Bushfires

What are grassfires and how do they behave?

Melbourne suburb with grassland

Nyasha Jokomo

Posted November 03, 2023

Grassfires spread much faster than bushfires and can be extremely dangerous. Understand what causes them, the risks involved and how to prepare for grassfires this summer.

Grassfires are often underestimated in urban areas. Grass can dry out quickly in high temperatures, and long grass can be a fire risk. These fires can spread rapidly, fueled by fine grasses, and can generate intense radiant heat.

The Country Fire Authority (CFA) urges the importance of understanding the characteristics and behaviour of grassfires to help reduce the risk to your family and property. By taking proactive measures to reduce fuel loads, maintain your home and stay vigilant, you could mitigate the risk of grassfires and help protect yourself, your family and your home.

The CFA has information to help all Victorians understand their risk and have a plan, including understanding the difference between grassfires near cities and towns and grassfires in rural areas. 

Characteristics of grassfires

Rapid spread

Grassfires are known for their rapid spread, travelling at speeds of up to 25 kilometers per hour. As grass is typically dry and combustible, grassfires are especially prone to spreading faster under windy conditions.

Fuel source

Grass can provide ample fuel for fires, and it ignites easily due to its low moisture content. This makes grassfires highly responsive to ignition sources like lightning strikes or sparks from vehicles.

Grass height

The taller and drier the grass, the more intensely it is likely to burn.

Early start

Grassfires can start earlier in the day than bushfires, as grass dries quickly in extreme heat, adding to its unpredictability.

Radiant heat

Grassfires can generate large amounts of radiant heat. This radiant heat can cause surfaces to catch fire and can be a danger to anyone caught in the open.

Long dry grass field on roadside

The taller and drier the grass, the more intensely it is likely to burn. Image: Getty.

Ways that grassfires can start

Extended periods of dry, hot temperatures with a lack of rainfall can make grassfires more likely. But this alone, cannot start a grassfire. That is why its important to understand what can start a grassfire.

Motor vehicles and grassfires

Motor vehicles, especially those with hot exhaust systems, pose a risk of starting grassfires when driving through dry grass.  The CFA advises to avoid pulling over onto grassy areas during the Fire Danger Period.

A smoldering cigarette

A cigarette dropped on the grass or thrown out a vehicle window is extremely likely to start a grassfire in very dry conditions. It is vital to fully extinguish cigarettes properly and dispose of them safely.

Embers from barbeques or campfires

Campfires often produce flying embers, so it is important to properly extinguish them to help reduce the likelihood of embers igniting surrounding grass. Barbeques can also retain heat after use, and should never be left unattended until they have completely cooled off.

Glass bottles

Glass bottles magnify the sun and can create a spark when left on or near very dry, long grass. Glass bottles should always be cleared out and disposed of correctly. 

Person pouring water onto portable barbeque tray

Properly extinguish barbeques to help reduce the likelihood of embers igniting surrounding grass. Image: Getty.

How grassfires behave

Understanding how fire behaves can help to manage grassfires more efficiently. Grassfires can start anywhere, including near urban areas. Therefore, it will help to be prepared and aware of the risks.

Weather influence and wind direction

Weather conditions, particularly wind and humidity, often have a significant impact on grassfire behavior. Low humidity and high winds can exacerbate the grassfire's spread. Grassfires are often more prevalent during dry seasons or droughts when vegetation is parched and more susceptible to ignition. When the wind changes direction, it can influence the size of the fire front making it larger.

Fire behaviour

Grassfires can produce spot fires, where embers or burning debris are carried by the wind and ignite new fires ahead of the main front. They typically burn close to the ground, primarily consuming surface vegetation.

The intensity can vary depending on factors like fuel load, like the length and moisture content of the grass, and wind speed. The terrain also plays a part in the spread and intensity as fire tends to move faster uphill as the flames catch on to taller grass in front of the fire.

Grassfires produce radiant heat which pre-heats the grass in front of the fire, making it even more flammable. This means they often burn quickly compared to bushfires, as they primarily consume fine fuels on the ground.

Smoke and visibility

Grassfires can produce significant smoke, reducing visibility and air quality. This can pose health risks and make firefighting efforts more challenging.

How to help minimise the risk of grassfires

Prepare your property ahead of bushfire season, as waiting until a grassfire approaches may be too late to effectively mitigate the risk to your home and contents.

Help protect your home

  • Keep up a regular home and garden maintenance routine by mowing the lawn and removing debris from gutters and pipes.
  • Seal gaps in windows and doors as best you can.
  • Remove and store flammable items (including wood piles) well away from your home.

 

person putting garden debris into wheel barrow in backyard

Clearing debris and mulch from your garden could help to prepare your property for bushfire season. Image: Getty.

What to do during a grassfire

If a grassfire starts near you, it is crucial to prioritize safety and take appropriate actions to protect yourself and those around you.

If you live in an urban area next to grassland, the CFA recommends to walk at least two streets away from the fire and if you are further away from the grassfire, stay where you are, as grassfires are unlikely to spread into built-up areas.

Be sure to monitor conditions and warnings.

If you see smoke or fire, avoid driving. Smoke can impact visibility on roads.

If you live in a bushfire-prone area, take steps to be prepared before the fire season, have an emergency survival kit and create a bushfire plan that details how and where to evacuate to in the event you need to leave.

Stay informed

Monitor the bushfire alert levels and Fire Danger Ratings in your area as these will also give you information on grassfires. Always follow the advice and direction of emergency services.

Those who will be in bushfire-prone areas should consider downloading the VicEmergency app on their smartphones and save the number to the VicEmergency Hotline: 1800 226 226.

If you are in a life-threatening situation, call 000 immediately. 

These resources and apps can help you during bushfire season:

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The information provided is general advice only. Before making any decisions please consider your own circumstances and the Product Disclosure Statement and Target Market Determinations. For copies, visit racv.com.au. As distributor, RACV Insurance Services Pty Ltd AFS Licence No. 230039 receives commission for each policy sold or renewed. Product(s) issued by Insurance Manufacturers of Australia Pty Ltd ABN 93 004 208 084 AFS Licence No. 227678.