Document v13nMG7nxJa2r3qM1d5Xzom5Y

operating conditions Since fencing and loca tion methods can be used only when a ma chine can be isolated, these methods will have limited use on most production setups Most production machines will require some kind of enclosure of the hazard points to comply with the OSHA regulations Types of guards There are several types of enclosures that are suitable for guarding hazard points de pending on how and where they are used The fixed guard is considered preferable to all other types and should be used m every case unless it has been definitely determined that this type is not at all practicable The fixed guard at all times prevents access to the dangerous parts of the machine Fixed guards may be adjustable to accom modate different sets of tools or various kinds of work Once adjusted, they should remain "fixed," and there should be no movement nor detachment of them Some fixed guards are installed at a distance from the danger point in association with re mote feeding arrangements which make it un necessary for the operator to approach the danger point A table of the safe distance of a guard fiom the danger point and the permissible size of openings in a fixed guard is given m the Pointof-Operation Guards section of this chapter Examples of fixed guards are found on power presses, sheet leveling or flattening machmes, milling machines, gear trains, drill ing machines, and guillotine cutters Interlocking guards. If a fixed guard can not be used, an interlocking guard should be fitted onto the machine as the first alternative Interlocking guards may be mechanical, elec trical, pneumatic, or a combination of types The interlocking guard prevents operation of the control that sets the machine in motion until the guard is moved into position so that the operator cannot reach the point of opera tion or the point of danger When the guard is open, permitting access to dangerous parts, the starting mechanism is locked, and a locking pm or other safety de vice prevents the mam shaft from turning or other basic mechanisms from operating When the machine is in motion, the guard cannot be opened It can be opened only when the machine has come to rest or has reached a fixed position in its travel An effective interlocking guard must satisfy three requirements, it must 1 Guard the dangerous part before the ma chine can be operated 2 Stay closed until the dangerous part is at rest 3 Prevent operation of the machine if the interlocking device fails Where neither a fixed guard nor an inter locking guard is practicable, mechanical in terlocks may be used Automatic guards. An automatic guard may be used, subject to limitations outlined in Table 29-A, where neither a fixed guard nor an interlocking guard is practicable Such a guard must prevent the operator from com ing in contact with the dangerous part of the machine while it is m motion, or must be able to stop the machine in case of danger (Table 29-A is on the next three pages ) An automatic guard functions independ ently of the operator, and its action is repeated as long as the machine is in motion An automatic guard is usually operated by the machine itself through a system of linkage or levers Whenever an automatic guard is used on a machine which is loaded and unloaded by hand, the operator always should use hand tools All of the foregoing types of guard are suitable for guarding points of operation, but only the fixed guard can be used foi guarding power transmission components (unless they are guarded by fencing or location as previ ously noted) Safeguarduig devices can be used in lieu of or m conjunction with barrier guards at the point of operation Presence-sensing devices (either radio or electronic beam), pullbacks, restraints, and two-hand trips may be used under specified conditions and constraints (See Chapter 32, "Cold Forming of Metals," for a fuller discussion of these devices ) (Text continues on page 800 ) 797