Disclaimer: This material is designed and intended for general informational purposes only, and is not intended, nor shall it be construed or relied upon, as specific legal advice. INTRODUCTION According to the Bureau of Labor Statistics, over 650 occupational fatalities and 92,000 injuries occur each year to workers who operate and maintain machinery. Although many of these accidents are due to other causes including improper lockout/tagout procedures, lack of effective machine safeguarding is the cause of a high number of injuries and fatalities as well. Machine safeguarding is one of the simplest and often least expensive, ways of preventing injuries. Any machine part, function, or process which may cause injury should be safeguarded. When the operation of a machine, or accidental contact with it, can injure the operator or others in the vicinity, the hazards should be either controlled or eliminated. HAZARDOUS MECHANICAL MOTIONS AND ACTIONS Recognizing the different types of hazardous mechanical motions and actions is the first step toward protecting workers from the danger they present. Safeguarding is required for dangerous moving parts in three areas: The point of operation: the point where work is performed on the material, such as cutting, shaping, boring or forming of stock. Power transmission apparatus: all components of the mechanical system which transmit energy to the part of the machine performing the work. These components include flywheels, pulleys, belts, connecting rods, couplings, cams, spindles, chains, cranks and gears. Moving parts, which include all parts of the machine that move while the machine is operating. Examples include reciprocating, rotating and transverse moving parts, as well as feed mechanisms and other parts of the machine. Motions The basic types of hazardous, mechanical motions are: Rotating motion. Even smooth, slowly rotating shafts can grip clothing, and through mere skin contact, force an arm or hand into a dangerous position. Injuries due to contact with rotating parts can be severe. Collars, couplings, cams, clutches, flywheels, shaft ends, spindles, meshing gears and horizontal or vertical shafting are some examples of common rotating mechanisms which may be hazardous. The danger increases when projections such as set screws, bolts, Page 1 Rev. 3-17-11
nicks, abrasions, burrs and projecting keys or set screws are exposed on rotating parts, as shown in Figure 1. Figure 1: Hazardous projections on rotating parts In-running nip points. Nip points are caused by rotating parts on machinery. There are three main types of in-running nip points. o Nip points created by parts rotating in opposite directions while their axes are parallel to each other. These parts may be in contact or in close proximity to each other, as shown in Figure 2. o Nip points created between rotating and tangentially moving parts. Some examples would be: the point of contact between a belt and pulley, a chain and a sprocket, and a rack and pinion, as shown in Figure 3. o Nip points created between rotating and fixed parts, which create a shearing, crushing or abrading action. Examples include: spoked flywheels, screw conveyors or an incorrectly adjusted abrasive wheel grinder and its workrest, as shown in Figure 4. Reciprocating motion. Reciprocating motions may be hazardous because a worker may be struck or caught between a moving and stationary part as it moves back and forth or up and down. See Figure 5 for an example of reciprocating motion. Transverse motion. Transverse motions (motions in a straight, continuous line) create a hazard because a worker may be struck or caught in a pinch or shear point by the moving part, as shown in Figure 6. Page 2 Rev. 3-17-11
Figure 1: Nip points created by parts rotating in opposite directions Figure 3: Nip points created by parts rotating and tangentially moving parts Page 3 Rev. 3-17-11
Figure 4: Nip points created by parts rotating and fixed parts Figure 5: Hazardous reciprocating motion Figure 6: Hazardous transverse motion Page 4 Rev. 3-17-11
Actions The basic types of hazardous mechanical actions are: Cutting actions. Cutting may involve rotating, reciprocating, or transverse motions. The danger in the cutting action exists at the point of operation where finger, arm, and body injuries can occur or where flying chips or scrap material can strike the eyes or face. Such hazards are present at the point of operation in cutting wood, metal, or other materials. Examples of mechanisms having cutting hazards include band saws, circular saws, boring or drilling machines, lathes, or milling machines, as shown in Figure 7. Punching actions. Punching occurs when power is applied to a slide for the purpose of blanking, drawing, or stamping metal or other materials. The danger in the punching action occurs at the point of operation where stock is inserted, held, and withdrawn by hand. Typical machines used for punching operations include power presses and punch presses, as shown in Figure 8. Shearing actions. Shearing involves applying power to a slide or knife in order to trim or shear metal or other materials. A hazard occurs at the point of operation where stock is inserted, held, and withdrawn. Typical machines used for shearing are mechanically, hydraulically, or pneumatically powered shears, as shown in Figure 9. Bending actions. Bending occurs when power is applied to a slide in order to draw or stamp metal or other materials. A hazard occurs at the point of operation where stock is inserted, held, and withdrawn. Equipment that uses bending action includes power presses, press brakes, and tubing benders, as shown in Figure 10. Figure 7: Examples of Dangerous Cutting Hazards Page 5 Rev. 3-17-11
Figure 8: Typical Punching Operation Figure 9: Typical Shearing Operation Figure 10: Typical Bending Operation Page 6 Rev. 3-17-11
GENERAL REQUIREMENTS FOR SAFEGUARDS Safeguards should meet the following minimum general requirements in order to protect workers from mechanical hazards: Prevent contact. The safeguard should prevent hands, arms, and any other part of the worker s body, including the person s hair or clothing, from coming into contact with dangerous moving parts. A good safeguarding system eliminates the possibility of the operator or another worker placing parts of their bodies near hazardous moving parts. Secure. Workers should not be able to easily remove or tamper with the safeguard, because a safeguard that can easily be made ineffective really isn t a safeguard at all. Guards and safety devices should be made of durable material that will withstand conditions of normal use. They should be firmly secured to the machine. Protect from falling objects. The safeguard should ensure that no objects can fall into moving parts. A small tool which is dropped into a cycling machine could become a projectile that could strike and injure someone. Create no new hazards. A safeguard defeats its own purpose if it creates a hazard of its own such as a shear point, a jagged edge, or an unfinished surface which can cause a laceration. The edges of guards should be rolled or attached in such a way that they eliminate sharp edges. Create no interference. Any safeguard which impedes a worker from performing the job quickly and comfortably might soon be overridden or disregarded. Proper safeguarding can actually enhance efficiency since its can relieve the worker s fears of injury. Allow safe lubrication. If possible, you should be able to lubricate the machine without removing the guard. Locating oil reservoirs outside the guard, with a line leading to the lubrication point, will reduce the need for the operator or maintenance employee to enter the hazardous area. OPERATOR TRAINING Even the most elaborate safeguarding system cannot offer effective protection unless the worker knows how to use it and why it is needed. Specific and detailed training is a critical part of any effort to provide safeguarding against machine-related hazards. Thorough operator training should involve instruction or hands-on training in the following: A description and identification of the hazards associated with particular machines. The safeguards themselves, how they provide protection, and the hazards for which they are intended. How to use the safeguards and why. How and under what circumstances safeguards can be removed, and by whom. Page 7 Rev. 3-17-11
What to do if a safeguard is damaged, missing, or unable to provide adequate protection. Operator safety training should be completed for new operators and maintenance personnel, when new or altered safeguards are put into service, or when workers are assigned to a new machine or operation. Operators should also be trained regarding the types of personal protective equipment and other clothing that should and should not be worn around machinery and equipment. While protective clothing can be helpful in many situations, it can be a hazard in others. For example, a protective glove can be caught in a rotating part, creating a very dangerous situation. Other parts of a worker s clothing may also present additional safety hazards. For example, loose-fitting shirts can become entangled in rotating spindles or other moving parts. Jewelry, such as bracelets and rings, can catch on machine parts or stock and lead to serious injury by pulling a hand into the danger area. Long hair is also a serious hazard when working around moving equipment. METHODS OF MACHINE SAFEGUARDING There are many ways to safeguard machines. The type of operation, the size or shape of stock, the method of handling, the physical layout of the work area, the type of material, and production requirements will help to determine the appropriate safeguarding method for each individual machine. As a general rule, power transmission apparatus (see Figure 2) is best protected by fixed guards that enclose the danger areas. For hazards at the point of operation, where moving parts are actually performing work, several kinds of safeguarding may be possible. Safeguards are generally grouped into the following classifications: 1. Guards 2. Devices 3. Location/Distance 4. Feeding and Ejection Methods 5. Miscellaneous Aids Each of these machine safeguarding methods are further described in the following sections. Guards Guards are physical barriers designed to prevent access to danger areas. There are four general types of guards. The advantages and limitations of each can also be found in the table in Appendix A. Fixed Interlocked Page 8 Rev. 3-17-11
Adjustable Self-adjusting Fixed Guards As its name implies, a fixed guard is a permanent part of the machine. It is not dependent upon moving parts to perform its intended function. It may be constructed of sheet metal, screen, wire cloth, bars, plastic, or any other material that is substantial enough to withstand whatever impact it may receive and to endure prolonged use. This guard is preferable to all other types because of its relative simplicity and effectiveness. Several examples of fixed guards are shown in the figures below. Figure 11: A fixed guard on a power press completely encloses the point of operation. The stock is fed through the side of the guard into the die area, with the scrap stock exiting on the opposite side. Figure 12: A fixed guard shielding the belt and pulley of a power transmission unit. An inspection panel is provided on top in order to minimize the need for removing the guard. Page 9 Rev. 3-17-11
To remain effective, the inspection panel cannot be removed while the machine is operating. Figure 13: Fixed guards on a band saw. These guards protect the operator from the turning wheels and moving saw blade. Normally, the only time for the guards to be opened or removed is for a blade change or maintenance. Figure 14: A transparent, fixed barrier guard is used on a press brake to protect the operator from the unused portions of the die. This guard is easy to install or remove. Page 10 Rev. 3-17-11
Interlocked Guards When an interlocked guard is opened or removed, the mechanism and/or power automatically shuts off or disengages and the machine cannot be started until the guard is back in place. An interlocked guard can use electrical, hydraulic, or pneumatic power or any combination of these. Replacing the guard should not automatically restart the machine. A household example of an interlocked guard is that on a clothes dryer. When the door is opened, the machine shuts off. When the door is shut, the machine starts again only when the start button is pushed. Several examples of interlocked guards are shown in the figures below. Figure 15: An interlocked barrier guard mounted on an automatic bread bagging machine. When the guard is removed, the machine will not function. Figure 16: The beater mechanism of a picker machine is covered by an interlocking barrier guard. The guard cannot be raised while the machine is running, nor can the machine be restarted with the guard in the raised position. Page 11 Rev. 3-17-11
Adjustable Guards Adjustable guards are useful because they allow flexibility in accommodating various sizes of stock. Several examples of adjustable guards are shown in the figures below. Figure 17: Similar to the fixed guard in Figure 11, but the bars on this guard adjust to accommodate the size and shape of the stock. Figure 18: Adjustable guard on a router allows the operator to change the guard height depending on the thickness of the stock. Page 12 Rev. 3-17-11
Self-Adjusting Guards The openings of self-adjusting guards are determined by the movement of the stock. As the operator moves the stock into the danger area, the guard is pushed away, providing an opening which is only large enough for the stock to enter. After the stock is removed, the guard returns to the rest position. The guard protects the operator by placing a barrier between the danger area and the operator. The guards may be constructed of plastic, metal, or other substantial material. Self-adjusting guards offer different degrees of protection. Several examples of self-adjusting guards are shown in the figures below. Figure 19: A radial arm saw with a self-adjusting guard. As the blade is pulled across the stock, the guard moves up, staying in contact with the stock. Figure 20: A self-adjusting guard enclosure mounted on a jointer. The guard is moved from the cutting head by the stock. After the stock is removed, the guard will return, under spring tension, to the rest position. Page 13 Rev. 3-17-11
Devices A safety device may perform one of several functions. It may stop the machine if a hand or any part of the body is placed in the danger area; restrain or withdraw the operator s hands from the danger area during operation; require the operator to use both hands on machine controls, thus keeping both hands out of danger; or provide a barrier which is synchronized with the operating cycle of the machine in order to prevent entry into the danger area during the hazardous part of the cycle. The advantages and limitations of each can also be found in a table in Appendix B. Presence-Sensing The photoelectric presence-sensing device, commonly known as a light curtain, uses a system of light sources and controls which can interrupt the machine s operating cycle. If the light beam is broken, the machine stops and will not cycle. This device can only be used on machines that can be stopped before the worker is able to reach into the danger area. The design and placement of the sensing devices depends on the time it takes to stop the mechanism and the speed at which the employee s hand can reach across the distance from the guard to the danger area. An example of a presence-sensing device is shown in the figure below. Figure 21: Photoelectric presence-sensing device (light curtain) on a part-revolution power press. When the light beam is broken, either the ram will not start to cycle, or, if the cycle has begun, the stopping mechanism will be activated so that the press stops before the operator can enter the danger area. Page 14 Rev. 3-17-11
Pullbacks Pullback devices use a series of cables attached to the operator s hands, wrists, and/or arms. This type of device is primarily used on machines with stroking action. When the slide/ram is up between cycles, the operator is allowed access to the point of operation. When the slide/ram begins to cycle, a mechanical linkage automatically pulls the operator s hands away from the point of operation. It is important to verify that the pullback device is properly adjusted. If the straps are too long, the operator may be able to reach into the point of operation during the closing cycle. If the straps are too short, the operator s arms may be pulled back too far, which is an ergonomic hazard that could lead to shoulder problems. An example of a pullback device is shown in the figure below. Figure 22: A pullback device on a press brake. When the slide/ram is in the up position, the operator can feed material by hand into the point of operation. When the press cycle is actuated, the operator s hands and arms are automatically withdrawn. Restraints The restraint device, also known as a holdout, uses cables or straps that are attached to the operator s hands and a fixed point. The cables or straps need to be adjusted to let the operator s hands travel within a predetermined safe area. There is no extending or retracting action involved. Hand feeding tools, such as those shown in Figure 23, are often necessary if the operation involves placing material into the danger area. An example of a restraint device is shown in Figure 24. Figure 23: Several hand feeding tools. These tools should not be used as machine safeguards; they are merely a supplement to the protection other guards provide. Page 15 Rev. 3-17-11
Figure 24: A restraint device on a power press. Straps are attached to the operator s hands and to a post behind the workstation. Hand feeding tools are necessary in order to place the material into the point of operation. Safety Trip Controls Safety trip controls provide a quick means for deactivating a machine in an emergency situation. Examples of safety trip controls include pressure-sensitive body bars and safety tripwire cables. It should be noted that safety trip controls do not provide a physical safeguard, but rather shut down the machine before the situation becomes hazardous. Safety trip controls need to be manually reset to restart the machine. Simply releasing the tripwire to restart the machine will not ensure that the employee is out of danger when the machine restarts. A machine equipped with a safety tripwire cable is shown in the figure below. Figure 25: Safety tripwire cable on a calendar machine. When any part of the cable is pulled, the machine will shut down immediately. Page 16 Rev. 3-17-11
Two-Hand Control Two-hand controls are used to safeguard many machines in use today. The two-hand control requires constant, concurrent pressure on both control buttons to operate the machine. Two-hand controls can only be used on machines with a part-revolution clutch, brake, and brake monitor. With this type of device, the operator s hands are required to be at a safe location (on control buttons) and at a safe distance from the danger area while the machine completes its closing cycle. There are several things to consider when using two-hand controls as a safeguarding device. First, these devices should be checked regularly to ensure that the machine will operate only when both control buttons are pressed and held down simultaneously. When either control button is released, the slide/ram should reverse direction immediately. Also, the control buttons should be placed far enough apart to ensure that the operator cannot use one hand and another part of the body to start the machine, leaving the second hand to enter the point of operation. A machine equipped with twohand controls is shown in the figure below. Figure 26: Two-hand control buttons on a part-revolution clutch power press. Notice that the control buttons are protected by plastic guards to prevent accidental contact. Page 17 Rev. 3-17-11
Two-Hand Trip The two-hand trip is similar to the two-hand control except for one significant difference. Like the two-hand control, the operator presses both control buttons to begin the cycle. With the two-hand trip, however, as soon as the cycle starts, the operator can remove his/her hands from the trip buttons and the cycle continues to operate. Two-hand trips are commonly used with machines equipped with full revolution presses. The trip buttons need to be placed far enough from the point of operation to make it impossible for the operator to move his or her hands from the trip buttons into the point of operation before the first half of the cycle is completed. The distance from the trip buttons to the point of operation is determined by using the following safety distance formula: Where: Minimum Safety Distance = 63 inches/second x T(m) 63 inches/second=hand speed constant T(m) = the maximum time the press takes for the die closure after it has been tripped (seconds). o For full revolution clutch presses with only one engaging point, T(m) is equal to the time necessary for one and one-half revolutions of the crankshaft. o For full revolution clutch presses with more than one engaging point, T(m) is calculated as follows: T(m) = [1/2 + (1 divided by number of engaging points per revolution)] x time necessary to complete one revolution of the crankshaft (seconds). If the safety distance formula is used properly, the operator s hands will be kept far enough away to prevent them from being placed in the danger area prior to the slide/ram or blade reaching the full down position. A machine equipped with two-hand trip devices is shown in the figure below. Figure 27: Two-hand trip buttons on a full-revolution clutch power press. The two-hand trip buttons are located high enough to satisfy the safety distance formula. Page 18 Rev. 3-17-11
Gates A gate is a movable barrier that protects the operator at the point of operation before the machine cycle can be started. Gates are, in many instances, designed to be operated with each machine cycle. To be effective, gates should be interlocked with the machine so that the machine will not begin a cycle unless the gate is in place. The gate should be in the fully closed position before the machine can function. Several machines equipped with gates are shown in the figures below. Figure 28: Horizontal injection molding machine with a gate. The gate is interlocked to the machine, and it will not run unless the gate is fully closed. If the gate is opened while the machine is running, the machine will shut off as well. Figure 29: A gate on a power press. Like the gate in Figure 28, it is interlocked to the machine and it will not run unless the gate is fully closed. Page 19 Rev. 3-17-11
Safeguarding by Location/Distance The premise of safeguarding by location is fairly simple if the operator is far enough away from the hazard, it is not possible for him/her to be injured. A thorough hazard analysis of each machine and particular situation is absolutely essential before attempting this safeguarding technique. Organizations should consider all other types of machine safeguarding before determining that safeguarding by distance is an acceptable solution. To consider a machine to be safeguarded by location, the dangerous moving part of a machine should be so positioned that danger areas are not accessible or do not present a hazard to any worker during the normal operation of the machine. This may be accomplished by locating a machine so that the hazardous parts of the machine are located away from other areas where employees walk or work. This might involve positioning a machine with its power transmission apparatus against a wall and leaving all routine operations conducted on the other side of the machine. Other potential situations in which safeguarding by distance might be considered include: Constructing walls or fences around dangerous machines to restrict access. Have dangerous parts located high enough to be out of the normal reach of any worker. OSHA requires all parts below 7 to be guarded, but a 10 limit is common in many organizations. Positioning the operator s control station away from the hazard. Operator controls may be located at a safe distance from the machine if there is no reason for the operator to tend it. The feeding process can also be safeguarded by location if a safe distance can be maintained to protect the worker s hands. The dimensions of the stock being worked on may provide adequate safety. For instance, if the stock is several feet long and only one end is being worked on, the operator may be able to hold the opposite end while the work process is being performed. An example would be a single-end punching machine. However, depending upon the machine, protection might still be required for other personnel in the area. Feeding and Ejection Methods Many feeding and ejection methods do not require the operator to place his or her hands into the danger area. In some cases, no operator involvement is necessary after the machine is set up. In other situations, operators can manually feed the stock with the assistance of a feeding mechanism. Properly designed ejection methods do not require any operator involvement after the machine starts to function. The advantages and limitations of each can be found in Appendix C. Using feeding and ejection methods does not eliminate the need for guards and devices. Guards and devices should still be used wherever they are necessary and possible in order to protect operators from exposure hazards. The most common feeding and ejection methods are: Automatic feed Semi-automatic feed Automatic ejection Semi-automatic ejection Page 20 Rev. 3-17-11
Automatic Feed Automatic feeds are preferred because they reduce the exposure of the operator during the work process, and sometimes do not require any effort by the operator after the machine is set up and running. In addition to the machine safeguarding advantages of automatic feed machines, they also increase productivity and decrease the risk of repetitive motion type injuries associated with continuous part feeding. A machine designed for automatic feeding is shown in the figure below. Figure 30: A power press with an automatic feeding mechanism. Even though there is no operator interaction, the point of operation is still guarded with a transparent enclosure guard to prevent entry by others in the area. Semi-Automatic Feed With semi-automatic feeding, the operator uses a mechanism to place the piece being processed under the ram at each stroke. The operator does not need to reach into the danger area, and the danger area is completely enclosed. Several examples of semiautomatic feeding mechanisms are shown in the figures below. Figure 31: Semi-automatic chute feed. The chute may be either a horizontal or inclined chute into which each piece is placed by hand. Page 21 Rev. 3-17-11
Figure 32: A plunger and magazine feed. The pieces are stacked in the magazine and automatically drop into the empty hole when the plunger is removed from the die. When the plunger is pushed in, Slot A will align with Interlock B and the machine will trip. Automatic Ejection Automatic ejection may employ either an air-pressure or a mechanical apparatus to remove the completed part from a press, therefore eliminating the need for the operator to enter the danger area to remove the finished part. It may be interlocked with the operating controls to prevent operation until part ejection is completed. Automatic ejection still requires additional safeguards for full protection of the operator. Like automatic feeding mechanisms, automatic ejection mechanisms may also increase productivity and decrease the risk of repetitive motion type injuries associated with continuous finished part removal. Several examples of automatic ejection mechanisms are shown in the figures below. Figure 33: Air ejection and mechanical ejection of a finished part. Page 22 Rev. 3-17-11
Semi-Automatic Ejection Semi-automatic ejection mechanisms are often used in conjunction with semi-automatic feeding mechanisms. An example of a semi-automatic ejection mechanism is shown in the figure below. Figure 34: A semi-automatic ejection mechanism used on a power press. When the plunger is withdrawn from the die area, the ejector leg, which is mechanically coupled to the plunger, kicks the completed work out. Miscellaneous Aids While miscellaneous aids do not provide complete protection from machine hazards, they may provide the operator and others in the area with an extra margin of safety. Good judgment is needed whenever miscellaneous aids are used. Generally, miscellaneous aids take the form of an awareness barrier. An awareness barrier does not provide physical protection, but serves only to remind a person that he or she is approaching the danger area. Generally, awareness barriers are not considered adequate when continual exposure to the hazard exists. Awareness barriers, which are shown in the figures below, normally consist of: Ropes with warning signs attached Shields Page 23 Rev. 3-17-11
Figure 35: A rope with a warning sign is used as an awareness barrier on the rear of a power squaring shear. Although the barrier does not physically prevent a person from entering the danger area, the employee must reach, or step over, under, or through the barrier to reach the point of operation. Figure 36: Shields, another awareness barrier, may be used to provide protection from flying particles, splashing cutting oils, or coolants. Shields used for this purpose are generally made using a transparent material so the operator can see the part being worked on. Page 24 Rev. 3-17-11
FOR ADDITIONAL INFORMATION Occupational Safety & Health Administration: www.osha.gov Safety and Health Topics: Machine Guarding Machine Guarding etool EMC Insurance Companies: www.emcins.com Tech Sheets: o o o o o Abrasive Wheel Grinders Machine Safeguarding: Power Transmission Apparatus Machine Safeguarding: Table Saws Lockout/Tagout Program Lockout/Tagout Machine-Specific Procedures Loss Prevention Information manual: Lockout/Tagout Copyright Employers Mutual Casualty Company 2011. All rights reserved. Select images 2011 JupiterImages Corporation; diagrams courtesy of OSHA. Page 25 Rev. 3-17-11
APPENDIX A Guards Method Safeguarding Action Advantages Limitations Fixed Provides a barrier Can be constructed to suit many specific applications In-plant construction is often possible Can provide maximum protection Usually requires minimum maintenance Can be suitable to high production, repetitive operations May interfere with visibility Can be limited to specific operations Machine adjustment and repair often require its removal, thereby necessitating other means of protection for maintenance personnel Interlocked Shuts off or disengages power and prevents starting of machine when guard is open; should require the machine to be stopped before the worker can reach into the danger area Can provide maximum protection Allows access to machine for removing jams without time consuming removal of fixed guards Requires careful adjustment and maintenance May be easy to disengage jams Adjustable Provides a barrier that may be adjusted to facilitate a variety of production operations Can be constructed to suit many specific applications Can be adjusted to admit varying sizes of stock Hands may enter danger area protection may not be complete at all times May require frequent maintenance and/or adjustment The guard may be made ineffective by the operator May interfere with visibility Selfadjusting Provides a barrier that moves according to the size of the stock entering the danger area Off-the-shelf guards are often commercially available Does not always provide maximum protection May interfere with visibility May require frequent maintenance and adjustment Page 26 Rev. 3-17-11
APPENDIX B Devices Method Safeguarding Action Advantages Limitations Presencesensing Machine will not start cycling when the light field is interrupted When the light field is broken by any part of the operator s body during the cycling process, immediate machine braking is activated Allows more free movement for operator Simplicity of use Used by multiple operators Provides passerby protection No adjustment required Does not protect against mechanical failure Limited to machines that can be stopped mid-cycle Pullback As the machine begins to cycle, the operator s hands are pulled out of the danger area Eliminates the need for auxiliary barriers or other interference at the danger area Limits movement of operator May obstruct work space around operator Adjustments must be made for specific operations and for each individual Requires close supervision of the operator s use of the equipment Restraint (holdout) Prevents the operator from reaching into the danger area Little risk of mechanical failure Limits movement of operator May obstruct work space around operator Adjustments must be made for specific operations and for each individual Requires close supervision of the operator s use of the equipment Page 27 Rev. 3-17-11
Devices (cont.) Method Safeguarding Action Advantages Limitations Safety trip controls: Pressuresensitive bar Safety tripwire Stops machine when tripped Simplicity of use All controls must be manually activated May be difficult to activate controls Only protects the operator May require special fixtures to hold May require a machine brake Two-hand control Concurrent use of both hands is required, preventing the operator from entering the danger area Operator s hands are at a predetermined safe location Operator s hands are free to pick up a new part after first half of cycle is completed Requires a partial cycle machine with a brake Some two-hand controls can be rendered unsafe by holding with arm or blocking, thereby permitting one-hand operation Protects only the operator Two-hand trip Concurrent use of two hands on separate controls prevents hands from being in danger area when machine starts Operator s hands are away from danger area Can be adapted to multiple operations No obstruction to hand feeding Does not require adjustment for each operation Operator may try to reach into danger area after tripping machine Some trips can be rendered unsafe by holding with arm for blocking, thereby permitting one-hand operation Protects only the operator May require special fixtures Gate Provides a barrier between danger area and operator or other personnel Can prevent reaching into or walking into the danger area May require frequent inspection and regular maintenance May interfere with the operator s ability to see the work Page 28 Rev. 3-17-11
APPENDIX C Feeding and Ejection Methods Method Safeguarding Action Advantages Limitations Automatic feed Stock is fed from rolls, indexed by machine mechanism Eliminates the need for operator involvement in the area May increase productivity Other guards are also required for operator protection usually fixed barrier guards Requires frequent maintenance May not be adaptable to variation in stock size Semiautomatic feed Stock is fed by chutes, movable dies, plungers, etc. Eliminates need for operator involvement in the danger area Other guards are also required for operator protection usually fixed barrier guards Requires frequent maintenance May not be adaptable to variation in stock size Automatic ejection Work pieces are ejected by air or mechanical means Operator does not have to enter danger area to remove finished work May increase productivity May create hazard of blowing chips or debris Size of stock limits the use of this method Air ejection may present a noise hazard Semiautomatic ejection Work pieces are ejected by mechanical means which are initiated by the operator Operator does not have to enter danger area to remove finished work Other guards are required for operator protection May not be adaptable to stock variation Page 29 Rev. 3-17-11