Chain shot injures operator behind cab window

In 2004, the operator of a mechanical was trimming the butt end of a 12-inch log. The bar and were directly in line with the front window of the operator’s cab. The saw chain had been repaired with used connecting links. While the saw chain was operating at high speed, the chain broke. The whipping action of the broken chain end then caused a drive link to separate from the chain. It penetrated the ½-inch polycarbonate windshield of the cab. This “chain shot” struck the operator, causing severe internal injuries.

Although this incident occurred in 2004, chain shot is still a hazard and this older incident investigation report is being posted on the WorkSafeBC website for educational purposes.

Purpose of this report The purpose of this online incident investigation report is to identify the causes and contributing factors of this incident to help prevent similar incidents and to support preventive actions by industry and WorkSafeBC. This online version is not the official WorkSafeBC report. It has been edited to remove personal identifying information and to focus on the main causes and underlying factors contributing to this incident.

Notice of Incident information Number: 2004110596 Outcome: Injury Core activity: Mechanized falling/processing Region: Coastal British Columbia Date of incident: November 2004

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 1 of 18 NI number: 2004110596 www.worksafebc.com Table of Contents 1 Factual Information ...... 3 1.1 Workplace ...... 3 1.2 Sequence of events ...... 3 1.3 Chain shot ...... 5 1.4 Saw bar...... 5 1.5 Saw chain ...... 6 1.6 History of chain problems at the worksite ...... 9 1.7 Operator manuals ...... 10 1.7.1 Dangle head operator’s manual ...... 10 1.7.2 Saw chain manufacturer ...... 10 2 Analysis ...... 11 2.1 Saw bar orientation ...... 11 2.2 Windshield ...... 11 2.3 Saw cut drift ...... 11 2.4 Chain shot analysis ...... 12 2.4.1 Saw chain damage...... 12 2.4.2 Effect of previous chain breakage on rivet assemblies ...... 12 2.4.3 Saw chain repair ...... 13 2.4.4 Side loading ...... 13 2.4.5 Saw chain tension ...... 13 2.4.6 Saw chain speed ...... 13 2.5 Drive sprocket wear ...... 14 2.6 Chain wear ...... 14 2.7 Saw bar...... 14 2.8 The chain shot sequence ...... 15 3 Conclusions ...... 15 3.1 Findings as to causes ...... 15 3.1.1 Saw chain failure...... 15 3.1.2 Saw bar orientation ...... 16 3.1.3 Inadequate windshield protection ...... 16 3.2 Findings as to underlying factors ...... 16 3.2.1 Saw chain repair ...... 16 3.2.2 Saw chain speed ...... 16 3.2.3 Saw chain tension ...... 16 3.2.4 Excessive sprocket wear ...... 16 3.2.5 Severe side loading of chain ...... 16 3.2.6 Education and training ...... 16 4 Order Issued after the Investigation ...... 17 4.1 Order to the employer ...... 17 5 Health and Safety Action Taken ...... 17 5.1 WorkSafeBC ...... 17

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 2 of 18 NI number: 2004110596 www.worksafebc.com 1 Factual Information 1.1 Workplace The incident occurred in November 2004 at a site on the west coast of mainland British Columbia. The contractor that held the stump-to-dump arrangement with the licensee had subcontracted work to two other companies.

One of those companies owned the equipment involved in the incident, a forest machine with attached dangle head processor (see Figure 1). This equipment can be used for mechanical harvesting and/or processing of trees. In this incident it was being used for processing logs (delimbing and cutting to length). The windshield consisted of ½-inch thick polycarbonate. It was a replacement windshield as the previous one had been damaged.

Figure 1: Forest machine with attached dangle head processor.

1.2 Sequence of events On the day of the incident, workers and equipment were working on a slope with a roadway through the cut block. The cut block had been hand-felled. A grapple had placed trees in piles. A log loader operator was breaking down these piles and placing the trees on the roadway. The trees on the roadway were being processed (delimbed and bucked to length) and then laid into piles in preparation for loading onto a truck. A log loader was operating on the road below.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 3 of 18 NI number: 2004110596 www.worksafebc.com At some point during the day, the dangle head’s saw chain was thrown off the saw bar. The harvester operator put the chain back on.

At approximately 15:00 the harvester operator activated the saw of the dangle head in order to square the butt of a 12-inch fir log. The bar was directly in line with the front window of the operator’s cab. Near the end of the cut the chain broke and the operator heard a crack. A drive link with side plates broke free from the chain and was propelled through the ½-inch thick polycarbonate window (see Figure 2). This “chain shot” struck the operator, inflicting serious internal injuries. He was evacuated by helicopter to hospital.

Figure 2: Artist’s drawing of the path of the chain shot. The photograph shows a drive link with side tie strap similar to the chain shot that went through the window and struck the operator.

The incident was witnessed by the nearby log loader operator and by the faller, who heard the crack and saw sparks coming from the bottom of the saw shroud of the dangle head. There was a mark in the bottom of the shroud indicating that the shroud was struck by the free end of the saw chain.

Looking from the harvester operator’s perspective at the butt of the log involved in the incident shows that the saw cut “drifted” to the right side (see Figure 3). The “whiskers” or wood slivers at the lowest part of the cut indicate that the cut was not fully completed. The slivers indicate that the saw chain was thrown before the cut was fully completed.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 4 of 18 NI number: 2004110596 www.worksafebc.com

Figure 3: Log butt where the cut drifted.

1.3 Chain shot Chain shot is a phenomenon that can occur in mechanical harvesting and processing applications. It is the high-velocity separation of a piece or pieces of cutting chain from the end of a broken saw chain. These are highly dangerous as their kinetic energy can be equivalent to that of a bullet from a sporting rifle.

Chain shot can occur when the end of a broken chain is rapidly accelerated as a result of either an impact or a whip-like motion of the chain end. The shot typically occurs near the drive end of the cutting system (chain shot zone), but it can also come from the bar tip area, as it did in this incident. Chain shot exposes both machine operators and bystanders to a risk of serious injury or death from components thrown from the saw chain.

1.4 Saw bar The saw bar of the dangle head processor is used for felling trees or cutting tree stems to length (bucking). At the time of the incident, the saw was used for bucking.

The saw bar was manufactured by Oregon Cutting Systems Group, of Blount, Inc. The saw bar (also called a guide bar) has a groove around its edge that seats the drive link bottoms and guides them around the bar while the chain is moving. The groove was examined for wear after the incident. It was not observed to be damaged or excessively worn.

The harvester head rotates in two planes. When felling, the dangle head clamps the tree. The bottom saw is perpendicular to the tree and parallel to the ground. When the tree is cut, the dangle head controls the direction of the fall. The head must turn in the direction of the fall. When delimbing and bucking, the head can be rotated from right to left. The operator is able to position the harvester head to adjust the orientation of the saw bar for the task being performed.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 5 of 18 NI number: 2004110596 www.worksafebc.com With this model, the bottom saw bar was used. When controlling the saw manually, the operator presses and holds a button on the right joystick bar in the cab. Upon actuation, the saw bar moves out of its protective shroud and continues its motion downward through the log. It either fells the tree (with the saw bar plane parallel to the ground) or bucks the log after the tree has been delimbed (with the saw bar plane perpendicular to the ground, as shown in Figure 4). When the operator releases the button, the saw bar travels in an upward motion and returns to the shroud, and the hydraulic saw motor shuts off.

Saw bar

Figure 4: Saw bar in bucking position.

The saw bar had been damaged and repaired previously. At times when the machine was used for felling, cut trees had slipped downward onto the saw bar and bent it. The saw bar would be straightened afterward, but it was reported that bars would never be the same after repair.

1.5 Saw chain The saw chain involved was a continuous loop with 60 drive links mounted on the saw bar. A hydraulic motor in the dangle head rotates a drive sprocket that runs the chain. The chain has right-hand and left- hand cutters that cut the wood on the bottom side of the bar when bucking or felling. The chain involved in the incident was supplied by Oregon Cutting Systems. It was purchased in bulk by the company that owned the forest machine. The chain type is identified as 11bc. Individual loops of chain to fit the bar were not made by Oregon Cutting Systems.

Rivets hold the saw chain component parts together (see Figures 5 and 6). A factory-installed rivet on a ¾ pitch chain has a tensile strength of 6,700 pounds.1 The amount of rivet head material and its proper shape is critical to saw chain strength. New preset tie straps have two rivets that are already installed. The preset tie strap rivet goes through the drive link hole and then has either a cutter or tie strap placed

1 Chain pitch is the distance between any three consecutive rivets, divided by two.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 6 of 18 NI number: 2004110596 www.worksafebc.com over it. A second rivet head is then formed by hammering. After hammering, it is recommended that a specialty called a “spinner” be used to properly form the rivet head for maximum strength.

Figure 5: Orientation of components in a typical saw chain (based on a drawing in the Oregon Cutting Systems’ Mechanical Timber Harvesting Handbook).

Cutters

Tie strap

Rivet Drive link

Figure 6: Components of the saw chain with typically formed rivet heads.

Examination of the chain involved in the incident showed that there were hammered rivet heads with much less rivet head material than on a factory-installed rivet (see Figure 7). This indicates that used tie straps (with their rivets) had been used to repair the saw chain. The repaired tie straps rivet heads had not been formed by a spinner tool.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 7 of 18 NI number: 2004110596 www.worksafebc.com

Figure 7: Unformed rivet heads on cutter that had been previously repaired.

Saw chain gauge is the metal thickness of the drive links where they fit into the saw bar guide groove. The saw chain gauge of chain involved in this incident was 0.122 inches, the largest gauge supplied. Other gauges for harvesters are 0.063 inches and 0.080 inches.

The chain tension is adjusted with a pry bar and set screw. The recommended force applied to this bar was 150 pounds. The saw chain was tensioned by hand. However, even when the tension was tightened as much as possible, when the saw was running at full speed, the chain would rise out of the bar groove to the point where the bottom of some drive links cleared the top of the groove.

The distance between the cutter and the depth gauge (also called a “raker”) determines the thickness of wood being cut. This is because the depth gauge rides on the wood and the cutter edge follows behind. The cutter cannot chip out more wood than the distance to the depth gauge.

Cutters on the broken chain involved in the incident were examined as to angle radius, top plate cutting angle, side plate angle, and top plate filing angle, and no problem was found. The depth gauge setting was consistently one-half of the 0.060 inches stamped on the cutters, indicating that the rakers were not filed when the cutters were sharpened. Examination confirmed that the rakers had not been filed. The effect of this was that the saw chain cutters were cutting at only one-half as deep (0.030 inches) as the chain was designed for, resulting in lower productivity.

The saw motor is hydraulically powered by the forest machine. This model’s chain saw speed can be adjusted by the controls and is dependent on the number of sprocket spurs. The saw drive sprocket for this model is a double sprocket with nine spurs. The assembly can be reversed when one side becomes worn. The sprocket spurs were severely worn, and the wear was measured at 0.040 inches (see Figure 8).

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 8 of 18 NI number: 2004110596 www.worksafebc.com

Figure 8: Double sprocket showing significant wear

During examination of the dangle head, a WorkSafeBC engineer measured the rotation speed of the saw sprocket under power without a chain attached. It was measured by instrument at 8,723 revolutions per minute (rpm). Saw chains were not put onto the saw bar as the two other chains found on site contained rivets made with used parts. The product design engineer for Oregon Cutting Systems indicated that with the chain installed, the rpm drop is between 700 and 1,000 rpm. The actual maximum operating speed with chain is therefore approximately 7,700 rpm. This translates to a chain speed of over 8,000 feet per minute. The manufacturer’s recommendation is for a 6,000 feet per minute chain speed. The Oregon Cutting Systems engineer advised that the ¾ pitch chain speed should not exceed 7,000 feet per minute.

The chain speed was adjusted by feel. The operator’s manual gave no information on adjusting the chain speed, nor were any other guidelines used.

1.6 History of chain problems at the worksite • Thrown chain: The chain had been thrown off the saw bar many times in the past. The chain had been thrown on the same day just before this incident. The harvester operator had put it back on the saw bar. • Chain jamming: The chain had become stuck between the saw bar side and the nose sprocket on top of the saw bar on several occasions. This had jammed the chain so that it stopped. A hammer had been used to hit the stuck link free. • Chain breakage: There had been a history of chain breakage with the equipment. The saw chain had broken “thousands” of times. • Chain shot: The harvester operator indicated that he had experienced chain shot previously on several occasions. The projectile links did not cause any damage on those occasions.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 9 of 18 NI number: 2004110596 www.worksafebc.com 1.7 Operator manuals

1.7.1 Dangle head operator’s manual The manual for the dangle head available to the operator provides guidance for maintenance and operations. There are two safety sections in the manual. The first safety section, at the front of the manual, consists of two pages labelled “ATTENTION” with general safety items. There are no warnings about saw bar orientation, and saw chain maintenance is not addressed. The second safety section contains the following warning: “The saw is never allowed to be used so that the operator or any other person is on the saw line, in front of or behind the machine, not even further away. A broken chain can fly far with high speed.” This section does not contain any warnings regarding saw chain maintenance.

There are chain speed recommendations for 0.404 pitch chain only. There are no recommendations for chain speed with a ¾ pitch chain.

The manual states: “Worn drive sprocket must be replaced before it damages the chain.” The manual does not quantify the amount of wear.

1.7.2 Saw chain manufacturer Manufacturer’s instructions and recommendations referenced in this report are derived from the Oregon Cutting Systems’ Mechanical Timber Harvesting Handbook, which addresses saw bars and saw chain. At the time of the incident, the current publication date for the handbook was March 15, 2004. Note that this handbook was not available to the operator when the dangle head was purchased in 1999. At the time of preparing this report for WorkSafeBC.com, the current publication date is January 2012, and it is available online: http://www.oregonproducts.com/pdfs/Harvester_HandbookA106976af.pdf

The handbook is invaluable for its recommendations on operating and maintenance procedures for its brand of saw chain-based cutting systems for mechanical harvesters. It contains the following: • An emphasized warning about chain shot in the first pages. This warning explains clearly to operators what chain shot is and how it occurs. The warning is repeated in several places in the 2012 edition. • Specific instructions about the interrelationship between chain speed and feed force. • Specific instructions about saw chain maintenance and repair. • Specific instructions about recommended chain speeds for ¾ pitch chains. • Specific instructions on how to manually tension a saw chain. • Specific instructions for setting the depth gauges of the cutters.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 10 of 18 NI number: 2004110596 www.worksafebc.com 2 Analysis The analysis looks at why the chain shot was able to strike the operator in the cab and how factors such as saw chain repair, chain speed, sprocket wear, and side loading contributed to the incident.

2.1 Saw bar orientation The operator’s manual supplied with the harvester in 1999 contained only cursory information about saw bar orientation and did not emphasize the safety importance of this.

The log loader operator and the harvester operator stated to investigators that the orientation of the saw bar was in a direct line with the cab windshield and harvester operator when processing logs from right to left from the operator’s perspective. Some operators preferred this orientation because they could line up the exact cut more easily. However, since chain shot usually travels in the cutting plane of the saw bar, orienting the saw bar towards the cab puts the operator in the most likely chain shot path.

If chain shot did occur and was headed towards the cab, operators had to rely on ½-inch thick polycarbonate windshields to stop projectiles.

2.2 Windshield Although there had been other instances of windshield penetration from chain shot, those incidents did not share the tremendous kinetic energy involved in this 2004 incident. Injuries from previous incidents had been minor.

Forest machine suppliers have been regularly supplying ½-inch polycarbonate windshields. This thickness is not enough to stop a severe chain shot, as this incident shows. There are indications that 1¼-inch laminated polycarbonate materials are available for retrofits, and that they will be sufficient to stop penetration from the chain shots in the worst-case scenarios.

The Occupational Health and Safety Regulation, section 16.21(1), states that operators of mobile equipment must be protected against falling, flying, or intruding objects or materials.

2.3 Saw cut drift The cut from a saw can drift for several reasons, including but not limited to the following: • Dulled cutters • Damaged cutter • Unevenly filed cutters • Unevenly filed depth gauges • Jerky motion of an advancing tree that causes the saw bar to sway back and forth before entering the cut • Improperly working lockout that prevents the log from feeding horizontally while the cut is proceeding • A saw bar twisted or damaged along its longitudinal axis

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 11 of 18 NI number: 2004110596 www.worksafebc.com In this incident, the saw bar had been previously damaged and repaired. The saw chain was not cutting efficiently because the rakers were too high, so extra forces from the saw downstroke, and the possibility of frozen wood, could have caused the bar to twist, resulting in a “drifting” cut (as shown in Figure 3 on page 5). The “drift” can cause side loading at the top of the saw chain.

2.4 Chain shot analysis

2.4.1 Saw chain damage The chain loop was 60 links long. Analysis of the broken chain showed that there were missing parts: one right-hand cutter, the tie strap (with two rivets) holding the right-hand cutter, and a drive link. In addition, a drive link and a two-tie-strap assembly were recovered from the operator’s body.

Layout and examination of the chain showed severely damaged drive links. The damage to the drive links likely occurred as the chain broke and the drive links were damaged by the drive sprocket.

When the saw chain was arranged with severely damaged drive links at the sprocket end, the location of the chain failure along the bar could be identified. After matching the damaged drive links to the drive sprocket and placing the chain in the shape of the saw bar, investigators determined that the first break occurred in the area at the top (middle) of the saw bar. The chain saw most likely initially failed at the right-hand cutter that was missing. Based on the evidence of the missing pieces and the recovered pieces, the investigation found that the chain must have eventually broken in at least three places.

2.4.2 Effect of previous chain breakage on rivet assemblies The saw chain involved in the incident had broken previously. Examination showed that it had been repaired with used parts. Two other chains on site had also been repaired with used parts.

When a saw chain breaks, the head of the tie strap rivet can shear off and distort the metal (see Figure 9). About 40% of the material used to form the original rivet head is now lost. In addition, the metal left behind is distorted and weakened from the forces of the breaking action.

Distorted rivet with sheared head Unused rivet

Figure 9: Photograph of a damaged rivet and head beside an unused rivet.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 12 of 18 NI number: 2004110596 www.worksafebc.com 2.4.3 Saw chain repair Examination of the saw chain involved in the incident showed evidence of the chain being repaired with used parts. In several places, rivet head material was much less (approximately 40% less) than in the factory-installed tie strap rivets. If used rivet and tie strap assemblies are installed, the rivet head is not as thick as in a new rivet, and the joint will therefore not be as strong.

If a spinner tool is not used to properly form the rivet head, the edges of the rivet head where it is hammered down are thin and not properly formed over the edges of the hole it connects through (see Figure 7 on page 8). Insufficient and fatigued rivet head material makes the rivet head vulnerable to failure.

The operator’s manual supplied at that time did not address saw chain maintenance and repair. The information contained in the Oregon Cutting Systems’ Mechanical Harvesting Handbook (March 2004) was not available when the dangle head was purchased in 1999. The company did not obtain the 2004 handbook later, and therefore, the recommendations for saw chain maintenance and repair were not available to the operator.

2.4.4 Side loading There were problems involving thrown chain. The saw chain had been thrown just prior to this incident and had been replaced on the saw bar. The saw chain had also jammed between the saw bar and nose gear many times, to the point that the operator needed to strike the chain to dislodge it. Each of these events can weaken a chain.

Side-loaded chains often result in a partial chain throw where the chain is out of the bar groove on one side but still in the bar groove on the other side. The partial chain throw will have the chain out of the groove and jammed at the nose. Chain on the top side of the bar can get caught on a log if the bar is side-loaded.

2.4.5 Saw chain tension No matter how hard the operator tightened the tension on the saw chain, when the saw was running at full speed, the chain would rise out of the bar to the point where the bottom of the drive links would actually clear the top of the saw bar grooves. This is not unusual in manually tensioned saw chains. This is because of the centrifugal force of the speeding chain as it rounds the sprocket and then rounds the star gear at the bar tip. The pressure of the cut at the bottom of the saw bar holds the saw chain in the guide slot.

Chain and bar rail clearance increases by 50% or more as the chain comes to speed because the centrifugal force due to the chain speed elastically stretches the chain.

2.4.6 Saw chain speed The recommended chain speed for this harvester’s saw was 6,000 feet per minute. The maximum speed should not exceed 7,000 feet per minute. The chain speed at the time of this incident was estimated to be between 7,700 and 8,000 feet per minute. The higher the chain speed, the farther the chain comes out of the bar groove.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 13 of 18 NI number: 2004110596 www.worksafebc.com 2.5 Drive sprocket wear Examination of the drive sprocket showed that the sprocket spurs were severely worn (see Figure 8 on page 9 showing unacceptable sprocket wear). Measurements of the wear indicated 0.040 inches. The operator’s manual says only: “Worn drive sprocket must be replaced before it damages the chain.” It does not quantify how to evaluate wear. However, the Oregon Cutting Systems’ Mechanical Timber Harvesting Handbook (2004) recommended sprocket replacement when spur wear reaches a depth of 0.025 inches.

The investigating officer was informed that the sprocket was original equipment. Sprocket wear should closely match chain wear. In this case, there were numerous saw chain replacements in the period since the dangle head was purchased in 1999. When new chain is placed on a severely worn sprocket, there is a mismatch where the saw chain drive links mesh with the sprocket spurs. This can damage the chain drive links and contribute to chain breakage.

2.6 Chain wear The saw chain was properly sharpened. However, the depth gauges (rakers) were not filed (lowered) to match the diminishing cutters on successive cutter sharpenings. It is recommended that each cutter be maintained at the factory-gauge height of 0.060 inches, which was stamped on each cutter. The depth on the cutters in the chain involved in the incident was consistently in the range of 0.030 inches. Insufficient depth of the depth gauge has two effects in relation to this incident: • The cutters cut only half as deep as they should, requiring higher chain speed to cut at an acceptable rate. • The saw chain is cutting wood at only half the rate it is designed for. This does not provide for an efficient match for the saw bar downstroke forces. It is likely that the hydraulic load for the downstroke was higher than normal.

2.7 Saw bar Examination at the site did not show obvious damage or distortion of the saw bar. The saw bar was not removed from the dangle head. It was reported that the saw bar had previously been bent when felling trees. While felling, an insufficiently clamped tree trunk had slipped down onto the bar. Although the bar was repaired, it was reported that it was never the same.

Deformation can result in metallurgical change in the bent area. This is not easily seen. Repairs might straighten the bar but further adverse metallurgical change may occur. This change could contribute to a saw bar “twist” under the stress of high chain speed. The downstroke hydraulic loading forces of the saw bar were likely higher than normal because of inefficient wood cutting that resulted from the incorrect depth gauges.

There was further evidence suggesting bar damage. The saw chain had jammed many times at the point where the nose sprocket attaches to the saw bar. This can be explained by side loading of the chain. It can also be explained by a bar twisting under severe load. Here the chain rises above the saw bar groove in a direction not exactly matching where the drive links re-enter the groove. The shortest distance from the exit point of the drive sprocket to the first nose sprocket tooth is now on the outside of the bar grooves, and the chain jams.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 14 of 18 NI number: 2004110596 www.worksafebc.com The number of times the saw chain is reported to have been thrown from the dangle head saw is further indication of a bent or twisted bar. In this incident, a bent or twisted saw bar could explain the right- hand drift of the cut, which in turn side-loads the chain exiting the sprocket.

2.8 The chain shot sequence The “whiskers” observed at the bottom of the cut of the log being bucked confirm that the saw had not completed its cut and the whiskers identify the location in the cut where the saw chain failed.

The chain drivers were most likely damaged by the drive sprocket when the chain broke. This locates the chain on the bar at the time of failure. When the chain was laid around the bar with the damaged drivers next to the drive sprocket, the missing components and shot components were shown to have come from an area of the chain located slightly towards the drive sprocket and close to the middle of the top of the bar.

The chain was weakened from having been thrown several times before, running on an excessively worn drive sprocket, and being repaired with used tie straps that do not permit full-strength joints, and it suffered from substandard rivet heads. This chain with questionable integrity was run at higher than permitted speed, imposing excessive force. The bar integrity was compromised from having been straightened.

The weak chain running at excessive speed may have induced excessive twists in the compromised bar. When driven at speed, the chain drivers extend out of the bar groove at the top of the bar. At speed, a weakened chain stretches more than normal and drivers move farther out. At that time, the chain may also have been side-loaded as the chain cutters at the top of the bar contacted the wood as the cut “drifted.” This placed additional tensile loads on the chain and it snapped. A broken end could have struck the shroud and shed a cutter, drive link, and tie strap. It is also possible that a broken chain end could have shed the missing pieces when it flew past the bar nose and propelled the driver and tie straps free as it momentarily stopped when the chain end “whipped.”

It is clear that one end of the chain continued to move towards and past the bar nose. When the chain came tight, it, in effect, acted like a whip and at a minimum shed the driver with two attached tie straps. The drive link and tie strap assembly spun rapidly and were propelled at high velocity in line with the bar towards the front cab window made of ½-inch thick polycarbonate (lexan). (This shedding of components upon being subject to a whip action is known in the logging industry as “chain shot.”) The drive link with two tie straps attached struck the window end-on with enough energy to penetrate the window and continue on, striking and penetrating the operator’s body.

3 Conclusions 3.1 Findings as to causes

3.1.1 Saw chain failure The saw chain from the mechanical harvester bottom saw broke as the butt end of a 12-inch fir log was being cut. A drive link with two side links attached broke free and was hurled towards the cab of the forest machine, penetrating the cab window and striking the operator.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 15 of 18 NI number: 2004110596 www.worksafebc.com 3.1.2 Saw bar orientation The mechanical harvester operator oriented the saw bar in line with the forest machine cab while attempting to square the butt of a 12-inch fir log. At the time, it was thought chain shot could not penetrate ½-inch polycarbonate windshields and the windshield would protect the operator from projectiles.

3.1.3 Inadequate windshield protection The windshield of the forest machine cab made of ½-inch thick polycarbonate was insufficient to protect the operator from chain shot involving ¾ pitch saw chain.

3.2 Findings as to underlying factors

3.2.1 Saw chain repair Chain repairs had been made with used saw chain parts. Some rivet heads were inadequate in both volume and shape, leading to a weakness in the chain strength.

3.2.2 Saw chain speed The saw chain speed exceeded design limits. Higher speed increases the likelihood of breakage.

3.2.3 Saw chain tension The saw chain was tensioned by hand. Recommended tension was 150 pounds. It is very difficult for an operator to gauge the force on the lever used to tension the chain.

3.2.4 Excessive sprocket wear The wear on the sprocket spurs was excessive as the sprocket had never been replaced despite a number of chain replacements. This contributed to saw chain damage and increased the likelihood of breakage.

3.2.5 Severe side loading of chain The “drifting” of the cut involved in this incident indicates that the saw bar and chain were severely side-loaded. Although it was not determined that the saw bar bent or twisted under load, it is possible that it did, as examination of the saw chain did not show evidence of a cause of the side loading. In addition, the depth gauges were half the recommended depth. This caused extra loading forces on the saw bar during the downstroke, contributing to side loading.

3.2.6 Education and training The education and training for the harvester operator with regard to avoiding chain shot was insufficient. The employer did not have a copy of the manufacturer’s recommendations for saw chain repair and maintenance.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 16 of 18 NI number: 2004110596 www.worksafebc.com 4 Order Issued after the Investigation WorkSafeBC issued one order after the investigation. An order requires an employer to take steps to comply with the Workers Compensation Act or Occupational Health and Safety Regulation, to take measures to protect worker health and safety, or to fix a hazardous condition. An order is intended to ensure that unsafe conditions are identified and corrected and that the employer complies with the Act and the Regulation. An employer may ask the Review Division to review an order; the Review Division may confirm, vary, or cancel an order.

In addition to issuing orders, WorkSafeBC may recommend proceeding with an administrative penalty against an employer. Penalties are fines for health and safety violations of the Workers Compensation Act and/or the Occupational Health and Safety Regulation. For information on when penalties are considered and how the amount of the penalty is calculated, see the penalty FAQs on WorkSafeBC.com. Penalties imposed on firms are also listed on the web site.

4.1 Order to the employer This section summarizes the order issued to the employer. The investigation found that this employer was in contravention of the Workers Compensation Act, section 115(1)(a), which states that an employer must ensure the health and safety of all workers working for that employer. This includes ensuring that each machine and piece of equipment is capable of safely performing the functions for which it is used and ensuring that it is used and operated in accordance with the manufacturer’s instructions. It also includes ensuring that the installation, inspection, testing, repair, and maintenance of the equipment are carried out in accordance with the manufacturer’s instructions. (These requirements refer to section 4.3 of the Occupational Health and Safety Regulation.)

5 Health and Safety Action Taken In addition to the specific actions below, employers, workers, or others in industry may have taken measures to prevent a recurrence of this type of incident. Employers are expected to comply with any orders issued. At WorkSafeBC, the Lessons Learned committee examines recommendations from incident investigations to see what can be done to prevent similar incidents.

5.1 WorkSafeBC WorkSafeBC produced a hazard alert about this incident. http://www2.worksafebc.com/Publications/Posters.asp?ReportID=33634

WorkSafeBC also produced a slide show about this incident for mechanical harvester operators and employers. The slide show includes prevention measures. It is available on WorkSafeBC’s website: http://www2.worksafebc.com/Publications/Multimedia/SlideShows.asp?ReportID=33843

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 17 of 18 NI number: 2004110596 www.worksafebc.com Copyright © 2013 Workers’ Compensation Board of British Columbia. All rights reserved. WorkSafeBC (Workers’ Compensation Board of B.C.) encourages the copying, reproduction, and distribution of publications to promote health and safety in the workplace, provided that WorkSafeBC is acknowledged. However, no part of this publication may be copied, reproduced, or distributed for profit or other commercial enterprises or may be incorporated into any other publications or product without written permission of the Workers’ Compensation Board of B.C.

WorkSafeBC Investigations WorkSafeBC (Workers’ Compensation Board of B.C.) Page 18 of 18 NI number: 2004110596 www.worksafebc.com