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Mechanical Hazards and Machine Safeguarding

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1 Mechanical Hazards and Machine Safeguarding
Chapter 14 Mechanical Hazards and Machine Safeguarding

2 Major Topics OSHA’s requirements regarding machine guarding
Risk assessment in machine guarding Robot safeguards Lockout/tagout systems General precautions Taking corrective action

3 Common types of mechanical injury hazards
Cutting and Tearing: The seriousness of cutting and tearing the skin by a sharp edge depends on how much damage is done to the skin, veins, arteries, muscles, and even bones. Shearing: Power driven shears for severing paper, metal, plastic and composite materials are widely used in manufacturing. Such machines often amputated fingers and hands. Such tragedies typically occurred when operators reached under the shearing blade to make an adjustment or placed materials there and activated the blade before removing their hand. Crushing: Injuries from crushing typically occur when a part of the body is caught between two hard surfaces that progressively move together thereby crushing anything between them such as a metal stamping machine, meshing gears and belt pulleys. Breaking: Machines used to deform engineering materials in a variety of ways can also cause broken bones. Straining and Spraining: A strain results when muscles are overstretched or torn. A sprain is the result of a torn ligament in a joint. They cause swelling and intense pain. Puncturing: Punching machines have sharp tools that can puncture body parts and cause damage to internal organs if safety precautions are not observed or if appropriate safeguards are not in place.

4 Concept of safeguarding
Machine safeguarding is to minimize the risk of accidents of machine-operator contact. The contact can be because of inattention caused by fatigue, distraction, curiosity or deliberately taking a chance. From machine via flying metal chips, chemicals, and hot metal splashes, and circular saw kickbacks. Caused by direct result of machine malfunction, including mechanical and electrical failure.

5 OSHA’s requirements for machine guarding
29CFR – OSHA’s requirement for all industries: Types of guarding: One or more methods of machine guarding (barriers, two-hand switches, tripping devices, and electronic sensors) must be provided to protect people from point of operation hazards such as nip points, rotating parts, flying chips and sparks. General requirements for machine guards: Where possible guards should be affixed to the machine in such a way that they do not create hazards themselves. Guarding the point of operation: Any point of operation that might expose a person to injury must be guarded, in such a way as to prevent the machine operator from having any part of their body (including clothing, hair, etc.) in the danger zone during the operating cycle of the machine. Machines requiring point of operation guards: guillotine cutters, shears, alligator shears, power presses, milling machines, power saws, jointers, portable power tools, forming rolls, and calendars. Exposure of blades: Fans must be guarded if the blades are less than seven feet above the floor or working level – guards shall have no opening that exceeds one half inch. Anchoring fixed machinery: Machines that are designed to be in one location must be securely anchored to prevent movement.

6 Requirements for all safeguards
National Safety Council safeguard requirements: 1. Prevent Contact: safeguards should prevent human contact (operator or any other person) with any potentially harmful machine part. 2. Be secure and durable: Workers should not be able to render them ineffective by tampering or disabling them. 3. Protect against falling objects: safeguards must also shield the moving part of machines from falling objects. 4. Create no new hazard: safeguards with a sharp edge, unfinished surface, or protruding bolts introduce new hazards while preventing against the old. 5. Create no interference: safeguards that create interference are likely to be disregarded or disabled by workers feeling the pressure of production deadlines. 6. Allow safe maintenance: such as lubrication without the removal of guards.

7 Types of point-of-operation guards
1. Fixed guards: allow a permanent barrier between worker and the point of operation. Suitable for high production repetitive operations. May limit visibility, and normal cleaning and maintenance. 2. Interlocked guards: shut down the machine when the guard is not in place. Allows safe access to machine for removing jams or conducting routine maintenance. May be sometimes easily disengaged. 3. Adjustable guards: prevent against variety of different hazards. Do not provide dependable barrier as other guards.

8 Point-of-operation devices
Photoelectric devices: shut down the machine whenever the light field is broken. Do not protect against mechanical failure, and can be only used with machines that can be stopped. Radio frequency devices: are capacitance devices that stop the machine if the capacitance field is interrupted by the workers body or another object. Electromechanical devices: If the worker moves the contact bar beyond a specific point the machine will shut down. Pullback devices: pull the operator’s hand out of the danger zone when the machine starts. Restraint devices: hold the operator back from the danger zone. Safety trip devices: trip wires, trip rods, and body bars. Stop the machine when tripped. Two hand controls: require the operator to use both hands to activate the machine. Gates: provide barrier between danger zone and workers.

9 Advantages and disadvantages of feeding and ejection systems
Feeding and ejection systems can be effective safeguards if properly designed and used. Automatic Feed: systems feed stock to the machine from rolls. Eliminate the need of operators to enter the danger zone. Limited in type and variations in stock they can feed. Require auxiliary barrier guard and frequent maintenance. Semiautomatic feed: Chutes, movable dies, dial feeds, plungers, and sliding bolsters – same advantages as automatic feed. Automatic ejection: systems eject the work pneumatically or mechanically. Operators do not have to reach into danger zone. Disadvantages are debris and noise (pneumatic). Semiautomatic ejection: activated by operator. Similar advantages and disadvantages to automatic ejection.

10 Hazards of robots 1. Entrapment of worker between robot and solid surface. 2. Impact with a moving robot arm. 3. Impact with objects ejected or dropped by robot.

11 Robot Safeguards Erect a physical barrier around the entire perimeter of a robot’s work envelope. Should be able to withstand the force of the heaviest object the robot could eject. Shutdown guard that shuts the robot down if any person or object enters the work envelope. Sensitive doors or gates in the perimeter barrier that shut the robot down if opened. Safeguards are important because robots can be deceptive – may be at a stage between cycles, and make a sudden and rapid movement.

12 Lockout System Placing a lockout device such as a padlock on an energy isolating device to prevent the accidental or inadvertent energizing of a machine or piece of equipment (fig p 315).

13 Tagout system Placing a tag on a energy isolation device to warn people so that they do not accidentally or inadvertently energize a machine or equipment (see fig p. 315).

14 Impact of lockout/tagout system
Protect people in the workplace from hazardous energy while they are performing service or maintenance on machines, tools and equipment.

15 Main provisions of OSHA’s lockout/tagout system
Energy control program: Organizations must have an energy control program that have fully documented energy control procedures, provide employee training, and ensure periodic inspections. Energy control procedure: a statement on how the procedure will be used; procedural steps to shut down, isolate, block, and secure machines or equipment; steps designating the safe placement, removal and transfer of lockout/tagout devices and responsible person; specific requirements for testing machinery or equipment. Energy-isolating devices: for preventing the accidental or inadvertent release of energy on all machines and equipment. Device must be able to be locked out/ tagged out. Requirements for lockout/tagout devices: durable to withstand the environment to which they will be exposed. Employee training: provide initial training and retraining as required and certify that necessary training has been given to all employees (authorized, affected and other). Periodic inspections: At least annually, and certify the inspections have taken place. Applications of controls and lockout/tagout devices: follow appropriate procedure (see text book). Removal of Locks or tags: follow appropriate procedure (see text book). Additional safety requirements: follow specific procedure (see text book).

16 Risk Assessment in Machine Operation
Quantifying the level of risk associated with the operation of a given machine: Severity of potential injuries (S): S1 Slight injury (bruise, abrasion) S2 Severe injury (amputation or death) Frequency of exposure to potential hazards (F): F1 Infrequent exposure F2 Frequent to continuous exposure Possibility of avoiding the hazard if it does occur (P): P1 Possible P2 Less possible to not impossible Likelihood that the hazard will occur (L): L1 Highly unlikely L2 Unlikely L3 Highly likely

17 Evaluating lockout/tagout programs
Are all machinery or equipment capable of movement required to be deenergized or locked out during cleaning, servicing, adjusting or setup operations. Are all equipment control valve handles equipped with a means for locking out. Does lockout procedure require that all stored energy be released or blocked before the equipment is locked out. Are employees required to check the safety lockout by attempting a startup after making sure no one is exposed. After the safety is checked does the employee does the employee again place the switch in the off position. Have employees been trained not to start machinery if it has been locked out or tagged out. Are all workers notified when machinery or equipment they usually use is shut down and locked out for maintenance or servicing purposes. Before machine is activated are employees notified.

18 Summary The most common mechanical injuries are cutting and tearing.
Safeguarding involves devices or methods that minimize the risk of accidents resulting from machine-operator contact. OSHA standard for machine guarding is 29CFR The best safeguard for a robot is a barrier around the perimeter of its work envelope. Lockout/tagout is designed to prevent injuries from the accidental energizing of machines or equipment while they are shut down for maintenance or servicing. When hazards or hazardous behavior is observed corrective action should be taken immediately.

19 Home work Answer questions 1, 3, 9, 10, 11, and 13 on pages 320-321.
1. List and briefly explain the common types of mechanical injury hazards. 3. Summarize OSHA’s requirements for machine guarding. 9. Explain how to guard against the hazards associated with robots. 10. What is a lockout system? 11. What is a tagout system? 13. Summarize the main provisions of OSHA’s lockout/tagout standard.

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