The development of standard methods for evaluating the effectiveness of aerially applied bushfire suppressants
[摘要] Aircraft are often used to deliver suppressants during the direct attack of bushfires (wildfires). Suppressants reduce combustion thermodynamics by removing heat from the reactants. A range of suppressants are used in aerial firefighting including water and water containing commercially available surfactant (foam) or thickening (water enhancing gels) additives. This report presents methodologies for testing and comparing the efficacy of bushfire suppressants in a controlled environment.Evaluation methodsThe evaluation methods presented in this report were developed to quantify the effectiveness of bushfire suppressants in a controlled and representative testing environment. Three aspects of suppressant effectiveness were considered. These were:1. Wind-drift;2. Direct suppression; and3. Holding time.Wind drift is an important factor affecting aerial suppression effectiveness as it can prevent drops being delivered accurately and can cause to become dispersed and ineffective. A methodology for comparing how prone suppressants are to wind drift was developed. This involved suppressants falling through a uniform laminar wind field within a wind tunnel (the CSIRO Pyrotron). Suppressants were delivered in droplet form through a pressurised spray system and as a cohesive mass involving a bursting balloon.The direct suppression evaluation methodology was developed to determine the volume of suppressant required to extinguish a standard uniform fire (consistent behaviour) within the CSIRO Pyrotron. This is the most important of the evaluation methodologies as it simulates the intended operational application of suppressants in a quantifiable and repeatable way. Suppressants were delivered onto a fast spreading headfire (2.5 m min-1) using bursts of the spray system so that the minimum amount of suppressant could be used to extinguish all flaming combustion and stop fire progression. The standard fire environment was created using a 1.5 m ignition line igniting a fuel bed comprised of eucalypt litter (1.2 kg m-2) with a fuel moisture content of 7% and a constant wind speed of 2 m s-1.The holding time evaluation focused on the longevity of the suppressive effect. Two methodologies were developed. The first compared the relative drying rates of different suppressants. The second methodology determined how long different suppressants can resist ignition. These methodologies were found to generate comparable results. The drying rate method was determined to be the better evaluation method because it was less complicated to undertake and had fewer sources of error.A method for quantifying the characteristics of falling suppressant drops was also developed. This used high speed videography to measure the velocity, break-up heights and droplet composition of suppressants released from a height of 10 m....
[发布日期] 2015-08-14 [发布机构] CSIRO
[效力级别] [学科分类] 地球科学(综合)
[关键词] [时效性]