME SPREAD To develop the fire flow pattern it is important to know: What direction did the fire burn? Where did the fire come from? Where did the fire go? Why did the fire move the way it did? After he completes the exterior view, the fire scene itself is observed. Again the investigator is determining how the fire traveled from one point to another.

4. FLAME SPREAD He will compare what he has observed in the scene with what he observed outside the scene. Finding where the fire stopped, or was extinguished now becomes the first place the investigator starts in tracking or following the flow back to the fires origin area. Once he develops a scenario or multiple scenarios, he again applies fire spread principles by testing and comparing scenarios with his flow observations that were first noted.

5. FLAME SPREAD The ultimate objective is to be able to recognize, eliminate and resolve any contradictions as to why the damage exists as it does.

6. FLAME SPREAD Definition further explained After ignition in the fuel-gas-air mixture, the flame that now evolved is either going to grow at some rate or stop and return to a smoldering stage or end. If the fuel-gas-air mixture stays within its flammable limits, the flame will begin spreading on the fuel surface. Fire can spread as a flame or in smoldering, however the later is much slower.

7. FLAME SPREAD Once the fire has established, the fuel that is burning or a new adjacent fuel may provide a path for the flame. A flames buoyancy (or gravitational pull) in combination with ventilation will assist or oppose its travel to the new fuel. Ventilation can be due to meteorological wind, a powered fan, or even the natural drafts that are induced by the fire.

8. FLAME SPREAD For the flame to spread on the fuel�s surface, it must pre-heat and start the pyrolysis in the next area, we will call this the target fuel region. The heat flux that is generated by the flames must be sufficient in order to pre-heat the target fuel region. Visualize the next fuel region as the target of the heat transfer.

9. FLAME SPREAD A Target Fuel is a fuel that is subject to ignition by convection and or thermal radiation such as from a flame or a hot gas layer. It might help to think of the next region that the flame will travel as being in the flames shadow. If no ventilation is present the shadow will be short and travel will be slow unless the target area is vertical like a wall.

10. FLAME SPREAD

11. FLAME SPREAD

12. FLAME SPREAD Many factors affect flame spread, some will be discussed below. No two fires will burn the same, except in a laboratory environment. As previously discussed, the human factor and environmental and fuel factors make each fire a unique scene.

13. FLAME SPREAD Factors affecting flame spread - Fuel type Simply a fuel is any material that yields heat through combustion. The majority of these fuels are organic and contain carbon and some combination of oxygen, hydrogen and sometimes other elements such as nitrogen. The composition of these materials into various products through time is continuously changing as man finds and invents new uses and other products. Each fuel product exhibits different physical and chemical properties that will affect the fuels combustibility and how it will react with other materials.

14. FLAME SPREAD Factors affecting flame spread - Fuel type Over the years the composition of furniture, for example, has changed drastically. For the most part, fuel weights have gotten lighter, however, heat release rates have climbed. The average cotton easy chair weighs between 17.7 and 31.8 kg (39 and 70 pounds) and heat release rate varies between 290 and 370kW. While a polyurethane easy chair tips in at 12.3 and 27.7 (27-61 pounds) and the heat release rate varies between 1350 and 1990 kW. What does the future bring?

15. FLAME SPREAD Factors affecting flame spread - Fuel type With just the heat release rate changes alone we can see that the polyurethane chair will burn differently than the cotton chair. Flame spread, fire patterns, and fire flow will change due to different fuel loads. It is important for the investigator to recognize and identify materials or material residue at the fire scene, since different fuels can have a dramatically different heat release rate as shown in the chair comparison above.

16. FLAME SPREAD Factors affecting flame spread - Fuel type Further, many fuels can spread flame much easier than others. One means of comparing interior finish materials is the Steiner Tunnel test, ASTM E84. Samples are exposed to a propane burner and the flame spread distance is measured down a 7.3 m (24 ft) tunnel. All materials are compared to red oak which has a flame spread rating of 100. If the material has a number higher than 100 than it spreads the flame further than red oak.

17. FLAME SPREAD Factors affecting flame spread - Geometry Geometry is relation of properties and measurements of solids, surfaces, lines and angles. Geometry considerations can start on the molecular level of how a fuel or material is bound together. Then we want to know how that material is used with others to compose objects used in the home, auto, office and industrial.

18. FLAME SPREAD Factors affecting flame spread - Geometry The geometry of objects and how they are arranged in proximity to each other will have an impact on fire spread. Last but not least, the containment of the objects or fuel load has a strong influence in the flame spread and fire development among different items in a room or structure.

19. FLAME SPREAD Factors affecting flame spread - Material Geometry The form of individual materials that make up objects such as chairs, clothing, carpeting, appliances etc. Going back to our comparison of a solid piece of pine vs. a pile of pine saw dust or shavings. Even though they are composed of the same material, the geometry of the material will have a dramatic difference on the ease of ignition and flame spread.

20. FLAME SPREAD Factors affecting flame spread - Material Geometry An other example would be solid cardboard vs corrugated cardboard. On a more basic level, polymers, such as polyurethanes, polyesters, etc have long chain molecules with very weak bonds holding them together, as opposed to celluosics, such as wool, wood, etc which have stronger bonds than polymers and require more energy to break them during the pyrolysis process. A textile with a fuzzy finish will burn easier than a similar material with a smooth finish.

21. FLAME SPREAD Factors affecting flame spread - Object Geometry The shape of the objects and how the materials are used together in the construction of the object will influence the flame spread on the object. As noted earlier, flat objects are harder to get flame spread on, while inside corners or concave surfaces, flames can spread with ease.

22. FLAME SPREAD Factors affecting flame spread - Object Geometry The shape of furniture, automobiles, decorations, appliances and machinery can trap heat, channel hot gas flow, re-radiate on itself or other objects to help spread the flame and affect the speed of fire growth. Where the ignition takes place on the object will also have an impact on the growth and development of the fire.

23. FLAME SPREAD Factors affecting flame spread - Fuel Load Arrangement Geometry As we go one step further with each object�s geometry, the distance between each object in the same compartment will also effect the heat transfer between the objects and hence, the flame spread and the rate of fire growth. A simple way to look at it is to visualize a fire load of 4 stuffed chairs in a given room.

24. FLAME SPREAD Factors affecting flame spread - Fuel Load Arrangement Geometry If there is one chair at the center of each of the four walls, a fire in one of these chairs would develop slower throughout the room as compared to a room with all 4 of the chairs close to one another. People arrange their furniture differently and many times place various accessories and amenities in between the furniture arrangement that became fuel that will enhance the transfer of heat and fire from one point to another.

25. FLAME SPREAD Factors affecting flame spread - Structural Geometry The geometry of the compartment or room plays an ever larger role in affecting flame spread and the rate of fire growth. One of the biggest factors is ventilation. How many openings, how large are the opening and where are the opening located which can provide the fire with fresh air. Windows, doors, ductwork, and even plumbing and wire penetrations, are all potential sources of ventilation.

26. FLAME SPREAD Factors affecting flame spread- Structural Geometry The physical shape of the area, such as the volume, height of ceiling, the shape of the ceiling, the number of alcoves or closets will have an impact on fire development. Smaller spaces maximize the heat transfer between objects and the compartment ceiling and walls. Larger spaces may take longer to heat up, however they have a larger reserve of air to aid the fire�s growth if sufficient fuel is available. Open floor plans vs compartmented floor plans can spread smoke and fire is very different ways.

27. FLAME SPREAD Factors affecting flame spread - Structural Geometry Type of construction will also have a dramatic impact on the fire growth and development. Combustible interior finish will add to the fuel load of the room. Non-combustible or limited combustible interior finishes will not contribute significantly to flame spread.

28. FLAME SPREAD Factors affecting flame spread - Structural Geometry The structural elements can become a factor later in the fire. The insulation of the room or type of structure, i.e. masonary, wood frame, etc will affect how well the room will retain heat and how smoke, heat and fire will spread through the structure. Other building systems such as automatic fire sprinklers need to be considered. Once the fire moves from the compartment of origin, then we must consider each of the geometries above to determine the reasons why the fire destroyed or damaged the remainder of the structure.

29. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow As a fire develops from the incipient stage, a circulation path also is established. As heat and by-products of combustion rise, cooler air is drawn in at the bottom. (Example � cigarette smoke draws to a candle flame). In order for the fire to grow, it will require 15 to 21% oxygen in the air that is being drawn in. Where does it come from? Compare this dilemma with yourself. Imagine locking yourself in a room or even your house. Would you run out of air? No, even with all the windows and doors shut tight, a structure is designed to �breathe�.

30. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow Some structures breath more or less than others depending on how and where they are constructed. Structures built above ground will also breathe through the floor verses a structure built on a concrete slab. In a fire with this type, the investigator might notice evidence of high heat at floor level. Fires will burn more intense where there is a richer level of oxygen.

31. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow As the fire progresses, the draft may be strong enough to open or even close doors, similar to a partially open door slamming shut when the A/C unit comes on. When the heat of the fire is sufficient to begin breaking windows, another ventilation source is now affecting the fire. A fire typically burns up and out. It will seek the easiest path in doing this. It doesn�t like to go around sharp corners; it will make easy curves to accomplish moving up and out.

32. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow Once it has breached ceiling, attic and finally the roof, it will begin to move faster now that it has escaped and has a source of oxygen at the bottom. If there is any air movement on the outside, the fire may tend to �lean� in the same direction as the air movement. The fire moves forward in that direction much faster than against the flow.

33. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow This is where the investigator first sees the signs of flow direction. Smoke, heat and fire patterns on windows and other openings will show him the flow direction. The impact of wind and weather may be subtle or dramatic. It is important for the investigator to determine the wind and weather conditions at the time of the fire.

34. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow

35. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow

36. FLAME SPREAD Factors affecting flame spread - Ventilation/fire flow