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Course 726 - Introduction to Machine Guarding

Safety guides and audits to make your job as a safety professional easier

Methods of Machine Safeguarding

Introduction

There are many ways to safeguard machines. The type of operation, size or shape of stock, method of handling, physical layout of the work area, type of material, and production requirements or limitations will help to determine the appropriate safeguarding method for the individual machine.

As a general rule, power transmission apparatus is best protected by fixed guards that enclose the danger areas. For hazards at the point of operation, where moving parts actually perform work on stock, several kinds of safeguarding may be possible. One must always choose the most effective and practical means available.

Five General Classifications of Safeguards

We can group safeguards under five general classifications.

  1. Guards
  2. Devices
  3. Location/Distance
  4. Potential Feeding and Ejection Methods
  5. Miscellaneous Aids

1. As a general rule, power transmission apparatus is best protected by which of the following?

a. Presence-sensing devices
b. Warning signs placed between the worker and the work
c. Fixed guards that enclose the danger area
d. Mechanical arm restraints

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Guards

Guards are barriers which prevent access to danger areas. There are four general types of guards:

Fixed Guards

As its name implies, a fixed guard is a permanent part of the machine. It is not dependent upon moving parts to perform its intended function. It may be constructed of sheet metal, screen, wire cloth, bars, plastic, or any other material that is substantial enough to withstand whatever impact it may receive and to endure prolonged use. This guard is usually preferable to all other types because of its relative simplicity and permanence.

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Safeguarding Action Advantages Limitations
  • Provides a barrier
  • Can be constructed to suit many specific applications

  • In-plant construction is often possible

  • Can provide maximum protection

  • Usually requires minimum maintenance

  • Can be suitable to high production, repetitive operations
  • May interfere with visibility

  • Can be limited to specific operations

  • Machine adjustment and repair often require its removal, thereby necessitating other means of protection for maintenance personnel

gsg photo power press
Fixed Guard. This fixed guard encloses the point of operation on a power press.
gsg photo power press
Fixed Guard. This fixed guard encloses a belt and pulley system.
gsg photo fixed guard
Fixed guard on bandsaw.

2. Which of the following guards is not dependent upon moving parts to perform its intended function?

a. Adjustable guard
b. Interlocked guard
c. Fixed guard
d. Self-adjusting guard

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Guards (Continued)

Interlocked Guards

gsg photo - Interlocked
Interlocked Barrier Guard: In this picture, the guard cannot be raised while the machine is running.

When this type of guard is opened or removed, the tripping mechanism and/or power automatically shuts off or disengages, and the machine cannot cycle or be started until the guard is back in place.

An interlocked guard may use electrical, mechanical, hydraulic, or pneumatic power or any combination of these. Interlocks should not prevent "inching" by remote control if required.

Replacing the guard should not automatically restart the machine. To be effective, all movable guards should be interlocked to prevent occupational hazards.

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Safeguarding Action Advantages Limitations
  • Shuts off or disengages power, stops the moving parts and prevents starting of the machine when the guard is open; should require the machine to be stopped before the worker can reach into the danger area
  • Can provide maximum protection

  • Allows access to the machine for removing jams without time consuming removal of the fixed guards
  • Requires careful adjustment and maintenance

     
  • May be easy to disengage 

3. Which type of guard automatically shuts off or disengages when it is opened or removed?

a. Adjustable guard
b. Interlocked guard
c. Fixed guard
d. Self-adjusting guard

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Guards (Continued)

Adjustable Guards

Adjustable guards are useful because they allow flexibility in accommodating various sizes of stock. The provide a barrier that may be adjusted to facilitate a variety of production operations.

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Safeguarding Action Advantages Limitations
  • Provides a barrier that may be adjusted to facilitate a variety of production operations
  • Can be constructed to suit many specific applications

  • Can be adjusted to admit varying sizes of stock
  • Hands may enter danger area - protection may not be complete at all times

  • May require frequent maintenance and/or adjustment

  • The guard may be made ineffective by the operator

  • May interfere with visibility

gsg photo - Interlocked
Adjustable Guard. This figure shows an adjustable enclosure guard on a bandsaw.
gsg photo - Interlocked
Adjustable Guard. This figure shows an adjustable enclosure guard on a bandsaw.

4. Which type of guard allows flexibility in accommodating various sizes of stock?

a. Adjustable guard
b. Interlocked guard
c. Fixed guard
d. Self-adjusting guard

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Guards (Continued)

Self-Adjusting Guards

The openings of these barriers are determined by the movement of the stock. As the operator moves the stock into the danger area, the guard is pushed away, providing an opening which is only large enough to admit the stock. After the stock is removed, the guard returns to the rest position. This guard protects the operator by placing a barrier between the danger area and the operator. The guards may be constructed of plastic, metal, or other substantial material. Self-adjusting guards offer different degrees of protection.

Click on the button below to see more information on self-adjusting guards.

 
Safeguarding Action Advantages Limitations
  • Provides a barrier that moves according to the size of the stock entering the danger area
  • Off-the-shelf guards are often commercially available
  • Does not always provide maximum protection

  • May interfere with visibility

  • May require frequent maintenance and adjustment

gsg photo - Self-Adjusting Guard
Self-Adjusting Guard. This guard is moved from the cutting head by the stock. It returns under spring tension.
gsg photo - Self-Adjusting Guard
Self-Adjusting Guard. The self-adjusting guard protects the operator by placing a barrier between the danger area and the operator.

5. As the operator moves the stock into the danger area, this guard is pushed away, providing an opening which is only large enough to admit the stock.

a. Adjustable guard
b. Interlocked guard
c. Fixed guard
d. Self-adjusting guard

Check your Work

Read the material in each section to find the correct answer to each quiz question. After answering all the questions, click on the "Check Quiz Answers" button to grade your quiz and see your score. You will receive a message if you forgot to answer one of the questions. After clicking the button, the questions you missed will be listed below. You can correct any missed questions and check your answers again.

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