House Protection

Most homes and other structures can be defended against wildfire if certain precautions have been taken beforehand. It boils down to an equation taking into account the heat load on the structure and the duration of the load. The higher the heat and the longer it lasts the more likely the structure will be lost. Anything that reduces the heat load by maintaining space between the structure and the fire will make a structure more likely to survive. Also, the longer the structure can tolerate high heat without bursting into flame the more likely it is to survive.

This is captured in Figure 14 (see print edition) copied from work being done at the U.S. Forest Service Fire Sciences Laboratory in Missoula, Montana. There, Dr. Cohen is developing a comprehensive Structure Ignition Assessment Model (SIAM) for use by fire agencies as well as homeowners. This is intended to be a more realistic and reliable guide than the simple models introduced earlier from Virginia and Utah.

Keep in mind that the most dangerous wildfire in Topanga is being driven by Santa Ana winds--which means that it is likely to pass over or around a structure within a few minutes--so exposure to heat may be severe, but of short duration. Exactly how it would affect any particular structure cannot be predicted, but this is a factor that needs to be considered.

For present purposes we will assume that brush has been cleared to local codes and that a minimum of a 30-foot defensible area immediately around the structure/home has been cleared. We will also assume that the roof is at least a Class A fire resistant roof and that vents have been protected. What can a homeowner or group of neighbors do to actively protect their homes?

A short list of feasible alternatives is:
1. Provide a source of water matched to the size of the structure(s) to be protected. The volume of water in gallons should be equal to or exceed the total volume of the structure to be protected expressed in cubic feet. This works for individual homes of normal home construction

2. Provide sufficient quantities of firefighting foam or gel

3. Provide sufficient hose to reach all parts of the structure(s)

4. Provide a pump of sufficient capacity

Sources of water for firefighting have to be provided by the homeowner. Unfortunately, for many reasons and over a long period Topanga has outgrown its piped water supply. We cannot be certain that in a major wildfire sufficient water at the needed pressure will be available everywhere in the Canyon.

A swimming pool is an excellent source of water for firefighting and is usually more than sufficient for the home it is attached to. For an individual home the solution is a floating pump which draws directly from the pool. Several manufacturers are available and have local dealers. The cost is in the range of $1,400-$3,000. Given the cost of replacing a home (or the sheer hassle of dealing with the aftermath even if the insurance company is cooperative) this does not seem an unreasonable figure.

Pumps and hose, however, require some maintenance and some training, both of which are continuing items. One cannot leave such equipment to gather dust for years at a time and expect it to function perfectly. Nor can one expect a person to operate such equipment in a real situation without periodic drills and practice.

Any reservoir of water will do--fish pond, water tanks required as a condition of building, or tanks purchased for the purpose of providing a firefighting reserve. I have two plastic tanks totalling about 1,300 gallons which I keep filled with winter runoff from my roof gutters.

Those 1,300 gallons are insufficient water for my house. They are sufficient when used in a foam or gel system to cover my house. Foam and gel are the latest additions to the homeowner's tools for self-defense. They work by capturing water in a relatively stable form that will cling to surfaces. When the heat from the fire arrives, it evaporates the water which keeps the underlying structure relatively cool. If other defensive measures have been effective and the fire moves on quickly enough, then the foam or gel will have done its job.

The tactics in case of the use of foam/gel are to foam the structure some time before the fire-front arrives. Just how long before is a matter of judgment and how long the foam/gel can be expected to remain effective. The homeowner can then go to a safe place to wait for the fire to pass. If this safe area is close to the home, the owner can return to deal with the fire's aftermath--smoldering embers, spot fires or whatever.

Houses are lost to these causes after surviving the main fire if no one is around to catch them. Perhaps the major advantage of the foams/gels is that an owner can take protective action, retreat to a safe place and yet return soon enough to deal with the embers and small fires. Using water alone, the owner has to stay throughout to keep the structure cool and wet until the fire-front has passed. Of course, the users of foams/gels must have prepared this safe place. The safe place, however, may be the house itself.

The maintenance and training requirements for foam/gel users are just as strict as for the users of water systems.

We have catalogs of hoses and pumps. How many and what kind of each are technical questions. The requirements for these are similar for water-only and foam/gel systems.

An alternative foam system uses pressurized nitrogen gas to lay foam over the whole house through a system of pre-installed pipes. One advantage of the system is that it can be triggered automatically. The other systems require that someone be present to operate them. These are large, relatively expensive systems that only experts can design and install. They minimize the burden on the homeowner and will operate even if the house is unattended.

A potential disadvantage is that these are one-time use systems that have to be maintained and reloaded after each use. It does sometimes happen that a change in wind speed or direction will cause a fire to reverse itself or come around to a previously burned area a second time. If there is sufficient unburned fuel to sustain the fire, or if embers are tossed up by the wind, a second threat could be created.

However, as we said, a wildfire is a complex phenomenon. Many strange and unusual things will occur in the course of any significant fire and most of them cannot be foreseen. Which of these general kinds of systems are a best fit for an particular home, structure or neighborhood is a function of particular characteristics.

A list, far from comprehensive, of dealers in these systems is in Appendix A.