Arc mapping
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Arc mapping is a technique used in fire investigation[1] that relies on finding the locations of electrical arcs and other electrical faults that occurred during a fire; the locations of the electrical faults can then, under some circumstances, indicate the progression of the fire over time.[2] It is usually performed by a forensic electrical engineer. It The technique relies on the assumption that, when heat from fire (or from hot gases caused by the fire) impinges on an electrical line (whether or not protected by a conduit), it will melt the wire insulation and cause an electrical fault at the first point that it reaches on the electrical line. For this to occur, the electrical line must be energized at the time that fire hits it.
Arc mapping often aims to determine the point of origin of the fire. A common assumption used in reaching this goal is that the fire expands uniformly in all directions as it burns, and maintains a circular shape centered on the point of origin; therefore, when an electrical fault occurs on an electrical line, the point of origin is on a perpendicular to that point. Contrary to this assumption, however, in many cases fire does not extend uniformly; in particular, large local fuel loads, venting, and air currents have a strong effect on fire progression.
Several other factors affect the locations where electrical faults occur. Electrical faults do not always occur where fire first reaches a conduit, but preferentially occur at bends in a conduit or at locations where wires are pressed together. The elevation of an electrical line has a strong effect on its exposure to heat, since temperatures in a fire are generally highest near ceiling level, except in the immediate vicinity of the point of origin. Protection from the fire is an important consideration: being located within a wall or being covered in fiberglass insulation will offer some protection to an electrical line, and will delay electrical faults.