Bucket Elevator Poster


Published on

  • Be the first to comment

  • Be the first to like this

No Downloads
Total Views
On Slideshare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Bucket Elevator Poster

  1. 1. Bucket Elevator Safe Work Procedures Teresa Long University of Houston-Clear Lake An off-track condition exacerbates the problem. Intense frictional heat generated by the belt rubbing on the inside of the elevator casing can ignite a dust cloud. Risks of explosive atmospheres within bucket elevators should be communicated to employees. Introduction Bucket elevator conveyors are used for vertically conveying bulk materials. Dust is generated and dispersed as buckets are loaded with product, move through the elevator, and then unload the product at the top. Problems arise when the dust generated by vertical conveyance of the product is combustible. Combustible dust fire and explosion hazards must be recognized in addition to unexpected energization or startup of process equipment that could cause harm to employees in close proximity. LOTO procedures that address combustible dust hazards (explosive atmospheres) must be included in OSHA Regulations and followed prior to maintenance operations on bucket elevators. Engineering controls, such as a black box to record mechanical data (similar to flight data recorder) for use in accident investigations, should be implemented for bucket elevators located inside a building (Kauffman). Bucket elevators are the most common location of primary explosions in the grain industry but combustible dust fire and explosion hazards are not as prevalent in other sectors. Other than an ignition source, elements of the explosion pentagon are inherent to bucket elevators. Manufacturing facilities generating combustible dust are not following safe work procedures as outlined by Conveyor Equipment Manufacturers Association (CEMA) during inspection, cleaning, or maintenance operations. “Conveyors shall not be operated unless all covers and/or guards for the conveyor and drive unit are in place. If the conveyor is to be opened for inspection cleaning, maintenance or observation, the electric power to the motor driving the conveyor must be LOCKED OUT in such a manner that the conveyor cannot be restarted by anyone; however remote from the area, until conveyor cover or guards and drive guards have been properly replaced (CEMA).” Mechanics Standing on Elevated Platform Source: CSB When the bucket elevator was restarted combustible iron dust was lofted into the air, forming a dust cloud. The dust cloud ignited and a fireball engulfed the workers, causing their burn injuries. One mechanic died from his injuries two days later. The other mechanic suffered nearly four months before succumbing. Trapped Key Interlock Switches could be installed to ensure bucket elevators cannot start if access doors are open. This would minimize the occurrence of combustible dust fires and explosions as well as injuries incurred from moving parts. Alternative process equipment, such as screw conveyers, have fewer inherent risks for a dust fire / explosion and can be installed in place of bucket elevators in some manufacturing processes where vertical bulk material transport is necessary. References Control of hazardous energy (Lockout / Tagout) procedures designed to safeguard employees during startup are ignored. Kauffman, C. William PhD, Professor (Retired), Department of Aerospace Engineering, University of Michigan, President, Explosion Research and Investigation Corporation, GEEIT Member. Telephone interview. 03 Apr. 2012. Discussion Astad, John C. Director, Combustible Dust Policy Institute. Personal interview. 18 Feb. 2012. On January 31, 2011 a combustible dust flash fire claimed two lives due to failure to follow Lockout / Tagout (LOTO) procedures during maintenance operations on a bucket elevator at a Tennessee manufacturing facility that produces atomized iron powder for the automotive industry. Elevator #12 is located downstream of an annealing furnace and conveys fine iron powder to storage bins and had been shut down until maintenance personnel could inspect it. The elevator was reported to be malfunctioning due to a misaligned belt. A dust collector associated with the elevator was also reported to have been out of service for two days prior to the incident. The elevator had experienced off-track conditions three times in the six months prior to the incident. The inspection panel at the base of the elevator was typically removed without implementing LOTO procedures. Witness statements indicate that the access panel near the head was also open. Two maintenance mechanics on the night shift were standing alone on an elevated platform adjacent to an open access panel at the bucket elevator head, checking the belt alignment. Neither believed the belt was off-track; LOTO procedures were not followed prior to starting maintenance operations. Since the elevator had been shut down due to a malfunction, product remained in the buckets. They requested via two-way radio that the operator in the control room restart the elevator. The elevator could neither be seen nor heard from the control room. Zeeuwen, Pieter. Principal Process Safety Specialist. Pieter Zeeuwen Consulting. Email interview. 20 Apr.2012. Remnants of Flame Retardant Clothing Worn by Mechanics Source: Confidential Bucket elevator access / inspections covers were left off the bucket elevator during the restart. Employees were aware of dangers from placing hands inside the elevator, but the risk of a dust explosion from a potentially explosive atmosphere existing within the elevator wasn’t effectively communicated. Conclusions Existing OSHA regulations for the control of hazardous energy (ignition sources) during bucket elevator LOTO procedures do not include a specific, formal combustible dust (explosive atmosphere) standard. OSHA generally issues citations via the General Duty Clause and relies on National Fire Protection Association (NFPA) Combustible Dust Standards. NFPA 654 does not provide specific safety guidance for identifying the hazards of a combustible dust fire or explosion. Leaving an access cover off provides the opportunity for a dust cloud or fireball to exit the opening during bucket elevator restart. Anderson, Eric P.E.. Consulting Engineer. Email interview. 12 Aug.2012. Safety, Installation & Service Instructions For Bucket Elevators. n.d. Screw Conveyor Corporation. Web. 06 Mar. 2012 http:// www.screwconveyor.com/bucketsafety.pdf. State of Tennessee. Department of Labor and Workforce Development, Division of Occupational Safety and Health. Hoeganaes Corporation Case File (#315334060). Nashville, Tennessee: n.p.,Print. 15 Feb. 2012. United States Department of Labor, OSHA. Establishment Search. n.d. Web. 17 Mar. 2012 http://www.osha.gov/pls/imis/ establishment.inspection_detail?id=315334060 United States. Chemical Safety Board. Hoeganaes Corporation Fatal Flash Fires. n.p.,Web. 05 Jan. 2012. http://www.csb.gov/investigations/detail.aspx?SID=100&Type=2&pg=1&F_All=y "Warning and Safety Reminders for Screw, Drag, and Bucket Elevator Conveyors", CEMA Document: SC 2004-01. n.d. Conveyor Equipment Manufacturers Association. n.d. Web. 02 Feb. 2012 http://ww.cemanet.org.