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Safe Work Practices When Using Cranes to Remove Trees
By Norm Hall
The use of mobile, truck-mounted cranes for tree work has increased dramatically in recent years. Accidents while using mobile cranes for tree work have also increased. This article will focus on safe work practices while using a mobile crane for removing trees.
The following is a quote from a website found while doing research for this article:
“Mobile cranes are responsible for the most accidents, injuries and fatalities of all the crane types.”
Please note that this statement is from all mobile crane use, not just tree removal.
The most practical place to start is with the ANSI Z133.1-2006 safety standard and what it states about safety and mobile crane operations. 
5.7.9.2 – The qualified crane operator and the person responsible for the work to be performed shall meet prior to the work to review the procedures to be followed. If the work involves a signal person and/or arborist being lifted, these persons shall participate in the review as well. A job briefing shall be done before any work begins, in accordance with subsection 3.1.4.
3.1.4 – “A job briefing shall be performed by the qualified arborist in charge before the start of each job. The briefing shall be communicated to all affected workers.”
These statements are telling us a thorough job briefing shall be done with the entire team and the crane operator. Details to include are: crane hand signals, who is going to climb and cut, does a co-worker need to set chokers for the climber, where to set the mobile equipment (truck/chipper, aerial lift, crane), landing zone, staging area for logs, who is bucking, chip dump site, vehicular and pedestrian traffic control and ground worker safety (don’t stand beneath a suspended load).
3.3.1 – “Emergency phone numbers shall be available when and where arboricultural operations are being carried out. Arborists and other workers on the jobsite shall be instructed as to the specific location of such information.”
All team members shall know the “Emergency Plan.”
5.2.7 – “The operator shall ensure adequate clearance exists and give warning prior to lowering outriggers. Pads shall be placed under outrigger feet when they are needed to ensure stable footing.”
Pads or cribbing shall be used to protect surfaces from outrigger damage.
5.7.3 – “Operators of hoisting equipment shall maintain a minimum approach distance from energized conductors in accordance with table 1 or 2, as applicable. A spotter shall be used when work is being performed in proximity to electrical conductors. Personnel assigned to work in proximity to the tree removal shall be trained and follow guidelines for electrical hazards (section 4, Electrical Hazards).”
Keep all crane parts a minimum of 10 feet away from energized lines.
5.7.7 – “Tree sections shall be rigged to minimize shock loading. Shock loading shall be avoided, and free fall is prohibited. A green weight log chart shall be available to the crew.”
5.7.8 – “Riding the load line of a crane while it is under tension shall be prohibited, except for the circumstances outlined in subsection 5.7.9.11.”
5.7.9 – “A qualified arborist may be hoisted into position utilizing a crane if the arborist is tied with an arborist climbing line and arborist harness, and secured to a designated anchor point on the boom line or crane.”
5.7.9.11 – “The qualified arborist shall be detached from the crane any time it comes under load tension.”
EXCEPTION
“When it has been determined that all reasonable possible alternate methods are inaccessible and attachment to the subject tree would create a greater safety risk due to its hazardous condition, the qualified crane operator and the qualified arborist shall allow the qualified arborist to remain attached to the crane when it is under load. Possible alternate methods include, but are not limited to; (a) the qualified arborist securing to the tree and detaching from the crane before it comes under load; (b) using a second crane; (c) using an aerial lift device; (d) using an adjacent tree.”
5.7.9.12 – “When the qualified arborist is attached to the crane while it is under load, the total weight shall not exceed 50 percent of the load capacity for the radius and current configuration of the crane.”
NOTE: It is highly recommended that the qualified arborist descend to the ground as soon as it is safe to do so after the cut has been completed.
Once at the jobsite
Crane hand signals must be incorporated into the job briefing. Go over the crane hand signals with all teammates and the crane operator. Designate a “main signal ground person” and determine if any “blind” lifts are going to be made. If the crane operator cannot see the arborist making the cut, it is a blind lift. Either a signal person or radio communications shall be used in all blind lifts. Any wood that is not to be chipped shall have a staging area that is clear of all crane and other wood  disposal operations.
Hoisting personnel
Hoisting personnel from the load line or ball is a controversial issue. Mark Adams wrote an article about hoisting personnel in the March 2007 issue of TCI Magazine (visit tcia.org, under Publications). Please refer to that article for further clarification. The personnel hoisting method we use is safe and doesn’t interfere with the hook or ball. The components are: a 17-ton, screw-pin shackle, a 2-foot ring & ring friction saver, and a steel, double-auto-locking carabiner. (See Figure 1)
In Figure 2, you can see the hoisting rig does not interfere with the hook or ball. The FS rings are positioned beneath the center line of the ball to prevent the climbing line from rubbing on the ball and getting abraded.
Sling identification data
All slings shall have the following data indelibly marked on them: (a) rope manufacturer and the date of manufacture; (b) rope fiber, diameter and length of sling; (c) average breaking strength in pounds and kilograms; (d) safe working loads (SWL) in pounds and kilograms (KGs) in vertical, choked, and basket configurations.
Critical lifts
In some states, a critical lift form must be filled out any time a critical lift is done. Check with your state authorities. A critical lift includes the following: (a) load exceeds 75 percent of the crane’s current radius and configuration; (b) lifts over or near energized lines; (c) hoisting personnel or a man cage; (d) blind lifts; (e) lifts over an operating facility or residence; (f) utilizing special hoisting or rigging equipment; (g) two or more cranes simultaneously hoisting the same load.
How many times do we hoist loads that weigh more than 75 percent of the crane’s capacity, hoist personnel or a man cage, do blind lifts, and use special rigging gear such as synthetic eye slings or spider legs? These are all considered critical lifts and must be done with caution and communicated to all teammates.
Sling angles
Sling angles have a direct and oftentimes dramatic effect on the rated capacity of a sling. This angle, which is measured between a horizontal line and the sling tie-off, may apply to a single-leg sling in an angled, vertical or basket hitch, or to a multi-sling spider leg system. Any time pull is exerted at an angle on a leg, the tension or stress on each leg is increased. To illustrate, each sling leg in a vertical basket hitch absorbs 500 pounds of stress from a 1,000 pound load. The same load, when lifted in a 60-degree basket hitch, exerts 577 pounds of tension on each leg. (See figure 3)
It is critical therefore, that rated capacities be reduced to account for sling angles. Angles less than 45 degrees are not recommended, and those below 30 degrees should be avoided whenever possible. Use the formula and chart shown to calculate the reduction in rated capacities caused by various sling angles. (See Figure 4.)
Sling hitch rated capacities
Every lift uses one of three hitches: vertical, choker or basket. (See figure 5)
Choke angle rating
If a load is hanging free, the normal choke angle is approximately 135 degrees. If the choke angle is less than 135 degrees, an adjustment in the sling’s rated capacity must be made. Choker hitches at angles greater than 135 degrees are not recommended, since they are unstable. Extreme care should be taken to determine the angle of choke as accurately as possible. (See figure 6)
In controlled tests where the angle was less than 120 degrees, the sling body always failed at the point of choke when pulled to destruction. Allowance for this phenomenon must be made any time a choker hitch is used to shift, turn or control a load, or when the pull is against the choke in a multi-leg lift.
Wire rope
Wire rope chokers have been the sling of choice in the past. One of the challenges using wire rope chokers is where to place the choker to minimize shock once the limb is cut. Using two or more wire rope chokers to try and “balance” a limb is challenging due to the fixed length of the chokers.
There are two ways to set an eye-&-eye wire rope choker. The most common is to take the choker off the hook and put one eye through the other to form a “choke.” The other method is to use an appropriate-size screw-pin anchor shackle in one eye to use as the “choke.” This way, the eye on the hook stays attached, and the screw pin shackle is unthreaded, installed around the leg of the choker and rethreaded. This method is safer due to the fact that the choker eye on the hook doesn’t have to be removed and replaced each cut, and the hook “gate” can be pinned closed.
One important factor to remember is, the choker eye must be set in the shackle pin to prevent the pin from unthreading during tensioning. (See Figure 7)
Synthetic webbing slings and rope
Synthetic webbing slings have been used in crane work due to their light weight and ease of use. They don’t kink like wire rope and seem to cinch better on wood. Their limitation is the fixed length as well.
Enter “synthetic spliced eye-slings.” They have a fixed, spliced eye on one end only. (See Figure 2, in the “bow” of the screw-pin shackle attached to the hook). The other end is used for a tie-off. The lengths we have are 20 foot, 30 foot and 36 foot. They are constructed of a polyester hollow braid, i.e. Tenex, Yalex, Nerex in a 5/8-inch diameter. For working in close proximity to energized lines, we also have some spliced eye-slings constructed of Dyneema SK60, a high-strength, low-weight exotic rope fiber that is dielectric. These spliced eye-slings have an average breaking strength of 27,000 pounds in ½-inch diameter and 40,000 pounds in 5/8-inch diameter, as opposed to 12,000 pounds and 18,000 pounds, respectively, in polyester hollow braid.
The benefit of using these slings is the unlimited length adjustment. The sling may be tied at any spot along the length, making it ideal for “balancing” limbs.
Knots
The knot, or hitch, of choice in crane work is the cow hitch. The cow hitch has two turns of rope on the wood and is easily untied after loading. The limitation of the cow hitch is that it needs enough rope to go around the limb or log twice. If the rope isn’t long enough to go around twice, a timber hitch will work. We, at The Care of Trees, have been adding one more turn at the throat to increase knot efficiency, in addition to the recommended five tucks. We named this knot “the better timber hitch.”
Notches
In certain situations, a notch cut is advisable to prevent the choker from sliding off the wood. If there isn’t a stub or flare to place the choker beneath, the possibility of the choker sliding off exists. In Figure 7 you can see a notch cut for the choker to fit into to keep it from sliding up and off the log.
Cuts
As a rule of thumb, use a cut that will shock load the crane the least. In most cases, with lateral limbs, this will be a straight slicing cut. Other situations may dictate a notch and back cut, or a step cut, depending on what the outcome is.
Conclusion
A crane removal is arguably the most complex operation you’ll run into in tree care. There are many variables in play, and the stakes are high. This article only scratches the surface of what one needs to know. When you plan that next crane job, make sure you invest enough time and resources for planning and preparation.
Norm Hall, CTSP, is also an ISA Certified Arborist and Tree Worker, and a regional trainer for The Care of Trees in Wheeling, Illinois. This article was excerpted from his presentation on the same subject at TCI EXPO 2008 in Milwaukee.
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