Safeguarding devices are controls or attachments that, when properly designed, applied and used, usually prevent inadvertent access by employees to
hazardous machine areas by:
• Preventing hazardous machine component operation if your hand or body part is inadvertently placed in the danger area;
• Restraining or withdrawing your hands from the danger area during machine operation;
• Requiring the use of both of your hands on machine controls (or the use of one hand if the control is mounted at a safe distance from the danger area) that are mounted at a predetermined safety distance; or
• Providing a barrier which is synchronized with the operating cycle in order to prevent entry to the danger area during the hazardous part of the cycle.
These types of engineering controls, which either prevent the start of or stop hazardous motion, may be used in place of guards or as supplemental control measures when guards alone do not adequately enclose the hazard. In order for these safeguarding devices to accomplish this requirement, they must be properly designed and installed at a predetermined safe distance from the machine’s danger area. Other safeguarding devices (probe detection and safety edge devices) that merely detect, instead of prevent, inadvertent access to a hazard are not considered primary safeguards.
(See Table 2 and Figures 13 through 17 for the types of safeguarding devices.)
|Types of Machine Guards|
|Type||Method of Safeguarding||Advantages||Limitations|
|Pullback Devices||Cords connected to operator’s wrists and linked mechanically to the machine automatically withdraw the hands from the point of operation during the machine cycle.|
|Restraint Devices||Wrists are connected by cords and secured to a fixed anchor point which limit operator’s hands from reaching the point of operation at any time.|
|Presence-Sensing Devices||Interlock into the machine’s control system to stop operation when the sensing field (photoelectric, radio frequency, or electromagnetic) is disturbed.|
|Presence-Sensing Mats||Interlock into machine’s control system to stop operation when a predetermined weight is applied to the mat. A manual reset switch must be located outside the protected zone.|
|Two-Hand Control||Requires concurrent and continued use of both hands, preventing them from entering the danger area.|
|Two-Hand Trip||Requires concurrent use of both hands, prevents them from being in danger area when machine cycle starts.|
|Type “A” Gate (moveable barrier)||Applicable to mechanical power presses. Provides barrier between danger area and operator (or other employees) until completion of machine cycle.|
|Type “B” Gate (moveable barrier)||Applicable to mechanical power presses and press brakes. Provides a barrier between danger area and operator (or other employees) during the downstroke.|
Secondary Safeguarding Methods
Other safeguarding methods, such as those described in the Performance Criteria for Safeguarding (ANSI B11.19-2003), may also provide employees with
some protection from machine hazards. Detection safeguarding devices, awareness devices, safeguarding methods and safe work procedures are described in this section. These methods provide a lesser degree of employee protection than the primary safeguarding methods and they are considered secondary control measures as they do not prevent employees from placing or having any part of their bodies in the hazardous machine areas.
Secondary safeguarding methods are acceptable only when guards or safeguarding devices (that prevent you from being exposed to machine hazards) cannot be installed due to reasons of infeasibility. Where it is feasible to use primary safeguarding methods, secondary safeguarding methods may supplement these primary control measures; however, these secondary safeguarding methods must not be used in place of primary safeguarding methods.
Probe Detection and Safety Edge Devices
A probe detection device (sometimes referred to as a ring guard) detects the presence or absence of a person’s hand or finger by encircling all or part of the machine hazard area. The ring guard makes you aware of your hand’s entry into a hazardous area and usually stops or prevents a hazardous machine cycle or stroke, thereby reducing the likelihood of injuring yourself in the point of operation.
These types of detection devices are commonly used on spot welders, riveters, staplers and stackers because primary safeguarding methods are not possible. However, probe detection devices do not prevent inadvertent access to the point-of-operation danger area; rather, they serve as a warning mechanism and may prevent the initiation of or stop the machine cycle if an employee’s hand or finger(s) is too close to the hazard area.
A safety edge device (sometimes called a bump switch) is another type of safeguard that detects the presence of an employee when they are in contact with the device’s sensing edge. A safety edge device protects employees by initiating a stop command when the sensing surface detects the presence of a person; however, they do not usually, when used by themselves, prevent inadvertent access to machine danger areas. Therefore, additional guarding or
safeguarding devices must be provided to prevent employee exposure to a machine hazard.
Awareness devices warn employees of an impending, approaching or present hazard. The first type is an awareness barrier which allows access to machine danger areas, but it is designed to contact the employee, creating an awareness that he or she is close to the danger point. Awareness signals, through the use of recognizable audible or visual signals, are other devices that alert employees to an approaching or present hazard. Lastly, awareness signs are used to notify employees of the nature of the hazard and to provide instructions and training information. OSHA standard 1910.145 provides design, application, and use specifications for accident prevention (danger, caution, safety instruction) signs and (danger, caution, warning) tags.
Safeguarding methods protect employees from hazards by the physical arrangement of distance, holding, openings or the positioning of the machine components to ensure that the operator cannot reach the hazard. Some safeguarding work methods include safe distance safeguarding, safe holding safeguarding and safe opening safeguarding. Requirements for these secondary control measures may be found in ANSI B11.19-2003.
Proper training and supervision are essential to ensure that these secondary safeguarding methods are being used properly. Safeguarding work methods may require the use of awareness devices, including the use of accident prevention signs where there is a need for warning or safety instruction.
Safe Distance Safeguarding
Safeguarding by safe distance (by location) may involve an operator holding and supporting a workpiece with both hands at a predetermined minimum safe distance or, if both hands cannot be used to hold the work-piece at a distance so that the operator cannot reach the hazard with the free hand. For example, the feeding process itself can create a distance safeguard if the operators maintain a safe distance between their hands and the point of operation. Additionally, where material position gauges are used, they need to be of sufficient height and size to prevent slipping of the material past the gauges.
Another example of a safe distance safeguarding method is the use of gravity feed methods that reduce or eliminate employee exposure to machine hazards as the part slides down a chute into the point of operation. Automatic and semiautomatic feeding and ejection methods can also protect the employee by minimizing or eliminating employee exposure with potentially hazardous machinery components. An employee places the part in a magazine which is then fed into the point of operation. Automatic and semiautomatic ejection methods include pneumatic (jet of air), magnetic, mechanical (such as an arm), or vacuum. Figures 18 and 19 illustrate different types of automatic feeding and ejecting methods.
Safe Holding Safeguarding (Safe Work-Piece Safeguarding)
Operator’s hands are maintained away from the hazardous portion of the machine cycle by requiring that both hands are used to hold or support the work-piece, or by requiring that one hand holds the work-piece while the other hand operates the machine. For instance, if the stock is several feet long and only one end of the stock is being worked on, the operator may be able to hold the opposite end while performing the work. The operator’s body
parts are out of the machine hazard area during the hazardous portion of the machine cycle. However, this work method only protects the operator.
Safe Opening Safeguarding
This method limits access to the machine hazardous areas by the size of the opening or by closing off the danger zone access when the work-piece is in place in the machine. Operators are prevented from reaching the hazard area during the machine operation; however, employee access to the danger area is not adequately guarded when the workpiece is not in place.
Safe Work Procedures
Safe work procedures are formal, written instructions which describe how a task is to be performed. These procedures should incorporate appropriate
safe work practices, such as prohibiting employees from wearing loose clothing or jewelry and requiring the securing of long hair with nets or caps.
Clothing, jewelry, long hair, and even gloves can get entangled in moving machine parts.
Complementary equipment is used in conjunction with selected safeguarding techniques and it is, by itself, not a safeguarding method. Some common complementary equipment used to augment machine safeguarding include:
Emergency Stop Devices
Emergency stop devices are designed to be used in reaction to an incident or hazardous situation and, as such, are not considered machine safeguarding.
These devices, such as buttons, ropepulls, cable-pulls, or pressure-sensitive body bars, neither detect nor prevent employee exposure to machine hazards; rather they initiate an action to stop hazardous motion when an employee recognizes a hazard and activates them. (See Figure 20.)
Work-holding equipment is not used to feed or remove the work-piece, but rather to hold it in place during the hazardous portion of the machine cycle.
Clamps, jigs, fixtures and back gauges are examples of work-holding equipment. This equipment may be used to reduce or eliminate the need for an
employee to place their hands in the hazard area.
Feeding and Ejection Systems
A feeding and ejection system (e.g., a gravity fed chute; semi-automatic and automatic feeding and ejection equipment), by itself, does not constitute
secondary safeguarding. However, the use of properly designed feed and ejection mechanisms can protect employees by minimizing or eliminating the
need for them to be in a hazard area during the hazardous motion of the machine.
Operators can use tools to feed and remove material into and from machines so as to keep their hands away from the point of operation. However,
this must be done only in conjunction with the guards and safeguarding devices described previously.
Hand tools are not point-of-operation guarding or safeguarding devices and they need to be designed to allow employees’ hands to remain outside
of the machine danger area. Using hand tools requires close supervision to ensure that the operator does not bypass their use to increase production.
It is recommended that these tools be stored near the operation to promote their use. To prevent injury and repetitive trauma disorders, hand-feeding tools should be shatterproof and ergonomically designed for the specific task being performed. (Figure 21 shows typical handfeeding tools.)
Foot controls that are not securely fixed at a safe distance do not constitute machine safeguarding because they do not keep the operator’s hands out
of the danger area. If you use foot-actuated controls that are not single-control safeguarding devices, they will need to be used with some type of guard or other safeguarding device.
Improperly used foot-actuated controls may increase productivity, but the freedom of hand movement increases the risk of a point-of-operation injury or amputation. Foot controls must be guarded to prevent accidental activation by another employee or by falling material. Do not ride the foot pedal. Ensure that the machine control circuit is properly designed to prevent continuous cycling. (See Figure 22 for an example of a properly guarded foot control.)
As an employer, you need to consider housekeeping practices, employee apparel, and employee training. Implement good housekeeping practices to promote safe working conditions around machinery by doing the following:
- Remove slip, trip, and fall hazards from the areas surrounding machines;
- Use drip pans when oiling equipment;
- Remove waste stock as it is generated;
- Make the work area large enough for machine operation and maintenance; and
- Place machines away from high traffic areas to reduce employee distraction.
Employees should not wear loose-fitting clothing, jewelry, or other items that could become entangled in machinery, and long hair should be worn under a cap or otherwise contained to prevent entanglement in moving machinery. Adequate instruction in the safe use and care of machines and supervised on-the-job training are essential in preventing amputation injuries. Only trained employees should operate machinery.
Train Employees in the Following:
- All hazards in the work area, including machine-specific hazards;
- Machine operating procedures, lockout/tagout procedures and safe work practices;
- The purpose and proper use of machine safeguards; and
- All procedures for responding to safeguarding problems such as immediately reporting unsafe conditions such as missing or damaged guards and violations of safe operating practices to supervisors.
In addition to employee instruction and training, employers need to provide adequate supervision to reinforce safe practices. Take disciplinary action
to enforce safe work practices and working conditions.
Inspection and Maintenance
Good inspection, maintenance and repair procedures contribute significantly to the safety of the maintenance crew as well as to the operators. To
ensure the integrity of the machinery and machine safeguards, a proactive, versus a break-down maintenance program needs to be established based
- Manufacturer’s recommendations;
- Good engineering practice; and
- Any applicable OSHA provisions (such as the mechanical power press inspection and maintenance requirements, contained in 1910.217(e)).
OSHA’s lockout/tagout (LOTO) standard, 29 CFR 1910.147, establishes minimum performance requirements for controlling hazardous energy and it is intended to complement and augment machine safeguarding practices. The lockout/tagout standard applies only if employees are exposed to hazardous energy during servicing/maintenance activities.
An employer may avoid the requirements of the LOTO standard if the safeguarding method eliminates your employees’ exposure to the machine danger area during the servicing or maintenance work by using Machinery and Machine Guarding methods in accordance with the requirements contained in 29 CFR 1910, Subpart O.
Additionally, because some minor servicing may have to be performed during normal production operations, an employer may be exempt from LOTO in some instances. Minor tool changes and adjustments and other minor servicing operations, which take place during normal production operations, are not covered by lockout/tagout if they are routine, repetitive and integral to the use of the machine for production and if work is performed using alternative effective protective measures that provide effective employee protection.
In short, a hazardous energy control program is a critical part of an overall strategy to prevent workplace amputations during machine servicing and maintenance activities, such as during the setting up of machines for production purposes, bypassing guards to clear jams or lubricate parts, and inspecting, adjusting, replacing, or otherwise servicing machine parts. Machine amputations occur when an employer does not have or fails to implement
practices and procedures to disable and control a machine’s energy sources during machine servicing and maintenance work.
[Content with recognition to OSHA]