Controlling the Hazard
One of the major hazards presented by ventilation controlled fires is the potential for rapid fire progress when ventilation is increased as firefighters make entry for fire control and search operations. Recognition of this hazard is only the first step in reducing the risk of firefighting operations. Extinguishing the fire reduces the threat to both firefighters and the buildings occupants. However, this generally requires entering the building and locating the fire. When hot smoke is overhead, this is a high risk operation. Two basic strategies are used to control the risk presented by operating below hot, fuel rich smoke. Cooling the hot gas layer to prevent ignition and ventilation to remove the smoke from the compartment or building.
Subsequent articles will examine key fire behavior indicators related to potential for extreme fire behavior and the use of gas cooling and ventilation to control the fire environment and increase firefighter and occupant safety.
Study and Discussion Questions Reading about fire behavior is considerably different than experiencing it first hand. Resist the temptation to brush off basic concepts as too simple or elementary or more detailed explanations as too complex. Making a connection between theory and your own experience or the experiences of others is an effective way to learn. Use these questions to focus your thinking on how basic fire behavior theory connects with incidents that you or other members of your crew have responded to.
2. What has to happen for the fire to ignite fuel rich smoke that is above the upper flammable limit (lots of fuel and not enough oxygen)? How can this occur during firefighting operations?
At your next fire, take a few minutes after the fire has been extinguished to examine the building and its contents. Is evidence of pyrolysis present (look for melted plastic, and partially charred materials)? What smoke conditions did you encounter upon making entry? Do you think that excess (unburned) pyrolizate was present in the hot smoke layer? How did fire behavior change after you made entry or initiated ventilation? Why or why not?
- International Fire Service Training Association. (1998). Essentials of Firefighting (4th ed). Stillwater OK: Fire Protection Publications
- Karlsson, B. & Quintiere, J.G. (2000). Enclosure fire dynamics. Boca Raton, FL: CRC Press.
- Drysdale, D. (2000). An introduction to fire dynamics. Chichester, England: John Wiley & Sons.
- Grimwood, P., Hartin, E., McDonough, J., & Raffel, S. (2005). 3D firefighting: Training , techniques, and tactics. Stillwater, OK: Fire Protection Publications.