Fire Pattern Persistence and Predictability on Interior Finish and Construction Materials During Pre and Post Flashover Compartment Fires.
R. Hopkins, G. Gorbett, P. Kennedy, 2007
Fire Science, Fire Patterns, Flashover, Full-room Involvement, Full-Scale Test Burn,
A series of eight full scale tests were conducted in identically constructed, finished and furnished compartments. In each of the tests with one exception all fires progressed to full room involvement. These test burns demonstrated fire pattern persistence and predictability during pre and post full room involvement fires. The full scale tests demonstrated that the fire patterns described in current literature are correct and when used properly can assist in the determination of the origin of a fire.
Abstract
Fire Patterns, as defined by NFPA-921 are the visible or measurable physical effects that remain after a fire. Fire Pattern analysis has been a key factor in the determination of the origin and cause of fires for the past 50 years. In 1985 the Advanced Fire Patterns Project was formed between the National Association of Fire Investigators (NAFI) and the Fire and Safety Engineering Technology Program, Eastern Kentucky University to complete research into the development of fire patterns on exposed surfaces. Since the formation of the project, considerable work has been undertaken to study fire growth and spread in both full scale and ¼ scale test burns. Much of the data generated has been utilized to supplement instruction in the area of Fire Pattern Analysis.
To date, more than seventy full-scale, half-scale, and quarter-scale burn tests have been completed at EKU as a result of the seminars sponsored by NAFI, EKU and later also co-sponsored by the National Fire Protection Association (NFPA). The research burns have enhanced the knowledge base of the fire investigation community.
Separate from the work done by the AFPRP, the National Institute of Standards and Technology, Center for Fire Research obtained funding from the United States Fire Administration to conduct full scale fire tests to study Burn Patterns. This research began in November 1994 with the final report “USFA Fire Burn Pattern Tests” issued in 1997. Included in the summary of results is the confirmation that “many of the concepts, investigative systems, dynamics of pattern production, and patterns analysis concepts put forward in the current, peer reviewed, standard text for fire pattern analysis in the profession, NFPA 921-1995, The Guide for Fire and Explosion Investigations were confirmed by the program’s testing.”
Another series of full scale fire tests were conducted as a result of funding provided by the National Institute of Justice, with a report “Full Scale Room Burn Pattern Study”, released in December 1997. Included in the section of the report, Discussion and Conclusion: “Significant differences in the condition and appearance of the burn rooms and furnishings were present between experiments with the same method of ignition. The differences consisted of the severity of burning, the locations of the patterns, and the types of patterns present. Overall, there was a lack of pattern consistency. As mentioned previously, ventilation effects are the likely cause of the pattern inconsistencies, and should be tightly controlled in future experiments.”
The purpose of this paper is to describe the results of the most recent full scale test burns that were conducted at Eastern Kentucky University and sponsored by the Advanced Fire Pattern Project. For the past 2 years a series of eight full scale tests were conducted in identically constructed, finished and furnished compartments. In each of the tests with one exception all fires progressed to full room involvement. Additionally, a full scale test was completed on a specially constructed and furnished room to assist in studying fire growth and spread and the resulting pattern formation in comparison to the fire patterns that were witnessed in a compartment of an actual compartment fire in which there had been a fatality.
These full scale test burns provided a considerable amount of data concerning fire pattern development and evolution during fire growth and spread.
As a result of the previous research conducted into the development of fire patterns, as well as the report recommendations of USFA and NIJ, the Advanced Fire Pattern Research Project (AFPRP) decided to conduct another series of tests. The next series of tests would be conducted in the same test facility with identical furniture for each series of two test burns. Factors, such as ventilation, would be controlled as much as possible. Each of the test burns would be instrumented with thermocouples and documented using 35mm, digital still and video photography.
Recent research into the development of fire patterns has shown that the primary mode behind fire pattern creation stems from the amount of heat flux on a materials surface. Therefore, the plume is the primary means of pattern production in the early stages of a fire. As the fire develops, a substantial upper layer begins to form and starts transferring heat to the wall and ceiling surfaces. This heat transfer can be regarded as relatively universal throughout the upper portions of the compartment, except at the plume interface. Obviously, at the interface of the plume the heat transferred will be greater and for a longer duration.
As the temperature in the upper layer increases and the duration of contact between the upper layer and the wall/ceiling surfaces increases, the heat flux on these surfaces reaches a critical threshold that begins damaging the material and creating patterns. Furthermore, the ceiling jet formed by the intersection of the plume will cause greater heat to be transferred first to the ceiling surface and later to the wall surfaces. The heat flux will be greater at the location where the ceiling jet passes over these surfaces and lessens as the velocity of the jet diminishes as it flows away from the centerline of the plume. In other words, the temperature of the affected surface is hottest near the plume centerline and becomes cooler as the distance from the centerline of the plume increases due to the cooling by heat losses to the ceiling. Thus, inflicting more damage and creating more distinct patterns at the centerline of the plume and lesser damage the further away from the centerline.
The ceiling jet and the gases from the upper layer begin to have a combined effect on the surfaces nearest the plume. As the compartment transitions through flashover and into full-room involvement, the upper layer descends to the floor and encompasses the entire volume of the compartment. Therefore, the walls, ceiling, and floor surfaces are now receiving almost identical heating or a similar magnitude of heat flux. Because of this, some fire investigators often regard the initial plume patterns as being destroyed or obscured. A major part of this research was to determine if the initial plume patterns persist past full-room involvement.
Specifically, these test burns demonstrated fire pattern persistence and predictability during pre and post full room involvement fires. The full scale tests demonstrated that the fire patterns described in current literature are correct and when used properly can assist in the determination of the origin of a fire.