1. Bucket Elevator Conveyor
Safe Work Procedures
Teresa Long
April 16, 2012

2. 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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. OSHA Grain Facility Standard
• Grain Sector Engineering Controls
– Bearing Temperature Sensors
– Belt Alignment Sensors
– Belt Speed Sensors
• None for Manufacturing Sector

9. 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

10. WARNING AND SAFETY REMINDER FOR
BUCKET 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.”

11. CEMA Safety Labels
• No explosive
atmosphere warning
label for bucket
elevators

12. 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 nonelectrical ignition sources

13. 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.

14. 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 .

15. 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.

16. 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.

17. LOTO procedures were not followed
prior to maintenance on bucket elevator
#12

18. • 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

19. • 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

20. 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.

21. Bucket elevator access/inspections covers were
left off the bucket elevator during the restart.
Product remained in the buckets.

22. 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.

23. Remains of the Flame Resistant Clothing worn
by the victims
FRC
Source: Anonymous

24. 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

25. What went Wrong?
Control Measures Failed
Source: nap.edu

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

27. LOTO
• LOTO fails to address explosive atmospheres
with access/inspection covers left off
• Employees not trained on LOTO procedures
• LOTO procedures not followed

28. Hazard Communication
• Risk not communicated
• Employees were not trained to understand
the potentially explosive atmosphere when
accumulated dust is dispersed in air

29. 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

30. 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)

31. 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)

32. 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)

33. 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

34. 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

35. 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

36. 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

37. 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>.