If bushfires are the lumbering dinosaur of fires, at times barely moving and at other times at rates of spread around 6kph, then grassfires are the terriers, always moving, always changing direction, instantly responsive to changes in the fire environment, waiting to nip your heels when you're not looking.

Use all the knowledge of bushfire behavior you have gained as a firefighter and adapt it to grassfires. The same three variables that affect bushfire behavior — fuel, weather and topography — also affect grassfire behavior. The big difference is the speed at which the changes in fire behavior occur and the risks this imposes on the firefighter.

LEARNING OUTCOMES

Firefighter training has a tendency to focus on bush and structure fire suppression skills. Considering that 75% of Australia is grassland and that a large percentage of our wildfires actually are grassfires, it's important that firefighters fully understand the inherently different strategies and tactics needed to safely suppress a grassfire.

1. Grass fuels are responsive to weather variables. The fact that most grass fuels are by classification a fine fuel, smaller than your little finger or less than 6mm, means they are highly responsive to changes in weather. Once the curing process is completed, grassfire behavior will be highly responsive to changes in relative humidity, fuel moisture content, temperature, and wind speed and direction.

   With an almost instant link to weather information and the availability of portable weather meters, such as the Skymate or Kestral 3000, today's firefighters have access to data that enables them to accurately predict rate of spread, fire shape and flame height. This information can be used by operations to formulate a safe grassfire suppression plan. Brigades should consider making these pocket weather stations standard equipment so that initial responders can accurately access local weather conditions and use the information to assist in the development of an effective safe suppression strategy.

2. Different grasses have different fire behavior characteristics. Fire behavior is determined by the structure and continuity of the fuel bed, fuel height, fuel load, degree of curing, and the fuel moisture content. Australia has five main grass fuel structure types — tropical, tussock, hummock, improved pasture and cropland — each with varying heights, rates of smolder and extinguishing methods.

3. Grass has a life cycle. All grass species have a lifestyle where the grass grows, flowers and dies. This process is called curing.

The proportion of dead grass in a pasture has a major effect on grassfire behavior. A study of grassland curing by the Victorian County Fire Authority found that:

• The state of grassland curing is critical to the initiation and spread of grassfires,
• Uncertainty in grassland curing estimates causes large uncertainty in fire danger estimates, and
• Grassland curing information heavily affects consequent fire management decisions and actions.

It's easy to assume that if the pasture is green then fire won't be sustained, but recent experience has shown that grass barely more than 50% cured and with very visible green shoots readily sustains fire and with sufficient wind will spread across the countryside.

Information on the degree of grass curing is now available from many meteorology Web sites. This information gained from satellite pictures gives firefighters a start in their decision-making processes. Preplanning of crew and equipment requirements, locations of suitable control lines and general warnings to the public can be based on this information. It's easy for fire planners to predict fire behavior at either end of the curing scale; it's when doubt exists over the percentage of curing that firefighters underestimate fire behavior.

GRASSFIRE CHARACTERISTICS

Just-cured grass is not readily set alight by embers, as good contact isn't made between the grass and the heat source. Mown grass or cut hay allows a better contact, so therefore they ignite more easily. Other things to keep in mind when determining grassfire intensity are:

Flame. The visual display of combustible gases emitted from the fuel bed, igniting in a flame flash often meters above the ground, makes it difficult to give accurate details about flame height. Fluctuations in wind strength and direction combined with changes in the fuel bed make any prediction of flame length or flame angle almost impossible.

As firefighters we need to observe the fire behavior; predict what the fire is going to do based on expected changes in fuel weather and topography; then decide what attack strategy is safest, head, flank or parallel.

The rule of thumb that I use for bushfires applies equally to grassfire. If the flames are more than two meters high then head attack is not recommended.

Residence time is the period during which fire remains burning on one spot on the ground. A fast-moving grass fire would have a short residence time compared with a scrub or forest fire. A heavy pasture may have a residence time of 15 seconds; a light pasture, five seconds; and a forest fire, more than an hour. It is calculated by dividing the flame depth with the rate of spread. Residence time is a key component of the flame zone, as it determines the flame depth.

Flame depth is the distance of continuous flame. It does not include isolated pockets or logs. It is calculated by multiplying rate of spread by residence time. A firefighter's chance of surviving a flame depth of more than a few meters is small. My rule of thumb is if you can't see the other side of the flame, then you shouldn't be in front of it.

Smolder time is the length of time fuel will smolder after the head fire has passed. This can vary from 60 seconds to several days. In the 2003 Northeast fires I saw clumps of tussock grass smoldering for more than two days. For firefighters this means a good control line and thorough blackout of the edge are necessary if they were to stop the progress of the fire in any sort of windy conditions.

Fire intensity is 500 times the fuel load and rate of spread. Even higher levels of intensity could be experienced at any point during the fire due to the variances and fluctuations of the wind. Flanks could become the head on any change in wind direction. This is what makes grassfire suppression so dangerous.

Fuel moisture content. Grass with a FMC above 15% needs sustained flame to ignite, but small embers can ignite a grassfire in areas with below 6% FMC.

TACTICAL RELIEF

All strategies should form part of an integrated community protection plan. This should start with community education programs containing information on ways for residents to protect their properties and followed up with support works from local fire brigades or land managers, such as fuel-reduction burns or roadside clearing, to enhance the works already performed.

Farmers should work with fire agencies to determine where the most appropriate locations to attack a grass fire are — that is where the most works should be conducted. They also should consider the direction the fires are going to move based on historic fire data. In Victoria, the predominant summer wind is northerly followed by a southwest wind change, so it is logical that the larger firebreaks need to be at the southern and northeast ends of the paddocks. Also it would make sense to consider plowing around trees in paddocks and plan the grazing of pasture to ensure that the eaten out paddocks form part of your defense strategy.

Tests conducted by the National Bushfire Research Unit have confirmed that in the majority of cases, high-intensity grassfires will cross fire breaks of up to 20 meters wide. Should the firebreak be aimed at protecting fences? Certainly a 1-meter firebreak should do that. If the break is designed to halt the spread or to be used as part of an overall strategy to pull the fire up, then other factors need to be considered.

Are there any trees within 30 meters of the break? What type of trees? Does the firebreak alone have to stop the run of the fire, or will it be supported by fire crew, backburning or combinations of both? The size and effectiveness of the break will depend on the answers. The same break has a 99.5% chance of being breached with trees present. Unless fire trucks are present, most fire breaks can't be expected to hold more than a low-intensity fire.

In reality, unless we are going to use the fire break as a place to start a back burn from, it must be more than 10 meters wide to have any chance of stopping a running grassfire on a day of high-fire danger.

Under no circumstances should direct attack be mounted on the head. Containment must begin from a secure anchor point and progress toward the head as the fire edge is knocked down — firefighters should always have one foot in the black and one foot in the green

The USDA Forest Service Appropriation-Use Manual is a quick-ready reckoner for firefighters. If you know the wind speed you are very quickly able to determine fire behavior and the difficulties encountered in suppression efforts.

DEVELOPING A SAFE STRATEGY

Different brigades in different states and different countries all have standard operating procedures that will determine the sequence of attack on a grass fire. In Victoria, there's RECEO: Rescue, Exposure, Containment, Extinguish and Overhaul. The overall priority is crew safety, followed by others' safety, property preservation and suppression.

To determine the safest suppression strategy, the crew leader must be able to accurately predict current and future fire behavior. One of the key determinants of grassfire behavior is the moisture content of the vegetation. Whereas forest vegetation may take months to dry out, pasture and crops can wither in a matter of weeks. Given accurate information on pasture and crop condition, grassland fire behavior can be predicted, giving weight to fire danger forecasts, total fire ban declarations and resourcing decisions.

The responding brigade can add to the known information about degree of curing and fire danger index by supplying data on local weather and actual fire behavior, as well as topographic and fuel load details. The first unit to respond should do an initial size-up before leaving the station of the fire's potential using their knowledge of local conditions and assets threatened, and then respond with an appropriate number and type of resources. On arrival they can determine priorities. Using the available support services the initial responders should seek an up-to-date weather report with any expected weather changes.

If it is safe to do so, an attack strategy based on all the information received may be implemented by the first crews arriving. By preplanning certain response triggers, adequate resources can be en route while the attack strategy is being fine-tuned.

An example SOP follows:

1) A preplanned response should be made based on the fire danger rating of the day. It's always easier to downsize after adjustments have been made for on-site conditions.

2) A head attack can be attempted if flame height is below two meters, if the width of the head fire is short or if it can be attacked from behind. The type of firefighting vehicle also will determine the attack method. Vehicles with under 1,000 liters of water are of more use supporting larger vehicles and should only attempt head attack in moderate conditions; otherwise flank attack is necessary.

3) On days of high fire danger, the aim should be to control the heel and flanks first with most crews on the flank when the wind change is expected. Only attack the head fire when conditions make it safe to do so.

4) Use the one-lick method in a strike team of five vehicles: The first knocks down, the second fills in the gaps, the third strengthens the line, the fourth blacks out and mops up smoldering material, and the fifth replaces the first empty vehicle.

5) Ensure crew safety. Use heat shields and wear all protective clothing, including face masks and goggles. Take the black with you and work from burnt ground, if possible. Drive safely, remembering the crew on the back are getting all the heat and smoke. Watch for fence lines, boggy areas, stump holes and burrows. Maintain water reserves

7) The officer in charge should stand back and direct the firefighting effort to ensure all vehicles are working together toward the same plan.

Greg Harry is a wildfire instructor for the Emergency Service Training Unit at Swinburne University. He was a project firefighter with the Department of Sustainability and Environment, Victoria, and now assists in the development and implementation of Project Firefighter training for the Port Phillip Region. He also is a lieutenant in the Gembrook Country Fire Authority.

BREAKING THE FIRE TRIANGLE

I received responses from around the world on ways that worked for grassfire suppression. Methods include:

High-power blower

For low-intensity grassfires, petrol-operated high-pressure air blowers have been successfully used where water supply is limited. Scientifically this should work, similar to blowing out a candle, and I am keen to get out the leaf blower and give it a try.

Navajo grass rake

This attachment is similar to a heavy-duty paddock harrow, which attaches to the side or rear of your vehicle. This method can cover large distances and is very successful on the flanks. It works by disturbing the continuity of the fuel bed and would certainly lower the fire intensity to a level that would allow easier suppression.

Fire truck wheels

By driving two vehicles in a line, I've been able to disturb the continuity of the fuel bed to halt the spread of a low-intensity grassfire and minimize the water needed for suppression. It also gave me a ready-made break in which I felt comfortable using a small backburn. This was quicker than using a rake-hoe and a lot easier.

Class A foam

A quick spray at 0.5% to wet down the fuel and then a covering at 2% and you can quickly and easily begin to backburn. The drip torch crew can progress as fast as the crew can lay the foam and a follow up crew can patrol the line and do any suppression if needed.

The Wyoming model uses an equipment grass unit with 300 gallons of Class A foam, a brush unit with 1,000 gallons of Class A foam, a 2,000-gallon water tanker and a 7,500-gallon nurse tanker. The grass and brush units work in tandem with the brush unit doing the knockdown and grass unit completing the extinguishment. Water units are used as needed and placed in safe zones along the fire edge supported by the nurse tankers.