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NIST Simulator Provides New Picture of LODDs

Written by:
Ed Comeau
USA 1-413-323-6002 (tel)
1-413-323-5295 (fax)
e-mail to:ecomeau@writer-tech.com
© 2000 writer-tech.com, llc
This article first appeared at firefighting.com



The investigation into the causes of a line-of-duty death is one of the most painful and difficult tasks a fire department will ever have to face. Determining the exact sequence of events and contributing factors that led to the death of a firefighter can take months. Even then, it’s an uncertain science—a blending of witness testimony, evidence collected at the fire scene and educated “best guesses” about what happened.

But an exciting new tool is helping departments hit by LODDs see a whole new picture of these incidents using the science of computer modeling. Given specific data from the scene, it creates three-dimensional and animated pictures of what may have happened at LODD incidents based on the laws of physics.

Developed by the Building and Fire Research Laboratory of the National Institute of Standards and Technology (NIST) Fire Safety Engineering Division, it’s called the Fire Dynamics Simulator (FDS). The FDS simulator is already offering valuable new insight into the sequence of events that led to recent LODDs, but this is only the beginning. NIST researchers hope the simulator will lead to realistic computer-based training to better prepare firefighters for the hazards they face.

NIST has been using computer modeling for years, but only recently has it reached a point where the simulator can be run on a desktop computer. The latest version has a feature called “Smokeview” that translates physical data into animation and 3-D graphics—making it much easier for the average fire investigator to use.

Dan Madrzykowski is leader of large fire research for the Building Fire Research Laboratory at NIST. “We noticed that a picture is worth a thousand words (in computer modeling). With the Smokeview aspect, instead of graphs and numbers, we can now generate a picture that will give a time and history,” he says.

NIST’s first opportunity to use FDS to help a department piece together events leading to LODD occurred last spring, when it assisted the District of Columbia Fire and Emergency Services Department (DCFEMS) in its investigation of the Cherry Road Fire of May 30, 1999. The fire took the lives of two Washington firefighters and left investigators with several baffling questions. DCFEMS contacted NIST and asked if they would be able to assist.
Since the fire occurred close to NIST’s facilities in Maryland, NIST was able to respond to the scene, evaluate the structure where the fire occurred and take the precise measurements that the computer model would need.

According to Captain Tim Gearheart, the safety officer for DCFEMS, “The only information we had to provide to NIST was the basic timeline.” They did not provide them with any timeline information regarding fire ground operations, because one of the questions they hoped the simulation would answer was specifically when did ventilation occur and what role did it play in the incident.
“As a committee, we were trying to explore every avenue and not leave any stone unturned,” says Gearheart.

SEE IT ONLINE

The result of the collaboration between NIST and DCFEMS is a simulation of the Cherry Road incident that is contained on a CD ROM. It can also be seen on the web at http://fire.nist.gov/6510.

Robert Duval, senior fire investigator for the National Fire Protection Association, assisted in the reconstruction and says FDS helped investigators take a large step forward. “The incident was confusing because of the timeline and the type of injuries. The committee was having difficulty visualizing what had happened,” Duval says. “Was it a backdraft or a flashover?”

By translating the physical data into graphics, the information suddenly takes on a new dimension that clarifies the significant contributing factors in a way that was not previously possible. “The CD shows the heat flow and the temperatures, by transposing that with the location of the firefighters…it cleared it all up and helped make sense of their injuries.”

One of the perplexing questions involved the timing of when a door was opened and how it affected the fire. By using the model, the investigators were able to run different scenarios and see what the computer would predict as the outcome. They could then match what the simulator showed with information they had collected from the scene and from witnesses.

“What we looked at in DC was ‘What would happen if we took this window out a little earlier, what would happened if we had ventilated on the roof, or opened this particular door,’” says Frank Washentiz, safety and occupational health specialist with the National Institute of Occupational Safety and Health (NIOSH). Washenitz works in NIOSH’s Division of Safety Research, and is responsible for conducting firefighter fatality investigations across the country. “This tool gives us an opportunity to answer a lot of questions that we could not ask without the fire model,” he says. (NIOSH also participated in the investigation of this incident and published a report on its findings.)

PUTTING IT TOGETHER

How is a simulation put together?

One of the first steps is to obtain a good set of measurements of the building where the fire occurred. This includes the room dimensions, the location of openings such as doors and windows, stairways and other features.

Next, it is critically important to identify what is referred to as the fuel package or fuel load that was involved in the fire, the total quantity of combustible contents of the space. NIST’s simulator is plugged into a database of the heat release rates of different types of furniture and furnishings, expressed as British Thermal Units (BTUs) or Kilowatts (kW) per second. The model divides the space involved in the fire into thousands of “cells.” In the DC simulations, the cells measured 8 inches by 8 inches by 4 inches high.
Once the physical data is entered into the computer, it is time to run the simulation. The computer will model the conditions for each cell, and then combine all of them together to provide the user with an overall prediction of the fire.

On a desktop computer with a 600 MHz processor it takes about 20 hours to run a single simulation, according to Madrzykowski. “That’s using 76,000 cells. If you increase the number of cells, you increase the computational size.”

So what did the Cherry Hill simulation show?
The fire occurred in a two-story townhouse, with a basement that was accessible from the exterior. Shortly after midnight, the occupants on the second floor were wakened when a smoke detector activated. They went down to the first floor and exited the building through the front door, leaving it open.

When firefighters arrived on the scene, they reported that heavy smoke was coming out of the open front door. Crews made entry, and removed a front window on the first floor from the interior to provide ventilation. Crews also removed windows on the second floor, front side.

Within approximately two minutes, another crew opened the sliding glass door on the basement and made entry. Within a short period, there was a rapid buildup of heat inside of the building. Firefighters on the first floor were able to escape, as were the firefighters in the basement. According to Madrzykowski, the firefighters in the basement reported that they saw a “tunnel” in the smoke that gave them a clear avenue of escape out the sliding glass door through which they had entered.

However, there were three firefighters operating inside of the building on the first floor near the stairway to the basement were trapped by the rapid heat buildup. Two firefighters were killed, while the third one, who was located in between the other two, suffered severe burns.

A puzzling aspect to the fire, reports Madrzykowski, was the extremely rapid heat buildup. “There were two experienced teams, with two charged hoselines. How come no one used a hoseline to defend themselves?” In addition, it was difficult to explain why it appeared that the middle fire fighter suffered severe burns, while the outer two were killed in the fire. One of the fatalities was burned in a directional fashion up the front of his body, while the other fire fighter was burned uniformly all over his body. What would account for the difference in burn patterns?

The fire had started in the basement. The NIST report described the following damage:

“The post fire investigation determined that the fire started near an electrical fixture in the ceiling of the basement. The basement had severe fire damage throughout, indicating a well-mixed, post-flashover fire environment. The stairway from the basement to the first floor also showed signs of flame impingement on the ceiling and walls. The door at the top of the basement stairs was open during the fire and had been partially burned away. The basement stairway opened into the living room on the first floor. The living room had significant deposits of soot throughout, with limited thermal damage. Most of the paper on the gypsum board walls and ceiling remained intact and sofas in the room only showed signs of pyrolization or limited burning on the upper portions of the back cushions and top surfaces of the seat cushions. Areas in the living room away from the basement door opening had less thermal damage.”
This unusual scenario puzzled the investigators from DCFEMS. By using the FDS, they were able to replicate the conditions that the firefighters were encountering and determine what the theoretical temperatures were inside of the building. According to the NIST summary…

" …the venting of the sliding glass doors in the basement increased the heat release rate of the fire very rapidly. The FDS calculation indicates that the opening of the basement sliding glass doors provided outside air (oxygen) to a pre-heated, under-ventilated fire compartment, which then developed into a post-flashover fire within 60 s. The fire filling the basement forced high temperature gases (approximately 820 °C (1500 °F)) up the basement stairwell at velocities in excess of 8 m/s (18 mph). The high velocity gas stream flowed into a pre-heated, oxygen depleted first floor living room. The FDS predictions show the hot gas flow moving across the living room ceiling and banking down the back wall of the townhouse. Between the doorway to the basement and the sofa on the back wall of the townhouse, the temperatures from approximately 0.5 m (1.6 ft) above the floor, to floor level are in the range of 180 °C to 260 °C (350 °F to 500 °F). These thermal conditions developed within seconds of the rapid fire growth in the basement."

The model showed that superheated gases moved up the stairs at approximately 18 miles per hour. This townhouse was only 33 feet deep, which meant that the gases moved through the townhouse in less than two seconds. One firefighter was in the direct path of this fast-moving body of super-heated air.

Another fire fighter was found near a wall. Based on the simulations, investigators believe that when the heat came blasting up the stairway, it encountered the wall, which served as a barrier and caused the heat to immediately move downward to where the firefighter was located.

As to why other firefighters were able to escape with only minor burns, Madrzykowski likened the interior conditions to that of a hair dryer. “The basement door acted as a high-velocity nozzle, but if you were off to the side, you were not in the direct path of the hot gas. Like a hairdryer, if you place your finger in front of it, your finger is hot, but if you move your finger an inch or two to the side, you’ll feel no heat.” This is why firefighters that were within just a few feet of the victims were able to feel the heat, yet still survive.

While the current model provides invaluable assistance, it has limitations, concedes Madrzykowski. It takes a certain level of expertise and knowledge, as well as a high-end PC to run the FDS. But as NIST continues to refine and further develop the program, Madrzykowski is hoping that they will be able to provide a tool that any firefighter can use on a desktop PC.

Another limiting factor (in the model) is the materials database. Not every material involved in a fire scene has been input into the materials database. NIST is continuing to input that data into the model.

“The science is fairly young,” he continues, “but a lot of progress has been made in the past generation. However, there has not been a lot of technology transfer…it needs to get out to the fire service.”
It’s not yet available to assist in every LODD, but the FDS simulator is being used to assist in investigations of a high-rise fire in New York City that killed three firefighters and a lightweight wood-truss roof structure fire at a fast-food restaurant in Houston that killed two firefighters.

TRAINING APPLICATIONS

Investigating these real-world LODDS in a variety of different scenarios is helping NIST to lay the foundation for training applications in the future. Madrzykowski hopes the FDS will soon evolve into a tool that any firefighter can use on a desktop PC.
The long-range goal is to develop a desktop simulator that can be made available to fire departments across the nation. Unlike other “games,” this one will be based on real-incidents and will abide by the laws of physics.

“Its value is to use it as a training tool,” he says. “The one thing that we hear from firefighters is that they are getting less and less on-the-job live-fire training because there are fewer fires and fewer training opportunities.”

Gearheart reinforced this point. “If NIST continues to get the funding they need to make it user-friendly…they are working in that direction, they just haven’t gotten to it yet. We hope that this incident helps to push it in that direction. As a training tool, it would be invaluable.”

COMMERCIAL APPLICATIONS

With the sponsorship of the U.S. Fire Administration, NIST is inputting data on the thermal properties of various materials used in firefighter turnout gear into FDS. Once that data in incorporated into the model, it can be used to assess the effectiveness of firefighter PPE.

“You will be able to assemble an ensemble using various materials such as Nomex or PBI, and then place this ‘target’ inside of the scenario,” says Madrzykowski. The user will then be able to evaluate the impact upon a firefighter when opening a particular window or door at a given time in the fire changes the environment. Madrzykowski is hoping that this will be available within several months.

Other plans include incorporating the physical properties of various hose streams into the FDS model, enabling users to evaluate the effectiveness of straight-stream versus fog nozzles, or see what impact compressed air foam might have on fire. “This is at least five years away,” says Madrzykowski.

One day in the not too distant future, he says, “The firefighter will be able to draw on a catalog of situations and see the impact of specific actions—like opening a door or ventilating the roof. “This will allow the user to see the impact in real time on various scenarios. By doing this on the desktop, it will hopefully become an ingrained response on the fireground when they are faced with a similar situation.”

FDS may facilitate better communications with firefighters as well. By using its animations, trainers may be able to demonstrate the concepts of heat flow and the other conditions encountered during firefighting that could only be previously demonstrated by equations and charts and graphs--not the most user-friendly method.

Madrzykowski notes this improved communication goes both ways. Scientists and engineers involved with FDS development are learning more from firefighters about the “real world” of firefighting than they ever could from inside a lab.

Copies of the FDS CD Rom of the Cherry Road Simulation can be obtained by contacting Madrzykowski at madrzy@nist.gov with your name and address.

You can download the full report on the Cherry Road simulation by clicking on this link:  http://fire.nist.gov/6510/

You can also contact NIST for more information regarding Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C., May 30, 1999 (Reference NISTIR 6510).



 
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