Complying with OSHA machine guarding standards
Answered by Wes Maertz, technical representative, Lab Safety Supply Inc., Janesville, WI.
Step 1: Identify the problem points
To identify the problem points in a machine, a basic understanding of mechanical hazards must be understood. The basic types of hazards are presented as motion hazards or action hazards. Examples of motion hazards include rotating (including in-running nip points), reciprocating and transversing. Examples of action hazards include cutting, punching, shearing and bending.
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. 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.
In-running nip point hazards are caused by rotating parts on machinery. There are three main types of in-running nips. The first type is created between parts rotating 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. The third type of nip point occurs between rotating and fixed parts, which creates a shearing, crushing or abrading action.
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.
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 The danger of this type of action occurs at the point of operation where stock is inserted, held and withdrawn by hand as with power presses.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 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 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.
Step 2: Safeguard selection
Once the hazard points have been identified, a safeguard can be used to prevent injury. As a general rule, power transmission apparatus are 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. Guards include four main types: fixed, interlocked, adjustable and self-adjusting. Devices also include four main types: presence-sensing, electromechanical-sensing, pullback and restraint.