Posts Tagged ‘Tactical Ventilation’

The ability to read the fire and predict likely fire behavior is a critical skill for both firefighters and fire officers. Previous posts have examined how to use the B-SAHF scheme to recognize critical fire behavior indicators and identify the stage of fire development, burning regime, and potential for extreme fire behavior such as flashover or backdraft. However, there is something missing!

Experience is critical to adapting standard procedures and practices to a complex and dynamic operational environment. However, learning about fire behavior and changes in fire conditions based on fireground observations are a bit like a black box test. Black box testing is a technique for testing computer software in which the internal workings of the item being tested are not known by the tester. This is not entirely true in the case of fire behavior, but there is much that we don’t know when assessing conditions on the fireground. How long has the fire been burning? What are the specific characteristics of the fuel? What sort of internal compartmentation is present? What exactly is the ventilation profile? Some of these factors can be determined during fire investigation and it is also possible to determine (with some degree of uncertainty) what influence these factors had on the outcome of the incident. Did you ever wonder how fire behavior would have changed if you had used different tactics? Unfortunately, in real life there are no “do overs”!

UL Tactical Ventilation Research Project

One of the people who has asked himself the question of what would have changed if different tactics were used is Underwriters Laboratories Fire Protection Engineer Steve Kerber.

Underwriters Laboratories (UL) has received a Firefighter Safety Research and Development Grant from the Department of Homeland Security (DHS). This research project will investigate and analyze the impact of natural horizontal ventilation on fire development and conditions in legacy (older, more highly compartmented) and contemporary (multi-level, open floor plan) residential structures.

Preliminary work has included review of literature related to horizontal ventilation and incidents in which ventilation had a significant influence on firefighter injuries and fatalities. In addition, UL has done preliminary work on the performance of various structural components such as single and multi-pane windows as preliminary input for design of full scale residential fire experiments.

In mid-December 2009, Steve Kerber met with the project advisory panel comprised of Captain Charles Bailey, Montgomery County (MD) Fire Department; Lieutenant John Ceriello New York City Fire Department, Firefighter James Dalton and Director of Training Richard Edgeworth, Chicago Fire Department, Chief Ed Hartin, Central Whidbey Island (WA) Fire & Rescue, Chief Otto Huber Loveland-Symmes (OH) Fire Department, and Chief Mark Nolan, Northbrook (IL) Fire Department. In addition, the advisory panel includes Fire Protection Engineers Dan Madrzykowski from the National Institute of Standards and Technology (NIST) and Dr. Stefan Svensson, a research and development engineer from the Swedish Civil Contingencies Agency.

Figure 1. Defining Experiment Parameters for the Contemporary Structure

The main task presented to the advisory panel at the first meeting was to aid in defining the parameters for the experiment; including fire location, changes in ventilation profile, timing of these changes, and instrumentation to measure effects on fire development and conditions.

UL Large Fire Research Facility

The ventilation experiments will be conducted at the UL Large Fire Research Facility in Northbrook, IL. From the exterior, this facility simply looks like a large industrial building (see Figure 2). However, the interior of the structure includes a unique facility for fire research.

Figure 2. UL Large Fire Research Facility

One of the facilities inside this building is a 100’ x 120’ (30.48 m x 36.58 m) with a ceiling height that is adjustable up to 50’ (15.24 m) (see Figure 3). All of the smoke resulting from tests in this facility is exhausted through a system designed to oxidize unburned fuel and scrub hazardous products from the effluent prior to discharge to the atmosphere. Tests are monitored from a control room that overlooks the large burn room.

Figure 3. Large Burn Room

Over the next month, the two residential structures to be used for the ventilation experiments will be constructed inside the large burn room at the UL Large Fire Test Facility. After construction is complete, a series of 16 full scale fire experiments is planned to evaluate a range of different horizontal ventilation scenarios.

Research with the Fire Service

Steve Kerber has often stated that it is essential that scientists and engineers conduct research with, not for, the fire service. Engagement between researchers and firefighters on the street is essential in advancement of our profession. With this ventilation research project, Underwriters Laboratories is actively engaged in this process.

The outcome of this project will not simply be an academic paper (but there might be one or more of those as well). As part of the DHS grant, UL will be developing an on-line course to present the results of the experiments and their practical application on the fireground.

Happy Holidays,

Ed Hartin, MS, EFO, MIFireE, CFO

This morning I begin the process of relocation to beautiful Whidbey Island, Washington. Later this week I begin my new job as Fire Chief with Central Whidbey Island Fire & Rescue.

Coupeville Harbor at Sunrise

As I have been packing and preparing for my move all weekend, I have not had time to develop an in-depth Monday morning post. However, I did run across an interesting video clip a few weeks ago that ties in well with our ongoing effort to develop skill in reading the fire.

R-Fire

On March 27, 2009 the Emerson and Red Oak Fire Departments were dispatched for a residential fire at 901 Lowell Ave in Emerson, IA. First arriving companies observed a fire on Floor 1 and smoke throughout the structure.

The following video clip appears to have been shot early in incident operations as positive pressure ventilation is being implemented.

Download the B-SAHF Worksheet to use as a reminder while watching the video clip.

As you view the video clip, what do the fire behavior indicators (particularly smoke and air track) tell you about the stage of fire development, burning regime, and effectiveness of tactical operations?

Questions

In addition to your general observations of B-SAHF indicators while you watched the video the first time, consider the following questions:

• Watch the video clip again and examine conditions at the inlet between 0:21 and 0:25. What does the presence of smoke (and particularly dark smoke) pushing from the inlet indicate?
• Continue the video and examine conditions between 1:02 and 1:10. What do you observe at this point? What do smoke and air track conditions indicate now?
• Continue on and examine conditions closely between 2:28 and 2:48. What does the variation in smoke and air track indicators at different points on the exterior of the structure tell you?

Back on Schedule!

I plan to be back on track with the next post in the series examining nozzle techniques on Thursday, November 12. I have been having an e-mail conversation BC Mike Walker of the Oklahoma City Fire Department regarding nozzle techniques and flashover. Mike is working on a research project regarding “right for reach and left for life”. Interestingly, when I received Mike’s first e-mail, I was in the process of outlining an upcoming blog post on the concept of “Battle Drills” to deal with or escape from conditions such as those resulting from unplanned changes in ventilation (window failure, wind, etc.).

Ed Hartin, MS, EFO, MIFireE, CFO

Open Enrollment CFBT Level I & Instructor Courses

CFBT-US, LLC and the Northwest Association of Fire Trainers (NAFT) will be offering CFBT Level I and Instructor Courses at the Clackamas County (OR) Fire District I CFBT facility.

CFBT Level I
7-9 November 2009
Course Fee: $335

CFBT Instructor
9-13 November 2009
Course Fee: $915

Instructor course participants receive a copy of 3D Firefighting: Training, Techniques, & Tactics and an extensive 2-DVD library of CFBT resources including the CFBT Level I curriculum. For information on these courses download a NAFT CFBT Brochure and the CFBT Level I and CFBT Instructor Course Information Sheets.

CFBT Workshop in Sandö, Sweden

From 12-16 October 2009, I will be participating in a CFBT workshop in Sandö, Sweden along with a small group of instructors from around the world. We will be studying the compartment fire behavior curriculum at the Swedish Civil Contingencies Agency (Myndigheten för samhällsskydd och beredskap (MSB)) College in Sandö.

Figure 1. Fire Behavior Training in Sandö

In January of 2009 MSB replaced the Swedish Rescue Services Agency, the Swedish Emergency Management Agency, and the Swedish National Board of Psychological Defense. The MSB maintains two fire service colleges, one in Sandö (see Figure 2) and the other in Revinge.

Figure 2. MSB College in Sandö

The International Conference of Fire and Rescue, Valdivia – Chile 2010 CIFR

My brothers with Company 1 “Germania” of the Valdivia, Chile Fire Department have taken on a tremendous task with delivery of the first International Conference of Fire & Rescue in Valdivia. The conference will be held 23-27 January 2010.

Conference presenters include a diverse cadre of instructors from around the world. I will be presenting a series of seminars on fire behavior as well as a hands-on CFBT workshop. Presentations will be simultaneously translated into English and Spanish (as applicable). Have a look at the Conference Web Site for more information on this tremendous learning opportunity.

NIOSH Death in the Line of Duty F2007-02

On November 23, 2006, Firefighter Steven Solomon, a 33-year-old career fire fighter was seriously injured during a ventilation induced flashover or related fire behavior event in an abandoned single story duplex in Atlanta, GA; he died as a result of these injuries 6 days later.

NOSH Report F2007-02 provides an excellent description of fire behavior indicators observed prior to the occurrence of extreme fire behavior and correctly identifies that increased ventilation without coordinated fire attack resulted in worsening fire conditions.

Several conclusions in the report were based on computational fluid dynamics (CFD) modeling using the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator software. As discussed in a previous post computer modeling is an excellent tool, but it is important to understand both its capabilities and limitations (see Townhouse Fire-Washington, DC: Computer Modeling)

It is crucial to bear in mind that fire models do not provide a reconstruction of the reality of an event. They are simplified representation of reality that will always suffer from a certain lack of accuracy and precision. Under the condition that the user is fully aware of this status and has an extensive knowledge of the principles of the models, their functioning, their limitations and the significance attributed to their results, fire modeling becomes a very powerful tool (Dele´mont & Martin, J., 2007, p. 134).

Review NIOSH Report F2007-02 and see if you agree or disagree with the conclusions regarding the type of extreme fire behavior phenomena involved in this incident.

Ed Hartin, MS, EFO, MIFireE, CFO

This post continues study of an incident in a townhouse style apartment building in Washington, DC with examination of the extreme fire behavior that took the lives of Firefighters Anthony Phillips and Louis Mathews.

A Quick Review

Prior posts in this series, Fire Behavior Case Study of a Townhouse Fire: Washington, DC and Townhouse Fire: Washington, DC-What Happened examined the building and initial tactical operations at this incident. The fire occurred in the basement of a two-story, middle of building, townhouse style apartment with a daylight basement. This configuration provided an at grade entrance to the Floor 1 on Side A and at grade entrance to the Basement on Side C.

Engine 26, the first arriving unit reported heavy smoke showing from Side A and observed a bi-directional air track at the open front door. First alarm companies operating on Side A deployed hoselines into the first floor to locate the fire. Engine 17, the second due engine, was stretching a hoseline to Side C, but had insufficient hose and needed to extend their line. Truck 4, the second due truck, operating from Side C opened a sliding glass door to the basement to conduct search and access the upper floors (prior to Engine 17′s line being in position). When the door on Side C was opened, Truck 4 observed a strong inward air track. As Engine 17 reached Side C (shortly after Rescue 1 and a member of Truck 4 entered the basement) and asked for their line to be charged, and Engine 17 advised Command that the fire was small.

Extreme Fire Behavior

Proceeding from their entry point on Side C towards the stairway to Floor 1 on Side A, Rescue 1B and the firefighter from Truck 4 observed fire burning in the middle of the basement room. Nearing the stairs, temperature increased significantly and they observed fire gases in the upper layer igniting. Rescue 1B and the firefighter from Truck 4 escaped through the basement doorway on Side C as the basement rapidly transitioned to a fully developed fire.

Figure 1. Timeline Leading Up to the Extreme Fire Behavior Event

The timeline illustrated in Figure 1 is abbreviated and focuses on a limited number of factors. A detailed timeline, inclusive of tactical operations, fire behavior indicators, and fire behavior is provided in a subsequent section of the case.

After Engine 17′s line was charged, the Engine 17 officer asked Command for permission to initiate fire attack from Side C. Command denied this request due to lack of contact with Engines 26 and 10 and concern regarding opposing hoselines. Due to their path of travel around Side B of the building, Engine 17 had not had a clear view of Side A and thought that they were at a doorway leading to Floor 1 (rather than the Basement). At this point, neither the companies on Side C nor Command recognized that the building had three levels on Side C and two levels on Side A.

At this point crews from Engine 26 and 10 are operating on Floor 1 and conditions begin to deteriorate. Firefighter Morgan (Engine 26) observed flames at the basement door in the living room (see Figure 8 which illustrates fire conditions in the basement as seen from Side C). Firefighter Phillips (Engine 10) knocked down visible flames at the doorway, but conditions continued to deteriorate. Temperature increased rapidly while visibility dropped to zero.

As conditions deteriorated, Engine 26′s officer feels his face burning and quickly exits (without notifying his crew). In his rapid exit through the hallway on Floor 1, he knocked the officer from Engine 10 over. Confused about what was happening Engine 10′s officer exited the building as well (also without notifying his crew). Engine 26′s officer reports to Command that Firefighter Mathews was missing, but did not report that Firefighter Morgan was also missing. Appearing dazed, Engine 10′s officer did not report that Firefighter Phillips was missing.

Figure 2. Conditions on Side C at Aproximately 00:28

Note: From Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 32. District of Columbia Fire & EMS, 2000.

Figure 3. Conditions on Side A at Aproximately 00:28

Note: From Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 29. District of Columbia Fire & EMS, 2000.

Firefighter Rescue Operations

After the exit of the officers from Engine 26 and Engine 10, the three firefighters (Mathews, Phillips, and Morgan) remained on Floor 1. However, neither Command (Battalion 1) nor a majority of the other personnel operating at the incident recognized that the firefighters from Engines 26 and 10 had been trapped by the rapid extension of fire from the Basement to Floor 1 (see Figure 4).

While at their apparatus getting a ladder to access the roof from Side B, Truck 4B observed the rapid fire development in the basement and pulled a 350′ 1-1/2″ (107 m 38 mm) line from Engine 12 to Side C, backing up Engine 17.

Figure 4. Location of Firefighters on Floor 1

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 18 & 20. District of Columbia Fire & EMS, 2000 and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 12-13, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology.

Engine 17 again contacted Command (Battalion 1) and requested permission to initiate an exterior attack from Side C. However, the officer of Engine 17 mistakenly advised Command that there was no basement entrance and that his crew was in position to attack the fire on Floor 1. Unable to contact Engines 10 and 26, Command denied this request due to concern for opposing hoselines. With conditions worsening, Command (Battalion 1) requested a Task Force Alarm at 00:29, adding another two engine companies, truck company, and battalion chief to the incident.

Firefighter Phillips (E-10) attempted to retreat from his untenable position at the open basement door. He was only able to travel a short distance before he collapsed. Firefighter Morgan (E-26) heard a loud scream to his left and then a thud as if someone had fallen to the floor (possibly Firefighter Mathews (E-26)). Firefighter Morgan found the attack line and opened the nozzle on a straight stream, penciling the ceiling twice before following the hoseline out of the building (to Side A). Firefighter Morgan exited the building at approximately 00:30.

Rescue 1B entered the structure on Floor 1, Side A to perform a primary search. They crawled down the hallway on Floor 1 towards Side C until they reached the living room and attempted to close the open basement door but were unable to do so. Rescue 1 B did not see or hear Firefighters Mathews (E-26) and Phillips (E-10) while working on Floor 1. Rescue 1B noted that the floor in the living room was spongy. The Rescue 1 Officer ordered his B Team to exit, but instead they returned to the front door and then attempted to search Floor 2, but were unable to because of extremely high temperature.

Unaware that Firefighter Phillips (E-10) was missing, Command tasked Engine 10  and Rescue 1A, with conducting a search for Firefighter Mathews (E-26). The Engine 10 officer entered Floor 1 to conduct the search (alone) while instructing another of his firefighters to remain at the door. Rescue 1A followed Engine 26′s 1-1/2″ (38 mm) hoseline to Floor 1 Slide C. Rescue 1B relocated to Side B to search the basement for the missing firefighter.

The Engine 26 Officer again advised Command (Battalion 1) that Firefighter Mathews was missing. Engine 17 made a final request to attack the fire from Side C. Given that a firefighter was missing and believing that the fire had extended to Floor 1, Command instructed Engine 17 to attack the fire with a straight stream (to avoid pushing the fire onto crews working on Floor 1). At approximately 00:33, Battalion 2 reported (from Side C) that the fire was darkening down. Engine 14 arrived and staged on Bladensburg Road.

Command ordered a second alarm assignment at 00:34 hours. At 00:36, Command ordered Battalion 2 (on Side C) to have Engine 17 and Truck 4 search for Firefighter Mathews in the Basement. Engine 10′s officer heard a shrill sound from a personal alert safety system (PASS) and quickly located Firefighter Phillips (E-10). Firefighter Phillips was unconscious, lying on the floor (see Figure 4) with his facepiece and hood removed. Unable to remove Firefighter Phillips by himself, the officer from Engine 10 unsuccessfully attempted to contact Command (Battalion 1) and then returned to Side A to request assistance.

Command received a priority traffic message at 00:37, possibly attempting to report the location of a missing firefighter. However, the message was unreadable.

The Hazmat Unit and Engine 6 arrived and staged on Bladensburg Road and a short time later were tasked by Command to assist with rescue of the downed firefighter on Floor 1. Firefighter Phillips (E-10) was removed from the building by the Engine 10 officer, Rescue 1A, Engine 6, and the Hazardous Materials Unit at 00:45. After Firefighter Phillips was removed to Side A, Command discovered that Firefighter Mathews (E-26) was still missing and ordered the incident safety officer to conduct an accountability check. Safety attempted to conduct a personnel accountability report (PAR) by radio, but none of the companies acknowledged his transmission.

The Deputy Chief of the Firefighting Division arrived at 00:43 and assumed Command, establishing a fixed command post at the Engine 26 apparatus. Battalion 4 arrived a short time later and was assigned to assist with rescue operations along with Engines 4 and 14.

Firefighter Mathews was located simultaneously by several firefighters. He was unconscious leaning over a couch on Side C of the living room (see Figure 4). Firefighter Mathews breathing apparatus was operational, but he had not activated his (non-integrated) personal alert safety system (PASS). Firefighter Mathews was removed from the building by Engine 4, Engine 14, and Hazardous Materials Unit at 00:49.

Command (Deputy Chief) ordered Battalions 2 and 4 to conduct a face-to-face personnel accountability report on Sides A and C at 00:53.

Questions

1. Based on the information provided in the case to this point, answer the following questions:
2. National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Reports examining incidents involving extreme fire behavior often recommend close coordination of fire attack and ventilation.
3. Did the fire behavior in this incident match the prediction you made after reading the previous post (Towhouse Fire: Washington DC-What Happened)?
4. What type of extreme fire behavior occurred? Justify your answer?
5. What event or action initiated the extreme fire behavior? Why do you believe that this is the case?
6. How did building design and construction impact on fire behavior and tactical operations during this incident?
7. How might a building pre-plan and/or 360^o reconnaissance have impacted the outcome of this incident? Note that 360^o reconnaissance does not necessarily mean one individual walking completely around the building, but requires communication and knowledge of conditions on all sides of the structure (e.g., two stories on Side A and three stories on Side C).
8. How might the outcome of this incident have changed if Engine 17 had been in position and attacked the fire in the basement prior to Engines 26 and 10 committing to Floor 1?
9. What strategies and tactics might have been used to mitigate the risk of extreme fire behavior during this incident?

More to Follow

This incident was one of the first instances where the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator (FDS) was used in forensic fire scene reconstruction (Madrzykowski & Vettori, 2000). Modeling of the fire behavior in this incident helps illustrate what was likely to have happened in this incident. The next post in this series will examine and expand on the information provided by modeling of this incident.

Ed Hartin, MS, EFO, MIFireE, CFO

References

District of Columbia (DC) Fire & EMS. (2000). Report from the reconstruction committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999. Washington, DC: Author.

Madrzykowski, D. & Vettori, R. (2000). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510. August 31, 2009 from http://fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf

National Institute for Occupational Safety and Health (NIOSH). (1999). Death in the line of duty, Report 99-21. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

This post continues study of an incident that resulted in two line-of-duty deaths as a result of extreme fire behavior in a townhouse style apartment building in Washington, DC.

A Quick Review

The previous post in this series, Fire Behavior Case Study of a Townhouse Fire: Washington, DC examined building construction and configuration that had a significant impact on the outcome of this incident. The fire occurred in the basement of a two-story, middle of building, townhouse style apartment with a daylight basement. This configuration provided an at grade entrance to the Floor 1 on Side A and an at grade entrance to the Basement on Side C.

The fire originated in an electrical junction box attached to a fluorescent light fixture in the basement ceiling (see Figures 1 and 2). The occupants of the unit were awakened by a smoke detector. The female occupant noticed smoke coming from the floor vents on Floor 2. She proceeded downstairs and opened the front door and then proceeded down the first floor hallway towards Side C, but encountered thick smoke and high temperature. The female and male occupants exited the structure, leaving the front door open, and made contact with the occupant of an adjacent unit who notified the DC Fire & EMS Department at 0017 hours.

Dispatch Information

At 00:17, DC Fire & EMS Communications Division dispatched a first alarm assignment consisting of Engines 26, 17, 10, 12, Trucks 15, 4, Rescue Squad 1, and Battalion 1 to 3150 Cherry Road NE. At 0019 Communications received a second call, reporting a fire in the basement of 3146 Cherry Road NE. Communications transmitted the update with the change of address and report of smoke coming from the basement. However, only one of the responding companies (Engine 26) acknowledged the updated information.

Weather Conditions

Temperature was approximately 66^o F (19^o C) with south to southwest winds at 5-10 mi/hr (8-16 km/h), mostly clear with no precipitation.

Conditions on Arrival

Approaching the incident, Engine 26 observed smoke blowing across Bladensburg Road. Engine 26 arrived at a hydrant at the corner of Banneker Drive and Cherry Road at 00:22 hours and reported smoke showing. A short time later, Engine 26 provided an updated size-up with heavy smoke showing from Side A of a two story row house. Based on this report, Battalion 1 ordered a working fire dispatch and a special call for the Hazmat Unit at 00:23. This added Engine 14, Battalion 2, Medic 17 and EMS Supervisor, Air Unit, Duty Safety Officer, and Hazmat Unit.

Firefighting Operations

DC Fire and EMS Department standard operating procedures (SOP) specify apparatus placement and company assignments based on dispatch (anticipated arrival) order. Note that dispatch order (i.e., first due, second due) may de different than order of arrival if companies are delayed by traffic or are out of quarters.

Standard Operating Procedures

Operations from Side A

The first due engine lays a supply line to Side A, and in the case of basement fires, the first line is positioned to protect companies performing primary search on upper floors by placing a line to cover the interior stairway to the basement. The first due engine is backed up by the third due engine. The apparatus operator of the third due engine takes over the hydrant and pumps supply line(s) laid by the first due engine, while the crew advances a backup line to support protection of interior exposures and fire attack from Side A.

The first due truck takes a position on Side A and is responsible for utility control and placement of ladders for access, egress, and rescue on Side A. If not needed for rescue, the aerial is raised to the roof to provide access for ventilation.

The rescue squad positions on Side A (unless otherwise ordered by Command) and is assigned to primary search using two teams of two. One team searches the fire floor, the other searches above the fire floor. The apparatus operator assists by performing forcible entry, exterior ventilation, monitoring search progress, and providing emergency medical care as necessary.

Operations from Side C

The second due engine lays a supply line to the rear of the building (Side C), and in the case of basement fires, is assigned to fire attack if exterior access to the basement is available and if it is determined that the first and third due engines are in a tenable position on Floor 1. The second due engine is responsible for checking conditions in the basement, control of utilities (on Side C), and notifying Command of conditions on Side C. Command must verify that the first and third due engines can maintain tenable positions before directing the second due engine to attack basement fires from the exterior access on Side C.

The second due truck takes a position on Side C and is responsible for placement of ladders for access, egress, and rescue on Side C. The aerial is raised to the roof to provide secondary access for ventilation (unless other tasks take priority).

Command and Control

The battalion chief positions to have an unobstructed view of the incident (if possible) and uses his vehicle as the command post. On greater alarms, the command post is moved to the field command unit.

Notes: This summary of DC Fire & EMS standard operating procedures for structure fires is based on information provided in the reconstruction report and reflects procedures in place at the time of the incident. DC Fire & EMS did not use alpha designations for the sides of a building at the time of this incident. However, this approach is used here (and throughout the case) to provide consistency in terminology.

First due, Engine 26 laid a 3″ (76 mm) supply line from a hydrant at the intersection of Banneker Drive and Cherry Road NE, positioned in the parking lot on Side A, and advanced a 200′ 1-1/2″ ( 61 m 38 mm) pre-connected hoseline to the first floor doorway of the fire unit on Side A (see Figures 1 and 2). A bi-directional air track was evident at the door on Floor 1, Side A , with thick (optically dense) black smoke from the upper area of the open doorway. Engine 26′s entry was delayed due to a breathing apparatus facepiece malfunction. The crew of Engine 26 (Firefighters Mathews and Morgan and the Engine 26 Officer) made at approximately 00:24.

Figure 1. Plot and Floor Plan-3146 Cherry Road NE

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 18 & 20. District of Columbia Fire & EMS, 2000; Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999, p. 12-13, by Daniel Madrzykowski & Robert Vettori, 2000. Gaithersburg, MD: National Institute of Standards and Technology, and NIOSH Death in the Line of Duty Report 99 F-21, 1999, p. 19.

Engine 10, the third due engine arrived shortly after Engine 26, took the hydrant at the intersection of Banneker Drive and Cherry Road, NE, and pumped Engine 26′s supply line. After Engine 10 arrived at the hydrant, the firefighter from Engine 26 who had remained at the hydrant proceeded to the fire unit and rejoined his crew. Engine 10, advanced a 400′ 1-1/2″ (122 m 38 mm) line from their own apparatus as a backup line. Firefighter Phillips and the Engine 10 officer entered through the door on Floor 1, Side A (see Figure 2) while the other member of their crew remained at the door to assist in advancing the line.

Truck 15, the first due truck arrived at 00:23 and positioned on Side A in the parking lot behind Engine 26. The crew of Truck 15 began laddering Floor 2, Side A, and removed kitchen window on Floor 1, Side A (see Figure 2). Due to security bars on the window, one member of Truck 15 entered the building and removed glass from the window from the interior. After establishing horizontal ventilation, Truck 15 accessed the roof via a portable ladder and began vertical ventilation operations.

Engine 17, the second due engine, arrived at 00:24, laid a 3″ (76 mm) supply line from the intersection of Banneker Drive and Cherry Road NE, to a position on Cherry Road NE just past the parking lot, and in accordance with department procedure, stretched a 350′ 1-1/2″ (107 m 38 mm) line to Side C (see Figure 2).

Approaching Cherry Road from Banneker Drive, Battalion 1 observed a small amount of fire showing in the basement and assigned Truck 4 to Side C. Battalion 1 parked on Cherry Road at the entrance to the parking lot, but was unable to see the building, and proceeded to Side A and assumed a mobile command position.

Second due, Truck 4 proceeded to Side C and observed what appeared to be a number of small fires in the basement at floor level (this was actually flaming pieces of ceiling tile which had dropped to the floor). The officer of Truck 4 did not provide a size-up report to Command regarding conditions on Side C. Truck 4, removed the security bars from the basement sliding glass door using a gasoline powered rotary saw and sledgehammer. After clearing the security grate Truck 4, broke the right side of the sliding glass door to ventilate and access the basement (at approximately 00:27) and then removed the left side of the sliding glass door. The basement door on Side C was opened prior to Engine 17 getting a hoseline in place and charged. After opening the sliding glass door in the basement, Truck 4 attempted to ventilate windows on Floor 2 Side C using the tip of a ladder. They did not hear the glass break and believing that they had been unsuccessful; they left the ladder in place at one of the second floor windows and continued with other tasks.

Figure 2. Location of First Alarm Companies and Hoselines

Note: Adapted from Report from the Reconstruction Committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999, p. 27. District of Columbia Fire & EMS, 2000.

Unknown to Truck 4, these windows had been left open by the exiting occupants. Truck 4B (two person team from Truck 4) returned to their apparatus for a ladder to access the roof from Side C. Rescue 1 arrived at 00:26 and reported to Side C after being advised by the male occupant that everyone was out of the involved unit (this information was not reported to Command). Rescue 1 and Truck 4 observed inward air track (smoke and air) at the exterior basement doorway on Side C and an increase in the size of the flames from burning material on the floor.

Engines 26 and 10 encountered thick smoke and moderate temperature as they advanced their charged 1-1/2″ (38 mm) hoselines from the door on Side A towards Side C in an attempt to locate the fire. As they extended their hoselines into the living room, the temperature was high, but tolerable and the floor felt solid. It is important to note that engineered, lightweight floor support systems such as parallel chord wood trusses do not provide reliable warning of impending failure (e.g., sponginess, sagging), failure is often sudden and catastrophic (NIOSH, 2005; UL, 2009).

Prior to reaching Side C of the involved unit, Engine 17 found that their 350′ 1-1/2″ (107 m 38 mm) hoseline was of insufficient length and needed to extend the line with additional hose.

Engine 12, the fourth arriving engine, picked up Engine 17′s line, completed the hoselay to a hydrant on Banneker Drive (see Figure 2). The crew of Engine 12 then advanced a 200′ 1-1/2″ (61 m 38 mm) hoseline from Engine 26 through the front door of the involved unit on Side A and held in position approximately 3′ (1 m) inside the doorway. This tactical action was contrary to department procedure, as the fourth due engine has a standing assignment to stretch a backup line to Side C.

Rescue 1′s B Team (Rescue 1B) and a firefighter from Truck 4 entered the basement without a hoseline in an effort to conduct primary search and access the upper floors via the interior stairway. Engine 17 reported that the fire was small and requested that Engine 17 apparatus charge their line.

Questions

Consider the following questions related to the interrelationship between strategies, tactics, and fire behavior:

1. Based on the information provided to this point, what was the stage of fire development and burning regime in the basement when Engine 26 entered through the door on Floor 1, Side A? What leads you to this conclusion?
2. What impact do you believe Truck 4′s actions to open the Basement door on Side C will have on the fire burning in the basement? Why?
3. What is indicated by the strong inward flow of air after the Basement door on Side C is opened? How will this change in ventilation profile impact on air track within the structure?
4. Did the companies at this incident operate consistently with DC Fire & EMS SOP? If not, how might this have influenced the effectiveness of operations?
5. Committing companies with hoselines to the first floor when a fire is located in the basement may be able to protect crews conducting search (as outlined in the DC Fire & EMS SOP). However, what building factors increased the level of risk of this practice in this incident?

More to Follow

My next post will examine the extreme fire behavior phenomena that trapped Firefighters Phillips, Mathews, and Morgan and efforts to rescue them.

Remember the Past

This week marked the anniversary of the largest loss of life in a line-of-duty death incident in the history of the American fire service. Each September, we stop and remember the sacrifice made by those 343 firefighters. However, it is also important to remember and learn from events that take the lives of individual firefighters. In an effort to encourage us to remember the lessons of the past and continue our study of fire behavior, each month I include brief narratives and links to NIOSH Death in the Line of Duty reports and other documentation in my posts.

September 9, 2006
Acting CAPT Vincent R. Neglia
North Hudson Regional Fire & Rescue Department, NJ

Captain Neglia and other firefighters were dispatched to a report of fire in a three-story apartment building in Union City. Upon their arrival at the scene, firefighters found light smoke and no visible fire. Based on reports that the structure had not been evacuated, Captain Neglia and other firefighters entered the building to perform a search. Due to the light smoke conditions, Captain Neglia was not wearing his facepiece.

Captain Neglia was the first firefighter to enter an apartment. Conditions deteriorated rapidly as fire in the cockloft broke through a ceiling . Captain Neglia was trapped by rapid fire progress and subsequent collapse. Other firefighters came to his aid and removed him from the building. Captain Neglia was transported to the hospital but later died of a combination of smoke inhalation and burns.

NIOSH did not investigate and prepare a report on the incident that took the life of Captain Neglia.

Ed Hartin, MS, EFO, MIFireE, CFO

References

District of Columbia (DC) Fire & EMS. (2000). Report from the reconstruction committee: Fire at 3146 Cherry Road NE, Washington DC, May 30, 1999. Washington, DC: Author.

Madrzykowski, D. & Vettori, R. (2000). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE Washington D.C., May 30, 1999, NISTR 6510. August 31, 2009 from http://fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf

National Institute for Occupational Safety and Health (NIOSH). (1999). Death in the line of duty, Report 99-21. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

National Institute for Occupational Safety and Health (NIOSH). (2005). NIOSH Alert: Preventing Injuries and Deaths of Fire Fighters Due to Truss System Failures. Retrieved August 31, 2009 from http://www.cdc.gov/niosh/fire/reports/face9921.html

This is the fourth in a series of posts dealing with flashover, to review prior posts see:

• Understanding Flashover: Myths and Misconceptions
• Understanding Flashover: Myths and Misconceptions: Part 2
• The Ventilation Paradox

As previously discussed flashover requires sufficient heat release rate for the temperature of fuel packages within a compartment to increase sufficiently to ignite and the fire to rapidly transition to the fully developed stage. However, during fire development in a compartment the fire often becomes ventilation controlled, with fire growth and heat release rate limited by the available air supply. In some cases, the fire generates sufficient heat release rate despite being ventilation controlled. In others, there is insufficient oxygen in the air supplied for the fire to reach flashover (unless ventilation is increased). All of this is fairly simple and straightforward if we are examining fire in a single compartment. This simple explanation of flashover is based on fire development in a single compartment, such as that described in the ISO 9705 Fire Tests-Full Scale Room Fire Tests for Surface Products6American Society for Testing and Materials (ASTM) Standard E 603-6 (Figure 1)

Figure 1. Full Scale (Six Sided) Room Fire Test Compartment

Note: Underwriters Laboratory (UL) fire test photo adapted from Fire Behavior in Single Family Dwellings, [PowerPoint Presentation], National Fire Academy.

Things get a bit more complex when a fire occurs in a multi-compartment building as individual compartments are interconnected smoke and flames may extend from compartment to compartment throughout the building.

Ventilation and Air Track

Contrary to the common fire service definition of ventilation as “[planned and] systematic removal of heated air, smoke, and fire gases and replacing them with cooler air (IFSTA, 2008), ventilation is simply the exchange of the atmosphere inside the building with that which is outside. This process is ongoing under normal, non-fire conditions. However, under fire conditions, ventilation also involves movement of smoke and air between compartments as well as discharge of smoke from the building and intake of air from outside the structure.

Remember! If you can see smoke coming from the building, ventilation is occurring (but not necessarily the type or amount of ventilation that you need to effectively control the fire environment and the fire).

The term air track is used to describe the characteristics of air and smoke movement (e.g., direction, velocity). The movement of both air and smoke are important, but the direction and path of smoke movement is particularly significant for several reasons:

• Smoke is fuel
• Hot smoke has energy

Through convection, smoke carries energy away from the fire compartment and transfers this energy to objects having lower temperature (such as other fuel packages or firefighters working inside the building). The rate of heat transfer is substantially dependent on temperature difference and in the case of convection on the velocity of the hot gases. Higher velocity and turbulence results in a higher rate of convective heat transfer (much the same as the increase in wind chill as wind speed increases in a cold environment).

Air Track on a Single Level

Examination of air track on a single level provides a simple way to illustrate the influence of air track on the movement of smoke (think fuel and energy) from compartment to compartment, fire extension, and multi-compartment flashover.

With no significant ventilation (with the exception of slight building leakage) smoke will fill the fire compartment and extend through openings such as doorways to adjacent compartments (see Figure 2). If insufficient oxygen is available from the air within the compartments the fire will become ventilation controlled and growth may slow and the fire may decay (heat release rate lessens)

Figure 2. Limited Ventilation

Note: Unless the building is tightly sealed, there is likely to be some leakage resulting in smoke discharge and inward movement of air.

If an opening is made in the presently uninvolved compartment, smoke will move from the fire to the opening, exiting out the upper area of the opening while cool air moves inward through the bottom of the opening and towards the fire (see Figure 3). This is a bi-directional air track.

Figure 3: Single Opening with Bi-Directional Air Track

As pointed out in The Myth of the Self-Vented Fire and The Ventilation Paradox, providing additional oxygen to a ventilation controlled fire results in increased heat release rate and may result in ventilation induced flashover. However, it is important to consider how this impacts adjacent compartments as well.

Increased heat release rate in a still ventilation controlled fire results in higher hot gas layer temperatures and increased smoke production. Increasing temperature and volume of the hot gas layer will cause it to lower and velocity to increase as the smoke moves through adjacent compartments and out ventilation openings. This increases both radiant and convective heat transfer and potentially speeds progression to flashover in adjacent compartments.

Horizontal tactical ventilation can be accomplished rapidly and may, under some conditions, be a useful approach to improving interior conditions. Increasing the number and size of horizontal openings can raise the level of the hot gas layer (by providing additional exhaust). However, when dealing with a ventilation controlled fire the increased oxygen supplied to the fire will increase heat release rate. In addition, in the absence of wind or application of positive pressure at the entry point, two openings at the same level will result in a bi-directional air track at both openings as illustrated in Figure 4.

Figure 4. Two Openings with a Bi-Directional Air Track

If heat release rate is sufficient, this may result in vent induced flashover in the compartments between the fire and the exhaust openings as illustrated in the following video clip.

Important! Horizontal ventilation is not a bad tactic. However, it is essential to recognize and manage the air track as well as ensuring that ventilation is coordinated with fire attack.

More to Follow

Examination of the flashover phenomenon will continue with a case study involving a 1999 fire in a Washington, DC townhouse that resulted in the line of duty deaths of two firefighters. This incident is particularly important as it is one of the first times that the National Institute of Standards and Technology (NIST) Fire Dynamics Simulator (FDS) and Smokeview were used for forensic fire scene reconstruction. This data, in conjunction with the District of Columbia Fire and EMS Reconstruction Report and National Institute for Occupational Safety and Health (NIOSH) Death in the Line of Duty Report provides a solid basis for understanding the impact of burning regime and air track in multi-compartment, ventilation induced flashover.

Ed Hartin, MS, EFO, MIFireE, CFO

References

International Fire Service Training Association (IFSTA). (2008). Essentials of firefighting (5^th ed.). Stillwater, OK: Fire Protection Publications.

I originally intended to write this post about the influence of air track on flashover in multiple compartments. However, after several conversations in the last week about the bathtub analogy and ventilation induced flashover, I had a change in plans.

The Bathtub Analogy

In Understanding Flashover: Myths and Misconceptions, I presented the bathtub analogy (Kennedy & Kennedy , 2003)as a simplified way of understanding how flashover occurs when a compartment fire is burning in a fuel controlled regime.

Flashover has been analogously compared to the filling of a bathtub with the drain open. In this practical, though not perfect, analogy water represents the heat energy. The quantity of water available is the total heat of combustion of the available fuels (fuel load). The size of the spigot and the water pressure control the amount of water flow that is the heat release rate. The volume of the bathtub is analogous to the volume of the compartment and its ability to contain the heat energy. The size and location of the bathtub drain controlling the rate of water loss is the loss of heat energy through venting and conductance. In this analogy, if the bathtub becomes full and overflows, flashover occurs. (Kennedy & Kennedy, 2003, p. 7)

Figure 1. The Bathtub Analogy-Fuel Controlled Burning Regime

Note: Adapted from Flashover and fire analysis: A discussion of the practical use of flashover in fire investigation, p. 7, by Patrick Kennedy & Kathryn Kennedy, 2003. Sarasota, FL: Kennedy and Associates, Inc.

All Models are Wrong

While the bathtub model provides a simple explanation and makes it easy to understand how flashover might occur, it is inaccurate. However, as Box and Draper (1987) stated: “Essentially, all models are wrong, but some are useful” p. 424).

Models or analogies provide a way of understanding based on simplification. This is useful, but this simplification, while providing a starting point for understanding can overlook important concepts or elements of a complex system. In the case of the bathtub analogy, simplification overlooks the criticality of oxygen to the combustion process.

Ventilation is the exchange of the atmosphere inside a compartment with that which is outside. This process is necessary and ongoing in any space designed for human habitation. In a compartment fire, ventilation involves the exhaust of smoke and intake of air from outside the compartment.  Note that this is different than tactical ventilation, which is the planned and systematic removal of hot smoke and fire gases and their replacement with fresh air. However, both normal and tactical ventilation involve exhaust of the compartment atmosphere and replacement with fresh air.

While the bathtub analogy is simple, and provides a useful starting point, it fails to address the air side of the ventilation equation. As ventilation is increased, the compartment looses energy through convection. However, if the fire is ventilation controlled (heat release rate (HRR)is limited by the available oxygen), increased ventilation will also increase HRR.

Revised Bathtub Analogy

For many years, firefighters have been taught tactical ventilation prevents or slows progression to flashover. Somewhat less commonly, firefighters have been taught to close the door to the fire compartment, limiting inward air flow and slowing fire growth (tactical anti-ventilation). My friend and colleague Inspector John McDonough of the New South Wales (AU) Fire Brigades refers to this as the Ventilation Paradox. Increased ventilation increases the HRR required for flashover to occur and may prevent or slow progression to flashover or it may (and often does) result in flashover. Reduction in ventilation may prevent or slow progress to flashover, but also reduces the HRR required for flashover to occur and (less commonly) may result in flashover. It depends! Not the answer that firefighters want to hear.

Making the bathtub analogy a bit more complex may provide a starting point for understanding the ventilation paradox. At the root of this apparent paradox is the impact of ventilation on the thermodynamic system and the relationship between oxygen and release of energy from fuel (Thornton’s Rule). See Fuel and Ventilation [LINK) for more information on Thornton’s Rule and the relationship between oxygen, fuel, and energy.

As illustrated in Figure 2, the revised bathtub analogy incorporates several changes. The inlet pipe has been enlarged (making it larger than the drain) and valves have been added to both the inlet and drain pipes. Most importantly, control of the valves is interconnected (but this is not shown visually as it makes the drawing even more complicated). Changing the position of either the inlet or drain, results in a corresponding change in the other valve.

Figure 2. Revised Bathtub Analogy-Ventilation Controlled Burning Regime

This analogy provides a reasonable (but still overly simplified and thus somewhat inaccurate) representation of a ventilation controlled compartment fire when normal building openings (e.g., doors, windows) serve as ventilation openings.

As illustrated in Figure 2, opening the drain also results in an increase in flow from the (larger) inlet, which without intervention is likely to result in the tub overflowing. In a compartment fire, increasing ventilation to a when the fire is burning in a ventilation controlled regime, increases convective heat loss, but HRR will also increase, potentially resulting in flashover.

Resolving the Paradox

Resolution of the problems presented by the paradox involve recognition of what burning regime the fire is in (fuel or ventilation controlled), understanding the influence of the location and size of ventilation openings on convective heat loss, understanding the influence of increased air intake on HRR, and coordination of ventilation and fire control tactics. On the surface, this all sounds quite simple, but is considerably more complex in practice.

Feedback

I would like to thank my friend and colleague Lieutenant Chris Baird, Gresham Fire & Emergency Services and my wife Sue for serving as my sounding board as I worked through the process of revising the bathtub analogy. As always your feedback and suggestions will be greatly appreciated.

Ed Hartin, MS, EFO, MIFireE, CFO

References

Box, G.& Draper, N. (1987). Empirical Model-Building and Response Surfaces, San Francisco: Wiley & Sons.

Kennedy, P. & Kennedy, K. (2003). Flashover and fire analysis: A discussion of the practical use of flashover in fire investigation. Retrieved July 30, 2009 from http://www.kennedy-fire.com/Flashover.pdf

Just over a year ago I had the idea to develop a blog focused on compartment fire behavior and firefighting. A bit of work on the technology side and I made my introductory post on 8 August 2008. That month the CFBT-US web site had 2900 page views, this past July the page view count was in excess of 24,000 with 4400 unique readers. While this is not a huge readership in terms of the total number of firefighters in the world who have English as a language, it shows significant growth.

Accomplishments

At the start of this adventure, I set a goal to post twice weekly (Monday and Thursday mornings) and for the most part have managed to keep this schedule. Dominant themes have included:

• Reviews of books, training programs, magazine/journal articles, and conference presentations
• Case studies based on National Institute for Occupational Safety and Health (NIOSH) and agency reports on significant incidents, injuries, and fatalities
• An ongoing series of posts examining the B-SAHF (building, smoke, air track, heat, and flame) organizing scheme for fire behavior indicators and reading the fire
• B-SAHF video and photo based exercises in reading and interpreting B-SAHF indicators to predict likely fire behavior and the impact of tactical operations
• Examination of extreme fire behavior phenomena such as flashover, backdraft, smoke explosion, and flash fire with an emphasis on understanding the underlying causes and influence of tactical operations on fire dynamics
• Discussion of research on positive pressure ventilation and wind driven fires conducted by the National Institute for Standards and Technology
• Identification of the potential learning opportunity presented by systematic investigation of near miss, injury, and fatality incidents
• Discussion of the importance of deliberate practice and the concept of the need for 10,000 hours to master your craft

Hopefully you have found these posts useful in developing your understanding of compartment fire behavior or have motivated you to take action and share your knowledge of our profession with others. I have benefited greatly from the thought process and effort of writing on a regular and systematic basis.

As a reference, I have prepared a printer friendly Compartment Fire Behavior Blog Index in portable document format (PDF) which includes the date, title, URL, and brief synopsis of post content.

I Need Your Help

Your comments and feedback are important to making the Compartment Fire Behavior Blog better. If I write something that you do not agree with or think that a concept could be expressed more clearly, please comment or question!

The Way Forward

I am currently working on a loose editorial calendar to help guide my writing over the next year. Several important themes will continue:

• Case studies and lessons learned
• Reading the fire and B-SAHF exercises
• Practical fire dynamics
• Review of books, magazine/journal articles
• Fire control and tactical ventilation

If there are topics you think should be on the list, please provide your input as a comment on this post.

My next several posts will get back to study of the B-SAHF scheme with a look at Heat Indicators and continuing examination of flashover. As I have been looking back over the last year, I find that I have taken two distinctly different approaches to sequencing posts. Some topics have been addressed in successive posts (e.g., case studies and discussion of wind driven fires) and others have alternated between several different topics (e.g., B-SAHF and flashover). From my perspective, each has its advantages and disadvantages. If you have a preference or opinion, please let me know!

Thanks for your readership and participation,

Ed Hartin, MS, EFO, MIFireE, CFO

This post reviews articles on positive pressure ventilation written by Watch Manager Gary West of the Lancashire (UK) Fire and Rescue Service and Battalion Chief Kriss Garcia of the Salt Lake City Fire Department. Gary, Kriss, and I were recently in Australia for a meeting of the Institution of Fire Engineers (IFE) Compartment Firefighting Special Interest Group and to present at the 2009 International Firefighting Safety Conference hosted by IFE-Australia.

Gary and Kriss are both strong advocates of positive pressure ventilation (PPV) and its use to support fire attack (positive pressure attack (PPA)). In August 2008, Gary’s article Positive Thinking was published in Fire Risk Management Journal and October 2008, Kriss’s article The Power of Negative Thinking was published in FireRescue magazine. While the titles appear to be contradictory, both of my colleagues had a common theme; the importance of education and training to ensure safe and effective tactical ventilation on the fireground.

Common Elements

Gary and Kriss both emphasize the benefits of effective use of PPV while cautioning that education in practical fluid and fire dynamics and tactical ventilation concepts must be integrated with training in PPV/PPA tactics.

Positive Thinking

Gary provides an overview of the three phased approach to PPV training and implementation commonly used in the UK. This approach is designed around building understanding of key concepts and competence in tactical skills while minimizing risk.

Phase I-Post Fire Control PPV: In this phase, PPV is limited to clearing smoke after the fire has been controlled. In many respects this is the simplest and safest application of PPV.

Phase 2-Defensive PPV: In Phase 2, PPV is used during firefighting operations to clear smoke logged areas not involved in fire. This approach requires confinement of the fire using structural barriers (e.g., closing doors) and placement of hoselines. This tactical approach is less common in the United States, likely due to differences in construction. However, use of PPV to clear and then pressurize attached exposures can be an effective tactic in limiting smoke and fire spread.

Phase 3-Offensive PPV (PPA): In the third phase, PPV precedes fire attack and has a direct influence on fire behavior as well as clearing smoke from the entry path and uninvolved areas of the building.

Gary concludes with reinforcement of the importance of education and training prior to implementation and the criticality of ongoing training and development:

It must be understood that PPV is a tool that will save the lives of casualties, and also reduce the risk to firefighters, if used correctly. Initial training should cover all aspect of fan configurations, the different phases of PPV, and include an understanding of the way in which fire behaves generally [emphasis added], among other things.

However, it cannot be emphasized enough that, if used incorrectly, PPV is a potentially life-threatening and, as such, an ongoing training and development programme ought to be available to all users [emphasis added] (P. 49).

Critique of Positive Thinking

Gary provides a solid overview of the three phased approach to PPV training and implementation used in the UK and advocates for progression to Phase 3, positive pressure ventilation in support of fire attack. However, I take exception to two statements made in this article.

The first relates to the relationship between the size of inlet and exhaust opening. “It is widely understood that the size of the exhaust(s) must add up to less than the surface are of the inlet in order that positive pressure is achieved.” This is incorrect. As outlined in my previous post, Positive Pressure Ventilation: Inadequate Exhaust, the exhaust opening should be at least equal to the size of the inlet and preferably two to three times the area of the inlet opening.

The second statement relates to water application technique. “Students have a temptation to apply water using pulsing and gas-cooling techniques. However, it is not necessary in this mode of PPV [Phase 3]. While of less concern than inadequately sized exhaust openings, use of PPV does not necessarily negate the use of gas cooling. Depending on firefighters operating location and conditions encountered, cooling hot gases may still be necessary, particularly away from the path leading from inlet to outlet. Nozzle techniques and water application should be determined based on conditions, not the ventilation tactic being used. However, that said, Gary is correct that excess steam produced during attack in the fire compartment will be carried out the exhaust opening.

Negative Thinking

Kriss shares much of Gary’s perspective regarding the value of PPV and in particular its use to support fire attack (Phase 3/PPA).  However, the main focus of The Power of Negative Thinking is on the practical aspects of the fluid dynamics involved in PPV. Kris points out that the application of positive pressure at an inlet simply adds a slight amount of pressure to direct the flow of fire effluent from the inlet to the exhaust opening(s).

Kriss states that “When PPA goes wrong, it’s usually attributable to one or two conditions, or their combination. First, mistakes result from a lack of coordination and control on the fireground including a lack of department wide training and education in the use of PPA.

Second, problems may arise from insufficient or not forward exhaust. When products of combustion are emitted under pressure adhead of the attack crews, substantial exhaust is need (P. 39).

One of the most important points that Kriss raises in this article is the importance of reading conditions at the inlet opening (which he refers to as the “ventilation” opening). “If heavy smoke and/or fire is returning to the attack entrance [and] exhausting above the blower, do not enter“ (p. 39) [additional emphasis added].

This article also outlines initial considerations for using PPV in support of fire attack Phase 3/PPA). Of particular importance is training and educating members in theory, application, and precautions involved in the offensive use of PPV. In addition, departments training and implementing the use of this tactic must define when it will be used (e.g., fire conditions, building types).

Critique of Negative Thinking

This article raises important points in developing an understanding of why PPV works (e.g., pressure differences) and provides a straightforward explanation of its safe use in support of fire attack. However, Kriss indicates that the pressure generated by the blower is less than that created by the fire and expansion of steam due to fire control operations. This is inconsistent with the results of research conducted by NIST (Kerber & Madryzkowski, 2008; 2009). On a related note, Kriss’s assumptions regarding pressure generated by steam expansion are dependent on excessive or inappropriate water application during fire suppression operations (which is not necessarily a given).

Final Thoughts

In these two articles, Gary and Kriss raise a number of important points and focus attention on the importance of understanding not simply what and how, but why. Kriss’s emphasis on the importance of having a decision-making framework and assessing conditions to determine if PPV is working prior to entry is absolutely critical. Sometime in the next couple of months I will expand on the topic of command, control, and coordination of fire control and ventilation.

Ed Hartin, MS, EFO, MIFireE, CFO

References

West, G. (2008, August). Positive thinking. Fire Risk Management, 46-49.

Garcia, K. (2008, October) The power of negative thinking. Fire Rescue, 38-40. Retrieved May 24, 2009 from http://positivepressureattack.com/images/pdfs/PowerOfNegativeThinking.pdf

Kerber, S. & Madrzykowski, D. (2008).Evaluating positive pressure ventilation In large structures: school pressure and fire experiments. Retrieved May 17, 2009 from http://www.fire.nist.gov/bfrlpubs/fire08/PDF/f08016.pdf.

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.

As discussed in my last post, lack of an adequate exhaust opening is a common factor when use of positive pressure ventilation causes or increases the severity of extreme fire behavior. Unfortunately there has not been a great deal of research examining why this is the case. Part of the challenge in conducting a scientific investigation of this issue is the tremendous variability in building configuration and fire conditions. Control of these variables becomes more difficult as building configuration becomes more complex and multiple fire scenarios are considered. However, this does not preclude improvement of our understanding of this important issue.

Burning Regime

How an increase in ventilation influences fire behavior is largely (but not entirely) dependent on burning regime. If the fire is fuel controlled, fire development is dependent on the characteristics, configuration and amount of fuel. When a compartment fire becomes ventilation controlled, fire development is limited by the available oxygen. In the ventilation controlled burning regime, increased ventilation results in increased heat release rate. See my earlier post Fuel and Ventilation for additional information on burning regime.

In most ventilation controlled fires, the concentration of gas phase fuel (i.e., unburned pyrolyzate and flammable products of incomplete combustion) is not sufficient to present threat of backdraft. In these cases, increased ventilation will generally result in one of the following outcomes:

• Increase in heat release rate that is not sufficient to result in a rapid transition to a fully developed fire (flashover)
• Rapid increase in heat release rate that results in flashover and a fully developed fire.
• Intervention by firefighters to control the fire before ventilation induced flashover can occur.

If the concentration of gas phase fuel is sufficient to present threat of backdraft, increased ventilation may result in a backdraft…or not (depending on the extent of mixing of air and smoke, presence of an adequate ignition source, etc.).

The greater the extent to which the fire is ventilation controlled and the higher the concentration of gas phase fuel, the greater the potential for extreme fire behavior following increases in ventilation. Positive pressure ventilation influences this process in several ways, if effective, gas phase fuel is removed from the structure (often burning outside the exhaust opening). If PPV is not effective, increased air flow is accompanied with turbulence and resultant mixing of fuel an air which increases the probability of ignition and rapid fire progression. In addition, pressure applied at the outlet increases confinement which may increase the violence of extreme fire behavior phenomena such as backdraft.

Fluid Dynamics

Movement of fluids (liquids and gases) should be of significant interest to firefighters. Both fireground hydraulics and tactical ventilation require an understanding of fluid dynamics. In examining the influence of inadequate exhaust opening size on the effectiveness of PPV and potential for extreme fire behavior, I found some parallels with fireground hydraulics.

Laminar Flow: Smooth movement of a fluid in parallel layers with little disruption between the layers. The following video clip illustrates laminar flow in a pipe.

Turbulent Flow: Fluid flow characterized by eddies and vortexes disrupting smooth movement. The following video clip illustrates turbulent flow in a pipe.

A number of characteristics influence flow characteristics when a fluid moves through a conduit such as a pipe, hoseline, or even a building. These include fluid characteristics such as viscosity and density, the roughness of the conduit, restrictions to flow, and velocity of the fluid.

For example, friction loss in 1-1/2″ (38 mm) hose is higher than that in 1-3/4″ (45 mm) hose at the same flow rate. Why? Velocity must be higher to move the same flow rate through the smaller hose. This results in increased turbulence and resulting loss in pressure. If a discharge gate is partially closed, this obstructs the waterway, creating turbulence and increasing friction loss. As illustrated in this example, increased velocity and the presence of obstructions both increase turbulence. How does this apply to PPV?

The extent of turbulence as air and fire effluent (smoke and fire gases) move through a building is influenced by the configuration of the building (e.g., walls, doorways), obstructions (e.g., furniture), and velocity. Turbulence increases mixing of fire effluent and air. If the concentration of unburned pyrolizate and flammable products of incomplete combustion is high, turbulence increases the potential of a flammable mixture. In addition, increased oxygen concentration and air movement across surfaces can result in transition from surface to flaming combustion, providing a source of ignition for the flammable mixture of fire effluent and air.

Outlet/Inlet Ratio

When using natural ventilation, the size of the inlet opening(s) should be larger than the exhaust opening(s). However, with positive pressure ventilation this is reversed. When using PPV. exhaust opening(s) should be at least as large and preferably two to three times as large as the inlet opening as illustrated in Figure 1.

Figure 1. PPV Efficiency Curve

Note: Adapted from Fire Ventilation (Svensson, 2000, p. 71)

For a detailed examination of the physics and mathematical explanation of how the positive pressure ventilation efficiency curve is derived, see Stefan Svensson’s excellent text Fire Ventilation.

If the outlet size is adequate, a unidirectional ventilation flow from inlet to outlet is created. If opening size is inadequate, turbulence is increased as fire effluent and air seeks an exit path. If no opening is made or if the opening is extremely small, fire effluent may push back out the inlet opening.

Watch the following video clip and focus your attention on the exhaust opening on Side B (at approximately 0:19) and fire behavior indicators immediately after the blower is placed at the door on Side A and started (at approximately 3:00)

Find more videos like this on firevideo.net

Even though there was an exhaust opening, it was of inadequate size. While this fire was likely progressing towards a ventilation induced flashover due to the effects of natural horizontal ventilation, increased airflow and turbulence caused by ineffective PPV  likely was a contributing factor in the way that this extreme fire behavior phenomena occurred.

Important: Implementation of PPV after entry and before the fire has been located and controlled presents a significant risk to firefighters. Risk can be minimized by either using positive pressure attack (implementing PPV prior to entry) or locating and controlling the fire before implementing PPV.

Next Steps

In the Education vs. Training in Fire Space Control, Kris Garcia (2008) wrote that we need to increase our focus on ventilation education, rather than simply training on ventilation skills. Effective use of PPV to support fire attack or following fire control requires an understanding of fire and fluid dynamics as well as skill in creating openings and the placement and operation of blowers.

My next post will examine review Positive Thinking, an article by Watch Manager Gary West of the Lancashire Fire Rescue Service (UK) published in the August 2008 issue of Fire Risk Management. In this article, Gary provides an excellent overview of the approach to PPV training and implementation taken by the UK fire service.

References

Svensson, S. (2005). Fire ventilation. Karlstad, Sweden: Swedish Rescue Services Agency.

Garcia, K. (2008, September). Education vs. training in fire space sontrol. Fire Engineering. Retrieved May 21, 2009 from http://positivepressureattack.com/images/pdfs/EdVsTng-GarciaFESept08.pdf

West, G. (2008, August). Positive thinking. Fire Risk Management, 46-49.