Fight Or Flee? -A Case Study of the Mount Macedon Bushfire
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WIT.3004.003.0147 CFA.300.032.0147 Ausi. For., J984, 47 (4), 230-236 Fight or flee? -A case study of the Mount Macedon bushfire &0(Jww A. G. Wltem<an& Jan & £epgus®ti•* Forestry Section, eacu)ty of Agriculture and Forestry, University of Melbourne, parkville, Vic. 3052 Summary Results from a'cteaDed study oT*r<oushfire on 16 February 1$83 at Mourit Macerfpfl. \0.cif.oru|lifig«est f^^e-bodied-residents J? ^6fc9re.^hrjf^Jgjt^y a ottsjffire should remain in their hoUsesfThar chances of survivingare excellent, and W=^ftent-tan" esjgsct-'jo-.Sye their fious^. Evacuation is a potential!) more perilous alternative for residents, and about WpSr'ee'm ofitbose'3 wfid'Ace riiighl expect to losethtSr houses*Provision should however be made to evacuate disabled or infirm persons and the residents of houses that are surrounded by exceptionally high fuel loads. The most important causes of house destruction were found to be fires originating in roofs, or in nearby structures such as garden sheds. % Introduction Strategies to be adopted by residents who are of residents. Analysis of the detailed data is still confronted by an uncontrolled bushfire warrant in progress. The aim of the present paper is to objective assessment. The major issue is whether address the one specific but important issue, that a resident should stay and defend his house, of "fieht or flee". flee in the hope of escaping the fire. Mount Macedon, a settlement 55 kr northwest of Melbourne, provides aj of this question. Mount Mace<3 developed in the mid 19th centuj wealthy residents of Melbourne fror heat and bustle of the new cXi^ftfanv splendid houses were built, most of which were eventually surrounded by large exotic gardens. More re cently, since the 1960s, modern houses have been built in the natural forest-covering parts of the town and the slopes of Mount Macedon itself. The population is largely permanent, with many people commuting to Melbourne for their em ployment. % On the evening of Ash Wednesday, 16 February 19S3, a severe bushfire swept through the town. Si.\ Jives were lost, and 234 houses were destroyed. After the fire, a survey was carried out in order to relate house survival to an array of hazard factors, including house deslgn.and construction materials, topography, garden and bushland vegetation, fire intensity, the proximity of fuels Rev-* and other building;, and the fire fighting activities •** 5wd; area boundarv Revved manuscript received 28 September J9S* Figure I. Localion and Boundaries of lht slurf} area. WIT.3004.003.0148 CFA. 300.032.0148 Fight or flee — A case study of the Mount Macedon bushfire 231 Survey of houses Fire intensity The study area is shown in Figure 1. Its boun The fire approached Mount Macedon through the daries were selected to match the limits of urban •Wombat State Forest, completely defoliating 80 development, which were generally well defined. per cent of the forest in its path (Rawson et at. Houses to the north of the town had been affected 1983). $§g£&&f sprtacf were extremely high, by a different fire 15 days earlier, and were ie£c|cdi$rJ|l£ft/h£between 2045 hrs (Eastern excluded from this study. Standard Daylight Saving Time) and 2130 hrs, and QB&l&ftfattwQi atej$e;dm*3iienWe~ The survey was conducted between June and ^l^C^edl^ount'Macedori^after Rawson et at. December 1983. iPft^SSlibusjesf n the study 83). Nevertheless, Franklin1 (pers. comm.) has 1 5 t area, I^BfPIP^S^^d^^ ' almost complete suggested that this estimate is conservative, and enumeration avoids the bias or lack of precision he believes that the fire travelled thcjliliiffrorn associated with sampling systems. The term the Calder Highway to the summit of Mount "house" was defined to include all inhabited Mac^on^^^WilSii^i^i^ His fiSures domestic dwellings, whether or not permanently ISiPpia rate of spread of 0B$i%MfbM are occupied. Semi-detached flats and bungalows ( ) unconfirmed and may in part reflect the extremes were regarded as part of the main house if of slope in that vicinity. An analysis of 21 spot • connected by a walkway or similar structure. estimates by residents of times the fire front passed through indicates that rates of spread in Interviews were conducted with residents of every the. town were of the order of 3-4 km/H, lower house for which a representative could be con than in the forest. tacted. The object of each interview was to discover as much as possible about the pre-fire lie forest had not been burnt for many years. environment and the sequence and timing of e litter component of fine fuels would have events during the fire. The accounts of differeq mulated to a "steady state" level of about respondents were cross-referenced to reduce as found by Attiwill et a/. (1978) in a effect of the distortions that inevitably aiw similar forest. Luke and McArlhur (1978) indicate conditions such as these, and this invojjedfcsktog that shrubs and bark contribute gpiaWiolii? W&$BBfin dry sclerophyll forests in Victoria, so residents to report on events and q/eumsrartces , relating to property other than then^jwjf. ^iW/BK0B&6tKU&BB&&* <r* probably about &£$gj$t and this level may have been further augmented by drought-induced leaf fall, In analysing the data relating to causes of ig and lower than usual decomposition rates (Luke nition, only those houses that were attended by and McArthur 1978). Adopting a r?te of spread residents have been included. Reports concerning of f^BPand a fuel load of S^^t the in these houses provide an objective framework for tensity of the bushire in the forest adjacent to the discussion of the problems that an occupant is town would have been ^^^^MP^^MI^'l^ likely to face. Other reports were inherently being a measure of the rate of heat release per o unreliable because visibility was impaired by unit length of fire front. This estimate is exclusive smoke during the passage of the fire; and various of any 0SK^SS^SSSS^SS^>^^the com- events, such as the breaking of windows by bustion of gl^lr^iil* radiant heat- or the ignition of structures by airborne embers, were likely to be obsers'ed only The fire crowned infrequently after entering the by those closcby. town, presumably because human activities had reduced fuel loads below the level found in the Residents who were present at their houses during unmodified forest. About ten per cent of houses the passage of the fire front are hereafter referred were subjected to a crown fire in the.adjacent to as "occupants"'. "Attended" houses comprise forest canopy, while 50 per cent were exposed to those where' one or more occupants sheltered as a surface fire intense enough to fully scorch ihe the fire passed. The presence of persons im surrounding trees. Almost 40 per cent of houses mediately before or after that time is treated were exposed to a less intense surface fire, but separately. Persons were counted as occupants if one which was nevertheless accompanied by more than about ten years old. irrespective of strong winds and innumerable airborne embers. their fire fighting ability. No cases were found of houses being attended only by children. • 1. L. Fr&nMin. District Forest Officer, Macedon. WIT.3004.003.0149 CFA.300.032.0149 c 232 Australian Forestry Scorch heights were less than 8 m in parts of the cent. The small sample sizes in Table I preclude study area (i.e. the town) indicating that fire definitive conclusions regarding the relative intensities were probably as low as 500 kW/m effectiveness of groups of one, two, and three or (Cheney 1978) in these places. Thus houses were more, persons; nevertheless, groups of three or exposed to fires of intensity ranging from more occupants were notably successful in that 60 000 kW/m, where the fire entered from the no houses in this category were lost. uncleared forest on the western edge of town, Few occupants were well prepared for a bushfire, down to about 500 kW/m within some other judging by their failure to reserve water supplies parts of the town. for fire fighting purposes. Only seven attended Prior to the Ash Wednesday fires, the upper limit houses were equipped with a pump and indepen of fire intensity in eucalypt forests was thought dent water supply, and twelve had little or no to be about 60 000 kW/m (Luke and McArthur water at all (Table 2). Two occupants attributed 1978), but based on the rates of spread recorded the loss of their houses to running out of water. for the-Macedon and other Ash Wednesday fires, Another simple precaution is to cover vents to the this figure how appears to be an under-estimate sub-floor space, so restricting the entry of embers; of the maximum attainable (Cheney 1983). Hence such precautions were however taken for only the fire that struck the study area was at, or near, four of the 194 brick and brick veneer houses the maximum intensity possible in south-eastern surveyed. Australia. The results from the study area are representative of a particularly severe situation. Table 2. Adequac) of water supplies at attended houses. Attendance and house survival Water supplies Fate of houses The numbers of houses that survived or were Survived Destroyed Total destroyed are summarised in Table I, together j|ibstantial: Independent with a cross classification by the number of . ,./t \rescrves, distributed persons in attendance. Some. f|||ililliii^|if^*V'ill h a non-electric rnp.