Understanding Machine Guarding
Many employees must use a machine, tool or piece of equipment in their jobs. Employees often do not understand the dangers lurking within the machine itself and why guards or barriers are necessary. Employees often believe that guards “get in my way. I just remove them and it makes my job easier.” However, they fail to realize that it only takes a second for an injury to happen; a distraction can cause a finger, hand, arm, or other body part to come in contact with part of the machine. These injuries may range from minor to severe and cause the employee pain, suffering, lost wages and lost work time. It is important for employees to understand that guards are provided to protect them from injury.
The Occupational Safety and Health Administration/Virginia Occupational Safety and Health (OSHA/VOSH) in 29 CFR 1910.212 requires that “One or more methods of machine guarding shall be provided to protect the operator and other employees in the machine area from hazards such as those created by point of operation, ingoing nip points, rotating parts, flying chips and sparks.” Simply put, if there is the potential of an employee coming in contact with a piece of moving machinery, it must be guarded.
In order to understand the concepts of machine guarding, there are three fundamental areas of a piece of machinery that should be guarded. These areas are the point of operation, the power transmission device and the operation controls. OSHA/VOSH defines these areas in the Machine Guarding eTool as follows:
- The point of operation is defined as the point where the work is being performed on the material. This would include cutting, shaping, boring or forming stock.
- The power transmission device is defined as all the parts/components of the mechanical system, which transmits energy to the part of the machine performing the work. This includes pulleys, belts, connecting rods, chains, gears, spindles and flywheels.
- The operation controls are defined as all the other moving parts of the machine, which move while the machine is in operation. This includes reciprocating, rotating, and transverse moving parts, as well as feed mechanisms and auxiliary parts of the machine.1
When trying to determine what parts of a machine need to be guarded, look for motions or actions that could possibly present a hazard to the employee. These can be divided into two categories:
Motions Rotating In-running nip point Reciprocating Transversing
Actions Cutting Punching Shearing Bending
All machinery, in some combination, present hazards to employees. To better understand and protect employees from these motions and actions, each will be defined.
- Rotating motion is when a part or piece of machinery turns around on an axis. It can grab hair, fingers, clothes, or other body parts and twist and pull them into the machinery.
- In-running nip points are a type of rotating motion. There are three main types:
- Parts rotating in opposite directions while their axes are parallel to each other. Example: rollers
- Rotating movement between a straight part and a round part. Example: belt and pulley or bicycle chain.
- Rotating movement against a fixed part. Example: an abrasive wheel and the work rest.
- Reciprocating motion is when a part or piece of machinery moves back-and-forth or in an up-and-down motion. This can cause an employee to get struck by or caught between a moving and stationary part. Example: a piston in an internal combustion engine.
- Transversing motion is movement in a straight, continuous line. Example: a belt drive.
- Cutting action involves all three types of motion, rotating, reciprocating, and transversing. The actual danger of the cutting action occurs at the point of operation. Example: various saws on wood or a drill bit coming into contact with material.
- Punching action is when power is applied to a ram for the purpose of stamping materials. The danger of the punching action occurs at the point of operation where the material is inserted, held, and removed. Example: power presses.
- Shearing action occurs when power is applied to a slide/knife in order to trim or cut materials. The danger of the shearing actions occurs at the point of operation where the material is inserted, held, and removed. Example: sheet metal brake.
- Bending action is when power is applied to a slide in order to stamp and draw materials. Example: tube benders and power presses.2
Now that the hazardous actions and motions have been defined, each piece of equipment located at your facility should be evaluated for the appropriate safeguards. A hazard assessment should be conducted to determine if any of the machinery used by the agency is dangerous or has missing guards. Evaluate the equipment looking for the following types of parts: (This list is not all-inclusive)
- Belts and pulleys
- Flywheels and gear wheels
- Shafts and spindles
- Chain and sprocket gears
- Guillotine blades
- Circular saws
- Drills and chucks
Look for machinery action related to: (This list is not all-inclusive)
- Shear points
- Crushing areas
- Cutting areas
- Entanglement areas
- Stabbing points
- Abrasion areas
- Anywhere something could be drawn into the machine
- Any protrusion that could cause an injury
OSHA/VOSH has developed a machine guarding checklist to help assist agencies in evaluating the hazards associated with machinery. This checklist can be obtained at the following website: http://www.osha.gov/Publications/Mach_SafeGuard/checklist.html.
Once these hazards have been identified, OSHA/VOSH requires the hazards to be controlled or eliminated. Use the hierarchy of controls (engineering, administrative, or personal protective equipment) to determine how these hazards can be controlled. In most cases, guards or barriers will have to be installed to help control the hazard. There are a several types of guards that can be used. They include:
- Fixed guards – do not have moving parts and prevent contact between the moving machinery and any part of the body.
- Interlocked guards – are moveable, with the moving part interconnected to control system of the machinery. Guards of this type are usually electrical, mechanical, hydraulic, pneumatic, or a combination. The interlock only allows the machine to operate when the guards are closed.
- Adjustable/self-adjusting guards – are flexible and allow the guard to move to accommodate various sizes of material. This is commonly seen on various types of saws.
- Automatic guards – move into position when the machinery is activated. They are also known as push away, push back, or pull back guards.
- Trip guards – stops the machinery when a person gets into a dangerous position and could be injured. Examples of theses types of guards are:
- Pullback/restraint guards – use a series of cables or straps attached to the employee’s hands, wrists, or arms and allows the employee only a limited range of motion. This prevents the employee’s body parts from entering a danger zone.
- Multiple hand controls – require that the employee provide concurrent pressure with both hands to activate the machinery. There are some controls that may also require the use of a foot pedal to ensure the employee’s body is out of the danger zone.
- Distance guards – prevent the employee from entering a dangerous area while the machinery is in operation. They are also known as gates or shields.3, 4
Determining the type of guard that is required for the machinery will be dependent on the hazardous motions or actions identified. Many times manufacturers have already determined the proper guards and either include them with the machinery or as an additional option for purchase. It is up to the agency to implement and enforce the use of guards on equipment.
While guarding equipment is an important injury prevention measure, OSHA/VOSH also has set some minimum guidelines that all guards must meet, including:
- The guards must be able to prevent an employee’s body part from making contact with any moving part of the machinery.
- The guards should not be easy to tamper with or to remove.
- The guards should protect against falling objects.
- The guard itself should not create a hazard in and of itself.
- The guards should not interfere with the employee’s task.
- The guards should be constructed so that they do not have to be removed during lubrication.5
Guards are installed on all kinds of machinery and equipment. Common everyday machinery that require guards are:
- Abrasive Wheels
- Hand and power tools
These tools are often overlooked and not recognized as needing guards. Safety switches on hand-held power tools such as drills, grinders, sanders, and reciprocating saws can be considered a guard. This switch requires constant pressure to activate the machinery. ; Employees should be discouraged from taping the switch in the “on” position. Abrasive wheels should be equipped with guards to protect the employee from the moving wheel and flying fragments in the event the wheel breaks. Pneumatic tools should be equipped with a variety of guards to prevent injury. They include the positive locking device to prevent the hose from separating from the tool and becoming a whip. Additionally, a safety clip should be installed to prevent the attachment from becoming a projectile if it disconnects from the tool. Circular saws, band saws, table saws, and other saws should not have the guards taped back or removed. This prevents an injury at the point of operation. OSHA/VOSH has several good illustrations and resources located on their website at http://www.osha.gov.
Employees are exposed to a variety of hazardous motions and actions associated with machinery. Many accidents and injuries are related to work practices involving the use and care of the machines. Some injuries are the result of improper lockout/tagout procedures or improperly mounted/installed machinery. Other injuries are related to removing or bypassing guards, or from using improper guards. Some injuries are the result of employees not being properly trained in the maintenance and use of the equipment. These employees may not recognize the hazards associated with the machinery. Additionally, employees may not have adequate personal protective equipment.
Remember, it is important that agencies evaluate their machinery for hazards and determine if the appropriate guards are in place. Look for the following potential conditions:
- Coming in contact or entanglement with machinery
- Becoming trapped between machine and fixed structure
- Coming in contact with material in motion
- Being struck by parts of machinery
- Being exposed to the release of potential energy
If any of these conditions are evident, the agency is not protecting it workers from hazards and is in violation of the OSHA/VOSH 29 CFR 1910 Subpart O standard.
1 U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at http://www.osha.gov/SLTC/etools/machineguarding/intro.html.
2 U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at http://www.osha.gov/SLTC/etools/machineguarding/motions_actions.html.
3 U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at http://www.osha.gov/SLTC/etools/machineguarding/guards.html.
4 U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at http://www.osha.gov/SLTC/etools/machineguarding/devices.html.
5 U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at http://www.osha.gov/SLTC/etools/machineguarding/additional_considerations.html.
U.S. Department of Labor, Occupational Safety and Health Administration. “29 CFR 1910 Subpart 0, Machinery and Machine Guarding.” Viewed December 7, 2005, at: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=10131.
U.S. Department of Labor, Occupational Safety and Health Administration. “Hand and Portable Powered Tools.” Viewed December 7, 2005, at: http://www.osha.gov.
U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding Checklist.” Viewed December 7, 2005, at: http://www.osha.gov/Publications/Mach_SafeGuard/checklist.html.
U.S. Department of Labor, Occupational Safety and Health Administration. “Machine Guarding eTool.” Viewed December 7, 2005, at: http://www.osha.gov/SLTC/etools/machineguarding/.
U.S. Department of Labor, Occupational Safety and Health Administration. “OSHA 10-Hour General Industry Outreach-Trainer Presentations, Machine Guarding.” Viewed December 7, 2005, at: http://www.osha.gov.
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