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30 May 2025
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Featured FRI Magazine article: Case study: Open ended firebreaks – a safer new technology for the future by Dr Winston and Lynne Trollope
Collecting ecological data in this type of terrain is a challenge
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62km of firebreak ignited in 40 minutes using aerial ignition
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successful open ended fire break along the border between South Africa and Lesotho
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https://www.frimedia.org/uploads/1/2/2/7/122743954/fri_vol_3_no_6.pdf
This week’s featured Fire and Rescue International magazine article is: Case study: Open ended firebreaks – a safer new technology for the future by Dr Winston and Lynne Trollope (FRI Vol 3 no 6). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Open ended firebreaks – a safer new technology for the future
By Dr Winston and Lynne Trollope
During 2014, the research and development division of Working on Fire has researched and developed the best operating procedures (BOPs) for new and innovative technology for burning firebreaks.
Conventional wisdom dictates that firebreaks are burnt at the beginning of winter when conditions, both of the weather and vegetation, is not optimal. This new technology focuses on optimal weather conditions that increase the safety of burning firebreaks and also factors in the condition of the grass fuel load.
Open ended firebreaks are ignited in the late afternoon when the temperature is dropping and the relative humidity is rising. On a clear cloudless night dew point is reached in the late evening and the fire dies.
Weather is all important when dealing with fire, a point the general public including farmers and wild life managers does not take into account. Weather in fact drives fire behaviour, particularly temperature, relative humidity and wind speed. Wild fires occur under ‘berg wind’ conditions with high temperatures, low relative humidities and high wind speeds. Grass curing is also an important factor impacting on fire behaviour; highly cured, dry grass increases the rate of spread of the fire.
Rural communities living along the Lesotho border in the Matatiele district are regularly threatened by cross border wild fires started mainly because of cattle rustling issues. These often devastating wildfires cause great hardship to local communities with schools, preschools, abodes and extensive grazing being lost. The Firewise program was initiated to educate local residents in these isolated areas to the dangers of uncontrolled fires to the community and provided simple measures and training to help mitigate the threats from wild fires.
The director of Firewise, Val Charlton, requested Working on Fire to assist with burning a firebreak just below the Lesotho border as a barrier to these wildfires between Ongeluksnek and Quaggasnek in KwaZulu-Natal, their main area of operation.
The best operating procedures for burning open ended firebreaks, as developed in the Kruger National Park where the research was initially conducted, dictate that the most opportune time to burn these firebreaks is in late summer or early autumn when the grass curing (the ratio of dry to green grass in the grass sward) is between 40 to 60 percent ie when the grass is still fairly green. The temperature must be less than 25 degrees Celsius, relative humidity higher than 50 percent and the wind speed less than 10km/hr.
The window of opportunity was very narrow as it was early June and if the venture was to be successful, the firebreak had to be burned before the first frost, which would escalate the grass curing to 100 percent. Collecting the basic ecological data on which to base the decision to burn (grass curing and grass fuel loads) was a challenge due to the inaccessibility and terrain of the area. In addition, the nearest weather station providing weather data for forecasting by the South African weather service was at Kokstad. The question was “How comparable would the weather forecast be to the actual weather at the higher altitudes at the time of the planned burn?”
A Kestrel weather meter recording data 24 hours per day was located at a higher altitude before the planned burn to record actual temperature, relative humidity and wind speed closer to the border. The Firewise team collected grass samples for estimating grass curing and measured grass fuel loads using a disc pasture meter. The actual grass curing at the higher altitudes (1 800 to 2 000m) was between 40 and 60 percent and the grass fuel load was between 1 900 and 3 000kg/ha depending on accessibility to grazing animals. Although the ecological criteria for burning moribund, old grass is 4 000kg/ha, it was decided that even though the grass fuel load was below the ecological recommendation, it was sufficient to burn a firebreak.
Finally the weather parameters as recorded by the Kestrel weather meter fell within the best operating procedures and the decision was taken by Bob Connolly, the operations manager of Working on Fire, that it was all systems go!
Open ended firebreaks ignited over long distances are achieved by aerial ignition using Australian RainDance equipment mounted in a Bell 206 helicopter, which primes ignition capsules and drops them out a chute. The ignition capsules were dropped at an altitude of 1 800m by the helicopter flying at 30m above ground level. The ignition line of 62kms was completed in 40 minutes!
Ignition time was 14h10 with the temperature reading of 11,3 degrees Celsius and wind speed 6,6km/hr. The fire died at 23h00 (temperature -4,3 degrees Celsius) and the relative humidity during the time of the fire oscillated between 28 and 41 percent. The average width of the successful firebreak was 200m.
The reconnaissance flight the following morning picked up four hot spots where fires were still burning in kloofs where the fuel loads were possibly higher due to lack of grazing. A helicopter with a Bambi bucket was sent in to douse the four smaller fires.
This remarkable achievement not only provides a welcome measure of protection from disastrous wildfires to isolated rural communities in South Africa but has also provided further insight into the role of weather in fire behaviour. On reflection, these results suggest that at lower altitudes, in warmer areas relative humidity is the controlling factor in extinguishing fires in the late evening whereas in higher, colder climes temperature is the factor that extinguishes the fire. This is a major breakthrough in fire behaviour!
This week’s featured Fire and Rescue International magazine article is: Case study: Open ended firebreaks – a safer new technology for the future by Dr Winston and Lynne Trollope (FRI Vol 3 no 6). We will be sharing more technical/research/tactical articles from Fire and Rescue International magazine on a weekly basis with our readers to assist in technology transfer. This will hopefully create an increased awareness, providing you with hands-on advice and guidance. All our magazines are available free of charge in PDF format on our website and online at ISSUU. We also provide all technical articles as a free download in our article archive on our website.
Open ended firebreaks – a safer new technology for the future
By Dr Winston and Lynne Trollope
During 2014, the research and development division of Working on Fire has researched and developed the best operating procedures (BOPs) for new and innovative technology for burning firebreaks.
Conventional wisdom dictates that firebreaks are burnt at the beginning of winter when conditions, both of the weather and vegetation, is not optimal. This new technology focuses on optimal weather conditions that increase the safety of burning firebreaks and also factors in the condition of the grass fuel load.
Open ended firebreaks are ignited in the late afternoon when the temperature is dropping and the relative humidity is rising. On a clear cloudless night dew point is reached in the late evening and the fire dies.
Weather is all important when dealing with fire, a point the general public including farmers and wild life managers does not take into account. Weather in fact drives fire behaviour, particularly temperature, relative humidity and wind speed. Wild fires occur under ‘berg wind’ conditions with high temperatures, low relative humidities and high wind speeds. Grass curing is also an important factor impacting on fire behaviour; highly cured, dry grass increases the rate of spread of the fire.
Rural communities living along the Lesotho border in the Matatiele district are regularly threatened by cross border wild fires started mainly because of cattle rustling issues. These often devastating wildfires cause great hardship to local communities with schools, preschools, abodes and extensive grazing being lost. The Firewise program was initiated to educate local residents in these isolated areas to the dangers of uncontrolled fires to the community and provided simple measures and training to help mitigate the threats from wild fires.
The director of Firewise, Val Charlton, requested Working on Fire to assist with burning a firebreak just below the Lesotho border as a barrier to these wildfires between Ongeluksnek and Quaggasnek in KwaZulu-Natal, their main area of operation.
The best operating procedures for burning open ended firebreaks, as developed in the Kruger National Park where the research was initially conducted, dictate that the most opportune time to burn these firebreaks is in late summer or early autumn when the grass curing (the ratio of dry to green grass in the grass sward) is between 40 to 60 percent ie when the grass is still fairly green. The temperature must be less than 25 degrees Celsius, relative humidity higher than 50 percent and the wind speed less than 10km/hr.
The window of opportunity was very narrow as it was early June and if the venture was to be successful, the firebreak had to be burned before the first frost, which would escalate the grass curing to 100 percent. Collecting the basic ecological data on which to base the decision to burn (grass curing and grass fuel loads) was a challenge due to the inaccessibility and terrain of the area. In addition, the nearest weather station providing weather data for forecasting by the South African weather service was at Kokstad. The question was “How comparable would the weather forecast be to the actual weather at the higher altitudes at the time of the planned burn?”
A Kestrel weather meter recording data 24 hours per day was located at a higher altitude before the planned burn to record actual temperature, relative humidity and wind speed closer to the border. The Firewise team collected grass samples for estimating grass curing and measured grass fuel loads using a disc pasture meter. The actual grass curing at the higher altitudes (1 800 to 2 000m) was between 40 and 60 percent and the grass fuel load was between 1 900 and 3 000kg/ha depending on accessibility to grazing animals. Although the ecological criteria for burning moribund, old grass is 4 000kg/ha, it was decided that even though the grass fuel load was below the ecological recommendation, it was sufficient to burn a firebreak.
Finally the weather parameters as recorded by the Kestrel weather meter fell within the best operating procedures and the decision was taken by Bob Connolly, the operations manager of Working on Fire, that it was all systems go!
Open ended firebreaks ignited over long distances are achieved by aerial ignition using Australian RainDance equipment mounted in a Bell 206 helicopter, which primes ignition capsules and drops them out a chute. The ignition capsules were dropped at an altitude of 1 800m by the helicopter flying at 30m above ground level. The ignition line of 62kms was completed in 40 minutes!
Ignition time was 14h10 with the temperature reading of 11,3 degrees Celsius and wind speed 6,6km/hr. The fire died at 23h00 (temperature -4,3 degrees Celsius) and the relative humidity during the time of the fire oscillated between 28 and 41 percent. The average width of the successful firebreak was 200m.
The reconnaissance flight the following morning picked up four hot spots where fires were still burning in kloofs where the fuel loads were possibly higher due to lack of grazing. A helicopter with a Bambi bucket was sent in to douse the four smaller fires.
This remarkable achievement not only provides a welcome measure of protection from disastrous wildfires to isolated rural communities in South Africa but has also provided further insight into the role of weather in fire behaviour. On reflection, these results suggest that at lower altitudes, in warmer areas relative humidity is the controlling factor in extinguishing fires in the late evening whereas in higher, colder climes temperature is the factor that extinguishes the fire. This is a major breakthrough in fire behaviour!