Mathematics is not a field that sparks much interest among tree workers – or people in general. But the field of probability plays a role in just about everything tree workers do. If you knew that the odds of being severely injured performing a specific task were one in five, you might approach it with greater caution – or avoid it altogether – than if the odds were one in one million.

Average annual fatality rate

The number tree workers would like to hear is anything less than four. This is in reference to the average annual fatality rate per 100,000 full-time equivalent (FTE) workers. If all the workers in the United States are placed in a common pool, the all-industry fatal-incident rate is usually between 3.4 to 3.8 per 100,000 FTE. You want to be in an occupation at or below this rate. If you are doing tree work, you are not even close to this number.

If we pool the approximately 1.3 million grounds maintenance workers, which includes tree workers, the annual fatality rate is about 17 per 100,000 FTE, meaning about 220 fatal incidents each year. The U.S. Bureau of Labor Statistics (BLS) does not separate out tree workers – they use the term “tree trimmers and pruners” – from the grounds maintenance workers in their fatality-rate calculations.

One reason is that the BLS is not sure just how many tree trimmers and pruners are out there or how many hours they typically work during a year, prerequisites for accurately determining an FTE rate. This is not too surprising, as tree workers may be associated with landscape, land-clearing and tree care companies, among others. If a worker is pruning or removing a tree while doing lawn care, for example, are they a tree worker or landscape worker?

BLS tree-worker statistics

The current BLS estimate is that there are about 63,700 tree trimmers and pruners. This excludes tree workers performing plant health care and landscape-related duties. But still, 63,700 workers employed in tree-pruning and removal operations is probably a significant underestimate. The BLS used these numbers to calculate a preliminary rate estimate, however, and reported a fatality rate of 110 per 100,000 tree trimmers and pruners. This rate is about 30 times higher than the all-industry average.

The BLS is not able to account for every fatal injury in every occupation, nor for every worker. But last year they reported about 5,100 fatal injuries among the 132 million workers in the U.S. Putting all these numbers together – all-industry fatalities and workforce versus tree-worker fatalities and workforce – yields a sobering statistic. Tree workers are slightly less than 0.05% of the U.S. workforce, but may account for about 1.4% of the work-related fatalities.

Equally disheartening is the non-fatal injury rate for tree workers. Non-fatal events are those where the injury results in days away from work. The BLS estimated the non-fatal rate for tree workers is 239 injuries per 10,000 workers (10,000 rather than 100,000 is used for non-fatal injuries). The all-industry non-fatal rate is 89 per 10,000 workers, about one-third the rate for tree workers. Another way to view this data is tree workers have about one fatal incident for every 14 non-fatal injuries. The all-industry ratio is about one fatal for every 350 non-fatal injuries. The short answer – tree workers do not survive their injuries.

Incidents and accidents

While these numbers give a broad picture of the risk of tree work, what incidents account for these fatal and non-fatal injuries? Incidents are placed into event or exposure categories:

• Contact with Objects or Equipment.
• Exposure to Harmful Substances or Environments.
• Falls, Slips, Trips.
• Overexertion and Bodily Reaction.
• Transportation Incidents and Violence and Other Acts by Persons or Animals.

If we look at these event or exposure categories for all industries, the number-one category for fatalities is traffic incidents, at 38.2%. These include vehicle collisions to being struck by passing traffic. They do not include the daily commute to and from work, which is one of the higher-risk activities for most workers.

The two event or exposure categories that account for the most fatal injuries to tree workers are Contact with Objects or Equipment and Falls, Slips, Trips. These two are always the top categories for tree-worker incidents. They exchange the number one and two spots every year or two, as the two most common events are being struck-by or a fall. The struck-by fatalities are mostly during manual tree felling, but struck-bys from falling branches during pruning or dismantling are also a significant hazard. The majority of falls are either from or with a tree or an aerial lift.

Last year, Contact with Objects or Equipment was the category with the most fatal incidents to tree workers, at about 43%. About half of these fatal incidents involved being struck by a falling tree. These incidents are as old as the art of tree felling. Either the worker cutting the tree – now the chain-saw operator – is struck as the tree falls or kicks back off the stump, or another worker is standing too close and is hit by the falling tree or debris.

If the chain-saw operator would proceed down their retreat path as soon as the back cut begins to open and the tree begins to fall, we could reduce struck-by-a-tree fatalities by almost half. If all other workers observed their minimum distance from the tree, one-and-a-half times the height of the tree for involved workers – those tending the pull lines – and two times the height of the tree for all other workers, we could significantly reduce the other half. It is that simple.

Struck-bys and mechanization

Logging is one of the few occupations that has a higher fatality rate than tree work. Logging had a fatality rate exceeding 190 fatalities per 100,000 FTE in the mid-1980s. Slightly more than two-thirds of these fatalities were from being struck by the falling tree. Falling branches and logs falling off trucks were also struck-by incidents.

The logging rate has been dropping in recent decades, though it is still above 100 fatalities per 100,000 FTE, as the industry shifts to mechanized harvesting. The growing popularity of the knuckle-boom-mounted grapple-saws, where the operator can remain away from the falling tree, may help reduce the fatality rate for tree workers as well.

More struck-bys

There are other struck-by incidents. A falling or swinging branch is also a common hazard source for tree workers, slightly less than 10% of tree care fatalities. The simplest way to reduce this number is by following an established command-and-response policy and delineating a drop zone. Climbers or aerial-lift operators cutting branches or stubs without warning, and ground workers wandering through an active drop zone, are connected to most of these incidents.

While there are many other struck-by hazards, a third one, at almost 7%, involves chippers. The majority of these are not the compressed-by or caught-in incidents, where an operator was pulled into the chipper. These still occur, but now more fatal incidents are due to an operator being struck by something else, typically a rope or winch line being caught in the chipper. A simple means to avoid these incidents is to practice good housekeeping. Keep all ropes bagged or on a tarp unless in use. Another means of reducing incidents is by stationing the chipper away from where climbing or rigging ropes will be in use.

Falls, Slips, Trips

The event or exposure category Falls, Slips, Trips is the second leading category for fatal incidents among tree workers. This accounts for about a third of our fatalities. Climbers represent about half of all the fall incidents and most of the non-fatal ones. Either they fall from the tree or fall with the tree. Climbers fall from failed anchors – the branch their system was attached to breaks – or being unsecured, usually “just for a second” while they isolate a line or switch climbing systems.

Climbers also continue to fall with trees. The tree either breaks just beneath them and they fall with the tree part, or the tree breaks at the base. Dynamic forces on a weakened trunk may be a factor in these incidents. We need to do a better job of inspecting trees. A common comment after the incident is “We thought the tree was sound.” We need to remember that the tree is also part of the rigging system, not just the lines and equipment. We once worked with manila ropes, and these were often the weakest link in the rigging. Now it may be the tree or tree part.

Aerial-lift operators also account for fatal incidents. The most common fall incidents occurred when the operator was not wearing fall protection. However, we also have incidents where they were wearing the appropriate fall protection but it was not attached to the boom. It is not enough to wear the harness; it must be attached properly as well!

A relatively new fall hazard involves the use of platforms with a gate. We are seeing tree workers flying these platforms without fall protection, then opening the gate to reach out to either cut or grab a branch. They are cutting or grabbing with one hand while holding the railing with the other and, unfortunately, lose their grip. Never fly a lift without fall protection properly worn and attached. Never open a gate on the platform once it is off the ground.

Contact with electricity

The third event or exposure category is Exposure to Harmful Substances or Environments. This category accounted for approximately 14% of tree-worker fatalities last year. Almost all of these involved contact with electric current. About half of the fatal incidents occurred to climbers through indirect contact with the primary distribution line. The indirect contact was either through a conductive tool, usually a metal pole saw, or a live branch (or palm frond) that hung on a line after the climber pruned it off but was still holding it.

It is not enough to observe the minimum approach distance for the worker. It also must be observed for the length of the conductive tool or the arc of the falling cut branch. And a sobering statistic for contact with electric current – the fatal : non-fatal ratio is not 1 in 14, our average, but 1 in 4. The survival rate for contact with electric current is not good.

We have covered most of the fatal incidents that occur to tree workers. We also have covered many of the non-fatal incidents except for two. Chain-saw accidents are a struck-by event. They are not a common hazard source for fatal injuries, but are one of the most common for non-fatal. Another common non-fatal incident that rarely involves a fatality is in the event category Overexertion and Bodily Reaction. These are typically sprains and strains from lifting, pulling, twisting and other movements. Not a major fatal-hazard source, but a major contributor to worker-compensation claims.

Final thoughts

A few final numbers and thoughts. First, the average age of a tree worker is 38 years old. We are gradually aging. The fatal rate increases with age, but not the incident rate. The older you are does not mean you are going to have more incidents. But it means that your body is going to suffer more from them. As you age, your body doesn’t tolerate the traumatic forces as well. You break, rather than bounce.

Second, work for a company that invests in training and has a safety policy. Companies that walk-the-talk, invest in their workforce and are serious about safety have fewer incidents. They also have less worker turnover.

Finally, work for a TCIA-accredited company. These companies are among those that have the fewest incidents!

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

This article was based on his presentation on the same subject during TCI EXPO ’22 in Charlotte, North Carolina. To listen to an audio recording created for that presentation, go to this page in the digital version of this issue of TCI Magazine online at tcimag.tcia.org and, under the Resources tab, click Audio. Or, under the Current Issue tab, click View Digimag, then go to this page and click here.