Archive for the ‘Random Thoughts’ Category

Continuing examination of NIST’s research on Firefighting Tactics Under Wind Driven Conditions, this post looks at the results of experiments involving use of wind control devices and external water application.

In my last post, I posed several questions about wind control devices to “prime the pump” regarding wind driven fires and potential applications for use of wind control devices.

Questions

Give some thought to how wind can influence compartment fire behavior and how a wind control device might mitigate that influence.

• How would a strong wind applied to an opening (such as the bedroom window in the NIST tests) influence fire behavior in the compartment of origin and other compartments in the structure?
• How would deployment of a wind control device influence fire behavior?
• While the wind control device illustrated in Figure 5 was developed for use in high-rise buildings, what applications can you envision in a low-rise structure?
• What other anti-ventilation tactics could be used to deal with wind driven fires in the low-rise environment?

Answers: Thornton’s Rule indicates that the amount of oxygen required per unit of energy released from many common hydrocarbons and hydrocarbon derivatives is fairly constant. Each kilogram of oxygen used in the combustion of common organic materials results in release of 13.1 MJ of energy. Fully developed compartment fires are generally ventilation controlled (potential heat release rate (HRR) based on fuel load exceeds the actual HRR given the atmospheric oxygen available through existing ventilation openings). Application of wind can dramatically increase heat release rate by increasing the mass of oxygen available for combustion. In addition to increasing HRR, wind can significantly increase the velocity of hot fire gases and flames (and resulting convective and radiant heat transfer) between the inlet and outlet openings.

Deployment of a wind control device to cover an inlet opening (window or door), limits oxygen available for combustion to the air already in the structure and normal building leakage. In addition, blocking the wind will also reduce gas and flame velocity between the inlet and outlet.

While wind driven fires are problematic in high-rise buildings, the same problem can be encountered in low-rise structures and wind control devices may prove useful in some circumstances. However, exterior attack (discussed later in this post) is more feasible than in a high-rise building and other tactics such as door control may also prove essential in managing hazards presented by wind.

Test Conditions

As outlined in my earlier post, Wind Driven Fires, NIST conducted a number of different wind driven tests using the same multi-compartment structure. Experiment 3 involved evaluation of anti-ventilation tactics using a large wind control device placed over the bedroom window. Wind conditions of 6.7 m/s to 8.9 m/s (15 mph-20 mph) were maintained throughout the test.

As with the baseline test, two ventilation openings were provided. A ceiling vent in the Northwest Corridor and a window (fitted with glass) in the bedroom (compartment of origin). During the test the window failed due to fire effects and was subsequently fully cleared by the researchers to provide a full window opening for ventilation.

Figure 1. Isometric Illustration of the Test Structure

Note: The location of fuel packages in the bedroom and living room is shown on the Floor Plan provided in Wind Driven Fires post.

Experiment 3 Wind Driven Fire

This experiment was one of several that investigated wind driven fire behavior and the effectiveness of a wind control device deployed over the bedroom window to limit inward airflow. The fire was ignited in the bedroom and allowed to develop from incipient to fully developed stage in the bedroom.

The fire progressed in a similar manner as observed in the baseline test described in my earlier post NIST Wind Driven Fire Experiments: Establishing a Baseline. In this experiment the fire involving the initial fuel packages (bed and waste container) and visible smoke layer developed slightly more slowly. However, the bedroom window failed more completely and 11 seconds earlier than in the baseline test.

Almost immediately after the window failed, turbulent flaming combustion filled the bedroom and hot gases completely filled the door between the living room and corridor and were impinging on the opposite wall. At 222 seconds (15 seconds after the window was completely cleared) flames were visible in the corridor and the hollow core wood door in the target room was failing with flames breaching the top corners of the door and a smoke layer developing in the target room. While most of the hot gases and flames were driven through the interior (towards the ceiling vent in the corridor), flames continued to flow out the top of the window opening (against the wind).

At 266 seconds conditions had further deteriorated in all compartments with no visibility in the corridor and increased deterioration of the door to the target room. At this point the air track at the window was completely inward (no flames outside the window).

The wind control device was deployed at 270 seconds. Unfortunately soot on the video cameras lenses precluded a good view of interior conditions. However, video from the thermal imaging camera no longer showed any flow of hot gases into the corridor (only high temperature).

At 330 seconds, shortly after removal of the wind control device flames were visible in the bedroom and the fire quickly progressed to a fully developed state. At 360 seconds, flames were pulsing out the window opening (against the wind).

The experiment was ended at 380 seconds and the fire was extinguished.

Heat Release Rate

As with the baseline test NIST researchers recorded heat release rate data during Experiment 3. As discussed earlier in this post, application of wind increased the amount of oxygen available for combustion and resulting heat release rate in comparison to the baseline test.

Figure 2. Heat Release Rates in Experiments 1 (Baseline) and 3 (Wind Driven)

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

Questions: Examine the heat release rate curves in Figure 2 and answer the following questions:

• What effect did deployment of the wind control device have on HRR and why did this change occur so quickly?
• How did HRR change when the wind control device was removed and why was this change different from when the window was vented?
• What factors might influence the extent to which HRR changes when ventilation is increased to a compartment fire in a ventilation controlled burning regime?

Wind Control Device Research and Application

NIST has continued research into the practical application of wind control devices with tests in Chicago and New York involving large apartment buildings and realistic fuel loading. For additional information on these tests and video of wind control device deployment, visit the NIST Wind Driven Fires webpage.

Fire Control Experiments

NIST researchers also conducted a series of experiments in the same structure examining the impact of various fire control tactics. These included application of water using solid stream and combination nozzles (using a 30^o fog pattern with continuous application). In addition, they examined the influence of coordinated deployment of a wind control device and low flow water application of water fog). In each of these tests, water was applied from the exterior of the structure through the bedroom window.

Water Fog Application: Experiment 6 involved application of water using a hoseline equipped with a combination nozzle at 90 psi (621 kPa) nozzle pressure, providing a flow rate of 80 gpm (303 lpm). The fog stream was initially applied across the window (no discharge into the bedroom). This had a limited effect on conditions on the interior. When applied into the room, the 30^o fog pattern was positioned to almost completely fill the window. This action resulted in a brief increase (approximately 4 MW) and then a dramatic reduction in HRR.

Solid Stream Application: Experiments 7 and 8 involved application of water using a hoseline equipped with a 15/16″ smooth bore nozzle at 50 psi (345 kPa) nozzle pressure, providing a flow rate of 160 gpm (606 lpm).� The solid stream was initially directed at the ceiling and then in a sweeping motion across the ceiling. In Experiment 8, the stream was then directed at burning contents in the compartment. Application of the solid stream had a pronounced effect, dramatically reducing heat release rate in both experiments.

Conditions varied considerably between these three tests (Experiments 6-8). This makes direct comparison of the results somewhat difficult. However, several conclusions can be drawn from the data:

• Exterior application of water can be effective in reducing HRR in wind driven fires.
• Both solid stream and fog application can be effective in reducing HRR under these conditions.
• Continuous application of water fog positioned to nearly fill the inlet opening develops substantial air flow which can increase HRR (this works similar to the process of hydraulic ventilation, but in reverse).
• A high flow solid stream may be more effective (but not necessarily more efficient) than a lower flow fog pattern if a direct attack on burning contents can be made.

Coordinated WCD Deployment and Water Application: Experiments 4 and 5 involved evaluations of anti-ventilation and water application using a small wind control device and 30 gpm (113.6 lpm) spray nozzle from under the wind control device. The effectiveness of the wind control device was similar to other anti-ventilation tests and application of low flow water fog resulted in continued decrease in HRR throughout the experiment.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Madrzykowski, D. & Kerber, S. (2009). Fire Fighting Tactics Under Wind Driven Conditions. Retrieved (in four parts) February 28, 2009 from http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part1.pdf; http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part2.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part3.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part4.pdf.

My last post asked a number of questions focused on results of baseline compartment fire tests conducted by the National Institute for Standards and Technology (NIST) as part of a research project on� Firefighting Tactics Under Wind Driven Conditions.� This post looks at the answers to these questions and continues with an examination of NIST’s experiments in the application of wind control devices for anti-ventilation.

Questions

Generally being practically focused people, firefighters do not generally dig into research reports. However, the information on the baseline test conducted by NIST raised several interesting questions that have direct impact on safe and effective firefighting operations. First consider possible answers to the questions and then why this information is so important (the “So what?”!).

Figure 1. Heat Release Rate Comparison

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

Heat Release Rate (HRR) Questions: Examine the heat release rate curves in Figure 1 and answer the following questions:

• Why are these two HRR curves different shapes?
• In each of these two cases, what might have influenced the rate of change (increase or decrease in HRR) and peak HRR?
• What observations can you make about conditions inside the test structure and heat release rate (in particular, compare the HRR and conditions at approximately 250 and 350 seconds)?

Answers: The HRR test for the bed and waste container was conducted under fuel controlled conditions (oxygen supply was not restricted). The higher HRR in the compartment fire experiment results from increased fuel load (e.g., additional furniture, carpet). After reaching its peak, HRR in the compartment fire drops off slowly as the fire becomes ventilation controlled and the fire continues in a relatively steady state of combustion (limited by the air supplied through the lower portion of the bedroom window)

The rate of change in heat release rate under fuel controlled conditions is dependent on the characteristics and configuration of the fuel. �However, in the case of the compartment fire test, the rate of change is also impacted by limited ventilation. As illustrated in the compartment fire curve, the fire quickly became ventilation controlled and HRR rose slowly until the window failed and was fully cleared by researchers.

At 250 seconds (when the window was vented) HRR rose extremely rapidly as the fire in the bedroom rapidly transitioned from the growth through flashover to fully developed stage. At 350 seconds the fire had again become ventilation controlled and was burning in a relatively steady state limited by the available oxygen.

The fully developed fire in the bedroom also became ventilation controlled due to limited ventilation openings, resulting in HRR leveling off with relatively steady state combustion based on the available oxygen.

Figure 2. Bedroom Temperature

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

Temperature Questions: Examine the temperature curves in Figure 2 and answer the following questions:

• What can you determine from the temperature curves from ignition until approximately 250 seconds?
• How does temperature change at approximately 250 seconds? Why did this change occur and how does this relate to the data presented in the HRR curve for Experiment 1 (Figure 1)?
• What happens to the temperature at the upper, mid, and lower levels after around 275 seconds? Why does this happen?

Answers: Temperature at the upper levels of the compartment increased much more quickly than at the lower level and conditions in the compartment remained thermally stratified until the ceiling temperature exceeded 600^o C. At approximately 250 seconds, the compartment flashed over resulting in a rapid increase in temperature at mid and lower levels. This change correlates with the rapid increase in HRR occurring at approximately 250 seconds in Figure 1. Turbulent, ventilation controlled combustion resulted in a loss of thermal layering with temperatures in excess of 600^o C from ceiling to floor. At around 275 seconds.

Figure 3. Total Hydrocarbons at the Upper Level

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

Total Hydrocarbons (THC) Questions: Examine the THC curves in Figure 3 and answer the following questions:

• Why did the THC concentration in the living room rise to a higher level than in the bedroom?
• Why didn’t the gas phase fuel in the living room burn?
• How did the concentration of THC in the bedroom reach approximately 4%? Why wasn’t this gas phase fuel consumed by the fire?

Answers: Oxygen entering the compartments through the window was being used by combustion occurring in the bedroom. Low oxygen concentration limited combustion in the living room and allowed accumulation of a higher concentration of unburned fuel. While the oxygen concentration in the bedroom was higher, the fire was still ventilation controlled and not all of the gas phase fuel was able to burn inside this compartment.

So What?

What do the answers to the preceding questions mean to a company crawling down a dark, smoky hallway with a hoseline or making a ventilation opening at a window or on the roof?

Emergency incidents do not generally occur in buildings equipped with thermocouples, heat flux gages, gas monitoring equipment, and pre-placed video and thermal imaging cameras. Understanding the likely sequence of fire development and influencing factors is critical to not being surprised by fire behavior phenomena. These tests clearly illustrated how burning regime (fuel or ventilation controlled) impacts fire development and how changes in ventilation can influence fire behavior. The total hydrocarbon concentration and ventilation controlled combustion in the living room would present a significant threat in an emergency incident. How might conditions change if the fire in the bedroom was controlled and oxygen concentration began to increase? Ignition of the gas phase fuel in this compartment could present a significant threat (see Fire Gas Ignitions) or even prove deadly (future posts will examine the deaths of a captain and engineer in a fire gas ignition in California).

Anti-Ventilation

For years firefighters throughout the United States have been taught that ventilation is “the planned and systematic removal of heat, smoke, and fire gases, and their replacement with fresh air”. This is not entirely true! Ventilation is simply the exchange of the atmosphere inside a compartment or building with that which is outside. This process goes on all the time. What we have thought of as ventilation, is actually tactical ventilation. This term was coined a number of years ago by my friend and colleague Paul Grimwood (London Fire Brigade, retired). It is essential to recognize that there are two sides to the ventilation equation, one is removal of the hot smoke and fire gases and the other is introduction of air. Increased ventilation can improve tenability of the interior environment, but under ventilation controlled conditions will result in increased heat release rate.

Another tactic change the ventilation profile and influence fire behavior and conditions inside the building is to confine the smoke and fire gases and limit introduction of air (oxygen) to the fire. Firefighters in the United States often think of this as confinement, but I prefer the English translation of the Swedish tactic, anti-ventilation. This is the planned and systematic confinement of heat, smoke, and fire gases and exclusion of fresh air. The concept of anti-ventilation is easily demonstrated by limiting the air inlet during a doll’s house demonstration (see Figure 4). Closing the inlet dramatically reduces heat release rate and if sustained, can result in extinguishment.

Figure 4. Anti-Ventilation in a Doll’s House Demonstration

For a more detailed discussion of the relationship between ventilation and heat release rate see my earlier post on Fuel and Ventilation.

Air Track and Influence of Wind

Air track (movement of smoke and air under fire conditions) is influenced by differences in density between hot smoke and cooler air and the location of ventilation openings. However, wind is an often unrecognized influence on compartment fire behavior. Wind direction and speed can influence movement of smoke, but more importantly it can have a dramatic influence on introduction of air to the fire.

While the comparison is not perfect, the effects of wind on a compartment fire can be similar to placing a supercharger on an internal combustion engine (see Figure 5). Both dramatically increase power (energy released per unit of time).

Figure 5. Influence of Wind

NIST Wind Control Device Tests

As discussed in Wind Driven Fires, the effects of wind on compartment fire behavior can present a significant threat to firefighters and has resulted in a substantive number of line-of-duty deaths. In their investigation of potential tactical options for dealing with wind driven fires, NIST researchers examined the use of wind control devices (WCD) to limit introduction of air through building openings (specifically windows in the fire compartment in a high-rise building) as illustrated in Figure 6.

Figure 6. Small Wind Control Device

Note: Photo from Firefighting Tactics Under Wind Driven Conditions.

Questions

Give some thought to how wind can influence compartment fire behavior and how a wind control device might mitigate that influence.

• How would a strong wind applied to an opening (such as the bedroom window in the NIST tests) influence fire behavior in the compartment of origin and other compartments in the structure?
• How would a wind control device deployed as illustrated in Figure 5 influence fire behavior?
• While the wind control device illustrated in Figure 5 was developed for use in high-rise buildings, what applications can you envision in a low-rise structure?
• What other anti-ventilation tactics could be used to deal with wind driven fires in the low-rise environment?

The Story Continues…

My next post will address the answers to these questions (please feel free to post your thoughts) and examine the results of NIST’s tests on the use of wind control devices for anti-ventilation.

References

Madrzykowski, D. & Kerber, S. (2009). Fire Fighting Tactics Under Wind Driven Conditions. Retrieved (in four parts) February 28, 2009 from http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part1.pdf; http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part2.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part3.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part4.pdf.

Ed Hartin, MS, EFO, MIFireE, CFO

My last post introduced a National Institute for Standards and Technology research project examining firefighting tactics for wind driven structure fires (particularly those occurring in high-rise buildings). The report on this research Firefighting Tactics Under Wind Driven Conditions contains a tremendous amount of information on this series of experiments including heat release rate, heat flux, pressure, velocity, and gas concentrations during each of the tests along with time sequenced still images (video and infrared video capture).

This post will examine the initial test used to establish baseline conditions for evaluation of wind driven fire conditions and tactics. Readers are encouraged to download a copy of the report and dig a bit deeper!

Test Conditions

In Wind Driven Fires, I provided an overview of the multi-compartment test structure and fuel load used for this series of experiments. To quickly review, the test structure was comprised of three compartments; Bedroom, Target Room (used to assess tenability in a compartment adjacent to the ventilation flow), and Living Room, along with an interconnecting hallway (between the Bedroom and Living Room) and exterior corridor. Fuel load consisted of typical residential furnishings in the bedroom and living room along with carpet and carpet pad throughout the structure. The target room (used to assess tenability in a potential place of refuge for occupants or firefighters) did not contain any furnishings. Different types of doors (metal, hollow core wood, etc.) were used in the tests to evaluate performance under realistic fire conditions.

Two ventilation openings were provided, a ceiling vent in the Northwest Corridor (providing a flow path from the involved compartment(s) into the corridor) and a window (fitted with glass) in the compartment of origin. During the fire tests, the window failed due to differential heating (of the inner and outer surface of the glass) and was subsequently removed by researchers to provide the full window opening for ventilation.

Figure 1. Isometric Illustration of the Test Structure

Note: The location of fuel packages in the bedroom and living room is shown on the Floor Plan provided in Wind Driven Fires post.

The structure was constructed under a large oxygen consumption calorimetry hood which allowed measurement of heat release rate (once products of combustion began to exit the ceiling vent). In addition, thermocouples, heat flux gages, pressure transducers, and bidirectional probes were used to measure temperature, heat flux, pressure, and gas flow within and out of the structure. Gas sampling probes were located at upper and lower levels, (0.61 m (2′) and 1.83 m (6′) below the ceiling respectively) in the bedroom and living room. Researchers measured oxygen, carbon dioxide, carbon monoxide, and total hydrocarbon concentration during each test.

Experiment 1 Baseline Test

This experiment was different than the others in the series as no external wind was applied to the structure. The fire was ignited in the bedroom and allowed to develop from incipient to fully developed stage in the bedroom.

After 60 seconds the fire had extended from the trash can (first fuel package ignited) to the bed and chair. At this point a visible smoke layer had developed in the bedroom.

120 seconds after ignition, the smoke layer had reached a thickness of 1.2 m (4′) in the bedroom, hallway, and living room. At this point, smoke had just started to enter the corridor. Conditions in the target room were tenable with little smoke infiltration.

At 180 seconds after ignition, the smoke layer was 1.5 m (5′) deep and had extended from the living room into the corridor. Flames from the bed and chair had reached the ceiling. Hot smoke and clear air was well stratified with a distinct boundary between upper and lower layers. Smoke had begun to infiltrate at the top of the door to the target room.

240 seconds after ignition the window started to fail due to flame impingement and the smoke layer extended from ceiling to floor in the bedroom. The smoke layer in the living room had reached a depth of 2.1 m (7′) from the ceiling. Temperature in the corridor remained well stratified.

248 seconds after ignition the researchers cleared the remaining glass from the window to provide a full opening for ventilation. As the glass was removed, the size of the fire in the bedroom and flames exiting the window increased. A thin smoke layer had developed at ceiling level in the target room.

At 300 seconds, flames had begun to burn through the wood, hollow core door to the target room and flaming combustion is also visible in the hallway at the bottom of this door. Flames continued to exit the top 2/3 of the window.

360 seconds into the test, the fire in the bedroom reached steady state (post-flashover), ventilation controlled combustion. The door to the target room has burned through with a dramatic increase in temperature as the room fills with smoke.

Suppression using fixed sprinklers and a hoseline began at 525 seconds.

Fire development during this experiment was not particularly remarkable with conditions that could typically be expected in a residential occupancy. So, what can we learn from this test?

Heat Release Rate

NIST researchers examined the heat release rate of individual fuel packages and combinations of fuel packages prior to the compartment fire tests. These tests conducted in an oxygen consumption calorimeter were performed with the fire in a fuel controlled burning regime. Figure 2 illustrates the heat release rate from the combination of waste container and bed fuel packages and the heat release rate generated during Experiment 1 (in which the initial fuel packages ignited were the waste container and bed located inside the bedroom.

Figure 2. Heat Release Rate Comparison

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

Questions: Examine the heat release rate curves in Figure 2 and answer the following questions:

• Why are these two HRR curves different shapes?
• In each of these two cases, what might have influenced the rate of change (increase or decrease in HRR) and peak HRR?
• What observations can you make about conditions inside the test structure and heat release rate (in particular, compare the HRR and conditions at approximately 250 and 350 seconds)?

Temperature

During the experiments temperature was measured in each of the compartments at multiple levels. Figure 3 illustrates temperature conditions in the bedroom at 0.03 m (1″), 1.22 m (4′) and 2.13 m (7′) down from the ceiling during Experiment 1.

Figure 3. Bedroom Temperature

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions. Position.

Questions: Examine the temperature curves in Figure 3 and answer the following questions:

• What can you determine from the temperature curves from ignition until approximately 250 seconds?
• How does temperature change at approximately 250 seconds? Why did this change occur and how does this relate to the data presented in the HRR curve for Experiment 1 (Figure 2)?
• What happens to the temperature at the upper, mid, and lower levels after around 275 seconds? Why does this happen?

Total Hydrocarbons

In addition to HRR and temperature, researchers measured gas concentrations inside the compartments at the upper and lower levels. Figure 4 shows the concentration (in % volume) of total hydrocarbons in the bedroom and living room. Concentration of total hydrocarbons is a measure of gas phase fuel (pyrolysis products) in the upper layer.

Figure 4. Total Hydrocarbons at the Upper Level

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions. Position.

Questions: Examine the THC curves in Figure 4 and answer the following questions:

• Why did the THC concentration in the living room rise to a higher level than in the bedroom?
• Why didn’t the gas phase fuel in the living room burn?
• How did the concentration of THC in the bedroom reach approximately 4%? Why wasn’t this gas phase fuel consumed by the fire?

The Story Continues…

My next post will address the answers to these questions (please feel free to post your thoughts) and provide an overview of NIST’s initial tests on the use of wind control devices for anti-ventilation.

Ed Hartin, MS, EFO, MIFireE, CFO

Weather, Topography, and Fuel

In S-190 Introduction to Wildland Fire Behavior, firefighters learn that weather, topography, and fuel and the principal factors influencing fire behavior in the wildland environment. How might this important concept apply when dealing with fires in the built environment? Factors influencing compartment fire behavior have a strong parallel to those in the wildland environment. Principal influences on compartment fire behavior include fuel, configuration (of the compartment and building), and ventilation.

Wind Driven Compartment Fires

As buildings are designed to minimize the influence of weather on their contents and occupants, weather is not generally considered a major factor in compartment fires. However, this is not always the case. As wildland firefighters recognize, wind can be a major influence on fire behavior and strong winds present a significant threat of extreme fire behavior.

Under fire conditions, unplanned ventilation involves all changes influencing exhaust of smoke, air intake, and movement of smoke within the building that are not part of the incident action plan. These changes may result from the actions of exiting building occupants, fire effects on the building (e.g., failure of window glass), or a wide range of other factors.

Changes in ventilation can increase fire growth and hot smoke throughout the building. Failure of a window in the fire compartment in the presence of wind conditions can result in a significant and rapid increase in heat release. If this is combined with open doors to corridors, unprotected stairwells, and other compartments, wind driven fire conditions have frequently resulted in firefighter injuries and fatalities (see Additional Reading).

NIST Research on Wind Driven Fires

From November 2007 to January 2008, the National Institute of Standards and Technology conducted a series of experiments examining firefighting tactics dealing with wind driven compartment fires. The primary focus of this research was on the dynamics of fire growth and intensity and the influence of ventilation and fire control strategies under wind driven fire conditions. The results of these experiments are presented in Fire Fighting Tactics Under Wind Driven Conditions, published by The Fire Protection Research Foundation.

Tests conducted at NIST’s Large Fire Test Facility (see Figure 1) included establishment of baseline heat release data for the fuels (bed, chairs, sofa, etc), full scale fire tests under varied conditions (e.g., no wind, wind), and experiments involving control of the inlet opening and varied methods of external water application.

Figure 1. NIST Large Fire Test Facility

Note: Photo adapted from Firefighting Tactics Under Wind Driven Conditions.

The objectives of this study were:

• To understand the impact of wind on a structure fire fueled with residential furnishings in terms of temperature, heat flux, heat release rate, and gas concentrations
• To quantify the impact of several novel firefighting tactics on a wind driven structure fire
• Improve firefighter safety

After conducting a series of tests to determine the heat release rate characteristics of the fuels to be used for the full scale tests, NIST conducted eight full scale experiments to examine the impact of wind on fire spread through the multi-room test structure (see Figure 2) and examine the influence of anti-ventilation using wind control devices and the impact of external water application.

Multi-Room Test Structure

All tests were conducted under the 9 m (30′) x 12 m (40′) oxygen consumption calorimetry hood at the NIST Large Fire Test Facility. The test structure was comprised of three compartments; Bedroom, Target Room (used to assess tenability in a compartment adjacent to the ventilation flow), and Living Room, along with an interconnecting hallway and exterior hallways. A large mechanical fan was positioned 7.9 m (26′) away from the window in the bedroom of the test structure (see Figure 2) to provide consistent wind conditions for the experiments.

Figure 2. Configuration of the Multi-Room Test Structure

Note: Adapted from Firefighting Tactics Under Wind Driven Conditions.

The structure was framed with steel studs and wood truss joist I-beams (TJIs) used to support the ceiling. The interior of the compartments were lined with three layers of 13 mm (1/2″) gypsum board. Multiple layers of gypsum board were used to provide the durability required for repetitive experiments (the inner layer was replaced and repairs made to other layers as needed between experiments).

Used furnishings were purchased from a hotel liquidator to obtain 10 sets of similar furniture to use in the heat release rate and full-scale, multi-compartment experiments. Fuel used in the tests included furniture, nylon carpet, and polyurethane carpet padding (the position major furniture items are illustrated in Figures 2 and 3).� Fuel load was 348.69 kg (768.73 lbs) in the bedroom, 21.5 kg (47.40 lbs) in the hallway, and 217.6 kg (479.73 lbs) in the living room (no contents were placed in the target room).

Figure 3. Bedroom and Living Room Fuel Load

Note: Photos adapted from Firefighting Tactics Under Wind Driven Conditions.

NIST researchers conducted a series of eight full-scale, multi-compartment fire tests. In each case, a fire was started in the Bedroom using a plastic trash container placed next to the bed (see Figure 3).

Figure 3. Placement of the Trash Container

Note: Photos adapted from Firefighting Tactics Under Wind Driven Conditions.

Experiments

The eight tests provided the opportunity to study the dynamics of wind driven compartment fires and several different approaches to limiting the influence of air intake and controlling the fire.

Experiment 1: This test was performed to establish baseline conditions with no wind

Experiment 2: Evaluation of anti-ventilation using a large wind control device placed over the window

Experiment 3: Evaluation of anti-ventilation using a large wind control device placed over the window (second test with a longer pre-burn before deployment of the wind control device).

Experiment 4: Evaluation of anti-ventilation and water application using a small wind control device and 30 gpm (113.6 lpm) spray nozzle from under the wind control device.

Experiment 5: Evaluation of anti-ventilation and water application using a small wind control device and 30 gpm (113.6 lpm) spray nozzle from under the wind control device (second test with a lower wind speed)

Experiment 6: No wind control device, application of water using a hoseline equipped with a combination nozzle at 90 psi (621 kPa) nozzle pressure, providing a flow rate of 80 gpm (303 lpm).

Experiment 7: No wind control device, application of water using a hoseline equipped with a 15/16″ smooth bore nozzle at 50 psi (345 kPa) nozzle pressure, providing a flow rate of 160 gpm (606 lpm) (test was conducted with the living room corridor door closed).

Experiment 8: No wind control device, application of water using a hoseline equipped with a 15/16″ smooth bore nozzle at 50 psi (345 kPa) nozzle pressure, providing a flow rate of 160 gpm (606 lpm) (second test with the living room corridor door open).

Note: The nozzles for these tests (100 gpm at 100 psi combination nozzle and 15/16″ solid stream nozzle were selected as to be representative of those used by the fire service in the United States (personal correspondence, S. Kerber, February 28, 2009). However, it is important to note that in comparing the results, that the combination nozzle was under pressurized (80 psi, rather than 100 psi) resulting in large droplet size. In addition, the 100 gpm flow rate was 50% of that applied through the solid stream nozzle and is likely considerably lower than the flow capability of combination nozzles typically used with 1-3/4″ (45 mm) hose.

Important Findings

The first experiment was conducted without any external wind or tactical intervention. The baseline data generated during this test was critical to evaluating the outcome of subsequent experiments and demonstrated a number of concepts that are critical to firefighter safety:

Smoke is fuel. A ventilation limited (fuel rich) condition had developed prior to the failure of the window. Oxygen depleted combustion products containing carbon dioxide, carbon monoxide and unburned hydrocarbons, filled the rooms of the structure. Once the window failed, the fresh air provided the oxygen needed to sustain the transition through flashover, which caused a significant increase in heat release rate.

Venting does not always equal cooling. In this experiment, post ventilation temperatures and heat fluxes all increased, due to the ventilation induced flashover.

As discussed in early posts, Fuel & Ventilation and Myth of the Self Vented Fire understanding the relationship between oxygen and heat release rate, the hazards presented by ventilation controlled fires, and the influence of ventilation on fire development is critical to safe and effective fireground operations.

Fire induced flows. Velocities within the structure exceeded 5 m/s (11 mph), just due to the fire growth and the flow path that was set-up between the window opening and the corridor vent.

Avoid the flow path. The directional nature of the fire gas flow was demonstrated with thermal conditions, both temperature and heat flux, which were twice as high in the “flow” portion of the corridor as opposed to the “static” portion of the corridor in Experiment 1 [not wind driven]. Thermal conditions in the flow path were not consistent with firefighter survival.

Previous posts have presented case studies based on incidents in Loudoun County Virginia and Grove City, Pennsylvania in which convective flow was a significant factor rapid fire progress that entrapped and injured firefighters, in one case fatally. Previous NIST research investigating a multiple line-of-duty death that occurred in a townhouse fire at 3146 Cherry Road in Washington, DC in 1999 also emphasized the influence of flow path on fire conditions and tenability.

More to Follow

Subsequent posts will examine the NIST wind driven fire tests in greater detail.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Madrzykowski, D. & Kerber, S. (2009). Fire Fighting Tactics Under Wind Driven Conditions. Retrieved (in four parts) February 28, 2009 from http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part1.pdf; http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part2.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part3.pdf;http://www.nfpa.org/assets/files//PDF/Research/Wind_Driven_Report_Part4.pdf.

Madrzykowski, D. & Vettori, R. (2000). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999. Retrieved March 1, 2009 from http://fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf

Additional Reading

The following investigative reports deal with firefighter line of duty deaths involving wind driven fire events during structural firefighting.

National Institute for Occupational Safety and Health (NIOSH). (1999). Death in the line of duty, Report F99-01. Retrieved February 28, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face9901.pdf

National Institute for Occupational Safety and Health (NIOSH). (1999). Death in the line of duty, Report F98-26. Retrieved February 28, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face9826.pdf

National Institute for Occupational Safety and Health (NIOSH). (2002). Death in the line of duty, Report F2001-33. Retrieved February 28, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200133.pdf

National Institute for Occupational Safety and Health (NIOSH). (2007). Death in the line of duty, Report F2005-03. Retrieved February 28, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200503.pdf

National Institute for Occupational Safety and Health (NIOSH). (2008). Death in the line of duty, Report F2007-12. Retrieved February 28, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face200712.pdf

Prince William County Department of Fire and Rescue (2007). Line of duty investigative report: Technician I Kyle Wilson. Retrieved February 28, 2009 from http://www.pwcgov.org/default.aspx?topic=040061002930004566

Texas State Fire Marshal’s Office. (2001). Firefighter Fatality Investigation, Investigation Number 02-50-10. Retrieved February 28, 2009 from http://www.tdi.state.tx.us/reports/fire/documents/fmloddjahnke.pdf

As discussed in previous posts, fuel and ventilation are the major controlling factors in compartment fire development. Compartment fires begin with the ignition of a single item. If energy is released at a sufficient rate, the fire will extend to other fuel and begin to influence the compartment environment. A single burning item or object exposed to heat transfer resulting from a fire is referred to as a fuel package. Fuel packages can be comprised of a single fuel (e.g., wood, plastic) or they may be composites of a number of different materials (e.g., upholstered chair, sofa, or mattress). This post will examine a familiar fuel package often involved in residential fires, the ordinary sofa.

The Sofa as a Fuel Package

Upholstered furniture such as chairs, recliners, love seats and sofas are common fuel packages in the living room or family room of a residential occupancy. A single upholstered chair is likely to provide sufficient energy and heat release rate to take a 3.05 M x 3.66 M (10′ x 12′) room to flashover. A sofa on the other hand can provide three times the energy and heat release rate as a single chair.

Figure 1. Upholstered Furniture as a Composite Fuel Package

As illustrated in Figure 1, upholstered furniture such as a couch is a composite of a number of different materials, most of which are fuel. The frame is generally constructed of metal, wood or an engineered wood product such as plywood or particleboard. In older furniture, padding consisted of natural fiber materials, while modern furniture generally has some type of plastic foam padding. The upholstery can be natural fiber fabric or some type of synthetic material. Most of the synthetic materials used in furniture construction have more potential energy per unit mass (kg or lb) than wood or natural fiber padding and fabric.

Ignition Scenarios

Open flame, smoldering combustion (e.g., carelessly discarded cigarette), or hot objects (e.g., portable heater) can provide sufficient energy to ignite upholstered furniture. Smoldering combustion can progress slowly through layers of material, resulting in a large quantity of toxic and flammable products of incomplete combustion and may even self-extinguish. However, if smoldering combustion reaches the edge or surface, or if the initial ignition resulted in flaming combustion, the fire may transition rapidly from an incipient to growth stage fire.

Potential Heat Release Rate

Given an adequate supply of oxygen heat release rate is dependent on fuel type(s) and geometry. For example, the heat release rate (HRR) from a burning sofa can quickly reach as high as 3 MW as illustrated in Figure 2. This is easily enough to result in extension to other fuel packages and result in rapid transition from the growth stage to a fully developed fire in the compartment (flashover).

Figure 2. HRR from a Couch

This HRR curve was adapted from National Institute for Standards and Technology (NIST) tests of fuel packages. Phographs, video, and detailed test data are available on the NIST Building Fire Laboratory web site.

Ventilation Controlled Burning Regime

In many cases, the developing compartment fire becomes ventilation controlled and HRR is diminished, failing to reach the peak illustrated in Figure 2. When the fire becomes ventilation controlled, fuel continues to pyrolize, transitioning from solid to gas phase fuel in the smoke layer. If the compartment is tightly sealed, the fire may self-extinguish. However, an increase in ventilation (e.g., failure of a window or opening a door to gain access for firefighting operations) can result in a rapid increase in heat release rate, and potentially a transition to a fully developed fire (ventilation induced flashover).

Things to Think About

This post examined a common piece of furniture found in most residential occupancies. Consider that there are many others and that fuel packages can also include interior finish such as carpet and structural materials. Wildland firefighters are well aware of the hazards presented by different fuel models, structural firefighters should consider the types of “fuel model” presented by different types and configurations of contents and structural materials in the built environment.

Ed Hartin, MS, EFO, MIFireE, CFO

Broken Links

Thanks to Lieutenant Matt Leech of Tualatin Valley Fire and Rescue for letting me know that there are a number of broken links in my earlier blog posts. A fix is in the works and hopefully all links will be functional by next Monday.

Historical Perspective

While researching the Iowa Fire Flow Formula, I came across some interesting information (trivia?) related to the use of water fog for firefighting. In The Safe and Effective Use of Fog Nozzles: Research and Practice, John Bertrand and John Wiseman observed that fog nozzles have been in existence for more than 100 years.. Early versions of this type of nozzle were imported to the United States from Europe.

In 1924, Glenn Griswold, a firefighter from Colorado Springs moved to California and joined the newly formed Los Angeles County Fire Protection District. He quickly rose to the rank of Captain and was assigned to Station 17 in Santa Fe Springs. Captain Griswold applied his prior education as a hydraulic engineer to the practice of firefighting and experimented with development of a nozzle to break water into small droplets. Eventually he patented the design under the name Fog Nozzle.

Subsequent innovations in the design of combination nozzles resulted in nozzles that could maintain the same flow rate regardless of pattern, adjustable flow nozzles could be set to provide different flow rates while maintaining consistent flow for all patterns, and finally automatic nozzles that maintained a relatively constant nozzle pressure through a specific flow range.

However, there was a reference to the January 1877 issue of Scientific American in Nelson�s Qualitative Fire Behavior that intrigued me. He stated that this article extolled the virture of little drops of water and the latent heat of steam and that it attempted to point out in a scientific manner that spray or fog nozzles could greatly increase the efficiency of the fire service.

I located a copy of the magazine in the archives of the Portland State University library. The article that Nelson referenced, was actually a letter to the editor written by Charles Oyston of Little Falls, NY.

Scientific American, January 1877

To the Editor of the Scientific American

In our issue of December 30, you recommend discharging water through perforated pipes in the form of spray for extinguishing fire. If water in the form of spray be a good extinguisher, as it undoubtedly is, as numbers of proofs exist in our factories and picker rooms, why do not our fire departments use it in that form in all cases where they can? Leaving firemen to answer that question, I will proceed to adduce a few facts in support of the theory that a spray is the true method of applying water wherever the burning object can be reached by it.

Water operates, in extinguishing fire, by absorbing the heat and reducing the temperature of the burning substance so low that fire cannot exist; and as the amount of heat that water will absorb depends on the amount of surface of water in contact with the fire, the more surface we can cover with a given amount of water the better. As flame is the principle propagator of fire, to arrest it is the first thing to do; and as it is more than three thousand times lighter than water, and in most cases a mere shell or curtain, a fraction of an inch thick, the extreme absurdity of trying to subdue it with solid streams of water will be apparent. If a man in the character of a sportsman were to fire an inch ball into a flock of humming birds, with the intention of killing as many as possible, he would be regarded as a fool; but if he were to melt the inch ball up, and cast it into shot one thirtieth of an inch in diameter, he would have twenty-seven thousand such shot, and their aggregate surface would be thirty times greater than the inch ball. If he were to load his gun with this shot and fire into the flock, at proper distance, the slaughter of the little beauties would be terrible; and if a fireman would divide up his stream into spray, so that he could cover thirty times more flame, he might expect a corresponding result. The globules of water would be so small that a large portion of them would be heated through and converted into steam; and as steam contains five more heat (latent) than boiling water, we gain a great advantage in this. Steam is also an excellent extinguisher, and this is an additional advantage. As a large portion of this water is converted into steam when applied in the form of a pray, a small amount serves, and the damage by water is very small.

If the first two engines that reached the burning Brooklyn theater could throw five hundred gallons of water each minute, and divide every cubic inch of water into sixty thousand drops, in two minutes the smoke and heat would have been sufficiently subdued to have enabled outsiders to enter and rescue the unfortunate inmates. I am well aware that this statement may seem extremely absurd to firemen who have never experimented in this line; but before they condemn it, let them take out a couple of engines and try the experiment. The barbarous system now in use that so frequently desolates portions of our cities, fills our houses with mourning and our cemeteries with new-made graves, must give way to the dictates of Science. Humanity demands it, and I call on the scientists and chemists throughout the land to aid in introducing this needed reform.

Little Falls, N.Y. Charles Oyston
Scientific American Vol. XXXVI No. 4, Page 52
January 27, 1817

The Rest of the Story

Oyston does not mention that he holds a patent for a device called Improvement in Nozzles which used a series of movable hooks inside a relatively standard solid stream nozzle to create a broken stream pattern of broken droplets. In the Fire Stream Management Handbook, David Fornell astutely observes that attempting to introduce change in the 19th century was apparently as difficult as it is today.

While it is obvious that Oyston is not a firefighter or fire protection engineer with a sound understanding of the tactical applications of straight streams and water fog in firefighting operations, he did have a reasonable grasp of the basic physics involved in the use of cooling for fire control and extinguishment.

His call for scientists and chemists to weigh in on the issue resonated strongly with me as firefighters stand across a chasm from scientists, engineers, and researchers. Much progress has been made in this regard in other nations such as Sweden and in the US by the work of the National Institute for Standards and Technology (NIST) and others. However, this integration of science with the practical experience of firefighting needs to continue and be expanded.

Ed Hartin, MS, EFO, MIFireE, CFO

The Incident

Kernersville Fire Rescue and responded to a residential in the 1300 block of Union Cross Road shortly after 0200 hours on January 14, 2009. Occupants had been evacuated by two civilians returning home from work at a nearby Dell computer plant. First arriving units initiated offensive operations and began primary search to ensure that all occupants were out of the residence.

Less than 15 minutes into initial operations, an explosion occurred resulting in partial collapse of the building. Kernersville Firefighter Jay Coleman and three firefighters from the Winston-Salem Fire Department were caught in the collapse, but were able to self-extricate. Firefighter Coleman suffered minor injuries.

Chief Walt Summerville of Kernersville Fire Rescue reported “as we entered the building and began to ventilate and to flow air by moving hose lines, the heated gases got the air it needed”.� Chief Summerville believes the explosion was a backdraft, which was caused by a build-up of smoke in the crawl space of the home.

Explosion Captured on Video

A Kernersville police officer’s dashboard camera caught a burning home as it suddenly exploded. The police car was (appropriately) positioned a considerable distance from the house and provides a view of Side A from the Alpha/Delta corner. Watch the video several times to get a general sense of what happened Then download and print the B-SAHF Worksheet and identify any key indicators that might have be visible in the video.

Post fire video and an interview with Firefighter Coleman are available on the WGHP Fox Channel 8 web site.

At this point, information available about this incident is limited to news reports and video. However, we will be in touch with Kernersville Fire Rescue in an effort to obtain more detailed and fire behavior focused information about this incident. More to follow!

Important Lessons

An initial look at the limited information available about this incident points to several important considerations:

• Conditions can vary widely in different compartments. In this incident (like many others) flaming combustion is visible in one location, while extremely under-ventilated backdraft conditions exist elsewhere.
• Backdraft can occur in an entire building, one or more habitable compartments, or in a void space.
• Backdraft indicators may be pronounced, they may be subtle, or may not be visible from firefighters working positions.

Ed Hartin, MS, EFO, MIFireE, CFO

As discussed in Estimating Required Fire Flow: The National Fire Academy Formula, there are a number of ways to estimate required (total) fire flow or tactical rate of flow (required for fire attack). This post examines the groundbreaking work of Keith Royer’s and Floyd W. (Bill) Nelson’s work in development of a method to identify the volume and flow of water necessary for fire control with water fog.

The fire service often accepts (or rejects) concepts, theories, and practices based on what is written in training manuals, trade magazines, or presented by well known speakers. Others take the message and pass it along, trying to improve or simplify the message. Much can be lost in the translation. While we are strongly influenced by tradition, we occasionally forget history, and valuable work that was done by our predecessors is forgotten or misinterpreted. This is particularly true in the case with regard to Royer’s and Nelson’s volume and rate of flow formulas.

Origins of the Iowa Formula

In 1951, Keith Royer and Floyd W. (Bill) Nelson were hired by Iowa State University to manage the Engineering Extension Service Firemanship Training Program. Royer and Nelson both became involved in the Exploratory Committee on the Application of Water, a research team comprised of fire service, fire protection engineering, and fire insurance representatives. The principal work of the Exploratory Committee was investigation of the use of water fog for firefighting.

One critical question faced by Royer and Nelson was how much water was necessary to control a fire with water fog? In his book Qualitative Fire Behavior (1989), Nelson observed: “In principle, firefighting is very simple. All one needs to do is put the right amount of water in the right place and the fire is controlled.”� Royer and Nelson recognized that heat release from the fire must be balanced by the energy required to heat water to its boiling point and change it to steam. Through their research, they discovered that too little or too much water was considerably less effective than the right amount.

Note: While math is considerably simpler when using standard international (SI) units, Royer and Nelson did their work in traditional units (e.g., feet, gallons, British thermal units, degrees Fahrenheit). For now, I will stick with traditional units to illustrate how the Iowa Formula was developed. Safe and Effective Use of Fog Nozzles: Research and Practice (Wiseman & Bertrand, 2003) includes adaptation of the formula to the use of SI units.

Based on the results of their research on extinguishing compartment fires, Royer and Nelson developed the following formula to determine the volume of water (in gallons) required to control a fire in a given size compartment.

Royer and Nelson based this formula on the following two concepts:

1. Water converted to steam expands at a ratio of 1700:1, as a result one gallon of water (0.13 ft³) produces 221 ft³ of steam. However, in practical application it is unlikely that all of the water would be converted to steam. Royer and Nelson estimated the efficiency of this conversion at 90%, resulting in production of 198.9 ft³ of steam per gallon. They rounded this value to 200 to simplify calculation.
2. In 1955 the Factory Mutual Laboratories determined that oxidization of ordinary fuel with 1 ft³ of oxygen (at standard temperature and pressure) resulted in release of 535 British thermal units (Btu) of energy. Based on an atmospheric oxygen concentration of 21% and substantive reduction or cessation of flaming combustion at 15% concentration, Royer and Nelson estimated that seven percent (of atmospheric concentration of oxygen) was available to support flaming combustion. This led them to estimate that combustion of ordinary fuel with 1 ft³ of air would result in release of 37 Btu. Combustion of ordinary fuel with 200 ft³ of air (would therefore release 7,400 Btu. One gallon of water, raised from a temperature of 62^o F to 212^o F and completely converted to steam will absorb 9330 Btu. As with their calculation for steam production, an efficiency factor of 90% can be applied, resulting in absorption of 8397 Btu. This illustrates that a single gallon of water converted to steam will absorb the energy released by combustion of ordinary fuel with 200 ft³ of air.

Note: There are a few problems in using volume when discussing the energy released based on the quantity of oxygen or air in the combustion reaction. Chief of which is the variation in volume based on temperature. It would be more appropriate to speak to the mass of oxygen or air. However, Royer and Nelson based their approach on volume, so we will follow this line of reasoning (recognizing that while it is simple to understand, it has significant limitations).

Royer and Nelson used these concepts to support their formula to determine the volume of water required to control a fire with water fog.

Volume and Flow Rate

The volume formula, while a good start, still did not identify the required flow rate. The required volume could be delivered over various periods of time and still control the fire. If water was applied over a one minute period, the volume formula could be used to determine flow rate directly. However, Royer and Nelson estimated if water was applied in the right place, most fires could be controlled (but not necessarily extinguished) with water fog in less than 30 seconds. Given this timeframe, the volume formula translated into the rate of flow formula as follows:

Limitations

The Iowa Rate of Flow Formula is designed to estimate the flow rate required to control a fire in a single open area of a building with a 30 second application of water fog. This approach requires foreknowledge of the building and made the Iowa rate of flow formula most suited for preplanning, rather than tactical application.

That said, this does not mean that you cannot apply this formula (or its concepts) tactically based on the estimated area of involvement in a building that has limited compartmentation (e.g., multiple, interconnected compartments, open doors, unprotected shafts). However, it is essential to remember that Royer and Nelson based their formula on a 30 second application (potentially from multiple points) outside the compartment, and not working your way from compartment to compartment as is typically done in offensive, interior firefighting operations.

Additional Considerations

The concept that water applied to the fire compartment will turn to steam and fill the space, displacing air and hot smoke is a foundational principle of the indirect and combination attack as discussed by Lloyd Layman, Keith, Royer and Bill Nelson. This physical reaction is also commonly accepted as fact within the fire service. However, the science is a bit more complicated.

Royer and Nelson are correct in assuming that at its boiling point water converted to steam will expand 1700 times and not increase in temperature. However, water converted to steam while passing through the hot gas layer does not increase the total volume of gas and vapor in the space. The expansion of steam is more than counterbalanced by contraction of the hot gas layer due to cooling. On the other hand, water that passes through the hot gas layer (without taking energy from the gases) and converts to steam on contact with compartment linings (walls, ceiling) results in addition of the volume of steam to the volume of air and smoke in the compartment. This is not commonly understood and will be the subject of a later post. Steam formed at 212^o F (100^o C) can continue to absorb energy if the temperature of the fire environment is above 212^o F (100^o C) and will continue to expand (while the hot gases correspondingly contract).

One of the fundamental assumptions central to the Iowa formula is that the oxygen available to the fire is limited to that contained within the volume of the fire compartment. However, this is unlikely. If smoke is visible, ventilation (i.e., exchange of the atmosphere in the compartment with outside air) is taking place to some extent. In addition, if the compartment is not totally isolated from the remainder of the building, air track (movement of smoke and air) will provide additional oxygen to the fire. However, Royer and Nelson did identify an extremely important and often overlooked point. The Iowa tests showed that the heat release rate from actual compartment fires was less than the value based on the potential heat release from the fuel involved due to limitations in ventilation.

In a compartment fire, heat release rate is often (except in the incipient and early growth stage) limited by ventilation. One of the most important lessons that can be learned from Royer’s and Nelson’s work is that the flow rate and volume of water required for fire control is related not only to the method of attack, but also to the ventilation profile of the compartment or building involved.

Building on the Past

The National Fire Academy Fire Flow Formula (see Estimating Required Fire Flow: The National Fire Academy Formula) is based on synthesis of the experience of a group of experienced fire officers. On the other hand, the Iowa Formula is based on analysis of extensive empirical evidence developed during live fire tests. These formula each have different assumptions and are designed for different purposes. However, both provide useful information if they are used as intended. Future posts will examine the topic of fire flow from an international perspective, looking at the approaches taken by Cliff Barnett from New Zealand and my colleague Paul Grimwood from the United Kingdom.

For more information on Fire Flow, visit Paul Grimwood’s website www.fire-flows.com. Paul has amassed a tremendous amount of information on this topic from around the world.

Ed Hartin, MS, EFO, MIFireE, CFO

Application of the appropriate flow rate is critical to fire control. However, how can we estimate the flow rate that is necessary?

There are a number of methods that can be used to estimate or calculate required flow rate for fire control. One method is to simply use your experience (which may work quite well if you have been to a large number of fires and paid attention to flow rate). However, if you do not have a large base of experience to draw on or need to apply flow rate estimation in a preplanning context, other methods are necessary. One of the most common methods used in the United States is the National Fire Academy (NFA) Fire Flow Formula.

Development of the NFA Formula

In the mid 1980s the development team for the National Fire Academy Field course Preparing for Incident Command developed this formula to provide a simple method for estimating the flow requirements for offensive, interior operations where a direct attack was used to control and extinguish the fire.

Interestingly enough the NFA Fire Flow Formula is not based on science (at least not physical science). The developers tapped into another valid source of information, knowledge of experienced fire officers.

The course developers designed a number of plot and floor plans showing different sizes of building with different configurations (e.g., rooms, doors, windows) with varied levels of involvement. These drawings were distributed to students attending the academy and they were asked how their fire department would control the fire (with the emphasis on the number, placement, and flow rate of hoselines).

There are three major parameters used for the scenarios based on these plot and floor plans.

• All scenarios were designed to involve offensive, interior firefighting operations and as such, fire involvement was limited to 50% or less of the total floor area of the building.
• Operations were to be conducted as they normally would, with initial operations started by the first arriving company and additional tactics implemented as resources arrive.
• Primary search and ventilation tactics would be performed concurrently with fire control operations.

The student’s responses were collected and analyzed. For each scenario, when the floor area of the involved area in square feet (ft²) was divided by the total flow rate in gallons per minute (gpm) for all hoselines used for attack, backup, and exposure protection; the average result was three. Turning this around, flow rate in gpm can be determined by dividing the area of involvement in ft² by three.

In that the exterior of the building can be determined more easily than the area of involvement, the formula was adapted to determine the flow rate based on building size and approximate percentage of involvement as illustrated below:

Note: This method does not translate easily into standard international (SI), simply converted the formula would be lpm = M²/0.07.

The course development team extended the application of this formula to include estimated flow required for exposure protection by adding 25% of the flow rate required for fire control (as determined by the basic formula) for each exposure. The full formula as used in preplan development is as follows:

The development team believed that this formula would also be applicable to defensive attack for levels of involvement above 50%. However, this was not validated using the same type of methodology as used to develop the base fire flow formula.

Limitations

It is important to remember the limitations of this fire flow estimation method:

• The NFA Fire Flow Formula is designed for offensive, interior operations involving direct attack.
• The formula becomes increasingly inaccurate if the level of involvement exceeds 50% or the resulting flow is greater than 1,000 gpm.
• This method is not designed for defensive, master stream operations (even though the developers believed that it would provide a reasonable estimate of required flow rate for defense.
• The formula is based on area, not volume. If the ceiling height exceeds 10’, the flow rate may be underestimated.
• The NFA Formula does not take into account the potential heat release rate of the fuel. Fuel with extremely high heat release rate may require a higher flow rate
• The developers of the NFA Formula made the assumption that the building was well ventilated (tactically). Increased ventilation can (if the fire is initially ventilation controlled) result in increased heat release rate.
• It may be tough to do the math at 0200 hours when faced with a rapidly developing fire! This method is best used in advance of the fire when developing preplans or working on tactical problems

Total Versus Tactical Rate of Flow

The most common application error is the belief that the formula determines the flow rate required for fire attack. This is incorrect! The formula determines the total flow rate required for attack, backup, and exposure protection lines. Use of this formula to determine the flow rate for the initial attack line (or lines) will greatly overestimate the required tactical rate of flow.

As discussed in It’s the GPM! and Choose your Weapon Part I, substantially exceeding the required tactical rate of flow has diminishing returns on speed of extinguishment and substantially increases the amount of water used. If excessive, water that is not used efficiently (i.e., turned to steam) increases fire control damage).

Using the NFA Base Fire Flow Formula (no exposures), roughly half of the flow rate is used for attack lines and the remainder is used for backup lines. The NFA formula provides an excellent method for estimating total flow rate requirements (which impacts on water supply and resource requirements). However, it must be adjusted (reduced by half) to determine the tactical rate of flow necessary for direct attack on the fire.

Other Approaches

As outlined in this post, the NFA Fire Flow Formula is intended for estimating the total flow rate required when making a direct attack and has a number of specific parameters that must be considered. Prior to introduction of the NFA formula, the Iowa Fire Flow Formula developed by Floyd W. (Bill) Nelson and Keith Royer. The Iowa Formula was developed quite differently, has substantially different assumptions, and will be the subject of my next post.

For more information on Fire Flow, visit my colleague Paul Grimwood’s website www.fire-flows.com. Paul has amassed a tremendous amount of information on this topic from around the world.

Ed Hartin, MS, EFO, MIFireE, CFO

LODD in 2008

In 2008, six firefighters in the United States lost their lives in extreme fire behavior events occurring while they were engaged in interior firefighting operations. In 2008 there was only one multiple fatality line of duty death as the result of extreme fire behavior. Of this six, three were career, two were volunteers, and one was paid on call. They ranged in age from 19 to 54 years of age with an average age of 34.8 years. However, this does not give us the real picture, it is important to look at each of these events.

Firefighter Rick Morris (54, Career), Sedalia, Missouri: Firefighter Morris died April 8, 2008, nine days after being burned in a flashover that occurred while attempting to locate the fire in a small single family dwelling He was survived by his wife and four children.

Firefighter Bret Lovrien (35, Career), Los Angeles, California: Firefighter Lovrien died and Engineer Anthony Guzman was seriously injured March 26, 2008 from traumatic injuries occurring as the result of a smoke explosion while forcing entry into a commercial building to investigate smoke from a fire in a utility vault. Firefighter Lovrien was survived by his brother, parents, stepmother, and grandfather.

Firefighter Justin Monroe (19, Paid On-Call) and Firefighter Victor Isler (40, Career), Salisbury, North Carolina: Firefighters Monroe and Isler died March 7, 2008 of thermal insult and carbon monoxide exposure following rapid fire progress (likely flashover) in a commercial fire. Three other firefighters also suffered burns in this incident. Firefighter Monroe was survived by his parents and brother. Firefighter Isler was survived by his wife and two children.

Lieutenant Nicholas Picozzi (35, Volunteer), Linwood, Pennsylvania: Lieutenant Picozzi died March 5, 2008 as a result of injuries received due to rapid fire progress (likely flashover) while searching for the seat of the fire in the basement of a small single-family dwelling. Assistant Chief Kenny Dawson Jr., Assistant Chief Chris Durbano, and Firefighter Tom Morgan Jr. were injured while attempting to rescue Lieutenant Picozzi. Lieutenant Picozzi was survived by his wife and two children.

Firefighter Brad Holmes (21, Volunteer) , Grove City, Pennsylvania: Firefighter Holmes died three days after he and and Lieutenant Scott King were burned as the result of flashover while conducting primary search on the second floor of a small two-family home on February 29, 2008. Firefighter Holmes is survived by his parents and brother.

Two of these incidents have been documented by an investigative report. NIOSH Report F2008-06 examines the incident in which Firefighter Brad Holmes died. The Post Incident Report on the Salisbury Millwork Fire by the Salisbury Fire Department examines the circumstances surrounding the deaths of Firefighters Justin Monroe and Victor Isler (NIOSH Report F2008-07 is pending). NIOSH is also investigating the deaths of Lieutenant Nick Pilozzi (NOSH F2008-08) and Firefighter Brett Lovrien (NIOSH F2008-11). The status of these reports is listed on the NIOSH Firefighter Fatality Investigation and Prevention Program Pending Investigations page.

Similarities and Differences

Three of these fatalities occurred in small residential structures. Of these, one occurred on the second floor, one on the first floor, and the other in the basement. Two of these fatalities occurred in an exposure, not initially involved in the fire. Three of these fatalities occurred in commercial occupancies. Two of the fatalities occurred at a major, greater alarm fire. In one of these incidents, firefighters were searching for a trapped occupant, in all other cases; the firefighters were searching for the fire.

It is critical to remember that extreme fire behavior can occur in any type of structure. In some cases, severe fire conditions are evident on arrival, but in others, there is little evidence of a significant fire. The sense of urgency resulting from persons reported, or a rapidly developing fire can result in tunnel vision and reduce focus on key fire behavior indicators (B-SAHF). It is essential to ensure that members have adequate training so that reading the fire is both second nature and a conscious part of their size-up and dynamic risk assessment process.

Are We Making Progress?

This number is considerably lower than the 18 firefighters who died in 2007 where extreme fire behavior was a causal or contributing factor (four events accounted for 15 of the 18 fatalities). Does this reduction indicate that we are doing a better job of recognizing potential for extreme fire behavior and are controlling the fire environment more effectively to reduce risk during offensive operations? Examining not only line of duty deaths, but department incident reports, data submitted to the National Firefighter Near Miss Program and news reports of fire incidents involving extreme fire behavior I have the feeling that this reduction is not completely due to improved safety and operational performance.
There have been a number of incidents over the last year that point to the need for continued efforts in the improvement of fire behavior training. Incidents in Loudoun County, Virginia (see Loudon County Virginia Flashover, Loudoun County Flashover: What Happened, Loudoun County Flashover: Escape from Floor 2, and Flashover & Survival Skills Training); Sacramento, California and Edmonton, Alberta resulted in multiple firefighters being trapped by rapid fire progress while working above the fire. In these incidents, a slight variation in circumstances or any delay in the action of those involved might have resulted in multiple line of duty deaths.

These three incidents do not necessarily make a trend, but examining near miss, injury, and line of duty death data points to lack of or loss of situational awareness as a factor in this type of incident. Situational awareness is inclusive of the ability to recognize key fire behavior indicators, prediction of likely fire development, and recognizing the impact (or lack of impact) of tactical operations on fire progression.

The Way Forward

In an earlier post, Outstanding Performance I discussed the importance of deliberate practice in developing expertise. Numerous studies have identified that world class performance requires 10,000 hours of intensive and deliberate practice. While engaging in deliberate practice several hours a day, every day for ten years might seem a bit excessive to the average firefighter, performance is strongly correlated with an individual’s level of deliberate practice. Hard work pays off!

Regardless of your level of knowledge and skill, I challenge you to increase your efforts to engage in deliberate practice. As a student of your craft it is critical to deepen your knowledge of fire behavior, examine incidents you respond to with a critical eye, and use case studies to gain insight into fire behavior, building construction, and the effect of tactical operations. Engage in safe and effective live fire training to provide an opportunity to apply your knowledge and skill in a realistic context.

CFBT-US is using the following logo to identify training materials and activities that promote deliberate practice.

Resolutions

Many people make New Year’s Resolutions to lose weight and exercise more. Given the firefighter fatality statistics related to heart disease and stress, these are important goals. I share these goals with many of you. However, I have a few other professional resolutions for 2009 (and beyond):

• Continue to be a student of my craft as a fire officer and educator, finding the time to engage in an increased level of deliberate practice.
• Continue working to reducing firefighter injuries and deaths due to extreme fire behavior by increasing firefighter’s knowledge of practical fire dynamics.
• Work to improve the quality of NIOSH Firefighter Death in the Line of Duty Reports by continuing to be a critical friend of the program.
• Work to improve the quality and focus of fire service training curriculum and training materials in the area of fire behavior.
• Work to ensure that professional qualifications and other consensus standards adequately identify the requisite fire behavior knowledge and skills for safe and effective operation on the fireground.
• Work to ensure that live fire training instructors have the knowledge and skills necessary to conduct safe and effective training.

I encourage you to join me in this effort. These improvements will not happen overnight, but we can accomplish a great deal if we persist and work together. It is easy to complain and find fault. It is much more difficult to step up and do the right thing to make things better, but that is what is needed.

Thanks for reading the CFBT Blog and best wishes for a safe and happy 2009.

Ed Hartin, MS, EFO, MIFIreE, CFO