origin matrix analysis paper

Published in Fire and Arson Investigator, Journal of the International Association of Arson Investigators (IAAI),

Volume 64, Issue 1, July 2013.

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ORIGIN MATRIX ANALYSIS: A SYSTEMATIC METHODOLOGY FOR THE

ASSESSMENT AND INTERPRETATION OF COMPARTMENT FIRE DAMAGE.

By: Andrew Cox, PE [email protected] Special Agent/Certified Fire Investigator (CFI)

Federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF)

United States Department of Justice

ACKNOWLEDGEMENTS:

Technical and Editorial Contributions From:

Steven Avato, Resident Agent in Charge ATF. Steven Carman Carman and Associates Fire Investigations. John Comery, Special Agent/CFI ATF. William Clark, Investigator New Hampshire State Fire Marshals Office (NHFMO). Justin Geiman, Fire Research Engineer ATF. Brian Grove, Fire Research Engineer ATF William Joa, Special Agent/CFI/Certified Explosives Specialist (CES) ATF. Michael Marquardt, Special Agent/CFI ATF. Lee McCarthy, Fire Research Engineer ATF. John Pijaca, Special Agent/CFI ATF. Keith Rodenhiser, Investigator NHFMO. David Wheeler, Fire Analyst NEFCO Fire Investigations. Nathan Wittasek, Senior Managing Engineer Exponent.

Thanks also to countless other investigators, engineers, and scientists who shared their ideas,

perspective, and experiences during development of the concepts presented in this paper.

INTRODUCTION

Fire investigators routinely assess and interpret fire scene patterns and damages in an effort to

develop hypotheses, and eventually draw conclusions about where a fire may have started and

how that fire spread throughout a structure. In the case of pre-flashover fires, there is rarely

disparity among fire investigators about the general area in which a fire originated. However,

despite significant advances in the science of fire investigation, it is still a relatively common

occurrence that two qualified fire investigators look at the same post-flashover fire scene

evidence and reach different conclusions regarding area of origin, and then ultimately cause.

The fact that different investigators can review the same fire scene damages, yet reach different

interpretations about how those damages were generated, has been, and continues to be the

premier problem in the evolution of fire investigation as a more reproducible scientific process.

It is recognized that no system will ever completely eliminate all disputes among investigators,

as an essential feature of origin and cause opinions is that they rely upon individual interpretation



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of data. Nevertheless, investigations that employ approaches based upon a solid scientific

foundation are more likely to yield substantially similar conclusions, rather than vastly differing

opinions.

A major road block in quality, scientific-based fire investigations may be a generalized lack of

understanding of the fundamental principles governing fire damage development among many

practicing fire investigators. Investigators must have a clear understanding not just of the fire-

related physics and material properties that are responsible for creating fire damages, but they

must also be able to justifiably interpret those damages in a meaningful and technically accurate

way. A number of resources, including texts like NFPA 921 Guide for Fire and Explosion

Investigationsi, organizations like the International Association of Arson Investigators (IAAI),

and educational institutions like the National Fire Academy (NFA), attempt to address the issue

of fire scene damage assessment and interpretation with some effectiveness, but the issue is by

no means resolved. The purpose of this paper is to outline a practical and logical thought process

to assist fire investigators in more accurately and consistently identifying correct areas of origin.

Before outlining this framework, a brief review of some fundamental fire science and damage

dynamics principles is required.

FIRE SCIENCE PRINCIPLES States of Matter and the Fire Tetrahedron

Two key fire science principles are of paramount importance in understanding post-flashover

fires. The first principle has to do with states of matter and how they relate to fire. The three

basic classifications of matter are solid, liquid, and gas. It is of critical importance that the

investigator understands that before flaming combustion can exist, solids and liquids must be

transformed into a gas through pyrolysis or a phase change. In other words, solids and liquids do

not themselves directly burn (except in special circumstances like smoldering combustion of

solids) and must be first transformed into a gaseous state. When sufficient heat is applied to a

solid or liquid fuel, it will change into a gaseous form, and only then will it be a potential fuel for

flaming combustion. This concept becomes particularly important in post-flashover fires

because entire compartments can become filled with pyrolized gases and the specific location of

solid and liquid fuels items may become irrelevant in subsequently developing patterns. More

detailed discussion of this topic will follow.

The second important principle is the fire tetrahedron. Fire investigators are commonly taught

that the presence of heat, fuel, an oxidizer, and an uninhibited chemical chain reaction are

required for a fire to exist. A more simplified model, the fire triangle, is also taught, and it

presumes that the uninhibited chemical chain reaction will exist if heat, fuel, and oxygen are

present in sufficient quantity and ratios. The simplified fire triangle model will be referred to for

much of this paper. In the post-flashover environment, the heat component of the fire triangle

comes from the energy generated by the uninhibited chemical chain reaction of the fire itself. As

discussed above, the fuel for the fire is in a gaseous form and is typically generated from

pyrolysis/vaporization of solid and liquid items. Finally, the oxygen component of the fire

triangle typically comes from the oxygen that is available in ambient air. Fire will only exist

where these three components (heat, fuel, oxygen) come together in appropriate ratios. In the

post-flashover environment, the critical components of the fire triangle are at times only co-



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located in areas remote from the origin of the fire because oxygen is only available in areas

proximate to ventilation openings.

To examine these concepts in further detail, consider a single point of origin fire developing in a

one room compartment with an offset doorway opening. The sole oxidizer for the fire in this

case is oxygen in ambient air. Refer to Figure 1 for a visual representation of this hypothetical

compartment, and note that for instructional purposes, the space has been arbitrarily divided into

four separate quadrants for analysis.

In the early pre-flashover development of the fire, fire conditions (the adequate combination of

heat, fuel and oxygen) are primarily limited to the quadrant of origin (Quadrant 1). The heat of

the fire causes proximate solid and liquid items to vaporize into a gas. That heated gaseous fuel

immediately mixes and reacts with oxygen in the air and burning occurs in the immediate area of

the original solid and liquid items. Heat, gaseous fuel, and oxygen, are present in the quadrant of

origin during the early stages of the fire. The remaining regions of the compartment, Quadrants

2, 3 and 4, lack one or more components of the fire triangle. While there may be ample oxygen

in these regions, there is insufficient heat or gaseous fuel to allow flames to exist in Quadrants 2,

3, and 4. As previously discussed, it is important to distinguish between fuels in the gaseous

form and fuels in the solid and liquid forms. There may be large quantities of solid and liquid

fuels in quadrants remote from the origin, but it is fuel in the gaseous form that is needed for

flaming fire to exist. Refer to Figure 2 for a visual representation of these concepts. Note that in

Figure 2 a red triangle is present in Quadrant 1 denoting that all three components of the fire

triangle consistent with flaming fire conditions are present in this area. Blue triangles are present

in Quadrants 2, 3 and 4 denoting that one or more components of the fire triangle are missing. In

this particular case, oxygen is the only component consistently present in Quadrants 2, 3 and 4

and the blue triangle represents that no flaming fire conditions are present in these areas.



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Assuming a sufficient and continued fire growth rate, flaming fire conditions will remain

primarily limited to Quadrant 1 prior to the onset of the transitional period known as flashover.

As the fire develops and approaches flashover, there may be intermittent fire extending from

Quadrant 1 into Quadrants 2, 3, and/or 4. The gaseous fuels generated within Quadrant 1 may

migrate in sufficient quantity to other quadrants and possess enough heat energy to allow

reaction with available oxygen. As a result, all conditions of the fire triangle may be

intermittently met in other quadrants, but prior to flashover, continuous fire conditions will

primarily exist only in the general area of origin, or Quadrant 1 in this case.

During the transitional stage of flashover, heat energy from the fire accumulates within and is

distributed throughout the compartment. This heat causes solid and liquid fuels throughout the

entire compartment to generate the requisite gaseous fuel. Due to the open doorway, sufficient

oxygen may still exist throughout the compartment, and all three conditions of the fire triangle

may be briefly met for large portions of the compartment. The result is the entire room appears

to become involved in fire, and the transition of flashover is often described as such by

observers. Refer to Figure 3 for a graphical representation of these concepts. Note that flashover

is not defined as a single point in time, but rather as a rapid transition period, which in very

general terms, leads from a fire in a room to a room on fire.ii It should also be noted that

flashover may not necessarily result in uniform flaming conditions throughout the entire

compartment. It may just appear that way from the exterior. Oxygen depletion in the

compartment during pre-flashover and early in the flashover transition may already inhibit

flaming combustion in portions of the compartment.



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In the post-flashover stage of a compartment fire, conditions change dramatically from what

occurs prior to flashover. In fact, up to this point, many investigators are likely to be familiar

and comfortable with the concepts that have been discussed. However, post-flashover fire

conditions are in many ways contrary to what has been historically taught throughout the fire

investigation community. Even published references such as NFPA 921, Guide for Fire and

Explosion Investigation and Kirks Fire Investigation provide information that may be misleading when trying to understand important concepts related to post-flashover fire

conditions.i,iii

Terms like full room involvement and graphical representations such as Figure 5.10.2.7 in NFPA 921 suggest that fire conditions exist uniformly throughout a compartment

during post-flashover conditions. A careful reading of the entire text of such references often

clarifies the misconceptions associated with certain terms and diagrams; nevertheless, these

misconceptions persist. In most cases, the post-flashover compartment environment may be

quite different from popular perception, and these differences are critical to the proper

investigation of such fires.

Flashover conditions cause the available oxygen within a typical compartment to be consumed in

a relatively short period of time. This lack of oxygen, commonly referred to as a ventilation

limited condition, controls what will ultimately take place in the post-flashover environment. In

the post-flashover fire compartment, tremendous amounts of heat energy have been generated,

much of which remains contained within the confines of the room. This heat energy is

effectively driving pyrolysis/vaporization of every exposed solid and liquid fuel within the space,

such that fuel gases fill the entire compartment, regardless of the location of those solid and

liquid items. These heated fuel gases are at or above their ignition temperature, but they can

only burn when they mix with the final component of the fire triangle, oxygen. Oxygen in the

fresh ambient air is supplied to the compartment only through ventilation openings such as doors

and windows, and even HVAC vents. Incoming fresh air quickly mixes with heated gaseous

fuel, completing the fire triangle. Therefore, fire will only exist in the areas proximate to

ventilation openings where this fresh air enters the compartment. This conceptual behavior has

been noted in numerous experiments involving underventilated compartments.iv,v,vi

Refer to

Figure 4 for a visual representation of these concepts. Despite the fact that the fire originated in

Quadrant 1, in the post-flashover fire environment, actual flaming fire conditions may

consistently exist only proximate to airflow from the vent in Quadrant 3. Irrespective of where

the fire started or where solid and liquid fuel items are located, in the post-flashover

environment, flaming fire conditions will consistently exist only in areas proximate to oxygen

supplying vents as depicted in Figure 4. This concept is the single most important factor in

correctly determining an area of origin in post-flashover fires, and it will be discussed further

below. In fact, the concept is so important, it is worth repeating. Irrespective of where a fire

started or where solid and liquid fuel items are located, in the post-flashover environment,

flaming fire conditions will consistently exist only in areas proximate to oxygen supplying vents.



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Before continuing, a couple of caveats should be noted. First, if a compartment is small, and the

ventilation opening is large, the post-flashover fire environment is likely to be nearly uniform

throughout the space. An example of this behavior is an open wall flashover cell demonstration

where an entire wall of a compartment is left open for instructional viewing. In such a fire, the

large ventilation opening supplies adequate fresh air (oxygen) to the entire space such that

conditions of the fire triangle are met throughout the compartment, and post-flashover exposures

are then likely to be somewhat uniform throughout the space. The fire dynamics of open wall

flashover cell demonstrations as described above may be a likely source of misleading

information. Investigators may observe such a demonstration, and then incorrectly presume that

the uniform post-flashover fire conditions they saw in the demonstration apply to other

compartments with smaller, more common openings, such as doors and windows.

Second, post-flashover fires generate high velocity flows and turbulence that can allow for fire

conditions and severe exposures to exist some distance from a vent. In the case of a small or

modestly sized residential room such as a bedroom, it is possible that the influx of fresh air at a

vent, such as the doorway in our example, has enough velocity, and associated momentum, to

enable fire conditions to extend beyond Quadrant 3 and into other quadrants. Therefore, when it

is said that burning in the post-flashover environment will occur proximate to ventilation openings, it must be understood that proximate is a relative term that must be considered in more

detail by the investigator.

Third, while post-flashover fire conditions may be primarily limited to areas near vents, the

remaining space will continue experiencing a significant heat exposure. Heat contained within

the compartment will continue to pyrolize solids and vaporize liquids throughout the space and

generate damage. In addition, air leakage due to typical construction techniques and turbulent

flows may allow pockets of burning in areas throughout a compartment. While significant, the

magnitude of these exposures is simply not as great as in areas of a vent where heat, fuel and

oxygen consistently and efficiently combine to generate intense flaming combustion.

Finally, the visual representations depicted in Figures 1-4 are a simplification of very complex

behavior, and are intended only as conceptual diagrams. Real fires may result in differences, but

an investigator who understands the simplified concepts above will be able to apply them to

differing and more complex circumstances and situations.



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DAMAGE DYNAMICS PRINCIPLES

With a better understanding of post-flashover compartment fire conditions, attention must now

be focused on how those fire conditions generate the damages investigators interpret. Materials

exposed to fire conditions experience a fire effect, considered to be the observable or measurable

changes in or on a material as a result of exposure to fire.i Examples of fire effects include

charring of wood, calcination of drywall, deformation of plastics or metals, and deposition of

soot. These generic fire effects result in incident and circumstance specific fire damage patterns

which frequently come in the form of observable shapes. For example, observable fire patterns

may be labeled as horizontal, vertical or angled lines of demarcation, V or U shaped charring

and/or deposition, or a circular hole in a floor. For the purposes of this paper, the term damage includes both generic fire effects and incident specific fire patterns. It is only through

interpretation of damage (fire effects and fire patterns), in conjunction with other investigative

information, that investigators may develop hypotheses regarding a fires origin and cause.

The three key factors influencing the nature and extent of fire damages include, (1) exposure

duration, (2) intensity of the impinging heat flux, and (3) the properties of the exposed material.

While these concepts are not new and have been discussed in other referencesvii

, they are rarely

clearly identified or explained in detail.

1. EXPOSURE DURATION: The longer a material is exposed to fire, the greater the extent of damages to that material. Consider an oak block of wood placed in a

woodstove fire for five minutes, and another oak block of similar size and properties

placed in the same woodstove fire for ten minutes. The block exposed for ten minutes

will comparatively have more significant observable damages because it was exposed to

the fire conditions for a longer period of time.

2. EXPOSURE INTENSITY: All other factors equal, a material exposed to fire conditions of greater heat intensity will exhibit greater damages. Consider a block of oak placed in a

high-intensity furnace for five minutes as compared to a similar block of oak exposed to

the woodstove fire for five minutes. Despite the same exposure duration, the block

placed in the furnace will exhibit a greater extent of damages because the exposure

intensity is more severe in the furnace.

3. MATERIAL PROPERTIES: Differing materials will respond differently to the same fire exposure. Consider a similarly sized block of lightweight pine wood placed in a

woodstove fire for five minutes compared to the oak block of the original example above.

Despite the same exposure duration and intensity, the lightweight pine block will be more

damaged due to its differing material properties. Material form should also be considered

as a material property. For example, oak wood shavings are in a form more susceptible

to damage than solid oak blocks.



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These simple examples of exposure duration, exposure intensity, and material properties are

often taught to fire investigators, and even the new investigator can grasp these concepts in the

context of the above outlined circumstances. However, problems arise when attempting to

understand and interpret such damages in the more complex scenario of an uncontrolled

compartment fire. Each of the three factors cannot be so easily isolated from one another in the

uncontrolled fire environment. Each factor affects the resulting overall observable damages

simultaneously and at different rates of magnitude over the entire life of a given fire scenario.

The complexity of damage dynamics in real world fires is a problem that even the most educated

and experienced investigator will find challenging. A framework for applying the fundamentals

of fire science and damage dynamics is needed to competently conduct any fire investigation.

That framework is a two step process that begins with an assessment of observable fire effects

and fire patterns. The second step in the process is interpreting those observed damages in a

meaningful context to develop hypotheses, and ultimately conclusions, about the origin of a fire.

DAMAGE ASSESSMENT

Damage assessment is the process by which the fires impact on objects and building materials are characterized. The investigator must identify distinguishable areas of fire effects and fire

patterns at a fire scene. A four step process of damage assessment is recommended:

1. DOCUMENT FIRE EFFECTS Fire investigators must first observe and identify fire effects, such as charring of wood, calcination of drywall, deformation of plastics or

metals, deposition of smoke, etc.

2. QUANTIFY FIRE EFFECTS If possible, fire effects may be quantified by measurement; however, the ability to make such quantitative measurements is often

limited by the availability and/or accuracy of suitable measurement techniques. Fire

effects are more commonly quantified by way of qualitative comparison. For example,

an investigator might document that one side of a sofa is more substantially consumed

than the other, simply by way of comparative observation.

3. DOCUMENT FIRE PATTERNS Fire investigators must observe and identify fire patterns. A fire effect or a collection of fire effects may come in the form of identifiable

shapes. Horizontal, vertical and angular lines of demarcation and geometrically shaped

patterns of interest are commonplace at fire scenes.

4. LABEL FIRE PATTERNS For discussion and reference purposes, fire patterns may be labeled to correspond to common geometrical shapes such as lines, triangles, circles,

cones. Identification of V and U shapes are also frequently employed. Such descriptors

are limitless, and are simply a label to facilitate in the communication of observations.

Damage assessment is simply a process of data collection, description, and organization.

Investigators must resist the temptation to interpret the meaning of individual fire effects and fire

patterns in isolation. It is understood that fire effects and fire patterns may provide useful insight

about the extent and direction of fire exposure; however, data collection must come before



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credible analysis. Fire effects and fire patterns are often believed to have a very specific

analyzed meaning, for example, a V-shaped pattern is often considered to have been generated

by a fire plume and indicative of fire origin. However, this may or may not be true. Individual

fire effects and fire patterns are of little value until they are considered in the context of other fire

effects and fire patterns, compartment geometry, ventilation conditions, construction features,

etc.

When possible, it is important that investigators discuss their observations of fire effects and fire

patterns, in hopes of reaching mutual agreement in assessment, prior to interpretation of those

damages. If investigators cannot agree on the nature and characteristics of observed damages,

then their interpretation of such damages is very likely to result in different conclusions.

DAMAGE ANALYSIS

Once fire effects and fire damages have been assessed and investigators agree on the observed

distinguishable areas of damage, it is time to interpret those damages. The magnitude of fire

effects may be utilized to characterize an area or areas that have experienced the most significant

cumulative exposure. Fire patterns may provide insight into direction of exposure. In

combination, fire effects and fire patterns are data which can be used to generate reasonable

hypothetical areas of potential origin. However, additional analysis is required.

In the interpretation of damages, it is helpful to utilize a comparative origin matrix analysis based

on the fundamentals of fire science and damage dynamics already discussed. Consider the single

compartment fire with a fire originating in Quadrant 1 as discussed previously. For simplicity,

assume the solid items/materials located throughout the space are relatively uniform. In the case

of a fire extinguished prior to flashover, the fire conditions and associated damages are generally

limited to the area of origin. This is depicted in Figure 5 by light blue shading in Quadrant 1.

Fire effects are anticipated to be most severe in Quadrant 1 where the fire originated. Also, fire

patterns may provide directional clues of a source heat exposure emanating from Quadrant 1. In

this case, even the novice investigator, with little training and experience, is likely to correctly

identify Quadrant 1 as the general area where the fire started.



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If the same fire were allowed to progress to flashover, it may result in relatively uniform

damages throughout the compartment in addition to those damages generated in Quadrant 1

during pre-flashover development of the fire. Flashover is a relatively short transition, but the

exposure intensity is great such that readily observable fire effects are likely generated on items

and surfaces throughout the space. Nevertheless, the cumulative fire effects imparted to the area

of origin (Quadrant 1) are still likely to be visibly more severe than in other quadrants. Fire

patterns are also still likely to provide directional clues of the original source exposure emanating

from Quadrant 1. Reference Figure 6 for a visual representation of this condition, and note that

darker shading corresponds to damage of greater significance. In this case, correct origin

determination becomes more complicated, but it is very likely that a distinguishable area of

heavier damage will exist in Quadrant 1. This distinguishable area of comparatively severe fire

damage, if present, is likely to help investigators to correctly identify the general area where the

fire started.

If the same fire were allowed to progress post-flashover for a short duration, ventilation effects

will likely begin to drive damage development. In the post-flashover fire, heat, fuel and oxygen

at levels sufficient for flaming combustion will only be consistently present in the area proximate

to the doorway vent. Therefore, intense fire conditions will only be present in Quadrant 3 in the

area of the vent because sufficient oxygen is unavailable in the remaining quadrants. Despite the

fact that intense fire conditions are present only in the area of the vent, the tremendous amounts

of heat contained within the compartment would continue to produce damage, although to a

lesser extent, in the rest of the compartment. Figure 7 conceptually represents this behavior. In

this instance, investigators may discover two distinguishable areas of fire effects, the first in

Quadrant 1 where the fire originated, and the second in Quadrant 3 where the doorway vent

allows fresh air to enter the compartment. In addition, fire patterns may provide directional clues

of source heat exposures emanating from Quadrant 1 and Quadrant 3. Up until this point in time,

the cumulative damages due to heat exposure duration and intensity have been more heavily

concentrated in Quadrants 1 and 3. However, it must be noted that the damages observed in the

originating quadrant may be significantly more subtle than those observed in the area of the vent.

In fact, due to the intensity of post-flashover conditions, notable damages near the area of origin

in Quadrant 1 may be perceived to be secondary to the damages observed in the area of the vent

and may easily be overlooked by investigators. While the total duration of exposure may be

longest in Quadrant 1, the tremendous intensities of post-flashover fire conditions will quickly



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start to generate damages that mask and overshadow all other cumulative damages within the

compartment. Quadrants 2 and 4 are likely to show signs of significant damage, but to a

comparatively lesser extent.

Finally, if the same fire were allowed to progress post-flashover for an extended duration,

ventilation effects are likely to completely dominate the damages generated and then observed.

Fire conditions would be limited primarily to Quadrant 3 where the doorway vent provides fresh

air, and the intensity of those fire conditions would be great. When the intense burning of post-

flashover conditions in Quadrant 3 is allowed to persist for an extended duration, the damages

generated there are likely to overshadow all other damages generated within the compartment

throughout the life of the fire. Almost without exception, investigators will observe a readily

identifiable area of comparatively significant damage associated with the vent, and the remainder

of the compartment will appear somewhat uniformly damaged to a lesser extent. The continued

heat exposure in the remaining Quadrants may mask originating fire damage indicators that

would be helpful to an investigator in determining the true area of origin. Only the very

perceptive investigator, with favorable material related damage factors, is likely to identify

secondary fire effects and/or patterns of value in the originating quadrant. In longer duration

post-flashover fires, the areas of the most severe fire effects and the most prominent fire patterns

are anticipated proximate to vents, and such areas of heavy damage are not necessarily

associated with the area of origin. In that case, it may be nearly impossible to correctly narrow

the area of origin within the compartment based solely on damage without additional data such

as facts, information, and evidence generated from circumstances, eyewitness accounts, timeline

information, pre-fire details regarding the contents of the room, etc. Reference Figure 8.



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ORIGIN MATRIX ANALYSIS

When examining a fire incident where the origin is unknown, it may be helpful for the

investigator to complete a cognitive process of analysis for hypothetical fires originating in each

of the identified quadrants until a matrix of scenarios is complete. Table 1 illustrates the origin

matrix analysis of possible outcomes to be considered. The investigator can then compare actual

scene observations (assessed damages) to the matrix of possible outcomes to help identify a

potential area or areas of origin (damage interpretation).

It is not uncommon for actual scene observations to resemble multiple matrix elements. In this

case, the investigator may be required to consider a range of origin and fire stage possibilities. In

fact, the investigator may not be able to narrow the area of origin to one, two, or even three

quadrants and may be resigned to interpret the whole room as a potential area of origin. The

investigator must then compare origin hypotheses to all available investigative information to

better characterize the validity of each potential area of origin. Additional data may allow the

elimination of certain quadrants as potential areas of origin, and this process of elimination is

often a very effective tool. Rather than focusing on which matrix scenarios fit, the investigator

may employ a process by which matrix scenarios are determined to be invalid and are

eliminated. The example combinations are endless, but real-world fire scene observations,

combined with additional data such as witness information, circumstances, and hypothetical

matrix scenarios are likely to lead an investigator to converge on a small number, or maybe even

a single, hypothetical matrix analysis outcome.



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COMPLICATIONS

Some readily identifiable complications are foreseeable and must be considered in any origin

analysis of a post-flashover fire incident and they are as follows:

a. The Material Property Factor of Damage Dynamics. b. Effects of Vent Flow Velocity and Momentum. c. Single vs. Multiple Points of Origin. d. Partial Extinguishment. e. Dynamic Ventilation Conditions.

Due to these complications, application of the concepts presented thus far may require some

additional thought and consideration.

Material Property Considerations

The discussion and examples up to this point have largely avoided the concept that material

factors must be assessed and considered in damage interpretation. Unfortunately, real world



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living spaces often contain a wide variety of materials with dramatically different susceptibilities

to fire/heat exposures. In addition, some areas of a living space, such as a rooms natural walking path of travel, may be void of furnishings or materials that inhibit an investigator from

comparing exposure damages to another area. As a result, material considerations may

complicate things considerably. For example, suppose that investigators observe significant fire

effects to a stack of lightweight wicker chairs in one area, and comparatively minor fire effects to

a solid oak desk in another area. When interpreting the exposure conditions that may have

caused the damages in each area, the investigator must somehow account for the fact that the

wicker chairs are more susceptible to damage. Accounting for such differences is likely to be

difficult, and if done improperly, can lead to erroneous conclusions.

In order to minimize discrepancies due to material considerations, it is recommended that

investigators do their best to compare damages to like materials in different areas. For example,

a furniture set where a sofa and loveseat are made of the same materials may allow for credible

damage comparisons of the different areas where they are located. Wall, floor and ceiling

coverings are in many cases uniform throughout a space, and may also allow for credible damage

comparisons. As the saying goes, investigators want to avoid comparing apples to oranges. The origin matrix analysis relies largely on comparing differential damages from one area to

another, and investigators must make efforts to utilize like materials in their comparisons so that

meaningful hypotheses may be developed and credible conclusions reached.

Effects of Vent Flow Velocity and Momentum

Although the previously presented quadrant theme is conceptually useful, consideration must be

given to the fact that fresh air inflows at vents during post-flashover conditions may have

significant velocities, and therefore momentum, associated with them. Those significant

velocities can extend fire conditions further into the compartment, and therefore produce

damages, some distance beyond what one might consider as proximate to the vent. Experimental results for residential-sized bedroom compartments have demonstrated that

damages generated during post-flashover conditions can extend beyond Quadrant 3 and into

Quadrant 2.viii,ix

It can be anticipated that the magnitude of fresh air inflows at vents during post-flashover

conditions are likely to be greatest at the horizontal center of the vent, where the effects of

friction losses due to the vent sides are at their minimum. In addition, one might assume the

direction of such flow is likely to be closely perpendicular to the plane of the vent. Reference

Figure 9. In the case of the compartment with an open doorway, those flows are most heavily

directed towards the wall opposite the door, or the C-Side wall in Quadrant 2.



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Recall that during post-flashover conditions two components of the fire triangle are generally

available throughout the entire space: heat and fuel gases. The only remaining component of the

fire triangle needed is oxygen (in fresh air). As the fresh air inflow from the vent enters the

compartment, that fresh air will begin to mix with the heat and fuel gases already present. When

mixed in sufficient quantities, flaming fire conditions will occur. Momentum of the fresh air

flow continues to transport these flaming conditions towards the wall in Quadrant 2, while at the

same time the additional heat produced from the flames will provide buoyancy to those flows.

Any solid object that obstructs those flows will be the recipient of very intense heat fluxes.

Rarely are solid objects placed directly in front of doorway vents, and as a result, it is an item or

items located within the flow further inside the compartment that becomes the first damage

indicator. In a smaller compartment, such as a typical residential sized bedroom, it is the wall

opposite the door in Quadrant 2, or any furnishing placed along that wall, that receives the brunt

of post-flashover fire damages.

The effects of vent flow velocity and momentum may require an alternative to the 4-quadrant

themed approach. In the case of smaller compartments more typical of residential bedrooms,

analytical divisions dissecting the compartment in half as in Figure 10 may be a better approach.

An analytical division of the compartment into three areas of consideration as in Figure 11 may

also be useful. The key is to recognize that post-flashover fire conditions may result in heavy

damages observed in both Quadrants 2 and 3, and therefore, it may be a more useful analytical

paradigm to combine these quadrants into a single arbitrary section, such as in Figures 10 or 11.

Tables 2 and 3 complete the matrix analysis for these alternative analytical divisions.



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Single v. Multiple Areas of Origin

The analyses presented so far have relied upon the assumption of a fire starting in a single area of

origin. Multiple areas of origin can also be considered, and their main point of difference

involves the accumulation of pre-flashover fire damages in multiple quadrants as opposed to just

one. Once the transition of flashover occurs, fire conditions will still migrate in the same fashion

towards ventilation openings providing fresh air, regardless of how many fires are present

initially and regardless of where those fires were originally located.



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Partial Extinguishment

In the case of larger fires, partial extinguishment is of significant concern. Suppression of a fire

in one area may substantively halt continued accumulation of damage in that area. If other areas

remain unsuppressed, fire conditions may cause continued accumulation of damages in those

areas, which are completely independent of origin and completely independent of post-flashover

ventilation generated damages. Such damages are simply a result of the continued duration of

fire/heat exposure due to a lack of or ineffective suppression activity.

Even after the fire service considers an incident to be under control, there are frequently areas

within the debris that continue to smolder and/or flame. It is not uncommon for large fire scenes

to experience smoldering conditions and small spot fires for days, which may at times even result

in larger rekindles. It must be remembered that such smoldering conditions and rekindles

continue to impart damages to materials, and that damage is of no relevance to origin or

ventilation conditions.

Investigators must obtain information about suppression activity and possible continued

exposures due to smoldering conditions and/or rekindles. Such circumstances can then be



18

included in the matrix analysis by adding another time element beyond long duration post-flashover, such as post-extinguishment, to the matrix.

Dynamic Ventilation Conditions

In many real world fire scenarios, ventilation conditions are not static throughout the life of the

incident. Fire conditions may cause previously closed vent openings to fail. The opposite may

also be true, and previously open vents may close, such as in the case where air flows cause a

door to shut. It is not uncommon for early observers of a fire to open doors or break windows in

an effort to gain entry or thinking they are providing a potential way of escape for occupants.

Ventilation tactics are almost always employed by the fire service. Dynamic ventilation

conditions may be considered in the matrix analysis by simply accounting for additional

accumulated damages in areas around a vent after it has been deemed to become open. It may be helpful to add another time element in the matrix to more clearly account for accumulation of

damages before, and then after, a vent opens.

Some ventilation openings may not supply any fresh air to a compartment. It is not uncommon

for elevated openings, such as high windows and ceiling vents, to act as an exhaust without

allowing for any inflow of fresh air. External conditions such as wind may also affect whether or

not a ventilation opening provides fresh air, acts as an exhaust, or both. If it is suspected a vent

might not supply fresh air to the fire compartment, the matrix analysis can be applied both ways

to cognitively consider the different damages anticipated for such a variation.

CONCLUSIONS

The origin matrix analysis offers a systematic means to effectively apply fire dynamics

principles to the analysis and interpretation of fire scene damages. Since the general concepts

remain the same, the origin matrix analysis may also be applied to more complex scenarios and

geometries, including fires involving multiple compartments and/or levels.

Several concepts derived from the origin matrix analysis and are worth reiterating:

1. Irrespective of where a fire starts, post-flashover fire conditions will produce ventilation induced exposures and corresponding damages in areas associated with fresh air supply

vents such as doors and windows.

2. The damages generated during post-flashover fire conditions can be difficult to interpret because they do not offer insight as to where a fire originated. Such damages are only

associated with, and result from, the ventilation openings that supplied fresh air during

the course of a fire.

3. Pre-flashover damages indicative of origin can and often do survive post-flashover exposures. In particular, origin patterns located away from fresh air supplying vents

experience a comparatively reduced continued exposure during post-flashover conditions.

Such a reduced exposure, may allow for pre-flashover damage patterns to persist for



19

some time, although there is a limit. Continued post-flashover heat exposures are likely

to eventually destroy pre-flashover patterns related to origin.

4. Investigators must be able to identify and then segregate fire scene damages that may be attributed to pre-flashover vs. post-flashover fire conditions. It is those damages which

cannot be attributed to post-flashover fire conditions that may provide the most

substantive clues for initial development of hypotheses regarding origin.

The origin matrix analysis offers a systematic thought process to more effectively understand

and interpret damages observed at a fire scene. Although only qualitative in nature, the origin

matrix analysis is extraordinarily useful in the investigation of fire incidents. With practice, this

type of analysis becomes second nature, and may be applied without the need for an investigator

to physically diagram each hypothetical scenario.

It should be recognized that the origin matrix analysis does not by itself guarantee accuracy in

origin determination. It is simply another tool for analysis and should not be applied in isolation

from other aspects of an investigation. The science of fire investigation requires consideration of

a much larger system of evidence and information beyond fire damage alone, to include facts,

circumstances, and data from other sources like witnesses.x,xi

As with any analytical tool, the

origin matrix analysis is best used in conjunction with other fire investigation approaches and

analyses.

i NFPA 921, 2011, Guide for Fire and Explosion Investigations, 2011 Edition, NFPA, Quincy, MA.

ii Fire Protection Handbook, 20th Edition National Fire Protection Association, 2008 (Section 2, Chapter 4,

Dynamics of Compartment Fire Growth). iii

Dehaan, John; Icove, David, Kirks Fire Investigation, Seventh Edition, Pearson Education Inc., Upper Saddle River, New Jersey, 2012. iv Fleischmann, Charles. Backdraft Phenomena. NIST-GCR-94-646, November 1993.

v Zhixin Hu, Yunyong Utiskul, James G. Quintiere, and Arnaud Trouve. A Comparison between Observed and

Simulated Flame Structures in Poorly Ventilated Compartment Fires. Fire Safety Sciene Proceedings of the Eighth International Symposium, 2005. vi Yunyong Utiskul, James G. Quintiere, Ali S. Rangwala, Brian A. Ringwelski, Kaoru Wakatsuki, and Tomohiro

Naruse. Compartment Fire Phenomena Under Limited Ventilation. Fire Safety Journal, Volume 40, Issue 4, June 2005. vii

Cox, Andrew, Damage Assessment and Origin Determination, Fire and Arson Investigator, July 2001 (Volume 51, Number 4). viii

Carman, Steven, Improving theUnderstanding of Post-FlashoverFire Behavior, Proceedings of the 3rd International Symposium on Fire Investigations Science and Technology (ISFI). Cincinatti OH, 2008. ix

Carman, Steven, Progressive Burn Pattern Development in Post-Flashover Fires, Fire and Materials Conference Proceedings, San Francisco, CA. 2009. x Avato, Steven; Cox, Andrew, Science and Circumstance, Fire and Arson Investigator, April 2009.

xi Geiman, Justin; Lord, James. Systematic Analysis of Witness Statements for Fire Investigation. Fire

Technology, 2011.

origin matrix analysis paper

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