Se 375 The question a: to the pre-conditions for fire storm is rot so clear because we dont really know what the dynarrics of a fire storm are. EISENBUD: Yeo. AYRES: Phere s a lot of argument over whether fire storms occur in forest fires, for exa.rple, Some fire service people sey yes and others say no, I's by no means a well-understood phenomenon, but as regards your main yvoint, which ‘» that cities would support conflaprations, it doesa't matter a great deal whether it's a fire siorm or a ctonflapration, EISENBUD: Yes. I don't see why this is the point, AYRES: One other point. You said something avout lenition our to twenty miles, This, of course, is very much a function of the weather, [think at 10 mepatons you get about twenty-two miles as the maximum rangeof ignition onan ultra clear day, if my memory is correct, But that’s a rare occasion, It does not appls to a yrouad burst. Ground bursts are not really so good at igmiting fires. [hn average weather, you have a lot of cloud cever, and of course about a fifth of the time in the eastern part of the country and in the upper Midwest there is actually rain or drizzle, [n such conditions the radius of thermal ignition is quite smalland, of course, it tends to be nonlinear with the weather conditions, So part of the time, cerhaps a fifth af the time, you would get fires ignited over a lara range lke twenty miles, A cood part of the time you would get fire. ignited out to, say, ten miles, and another part of the time vot much at all would happen, Further, let me adda remark which is somewhat conjectural based on experience with forest fires—and we don't have enough experience with city fires to really be very sure. The Forest Service has four categories of conditions, The worst category rs a condition where the fire is uacontrolNable. This has to do with the Cryness or the weather, the very low humidity, high winds and, in general, it requires something like ten days of drought before the fire. A cortain number cf fires occur inalltimes Buta great majority of che fire Camane that’s done by such fires is dove by fires which are synited during uncontrollable-type dry weather, DUNHAM: AYRES: One plus, two plus, three plus, four plus. At the other extreme, of course, there is che kind cf Gio. wre oa SESSION Vil