The national standard for the protection of life and property from wildfires is National Fire Protection Association (NFPA) 1144. The following material is a combination of NFPA1144 plus information from Colorado Sate University and other sources.
A wildfire has three main weapons: radiation of heat, convection, and firebrands. Through them it will seek and compromise the weakest link in a property’s defense measures. The best defense will counter those weapons by reducing the possibility that the fire can approach closely enough for harm and by selecting construction materials appropriate for the potential exposure. Surviving a wildfire requires proper management of the defensible area around the structure, use of appropriate roofing material, and to a lesser degree, use of appropriate siding material.
An additional line of defense can be the use of a temporary surfactant that is applied just before the onslaught of the fire (addressed in Wildfire protection - Barricade® Gel).
Defensible Area is the space around structures where vegetation and other fuels should be pruned, reduced, and/or removed. It is divided into three defensible zones which should be maintained to reduce the potential spread of fire both from the woodlands towards the structure and from the structure towards the woodlands. Creating a series of management areas in which different treatment techniques are applied provides protection without simply denuding the terrain. There must be a primary protection zone around each garage, storage building, barn, dining hall, cabin, etc. that is on the site. A fuel reduction zone should encompass all of those individual primary protection areas. The design of the individual primary protection areas will vary with the size, type, shape, and materials used in the construction of the buildings. The slope of the surrounding terrain and the types and sizes of nearby vegetation will affect the design of both the primary protection zone and the fuel reduction zone.
Appropriate roofing materials for this environment (all structures in or near woodlands) means fire resistant, i.e., a class “C” or higher rating. Wood shake or shingles should never be used on any structure in or near forests and or grasslands even if provided with a fire-resistive treatment.
Zone 1 is the primary protection area; it includes each building and everything that is found within 15 feet of the most exterior edges of the extended structure (it may extend 25 or even 50 feet during a drought). The extended structure encompasses the furthest edge of the structure’s eaves plus any attached structures, including decks. In this zone easily combustible vegetation (i.e., dead or dry vegetation, oily vegetation, and all woody plants) should be removed. Green grass is not a concern unless it becomes too tall.
Chimneys / Flues: In addition to maintaining the clear space around the building as described above, all vegetation that is within 10 feet of a chimney outlet should be removed. A scheduled maintenance program should keep the vegetation properly pruned or removed. Wood-stove flues and fireplace chimney openings should be provided with an approved spark arrestor constructed of 12-gauge or heavier welded or woven wire mesh with openings no larger than 0.5 inch.
Utilities: New gas, telephone, electric, or other utility feeds should be placed underground whenever practical. Existing above-ground utilities should have long-range plans for conversion to underground feeds if at all possible. Overhead lines and poles should not have significant amounts of combustible vegetation under or around them.
Flammables and Combustibles: If there is an LP tank on the property it should be at least 25 feet from any structure. It should not be disguised or hidden so well that it cannot be readily located and identified by fire fighters. It should be aligned so that a fireball emitting from the end will not be directed at a building if it explodes. No significant combustible vegetation should be in close proximity to the tank. Although distance is mentioned a rule of thumb should be 5-10 feet.
Zone 2 is the fuel reduction area that is the transition between Zones 1 and 3. The largest single factor in determining the size of this zone is the slope or grade of the land and where the structure is situated on this slope. It may be increased in times of severe drought. Grass should be kept mowed and vegetation should be kept to a low height.
Typically, the fuel reduction area extends from the edge of Zone 1 outward so that it encompasses a total of 75 to 125 feet from the structure. Where it overlaps the primary protection area of adjacent structures, those primary protection areas prevails. In Zone 2 the treatment of combustible vegetation is modified. Dead, dry, and oily vegetation are still removed, as are woody plants and trees that are stressed (e.g., diseased or insect infested), dying, or dead. Other trees and shrubs should just be pruned and thinned to reduce the potential fire load. Thinning should also be done along both main roads and emergency vehicle access trails into the property.
Management of potential fuel in the fuel reduction zone is important. Acceptable methods include grazing, mowing, mulching, composting, and controlled burns. The latter should only be done by qualified personnel, e.g., United States Forest Service (USFS) or local fire department firemen, and then only under controlled conditions with appropriate controls. Mulching must be done carefully as piles of mulch are like piles of hay, i.e., subject of spontaneous combustion if piled too high. In addition, mulch is still potential fuel.
Zone 3, the final area, is relatively loosely defined and extends from the edge of Zone 2 to the property lines. Here the forest or woodland should be managed in a more typical manner so that good tree health can be maintained. Dead or dying trees and bushes should be removed; those that are infected by insects, disease, or otherwise are not healthy should similarly be culled. Thinning may be advisable for proper vegetation management or to provide adequate access roads for emergency vehicles and personnel. Tree spacing will vary according to the species of tree. Pruning per se probably is not necessary in this zone, but it may be needed to provide adequate visibility from access roads or for similar needs.
All properties potentially subject to wildfires should be evaluated using a tool similar to the Wildfire Risk and Hazard Assessment Form. After completing the form appropriate corrective actions should be taken to reduce the potential of loss and to ensure the safety of the fire fighters. The jurisdiction having authority (JHA) will probably evaluate the property. If the property owner does not take adequate steps to prevent or minimize loss by wildfire, the JSA may red tag the exposed property. Such action may mean that fire fighters will not protect the property except to prevent spread to other property.
If the possibility exists that fire fighters cannot respond in a timely manner to a property, further evaluation regarding the use of surfactants such as described in Wildfire protection – Barricade® Gel would be prudent.
Class “C” Roof Coverings are fire-retardant, afford a measurable degree of fire protection to the roof deck, do not slip from position, and pose no flying firebrand hazard when in light fire conditions. While the fire conditions in a wildfire normally exceed those for which the roof covering is rated, it is considered satisfactory for the normal exposure.
Convection is one of the ways that wildfires advance – they can ignite combustible surfaces by coming into contact with them through air movement.
Defensible Space is the area between an improved property and a potential wildfire where combustible materials and vegetation have been removed or modified. It is created to reduce the potential for a building fire from spreading to the vast fuel source of the woodland (and vice versa) and to provide a safe working area for fire fighters who are protecting life and improved property from a wildfire.
Firebrands are another way that wildfires advance - burning materials are sent out by a fire in winds and updrafts caused by the fire. They are usually small embers but can be as large as twigs or small tree branches depending on the severity of the fire. A firebrand can be carried a very long distance in a wind.
Fuel Modification is the removal of fuel to reduce the likelihood of ignition for the purpose of fire control. It may consist of mechanical or chemical eradication of underbrush, pruning of dead, diseased, or infested shrubs or tree branches, or even controlled burns to create fire breaks.
Ground Fuels are materials such as grass, tree or shrub roots, decaying or rotting wood, leaves, sawdust, etc. that will support combustion and spread fire fall in this category.
Improved Property is land on which a building is placed, a marketable crop is grown, or other improvements have been made.
Radiation of Heat is one of the ways that wildfires advance – by radiating heat the same way the sun does when you stand in sunshine. Radiant heat can ignite combustible materials from distances of 100 feet or more.
Vegetation Classifications and examples: * Light: grasses, saw-grass, and tundra * Medium: light brush and small trees * Heavy: timber, hardwoods, and heavy brush * Slash: timber-harvesting residue
Please call us at 800-463-8546 to discuss this or any other risk management safety tip, or visit our web site at www.redwoodsgroup.com to learn more about JCC risk management issues.