An Analysis of Wood-Chipper Nonfatal Injuries: Us Versus Them

Chippers are on the short list of equipment that is essential for many arboricultural operations. These machines can convert entire trees into compact volumes that are easily transported. The shredded material also becomes a valuable commodity with far more uses – biofuels and mulch, to name two – than the traditional firewood market for brush. I would not want to do large-tree removals without one.

While mobile wood chippers are a safe and efficient means of managing woody brush, they are not without their hazards. They can shred any organic material that is inadvertently pushed or pulled into them. Incidents involving chippers occur every month in this country. The fatal ones are horrific and sometimes described as “total body fragmentation,” a term that leaves little to the imagination.

Fatal chipper injuries

The fatal incidents that receive the most attention are referred to as either “caught in” or “compressed by” incidents, where part of the operator’s body is pulled into the chipper. These often happen while the operator is working alone – dragging and feeding brush – while another tree worker cuts up the fallen tree. Sometimes the operator is pushing small, twiggy brush into the rollers, and the outreached hand is caught with most, or all, of the worker pulled through. Other times the operator stands on the feed table to free jammed brush and a foot is pulled in, often followed by the rest of the operator.

Most incidents are hands-first as they are pushing small brush in, but many times the circumstances are unknown, as the operator is working alone and no one witnesses the incident. Sometimes the other tree worker becomes suspicious, since it had been a while and the chipper operator has not returned for more brush. Other times, the worker hears a “weird sound” from the chipper and goes to investigate. They rarely hear a scream, as an operator can be pulled through a chipper in seconds – too quickly, perhaps, for the mind to process and react to what is occurring.

While “compressed-by” are common fatal chipper incidents, they are not the only ones. Fatal incidents also include operators being “struck-by” material – branches, cables and ropes – fed into the chipper. Fatal incidents also include being crushed by chippers when they fall off blocks while being repaired or struck by broken knifes when the housing cover is opened while the cutting wheel is still spinning. Operators have died from slipping off the chipper fender and striking their head on the pavement.

Nonfatal chipper injuries

Chipper fatalities have been widely discussed in TCI Magazine, as well as in other publications, and there is little need to have a detailed discussion of them here. As true with most equipment-related incidents, there are far more nonfatal injuries than fatal from chipper operation, and these are the focus here. The data on nonfatal chipping injuries comes from the same sources as those outlined in the May 2021 TCI Magazine article, “Chain-Saw Injuries: Us Versus Them.” These include various databases, with the U.S. Bureau of Labor Statistics, U.S. Occupational Safety and Health Administration and hospital emergency-department visits being the principal sources. As with the chain-saw injuries, hospital emergency-department (ED) visitations are an important source, as this data also includes the homeowner, who is the individual most frequently injured by chippers.

The chipper itself is not the primary source for all ED visits where chippers were mentioned in the reports. Sometimes they are a secondary source. For example, an operator is crushed between the chipper and the truck when a car collides with the chipper as the worker is stepping over the hitch. The car collision is the primary source, the chipper is secondary.

The focus of this article is incidents where the chipper is the primary source of the injury. Hence, incidents where a person is helping guide the chipper as it is backed onto the site and is struck are excluded. Struck by falling branch while chipping – since the chipper was stationed in the drop zone – also is excluded.

But if the hands or feet went into the rollers and a finger was severed, that is counted here. If the operator was struck by a branch that whipped as it was fed in and poked out an eye, that is here as well. So is someone who was injured when they opened the housing cover and were struck by debris. The chipper is the primary sources for all these injuries.

There are about 1,200 to 1,300 ED visits each year in the United States where wood chippers or shredders are a hazard source. This does not mean more than 1,200 tree workers show up in the ED each year with injuries related to chipper operations. Tree workers account for about 200 of the nonfatal injuries related to chipper operation. Many injuries during chipper operations occur to homeowners who are operating a chipper or shredder. The narrative to the ED reports sometimes began with “helping a neighbor with yard work,” or similar language.

Emergency-department visitation from chipper operations by tree workers

While tree-worker injuries were fewer in number than those for homeowners, the injuries were often more severe. This may be due to the size of the chippers, but this could not be determined from the data, as manufacturer information is often missing from the reports.

The most common traumatic injuries were amputations and fractures while feeding brush into the chipper. Fingers and hands were the appendages most likely injured while feeding brush into the chipper (36.5%). Most of these were “caught-ins,” where the fingers and hands were pulled into the rollers. However, clearing jammed material from the chipper while the disc was still spinning also causes finger and hand injuries (15.8%).

There were also amputations of hands, arms, legs and feet that were pulled through the rollers and cut by the knives (14.2%). These were more often injuries to the upper extremities. Amputations also occurred when changing knives and the tips of fingers were severed by the sharp edges.

Fractures were another injury and involved fingers, hands, arms and legs. Some of these were related to body parts compressed by the rollers, but others were from body parts caught in ropes that were being pulled into the chipper. Tree workers were dragged into the side of the chipper by the rope, and broken arms, legs and spines were the result of the impact. Arm fractures also occurred from being struck by debris after opening up the housing cover while the disc was still spinning.

Emergency-department visitation from chipper operations by homeowners

Chippers can be found lining rental centers. These rental machines range from 89-horsepower diesels designed for 12-inch-diameter logs to ones limited to chipping 6-inch material or smaller. “Chip your own tree,” the sign may say. Sounds good. Why hire a tree service when you can get a couple of buddies to help cut down and chip your tree? Chipping also seems to be an activity that draws in organizations, from service clubs to church groups, that want to help clean up a park of storm-damaged trees and turn the problem into welcomed mulch.

There are also smaller chipper/shredders for finer material, usually less than two or three inches. These have smaller gas engines, 10-horsepower or less, and there are even some electric-powered units. These smaller chipper/shredders are available for rent, though homeowners often own them. While most of the nonfatal incidents with chippers and shredders occur to homeowners, it is not possible to determine what percentage of injuries involved owned versus rented units.

Even though many of the chippers and shredders homeowners operate are smaller than what is commonly used among tree workers, they can still injure operators who ignore manufacturer’s instructions and common sense. Most of these injuries are treated in the ED, and the patient is released the same day.

Emergency-department visits where the patient was treated and released the same day

A review of the past 10 years of these ED visits showed the average age of a homeowner treated and released the same day was about 45. The range was three years to 90 years old. The three-year-old was standing at the back of the feed tray poking his head up to watch the brush go in and was struck by a branch that whipped as it was fed in.

The most commonly injured body parts for these ED visits were fingers and hands (45.5%). About half of these injuries were either lacerations or avulsions. The lacerations were deep cuts to the fingers, thumbs or palms that the operator could not manage with just pressure dressings, so they came into a hospital ED.

Avulsion is the term for soft-tissue injuries when the skin is torn away, leaving a flap. These are more than jagged lacerations, but not quite a full amputation. Avulsions usually happened while feeding the chipper and the hand was pulled into the rollers. However, there were also incidents of lacerations and avulsions from sharpening and changing knives.

The other half of finger and hand injuries were finger amputations or fractures. The amputations were ones that could be managed in the ED. These were to the fingertip and were not candidates for replantation by a surgeon.

The second most commonly injured body parts involved face and head injuries (12%). These occurred from operators being struck by brush as it was fed into the chipper. Homeowners often are not aware of the force with which brush can swing as it is fed into the chipper. They also typically do not wear basic personal protection equipment (PPE), so rarely will you see helmets with ear and eye protection. Most of these injuries were face lacerations from being struck by a branch that swung as it was being fed.

The third most commonly injured body part recorded for ED visits where the patient was treated and released the same day were to the eye (11.6%). These were corneal abrasions, an eye scratch. These happened when fine debris was caught in the eye, sometimes when the operator took off their safety glasses to wipe off sweat and pushed wood particles beneath the eyelid. But most times they were not wearing safety glasses and the eyes were directly exposed to dust and particles.

The fourth most commonly injured body part was the lower arm, including the wrist (5.1%). These injuries were not from being pulled into the chipper, but from being struck by material coming out of the chipper or swinging as it was pulled in. The body position is unknown, but the narratives sometimes say that the patient was standing behind the chipper when the piece struck them.

There also were injuries from ropes being pulled in with the brush and becoming entangled around an extremity, a leg or an arm, an incident homeowners share with tree workers. Regardless of who is feeding the chipper, practicing good housekeeping, where there is clear separation between brush and ropes, is a good idea. There were also several incidents of heat exhaustion and even asthma attacks from the dust.

About 8% of all the incidents where the operator was treated and released were not directly related to chipping. These occurred during hitching, when fingers found themselves in the wrong spot at the wrong time, to backing the chipper onto the site and running over the foot of the spotter.

Emergency-department visits where the patient was admitted to the hospital

Approximately 120 of the ED visits each year had the patient admitted to the hospital. The average age was about 50 for homeowners who were hospitalized from chipper- and shredder-related injuries. The ages of these injured operators ranged from a surprising two to 83 years old. The two-year-old crawled onto the feed table and pushed a twig in while dad was working in the yard cleaning up brush. The toddler survived, but lost a hand.

The most common body-part injury homeowners experienced during chipping operations that required admission to the hospital was again to the fingers and hands (59.3%), but these injuries were the far more serious amputations and fractures. These incidents mostly occurred while feeding brush into the chipper. The finger amputations involved more than the tip, and some were reattached in surgery. Interestingly, left fingers, hands and arms were injured more than the right for tree workers, while it was the opposite for homeowners.

Fractures were associated with many of these lacerations and avulsions. These were open fractures (a broken bone where the skin was not intact). The fractures also occurred during chipping, as the caught appendage was pulled through the rollers or was pinched by the brush as it was being compressed by the rollers. Hand fractures also occurred from the operator opening the housing cover and being struck by debris or the cover.

The second most common body injury was to the lower leg (11.1%). These were usually crushed and fractured legs that were caught in the rollers (including those of a 5-year-old) or pinched by brush. Some involved legs being caught by a rope and dragging the worker toward the chipper, breaking a leg in the process.

The third most common injury was to the eye (7.4%). Eye injuries occurred from being struck by branches and twigs as they were fed into the chipper. Some impacts were so violent that they shattered safety glasses. A common eye injury was a ruptured globe involving the sclera (the white part of the eye) and the cornea (the clear window on the front of the eye). Some of these eye injuries were associated with head trauma, again from a violent impact from a swinging branch being fed into the chipper.

Homeowner operation of chippers and shredders

A major problem with chipper use by homeowners is the apparently casual attitude they have for operating this equipment. Some key operating procedures that must be emphasized with rentals are:

Feed from the left side of the feed table. Often, the injured operator was standing directly behind the machine while pushing the brush in. This position increases the risk of being struck by a branch. Surprisingly, some of the videos for renting a chipper show the operator feeding in a branch while standing directly behind the feed table.

Never permit hands or feet to pass beyond the plane of the infeed hopper. Pushing small material in with the hands or clearing jams with feet and having them caught are common injuries.

Always wear a helmet, hearing protection and eye protection. Eye protection will reduce minor injuries, from dust and particles in the eye to ruptured globes. A helmet must be worn and can provide head protection from the impact of swinging brush. A helmet with a face shield is a good idea for homeowners. Some of the videos for rentals show operators only wearing eye and hearing protection.

Be cautious of wearing gloves. Gloves can protect hands from minor cuts and scrapes, but they also can become a catch point for brush. Gauntlet-type gloves must never be worn when operating a chipper, but few homeowners seem to understand the need to wear close-fitting gloves. Rental safety videos seem to ignore this requirement.

Do not allow untrained people to feed the brush, and do not allow anyone under 18 to operate the unit. Approximately 3.5% of the nonfatal injuries occurred to operators 17 years old or younger. Surprisingly, almost 3% were to operators less than 12 years old. Chippers and shredders are not toys.

Obviously, the best advice to homeowners is to hire a professional tree company to do the work and just avoid the hazards of a chipper. When you compare the cost of professional tree work to that of a hand amputation – up to $60,000 or more for the surgery alone – paying someone else to remove the tree does not seem that expensive.

And for the tree worker, find a copy of the 2017 ANSI Z133 for Arboricultural Operations – Safety Requirements and follow all of Section 5.3 Brush Chipper and Section 8.7 Brush Removal and Chipper every time you operate these machines.

John Ball, Ph.D., BCMA, CTSP, A-NREMT (Advanced – National Registry of Emergency Medical Technicians), is professor of forestry at South Dakota State University and a Board Certified Master Arborist.