Wildfires are part of a natural process that maintains the health of the environment. Efforts to curb wildfires in order to keep the local community safe from fire related accidents have short term benefits. But this type of human intervention is detrimental to the environment in the long run.
Wildfires can spread rather quickly, covering vast areas in just a matter of minutes. Wild-land urban interface (WUI) areas, the transitional area located right on the edge between urban areas and wild/uncultivated land, have seen a rise in population in recent times, along with an increasing demand for the infrastructural needs to support that population.
A fire-wise construction becomes particularly important in the case of properties located in WUI areas. Fire-wise construction and designs can increase a property’s resiliency by 85%.
Understanding Fires
Wildfires break out when the circumstances are conducive for little sparks to turn into massive flames. This depends on three basic components:
- Fuel – Fires feed on the vegetation that surrounds the property. The intensity and scale of the fire depends largely on the type of vegetation and how combustible they are.
- Topography – The type of terrain along with natural land formations such as slopes, valleys, saddles, ridges and so on greatly affect the ease with which a wildfire can spread.
- Weather – Wind, humidity, temperature and oxygen content are individual factors in a location’s weather conditions that collectively contribute to wildfires.
While weather conditions are beyond our control, the topography of a site location can be altered to some extent. The type of vegetation on the property premises and in the vicinity can also be modified. The construction and design of the property itself is entirely in our control.
There are three main ways in which fires can spread.
- Convection – As fire burns, hot gases move up creating horizontal winds and vertical air currents as air from below rushes in to replace the rising air.
- Firebrands – The vertical air currents carry partially burned material known as firebrands and deposit them in the immediate surroundings such as trees, buildings and grass.
- Radiation – Fires radiate a lot of heat. This radiation moves in straight lines and can also make structures warm and dry. Some building materials can ignite due to the radiation even before the fire actually reaches the structure.
- Direct Contact – This is when the fire comes directly in contact with the building.
Choice of Location
The place where a property is constructed should be carefully selected after taking all the relevant factors into consideration.
Site Suitability
Some basic measures while choosing a fire-wise location have been listed below:
- Construct your property in areas where vegetation is limited.
- Make sure the ground on which the property is built is level.
- The property should have easy entry and exit routes with emergency alternatives.
Aspect
When located over mountainous terrain, the cardinal direction that the slope faces, also known as its aspect, determines how fire-wise a property is. South facing slopes in the northern hemisphere receive more sunlight throughout the year and hence the vegetation is less, drier and more prone to catching fire. East and west facing slopes are more densely vegetated than south facing slopes. However, they tend to become extremely dry during the hot months of summer. The vegetation on northward facing slopes is the thickest. The moisture content over here is also the highest throughout the year as they receive the least amount of sunlight. However, when fires break out in these regions, they tend to be severe because of the abundance of organic fuel.
Topographical Features
Locations with ridge tops, canyons, gullies and other unique landforms should ideally be avoided.
- Valleys: Wildfires burn with a lot of vigor when they transit these enclosed spaces.
- Ridges: Fires gain in momentum as they climb a ridge’s surface. There are no shelter points on a ridge which exposes the property to danger.
- Saddles: Saddles can be thought of as shallow valleys. Their structure is ideally suited to propagate fires.
- Slope: Fires can spread easily when the ground is inclined by more than 30%.
Defensible Space
The defensible space can be defined as the entire area around a property’s location on which all combustible material such as trees, plants and shrubs have been modified adequately to minimize the extent of damage in the event of an approaching fire. The design and construction of defensible spaces vary from place to place and depend on a variety of factors such as slope, aspect, type of vegetation and density of vegetation overgrowth.
The defensible space of a property can be broken down into three specific zones.
Zone 1
This is the entire area covering a 30 feet radius that circles a property (including the parcel of land on which the property is located).
Recommendations
- Avoid all combustible substances.
- Use irrigated grass, stone patios, and rock gardens
- Clean up the roofs and gutters before the fire season commences.
- Trim all overhanging branches before the fire season commences.
Zone 2
This is the circular ring area that lies between the outer edge of zone 1 and extends up to a radius of 70 feet around the property.
Recommendations
- Use only individual trees that are at a fair distance from one another.
- Ensure that there is sufficient crown space between trees – the space between the top of trees.
- Get rid of ladder fuels – trees of different heights placed next to each other that allow a fire from the ground level to climb to the top of the trees.
- Gravel paths and paved walkways can provide useful firebreaks in this zone.
- This zone can be used for garages, sheds and other peripheral storage structures.
Zone 3
This area begins from the outer edge of zone 2 and extends outwards. Vegetation is the thickest in this area
Recommendations
- Remove damaged trees, especially those corrupted by insects and tree diseases. Pruning is not required in this section.
- Monitoring the space between individual trees largely depends on the type of vegetation.