BACKGROUND OF THE INVENTION
 The use of hand tools presents, even to experienced mechanics, risks of injury to the hands, fingers and knuckles ranging from minor cuts and abrasions to more serious lacerations, dislocations, and broken bones. In using a wrench to tighten or loosen a nut, for example, the tool frequently slips, causing the user's hand to scrape against the sharp protruding edges of metal components. The risk of infection and other complications resulting from even relatively minor hand injuries is heightened by the fact that mechanical work is typically performed in an environment in which dirt and grease are prevalent and likely to enter any open wound or abrasion.
 Another area of health risk to hand tool users involves the inhalation of dust and particles that are released into the air from the action of the tool on the work material. For example, an automotive mechanic using an air-powered wrench or "gun" to remove, adjust or install brake drums or rotors, is exposed to asbestos-laden dust released from the surface of the brake linings. Since compressed air is typically vented from an exhaust port in the front of such air guns and is directed toward the brake linings, it contributes to the dust inhalation problem by loosening more particles and entraining fine and microscopic particles such that they remain suspended in the air for longer durations. Thus, even if the mechanic is wearing a protective face mask while operating the air gun, asbestos-laden fine/microscopic particulates will remain suspended in the air of the work environment and will be inhaled when the face mask is removed.
 Similarly, the operation of loosening a bolt with an air-powered wrench or ratchet tool is apt to abrade painted surfaces, causing fine particles of lead-based paints to become entrained by the tool's exhaust air. In other applications, the action of the air-powered tool may abrade masonry, generating silica dust, or chemically treated lumber, generating dust contaminated with arsenic or chromium.
 Another risk encountered by hand tool users is electrical shock. When the user's hand is exposed, it may come into contact with electrical wiring that is connected to the work material, causing the user to sustain a shock.
 The existing art in the field of protection for hand tool users is inadequate to address these risks. The most common form of hand protection is work gloves, but gloves inherently limit the mobility of the user's fingers, particularly when precision work is involved. The thicker the glove material, the more the user's digital dexterity is compromised. Thinner, more flexible glove materials allow greater hand/finger mobility, but at the cost of less protection from injury. In connection with the use of air-powered hand tools, gloves provide no ability to prevent the entrainment of deleterious particles from the work material. Nor do they typically provide the user's hand with insulation from electrical shock.
 While there are patents directed to shields for use with hand tools, W. D. Sullivan, U.S. Pat. No. 792,475 and Steven A. Sullivan, U.S. Pat. No. 5,898,937, neither of these provide flexible hand protection, and thus they unacceptably limit digital dexterity to a degree incompatible with the more sophisticated hand tools in use today, which often require use of the fingers to activate controls. Moreover, existing hand shields do not provide insulation from electrical shock or suppression of air-borne particulates associated with use of air-powered hand tools. The patents that do provide dust protection in connection with tool use, such as Kelly, Sr., U.S. Pat. No. 4,214,317, Whitman, U.S. Pat. No. 5,220,753, Azar et al., U.S. Pat. No. 5,527,207, and Radigan, U.S. Pat. No. 6,108,912, do not provide simultaneous hand protection.
 Therefore, there is an unanswered need in the current art for a shield for use with hand tools which will: (a) protect the hand, fingers and knuckles from injury without compromising manual and digital dexterity, (b) suppress the generation and entrainment of deleterious particulates in connection with the use of air-powered tools, and (c) insulate the hand from electrical shock.
SUMMARY OF THE INVENTION
 The present invention addresses the need for a hand shield adapted for use with both manual powered and air-powered tools which will not significantly limited mobility of the user's hand and fingers and will suppress the generation and entrainment of fine particles associated with abrasion of the work material and venting from air-powered tools. The invention uses a flexible durable material, such as extruded plastic or a heavy canvas cloth, to cover the back of the hand and fingers, so that they are protected from injuries resulting from contact with the work material. By covering only the back of the hand, the flexible shield leaves the user's fingers free to grasp the tool and manipulate levers, triggers, switches, buttons, or other controls needed to activate and adjust the tool's operations. In connection with the use of air-powered tools, the flexible shield is formed to cover the area from which exhaust air is vented and divert it downward and backward, away from both the user's face and the work material. Consequently, the compressed air is not directed toward the work material and does not loosen and entrain fine particles from that material or by contact with electrical wiring/connections.
 A protective hand shield having features of the present invention comprises a single-piece flexible shield fitting around the body of a hand tool and accommodating the handling of the tool by the user. Through a rear open side of the shield, the user's hand is extended to grasp the tool, with the fingers free to manipulate the functions of the tool. A forward closed side of the shield encloses the back of the user's hand that faces the work material. The forward closed side of the shield is thus oriented towards the action of the tool, e.g. tightening or loosening a nut, and protects the hand, fingers and knuckles from any injury which may be caused by slipping or rubbing against the surface of the work material or by contact with electrical wiring/connections.
 A working opening is provided in the forward closed side of the shield so that the working end of the hand tool may protrude out of the shield and engage the work material. In an alternate embodiment, one or more straps or fasteners extend across the rear open side of the shield and around the user's hand, thereby preventing the shield from slipping out of position on the hand and exposing areas of the hand to injury.
 In an alternative embodiment designed for compatibility with air-powered hand tools, the shield extends to cover the area of an air-powered hand tool where exhaust air is vented from the tool. The flow of the exhaust is redirected downward and backward through the interior of the shield and is released through the back and bottom of the rear open side. This prevents the exhaust air from being directed toward the work material and loosening and entraining fine particles therefrom, which may include harmful dust and contaminants, and causing such particles to become suspended in the air of the work environment where it would be inhaled by the user and others. In this embodiment, the rear open side of the shield is designed to accommodate the compressed air inlet of the air-powered tool.
 The present invention thereby fulfills the need for a flexible shield which may be utilized to protect the user's hand while affording the hand and fingers freedom to move and manipulate the tool and its controls. In connection with the use of air-powered tools, it also provides a means of suppressing the production of harmful particulates from the work material and the entrainment of such particulates in the work environment where they may be inhaled. The present embodiment is not limited in its application to particular types of tools, but is readily adaptability for use with any type of hand tool.
BRIEF DESCRIPTION OF THE DRAWINGS
 FIG. 1 is a side elevation view of the protective hand shield mounted on an air-powered wrench, which is shown in ghost view.
 FIG. 2 is a front perspective view of the protective hand shield mounted on an air-powered ratchet, which is shown in ghost view.
DESCRIPTION OF THE INVENTION
 As shown in FIGS. 1 and 2, a protective hand shield embodying the features of the present invention 10 comprises a flexible shield 11 with a forward closed side 12 and a rear open side 13. The shape of the flexible shield 11 is adaptable to various hand tools 15. A typical air-powered wrench "gun" 15 is shown in FIG. 1, and an air-powered ratchet 15 is shown in FIG. 2. In each case, a working opening 14 is provided in the forward closed side 12, which opening is designed to fit around the hand tool 15 yet still allow the working end of the tool 15 to protrude from the flexible shield 11 and engage the work material (not shown). Additionally, the shape of the shield 11 may be adapted to accommodate the compressed air inlet 16 on an air-powered hand tool 15. The shield 11 is fabricated from a material, such as extruded plastic or canvas cloth, which is durable and thick enough to prevent injury to the user's hand, but also light-weight and flexible enough so as not to hinder hand and finger movements. Optimally, the material from which the shield 11 is fabricated is a good electrical insulator.
 The forward closed side 12 is molded to conform to the shape of the back of the hand, knuckles and fingers. The molding of the forward closed side 12 accommodates both right and left handed users. The a rear open side 13 accommodates the insertion of the user's hand and affords sufficient space for the hand to maneuver and manipulate the hand tool 15. With respect to the relative proportions of the forward closed side 12 and the rear open side 13, the shield 11 is configured such that the back of the hand is fully enclosed but the fingers and the wrist remain unencumbered.
 As applied to an air-powered hand tool 15, the flexible shield 11 is designed to redirect the air released by the exhaust air vent 17. The forward closed side 12 is formed to cover the area of the exhaust air vent 17 such that the exhaust air is diverted downward and backwards, escaping through the rear open side 13 towards the ground, rather than being directed at the work material (not shown). This prevents the exhaust air from entraining dust and/or particles from the surface of the work material (not shown) and prevents such airborne dust/particles, which may contain harmful constituents, from becoming suspended in the air of the workplace where they may be inhaled by the user and others.
 In an alternate embodiment, in order to secure the shield 11 in the optimum protective position, one or more straps or fasteners 18 extend across the rear open side 13 and around the user's hand. Such straps or fasteners may be fabricated of a flexible plastic, cloth, or elastic material
 In practice, the user places the flexible shield 11 over the hand tool 15 by sliding the working opening 14 over the functioning end of the tool 15. In the case of an air-powered tool, the forward closed side 12 is placed over the exhaust air vent 17 and the rear open side 13 is aligned with compressed air inlet 16. The user inserts his/her hand through the rear open side 13 around the hand tool 15, positioning the knuckles in the molding of the forward closed side 12. In an alternate embodiment, one or more straps or fasteners 18 are placed around the user's hand to secure its position in shield 11.
 While the present invention has been described is some detail with reference to certain currently preferred embodiments, other embodiments are feasible and will readily suggest themselves to those skilled in the art. Therefore, the spirit and scope of the appended claims are not limited to the description of the preferred embodiment contained herein.