Safe Operation of Stone Quarry Machine
Safe Operation of Stone Quarry Machine
On March 29, 2003, a 44-year-old Hispanic stone quarry supervisor was killed when he was struck by a machine part while servicing a rock crushing machine. The victim and two workers were working during the weekend when the quarry was shut down. The incident occurred at a rock quarry located in a quiet rural-suburban area. The quarry mined basalt, a common, dense, fine-grained igneous rock with a dark gray color. Production began with the drilling of holes into the quarry’s rock face and filling the holes with an ammonium nitrate-based explosive compound. After blasting, the rock was collected in large industrial dump trucks and transported to the primary crushing machine that reduced the large blasted rocks into smaller pieces. This crusher was a Jaw Crusher that smashed rocks by compressing them between two massive steel jaws. These rocks were then conveyed to a secondary crusher, which further reduced them in size. The rocks would go through the secondary crusher several times until they reached the proper size and would fall through sizing screens. The screened gravel was sorted by size and used in the asphalt operation or sold as bulk gravel. The quarry processed about three million tons of material per year.
They were working on a rock crusher, a large machine that produced gravel by crushing rocks that had been blasted from the side of the quarry. On this day, the crew was making an adjustment to the crusher that would change the size of the crushed rock. This required taking off a retaining clamp and removing a large metal shim that determined the size of the crushed rock that the machine produced. The machine had been shut down, and it was quiet enough for the crew to talk easily to each other. The victim was standing under the shim assembly as his co-worker removed the two large nuts that held down the retaining clamp. As he loosened the second nut, the worker felt something was wrong and asked the victim if he should continue. The victim said to continue, and the worker removed the last bolt, releasing a 1,000 pound machine part. It struck the victim on the head, killing him instantly. NJ FACE investigators recommend following these safety guidelines to prevent similar incidents:
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Introduction
The victim’s employer was a stone quarry that mined and processed basalt (traprock) into crushed stone products such as gravel. Much of the gravel was used in a separate asphalt plant that also operated at the quarry. The parent company has been in business for 40 years and employed about 500 union and supervisory workers, 35 of whom worked at the incident site. Three quarries were owned and operated by the company; this quarry had been purchased from another company in 1979. The company had a safety officer who enforced a comprehensive written safety and health program at the three plants. Employee safety meetings were held each week using lesson modules on different safety topics.
Safe Operation of Stone Quarry Machine Investigation
The Mine Safety and Health Administration was notified and initiated an investigation of the incident the same day. Their investigation report notes some important details related to the servicing of the rock crusher and how it contributed to the incident:
1. In 1983-84, the crusher was repaired after a cast section of the toggle block retaining clamp assembly broke off. At that time, the machine manufacturer provided instructions for upgrading the clamp assembly as it was repaired. Modifications included adding the “jam” nuts to retain the top of the assembly and increasing the length of the 3-inch diameter bolts from 54 inches to 60 inches to allow for the additional space needed for the new nuts and hardware. The repair and modifications were successfully completed by quarry personnel.
2. In November 2002, the 3-inch-diameter bolts on the clamp assembly were replaced after they had become bent. During the repair, the old bolts were driven out of the bottom clamp and replaced with two bolts of different lengths, 54 and 60 inches respectively. MSHA noted that the “replacement bolts did not provide sufficient length and thread area for installation of the jam nuts.”
3. Once the top retaining clamp was fastened, the location where the jam nuts would normally be installed was blocked from view.
Safe Operation of Quarry Machine Suggestions / Discussion
Recommendation #1: Employers should develop, implement, and enforce written procedures for servicing machinery.
Discussion: In this incident, the victim was directing a job that was routine but was not outlined in writing. During this operation, the crew did not support the assembly with a wooden brace as they had during previous work on this machine. Also, during the replacement of the bent bolts, only one set of nuts were used to secure the retaining clamp. These were critical changes in procedure that resulted in the clamp being released when the nuts were removed. NJ FACE recommends that the employer develop standard written operating procedures for servicing machinery. This would include a lock-out / tag-out program to de-energize the machine, detailed instructions for the service, and a checklist to ensure that all the parts were properly replaced. Most of this information may be in the manufacturer’s service manual for the machine. Should the maintenance be beyond the expertise of the employees, the employer should contract with a maintenance service.
The employer stated during the FACE investigation that, after the incident, they designed and welded a permanent metal brace to the assembly to prevent its falling through the machine.
Recommendation #2: Employers should conduct a job hazard analysis of all work activities with the participation of the workers.
Discussion: To prevent incidents such as this, NJ FACE recommends that employers conduct a job hazard analysis of all work areas and job tasks with the employees. A job hazard analysis should begin by reviewing the work activities that the employee is responsible for and the equipment that is needed. Each task is further examined for mechanical, electrical, chemical, or any other hazard the worker may encounter. The results of the analysis can be used to design or modify a written standard operating procedure or employee job description. Additional information on conducting a job hazard analysis is included in the Appendix.
Recommendation #3: Employers should consider providing written signs and materials in the native language of their employees.
Discussion: Language was not a factor in this incident since the supervisor and workers were all fluent in Spanish. However, to prevent potential problems with language, NJ FACE recommends providing written signs, procedures, and training materials in the native language of the workers.
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