In the previous FireSmart article “Breaking the Wildfire Disaster Cycle”
the impact of wildfire on people’s lives and communities was discussed. Article 2, “Taking Control”, outlines a few simple concepts for evaluating wildfire hazard factors on your property along with some basic recommendations to mitigate those hazards.WILD LAND FIRE IS AN ESSENTIAL NATURAL
event and for the most part inevitable in most Canadian ecosystems. It plays a key role in the regenerative renewal of our forests as well as reducing the overall fire fuel load. Communi- ties can become compatible with the natural process of fire. In other words, when home- owners take direct action to protect their properties, they become a wildfire adapted community.
To understand the mechanisms of structur- al ignitions during a Wildland Urban Inter- face or WUI fire, controlled burn research was conducted during the International Crown Fire Modeling Experiments in Fort Providence, Northwest Territories. Large scale burn test sites were created. Simulated structures built using common construction techniques and materials were placed at various distances from the edge of the burn area. The burn zones were ignited and each structure was carefully observed to determine the impact. The results were surprising.
With regards to the fire front it self, if the buildings had a minimum spacing of 10 meters clearance from the leading edge of the fire and were built with non-flammable roofing materials, 85% to 90% survived the initial blaze. It was not the intense radiated heat from the wall of fire that ignited the structures. More than 50% of constructed fuels that did ignite were caused by an accumulation of burning embers driven by the blaze generated convective winds. Once the constructed fuel load ignited, total destruction was the rule. It is a simple statement with enormous implica- tions....Fire spreads only into and onto loca- tions with fuels that support combustion and this includes your home. In a WUI fire event, unless you have taken appropriate mitigating measures prior to the blaze, your home will be part of the problem.
A house burns because of its interrelation- ship with everything in its surrounding “Igni- tion Zone”. These zones are prioritized based on the distance away from the structure. Pri- ority Ignition Zone 1 includes the house and its immediate surroundings extending out to 10 meters. Zone 2 encompasses all elements out to 30 meters and Priority Zone 3 extends outward up to 100 meters. The first step is a Priority Zone 1 assessment starting with the home and its immediate surroundings. Using a FireSmart Structure and Site Hazard Assessment form, homeowners evaluate their property based on key structural criteria, building materials used, landscape elements, aspect and vegetation. Points are assigned to the observations. These points are then tallied to provide an overall score. The lower the accumulative score, the safer the property is. Once the risks have been identified, measures can then be taken to alter wildfires potential relationship with the property. The process is repeated for Priorty Zones 2 and 3 but the specific elements being evaluated are different. The biggest bang for your buck will likely lie within Priority Zone 1 so this is the best place to begin.
START BY LOOKING AT YOUR roof, gutters and soffit system. If the roofing material is non combustible such as metal, tile or asphalt, you would score well. Unrated wood
shakes provide no fire protection and score poorly. The roof should be clear of debris such as branches, small twigs, moss and pine needles. Accumulations of these can be easily ignited after long dry spells. This is particularly true for gutters as they have a bad habit of collecting combustible materials. Any overhanging branches should be cut back or the offending tree should be considered for removal. Eaves with closed off soffits and underside vent screening (mesh no larger than 3 millimeters) will score well. Open eaves with non screened vents are not desirable as burning embers may collect under the roofline during a wildfire.
Outdoor living spaces such as decks and balconies, built out of non-combustible materials score best. Those built of flammable materials are less desirable. They should also be fully sheathed in below or they will score poorly. These spaces often trap embers and ignite any stored materials. Once ignited, the structure above is quickly consumed. Siding made of non-combustible materials such as concrete, brick, stone or hardi-plank would score best. Next best are log and heavy timber walls as they provide more fire resist- ance than board siding. Scoring worst is wood shake or vinyl siding finishes.
WINDOWS ARE OFTEN A WEAK SPOT IN the structure as extreme heat can cause the window glazing treatment to fail. As the window collapses, an opening is created allowing firebrands to enter the interior space. The larger the window, the more vulnerable they become. Tempered or thick plate glass is most heat resilient while single pane windows score poorly as they provide virtually no fire protection. It is not expected that a homeowner would choose to change out the windows but where the window space has the highest exposure potential, particular
attention should then be applied to the vegetative treatments.
The location of adjacent combustibles play a huge roll. Fire wood or construction supplies stored on or under decks or directly next to an exterior wall are extremely vulnerable to collecting em- bers. These should be moved at least 10 meters from your home. Small quantities of heating wood can be brought in closer seasonally when wildfire potential is minimal.
Propane tanks should be located an appropriate distance away from structures, 10 meters is preferred. Any flammable vegetation should have a minimum 3 meter clearance from the tank.
VEGETATION MANAGEMENT WITHIN
Priority Zone 1 is paramount. The idea is to create a fuel modified area in which flammable vegetation surrounding buildings is either eliminated or converted to less flammable species. This fuel free zone should extend outward in all directions 10 meters on flat terrain. In particular, coniferous shrubs such as Juniper, Mogul Pine and ornamental Cedars are notorious for explosive combustion. If they are located adjacent buildings, they should be moved or substituted. Deciduous replacements, consistent with ecological factors can have additional positive benefits retaining valuable moisture and humidity during the dry seasons. Buildings located on slopes will need different criteria and firebreak spacing. The key consideration here is how to break the path fire takes towards or away from a building.
The aspect and location of the structure in reference to slope plays an enormous roll in FireSmart scoring. South facing slopes dry out quicker than those facing North. Fire has a tendency to be driven uphill with greater speed therefore structure setbacks with proximity to shrubs and trees become unique scoring considerations.
ROOF MOUNTED SPRINKLER SYSTEMS rate well and provide a good layer of protection duringawildfireevent. Theysoakthestructure lessening the impact of firebrands contact as well as increasing the surrounding areas relative humidity. Unfortunately, power may fall victim to flames and pump systems often rely on electricity. If they can run independent of power and have an adequate water supply, they will be effective. Keep in mind you may be asked to evacuate in which case their reliability would be uncertain.
CLEARING SURROUNDING VERTICAL FUEL load is a key element to improving your FireSmart score. Removing ladder fuel (low hanging branches) up to 2 meters from ground level will break ground fires path to the trees crown and is an easily implemented precaution.
WE ARE SCRATCHING THE SURFACE ON Priority Zone 1 and it may seem overwhelming. The fact is, many elements on your property may already score well. It might take only small modifications to improve the overall score you’re trying to achieve.
To truly make a comprehensive FireSmart plan, many more details should be considered which also include Ignition Priority Zones 2 & 3 extending outward to encompass the entire neighbourhood. Article three will discuss this evaluation process and what programs exist to create a FireSmart community.
For more detailed information, you can go to www.firesmart.ca
– Mike Gall, Quadra Island Fire Dept
A house burns because of its interrelationship with everything in its surrounding “ignition zone”. Zones are prioritized based on their distance away from the house.