Crushed hands and arms, severed fingers, blindness -- the list of possible machinery-related injuries is as long as it is horrifying. There seem to be as many hazards created by moving machine parts as there are types of machines. Machine guards are essential for protecting workers from needless and preventable injuries.
A good rule to remember is: Any machine part, function, or process which may cause injury must be machine guarded. When the operation of a machine or accidental contact with it can injure the operator or others in the vicinity, the hazards must be either controlled or eliminated.
This course describes the various hazards of mechanical motion and presents some techniques for protecting workers from these hazards. General information covered in this chapter includes -- where mechanical hazards occur, the hazards created by different kinds of motions and the requirements for effective machine guards, as well as a brief discussion of non-mechanical hazards.
Dangerous moving parts in three basic areas require machine safeguarding:
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.
Other moving parts: all parts of the machine which move while the machine is working. These can include reciprocating, rotating, and transverse moving parts, as well as feed mechanisms and auxiliary parts of the machine.
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A wide variety of mechanical motions and actions may present hazards to the worker. These can include the movement of rotating members, reciprocating arms, moving belts, meshing gears, cutting teeth, and any parts that impact or shear. These different types of hazardous mechanical motions and actions are basic in varying combinations to nearly all machines, and recognizing them is the first step toward protecting workers from the danger they present.
The basic types of hazardous mechanical motions and actions are:
"Rotation" is circular motion around an axis or center such as rotating collars, couplings, cams, clutches, flywheels, shaft ends, and spindles that may grip clothing or otherwise force a body part into a dangerous location. Even smooth surfaced rotating machine parts can be hazardous. Projections such as screws or burrs on the rotating part increase the hazard potential.
The danger increases when projections such as set screws, bolts, nicks, abrasions, and projecting keys or set screws are exposed on rotating parts, as shown in the figure to the right. See the image to the right. This worker's equipment got caught on a rotating shaft resulting in a tragic fatality. You should consider exposure to rotating parts as an "imminent danger" situation that must be corrected immediately.
In-running nip point hazards are caused by the rotating parts on machinery. There are three main types of in-running nips.
Reciprocating motions are back-and-forth or up-and-down motions that may strike or entrap an employee between a moving part and a fixed object. Reciprocating motions may be hazardous because, during the back-and-forth or up-and-down motion, a worker may be struck by or caught between a moving and a stationary part.
A transverse motion occurs in a straight, continuous line that may strike or catch an employee in a pinch or shear point created by the moving part and a fixed object. Transverse motion (movement in a straight, continuous line) creates a hazard because a worker may be struck or caught in a pinch or shear point by the moving part.
Warning: Exposure to rotating shafts is the most dangerous machine safeguarding hazard. It is so dangerous we wanted to mention it again before moving on to other topics. There have been numerous accidents due to exposure to rotating shafts and, unfortunately, most of these accidents result in a fatality.
The danger of exposure to rotating shafts increases when projections such as set screws, bolts, nicks, abrasions, and projecting keys or set screws are exposed on rotating parts (see image to right). The image below on the right shows what can happen when a worker gets caught on a rotating shaft. In this case, massive internal injuries resulted in a tragic fatality. You should consider exposure to rotating parts as an "imminent danger" situation that must be corrected immediately.
Cutting actions may involve rotating, reciprocating, or transverse motion. The danger of cutting actions exists at the point of operation where finger, arm, and body injuries can occur and where flying chips or scrap material can strike the head, particularly in the area of the eyes or face. Such hazards are present at the point of operation in cutting wood, metal, or other materials.
Examples of mechanisms involving cutting hazards include band saws, circular saws, boring or drilling machines, turning machines (lathes), or milling machines.
Punching actions result when power is applied to a slide (ram) for the purpose of blanking, drawing, or stamping metal or other materials. The danger of this type of action occurs at the point of operation where stock is inserted, held, and withdrawn by hand.
Typical machines used for punching operations are power presses and ironworkers.
Shearing action 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.
Examples of machines used for shearing operations are mechanically, hydraulically, or pneumatically powered shears.
Bending action results 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.
What must a machine guard do to protect workers against mechanical hazards?
Machine guards must meet these minimum general requirements:
Today many builders of single-purpose machines provide point-of-operation and power transmission safeguards as standard equipment. However, not all machines in use have built-in safeguards provided by the manufacturer.
Guards designed and installed by the builder offer two main advantages:
User-built guards are sometimes necessary for a variety of reasons. They provide the following advantages:
User-built guards also have disadvantages:
Under many circumstances, metal is the best material for guards. Guard framework is usually made from structural shapes, pipe, bar, or rod stock. Filler material is generally expanded, perforated, or solid sheet metal or wire mesh. It may be feasible to use plastic or safety glass where visibility is required.
Guards made of wood are not generally recommended because of their flammability and lack of durability and strength. However, in areas where corrosive materials are present, wooden guards may be the better choice.
Even the most elaborate machine safeguarding system cannot offer effective protection unless the worker knows how to use it and why. Specific and detailed training is therefore a crucial part of any effort to provide machine safeguarding against machine-related hazards. On-the-Job training (OJT) is the most effective how-to training method for training machine guard safety.
When workers get injured from exposure to moving parts, a high percentage end up fatalities. It's important to make the training serious and "memorable." Thorough operator training should involve instruction or hands-on training in the following:
This kind of safety training is necessary for new operators and maintenance or setup personnel, when any new or altered machine guards are put in service, or when workers are assigned to a new machine or operation.
To get the point across and make the training memorable, you should emphasize the serious or fatal consequences of failure to follow safe work practices. Here's a couple of ideas:
Using engineering controls to eliminate the hazard at the source offers the best and most reliable means of machine safeguarding. Therefore, engineering controls must be the employer's first choice for eliminating machine hazards. But whenever engineering controls are not available or are not fully capable of protecting the employee (an extra measure of protection is necessary), operators must wear protective clothing or personal protective equipment.
If it is to provide adequate protection, PPE must be:
It is important to note that protective clothing and equipment can create hazards.
Watch the video above and you'll understand how important it is not to let your hair hang down or wear gloves, loose clothing, or jewelry when working around rotating parts. Fatalities associated with rotating parts are gruesome. NEVER work around rotating parts without proper guarding. Enough said.
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If you have time, watch this Safety Memos video: Don't Touch Guards! - Machine Guard Safety. We recommend subscribing to the Safety Memos channel. It's a great source for short videos you can present in safety meetings or training.