TO: Director, National Institute for Occupational Safety and Health
FROM: Iowa FACE Program
SUBJECT: Construction worker killed by hydraulic excavator while working in trench.
A 26-year-old construction worker was killed while trying to remove a concrete sewer casing in an 8-foot deep trench. He was part of a crew constructing new sanitary sewer lines along a residential street. The victim was standing inside an iron trench box, while a hydraulic excavator was being used to remove the concrete casing around a sewer pipe. The victim was giving hand signals to a co-worker operating the excavator above him because it was impossible for the operator to see the bottom of the trench where the casing was located. While prying off the casing with sideways pressure, the bucket teeth slipped off the edge of the concrete and the excavator arm and bucket snapped toward the victim, crushing him against the metal side of the trench box (see diagram). The excavator operator immediately moved the bucket away from the wall and went to aid his co-worker, who was still conscious. The man soon became unresponsive and was pronounced dead approximately one hour later in a local hospital from severe internal chest injuries.
RECOMMENDATIONS based on our investigation were as follows:
1. Employers should train supervisors and workers to always position themselves a safe distance from hydraulic machine components, out of the machine's line of travel.
2. Employers should train workers regarding safety when working in close proximity to heavy machinery.
3. Alternative working methods should be considered to eliminate the need to work close to a hydraulic bucket while in a trench box.
In the spring of 1996, a 26-year-old construction worker was killed while laying new storm sewer lines in Iowa. The Iowa FACE program became aware of the incident from a newspaper article and began an investigation. Information was gathered from OSHA, newspapers, and employee statements. One investigator from the Iowa FACE program made a site visit to the company office several weeks after the accident. No visit was made to the construction site for the work had already been completed.
The employer was a general contractor who had been in business for over 30 years. They had several work crews for concrete, iron erection, tiling, building construction, etc. The company had 40 employees, with six employees on the storm sewer crew. The victim had worked for this company for seven years, spending most of his time on this water/sewer crew.
Safety training for new employees included routine safety talks conducted on-site for specific construction hazards, and an annual full-day safety training program. No written safety procedures were in place specific to excavator safety while working in a trench. The company had a good safety record with no overnight hospitalizations due to work injuries. Company representatives state that employees have been disciplined for unsafe working behaviors in the past. This was the companys first work-related fatality.
The victim and the excavator operator (site supervisor) were working together preparing a residential area for insertion of new sewer pipes. In the bottom of an 8-foot hole was a concrete casing around an existing pipe that the men were trying to remove. An iron trench box, measuring approximately 20 long, 8 tall, and 8 wide, was in the hole. The victim was standing in the trench box giving hand signals to the excavator operator above him. He was positioned between the excavator bucket and the inside wall of the trench box (see diagram). The men were trying to carefully remove the casing without damaging the pipe. In the process of prying off the casing, the bucket teeth slipped off the edge of the concrete, and the bucket and arm of the excavator snapped toward the victim, crushing him against the wall of the trench box, causing chest and abdominal injuries. An ambulance was immediately called but when it arrived the man was unresponsive. He was pronounced dead about an hour later in a local hospital.
There was water in the bottom of the trench, which obscured the view of the concrete encasement. The operator was not able to see the edge of the bucket, to determine how good a grip he had on the casing, and it is likely the victim did not see it either due to the water. The combination of water in the trench and the need for hand signals contributed to this hazardous situation. When the bucket slipped, it immediately swung to the side toward the victim. This was caused by a combination of accumulated tension in the arm of the hydraulic excavator, and the slight delay before the operator could react and stop the bucket. It appears there was nothing mechanically wrong with this excavator, nor did the operator appear to make an error or misunderstand a hand signal.
After this incident, the concrete casing was eventually removed using an air-powered jack hammer. The company was cited by OSHA for failure to instruct their employees in the recognition and avoidance of unsafe conditions.
CAUSE OF DEATH
The cause of death as taken from the death certificate was, "closed thoracic and abdominal trauma" An autopsy was performed which confirmed the above.
RECOMMENDATIONS / DISCUSSION
Recommendation #1 Employers should train supervisors and workers to always position
themselves a safe distance from hydraulic machine components, out of the machine's line of travel.
Discussion: This operator and worker were accustomed to working in close quarters, between the bucket and the trench box wall. The victim was in a dangerous position, too close to the operating range of the excavator bucket, in line with the force being applied by the bucket. When prying and lifting a heavy concrete object with any hydraulic machine component, dangerous movements of the machine may occur if the bucket slips. Working close to a hydraulic bucket is inherently dangerous in the best of conditions. In addition, there can be significant play in the mechanical linkages which allows tension in the hydraulic arm of the excavator. The operator was not able to appreciate the hazard since he could not see the exact position of the bucket and the concrete casing, relying on hand signals from the victim. Operators must know the location of all workers around their machines and not allow them to work in close proximity to the bucket. Employers, site managers, and owner/operators using hydraulic equipment need to be reminded of the potential for slipping and unintentional movements, and must specify safe distances and follow safe operating procedures at all times.
Recommendation #2 Employers should train workers regarding safety when working in close proximity to heavy machinery.
Discussion: There are no guidelines which prohibit a worker from being in a trench box while a hydraulic excavator is being used in the same trench box. According to the company's General Safety Rules, employees are to "stay out of the swing line of buckets or drags." It is common sense to advise staying clear, if possible, from the working reach of a machine attachment, however many times this is impractical, as in this case, when visual sight of the casing was obstructed. The company now recommends that employees make sure they are out of the "immediate range of the attachment". This is a decision that each employee must make on-the-job, and experience and common sense are key factors. In this case the worker placed himself in a dangerous position between the bucket and the trench box wall. Workers should be trained to stay clear from machinery components when force is being applied, knowing that unintentional movements may occur.
Recommendation #3 Alternative working methods should be considered to eliminate the need to work close to a hydraulic bucket while in a trench box.
Discussion: This concrete casing was eventually removed using an air-powered jack hammer, eliminating the need to work in close proximity to the excavator bucket, which is clearly hazardous. It might be preferable to use jack hammers to remove similar casings in the future. Due to the prying nature of this procedure, considerable sideways force was being applied to the bucket teeth. Using jack hammers would eliminate this sideways force and protect workers in the trench. Both the victim and the operator seemed unaware of the danger created by using the bucket in this fashion. According to photographs of the scene, there was significant room in the trench box for the victim to stand clear of the bucket, out of the swing line for the procedure they were attempting.
|Wayne Johnson, M.D.||Risto Rautiainen, M.Sc.Agr.|
|Trauma Investigator (FACE)||Coordinator|
|Institute for Rural & Environmental Health||Great Plains Center for Agricultural Health|
|University of Iowa -- Iowa City, Iowa||Institute for Rural & Environmental Health|
|University of Iowa -- Iowa City, Iowa|