Course 154 Machine Safeguarding: Basic

Hazards of Moving Parts


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Good machine safeguarding makes it very difficult for anyone to be exposed to the danger zone.

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.

Where Mechanical Hazards Occur

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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1. When the operation of a machine or accidental contact with it can injure the operator or others in the vicinity, _____.

a. exposure must be limited to authorized or affected employees
b. the hazards must be either controlled or eliminated
c. something must be done to let employees know
d. the equipment must be placed out of service

Hazardous Mechanical Motions and Actions

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Many machines expose workers to hazardous motions and actions.

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:

  • Motions
    • rotating (including in-running nip points)
    • reciprocating
    • transversing
  • Actions
    • cutting
    • punching
    • shearing
    • bending

2. Which of the following is considered a mechanical action?

a. bending
b. rotating
c. reciprocating
d. transversing


Rotating parts
Rotating parts

"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 Points

In-running nip point hazards are caused by the rotating parts on machinery. There are three main types of in-running nips.

  • 1. Parallel rotating parts: Parts can rotate in opposite directions while their axes are parallel to each other. These parts may be in contact producing nip point. Stock fed between the rolls may also produces nip points. This danger is common on machines with intermeshing gears, rolling mills, and calenders.
  • 2. Tangentially moving parts: Tangentially moving nip points are also created between rotating and tangentially moving parts. Some examples would be: the point of contact between a power transmission belt and its pulley, a chain and a sprocket, and a rack and pinion.
  • 3. Rotating and fixed parts: Nip points can occur between rotating and fixed parts which create a shearing, crushing, or abrading action. Examples are: spoked handwheels or flywheels, screw conveyors, or the periphery of an abrasive wheel and an incorrectly adjusted work rest.
Rotating parts
Rotating and fixed parts
Rotating parts
Tangentially moving parts
Rotating parts
Parallel rotating Parts

3. A flywheel would present which type of nip point hazard?

a. Parallel rotating parts
b. Tangentially moving parts
c. Rotating and fixed parts
d. Opposed rotating parts

Motions (Continued)

Reciprocating Motions

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.

Transverse Motions

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.

Rotating shaft bolts can cause a fatality.

Rotating Shafts

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.

Rotating parts
Rotating parts are always dangerous and can kill.
Reciprocating motions
Transverse motions
Transverse motions
Reciprocating motions

4. Which of the following motions is the most dangerous and usually results in a fatality if an employee contacts it?

a. Tangentially moving part
b. Rotating shaft
c. Transverse motion
d. Reciprocating motion


Cutting Actions

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

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.

Punching action
Punching action
Cutting action
Cutting actions

5. Where does the hazard exist from cutting and punching actions?

a. At the nip point
b. At the point of operation
c. At the end of the machine
d. At all points along the edge of the part

Actions (Continued)


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.

bending action
Bending action
Shearing action
Shearing action

6. In both _______ and ______ actions, a hazard occurs at the point of operation where stock is inserted, held, and withdrawn.

a. transversing, reciprocating
b. punching, cutting
c. cutting, stamping
d. shearing, bending

Requirements for Machine Guards

Manatoba CA - Machine Safeguards: The Basics.

What must a machine guard do to protect workers against mechanical hazards?

Machine guards must meet these minimum general requirements:

  • Prevent contact: The machine guard must prevent hands, arms, and any other part of a worker's body from making contact with dangerous moving parts. A good machine 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 machine guard, because a machine guard that can easily be made ineffective is no machine guard at all. Guards and safety devices should be made of durable material that will withstand the conditions of normal use. They must be firmly secured to the machine.
  • Protect from falling objects: The machine guard should ensure that no objects can fall into moving parts. A small tool which is dropped into a cycling machine could easily become a projectile that could strike and injure someone.
  • Create no new hazards: A machine guard 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, for instance, should be rolled or bolted in such a way that they eliminate sharp edges.
  • Create no interference: Any machine guard which impedes a worker from performing the job quickly and comfortably might soon be overridden or disregarded. Proper machine safeguarding can actually enhance efficiency since it can relieve the worker's apprehensions about injury.
  • Allow safe lubrication: If possible, one should be able to lubricate the machine without removing the machine guards. Locating oil reservoirs outside the guard, with a line leading to the lubrication point, will reduce the need for the operator or maintenance worker to enter the hazardous area.

7.Which of the following would meet the criteria for suitable machine guard design?

a. A 1-inch wire mesh that allows lubrication of moving parts
b. A guard made of thin transparent plastic to provide visibility
c. A rope net with 2-inch web openings
d. A solid metal guard bolted to prevent entry

Machine Guard Construction

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Machines guards must be substantial. Metal is best. Wood is not recommended.

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.

Advantages of Builder-Designed Guards

Guards designed and installed by the builder offer two main advantages:

  • They usually conform to the design and function of the machine.
  • They can be designed to strengthen the machine in some way or to serve some additional functional purposes.

Advantages of User-Built Guards

User-built guards are sometimes necessary for a variety of reasons. They provide the following advantages:

  • Often, with older machinery, they are the only practical safeguarding solution.
  • They may be the only choice for mechanical power transmission apparatus in older plants, where machinery is not powered by individual motor drives.
  • They permit options for point-of-operation safeguards when skilled personnel design and make them.
  • They can be designed and built to fit unique and ever changing situations.
  • They can be installed on individual dies and feeding mechanisms.
  • Design and installation of machine safeguards by plant personnel can help to promote safety consciousness in the workplace.

Disadvantages of User-Built Guards

User-built guards also have disadvantages:

  • User-built guards may not conform well to the configuration and function of the machine.
  • There is a risk that user-built guards may be poorly designed or built.

Guard Material

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.

8. What is one advantage of user-built machine guards?

a. They usually conform to machine design and function
b. With older machinery, they may be the only option
c. There is reduced risk that poor design might create hazards
d. They limit point-of-operation exposure to hazards


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:

Supervisor Safety Tips - Vivid Learning Systems.
  1. a description and identification of the hazards associated with particular machines;
  2. the machine guards themselves, how they provide protection from specific hazards;
  3. how to install, inspect, use, and maintain machine guards;
  4. how and under what circumstances machine guards can be removed, and by whom (in most cases, repair or maintenance personnel only); and
  5. what to do (e.g., contact the supervisor) if a machine guard is damaged, missing, or unable to provide adequate protection.
  6. the serious and fatal consequences of failure to use safe work practices when working around moving parts.
A worker's loose clothing caught on these rotating shaft bolts causing a fatality.

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.

How to Get the Point Across

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:

  • A graphic video, like the one above, about a fatal accident can be quite effective in getting the message across to employees. When employees are affected emotionally by an experience in training, they will more likely remember the message.
  • A story of an actual accident, how it happened, and what would have prevented it, can also be very effective. Here is an example below:
    • A paper mill employee was killed after he became entangled in a rotating shaft at the company's paper mill. The worker, employed at the company for less than two weeks, was buffing the shaft when his clothing got caught on the rotating bolt heads of the shaft. (see image immediately above)

9. What is the most effective way of "getting the point across" in safety training?

a. Emphasize the consequences
b. Classroom discussion
c. Videos and lecture
d. Group exercises and written exams

Protective Clothing and Personal Protective Equipment

Direct Machine Guarding - MSC Industrial Supply Co.

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:

  1. appropriate for the particular hazards;
  2. maintained in good condition;
  3. properly stored when not in use, to prevent damage or loss; and
  4. kept clean, fully functional, and sanitary.

It is important to note that protective clothing and equipment can create hazards.

  • Protective gloves can become caught on or between rotating parts,
  • Loose-fitting shirts might become entangled in rotating spindles or other kinds of moving machinery.
  • 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, or amputating fingers.
  • Always arrange hair, including beards, so that it does not hang free. Workers have literally been scalped or killed when their hair has been caught in rotating parts.

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.

10. What are the most likely consequences of failing to follow safe work practices when working around moving parts?

a. Damaged products
b. Possible reprimand
c. Serious injury or fatality
d. Embarrassment

Check your Work

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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.

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