What Is A Fuel Break?

Last updated on April 17, 2018

In order to protect your home from future wildfires, it is important to clarify what is meant by the terms ‘firebreak’, ‘fuel break’, ‘shaded fuel break’, unshaded fuel break and ‘fuel management band / strip / measures’ as these terms are frequently used interchangeably.

Since the 2017 fires, the Portuguese Government has reacted by issuing a raft of new laws and amendments, reinforcing their 2006 fuel management measures…which had obviously been ignored.

One of the latest amendments features increased penalties for non-compliance and has apparently caused much confusion, anger and panic tree cutting, with some people obliterating all their trees, including healthy deciduous ones…often in the middle of towns. Either the laws are being misinterpreted or local municipalities are putting their own visions of fuel management in their notices and brochures. It did not help when a misleading email warning (see below) was sent to householders from the Tax Authority.

Misleading Email from Tax Authority

“Before it is too late, before it reaches you, clear the bush 50 metres around your house and 100 metres in an area around all villages. This must be done before March 15th.”

The public needs to:

Clear the bush and cut down trees:
50 meters around houses, warehouses, workshops, factories or shipyards;
100 metres on land around villages, campsites, industrial parks, logistics areas and landfill sites
Cut trees 4 metres above the ground and keep them at least 4 metres away from each other
Cut all trees and shrubs within 5 metres of the house and stop branches from growing onto the roof;

“If you do not do this by March 15th, you may be subject to a fine ranging from €140 to €5,000 for individuals and from €1,500 to €60,000 for entities.

“Until May 31st, councils can clean around properties if the property owner does not. Owners are required to allow access to their land and to reimburse the Council for the amount spent on cleaning.”

Why this is a such a blatantly wrong interpretation of the law…

There is no indication who is effected and should be clearing the ‘bush’. Only householders in rural locations where they adjoin the forests, need to clean their land. This omission may account for why healthy deciduous trees are being destroyed in the middle of towns, gardens and parks.
The use of the word ‘cleared’ is wrong as it implies all vegetation must go. ‘Cleaned’ is the operative word that needed to be used – clean all the undergrowth, combustible debris on the ground and ladder fuels.
No trees, not even pine and eucalyptus, are required to be cut. Obviously they can be cut if you want to but they are only legally required to be thinned and pruned to the required distance between the canopies and branch height, which is specified for pine and eucalyptus only at 10 metres and ALL other trees at 4 metres. Small wonder the effected rural population is destroying all their trees left, right and centre.
There is no attempt to distinguish the tree types, as the law does. Hence, fruit trees, olives and vines are being decimated.
There is no advice on clearing the tree debris after cutting. Left on site, this debris will become such good ground fuel for the next wildfire that it practically negates the cutting of the trees in the first place!

Lack of fuel management and the Pedrógão Grande fire…

“… fuel management measures around communications and around population clusters had not been fulfilled. The proximity between houses and trees in these clusters, due to lack of resources of the owners, created a situation of great risk to the homes. In communications, the obligations of the management entities and / or concessionaires had not been in accordance with legal requirements”. Source: CTI report

“The technicians of the forest producer organisations and the GTF – Gabinete Técnico Florestal / Technical Forestry Office were unanimous with regard to the great difficulty in enforcing the legislation on the defence of houses and agglomerations by implementing the secondary network of fuel management bands. The difficulties stemming from the problems of identifying the owners (sometimes even in the case of urban buildings), due to their absence and to the existence of undivided properties due to unregulated inheritances”. Source: CTI report

What is fuel?

Fuel is defined as any plant material such as grass, leaf litter and live vegetation which can be ignited and sustain a fire.

Fuel can be further grouped as:

Fine fuel: Grass, leaves, bark and twigs less than 6 mm in diameter that ignite readily and are burnt rapidly when dry. It is the availability, arrangement, size, quantity and moisture content of the fine fuel that plays a key role in determining the rate of spread and intensity of a forest fire.
Heavy fuel: Dead woody material, greater than 25 mm in diameter which is in contact with the soil surface, ie. fallen trees and branches.

The arrangement of vertical fuel can be grouped:

Canopy Fuel: The crowns (leaves and fine twigs) of the tallest layer of trees in a forest or woodland.
Bark Fuel: The flammable bark on tree trunks and upper branches.
Elevated Fuel: Shrubs and juvenile understorey plants up to 2 – 3 metres height.
Near-Surface Fuel: Grasses, low shrubs and heath plants like gorse and heather, sometimes containing suspended components of leaves, bark and twigs.
Surface Fuel: Leaf, twigs and bark on the ground or partially decomposed.

Layers of vegetation. Source: Tasmania Fire Service

What is a firebreak?

A firebreak is an area where all vegetation and organic matter is removed down to bare soil. Firebreaks can also be natural, such as rivers or streams, or artificial such as roads or ploughed agricultural fields…see the road in the header picture above.

A firebreak denies a fire any combustible material and reduces radiant and convective heat.
They are used to prevent advancing ground flames from coming into direct contact with buildings or other important structures.
A firebreak should technically be 2-3 times as wide as the height of the nearest ground vegetation.
Firebreaks may require frequent maintenance to remove invasive vegetation on the bare soil.
Creating a clean hard surface pavement 1 to 2 metres wide around the whole of your house is an example of a firebreak. This could be made of cement, crushed stone, large stone gravel or flag stones. This is recommended in Portuguese law whenever possible and you may already have a partial one if a side of your house faces a road.

What is a shaded fuel break?

A shaded fuel break is a strip or area of land (typically forested) which has been strategically modified or altered so living trees, undergrowth, dead branches, pine needles or fallen logs, (basically any potentially combustible material) are reduced or removed to break up the continuity of fuel and limit a fire’s ability to spread rapidly. See the header picture above – the burnt land on the right was a shaded fuel break, which kept the fire low on the ground with minimum fuel until it stopped at the road firebreak.

Within a fuel break, tall trees are thinned to reduce crown-to-crown overlap, particularly if any flammable trees such as conifers or eucalyptus are retained in the fuel break zone.
Deciduous trees are retained in a fuel break and additional trees of this type may be planted. They are generally fire-resistant because of the high water content in their leaves. A deciduous tree canopy can absorb and deflect a lot of radiant heat and may reduce the potential of crown combustion of flammable conifers.
Understorey live trees (saplings generally), climbing shrubs or tall plants should be reduced or removed to create vertical separation between fuel layers.
Deep ground tree litter, dead wood, logs, tree stumps and dead or dying trees should be removed.
Where possible retain the spaced trees in clumps.
Groups or single shrubs and perennial plants should be spaced to create horizontal separation.
All cutting debris must be removed from the site.
Keep grass cut and herbaceous shrubs pruned.
Fires can burn through a fuel break but at reduced speed and intensity, allowing fire suppression activities.
To be effective, fuel breaks need to be much wider than firebreaks.
Fuel breaks require less maintenance than firebreaks.
Fuel breaks allow access and space for fire prevention measures such as planned burning and maintenance of the area with further mechanical tree and undergrowth thinning.
Fuel breaks allow access, space and better safety for fire-fighters and fire combat measures like direct fire suppression and back-burning.
The separation between the building/structure and a fire improves its ‘defendability’ by reducing the radiant heat load on the building and short range ember spot fires.

What is an unshaded fuel break?

A fuel break without shade is usually a large opening cleared of woody vegetation so changing the vegetation to grass and low scrub bushes. It is not taken down to bare earth like a firebreak.

What is a fuel management band / strip / measure?

Fuel management is just a generic term for creating a defensive space against wildfires using any or a combination of the above methods.

In Portugal there are 3 types of fuel management networks in forest areas: primary, secondary and tertiary, defined by the Law 17/2009. The most important differences between them are in terms of fuel management band size and scale…

Primary networks contain the widest fuel management bands and operate at district level in rural areas. The functions include decreasing fire spread, facilitating direct fire-fighting, isolation of potential fire ignition points and protection of communication channels, social infrastructure, built up areas and forest stands of special value.
Secondary networks contain narrower fuel management bands and operate at municipal level in rural areas. They are for the protection of populations and infrastructures as well as isolation of potential fire ignition points and protection of communication channels, social infrastructure, built up areas and forest stands of special value.
Tertiary networks contain the narrowest fuel bands and operate at parish level in rural areas. They function only for isolation of potential fire ignition points relying on the electrical and divisional management of local forestry or agro-forestry management units.

In Portugal, any defensive spaces created to protect against wildfires are known as Fuel Management Bands / Faixas de Gestão de Combustivel and there is no distinction between a firebreak or fuel break.

According to the current Portuguese laws and amendments, it is shaded fuel breaks (strategically spaced trees and vegetation) that need to be created in the 50 m and 100 metre zones.

So basically you should aim to go from this…

Vegetation before land cleaning

To something like this…

Vegetation after land cleaning

Who needs a fuel break?

In Portugal any one who lives in or owns a building / structure in a rural area or zone that adjoins or overlaps with forested land (particularly unmanaged pine and eucalyptus forest) needs to create a fuel break / fuel management band. This is where the risk to life and property is greatest from wildfires. It is also known as the ‘urban-rural interface’ and includes roads, railways, electricity and gas supply lines or any other infrastructure that may be within the area.

Who does not need a fuel break?

In Portugal any one that does not live or own a building / structure in the above urban-rural interface, ie. in towns, cities or built-up areas. Rural fallow fields, pasture areas and gardens do not require a fuel break.

Fuel breaks on slopes

Portuguese law does not identify slopes as requiring particular attention when creating a fuel management band. In most cases the blanket 50 metres width will suffice around properties on moderate gradients but on very steep hills or slopes the widths, lengths and tree spacing may need to be to be increased.

This is particularly necessary on forest roads, as well as main highways, which are frequently cut into hillsides with very steep up-slopes and down-slopes – the stipulated 10 metre fuel break is not adequate. It is these roads, as well as the main highways, that become the escape routes for village populations threatened by fire. As we saw in 2017, the lack of adequate or indeed, any fuel break protection along the roads contributed to the disastrous consequences. Read more about wildfires and fuel breaks on slopes

Header Photo: University of California, Agriculture and Natural Resources