66 Guarding

The basic premise of guarding is to prevent exposure to hazardous things in the workplace. The regulations and requirements for machinery guarding are primarily contained in OSHA regulations 1910.211 through 1910.222, and 1910.263(c), revised as of July 1, 1990. Additionally, OSHA has published a booklet, Concepts and Techniques of Machine Safeguarding (OSHA 3067, 1980), which more simply explains and illustrates the various ways of guarding machinery.

Often related to guarding matters, OSHA also requires certain signs and markings to designate hazards. These are contained in OSHA regulations 1910.144 and 1910.145.

In general, any machine component or operation that could cause injury must be effectively guarded. Most mechanical hazards are associated with the following three situations.

• Point of Operation: The point in the machinery where cutting, shearing, shaping, material removal, or forming operations are performed.

• Power Transmission Equipment: The machinery components that transmit power through the machinery. This includes sheaves, belts, connecting rods, cams, couplings, chains, gears, cogs, flywheels, spindles, sprockets, and shafts.

• Other Moving Parts: This includes the moving parts of the machinery not directly associated with the first two categories such as feed mechanisms, augers, flyball governors, moving fixtures, control mechanisms, and so on.

An easy rule to consider with respect to whether guarding is needed is could a person put his face in it without harm occurring? If not, protective guarding is needed.

A machine guard can take many forms. The most common is the direct barrier. A barrier simply prevents contact being made with the dangerous item while it is operating. A common example is the chain guard on a bicycle. It prevents the inadvertent contact of a person's leg or clothing with the bicycle chain and sprockets. Without the chain guard, clothing or skin could become entangled at the pinch point between the chain and sprocket, or snagged by the irregularities of the moving chain links.

For a barrier to be effective guard, a person should not be able to easily remove it and it should be durable. In some industries where pay is based on piecework, an operator may be tempted to remove a guard in order to save time and increase his pay. Of course, such removal may substantially increase the risk of injury. Such an easily removable guard may constitute an invitation to circumvent the guard. Similarly, a guard that easily breaks apart or wears out is not considered effective. The guard must stand up to normal wear and tear, including bumps and impacts from tooling that might be associated with routine work in that area.

To protect the operator from his own inadvertent action, or those of others, guards that might be removed occasionally by the operator for legitimate reasons can be equipped with trip switches or interlock devices. This will disable the operation of the machinery when the guard is removed. Thus, a person who is engaged in resetting some mechanism and is obscured from sight will not accidentally be injured by another person who unknowingly attempts to operate the machinery.

A barrier guard should also cause no new hazard and should allow the operator to work unimpeded. Guards made of sheet metal with sharp edges may create a new laceration hazard where there was none before. Guards that get in the way of work or aggravate a worker often are circumvented and workers will connive to get rid of them if possible.

Guarding by the use of direct barriers is often considered the preferred method of guarding. This is because no special training or actions by the operator are needed. The hazard is eliminated at the source. However, some situations do not easily lend themselves to this method and require alternative guarding techniques, such as protective clothing or equipment.

Protective clothing or equipment is especially useful where there is a danger of chemical splash, high intensity noise or light, noxious vapors, or similar hazards that cannot be fully eliminated by good practices or design. In essence, instead of putting a guard around the hazardous item, the guard is put around the person.

Items such as face shields, ear plugs, helmets, protective cloaks and coats, respirators, goggles, and steel-toed boots are in the category of protective clothing and equipment. Whenever possible, however, the root source of the hazard should be eliminated or reduced by design and engineering.

In instances where a machine's hazardous equipment cannot be effectively safeguarded by a fixed barrier, various electromechanical safety devices can be utilized to prevent contact. For example, photoelectric sensors can be used to determine if a person's hands or body is in a danger zone. While they are in this zone, the machine is disabled. Such a device is often used in power brake presses, where the duration of action is very short, but the force of the forming action is sufficient to severely maim or sever body parts.

Pullback devices are often used on machines with stroking actions. A pullback device allows an operator to manipulate a workpiece at the point of operation when the punch or shear blade is in the "up" position. When the machine begins its downstroke, cables attached to the operator's wrists automatically ensure that his hands are pulled clear of the work area.

Alternately, a two-handed trip switch can often accomplish the same effect. In such a system, the operator must have both hands and sometimes both feet simultaneously pressing independent switches before the machine will operate. This ensures that the operator's hands and feet are out of harm's way.

Trip wires and trip bars are devices that disable a machine when depressed or activated. The devices are used when operators have to work near equipment pinch points or moving machinery and there is a risk of falling into the equipment.

While not strictly guards, other safety devices that prevent inadvertent injury by machinery should not be overlooked. Such devices include safety blocks and chocks, lock-outs on power disconnect boxes, lock-outs on pneumatic and hydraulic valves, push sticks and blocks forefeeding materials, and so on (see OSHA 1910.147).

A machine can also be safeguarded by location: that is, it can be so placed that a person cannot normally get to it or to its hazardous equipment. Access to hazardous machinery can be denied by fence enclosures or by fixed wall barricades. Safety can even be further assured by placing a safety switch in the door or gate that will stop the machinery when the enclosure is entered.

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