Reading the Fire:
Building Factors Part 3
While I have not had much input (via Twitter or post comments), I have been working on the Building Factors map to include factors related to the surrounding environment and to revise fire protection systems, construction, fuel, size, and ventilation profile.
Previous versions of the fire behavior indicators (FBI) concept map considered wind effects as a component of air track (which it influences significantly), but did not consider other environmental influences on fire behavior. After considerable thought, I recognized that building factors (and to some extent all of the FBI) can be viewed like Matryoshka Dolls (nested Russian dolls) when used to think about a single compartment, the building, or the building in its surrounding environment.
Environmental factors include exposures (which fire can extend from or to), ambient weather conditions, and terrain. Weather and terrain likely deserve a bit of explanation. While these factors are recognized as major players in wildland fire behavior, their influence is often not as quickly recognized in the built environment. Wind is likely the greatest meteorological concern when dealing with compartment fires. As discussed in prior posts (Wind Driven Fires, NIST Wind Driven Fire Experiments: Establishing a Baseline, Evaluating Firefighting Tactics Under Wind Driven Conditions), wind driven fires present a significant threat to firefighters. However, while buildings are generally designed to minimize the impact of temperature, humidity, and precipitation on their occupants, these factors can influence fire behavior directly or indirectly. For example, combustible exterior surfaces (e.g., wood shingle or shake roofs) present an increased hazard if humidity is low and ambient temperature is high. The influence of terrain may not be quite as obvious. In some cases, terrain may influence wind effects and in others slope may result in differences in elevation on each side of the building. When unrecognized, this has been a factor in a number of firefighter fatalities due to the resulting air track and path of fire spread from lower, to upper floors. For example see NIOSH (1999) Death in the Line of Duty Report F99-21 and Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C. (NIST, 2000).
Fire Protection Systems
Fire suppression systems such as automatic sprinklers can obviously have a direct influence on fire development in a protected compartment. Similarly, fire detection may reduce the time between ignition and intervention by the fire department. However, prior versions of the FBI concept map did not include passive fire protection such as fire rated separations (other than generically as compartmentation).
Construction & Fuel
Prior versions of the FBI map linked Building to Contents and Construction. I have changed this to consider both contents and construction as fuel, while maintaining a link between building factors and construction as there are other facets of construction that can influence fire behavior. However, this area of the map remains a bit tentative (with more work to be done). Other changes to this part of the map include the addition of fire load density (kJ/m2) and increasing clarity of the concepts related to flow rate requirements for fire control.
The concept of size can be a bit confusing as it applies to individual compartments (habitable or void spaces), interconnected compartments, and the entire building. Refinements include the addition of void spaces and normal door position to the concept of compartmentation.
Thermal performance of potential openings has been added to ventilation profile, recognizing that single pane windows perform considerably different than multi-pane, energy efficient windows under fire conditions. In addition, a note was added to clarify that ventilation may be from compartment to compartment or from the building to the external environment.
Figure 1. Building Factors Concept Map v188.8.131.52
You can also download a larger, printer friendly version of the Building Factors Concept Map v184.108.40.206 (including notes made during development). Several colleagues who have had a look at this map observed that it is extremely complicated. While this is true, if you take the time to examine each of the factors and give some thought to the interrelated influences on fire behavior, it becomes a bit clearer. Remember that this is my representation of the concepts, yours will likely be a bit different! As always, feedback is greatly appreciated.
Subsequent posts will examine the rest of the B-SAHF (Building, Smoke, Air Track, Heat, & Flame) organizing scheme for fire behavior indicators.
Ed Hartin, MS, EFO, MIFireE, CFO
National Institute for Occupational Safety and Health (NIOSH) (1999) Death in the line of duty report F99-21. Retrieved July 2, 2009 from http://www.cdc.gov/niosh/fire/pdfs/face9921.pdf
National Insitute for Standards and Technology (NIST). Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington D.C. Retrieved July 2, 2009 from http://www.fire.nist.gov/CDPUBS/NISTIR_6510/6510c.pdf