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General OSHA Machine Guarding Requirements

Moving machine parts create workplace hazards—it's an undeniable fact. The list of possible machinery-related injuries is as long as it is horrifying. That's why machine guards are so vitally important. Machine safeguards can help you protect workers from needless and preventable injuries.

OSHA's requirements for machine guarding are found in 29 CFR 1910 Subpart O Machinery and Machine Guarding. The regulation is broken down in the following components:

1910.211—Definitions
1910.212—General requirements for all machines
1910.213—Woodworking machinery
1910.214—Cooperage machinery [Reserved]
1910.215—Abrasive wheel machinery
1910.216—Mills and calendars in the rubber/ plastics industries
1910.217—Mechanical power presses
1910.218—Forging machines
1910.219—Mechanical power-transmission apparatus

General requirement 1910.212 (a)(1) states that one or more methods of machine guarding must be used to protect operators and other employees in the machine area from hazards. Hazards include those created by point of operation, in-going nip points, rotating parts, flying chips and sparks.

Hazardous Mechanical Motions and Actions

The first step toward protecting workers from hazardous mechanical motion and action is to identify the problem points of each machine and the respective dangers 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

Examples of Hazardous Mechanical Motions

Rotating motion can be dangerous—even smooth, slowly rotating shafts can grip clothing, and through mere skin contact, force an arm or hand into a dangerous position.

Collars, couplings, cams, clutches, flywheels, shaft-ends, spindles and horizontal or vertical shafting are some examples of common rotating mechanisms that may be hazardous. The danger increases when bolts, nicks, abrasions, and projecting keys or set screws are exposed on rotating parts. According to 29 CFR 1910.219 (L), these must be made flush or guarded.

ROTATING PULLEY WITH SPOKES AND PROJECTING BURR ON FACE OF PULLEY
ROTATING SHAFT AND PULLEYS WITH PROJECTING KEY AND SET SCREW
ROTATING COUPLING WITH PROJECTING BOLT HEADS

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

Parts can rotate in opposite directions while their axes are parallel to each other. These parts may be in contact or in close proximity to each other. In the latter case the stock fed between the rolls produce the nip points. This danger is common on machines with intermeshing gears, rolling mills and calendars.

The second type of nip point is created between rotating and tangentially moving parts—such as the point of contact between a power transmission belt and its pulley, a chain and its sprocket or a rack and pinion.

The third type of nip point occurs between rotating and fixed parts which creates a shearing, crushing or abrading action. Common examples include spoked handwheels on flywheels, screw conveyors or the periphery of an abrasive wheel and an incorrectly adjusted works rest.

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 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 moving parts.

Examples of Hazardous Mechanical Actions

Cutting action involves rotating, reciprocating or transverse motion. The danger of cutting action exists at the point of operation where finger, head and arm injuries can occur and where flying chips and scrap material can strike the eyes or face. Cutting actions are dangers with bandsaws, circular saws, boring or drilling machines.

Punching action results 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 as with power presses.

Shearing action involves applying power to a shear or knife in order to trim or shear metal or other materials. A hazard occurs at the point of operation where stock is actually inserted, held and withdrawn. Common examples are hydraulically or pneumatically powered shears.

Bending action results when power is applied to a slide in order to draw or stamp metal or other material. A hazard occurs at the point of operation where stock is inserted, held and withdrawn, such as power presses.

Requirements for Safeguards

Safeguards must meet these minimum general requirements:

1. Prevent contact: The safeguard must prevent hands, arms or any other part of a worker's body from making contact with dangerous moving parts.
2. Be secure: Workers should not be able to easily remove or tamper with the safeguard. Guards and safety devices should be made of durable material that will withstand the conditions of normal use. They must be firmly secure to the machine where possible or secured elsewhere if for any reason attachment to the machine is not possible.
3. Protect from falling objects: The safeguard should ensure that no objects can fall into moving parts.
4. Create no new hazards: A safeguard defeats its own purpose if it creates a hazard of its own such as a shear point, a jagged edge, or an unfinished surface.
5. Create no interference: Any safeguard which impedes a worker from performing the job quickly and comfortably might soon be bypassed or disregarded. Proper safeguarding can actually enhance efficiency since it can relieve a workers apprehensions about injury.
6. Allow safe lubrication: If possible, one should be able to lubricate the machine without removing the safeguard. 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.

Types of Machine Safeguarding

There are many ways to safeguard machinery. The type of operation, the size or shape of stock, the method of handling, the physical layout of the work area, the 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 area. For hazards at the point of operation, where moving parts actually perform work or stack, several kinds of safeguarding are possible. One must choose the most effective and practical means available.

Safeguards can be grouped under five general classifications: guards, devices, safety controls, gates and location/distance.

1. Guards (four main types)

Fixed guards are a permanent part of the machine. These guards are usually preferable to all other types because of its relative simplicity and permanence.

Interlocked guards automatically shut off or disengage the machine when the guard is opened or removed by tripping mechanism and/or power. The machine cannot cycle or be started until the guard is back in place.

Adjustable guards are useful because they accommodate various sizes of stock.

Self-adjusting guards allow the opening of the barrier to be determined by 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 for the stock.

2. Devices (four main types)

Presence-sensing devices are divided into two subgroups. Photoelectrical use a system of light sources and controls that can interrupt the machine's operating cycle. Radiofrequency or capacitance devices use a radio beam that is part of the machine circuit. When the capacitance field is broken, the machine will stop or will not actuate.

Electromechanical sensing devices have a probe or contact bar which descends to a predetermined distance when the operator initiates the machine cycle. If there is an obstruction preventing it from descending to its full, predetermined distance, the control circuit does not actuate the machine.

Pullback devices utilize a series of cables attached to the operators hands, wrist and/or arms. These devices are primarily used on machines with a striking action. When the slide/ram is up, the operator is allowed access to the point of operations. When the slide/ram begins to descend, a mechanical linkage automatically assures the withdrawal of the hands from the point of operations.

Restraint devices allow the operator's hands only to travel in a predetermined safe area.

3. Safety Controls

Safety trip controls, such as pressure-sensitive body bar, safety tripod, or safety tripwire cable, provide a quick means for deactivating a machine.

Two-hand controls take both hands and constant pressure on the controls for the machine to operate.

4. Gates

Gates are movable barriers that protect the operator at the point of operation before the machine cycle can be started.

5. Location/Distance

Though not actual guards, location and distance can be used to keep employees safe. Placing a machine in an infrequently traveled area or locating the machine so its dangerous moving parts are not accessible/do not present a hazard to a worker during the normal operation of the machine are examples. A thorough hazard analysis of each machine and particular situation is absolutely essential before using this safeguarding technique.

Guard Construction

Guards designed and installed by the machine producer have two main advantages: they usually conform to the design and function of the machine and they can be designed to strengthen the machine in some way or to serve some additional functional purpose.

User-built guards are sometimes necessary for a variety of reasons—and can have some advantages. Often, with older machinery, they are the only practical solution. They also may be the only choice for mechanical power transmission apparatus in older plants. User-built guards can be designed and built to fit unique and even changing situations, can be installed on individual dies and feeding mechanisms and the design and installation of machine guards by your own workers can help promote safety consciousness in your workplace.

However, there are some disadvantages. User-built guards may not conform well to the configuration and function of the machine and there is a risk that user-built guards may be poorly designed or built.

Guard Materials

Metal, plastic and wood are all used as construction materials for machine guards. In many circumstances, metal is the best material for guards. It may also be feasible to use plastic where higher visibility of the machine is required. Guards made of wood are generally not recommended because of their flammability and lack of durability and strength.

However, wood guards may be used in the woodworking and chemical industries and in industries where the presence of vapors or gases or where manufacturing conditions would cause the rapid deterioration of metal guards. Wood guards are also allowed in construction work and outdoor locations where extreme cold make metal guards undesirable. In all other industries, wood guards are not allowed (29 CFR 1910.219 (O)(2)).

Please click here to review LSS's product offerings for machine guarding applications.

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