"Shelter in place," aka SIP, is incendiary to those who absolutely reject the idea of anyone staying home while a wildfire passes by. These individuals are attacking the emphasis on SIP and the de-emphasis of evacuation in the Stonegate Merriam Mountains project and the recently published San Diego County Department of Planning and Land Use fire protection plan guidelines. Their attacks produce lots of heat but shed little light on the issues at hand. I'd like to try to illuminate the topics of injury from flame and smoke, SIP, evacuation and fire protection with some basic facts and logic.

Flames radiate heat along a line of sight. Thus, if you cannot see the flames, the thermal radiation cannot see or burn you. The wall of your house blocks the line of sight. The farther the house is from the flames, the less the radiated heat that strikes it; if the distance is doubled, the radiated heat drops by about 75 percent, tripled, about 90 percent. These facts dictate the basic necessary conditions for SIP -- a fire-resistive house surrounded by defensible space -- and it works. The radiant heating lasts for only the few minutes it takes for the flame front to pass by. The Australians have incorporated additional critical human factors, and SIP is governmental policy Down Under. San Diego County has based their version of SIP on fire-resistive construction and defensible space, but has ignored the human factors.

Embers can continue for hours and need to be extinguished if they strike the house. That is why the Australians call their version of SIP "Stay and Defend or Go Early," or SOGE. The house defends the occupant from radiant heat, and the occupant defends the house from embers. This symbiotic relationship requires a willing, healthy occupant to Stay and Defend. The young, old, ill, unwilling and all others at-risk must be evacuated in a planned fashion. SOGE incorporates advance planning, education and cooperation of all stakeholders (government, firefighters and citizens). That is the policy in Australia.

There are approximately 3,000 U.S. fire deaths annually. About 80 percent are attributed to smoke inhalation in structure fires. About 30 -- i.e., only 1 percent of all U.S. fire deaths -- occur in wildfires. Wildland firefighters are regularly exposed to wildfire smoke but do not regularly die from smoke inhalation. The No. 1 cause (almost 50 percent) of U.S. firefighter deaths is cardiac arrest or heart attack. Australian SIP occupants do not regularly die from smoke inhalation. Autopsies on wildfire victims, including those who perished fleeing the 2003 Cedar fire, only rarely invoke smoke as the cause of death. Wildfire smoke per se is not a valid argument against SIP for healthy occupants.

In contrast to Australia, the San Diego County Department of Planning and Land Use calls SIP a "last resort" measure if adequate evacuation routes cannot be built. This is the antithesis of a planned Go Early policy, and imposes SIP on an at-risk population. SIP is apparently gaining traction in the U.S. wildland firefighting community. Stay and Defend or Go Early is a workable policy. However, the San Diego version of SIP as defined by the planning and land use department is incomplete and unsatisfactory.

There are established techniques for planning community evacuation strategies considering population size and distribution, roadway layout, trigger zones, etc. The fire protection codes in San Diego County ignore all of this, requiring only a perfunctory number of roads in and out, regardless the size of the community. The fallacy of this is obvious from a simple example. If 5,000 vehicles are to be evacuated from a community of 2,500 homes at 800 vehicles per hour for each lane of traffic, and there are four outbound lanes, then it would take 5,000/3,200, or a minimum of 1.5 hours to evacuate. A more realistic minimum evacuation time would be under 30 minutes, requiring increasing the number of outbound lanes to at least 12, or reducing the number of homes to at most 800, or something in between. Thus, evacuation planning may influence the very design of a community, and should be an integral part of the Department of Planning and Land Use process.

Before deployment, SIP must be integrated with a preplanned evacuation strategy for at least the subpopulation at risk. The balance (0 percent to 100 percent) between SIP and evacuation must be calculated for each given community.

The present San Diego County version of SIP is devoid of critical human factors. The present San Diego County version of Shelter in Place needs considerably more work before it can be considered safe and effective.

Hidden Meadows resident Peter A. Orner, M.D., Ph.D. is a physician, engineer and a consultant and expert in the biomechanics of injury causation. Dr. Orner is a clinical professor on the teaching faculty in the Department of Medicine at UC San Diego, and a former professor of mechanical engineering. Dr. Orner is the president of the board of directors of the Deer Springs Fire Protection District; the opinions expressed here are his own and not on behalf of the board.