There are many possible ignition sources for exterior fire exposures in an Urban-Wildland Interface fire. There are often plants adjacent to the structure, and sometimes stacks of firewood or other combustible materials. These materials can be ignited by flying embers (firebrands). On patios and decks one finds plastic or wood furniture that can also ignite from firebrands produced by the fire. All of these items can be considered ignition sources to expose the building or the deck to a substantial flame source for some period of time. However, one category of possible ignition sources that has been studied extensively can be categorized as "Trash Bags and Trash Containers," also commonly found adjacent to buildings and decks. Babrauskas¹ gives the heat release rate (HRR) for typical trash-bag fires as shown in Fig. 1, which is derived from Lee².

Figure 1. Heat release rates for trash bags.

For our deck and wall/windows tests we have chosen the following HRR:

• Decks 80 kW (equivalent to about 1 kg of paper trash); 3 and 8 minutes.
• Walls/windows 150 and 300 kW (equivalent to about 2 and 4 kg of paper trash); 3 minutes

These are very conservative exposures since the UWI fuel loading near structures is often much greater  than these values.

---

1. Babrauskas, V., Burning Rates, Section 2, Chapter 1 in SFPE Handbook of Fire Protection Engineering, 2nd edition, (P.J. DiNenno, editor-in-chief), Society of Fire Protection Engineers, Boston (1995), pp 2-1 to 2-15.

2. Lee, B. T., Heat Release Rate Characteristics of Some Combustible Fuel Sources in Nuclear Power Plants, NBSIR 85-3195, National Bureau of Standards, Washington (1985).

---