Abstract:
A chain saw hazard warning light and method for using same. A pair of oppositely-directed light sources emit light beams throughout a chain shot hazard warning zone through rectilinear, slotted openings at opposite ends of a housing. The light beams turn on, if and only if, the cutting chain is rotating about the chain guide bar; alternatively, initiation of rotation of the cutting chain is delayed to permit the light beams to turn on some time prior thereto. The zone is defined by first and second pairs of planes that diverge in opposite directions from the chain guide bar, said planes being disposed at equal, acute angles (most preferably 15°) to, and on opposite sides of, a plane that includes the chain guide bar.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/461,991 for the same invention, filed on Jan. 26, 2011, the disclosure of which is incorporated herein. 
     
    
     STATEMENT REGARDING FEDERALLY APPROVED RESEARCH OR DEVELOPMENT 
       [0002]    None. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention relates generally to power chain saws and, more particularly, to safety devices as may be applied to alerting persons in the vicinity of a chain saw that they are in a zone of danger for potential injury from flying chain fragments in the event of a break in a cutting chain. More specifically, the present invention pertains to a chain saw hazard warning light, and a method for using the same, to warn personnel away from a zone of danger during operation of the chain saw portion of a forest harvester. 
         [0005]    2. Background Art 
         [0006]    Power chain saw operators and nearby personnel have incurred bodily injury and even death when hit by flying fragments of a broken cutting chain. This phenomenon, sometimes referred to as “chain shot,” can happen both on a manual chain saw as well as on a forest harvester equipped with a chain saw. Causes for breakage include improper chain tension, maintenance or repair, a damaged chain drive sprocket, chain guide bar and/or cutting chain, improper chain guide bar and chain lubrication, or excessive chain speed. Since a cutting chain can travel as much as 15,000 revolutions per minute around a chain guide bar, broken chain fragments will virtually always fly off at high velocity close to or within a plane that includes the chain guide bar. The direction of movement of chain fragments can be either in the direction that the chain guide bar is pointing at the time of chain breakage or in the opposite direction. In the case of a forest harvester, there is a direct hazard to the operator in the harvester cab when the chain guide bar is pointing toward the cab because chain shot has been known to penetrate the cab window under those circumstances and strike the operator within the cab. 
         [0007]    One approach to reducing the hazard presented by a broken cutting chain has been to impose restrictions on the movement of broken chain ends and chain fragments. For a hand-held chain saw, U.S. Pat. No. 7,690,407 B2 issued to Annala disclosed a protective wall positioned in the vicinity of the chain drive gear that was capable of receiving the movement of the tail of the broken cutting chain and guiding the broken chain in a desired direction. U.S. Pat. No. 5,101,567 issued to Cool disclosed a safety switch that deenergized the chain drive of a hand-held chain saw in the event of a break in the cutting chain, and also disclosed a chain braking mechanism and safety guard to effect stoppage of the cutting chain motion. U.S. Pat. No. 4,805,308 issued to Ritola disclosed a roller attachment to the handle of a hand-held chain saw. The roller was aligned with the chain guide bar so as to extend substantially perpendicularly through the plane defined by the chain guide bar in order to intercept the saw chain should it become derailed. U.S. Pat. No. 4,315,370 issued to Horne disclosed a finger piece that acted as a safety surface in the event of breakage of the cutting chain on a hand-held chain saw. The finger piece was located far enough forward from the chain drive to force the whipping length of the chain to pivot and catch the broken chain. 
         [0008]    The present invention, however, takes a different approach to the chain shot problem—namely, provision of a hazard warning light, preferably a flashing strobe light, illuminating just the chain shot danger zone to warn personnel away from that zone during operation of a chain saw. In other contexts, flashing lights and focused warning sounds have been used to warn of safety hazards. U.S. Pat. No. 6,587,043 B1 issued to Kramer disclosed a driver warning system that detected vehicle handling conditions and produced warnings in the form of arrays of flashing lights and/or a warning buzzer directed to the vehicle driver only, the intensity of which warnings was correlated to the seriousness of the safety hazards detected by the system. Patent Application No. US 2007/0102591 A1 of Toth disclosed a warning system for intersections, particularly railway crossings, that could identify when a train or vehicle was approaching an intersection and emit a sound warning beam that was focused into a danger zone. The approach taken by Kramer, i.e., by analogous reasoning, directing a hazard warning to the operator of a chain saw only, would be inadequate because nearby personnel who may be endangered by chain shot would not receive the warning. The approach taken by Toth, i.e., by analogous reasoning, focusing and projecting a sound warning into a chain shot zone of danger, would also be inadequate because the loud noise generated by the chain saw itself would tend to drown out the sound warning such that nearby personnel would likely not hear it. 
       SUMMARY OF THE INVENTION 
       [0009]    Thus, there remains a need for a chain saw hazard warning light that projects a warning light into a chain shot danger zone whenever the cutting chain of a power chain saw is rotating around the chain guide bar thereof. The term “chain saw” is here defined to include an electrically-powered, hand-held power chain saw as well as any power chain saw that is attached to, suspended from, or incorporated into a dangle head carried by an articulated boom of a forest harvester carrier. The danger zone certainly must include the plane that includes the chain guide bar portion of the chain saw, but, to adequately protect nearby personnel, the danger zone needs to be somewhat wider than that. Thus, the danger zone is defined by first and second pairs of planes that diverge in opposite directions away from the chain guide bar, said planes being disposed at equal, acute angles to, and on opposite sides of, the plane that includes the chain guide bar. The acute angles formed at the intersections of those pairs of planes with a plane that includes the chain guide bar are preferably in the range 10 to 20 degrees, and most preferably 15 degrees. 
         [0010]    Accordingly, it is an object of the present invention to provide a first beam of light that is projected into a chain shot danger zone in a first direction and a second beam of light that is projected into said chain shot danger zone in a second, opposite direction, if and only if, the cutting chain is rotating about the chain guide bar. 
         [0011]    In order to limit the first and second beams of light to illuminate the chain shot danger zone only, it is a further object of the invention to provide a housing that extends from a first end wall to a second, opposite end wall, said first and second end wall each having a slotted opening to permit-passage of said first and second light beams therethrough, together with a first electric light source means mounted within said housing adjacent to, and distance d from, said first slotted opening and facing said first direction, and a second electric light source means mounted within said housing adjacent to, and distance d from, said second slotted opening and facing said second direction, wherein each said slotted opening is rectilinear and is defined by a first parallel pair of sides having height H joined by a second parallel pair of sides having width W, and wherein said first pair of sides is parallel to said plane that includes said chain guide bar. 
         [0012]    In a preferred embodiment of the invention, it is a still further object that H is greater than W, and W and d are each chosen such that arctangent (W/2d) is preferably is in the range to π/18 to π/9 radians, corresponding to 10 to 20 angular degrees. 
         [0013]    According to one aspect of the invention, it is another object of the invention to employ a linear array of light emitting diode strobe lights for each of said first and second electric light sources, aligned parallel to said first sides of said first and second slotted openings, respectively. 
         [0014]    According to another aspect of the invention, for a chain saw that is mounted within an interior portion of a chain box for pivotal movement of the chain guide bar thereof between a retracted position within said chain box and an extended, cutting position outside said chain box, wherein said chain box is pivotally attached to an articulated boom that is carried by a forest harvester carrier, said chain box having a pair of side walls joined by a rear wall and said chain box having an open front to permit pivoting of said chain saw to a cutting position, hereinafter referred to as a harvester-mounted chain saw, it is another object of the invention to attach said housing to said interior portion of said chain box such that said first end of said housing faces toward said first direction and said second end faces said rear wall of said chain box; and said rear wall has a slotted opening in registry with said second slotted opening and is dimensioned to permit passage of said second light beam therethrough. 
         [0015]    It is another object of the invention to provide a wire tap for such a harvester-mounted chain saw, wherein said harvester-mounted chain saw includes a hydraulic motor for rotating said cutting chain around said chain guide bar, and said forest harvester carrier includes an electric battery and chain saw switch means wired to said battery for activating and deactivating said hydraulic motor, wherein said wire tap conducts electric current from said switch means to said first and second light sources if, and only if, said switch means is closed and said cutting chain is revolving about said chain guide bar. 
         [0016]    To achieve these objects of the invention, there is provided means for emitting a first light beam in a first direction within a chain shot warning zone; means for emitting a second light beam in a second, opposite direction within said warning zone; and means for energizing said first and second means for emitting a light beam to cause said means to emit light if, and only if, said cutting chain is rotating about said chain guide bar; wherein said warning zone is defined by first and second pairs of planes that diverge in opposite directions from said chain guide bar, said planes being disposed at equal, acute angles to, and on opposite sides of, a plane that includes said chain guide bar. 
         [0017]    In a preferred embodiment of the invention, said means for emitting said first and second light beams includes a housing that extends from a first end wall to a second, opposite, end wall, said first and second end walls each having a slotted opening to permit passage of said first and second lights beams therethrough, respectively; a first electric light source means mounted within said housing adjacent to said first slotted opening and facing said first direction; and a second electric light source means mounted within said housing adjacent to said second slotted opening and facing said second direction. 
         [0018]    Preferably, each said slotted opening is rectilinear and is defined by a first, parallel pair of sides having height H joined by a second parallel pair of sides having width W; said first pair of sides is parallel to said plane that includes said chain guide bar, H is greater than W, and arctangent (W/2d) is in the range to π/18 to π/9 radians, corresponding to 10 to 20 angular degrees. 
         [0019]    Advantageously, said first and second light sources each include four light emitting diode strobe lights aligned parallel to said first sides of said first and second slotted openings, respectively. 
         [0020]    In the case of a harvester-mounted chain saw that is mounted within an interior portion of a chain box for pivotal movement of its chain guide bar between a retracted position within the chain box and an extended, cutting position outside of the chain box, wherein the chain box has a pair of side walls joined by a rear wall, and the chain box has an open front to permit rotation of the chain saw to a cutting position, the housing of the chain saw hazard warning light is preferably attached to the interior portion of the chain box such that the first end wall of the housing faces toward the first direction and the second end wall of the housing faces toward the rear wall of the chain box; and the rear wall of the chain box has a slotted opening in registry with the second slotted opening of the second end wall of the housing and dimensioned to permit passage of said second light beam therethrough to illumine the entire chain shot danger zone. As is typically the case, such a harvester-mounted chain saw includes a hydraulic motor for rotating said cutting chain around the chain guide bar; the carrier includes an electric battery and chain saw switch means wired to the battery for activating and deactivating the hydraulic motor; and the means for energizing the first and second means for emitting a light beam to cause said means to emit light if, and only if, the cutting chain is in rotating about the chain guide bar includes a wire tap that connects the switch means to the first and second light sources and conducts electric current thereto if, and only if, the switch means is closed and the cutting chain is rotating around the chain guide bar. 
         [0021]    For use with a chain saw having a cutting chain mounted for rotation about a chain guide bar and with switch means operably connected to the chain saw for starting and stopping said rotation by energizing and deenergizing the chain drive thereof, respectively, there is further provided a method for projecting a warning light throughout a chain shot hazard warning zone if and only if, said rotation is, or will be within T seconds, occurring. The method comprises the steps of attaching to a chain saw or to a device to which the chain saw is attached, incorporated into, or suspended from, a chain saw hazard warning light, wherein the chain saw hazard warning light includes a housing that extends from a first end wall to an opposite second end wall, the first and second end walls each having first and second, rectilinear, slotted openings, respectively, said openings each having height H and width W. The chain saw warning light further includes a first electrical light source mounted within the housing a distance d from said rectilinear, slotted opening of said the first end wall and disposed for projecting a first light beam through said first slotted opening in a first direction throughout, and limited to, the warning zone, said first electric light source having a first pair of electrical wire leads; a second electric light source mounted within said housing a distance d from said rectilinear, slotted opening of the second end wall, and disposed for projecting a second light beam through said second slotted opening in a second, opposite direction throughout, and limited to, the warning zone, said second electric light source having a second pair of electrical wire leads. Further included within the chain saw hazard warning light are a first wire tap attached to a first wire lead of each said pairs of wire leads, and a second wire tap attached to said second wire leads of each of said second pairs of wire leads. The method further includes the step of wiring said first and second wire taps to the switch means. The warning zone is defined by first and second pairs of planes that diverge in opposite directions from said chain guide bar, said planes being disposed at equal, acute angles to, and on opposite sides of, a plane that includes said chain guide bar. Whenever necessary to achieve illumination throughout the entire chain shot hazard warning zone, the method further comprises the step of creating a slotted opening in any portion of said chain saw or in said device that interferes with the projection of light from said first and/or second lights sources into said zone Z in order to permit light to project from said sources throughout said zone whenever said rotation is occurring or will be occurring within T seconds. This is accomplished by interposing time delay means between the switch means and the chain drive of the chain saw so that closing the switch means turns on the hazard warning light before the cutting chain commences rotation about the chain guide bar. Optionally, the method further includes wiring electro-acoustic means into the switch means circuit to provide a sound alert to accompany the warning light. 
         [0022]    Thus, the instant invention provides these and other features and advantages that will become apparent from the detailed description and drawings set forth below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a perspective view of a felled tree being cross cut by a chain saw housed within a chain box attached to a dangle head processor of a forest harvester, which chain box that has been equipped with the hazard warning light of the present invention; 
           [0024]      FIG. 2  is an enlarged, perspective view thereof, showing that the cutting chain has broken and chain fragments that have been launched in opposite directions within the plane of the chain guide bar, as indicated by arrows; 
           [0025]      FIG. 3  is a further enlarged, perspective view thereof, showing the cutting chain still in motion about the chain guide bar, the felled tree removed, the chain saw pivoted about axis A-A to an extended, but lowered position, and the hazard warning light of the present invention attached to a side wall of the chain box above, and normal to, the axis A-A, and emitting a warning light as depicted by dashed lines; 
           [0026]      FIG. 4  is a reprise of  FIG. 3 , except that the chain saw is no longer in operation and has been pivoted about axis A-A up to a retracted position within the chain box, and, consequently, the hazard warning light is no longer emitting a warning light. 
           [0027]      FIG. 5  is a front, elevational view of the dangle head processor of the forest harvester, showing a slotted opening in a front wall of the chain box thereof to permit transmission of a hazard warning light beam therethrough whenever the cutting chain is in motion about the chain guide bar. 
           [0028]      FIG. 6  is a further enlarged, horizontal, fragmentary, cross-sectional view of the chain box taken along line  6 - 6  of  FIG. 5 , with the chain drive mechanism, chain guide bar and cutting chain removed for clarity, showing that, while the warning light beams extend in opposite directions along a plane C-C that is parallel and adjacent to a plane B-B that includes the chain saw bar, each of the beams deviates angularly and laterally from the plane B-B and thereby defines the shot chain warning zone that is illuminated by the two light beams. 
           [0029]      FIG. 7  is a front, elevational view of the hazard warning light of the present invention, removed from the chain saw housing for visual clarity. 
           [0030]      FIG. 8  is an enlarged, partially cut-away, right side, elevational view thereof, and showing the hazard warning light wired into a switch means circuit for the chain saw, wherein a time delay device and an electro-acoustic means are depicted in phantom outline to indicate that they are optional components of the circuit. 
           [0031]      FIG. 9  is a perspective view of an LED bar removed therefrom, comprising four strobe LED lights mounted within a solid, aluminum housing and a sealed, acrylic plastic lens. 
           [0032]      FIG. 10  provides an enlarged, elevational view of an exterior surface of a first end wall of the hazard warning light, its slotted opening and the first light source behind said opening; the second end wall thereof has an identical appearance. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]    Referring now to  FIG. 1 , a chain saw  10  is depicted as pivotally extended out of a chain box  12  and in the act of cross cutting a felled tree  14  that is encompassed by a pair of delimbing knives  25  and grasped between a pair of feed rollers  27 . The chain box  12  is incorporated into a dangle head processor  16  attached to an articulated boom  18  carried by a forest harvester carrier  20 . The forest harvester carrier  20  includes a cab  22  mounted over a parallel pair of treads  24 , as well as a hydraulic system (not shown) for actuating and controlling the treads  24 , cab  22 , boom  18 , dangle head processor  16  and chain saw  10 . A straight line  30  that extends from the chain saw  10  to the front window  26  of the cab  22  indicates a first light beam being generated in a first direction by the chain saw hazard warning light  100  of the present invention, which hazard warning light is installed within a hollow interior space  15  of the chain box  12 , as may be seen more clearly in  FIG. 3 . A second straight line  30 ′ extends through a slotted opening  13 S in a rear wall  13  of the chain box  12  in a second, opposite direction away from the chain saw  10  and chain box  12 , and depicts a second light beam generated by the hazard warning light  100 . The straight lines  30 ,  30 ′ lie in a plane B-B that includes the chain guide bar  10 B of the chain saw  10 ; see  FIG. 6 . Thus,  FIG. 1  depicts a hazardous condition for the operator (not shown) within the cab  22  of the forest harvester carrier  20  because, should the cutting chain  10 C break, chain shot  40  in the form of cutting chain links and/or fragments of the cutting chain could travel along a path close or identical to line  30 , penetrate the front window of the cab  22 , and strike the operator. Accordingly, when the operator sees the warning light  100  shining into the cab  22 , it is a visual warning to immediately move the dangle head processor  16  and/or interrupt the cutting action of the chain saw  10  to eliminate the danger. Alternatively, or in addition, in the event of a cutting chain break, chain shot  40  could travel in an opposite direction along, or close to, a path indicated by straight line  30 ′ and potentially injure nearby personnel positioned within the line of fire. 
         [0034]    In  FIG. 2 , the cutting chain  10 C is depicted as moving forward along a top margin of the chain guide bar  10 B (arrow  32 ) and as having broken and separated below a lower margin of the chain guide bar, with a proximal end of the cutting chain whipping around the chain box (arrow  34 ). Chain shot  40  is depicted as flying away from the chain saw  10  in a first direction, indicated by arrow  36 , and more chain shot is shown flying away from the chain saw in a second, opposite direction, indicated by arrow  38 , said first and second directions  36 ,  38  lying within the plane B-B that includes the chain guide bar. Since the cutting chain drive  10 D has not been deenergized yet, the hazard warning light beams  30 ,  30 ′ continue to shine within the plane B-B that includes the chain guide bar. 
         [0035]    In  FIG. 3 , the felled tree  14  has been removed for clarity, the chain guide bar  10 B is still in an extended position, the cutting chain  10 C is still revolving around the chain guide bar  10 B, and the first and second hazard warning light beams  30 ,  30 ′ are turned on. The hazard warning light  100  is here depicted as installed within a hollow, interior space of the chain box  12 . In this particular embodiment of the invention, the positioning and attachment of the hazard warning light  100  to the interior of the chain box  12  is adjacent to an interior surface of a left wall  12 L of the chain box, tucked away such that the chain saw can be pivoted, without interference from the hazard warning light, about axis A-A back to a retracted position within the chain box when it is not in use; see  FIG. 4 . A rear wall  13  joins the left wall  12 L and right wall  12 R of the chain box  12 . A slotted opening  13 S has been cut in the rear wall  13  of the chain box  12  to permit light to travel from the hazard warning light  100  through the rear wall in the second direction  30 ′. The chain box  12  is open at the front and thus presents no obstruction to transmission of light from the hazard warning light  100  in the first direction  30 . It will be understood however, that the hazard warning light  100  need not be installed within the hollow interior space  15  of the chain box  12 . It could be installed, for instance, to an exterior surface of the left wall  12 L or of the right wall  12 R of the chain box  12 . Other possible installation locations on the dangle head processor  16  will be apparent to persons of ordinary skill, provided only that care is taken to locate the hazard warning light  100  within, or near to, the plane B-B of the chain guide bar  10 B—preferably, within one meter of either side of said plane—and oriented so that, when energized, it will emit light beams in opposite directions  30 ,  30 ′. 
         [0036]    Referring now to  FIG. 6 , the hazard warning light  100  of the present invention is depicted installed within the hollow, interior space  15  of the chain box  12 , adjacent to an interior surface of the left wall  12 L thereof and adjacent to an interior surface of the rear wall  13  thereof. The axis B-B that includes the chain saw bar  10 B (bar omitted for the sake of clarity) is depicted as parallel and nearby to a plane C-C that longitudinally bisects the hazard warning light  100 . In the illustrated embodiment, plane B-B and plane C-C are so near to each other—e.g., less than 6 inches (16 cm) apart—that, for all practical purposes, they can be considered to be coplanar. In any event, the distance between plane B-B and plane C-C preferably should not exceed a man&#39;s stride or about one meter. Thus, for the purposes of the present invention, plane C-C is taken to be substantially coplanar with plane B-B and all references herein to the plane B-B are intended to refer equally to the plane C-C, and vice-versa.  FIG. 6  illustrates, therefore, that a chain shot warning zone Z is defined by a first pair of planes  50 ,  52  that extend angularly away from the hazard warning light  100  in a generally first direction and a second pair of planes  54 ,  56  that extend angularly away from said light in a generally second, opposite direction, thereby defining a chain shot warning zone Z. The angular deviation  8  of the planes  50 ,  52  from the plane B-B of the chain guide bar  10 B (coplanar with plane C-C) is preferably 10 to 20 degrees, and most preferably 15 degrees on either side of plane B-B. 
         [0037]    Although the warning zone Z as illustrated in  FIG. 6  is depicted in two dimensions only, it is actually three-dimensional as it includes a third, perpendicular, height dimension that is left unspecified in  FIG. 6 . But, since the purpose of the present invention is to provide a visual hazard warning to a chain saw operator and to nearby personnel whenever a chain saw is operating, the extent of the warning zone along the height dimension that is illuminated by the hazard warning light includes the usual eye level of such persons with respect to the instantaneous position of the chain guide bar. 
         [0038]      FIGS. 8 and 10  show that the hazard warning light  100  includes a housing  101  that extends from a first end wall  102  to a second end wall  104 , which first and second walls  100 ,  102  are joined at their upper and lower ends by a top wall  106  and bottom wall  108 , respectively, thereby defining a substantially closed, interior space. Left and right sides of the first and second end walls  102 ,  104  are joined by left and right side panels  110 ,  112 , respectively. Each of the end walls  102 ,  104  has a rectilinear, slotted opening  100 S having height H and width W;  FIG. 10 . It is seen in  FIG. 10  that the slotted opening  100 S is defined by a first, parallel pair of sides  118  having height H joined by a second parallel pair of sides  119  having width W. 
         [0039]    Means is provided for emitting a first light beam  30  in a first direction and a second light beam  30 ′ in an opposite direction throughout a chain shot warning zone Z. Said means includes a first light source  120  mounted within the housing  101  adjacent to, and at a distance d from, the slotted opening  100 S of the first end wall  102 , and a second light source  122  oppositely mounted within the housing  101  adjacent to, and at a distance d from, the slotted opening  100 S of the second end wall  104 . Preferably, each of the light sources  120 ,  122  comprises a linear array of four LED lights aligned and in registry with the slotted openings  100 S; most preferably, those are a linear array of four strobe LED lights that provide a flashing hazard warning when they are energized, such as the model STRB-4W vehicle strobe light. Said strobe light model has a 9 to 36 volts direct current operating range and is available, for example, on the Internet at www.superbrightleds.com; see  FIG. 7 . The distance d and the width W are chosen to make θ some desired angle according to the formula: arctangent (W/2d)=θ, where θ is measured in radians. For example, to achieve θ=15 degrees, which corresponds to π/12 radians, arctangent (W/2d) is set equal to π/12 or 0.26 (although some adjustment to this calculation may have to be made to allow for the thickness of the first and second walls  102 ,  104  and/or for the thickness of the rear wall  13  of the chain box  12 ). The height H is chosen to permit maximal illumination of the zone Z in the vertical dimension so as to be likely catch the eye of the chain saw operator and persons nearby whenever they are positioned within the chain shot warning zone Z and the chain saw  10  is in operating mode; thus, H will always at least be greater than W. In practice, W made equal to 0.45 inch (about 1.1 centimeter) and with d adjusted accordingly has provided the desired result. 
         [0040]    Means is provided for energizing the first and second light beams if, and only if, the cutting chain  10 C is rotating about the chain guide bar  10 B, as follows. Positive electrical leads of the first and second light sources  120 ,  122  are joined by a first wire nut  130  and negative electrical leads of said light sources are joined by a second wire nut  132 . A pair of wire taps  136 ,  138  have their first ends connected to the first and second wire nuts  130 ,  132  and their opposite, second ends are wired into a switch means circuit  220  that includes an electrical power source (e.g., electric battery  202  having a negative terminal wired to ground) and controls the starting and stopping of the chain drive  10 D of the chain saw  10 . In the case of a chain saw  10  that is attached to, suspended from, or incorporated into a dangle head processor  16  attached to an articulated boom  18  that is carried by a forest harvester carrier  20 , such switch means  200  is controlled by the operator in the cab  22  and, when the switch means is in a closed condition completes an electrical switch means circuit  220  that activates a hydraulic system to cause rotation of the drive shaft  208 S of a hydraulic motor  208  in driving engagement with the chain drive  10 D; see  FIG. 8 . Accordingly, if, and only if, the switch means circuit  220  is in a closed condition, and the cutting chain  10 C is thereby caused to rotate about the chain guide bar  10 B will electric current pass through the wire taps  136 ,  138  and thereby cause the light sources  120 ,  122  to illuminate the chain shot warning zone Z. In the case of an electrically-powered, hand-held chain saw  10  having electric switch means for triggering on and off an electric motor in driving engagement with a chain drive  10 D, the housing  101  is attached to the chain saw in or near the plane B-B of the chain guide bar  10 B (e.g. attached to a forehandle portion of the chain saw), and the taps  136 ,  138  are likewise wired into the electric switch means circuit  220  thereof and with like result. 
         [0041]    A still better warning can be provided by the chain saw hazard warning light  100 , both to persons within the chain saw hazard warning zone Z and to persons who are nearby and approaching it, if there is a time delay between the onset of emission of the first and second light beams  30 ,  30 ′ and the commencement of motion of the cutting chain  10 C around the chain guide bar  10 B. The time delay provides to persons within or approaching the chain saw hazard warning zone Z some time to leave the zone or change course to avoid the zone. This can be accomplished by interposing an electrical, time delay device  204  between the switch means  200  and the chain drive  10 D but not between the switch means and the chain saw hazard warning light  100 ; see  FIG. 8 . By this arrangement, a chain saw operator&#39;s closing the switch means  200  first energizes the hazard warning light  100  and only later, after a time delay, commences operation of the chain saw  10 . For this purpose, a suitable time delay could be, for instance, one to six seconds. Also optional is an electro-acoustical means  210  wired into the switch means circuit  220 , either in series with hazard warning light  100  as depicted in  FIG. 8 , or in parallel with the chain saw hazard warning light. The electro-acoustical means  210  can include a loudspeaker and/or an electric buzzer to emit sound into the chain shot hazard warning zone Z to accompany the light being emitted by the hazard warning light  100 , especially in the event that visitors are in or near the zone who are not normally in the area and are unfamiliar with the meaning of light emitted from the chain saw hazard warning light  100 . 
         [0042]    Although the above description and accompanying drawings relate to a specific, preferred embodiment of the present invention as presently contemplated by the inventor, it will be understood that various changes, modifications and adaptations may be made without departing from the spirit of the invention. It is intended that the invention not be limited to the particular terms used in the following claims and/or to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims.