The Effects on the Atmosphere of a Major Nuclear Exchange (1985) / Chapter Skim
Currently Skimming:
5 Fires
5 Fires
Pages 36-106
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 36... ...
It is clear that nuclear explosions can ignite large-scale fires (Broido, 1960. In addition, it has been estimated that the smoke emissions from nuclear-initiated fires could produce major atmospheric perturbations (Lewis, 1979; Crutzen and Birks, 1982; Turco et al., 1983a,b)
|
From page 37... ...
7. Combine the foregoing information to estimate the total quantity and optical characteristics of nuclear war smoke emissions.
|
From page 38... ...
bYf is the effective ignition yield in megatons, An is the average ignition area per megaton, my is the burden of combustibles per unit area, fb is the fraction of the combustibles burned, and ~ is the net smoke emission factor per unit of fuel, assuming in the case of urban fires that 50 percent of the smoke is promptly scavenged and removed from the plumes mainly as black rain. n CThe smoke consists of 20 percent graphitic carbon (soot)
|
From page 39... ...
, wartime city fires initiated by incendiary and nuclear bombing, massive wildfires and forest fires, and field experiments with large-scale fuel beds (Carrier et al., 1982~. Although few of these experiences are directly applicable to the nuclear war problem, all contribute to a general understanding of the properties and behavior of large-scale fires.
|
From page 40... ...
By contrast, most nuclear forest fires would probably be of type II. Historical fires are characterized by a limited number of ignition points, perhaps one ignition for each 50 to 500 km2 burned (Ayers, 1965~.
|
From page 41... ...
However, these conditions are still controversial, as they have never been tested on an appropriate scale. Moreover, in view of the atmospheric effects being considered here, it is not clear that firestorms and very intense mass fires need to be differentiated, except perhaps to refine the estimation of smoke injection altitudes (see below}.
|
From page 42... ...
For a 1-Mt low air burst, Figure 5.1 shows the thermal fluences (in calories per square centimeter incident on a surface normal to the line-of-sight through the burst point) as a function of distance from ground zero, and for various atmospheric Risibilities.
|
From page 43... ...
At a specific thermal fluence, small nuclear explosions are generally more efficient at igniting fires than large explosions because the thermal pulse has a shorter duration and larger peak intensity (in addition, there is a lower probability of significant atmospheric attenuation over the shorter ranges involved)
|
From page 44... ...
New bond typing paper White Ignites24b 30b 50b Cotton rags Black Ignites10 15 20 Rayon rags Black Ignites9 14 21 Cotton str ing Gray IgnitesLob 15b 21 b scrubbing mop (used) Cotton string Cream Igniteslob lob 26b scrubbing mop (weathered)
|
From page 45... ...
45 TABLE 5.2 (continued) Radiation Explosurea (cal/cm2 ~ Effect on 35 1.4 20 Material Color Material kt Mt Mt Construction Materials Roll roofing, mineral surface Ignites c >34 >116 Roll roofing, smooth Ignites _ c 3077 surface Plywood, Douglas fir Flaming 9 1620 during exposure Rubber, pale latex Ignites 50 80110 Rubber, black Ignites 10 2025 Other Materials ~ Aluminum aircraft Blisters 15 3040 skin (0.020 in.
|
From page 46... ...
Urban Ignition Some evidence that nuclear explosions are unique in their ability to ignite mass fires is offered by the Hiroshima and Nagasaki experiences. One crude estimate of the average energy release rate places the Hiroshima fire among the least intense of the mass fires of World War II (Martin, 1974~.
|
From page 47... ...
Factors Inhibiting Mass Fires Blast wave extinguishes many fires started by thermal radiation. Blast covers flammable materials with nonflammable debris.
|
From page 48... ...
It is expected that a large fraction of the combustibles in the rubblized zone would eventually burn, possibly with an exaggerated smoke emission confined to lower altitudes. If an effective firefighting effort could be mounted, many of the initial urban fires might be extinguished and fire spread substantially limited in the lower-overpressure regions (Kanury, 1976; FEMA, 1982~.
|
From page 49... ...
Nuclear forest fires would not resemble most forest fires of the past. It is conceivable, although uncertain, that, because of the simultaneous ignition over a large area and the fanning action of the afterwinds, some of the nuclear forest fires could develop into intense firestorms with towering smoke plumes.
|
From page 50... ...
Accurate flammability statistics are not available for the Soviet Union, but similar fire conditions are likely to prevail at the same times of the year (e.g., Shostakovitch, 1925~. The potential for fire spread in wildlands is illustrated by U.S.
|
From page 51... ...
cities in the NATO and Warsaw Pact countries is roughly 10 percent of the total urbanized area, or about 50,000 km2. These central urban zones, in which industrial/economic targets are concentrated, and near which significant military targets are often located, are likely to be hit by (e.g.,
|
From page 52... ...
nuclear explosions, are heavily loaded with combustibles, and are expected to burn vigorously. Considering the typical design of cities, with most facilities and activities concentrated at the center, it appears that less than 10 percent of the total urban area may hold 50 percent or more of the total urban combustible material.
|
From page 53... ...
Because of the potentially unique character of nuclear forest fires, a larger quantity of fuel might be consumed, as noted earlier. Nevertheless, it is assumed here that 0.4 g/cm2 of fuel would be burned in nuclear forest fires, which is typical of many natural forest fires (Wright and Bailey, 1982; Crutzen et al., 1984~.
|
From page 54... ...
Factors that could increase the potential fire damage include the following: 1. Confinement of the heaviest combustible loadings within the areas most likely to suffer multiple detonations, i.e., co-location of flammable materials and key urban and industrial targets.
|
From page 55... ...
Tur co, private communication, 1984; Broyles, 1984; Crutzen et al., 1984~. Forest and Wildland Fuels Consumed As in the case of urban fire ignition, a number of complex factors could affect the area and the quantity of wildland fuels consumed in a nuclear exchange.
|
From page 56... ...
involving explosions over heavily forested areas (used for camouflage) ; tactical weapons are particularly effective in forest fire ignition (Woodie et al., 1983~.
|
From page 57... ...
It should be obvious that such tactics would significantly increase the areas of wildfires. The total area of forest fires in the baseline nuclear war is thus taken to be 250,000 km2, with all other related fires neglected.
|
From page 58... ...
Photographs show black plumes rising over industrial fires, and satellite images show wildfire plumes extending downwind for hundreds of kilometers-direct evidence that large fires can cause profound local optical and physical perturbations of the atmosphere (e.g., Davies, 1959~. The important properties of smoke are the quantity generated per unit mass of fuel consumed, the particle composition and size distribution, the specific extinction and absorption coefficients (expressed in square meters per gram)
|
From page 59... ...
, although the opposite effect is seen in other materials (Seeder and Einhorn, 1976; Tewar son, 19827. In nonflaming combustion, smoke emissions typically increase markedly when the samples are radiatively heated, but decrease in certain materials such as polyurethane foam when the air supply is preheated (Seeder and Einhorn, 1976; Bankston et al., 1981~.
|
From page 61... ...
For dry construction lumber, furniture, paper, and other cellulosic materials, an average flaming/smouldering smoke emission factor of 3 percent can be used (Rabash and Pratt, 1979~. In subsequent baseline estimates, an average smoke emission factor of 4 percent is adopted for all urban fires (before smoke scavenging and removal in the fire plumes -- see below)
|
From page 62... ...
The size distribution of smoke particles may be represented by a log normal distribution, nO 1 In ~ r/r nfr)
|
From page 63... ...
is approximately 4.3 times the number median radius. Several factors may lead to changes in the size distribution of smoke particles within the plume of a mass urban fire: 1.
|
From page 64... ...
just above a large, intense test fire in the Flambeau series. Concentrations of smoke particles measured in prescribed forest fire plumes are typically about 105/cm3 in the plume core close to the fire (Packham and Vines, 1978~.
|
From page 65... ...
Since the rate of energy release in a fire can be related to the rate of fuel consumption and thus to the rate of smoke production, the calculated rate of air mass flow through the fire may be used to deduce an initial smoke particle concentration. Assuming a smoke emission factor of 0.04 g/g and a heat of combustion of 4 x 104 J/g for oil, Benech's data imply a maximum concentration of about 1 x 106/cm3 of 0.1-pm smoke particles just above the fire.
|
From page 66... ...
These results indicate that the optical properties of smoke are not particularly sensitive to the initial coagulation of the smoke particles. Sooty smoke, moreover, exhibits the same typical extinction and absorption coefficients for a wide range of combustion sources and aging periods (e.g., Janzen, 1980~.
|
From page 67... ...
AS the droplet evaporated, the collected smoke would combine to form a single larger particle. Accordingly, cloud drop collection may on occasion be more efficient than coagulation in modifying the smoke particle size distribution in the early plume.
|
From page 68... ...
Optical Properties The optical properties of smoke clouds depend on the size distribution, composition, and morphology of the smoke particles. The optical properties determine the ultimate impact of nuclear smoke emissions on solar insolation and climate.
|
From page 69... ...
The long-wavelength infrared properties of smoke clouds may affect the heat balance of the perturbed atmosphere. In the infrared, the specific extinction coefficients of most smokes lie between O.1 and 1 m2/g; that is, roughly one order of magnitude below the visible extinction values (Volz, 1972; O'Sullivan and Ghosh, 1973; Roessler and Faxvog, 1979, 1980; Uthe, 1981; Vervisch et al., 1981; Bruce and Richardson, 1983~.
|
From page 70... ...
. At a wavelength of 10 Am, the overall variation in the calculated specific extinction coefficient is about a factor of 2 for all mode radii up to about 1 um (i.e., for spherical smoke particles that lie within the Rayleigh extinction regime; Deirmendjian, 1969; Kerker, 19693.
|
From page 71... ...
fires in forests produce about twice as much smoke as prescribed forest fires, per unit mass of fuel burned (Sandberg et al., 1979; McMahon, 19831. An average baseline smoke emission factor of 3 percent, consistent with the wildfire data, is assumed below.
|
From page 72... ...
However, over the long term, the infrared effects of wildfire smoke would appear to have little significance. The optical anomalies produced by forest fire smoke plumes provide some information on the properties of the smoke particles.
|
From page 73... ...
Hence most of the smoke injection following a nuclear exchange would occur over a relatively short time (assuming that the exchange itself would be executed within a few days}. Except in cases of unusually dry and windy weather, nuclear forest fires would probably burn out within 1 week.
|
From page 74... ...
may be correlated very well with this simple plume theory. If the plume equations are extrapolated to large-scale urban fires, a rough estimate of potential smoke injection heights can be obtained (Martins, 1984~.
|
From page 75... ...
Because forest fires generate only a small fraction (about 17 percent) of the total smoke emission in the present baseline case, attention is focused here on urban fires.
|
From page 76... ...
Evidence pointing to stratospheric injection includes collection of wildfire smoke particles in the stratosphere (Cadre, 1972) , and hydrodynamic calculations of fire plumes punching well into the stratosphere (e.g., Br ode et al., 1982; Cotton, 19841.
|
From page 77... ...
(1983a,b) discussed possible scavenging processes, such as nucleation and collection by rain and cloud drops, and concluded that up to 50 percent of the smoke could be removed from the plumes of intense fires and 25 percent from the plumes of other large urban fires (however, on the basis of observations, no significant early scavenging was assumed in the case of forest fire plumes)
|
From page 78... ...
. Windblown debris has been observed in the plumes of forest fires (Radke et al., 1983)
|
From page 79... ...
In fire plumes, longer droplet lifetimes could be expected. For the baseline calculations, it is assumed that, on the average, 50 percent of the smoke emissions from urban fires is promptly removed *
|
From page 80... ...
ESTIMATING SMOKE EMISSIONS IN A MAJOR NUCLEAR EXCHANGE Baseline Estimates The nuclear war scenarios considered in this report are highly generalized. No detailed information is given regarding explosion yields or heights of burst for specific targets, or the duration of the exchange.
|
From page 81... ...
The estimated smoke emissions are very uncertain, however; some of the sources of uncertainty are discussed below. The total quantity of combustibles consumed in the baseline war scenario is 8500 Tg (7500 Tg in urban fires and 1000 Tg in forest fires)
|
From page 83... ...
In the case of forest fires, it is assumed, on the low side, that no smoke emissions would occur. On the high side, a fourfold increase in the burned area and a smoke emission factor of 0.05 g/g are assumed, yielding a forest smoke emission of ~200 Tg.
|
From page 84... ...
is also less important, owing to the general protection of urban combustibles from the weather. Optical Depth Excursions Given the range of smoke emissions just described and the possible variations in smoke optical properties summarized in Table 5.7, ranges of average optical depths (at visible wavelengths)
|
From page 85... ...
7. Forest fire smoke emissions per unit area burned (factor of 2 to 3 in the fraction of biomass fuel consumed, factor of 2 in the mass of smoke emitted per unit mass of fuel burned, factor of 3 in the graphitic carbon mass fraction, factor of 2 to 3 in the mean particle size, and factor of 1.5 in the average particle bulk density)
|
From page 86... ...
The uncertainty factors defined above cannot simply be multiplied to estimate absolute ranges of equally likely values for composite parameters such as smoke emissions and optical depths. The factors do not correspond to intervals of statistical significance, in which the central (or baseline)
|
From page 87... ...
A laboratory study of the scavenging of sub-micron aerosol by charged-raindrops. Pages 551-560 In Precipitation Scavenging, Dry Deposition and Resuspension, edited by H.R.
|
From page 88... ...
Tangren (1963) Prediction of Fire Spread Following Nuclear Explosions.
|
From page 89... ...
Measurements of cloud condensation nuclei and cloud droplet size distributions in the vicinity of forest fires.
|
From page 90... ...
Pages 1-13 in Precipitation Scavenging, Dry Deposition and Resuspension, edited by H.R. Pruppacher, R.G.
|
From page 91... ...
Ryan (1976) Some chemical and physical characteristics of emissions from forest fires.
|
From page 92... ...
(1912) Forest Fires: Their Causes, Extent and Effects, with a Summary of Recorded Destruction and Loss.
|
From page 93... ...
Airborne studies of particles and gases from forest fires.
|
From page 94... ...
(1950) The widespread smoke layer from Canadian forest fires during late September 1950.
|
From page 95... ...
Adams (1979) Forest fire smoke plume documentation.
|
From page 96... ...
Fire spread from tactical nuclear weapons in battlefield environments. PSR Note 566 Santa Monica, Calif.: Pacific Sierra Research Corp.
|
From page 97... ...
. The heat release rate was about 109 J/s for 20 to 30 min (a total energy release of about 0.5 kt)
|
From page 98... ...
The so-called Mack Lake fire in the Huron National Forest, Michigan, on May 5, 1980, burned 100 km2 in 6 h; though the highly bent plume rose to only 4.6 km in the intense crosswind, the heat release rate has been estimated at 1.6 x 1011 J/s. However, the highest free-burning-fire heat release rates are associated with firestorms, the exceptional heat-cyclone consequences of massive incendiary air raids on urban targets during World War II.
|
From page 99... ...
Sooty ash showered downwind as far as 29 km for several days (Irving, 19651. Smoke Obscuration There are accounts of smoke so thick from Pacific Northwest forest fires that navigation on the Columbia River and other inland waterways was brought to a standstill in 1849 and 1868.
|
From page 100... ...
(1970) The physics of fire whirls.
|
From page 101... ...
Fire Plumes There are three sources of moisture for fire plumes: water of combustion, evaporated surface water, and entrained water vapor. Most combustible materials generate <1 g-H2O/g-burned.
|
From page 102... ...
An upper limit to the water injection by fires in a nuclear conflict is in the vicinity of 500,000 Tg. This figure assumes that the initial fire plumes occupy a volume of 1017 m3 (about one-tenth of the volume of the northern hemisphere mid-latitude troposphere)
|
From page 103... ...
The fire plume water injection of about 4000 Tg/km up to 9 km is typically <1 percent of the ambient water vapor at any level in this height interval. The total fire H2O injection is <0.5 percent of the global water vapor burden, and represents about 45 min of the normal global atmospheric water budget.
|
From page 104... ...
During the first week after the start of a nuclear war, the localized explosion clouds and fire plumes could hold significant quantities of condensed water. The visible and infrared opacities of these clouds could be very large (>>1~.
|
From page 105... ...
The clouds tended to rise and spread horizontally at a faster rate than would be expected if only ambient air motions were acting. Direct observations of large sooty smoke clouds reveal the same behavior (Davies, 1959~.
|
From page 106... ...
Nuclear winter: Global consequences of multiple nuclear explosions. Science 222:1283-1292.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.