The efficacy of gel suppressants in grassfires: Prototype tanker field trials

[摘要] A field study was conducted to investigate the efficacy of gel suppressants delivered from a prototype tanker for use during grassfires.Three different tactical applications were evaluated; control lines, structure protection, and direct attack.Testing was undertaken in a well cured (87%) lightly grazed (4.2 t/ha) grassy paddock on a day with a very high grassland fire danger.Experimental fires were lit as head fires to provide as high intensity as possible (2000 – 5400 kW/m).Control line tests were undertaken to determine the effective time period that gel control lines constructed by the tanker could be expected to stop the progression grass fires.Control lines were 2 metres wide, prepared with a 1.1% gel concentration and had coverage levels around 2.1 l/m2.They were positioned in the path of head and flank fires and impacted between 0.6 and 4.25 hours after the suppressant was applied to the grassy fuel. Only two of the 21 gel control lines stopped fire spread.These had been recently rehydrated (36 – 42 minutes prior) and were impacted by low intensity flank fires.The rapid drying of the gel suppressants and the flame contact with the tops of the treated grassy fuels allowed fire spread through treated control lines.Flank fires passed over control lines when brief (1 sec) changes in wind direction caused flames to lean directly into them.The results here indicated that gel control lines are ineffective in stopping grassfires during elevated fire danger conditions.The effectiveness of gels for protecting structures impacted by fire was investigated in two experimental fires.Two identical weatherboard structures were placed in the path the fires.One structure was treated with 2.5% gel mixture while the other was left as an untreated control.Treatments were applied 40 minutes and 3 hours prior to the ignition of test fires.The results of these experimental fires were inconclusive because the structures received different fire impacts as a result of small scale irregularities in the fire fronts which significantly influenced the observed damage.These tests demonstrate the difficulties in obtaining repeatable conditions within field experimental fires.Therefore it is recommended that further testing be undertaken in a controlled laboratory setting.Two fires were lit to observe the effectiveness of direct attack of gel suppressants applied from the gel tanker.The findings were limited because the tanker had not previously been used to apply gel for direct attack and the application did not reflect the dynamic use of nozzle settings that typically occurs during wildfire operations and the fire conditions could only be partially quantified.While these tests demonstrated that the tanker could be applied in a direct attack role, further testing is required to determine if and how much improvement gel suppressants provide over water in grassland fuels.Laboratory testing would be the most appropriate means for investigating this issue.These field tests have demonstrated that the prototype gel tanker is capable of performing these tactical roles.However, questions remain regarding the effectiveness of gel suppressants in structure protection and direct attack.Further evaluation of the gel tanker should investigate other roles for applying gel suppressant, e.g. treating trees with fibrous bark on the edges of planned burns to limit potential spotting.

[发布机构] CSIRO

[学科分类] 地球科学(综合)