Bucket Elevator Conveyor Safe Work Procedures

Teresa LongApril 16, 2012

Bucket elevators are the most common location of primary explosions in the grain industry but are not as prevalent in other sectors. Combustible dust fire and explosion hazards are not recognized in the manufacturing sector.

Source: go4b.com.uk

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

• Problems arise when dust generated is combustible

Recipe for a Dust Explosion

Other than an ignition source, elements of the explosion pentagon are inherent to bucket elevators used in both the grain and manufacturing sectors. To ensure safe operation, Best Industry Practices must be adhered to.

OSHA Regulation vs. Best Industry Practices

• Bucket elevators used in the Grain Sector are regulated under OSHA Grain Facility Standard 29 CFR 1919.272

• Bucket elevators used in the manufacturing sector fall under NFPA Combustible Dust Standards, Best Industry Practices

Opportunities for Improving Safe Work Practices

• OSHA Lockout / Tagout (LOTO) Regulations should include combustible dust (explosive atmosphere) hazards

• Combustible dust hazards should be communicated via outreach, education, and training

• Hazardous (classified) locations should be defined and implemented for all ignition sources

National Fire Protection Association (NFPA)

Combustible Dust Standards

• NFPA 61 Agricultural and Food Processing Facilities• NFPA 484 Combustible Metals • NFPA 654 Chemicals• NFPA 664 Wood Processing Facilities • NFPA 665 Sulfur Fires and Explosions

OSHA Grain Facility Standard

• Grain Sector Engineering Controls– Bearing Temperature Sensors– Belt Alignment Sensors– Belt Speed Sensors

• None for Manufacturing Sector

Additional Best Industry Practices

“Elevators should be started with buckets empty. Starting under load places undue strain on chain / belt and drive machinery. Therefore, it is imperative to allow all buckets to empty before stopping elevator.” (Screw Conveyor Corporation)

•Potential ignition source

WARNING AND SAFETY REMINDER FORBUCKET ELEVATOR CONVEYORS

CONVEYOR EQUIPMENT MANUFACTURERS ASSOCIATION (CEMA)

“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 Safety Labels

• No explosive atmosphere warning label for bucket elevators

Hazardous Classified Locations

• OSHA Hazardous Classified Locations are for electrical ignition sources only– Class II-Combustible Dust• Division I and Division II

• ATEX and DSEAR use zoning to define hazardous areas (20, 21, 22) for both electrical and non-electrical ignition sources

On January 31, 2011 a fatal incident occurred due to failure to follow LOTO procedures during maintenance operations on a bucket elevator at

a Tennessee manufacturing facility that produces atomized iron powder for the

automotive industry.

Two maintenance mechanics on the night shift were inspecting bucket elevator #12, located downstream of an annealing furnace, which conveyed fine iron powder to storage bins .

Elevator #12 had experienced off-track conditions 3 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.

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.

LOTO procedures were not followedprior to maintenance on bucket elevator

#12

• Mechanics standing adjacent to an open access panel at the bucket elevator head did not believe that the belt was off-track

• 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

• Bucket elevator #12 had been shut down until maintenance personnel could inspect it

• Two mechanics were standing alone on an elevated platform near the top of the bucket elevator

Source: CSB

Employees were aware of dangers from placing hands inside the elevator, but the risk of a dust

explosion from a potentially explosive atmosphere within the elevator wasn’t

effectively communicated.

Bucket elevator access/inspections covers were left off the bucket elevator during the restart.

Product remained in the buckets.

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.

Remains of the Flame Resistant Clothing worn by the victims

Source: Anonymous

FRC

Both maintenance mechanics succumbed to their burn injuries

• The first mechanic died from his injuries two days later

• The second mechanic suffered for nearly four months

What went Wrong?Control Measures Failed

Source: nap.edu

Administrative Controls

• No written housekeeping procedures• Dust accumulations existed • Flash fires and near-misses occurred periodically but were rarely reported

LOTO

• LOTO fails to address explosive atmospheres with access/inspection covers left off

• Employees not trained on LOTO procedures• LOTO procedures not followed

Hazard Communication

• Risk not communicated • Employees were not trained to understand

the potentially explosive atmosphere when accumulated dust is dispersed in air

Citation

"When the top panel was removed it left a 13 inch long by 11 inch high hole. When the bottom panel was removed it left an 11 1/2 high by 8 inch wide hole. Both of these holes were large enough for an employee to place his hands also."

TOSHA Citation 29 CFR 1910.147(c)(4)(i) LOTO

Citations

“Exposure to fire/explosion hazard: During the inspection the CHSO observed large accumulations of fugitive iron dust ….depth of the iron dust ranged from ½ to 4 inches”•Employees unaware of any documented housekeeping procedures

TOSHA Citation 29 CFR 1910.22 (a)(1)

Citation

“The employer’s written energy control procedure was not consistently being utilized when tracking adjustments were made on Elevator 12.”“Additionally, the energy control procedure was not always utilized when employees removed inspection panels on the elevator”

TOSHA Citation 29 CFR 1910.147 ©(4)(i)

Citations

“Exposure to potential combustible dust hazard: during the inspection it was determined that employees had not been effectively trained on the hazards of combustible iron dust nor where to locate the MSDS”“One employee …….stated he had never seen the MSDS for the iron dust and was not sure where to locate it.”

TOSHA Citation 29 CFR 1910.1200(h)(2)(iii)

Solutions

• Black box to record mechanical data (similar to flight data recorder) for use in accident investigations

• Interlocks (safety switches) that can’t be overridden from the control room

• Alternative process equipment with fewer inherent risks for a dust fire / explosion

Solutions

• OSHA Standard needed for combustible dust (explosive atmospheres)

• Implement hazardous (classified) locations for all ignition sources

• Communicating explosive atmosphere risks to employees through outreach and training

Solutions

• LOTO procedures that address combustible dust hazards (explosive atmospheres) must be included in OSHA Regulations

• LOTO procedures must be performed prior to maintenance operations on bucket elevators

Conclusions

• Identifying all ignition sources comprehensively communicates the risk

• Recognizing explosive atmospheres in LOTO minimizes accidents

• Improving Safe Work Practices as a result of lessons-learned from the bucket elevator #12 flash fire can save lives

Works Cited

Kauffman, C. William. Telephone interview. 03 Apr. 2012.

Astad, John C. Personal interview. 18 Feb. 2012.

Safety, Installation & Service Instructions For BUCKET ELEVATORS. n.d. Screw Conveyor Corporation. 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., 15 Feb. 2012.

United States Department of Labor, Occupational Safety & Health Administration. n.d. 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.: n.p., 05 Jan. 2012.

WARNING AND SAFETY REMINDERS FOR SCREW , DRAG , AND BUCKET ELEVATOR CONVEYORS, CEMA Document: SC

2004-01. n.d. Conveyor Equipment Manufacturers Association. 02 Feb. 2012 <http:////www.cemanet.org>.