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4 <br />Retention of hazard trees, even those with significant wildlife value, is not <br />appropriate in public use areas were the likelihood of a target is highly probable. <br />Developing the Hazard Rating <br />The hazard rating is based on three components of the evaluation; failure <br />potential, size of defective part and target rating. Each component is assigned a <br />value of 1 to 4 and then totaled up. Generally speaking a tree hazard with a high <br />rating will have a higher level of risk to activity in and around it than one that <br />receives a lower rating. The hazard rating is one of the tools used to prioritize <br />abatement treatments. The three components are as follows: <br /> <br /> Failure Potential (4 points) – identifies the most likely failure and rates <br />the likelihood that the structural defect(s) will result in failure within the <br />inspection period. Examples of ratings are: <br />1 – Low; defects are minor (e.g. dieback of twigs, small wounds with <br />good wound wood development). <br /> <br />2 – Medium; defects are present and obvious (e.g. cavity <br />encompassing 10-25% of the circumference of the trunk, co-dominant <br />stems without included bark). <br /> <br />3 – High; compounding and/or significant defects present (e.g. cavity <br />encompassing 30-50% of the circumference of the trunk, multiple pruning <br />wounds with decay along a branch). <br /> <br />4 – Severe; defects are very severe (e.g. heart rot decay, conks along <br />the main stem, cavity encompassing more than 50% of the trunk). <br /> <br /> <br /> Size of Defective Part (4 points) – rates the size of the part most likely <br />to fail. The larger the part that fails, the greater the potential for <br />damage. Examples are: <br />1 – Most likely failure less than 6” in diameter. <br /> <br />2 – Most likely failure 6-18” in diameter. <br /> <br />3 – Most likely to failure 18-30” in diameter. <br /> <br />4 – Most likely to failure greater 30” in diameter. <br /> <br /> Target Rating (4 points) – rates the use and occupancy of the area <br />that would be struck by the defective part. Examples are: <br />1 – Occasional use (e.g. hiking, jogging, cycling trail). <br /> <br />2 – Intermittent use (e.g. picnic area, day-use parking, main roads). <br /> <br />560