8,450 known non-fatal amputation cases (involving days away from work) occurred in 2005 for all of private industry. The most prevalent injury source was, by far, machinery, which accounted for approximately 60% (5,080 instances) of the amputation cases. The machinery listed here cause amputation injuries, and appropriate safeguarding and hazardous energy control (lockout/tagout) methods are addressed in this section.
Employers need to consult the OSHA standard for specific machinery to ensure compliance with all requirements. For other types of hazardous sources of injury, see Appendix B.
Machinery Associated with Amputations
- Mechanical Power Presses
- Power Press Brakes
- Powered and Non-Powered Conveyors
- Printing Presses
- Roll-Forming and Roll-Bending Machines
- Shearing Machines
- Food Slicers
- Meat Grinders
- Meat-Cutting Band Saws
- Drill Presses
- Milling Machines
- Grinding Machines
Hazards of Mechanical Power Presses
Although there are three major types of power presses—mechanical, hydraulic, and pneumatic— the machinery that accounts for a large number of workplace amputations are mechanical power presses.
In mechanical power presses, tools or dies are mounted on a slide, or ram, which operates in a controlled, reciprocating motion toward and away from the stationary bed or anvil containing the lower die. When the upper and lower dies press together – to punch, shear or form – the workpiece, the desired piece is produced. Once the downstroke is completed, the re-formed work-piece is removed either automatically or manually, a new work-piece is fed into the die, and the process is repeated. (See Figure 23.)
Controls for Machines with Clutches
Certain machines can be categorized based on the type of clutch they use—full-revolution or part-revolution. Differing modes of operation for
these two clutches determine the type of guarding that can be used.
Full-revolution clutches, once activated, complete a full cycle of the slide (lowering and raising of the slide) before stopping at dead center and cannot be disengaged until the cycle is complete.
So, presence-sensing devices will not work and operators must be protected during the entire press operating cycle. For example, properly applied barrier guards or two-hand trip devices that are installed at a safe distance from the hazard area may be used.
Machines incorporating full-revolution clutches, such as mechanical power presses, must also incorporate a single-stroke device and anti-repeat feature.
The majority of part-revolution presses are air clutch and brake. They are designed to trap air in a chamber or tube. When the compressed air is put into these chambers, the clutch is engaged, the brake disengaged and the press makes a single stroke. To stop the press, the
reverse takes place. Thus, the part-revolution clutch can be disengaged at any time during the cycle to stop the cycle before it completes the downstroke.
For safeguarding purposes, part-revolution mechanical power presses can be equipped with presence-sensing devices, but full-revolution mechanical power presses cannot.
NOTE: Likewise, most hydraulic power presses and their associated control systems are similar to part-revolution mechanical power presses in that the slide can be stopped at any point in the cycle.
In order to ensure the integrity of the safety-related functions, safeguarding devices (such as presencesensing devices) may only be used on hydraulic
power presses that are properly designed and constructed (in accordance with good engineering practice) to accommodate the safeguarding system.
Refer to OSHA’s Machine Guarding eTool for additional information on hydraulic presses.
Amputations occurring from the point of operation hazards are the most common types of injuries associated with mechanical power presses.
Improperly applied safeguarding methods (such as using a guard with more than maximum allowable openings or 2-hand palm buttons that are mounted within the safety distance of the press) may allow operators unsafe access to the press’s hazardous area. These unsafe conditions may result in an amputation when an operator, for example, instinctively reaches into the point of operation to adjust a misaligned part or release a jam. Also, amputations occur when an operator’s normal feeding rhythm is interrupted, resulting in inadvertent placement of the operator’s hands in the point of operation. Such injuries usually happen while the operator is riding the foot pedal. Additionally, some amputations are linked to mechanical (such as the failure of a singlestroke linkage), electrical (such as a control relay failure), or pneumatic (such as the loss of air pressure to the clutch/brake) machine component failure.
Examples of inadequate or ineffective safeguarding and hazardous energy control practices include the following:
- Guards and devices disabled to increase production, to allow the insertion of small-piece work, or to allow better viewing of the operation.
- Two-hand trips/controls bridged or tied-down to allow initiation of the press cycle using only one hand.
- Devices such as pullbacks or restraints improperly adjusted.
- Controls of a single-operator press bypassed by having a coworker activate the controls while the operator positions or aligns parts in the die, or repairs or troubleshoots the press.
- Failure to properly disable, isolate press energy sources, and lockout/tagout presses before an employee performs servicing or maintenance work.
Case History #1
While using an unguarded, foot-pedal-operated, full-revolution mechanical power press that made trip collars for wood stoves, an employee used his hands to feed and remove finished parts and scrap metal. He placed the completed part to the left side of the press, and then turned to place the scrap in the bin behind him. As he turned back to face the press, he inadvertently stepped on the foot pedal and activated the press while his hand was in the die area. His left hand was amputated at the wrist.
Case History #2
An employee was operating an unguarded 10-ton, full-revolution mechanical power press to stamp mailbox parts, and using a hand tool to load the press, she placed her left hand in the lower die to reposition a misaligned part. At the same time, she inadvertently depressed the foot pedal, activating the press and crushing her left index finger.
Case History #3
A power press operator and helper were instructed to temporarily halt production and each employee decided to perform servicing tasks. The operator had a problem with a hydraulic fluid leak and decided to deflect the liquid spray by installing a temporary barrier while, at the same time, the helper decided to clean up the metal chips from the press area. The operator then activated the press and repositioned the press slide in order to install the cardboard barrier. This mechanical power press action fatally crushed the helper’s head because his head was between the dies while he was in the process of cleaning up the metal chips.
Source: OSHA IMIS Accident Investigation Database.
Safeguarding Mechanical Power Presses
Mechanical power presses are extremely versatile and selecting appropriate safeguarding methods depends on the specific press design and use. You should consider the press, the type of clutch used,the stock size, the length of production runs, and the method of feeding.
You can use primary safeguarding methods, such as guards or safeguarding devices, to prevent injuries. For example, 29 CFR 1910.217 requires employers to provide and ensure the use of point of operation guards or properly installed devices on every operation performed on a press when the die opening is greater than 1/4 inch.
In addition, guards must conform to the maximum permissible openings of Table O-10 of 29 CFR 1910.217. Guards must prevent entry of hands or fingers into the point of operation through, over, under, or around the guard.
Mechanical Power Press Safeguarding Methods by Clutch Type
- Point of Operation Guard
- Type A Gate
- Two-Hand Trip
- Point of Operation Guard
- Type A Gate
- Type B Gate*
- Two-Hand Control*
- Presence-Sensing Device*
*”Hands-in-Die” operations require additional safeguarding measures: See 1910.217(c)(5).
Mechanical power press point of operation safeguards must accomplish the following goals:
- Prevent or stop the normal press stroke if the operator’s hands are in the point of operation; or
- Prevent the operator from reaching into the point of operation as the die closes; or
- Withdraw the operator’s hands if inadvertently placed in the point of operation as the die closes; or
- Prevent the operator from reaching the point of operation at any time; or
- Require the operator to use both hands for the machine controls that are located at such a distance that the slide completes the downward travel or stops before the operator can reach into the point of operation; or
- Enclose the point of operation before a press stroke can be started to prevent the operator from reaching into the danger area before die closure or enclose the point of operation prior to stoppage of the slide motion during the downward stroke.
Source: 29 CFR 1910.217(c)(3)(i).
“No Hands-in-Die” Policy
In general, a “no-hands-in-die” policy needs to be implemented and followed whenever possible – that is, in the event the press is not designed for “hands-in-die” production work. Under this policy, operators must never place their hands in the die area (point-of-operation) while performing normal production operations. Adherence to this safety practice will reduce the risk of point of operation amputations.
In terms of part-revolution mechanical power presses that use a two-hand control, presencesensing device or type B gate, OSHA does allow “hands-in-die” operation if the press control reliability and brake monitoring system requirements are met. If these press design safety features are not complied with, then employers must incorporate a “no-hands-in-die” policy.
Source: 29 CFR 1910.217(c)(5).
Other Controls for Mechanical Power Press Servicing and Maintenance
Secondary safeguarding methods may be used alone or in combination (to achieve near equivalent protection) only when the employer can show that it is impossible to use any of the primary safeguarding methods. The following are some work practices, complementary equipment and energy control measures that may be used to supplement primary safeguarding:
- If employees operate presses under a “nohands-in-die” policy using complementary feeding methods such as hand-tool feeding, employers still must protect operators through the use of primary safeguarding methods, such as a properly applied two-hand control or trip safeguarding device. Hand-tool feeding alone does not ensure that the operator’s hands cannot reach the danger area. (Figure 24 illustrates the use of hand-feeding tools in conjunction with pullbacks on a power press.)
- Removing scrap or stuck work with tools is required even when hand feeding is allowed according to 29 CFR 1910.217(d)(1)(ii). Employers must furnish and enforce the use of hand tools for freeing or removing work or scrap pieces from the die to reduce the amount of time an operator’s hand is near the point of
- Control point of operation hazards created when guards are removed for set-up and repair by operating the machine in the inch mode. This involves using two-hand controls (or a single control mounted at a safe distance from the machine hazards) to gradually inch the press through a stroke when the dies are being tested on part-revolution clutch presses.
- Observe energy control procedures and practices for press servicing and maintenance work. For example, the changing of dies on a mechanical power press requires the employer to establish a die-setting procedure that employs pointof-operation safeguarding method(s) such as the safe usage of an inch or jog safety device for die set-up purposes together with LOTO. These devices safely position the mechanical power press slide utilizing a point-of-operation safeguarding technique. Thus, an energy control procedure for these types of presses would need to integrate both point-of-operation safeguarding method(s) for slide positioning as well as LOTO procedures for the die setting operation.
Additional power press energy control precautions(e.g., use of safety blocks; LOTO the press disconnect switch if re-energization presents a hazard) will be necessary if employees need to place their hands/arms in a press working area (the space between the bolster plate and the ram/slide) to perform the servicing and/or maintenance activity (such as adjusting, cleaning or repairing dies) because the inch or jog safety device will not protect employees from ram movement due to potential mechanical energy (resulting from the ram/slide position and associated gravitational force), press component or control system malfunction, or press activation by others.
At times, OSHA recognizes that some minor servicing may have to be performed during normal production operations, so a lockout/tagout exception is allowed.
See the 29 CFR 1910.147(a)(2)(ii) Note for details. For example, a press operator may need to perform a minor die cleaning task on a regular basis for product quality purposes and the use of safety blocks – inserted between the press dies – that are interlocked with the press electrical controls would constitute effective protection. Properly designed and applied safety block interlocks may be used in lieu of locking or tagging out the press’s electrical
energy source for purposes of the minor servicing exception.
Source: 29 CFR 1910.147(a)(2)(ii) Note.
Training is essential for employee protection. As an employer, you should:
- Train operators in safe mechanical press operation and hazardous energy control (lockout/tagout) procedures and techniques before they begin work on the press.
- Supervise operators to ensure that correct procedures and techniques are being followed.
In addition, work practices such as regular mechanical power press inspection, maintenance, and reporting are essential.
- 29 CFR 1910.217(e)(1)(i) requires a program of periodic and regular inspections of mechanical power presses to ensure that all of the press parts, auxiliary equipment and safeguards are in safe operating condition and adjustment. Inspection certification records must be maintained.
- 29 CFR 1910.217(e)(1)(ii) requires you to inspect and test the condition of the clutch/brake mechanism, anti-repeat feature, and single-stroke mechanism on at least a weekly basis for presses without control reliability and brake system monitoring. Certification records must be maintained of these inspections and the maintenance performed.
- 29 CFR 1910.217(g)(1) requires the reporting of all point of operation injuries to operators or other employees within 30 days to either the Director of the Directorate of Standards and Guidance, OSHA, U.S. Department of Labor, Washington, DC 20210, or the state agency administering a plan approved by OSHA.
You can also use the Internet to report injuries (www.osha.gov/pls/powerpress/mechanical.html).
[Content with recognition to OSHA]
Specific Machine Hazards Part 2