Radiant heat from the flames may become hot enough to ignite combustible materials before the flames themselves impinge on your house. That is why exposed wood is given fire resistive ratings based on thickness. A 6"x6" post will take longer to burn through and collapse than a 4"x4". If your house has wooden siding or exposed wooden structural members, this section is for you.

Air is a good insulator, thus the universal urging in the literature for owners to maintain at least a 30-foot ring of clear space around their homes. If the wind is not too high, or the surrounding brush not too dense, this cleared space alone could go a long way toward protecting your home--always expecting that the roof will be a Class A fire resistant one.

Most material dealing with this cleared or defensible space advocates banning plantings or trees. That may be too categorical. The key is to ensure that whatever is in that space cannot support flames long enough to impinge on the structure directly or, viewed another way, that the burning of anything in that space will not generate enough heat to ignite the structure.

Isolated trees, or hedges and plantings kept well trimmed, might still fit the bill, but always with the proviso that flames from vegetation inside that space cannot reach the structure itself.

There is good evidence from large fires that structures with a 30-foot cleared space have much higher chances of survival even without any help from owners or firefighters. Figure 10 [in the print edition] shows that while 40% of dwellings with brush immediately adjacent were destroyed, the percentage fell to less than 5% if brush were kept at least 30 feet away.

Figure 14 [in the print edition] makes rather a worst case because it assumes a fire probably larger than most we would have to deal with-a flame-front some 60' high by 150' long (20x50 meters). The simulations we sponsored suggest flame heights in Topanga might seldom reach such heights or solid widths. We can't say what they will be, although the aim of Dr. Cohen's work is to devise a model that can be applied to individual cases. In the meanwhile, note that the reason the curve representing ignition time rises so steeply is that air--space--is a good heat insulator.

Most new homes in Topanga are being built with stucco walls. This is certainly safer in the event of a fire, but it is not entirely sufficient. Remember that wooden beams supporting decks and roof overhangs are vulnerable, and if ignited could carry fire through the wall into the house itself. Even stucco is no defense against hot flames directly up against the wall so that heat ignites what may be behind the stucco. The flame itself may crack the stucco and penetrate the wall.

For wood siding there are fire retardant treatments that can be pressure-sprayed onto existing wooden structures. Much is claimed for these, but their true effectiveness and how long the treatments remain effective are not known. For structures such as these the solutions are good brush clearing and vegetation control together with active firefighting methods.

These methods involve a pump and independent power supply, hoses and independent water supply. A gas-powered pump and a sufficient water supply would permit a homeowner to defend his home, especially if brush clearing had been well done. Today, technology has improved on plain water. Various configurations of foam and gel additives are available that permit more latitude in the time when such treatments could be applied and greatly improve the firefighting effectiveness of plain water. More details about these systems are given below in the section "If You Stay"