WILD FIRE EFFECTIVE SUPPRESSION CALCULATOR

Transcription

1 THE WILD FIRE IMPACT EFFECTIVE SUPPRESSION EFFORT CALCULATOR 1

2 PROJECT OUTLINE THE WILD FIRE IMPACT EFFECTIVE SUPPRESSION EFFORT CALCULATOR In October 2010 a Grass Fire Simulator was reintroduced into the training program of CFS Region 5 (the South East of South Australia) There are a number of issues that need to be resolved in order to achieve maximum successful outcomes, both from the use of this training aid and in the field. The amount of water, the litreage applied per meter, the speed of travel and the number of appliance loads must be accurately calculated for successful suppression. The Wild Fire Impact Effective Suppression Effort Calculator (hereinafter called the WIESE calculator) is currently being developed as a simple tool, easily managed in the field, but which translates directly into either the control room or a training scenario It is confidently expected, after further development, that the WIESE calculator will be capable of delivering accurate measurements on amount of water required, litreage to be applied per metre, speed of travel and the required number of appliance loads. Severe fire events in recent years dictate a need for a much more accurate and measured approach to fire suppression. Our fire trucks have never been calibrated for speed and volume per meter and our Brigade Captains and truck drivers are working with un-calibrated fire appliances. Rural Fire Services appear not to have any sound basis on what amount of resources are responded to rural grass fires that takes into account weather, fuel and suppression, and fire spread. The WIESE calculator has been developed to allow for much more effective delivery of suppression methods for grass in flat to undulating terrain. The same principles used in this edition of the WIESE Calculator would apply for other terrain, including both Mallee Scrub and Forested Land, but further work will be needed to factor in the appropriate suppression techniques for differing fuel load/topography situations etc. I have used my fifty plus years of fire fighting experience to make specific and targeted observations and have developed the WIESE Calculator to allow personnel to easily and accurately assess the connection between Fuel Load, Weather, Litres of water Delivered Per meter and fire spread. Given that there is a definite link between litres per metre, fuel load and fire control, there is an equally definite link between nozzle size and type used and control of a fire which occurs when the Grassland Fire Danger Index (FDI) exceeds 20. Not applying sufficient water contributes to many rekindles. This is not so much of a problem below an FDI of 20. Insufficient application of water ABOVE FDI OF 20 can lead to fires not being effectively controlled. To achieve the ground speed and flow rate required for suppression; both nozzle size, type and pressure must be accurately adjusted. It is essential for a successful outcome for a fire event that: 2

3 The length of the fire edge to be extinguished The probable amount of hectares to be burnt The distance that the fire will travel Can be accurately assessed at any given time. In order to achieve successful suppression, it is necessary to accurately calculate the speed of travel of the fire appliances in use. In addition to calculating the required speed of travel, accurate assessment of both the rate of water flow and water pressure is needed. Effective suppression requires appliances to be travelling at the correct speed for water application and getting maximum amount of water to where it required without loss.(i have measured in excess of 50% water loss occurring) PROJECT REPORT The WIESE Grassland Fire Resource Calculator (demonstrated below) aims to provide Fire Appliance crews and Fire Managers with a tool that can assist in better delivery of a desired result by inputting all the variables: temperature, relative humidity (RH), wind, fuel load, water per minute, water per metre and time elapsed since fire ignition. 3

4 Fire behaviour predictions for the calculator have been taken from the CSIRO Grassland Fire Danger Meter MK 4. The fire suppression rates above have been collected and confirmed from numerous experiments, observations and reports from fires and trials conducted by myself. I have been extensively involved with fire suppression and the South Australian Country Fire Service (CFS) for more than fifty years and attended well in excess of 3000 fires during this time. I have always been intrigued by the different results achieved. Some Brigades and personnel can get good results in extinguishing grass fires whilst others suffer numerous rekindles, sometimes to the extent that the whole flank relights and wastes the intense, hard-fought effort that has been invested already. I spent many years pondering this anomaly and felt challenged to develop a calculator that could simultaneously track fire behaviour and suppression. About four years ago I started to develop a calculator that would commence the task of meeting this challenge. I did not have the skill to personally develop a computer model of the calculator (figure 1) and was not prepared to commit funds to the project at that early stage. Through the generosity of the CFS Foundation Grant I have been given the confidence and opportunity to take the calculator project to a more advanced level of operability. The Foundation Funds have also permitted me to further develop my expertise and credibility with the people I have spoken with about the project. My first task was to contact Mr Phil Cheney in Canberra. Mr Cheney is a former member of the Bushfire Behaviour and Management Group of CSIRO Forestry and Forest Products. Mr Cheney agreed to meet and discuss the project. I was able to travel to Canberra for this meeting. Mr Cheney commented that the idea was sound and he was of the opinion that water wastage through drift and incorrect placement was a big variable in the calculations. The work that I had previously carried out on water wastage was not part of the original project but I now saw the need 4

5 to further develop the project by studying the quantities of water being lost and where it was actually going to. SA Country Fire Service provided funding for twelve catchment trays which enabled my trials to indicate losses well in excess of 50% of the water stream to be a common occurrence. I have been unable to get a clear answer as to exactly how much water is the correct amount to apply per meter of fire edge or what is the correct speed to deliver sufficient water. My farming experience involved boom spray chemical applications and fertiliser and seed application calibration. Why have fire appliances not been calibrated? (Comments from some people in regard to water usage ranged from 4 metres per litre to 40 litres per metre) I have spent considerable time working with fire fighting foam and water to try to get good penetration in wheat stubble. I wished to determine how much water is required to wet this fuel profile. This foam was well aerated but did not give good penetration. All trials were conducted with the nozzle in a set position on the front of the truck. My questions What was the most effective spray pattern? What angle would give the best penetration? What angle was least likely to blow burning embers onto the unburnt area? What angle got the most water to the fire without loss? All my trials were carried out at a set speed of 20kph. This speed could head most fires and would be achievable on most grassland and cereal cropping land in South Australia. The water delivery rate needed to be calibrated to the truck speed. Trials were aimed at discovering the best position to mount nozzles in order to achieve results. This would offset the potential variables introduced by human error of angle estimate. The shape of the water stream can be changed to provide more water on the unburnt fuel section rather than the fire side. This provides a thorough wetting down of the fuel profile. How thoroughly does the strip need to be saturated before burn through is prevented? The head of the fire has the most intense fire behaviour and we need to be able to apply more water to the head of the fire with minimal evaporation to try to lower this intensity and cause the fire to stop at the water line. I then conducted trials on actual fire with three mediums, plain water, and water with fire fighting foam added and Blaze Tamer 380. Blaze Tamer gave the best penetration to the fuel profile and worked well under actual fire conditions. These trials with live fire indicated to me that it may not be necessary to place all the water on the fire; but instead to place a sufficient percentage of water onto the unburnt ground (fuel) that wetted the profile and prevented rapid evaporation and did not support combustion. 5

6 Our usual method of low flow rate and high wastage ensures that we will never be effective on a day of high fire danger. If we routinely attack initially with high pressure and volume we will be more effective on days of high fire danger. We can then always reduce pressure after assessing the effectiveness of our attack to conserve water. The large areas of land and high stock and property losses occur on days of high fire danger, not on days of low risk. We should therefore prepare for the worst and maximise the benefit of the fire resources we have available whilst using the days of low risk to practise and perfect techniques. Water is lost by the nozzle operator. This loss can be minimised by mounting the nozzle onto the bull bar or monitor in a better fixed position. The truck driver can then control this nozzle operation by using the steering wheel. This provides the shortest distance to the fire and the best angle to penetrate the vegetation. The water should not be applied through the flames. Small droplets that are directed through the flame from a distance will be subject to high evaporation. The only effective way to extinguish the fire is for water to contact the fuel at the base of the fire. Water that is applied from the back of the appliance needs to travel a greater distance to the fire which increases drift and loss. Water aimed from the bull bar does not need to travel as far and has more velocity to ensure profile penetration. The correct angle of water delivery can be better maintained from the front of the truck and a side benefit to this is the cooling effect for the front (radiator) and cabin (crew) area of the appliance. Once the head of the fire is reached there needs to be extra water per metre applied to absorb the additional heat and still wet a sufficient strip to prevent a rekindle. I believe this can be done with the use of a nozzle that can deliver good range of at least ten metres, whilst delivering water to the ground along most of the nozzle range. From my observation of fire I think that it is achievable at the head because the intense flame would be stopping the wind close to the fire front or may even be drawing air in to feed the flame. Excerpts follow to explain the science theory of fire intensity and firebreaks. I also observed with Blaze Tamer 380 that I could apply water 10 meters away and obtain 100% success. This would require further testing. If this is possible then we could operate at a higher level of safety to crew and appliances. Excerpt from Grassfires fuel, weather and fire behaviour by Phil Cheney and Andrew Sullivan. Fire Intensity. The rate of spread of each meter of the fire perimeter varies depending on its location on the perimeter; at the head where the rate of spread is greatest, the fire intensity is greatest and at the back of the fire where the rate of spread is least, intensity is least. Fires are usually characterised by the intensity of the head fire. A theoretical illustration of the relative intensity calculated for each metre around the perimeter of a grassfire is shown in Figure 3.9. In reality the intensity of the flank fire can range from the intensity of the head to the intensity of the back fire as it responds to fluctuations in wind direction as discussed the section Flanking Fires above. 6

7 The intensity of a grassfire may range from a 10kW/m backing fire in light fuels to kW/m at the head of a very fast wildfire. Fire intensity is useful when comparing fires in the same fuel type, but should not be used to compare fires in different fuel types for example, those in grass with those in forest fuels. Because of the very different combustion characteristics of the two fuels, the behaviour and flames of a forest fire will be very different from those of a grassfire of the same calculated intensity. Excerpt from FESA by Ralph Smith p 15 7

8 Firebreaks Firebreaks are very effective in grassy fuels particularly when the fire is not spotting. The following table provides an indication of the width of firebreak required when associated with a known (estimated) fire intensity and a basic type of vegetation (e.g. spotting or non-spotting). The widths nominated are a guide only. Intensity (kw/m) Firebreak width (m): Firebreak width (m): Anticipated success Spotting vegetation Non-spotting vegetation High Moderate Source: Interpreted from Grassfires fuel, weather and fire behaviour by Cheney and Sullivan, An interpretation of the above information is that a firebreak that is 10 metres wide will provide the fire manager with a reasonable level of expectation that a fire will be held. If the fuel is a spotting fuel minimization of the impact of the spotting can be achieved by having suppression resources available on-site and this will increase the likelihood of containing the fire. Excerpt from Grassfires fuel, weather and fire behaviour by Phil Cheney and Andrew Sullivan. The fire creates its own wind. One of the most common statements about bushfires is: The fire creates its own wind and you can t do anything about it after that!. The problem here is not the initial proposition that the fire creates a wind field around it it does but rather the idea that the in-draught winds induced by the fire keep driving it forward independently of the prevailing weather conditions. Fires in heavy fuels such as forest slash from clearing operations generate very powerful convection currents which at times may form fire whirlwinds or fire tornados as consequence of the high rate at which heat is released by the fire. These currents can induce strong in-draught winds that are drawn into the fire zone from all around. When the prevailing wind is less than 15km/h, this convection will dominate the prevailing wind and the fire is actually contained by its own indraughts. In grassfires, however, the total fuel load is relatively light and the in-draught winds will contain the fire only when the prevailing wind is light (less than 5km/h). In forward-spreading fires, the convection column is inclined by the prevailing wind. The main indraught is into the back of the flames behind the fire front. This in-draught increases the speed of the prevailing wind behind the fire and is drawn downward into the combustion zone before being carried up into the convection column. The convection column effectively blocks the prevailing wind, creating a zone of light and variable wind for some distance ahead of the fire front (Fig 10.1) The increase in perimeter of the fire, although the decrease in wind speed may extend several hundred metres downwind of an intense fire. During experiments with grassfires in light fuels, it was possible to walk about 20m behind the flames in a zone of clear air as the in-draught was pulling smoke-free air down into the head fire. This structure can be readily observed when a fire passes over a firebreak; the enhanced wind behind the 8

9 flame front flattens the flames after they hit the break (see Fig 8.6). This wind may be strong enough to move smouldering debris on the ground. As discussed in Chapter 6, the behaviour of a fife is strongly influenced by the thermal structure of the atmosphere and gusts and lulls in the prevailing wind. When the wind speed drops during a lull, the enhanced wind behind the fire front does not keep propelling the fire forward. Rather, the convection column straightens and its base may move back onto the burnt area, creating an indraught on the downwind side of the fire front. This dramatically slows the fire s spread. The process of applying water at an increased rate from two nozzles whilst still using the first nozzle to thoroughly wet the profile, over a desired width of head fire, I believe should also blow a considerable amount of flammable fuel away from the fire edge and onto burnt ground. This would reduce possible rekindles and may well ensure a better result. More efficient use of water means more fire can be effectively extinguished with the available water in less time. The use of the meter demonstrates the gains that are achievable. If one looks at how the fire would travel using less water per metre and a greater speed you will start to appreciate the percentage gains that are achievable. About the calculator The calculator involves the following information: use of data from the CSIRO Grassland Fire Danger Meter converted to computer data, litres of water per metre, litres of water per minute to be 9

10 delivered to the nozzle as well as truck capacity, calculation of perimeter gain, time from ignition and actual appliance numbers. Inputting the fire danger index (FDI) reading and a fuel load estimate will allow the meter to estimate the number of fire appliances and loads of water required and the distance the fire will travel before suppression is achieved. How many minutes to contain and the amount of fire edge to extinguish are variables that may still require some fine tuning to get correct but I am unable to do this until I get more data and conduct further experimentation using the estimations for these variables. I have experimented with a slab of hot concrete and mixtures of extinguishment placed side by side. I observed that a given quantity of plain water placed onto the hot concrete will generally evaporate within two three minutes whilst the water with an additive will usually last up to ten fifteen minutes. If this is the same in grass then this variance in evaporation rate could be an advantage when used correctly. The Wiese Suppression Fire Calculator can improve the awareness of water usage, time, weather, fuel loads, effective fire behaviour and suppression, thus giving a good indication of how many resources should be responded to a grass or stubble fire as an initial response to achieve a desired result. Conclusion Trials in April 2013 of the Wiese Suppression Fire Calculator at Mundulla in barley stubble indicated it is possible to achieve fire suppression with one litre per meter rather than the four litres per meter which has been common on similar fires. This is a 400% gain on water efficiency. This coupled with an earlier containment time probably would give another 400% gain by not suffering as much area burnt which in turn saves on fuel and damage costs and the invaluable expense of volunteer time spent on fire suppression. This approach combined with more efficient nozzle design, the ability to operate more effectively on days of higher Fire Danger and the addition of additives to the water, which has the ability to slow evaporation and glue the water stream together with less drift, will no doubt provide even further improvement. Changes to possible disadvantages of appliances The size of appliance cabs has increased and the mounting of monitors and hoses has moved further to the rear of the appliances. This changes angles of water application. Fire nozzles have changed to a cone type spray which results in more water loss from drift. Appliance engine power and speed have increased which has permitted the overly-enthusiastic driver to very easily travel too fast along the fire line, when no one has ever provided a sound guide as to what is the desired speed. 10

11 I believe in recent years we have come to rely on the use of more appliances and aircraft at initial call-out to get us out of trouble, when instead or as well we could be using more effective fire appliances with greatly increased capability when the limited water capacity is better utilised. Many times we hear the cry that the appliance driver is going too fast for the job, which allows rekindles to occur. Many brigades believe they need a second nozzle to pick up what is missed. My observations are, that generally the water that is applied in a backwards direction as the appliance has passed does not reach the rekindle target and is therefore mostly lost water. The real issue is actually the rate that water is applied. It should be increased in conjunction with ensuring the accuracy and arrangement of the water is correct, to enable delivery of the exact amount per metre, to the best location at the desired speed (i.e. calibration) to achieve the safest, quickest extinguishment. At this point I was left with two dilemmas. 1. Who do I get to try and develop this program? I chose Amos Mills to develop the program. He had no prior knowledge of fire behaviour but an extensive expertise with computer programming. 2. What would I do to identify where the water is going? Previous experience with a boom spray has made me very aware of spray drift. I started to look at where the water could be lost. There are many causes of water loss and wastage that I will address later in this report. For the WIESE Calculator the following information needs to be gathered for input. Fire Danger Index (FDI) Current fuel load for the fire are in three categories. Natural/ un grazed grass Grazed/ mown grass Eaten out The calculator uses this to predict the forward speed of fire, quantity of fire appliances, distance travelled and anticipated time elapsed before fire will be contained. Press Chart it to get a graph of what is happening and what should happen for the conditions on the fire ground if the resources are correct. I have based all my trials at an average travel speed of 20kph. I have then worked on getting a stream of water that can hold together and be delivered to where it is aimed to be placed and be effective in extinguishing the fire. The most common nozzle on CFS appliances, in my estimation, is giving the worst result for grassland fire fighting. I have developed a nozzle that would meet my expectations of capabilities. 11

12 These findings allow a quantity for resources and capability to be determined. By playing with the inputs in the WIESE calculator for amount of water per minute, size of appliance, fuel loading, or perimeter factor it can be identified that big improvements are possible in the time it takes to suppress the fire. This means that fewer resources are required to achieve greater saves of environmental and physical assets, thus ensuring greater effectiveness on days of higher FDI. To use less water per meter from the appliance requires everyone to learn what has to happen to stop wasting water and to act upon this knowledge. I have seen results that exceed seven litres per meter and have knowledge of other results that have been above thirteen litres per meter. I have seen in excess of 2000 metres of stubble extinguished with only 2000 litres of water but have also seen 3000 litres of water used to achieve absolutely no result. Greater consistency would achieve highly improved results. Over the past summer whilst conducting my trials I have used in excess of 150 appliance loads of water which equates to more than 450,000 litres. I have tried and trialled different types of nozzles for different types of grassland fuels at different speeds and with nozzles placed in different positions on the appliance and spraying at varied angles. I have trialled nozzles that are more water efficient on the monitor (Driver s side) of six separate appliances. They were used to good effect at the actual fires that were responded to. The Brigades trialling the nozzles were not aware of the likely benefits prior to this use and were understandably sceptical of the stated benefits. They were not in a position to implement all the refinements so further improvement is definitely possible. Fires where these try-outs occurred include: Red Bluff Road Senior. Good results from Mundulla, Bordertown, Wolseley. Fatchens Cannawigara. A very good result with one appliance taking out the head fire with no rekindle occurring.. Tilley Swamp. Very good result with fire emerging from scrub and very few appliances present. Days of lightning strikes showed that appliances with the nozzles had good effectiveness whilst the others were having difficulty. For example Bordertown 34 was very successful in heavy stubble whilst Kongal 24 could not achieve a result. 12

13 The Calculator The Wiese Fire Resource Calculator has seven separate sections. Section 1 Fire Danger Index Degree of fuel curing Temperature Relative Humidity Wind (KPH) Section 2 Truck and nozzle flow Litres per metre Flow rate litres per minute Truck water storage capacity Section 3 Fire and Time estimates Travel time to fire from ignition (minutes) Perimeter factor Section 4 Summary of Results Fire Danger Index Section 5 The Rate of Forward Speed Natural / ungrazed grass Grazed / mown grass Eaten Out Section 6 Expected truck speed (kph) Intercept distance (km) 13

14 Required appliances Intercept time (minutes from ignition) Section 7 Chart it! This is a graph showing fire speed in minutes, suppression rate in minutes, litres per perimeter and time. The information can be quickly processed by the program and gives useful information to fire managers with regard to the likelihood of success or failure for their actions taken to achieve fire control. Example Suppression of water rate per minute and per metre FDI Litres Litres Fire Speed Tanker Tanker Intercept Intercept per metre per minute Speed Numbers Distance time minutes in kms from ignition N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A To achieve a successful result we need to know how much water per metre is required, cease our water wasting practices and responding early with sufficient resources. Fires on days of low FDI do not matter too much, but as the FDI increases we need to ensure our response and suppression effectiveness matches the fire. Better nozzles are more at higher FDI s. Good suppression with one litre per metre of water that is 3000 metres per appliance load should be achievable. By comparison, one aircraft load will usually only achieve metres. 14

15 To maintain 300 litres per minute going onto a fire we would probably need 5 6 appliances unless the water supply is very close and of sufficient size. SUMMARY The Meter would be very useful to better predict a good response of fire resources on any given day and fire. By making better use of water and not losing it to drift and inaccurate application, along with applying the correct amount per metre in a one pass operation, would give a far more effective result. By having a calibrated water application of a set amount per metre and applying water at a faster rate per minute, but the desired same amount per metre and travelling at a faster pace, means there is less perimeter to extinguish. If this is modelled on the meter you will see this can very easily save halve of the water required, because the fire has not travelled as far. In trials with various nozzles and application rates, I have found it is possible to lose well over 50% of the water. My trials have indicated that for running grass fire suppression from a fire truck, the current nozzle being supplied is the worst nozzle for water loss. I have trialled this method in heavy stubble on my own property at Mundulla, with an FDI of near 30 and a flame height of 5-6m. I found that 1 litre per metre was effective on the flanking fire and increased the delivery to near 2 litres per metre at the head and maintained the same truck speed of 20kph with very good results. I have developed a nozzle that can deliver this result and be mounted in place of the normal monitor. I have trialled this same method with nozzles mounted to a fixed position to the front of a 34 appliance. I am of the opinion that we could achieve a better result and higher level of safety by having nozzles in a fixed position on the front of the appliance, with the water delivery controlled via solenoid valves near the driver s seat. If these trials and developments are correct, then one can see for a very modest outlay on truck improvements and operation, we could expect to have a considerable gain in performance on days of high fire danger in grass and stubble across a large area of South Australia and indeed Australia. DISCLAIMER The WIESE Grassland Fire Resource Calculator only provides a guide to the number of appliances and is still in an experimental stage of development. No warranties or indemnities are given to its accuracy or usefulness in any particular case. Use by trained personnel is advised. For further information please contact Brian Wiese Mobile

16 ACKNOWLEDGEMENTS Phil Cheney Andrew Sullivan Dennis and Heather Hudd (photography) Trevor Crane, Trevor Carter and Kym Altmann Mundulla CFS Brigade Murray Sherwell (advice) John Probert (test trays) Amos Mills (computer programming) Wendy Wiese Brenton and Michelle Jettner, Anita and Grant Lewis, Roslyn and Tony Doudle David Fry Keith Signs SA Country Fire Service (use of 34 appliance to conduct trials) Marg Ludwig BIBLIOGRAPHY 1. Bushfires fuel, weather and fire behaviour by Phil Cheney and Andrew Sullivan. CSIRO Publication 1997 ISBN (pages 18,19) 2. Guide and Tables for Bush Fire Management in Western Australia by Ralph Smith. FESA Publication 2009 ISBN