Roberto N. Barbosa | 8/14/2010 12:20:47 AM
If we understand the principles of machine hazards and how to recognize them we will avoid and prevent serious injury. The most common machine hazards that we need to learn to recognize are:
· Pinch points
· Wrap points
· Shear points
· Crush points
· Pull-in points
· Freewheeling parts
· Thrown objects
· Stored energy
· Slips and falls
· Slow-moving vehicle
· Second party
Pinch points on rotating parts are formed when two objects move together and at least one of them moves in a circle. For instance, the point at which a belt runs onto a pulley. These points are also referred to as mesh points, run-on points and entry points. They exist most frequently in power transmission devices such as belt drives, chain drives and gear drives. Feed rolls which draw crops or feed material into a machine are other examples.
Serious injury can occur when hands, feet or other body parts are caught directly in pinch points or when they are drawn into the pinch points by loose clothing. Contact with pinch points may be made when persons brush against unshielded rotating parts or by slipping and falling against them. In some instances, people become entangled in pinch points when they deliberately take chances and reach or work near rotating parts. Machines operate too fast for a person to withdraw from a pinch point once he or his clothing is caught in it.
Avoiding pinch points
Manufacturers provide shields for pinch points on farm machinery. But some pinch points, such as feeder rollers on corn heads and silage choppers, are not shielded because they must be open in order to perform their intended function. Shields are probably the most effective means of protecting people from pinch points. Always replace shields if you must remove them to repair or adjust a machine. Remember that a portion of the money you paid for the machine went for safety research and design and for the actual hardware involved in shielding. Get your money’s worth and protect yourself – always keep shield in place.
For pinch points that cannot be shielded, the best protection available is operator awareness. Know the locations of the pinch points on your machinery. Avoid being near them when the machine is operating. And above all, never attempt to service or unclog a machine until you have disengaged all power and shut off the engine and all parts have stopped moving.
September 30, 1996. A 61-year-old dairy farmer was killed when his head was caught in a cattle-feeding machine. The incident occurred at the family farm in the cattle-feeding pen. The victim was operating a center-drive feeding machine, which directed corn from a nearby silo and transferred it to a conveyor belt that evenly distributed the feed into a 100-foot-long feeding trough. It is suspected that the farmer was trying to service the machine when his head was caught between the moving conveyor and a wooden support beam. Source: New Jersey FACE Report.
Any exposed machine component that rotates is a potential wrap point, but rotating shafts are most frequently involved in wrap-point accidents. Often, the wrapping begins with just a thread or frayed piece of cloth, such as on a cuff or sleeve, catching on the rotating part. Then the strong fibers and the cloth itself wrap around the rotating part with such a firm grip there’s no escape.
The part continues to rotate and because of the power involved can entangle and injure arms and legs. The more you pull, the tighter it wraps. It all happens in a split second. If the clothing would tear away, a person might escape serious injury, but work clothes are usually too rugged to tear away safely. Long hair can also be caught and wrapped around rotating parts, causing serious, permanent injury.
Smooth shafts often appear harmless, but they can wrap and wind clothing. Rust, nicks, dried mud or dried manure may make them rough so they’ll be more likely to catch clothing if someone leans against them. Even shafts that rotate slowly must be regarded as potential wrapping points.
Ends of shafts that protrude significantly beyond bearings can also wrap up clothing. Splined, square and hexagon-shaped shafts are likely to be more aggressive than smooth shafts. Couplers, universal joints, keys, keyways, pins and other fastening devices on rotating components are even more aggressive in entangling and wrapping clothing.
November 16, 1995. A 32-year-old male was killed when he was caught in a rotating PTO shaft. The farm worker was helping one of the owners of the farm load corn from the silage wagon into the feeding trough. The PTO connecting the tractor to the silage wagon was not covered by a safety guard. Recent heavy rains had made the area slick and muddy. The owner was nearby when he heard the victim yell. He found the victim wrapped around the rotating PTO. The farm worker suffered severe damage to the spinal cord, skull and left leg. Source: Kentucky FACE Report.
Shear points are created when the edges of two objects are moved toward or next to one another closely enough to cut a relatively soft material. Perhaps the most universal example is a set of hedge-trimming shears.
Cutting points are created by a single object moving rapidly or forcefully enough that it cuts a relatively soft object. A table knife, a hand-held grass sickle and a rotary lawn mower blade are examples of single object that can cut because of their sharpness and the force or speed at which they move into softer objects.
Devices designed to cut or shear
Various types of shearing and cutting devices are provided on farm machines to cut crop materials for livestock feed. The shearing and cutting parts may rotate, or they may move in reciprocating or sliding motions. Examples are sickle bar mowers, rotary shredders and cutters and cutter heads of forage harvesters. Because they must cut crop materials at rates of several tons per hour, they are very aggressive. They do not know the difference between crop material and fingers, hands or feet. And because they must cut crop materials, they usually cannot be guarded to prevent hands or feet from entering them.
Devices not designed to cut or shear
Cutting or shear points are also created by devices that are not actually designed to cut or shear, but in doing their intended jobs, they move near other parts in such a way that they may also cut or shear objects that are incorrectly placed too close to the functioning part. Examples of these include grain augers or chain and paddle-flight conveyors, or hinged implement frame members that move when an implement is raised or lowered.
Avoiding shear points
Because some cutting and shear points on farm machines cannot be guarded to prevent contact and injury, you must learn to recognize those potential hazards and plan activities so you, your assistants and bystanders will not be exposed to the potential hazards.
February 24, 1995. A 27-year-old agricultural maintenance worker was killed while repairing a silo bottom-unloading auger. The victim was working inside a cement silo filled with corn silage, repairing a sweep auger that was damaged because of frozen feed inside the silo. The victim was lying inside on the floor of the silo behind the auger safety shield when he shouted that he was clear of the auger. A workmate outside at the electric control panel turned on the auger for approximately 15 seconds to dislodge frozen corn silage in the auger. During that time the victim apparently reached to move a trouble-light hanging near the auger and got caught in the moving auger knives, severing his arm and shoulder and causing severe chest injury. Source: Iowa FACE Report.
Crush points are created when two objects move toward each other or one object moves toward a stationary object. This can occur in a reciprocating or sliding motion. It often involves a second person who accidentally moves one object against another not realizing the first person may have a finger, hand or foot between the two objects. For example, hitching tractors to implements may create potential crush points when two persons are involved. However, it often involves only one person. For example, a person may move a part or engage power with one hand while the other hand is in a hazardous position, or he works under a heavy object that he hasn’t securely blocked to prevent it from falling on him.
Sheet metal used as tractor hoods or as doors on combines may also crush or cut if a hand is in the way when they are closed. Keep in mind that when any two objects can move closer together, a dangerous crush point can exist.
Avoiding crush points
You must do two things to avoid being crush or pinned.
First, you must recognize all potential crushing situations. Some of these are mentioned in examples above.
Second, you must stay clear of the hazards. This statements seems simple and obvious, but many people are killed and injured because they don’t obey this simple rule. Be constantly alert to situations in which you may be crushed. Block all objects securely if you must work under them. If an implement can roll freely, whether you’re working on it or storing it, block the wheels so it will not roll. When two people hitch implements, make sure both are aware of the danger. At all times know what the other person is doing.
March 16, 1999. A 71-year-old farmer was killed when a stalk shredder he was working on fell and crushed him. He had raised it hydraulically and was working underneath it. The shredder was not blocked up and the hydraulic shutoff valves to the tractor (to which the shredder was attached) were not shut off. It appears the hydraulics on the tractor leaked at the connection, which allowed the shredder to slowly fall on the victim. Source: Nebraska FACE Report.
Pull-in accidents often happen when someone attempts to remove a corn stalk, hay, weeds or other plants from feed rolls or other rotating parts. People may be pulled into the moving parts of the machine and be seriously hurt.
The real cause of the accident is attempting to remove material while the machine is running, thinking that the machine will pull in the plugged material and be more quickly cleared. It may clear more rapidly, but it may also take in hands and feet with the crop or trash materials.
Another situation that leads to pull-in accidents is attempting to feed materials by hand into feed rolls, grinders, forage harvesters or similar machines to help them along. The primary reason people misjudge machines is that machines are generally faster than people, and people don’t always recognize that fact.
Consider a person attempting to remove a corn stalk from corn picker rolls. The stalk rolls rotate at about 12 feet per second. The person pulls on the corn stalk with his hand about two feet from the rolls. Without warning the rolls suddenly take the stalk in at 12 feet per second. It takes the person 0.3 seconds just to tell himself to release his grip on the corn stalk. That’s the average human reaction time. In that split second, the corn stalk travels 3.6 feet between the stalk rolls, and that’s 1.6 feet beyond where his hands grips the stalk. His hand is taken into the rolls because the machine is faster than he is.
Avoiding Pull-in Accidents
To avoid pull-in accidents, first recognize the potential hazards such as those outlined and illustrated in this chapter. Second, realize that you can’t win speed contest with farm machines. They are designed to handle crop materials, to harvest them or to cut them into smaller pieces for livestock feed. It’s almost impossible to design them to do their job and not injure people who don’t use them properly.
Clean, lubricate, unplug or hand feed a machine only when it is shut down. Always disengage power, shut off the engine and wait for all parts to stop moving before performing any of these operations unless the operator’s manual instruct you to do otherwise.
June 17, 1998. A 17-year-old male died when he became trapped in a round baler that caught fire. The farm worker was alone, baling dried wheat straw for hay. Evidence suggests that the round hay baler became jammed, and the clutch temporarily shut down the power take-off device. The worker apparently climbed on top of the baler to clear the jammed wheat straw by using his feet. The jam cleared, and the clutch put the PTO back into motion. The baler rollers suddenly started moving and trapped the worker’s leg inside the baler. The rollers and belts spinning around the hay started a fire. The worker died on the scene from smoke inhalation and burns. Source: Oklahoma FACE Report.