A tree is considered to be hazardous if it is structurally unsound and there’s a potential target.  Conversely an unsound tree in an area with no target is not considered to be hazardous.  A tree becomes structurally unsafe for a variety of reasons such as weak structure, decay of trunks and branches, cankers, root loss or root decay just to name a few.  Health and safety assessments can range from casual observations to detailed evaluations which may include climbing inspections and/ or root crown excavations.  Formal tree hazard evaluation reports can be provided for projects requiring health and safety studies.