Alaska FACE 98AK023
January 11, 1999
Apprentice Lineman Killed When Caught in Trencher
A 26-year-old apprentice lineman was killed when he was caught in a trencher. The apprentice (the victim) was removing a small berm by shoveling it back into a partially dug trench. The incident was not witnessed. It was surmised that the victim either lost his balance and fell toward the active machinery or the digging chain caught his clothing and pulled him into the trench. An electrical engineer and an inspector (the witnesses) standing at the opposite end of the trench noticed a rapid movement and something bright thrown in the air (the victim’s hard hat) near the trencher. They immediately called to the operator. The trencher was stopped and moved away from the trench. Co-workers went into the trench to locate the victim as one of the witnesses called on his cellular phone for emergency assistance. The victim was located and pronounced dead at the scene.
Based on the findings of the investigation, to prevent similar occurrences, employers should:
Additionally, owners of early model trenching equipment should:
At 1:15 PM on September 1, 1998, a 26-year-old male apprentice lineman (the victim) was caught in a trencher. On the same day, Alaska Department of Labor (AK-DOL) notified the Alaska Division of Public Health, Section of Epidemiology. An investigation involving an Injury Prevention Specialist for the Alaska Department of Health and Social Services, Section of Epidemiology ensued on September 2, 1998. The incident was reviewed with AK-DOL officials. Local police department, Medical Examiner, and AK-DOL reports were requested.
The company involved in the incident was privately owned and had been in business since 1946. The company was primarily engaged in electrical work. The majority of its 160 employees in Alaska were seasonally employed of which 70% were electrical and commercial linemen. Apprentices made up 15-20% of their workforce. The company had hired the victim as an apprentice lineman approximately 2 weeks before the incident. This was the victim’s first assignment with the company. At the time of the incident, the victim and his supervisor (trencher operator) were excavating a trench for the installation of two utility cables.
The company had a written safety program that detailed specific work practices and employee conduct at the work site. All employees attended an orientation to the company’s safety program upon initial hire. On-the-job safety training usually addressed personal protective equipment, hazard identification, work practices, machinery and equipment use, and driver safety. Since the company normally contracted their services to a general contractor, employees were also required to attend all safety training classes conducted by or on behalf of the general contractor. The individual crews also conducted weekly toolbox meetings.
The company had been contracted to install electric power and fiber optic cables underground along the shoulder of a raised roadbed. The crew consisted of two journeymen (foremen)/ operators, two apprentice linemen, an additional equipment operator, and a mechanic. As required by the labor standards for apprenticeship programs, the apprentices were under the supervision of a journeyman. The crew, including the apprentices, was hired from the electrical workers’ union hall. In general, apprentices with low hours were hired for dirt work and general labor. As they accumulated hours and experience, they graduated to job duties that required more technical skills and knowledge.
The crew arrived at the site 6 days before the incident to organize and prepare equipment and supplies before they began digging the utility trench. On the day of the incident, the foremen completed a site survey. Both foremen were experienced machine operators with 10 years or more of trenching experience and trencher operation.
The cable placement area along the road was level. The roadbed consisted of compacted dirt and gravel that was estimated to be at least 10 feet in depth. The trench was being dug approximately 10 feet from the shoulder of the roadbed and was about 16 inches wide and 5 feet deep (Figure 1). As the trencher moved forward, the end of the trench near the trencher was sloped, which corresponded with the 45 to 60 degree boom angle during excavation. Weather on the day of the incident was mixed heavy mist and rain. The road surface was wet with puddling of water across the surface and in tire ruts. Wind was generally from the east and estimated at 25 to 30 MPH with gusts up to 37 MPH. In addition to their normal personal protective equipment (hard hats, gloves, and boots), workers were wearing conventional rain jackets and pants.
The excavation machinery in this incident was a trencher that was purchased in 1984. The trencher consisted of a transport frame with an 8-foot boom. The operator’s seat and controls were located on the side of the transport frame near the boom. Track length on the vehicle was ll feet. The overall width was 8 feet (Figure 2). Safety placards were affixed, including a placard on the boom with the words, "STAY CLEAR OF MACHINE". A 14-inch wide digging chain consisted of linked metal plates with attached cutters (or teeth) which rotated around the boom. The chain moved across the top of the boom away from the transport frame. The chain speed was variable, however it moved approximately 4 feet per second during normal operation. The chain removed dirt from the trench by pulling it back into the transport frame and onto a side-boom conveyor that discharged to a windrow pile or main excavation berm (Figure 2b). Dirt could be directed to either side of the trencher. The finished trench had a uniform bottom and vertical sides that were about 2 inches wider than the chain width.
In this incident, the trencher was not equipped with a crumber shoe or dirt drags. The crumber shoe could be connected to an arm that extended over the boom and chain. Its purpose was to prevent clumps of dirt and rock from being thrown back into the trench and to preserve a level surface on the trench floor. Dirt drags were plates positioned between the tracks and angled to pull dirt back into the trench along the boom (Figure 3). Dirt drags for this model were available from the manufacturer as optional attachments. In later models, dirt drags were included in the standard design.
Without dirt drags, small secondary berms, approximately 8 inches in height, were deposited on either side of the trench as the digging chain removed dirt. If left in place, the excess dirt would be pushed back into the trench when the cable was installed. Depending on the type of cable, the surface and depth of the trench bottom may be critical for proper installation. It was common practice to remove the secondary berms by stationing one or two people on either side of the trench to shovel the dirt back onto the boom to allow the chain to pull it onto the conveyor.
On the day of the incident, the victim and a co-worker were alternately assigned to work along the northwest side of the trench. During the tailgate safety meeting prior to the operation, all the workers were warned not to get too close to the edge of the trench or near the teeth of the trencher. The trencher operator demonstrated how to shovel dirt back against the boom so it fell into the space between the boom and the trench wall. The shovellers were instructed to work 2 to 3 feet from the edge of the trench and 3 to 4 feet from the chain where it entered the ground (Figure 1b). They were to keep pace with the trencher and stay near the end of the tracks. The victim’s co-worker shovelled first. The operator dug a 20-foot test trench before lunch. The test trench appeared to be stable with no signs of sloughing. At 12:45 PM, the victim replaced his co-worker. It is not known if the victim had zipped his rain jacket. The victim and the operator dug an additional 85 feet as the other crew members laid the first 50 feet of the electric power cable and began to partially backfill the trench before putting the fiber optic cable in place. An electrical engineer and an inspector (the witnesses) were standing at the beginning of the trench. Neither witness saw the victim standing near the trencher. The trencher was moving at 4½ to 5 feet per minute. The operator (who sat facing towards the transport frame – Figure 1b and 2b) was looking to his right, the direction of travel, to maintain his alignment when he heard the trencher motor change speeds. He stopped the chain. At the same time, the witnesses saw a rapid movement near the side of the trencher. They yelled to the operator and ran toward the trencher. The victim’s hard hat and shovel were found lying on the ground (on the north side of the trench) a few feet from the trencher.
The operator raised the boom out of the trench to a horizontal position. When it was determined that the victim was in the trench, buried under several inches of dirt, co-workers entered the trench, went under the boom, and located the victim. One of the witnesses called the site’s main operations center on his cellular phone and requested emergency assistance. An emergency trauma technician arrived at the site minutes later. At this time, rescue efforts were stopped briefly to move the trencher forward so rescuers would not be under the raised boom. The victim was uncovered and pronounced dead at the scene by emergency rescue personnel.
Following the incident, a small, half moon-shaped depression, 6 inches at its widest point and 14 to 18 inches long, was found at the edge of the trench near the victim’s last working location. It could not be conclusively determined when or how the depression along the trench edge was made. In addition, a section of the north trench wall collapsed during the removal of the victim. While the collapse of the wall occurred during recovery efforts, the exact cause of the collapse could not be determined. Ground conditions along the first 20 feet of the trench and adjacent roadbed appeared stable, however the additional 85 feet was not checked prior to the incident. Cracking was visible along the shoulder of the road adjacent to the trench following the incident, possibly indicating a change in the roadbed and trench wall stability. Wet weather conditions may have affected soil stability. It is also possible that the stability of the walls was the same for the entire 105 feet of trench and that the collapse was due only to the efforts of the rescuers.
The final event that led to the victim being in the trench could not be determined. The following are possible sequences leading to the incident:
1) The victim lost his balance or tripped and fell forward, either into the trench or onto the chain. Weather conditions (wind and rain) may have contributed to a possible loss of balance. As the soil became more saturated from the rain, the ground may have become less stable. The victim’ s weight on the edge of the trench may have caused the edge to collapse or slough into the trench. The victim may have also lost his balance from a sudden gust of wind or his shovel may have inadvertently contacted the chain or teeth, causing him to be knocked or pulled off-balance.
2) The victim’s clothing caught on the digging chain or tooth. Loose clothing is more easily caught in moving parts. The action of shovelling or a strong wind may have brought an unzipped jacket into close proximity of the moving chain.
3) The victim crossed the trench near the chain and was caught on chain or tooth. The victim’s position immediately before the incident could not be determined. The victim may have crossed the trench to observe the conveyor and windrow pile. Or he may have walked around the front of the trencher and then crossed the trench to return to his position.
CAUSE OF DEATH
The medical examiner’s report listed the cause of death as multiple blunt trauma injuries due to industrial equipment incident.
Recommendation #1: Employers should ensure appropriate trencher attachments are used.
Discussion: In this incident, the secondary berm needed to be removed to preserve the trench floor. Manufacturers have recognized the increased risk of injury for anyone standing near the edge of the trench, above or near the digging chain. Employers should follow manufacturer’s recommendations for operation of trenching equipment and ensure the use of manufacturer suggested attachments (e.g., crumber shoe, dirt drags, and direct cable installation devices) to reduce risk of injury to workers. If it is necessary to manually move a berm (for example, to comply with utility installation specifications), dirt should be moved away from the trench edge after the trencher has passed and a safety zone can be maintained.
Recommendation #2: Employers should ensure workers maintain a minimum 10-foot safety zone around an active digging chain and conform to all safe work practices for machinery.
Discussion: Except for the operator, workers should never be allowed near the digging chain while it is in operation and should maintain a minimum 10-foot safety zone. Employers should eliminate procedures that place workers within the safety zone when the digging chain is in motion. The speed of the digging chain may be deceptive, and while a crumber shoe or other attachment may help maintain the finished trench, the chain can still discharge rocks and dirt into the surrounding area.
In this incident, workers entered the trench and went under the boom to locate the victim. Although this was an emergency situation, rescuers should never place themselves in a hazardous situation to render aid (rescue fever). A loose fitting or damaged line could have lead to a sudden loss of hydraulic fluid (pressure), causing the raised boom to fall. Workers should never be allowed under raised equipment or attachments unless supported by a hoist or blocks. If the equipment cannot be supported, it should be moved to eliminate the hazard.
Recommendation #3: Employers should ensure that a job safety analysis has been performed on all work-related tasks.
Discussion: A job safety analysis (JSA) is a procedure used to review methods or steps for a task, identify potential hazards, and outline recommended actions and procedures to be used to eliminate or control hazards. Key to an effective JSA is input from workers performing the task(s). Through their observations and experience, tasks can be broken down to a sequence of steps or actions, which are used to identify hazards connected to the task or produced by the environment. Employers, supervisors, and safety managers can then review and modify current safety strategies used to safeguard workers and promote a safe work environment. Three ways to resolve potential hazards are:
Recommendation #4: Employers should consider installing illustrated safety placards that depict dangers associated with an active trencher.
Discussion: In this incident, safety placards on the trencher were written. While the words were clear and appropriate, the implied danger of the active digging chain was not recognized. Employers should consider using illustrated safety placards. Illustrated placards present information in the clearest possible manner (Figure 4). Workers can more easily associate actions to potential hazards. Employers should contact equipment manufacturers for illustrated safety placards.
Figure 1a. View of trencher and road
Figure 1b. Schematic diagram of incident scene (not to scale)
Figure 2a. Side view of trencher Figure 2b. Front view of trencher
Figure 3. Position of installed dirt drags (not to scale)
Figure 4. Illustrated safety placard
Fatality Assessment and Control Evaluation (FACE) Project
The Alaska Division of Public Health, Section of Epidemiology performs Fatality Assessment and Control Evaluation (FACE) investigations through a cooperative agreement with the National Institute for Occupational Safety and Health (NIOSH), Division of Safety Research (DSR). The goal of these evaluations is to prevent fatal work injuries in the future by studying the working environment, the worker, the task the worker was performing, the tools the worker was using, the energy exchange resulting in fatal injury, and the role of management in controlling how these factors interact.
To contact Alaska State FACE program personnel regarding State-based FACE reports, please use information listed on the Contact Sheet on the NIOSH FACE web site Please contact In-house FACE program personnel regarding In-house FACE reports and to gain assistance when State-FACE program personnel cannot be reached.