This document provides background information on combustible dust hazards and explosions. It discusses the conditions required for a dust explosion (combustible dust, oxygen, ignition source, and dispersion/confinement), and summarizes several catastrophic dust explosions that have occurred since 1995 involving metals, plastics, fibers, and other combustible materials. Key hazard mitigation techniques are identified, including controlling dust accumulations, ignition sources, and implementing designs to contain damage from potential explosions. Common processing equipment that poses dust explosion risks such as dust collectors, blenders, dryers and conveying systems are also outlined.
5. Malden Mills
• 12/11/1995
• Lawrence , MA
• 13 hospitalized
• No citations
• Made nylon fibers and suspected the
static electricity ignited the fibers that were
glues to make fibers stand on end in the
fleece making process.
8. Jahn Foundry
• 2/25/1999
• Springfield, MA
• 3 fatalities, 9 hospitalized
• General duty, electrical and housekeeping.
$115k
• Secondary explosion ignited phenol
formaldehyde resin. Initial cause is not sure.
• Heavy deposits of resin dust were found in the
flexible exhaust ducts serving the ovens in the
shell molding stations
10. Ford River Rouge Power
Plant
• 2/1/1999
• Dearborn , MI
• General Duty egregious, 1.5M
• Natural gas boiler explosion triggered
secondary coal dust explosion that had
accumulated on building and equipment
surfaces
12. Rouse Polymerics
• 5/16/2002
• Vicksburg, MS
• 5 fatalities, 7 injured
• 23 serious, 2 unclassified 210K to 187k
• Fire in the baghouse, then rubber dust
explosion
13. Combustible Dust Explosions History
• January 29, 2003 -
West
Pharmaceutical
Services, Kinston,
NC
– Six deaths, dozens of
injuries
– Facility produced
rubber stoppers and
other products for
medical use
15. West Pharmaceutical
Services
• Combustible dust was ignited by some ignition
source causing an initial explosion in the Milling
Room, which dislodged ceiling tiles, steel
beams, and wall panels, and also putting a large
quantity of combustible dust from these areas
into suspension, which was added fuel to the
blast wave from the first explosion, creating a
second and larger explosion.
16. CTA Acoustics
• 02/20/2003
• Corbin , KY
• 7 fatalities, 37 injured
• 4 serious including
1910.307b, 28k
• Fiberglass fibers and
excess phenolic resin
powder probably went to
the oven while workers
were using compressed
air and lance to break up
a cogged bag house filter.
17. Combustible Dust Explosions History
• October 29, 2003 -
Hayes Lemmerz
Manufacturing Plant
– Two severely burned
(one of the victims died)
– Accumulated aluminum
dust
– Facility manufactured
cast aluminum
automotive wheels
18. Hayes Lemmerz International
• 10/29/2003
• Huntington IN
• One fatality, one injured
• 6 serious, 42k
• General duty and 1910.307b cited
• A dust collector attached to the recycling
equipment exploded. The explosion propagated
through piping to a furnace where the burned
employees were working
22. What Combustible Dusts are explosible?
• Some Metal dust
• Wood dust
• Coal and other carbon dusts.
• Plastic dust
• Biosolids
• Organic dust such as sugar,
paper, soap, and dried blood.
• Certain textile materials
23. What metal dusts are explosive?
• B – 110 MEC g/m3
• Mg – 15.7
• AL – 80-120
• Si – 200
• S – 100
• Ti – 70
• Cr – undetermined
• Fe – 220-500
• Ni - NF
• Zn – 300 to NF
• Nb – 420 to
undetermined
• Mo – NF
• Sn – 450
• Hf – 180
• Ta – 400
• W – 700-undetermined
• Pb - NF
24. Which Industries have Potential Dust
Explosion Hazards?
• Agriculture
• Chemical
• Textile
• Forest and furniture products
• Metal Processing
• Paper products
• Pharmaceuticals
• Recycling operations (metal, paper, and plastic
recycling operations.)
• Coal Power plants and coal processing facilities
25. CSB Recommendations To OSHA
1) Issue a standard designed to prevent combustible dust fires and explosions
in general industry
2) Revise the Hazard Communication Standard (HCS) (1910.1200) to clarify that
the HCS covers combustible dusts
3) Communicate to the United Nations Economic Commission (UNECE) the
need to amend the Globally Harmonized System (GHS) to address
combustible dust hazards
4) Provide training through the OSHA Training Institute (OTI) on recognizing
and preventing combustible dust explosions.
5) While a standard is being developed, implement a National Special
Emphasis Program (SEP) on combustible dust hazards in general
industry
26. NFPA 654 (2006) Definitions
Combustible dust. A combustible particulate solid that presents a fire or
deflagration hazard when suspended in air or some other oxidizing medium
over a range of concentrations, regardless of particle size or shape.
Combustible Particulate Solid. Any combustible solid material composed of
distinct particles or pieces, regardless of size, shape, or chemical
composition.
Hybrid Mixture. A mixture of a flammable gas with either a combustible dust
or a combustible mist.
What is Combustible Dust?
Definitions and Terminology
27. Definitions and Terminology
NFPA 69 (2002), and 499 (2004) Definitions
Combustible Dust. Any finely divided solid material 420
microns or less in diameter (i.e., material passing through a
U.S. No 40 Standard Sieve) that presents a fire or explosion
hazard when dispersed
1 micron (µ)
= 1.0 x 10-6
m = 1.0 x 10-4
cm = 1.0 x 10-3
mm
420 µ
= 420 x 10-4
cm = .042 cm
= 0.4mm
A typical paper thickness is approximately 0.1mm
What is Combustible Dust?
29. Class II locations are those that are hazardous because of the presence of
combustible dust. The following are Class II locations where the combustible
dust atmospheres are present:
Group E. Atmospheres containing combustible metal dusts,
including aluminum, magnesium, and their commercial alloys, and
other combustible dusts whose particle size, abrasiveness, and
conductivity present similar hazards in the use of electrical equipment.
Group F. Atmospheres containing combustible carbonaceous
dusts that have more than 8 percent total entrapped volatiles (see
ASTM D 3175, Standard Test Method for Volatile Matter in the Analysis Sample
of Coal and Coke, for coal and coke dusts) or that have been
sensitized by other materials so that they present an explosion
hazard. Coal, carbon black, charcoal, and coke dusts are examples of
carbonaceous dusts.
Group G. Atmospheres containing other combustible
dusts, including flour, grain, wood flour, plastic and chemicals.
Class II Locations
Definitions and Terminology
30. Deflagration Vs. Explosion
Deflagration. Propagation of a combustion zone at a speed that
is less than the speed of sound in the unreacted medium.
Detonation. Propagation of a combustion zone at a velocity
that is greater than the speed of sound in the unreacted
medium.
Explosion. The bursting or rupture of an enclosure or a
container due to the development of internal pressure from
deflagration.
Explosion
Deflagration
Detonation
Definitions and Terminology
31. How are MEC and LFL Different?
Minimum Explosible Concentration (MEC)
The minimum concentration of combustible dust suspended in
air, measured in mass per unit volume that will support a
deflagration.
The lower flammable limit is the lowest concentration of a combustible
substance in an oxidizing medium
Lower Flammable Limit (LFL)
Upper Flammable Limit (UFL)
The upper flammable limits is the highest concentration of a combustible
substance in an oxidizing medium that will propagate a flame.
Definitions and Terminology
32. Source: Dust Explosions in the Process Industries, Second Edition, Rolf K Eckhoff
Explosible Range
33. Definitions and Terminology
Minimum Ignition Temperature (MIT). The lowest
temperature at which ignition occurs.
Lower the particle size – Lower the MIT
Lower the moisture content - Lower the MIT
Minimum Ignition Energy (MIE). The lowest electrostatic
spark energy that is capable of igniting a dust cloud.
Energy Units (millijoules)
Decrease in particle size and moisture content – decreases MIE
An increase in temperature in dust cloud atmosphere - decreases MIE
Deflagration Index, Kst – Maximum dp/dt normalized to 1.0 m3
volume.
Pmax – The maximum pressure reached during the course of a
deflagration.
34. Dust explosion class Kst (bar.m/s) Characteristic
St 0 0 No explosion
St 1 >0 and <=200 Weak explosion
St 2 >200 and <=300 Strong explosion
St 3 >300 Very strong explosion
Deflagration Index - Kst
Kst = (dP/dt)max V1/3
(bar m/s)
where:
(dP/dt) max = the maximum rate of pressure rise
(bar/s)
V = the volume of the testing chamber (m3
)
45. Types of Equipment Used in Dust
Handling
• Bag Openers (Slitters)
• Blenders/Mixers
• Dryers
• Dust Collectors
• Pneumatic Conveyors
• Size Reduction Equipment
(Grinders)
• Silos and Hoppers
• Hoses, Loading Spouts,
Flexible Boots
46. U.S (1985 -1995) U.K ( 1979-1988) Germany (1965 – 1980)
Material
Number of
Incidents
% Number of
Incidents
% Number of
Incidents
%
Dust Collectors
Grinders
Silos/Bunkers
Conveying System
Dryer/Oven
Mixers/Blenders
Other or Unknown
156
35
27
32
22
>12
84
42
9
7
9
6
>3
23
55
51
19
33
43
7
95
18
17
6
11
14
2
31
73
56
86
43
34
20
114
17
13
13
10
8
5
27
Total 372 100 303 100 426 100
Equipment Involved in Dust Explosions
Source: Guidelines for Safe Handling of Powders and Bulk Solids, CCPS, AICHE
47. Blenders/Mixers
• Heat Generation due
to
– Rubbing of Solids
– Rubbing of internal
parts
• Electrostatic Charging
of the Solids
• Dust Formation inside
of the equipment
Source: http://www.fedequip.com/abstract.asp?
ItemNumber=17478&txtSearchType=0&txtPageNo=1
&txtSearchCriteria=ribbon_mixer
48. Dust Collectors
• Presence of easily ignitable
fine dust atmosphere and high
turbulence
• Experienced many fires over
the years due to broken bags.
• Ignition source is electrostatic
spark discharges
• Another ignition source is
entrance of hot, glowing
particles into the baghouse
from upstream equipment
Fabric Filters (Baghouses)
49. Aluminum Dry Dust Collector
• Dry Type collectors located
outside
• Explosive Dust Warning sign
on collector
• Collectors or cyclone have
temperature alarms
• No recycling of air from
powder collectors
• Collector ductwork blanked
before repairs
• Filter cannot be synthetic
• Dust removed AT LEAST once
a day
• Dust put in sealed tight metal
containers
50. Pneumatic conveying system
• Downstream equipment have high
rate of risk for fires and explosion
– Static electricity is generated from
particle to particle contact or from
particle to duct wall contact.
– Heated particles which are created
during grinding or drying may be
carried into the pneumatic
conveying system and fanned to a
glow by high gas velocity.
– Tramp metal in the pneumatic
system may also cause frictional
heating.
– Charged powder may leak from
joints to the atmosphere and
electrostatic sparking can occur
resulting in an explosion.
Figure source:www.flexicon.com/us/products/PneumaticConveyingSystems/index.asp?gclid=COa2kKWK4o8CFQGzGgodikc9Dg
53. Pneumatic conveying systems
(Cont.)
• Prevention and Protection systems
– Venting
– Suppression
– Pressure Containment
– Deflagration Isolation
– Spark detection and extinguishing system
– Use of inert conveying gas
54. Silos and Hoppers
• No inter-silo Venting
• Silos and hoppers shall be located outside the
buildings with some exceptions
• Air cannons not to be used to break bridges in silos
• Detection of smoldering fires in silos and hoppers
can be achieved with methane and carbon monoxide
detectors
• Pressure containment, inerting, and suppression
systems to protect against explosions
• Venting is the most widely used protection against
explosions
57. Dust Control
Design of facility & process
equipment
Contain combustible dust
Clean fugitive dust
Regular program
Access to hidden areas
Safe cleaning methods
Maintenance
58. Aluminum
• Machining operations provided
with dust collection
• Daily removal of turnings and
chips
• Grinding operation dust
collection separate from
buffing/polishing operations
• Vacuum Cleaners only used
that are approved for
aluminum dust
• No compressed air cleaning
unless no other method
available.
59. Dust Layer Thickness
Guidelines
1/8” in grain standard
Rule of thumb in NFPA 654
1/32” over 5% of area
Bar joist surface area ~ 5%
Max 20,000 SF
Idealized
Consider point in cleaning cycle
60. Housekeeping
• Maintain dust free as possible
• No blow down unless All electrical power
and processes have been shutdown.
• No welding, cutting or grinding unless
under hot-work permit
• Comfort heating equipment shall obtain
combustion air from clean outside source.
61. Aluminum
• Building
noncombustible
• Surfaces where dust
can collect have 55
degrees sloping
design
• Explosion venting for
aluminum powder
processing building
Note: For example, a 1/8 inch thick
layer of dust, once disturbed, can
easily form a dangerous cloud that
could explode.
62. Ignition Source Control
Electrical equipment
Static electricity control
Mechanical sparks & friction
Open flame control
Design of heating systems & heated surfaces
Use of tools, & vehicles
Maintenance
63. Damage Control Construction
Detachment (outside or other bldg.)
Separation (distance with in same room)
Segregation (barrier)
Pressure resistant construction
Pressure relieving construction
Pressure Venting
Relief valves
Maintenance
64. Explosion Venting
• The vent opening must be
sized to allow the expanding
gases to be vented at a rapid
rate so that the internal
pressures developed by the
explosion do not compromise
the structural integrity of the
protected equipment
• The volume of the equipment
to be protected
• The maximum pressure during
venting (Pred)
• The KSt of the dust (or
fundamental burning velocity
of a gas)
• The burst pressure of the
explosion
65. Explosion Venting
• NFPA 68
• It is the discharge of heat
and flame that make
indoor application of
explosion venting
undesirable
• Vented flame igniting
dusts or vapors indoors
creates a secondary
explosion hazard.
67. NEP/ Industry Application
– Agriculture
– Chemicals
– Textiles
– Forest and furniture products
– Metal processing
– Tire and rubber manufacturing plants
– Paper products
– Pharmaceuticals
– Wastewater treatment
– Recycling operations (metal, paper, and plastic.)
– Coal dust in coal handling and processing facilities.
68. Employee Training
• Extensive Employee
training required
• Hazards of the process
• Emergency Procedures
• Location of Electrical
switches and alarms
• Fire fighting for incipient
fires
• Evacuation
• Equipment operation,
start up and shutdown,
and response to upset
conditions.
Fan housing is eroded, which is
typically caused by dust leaking
through or past the filters.
69. Other Programs
State plan participation in this national emphasis effort is strongly
encouraged but is not required.
does not replace the grain handling facility directive, OSHA Instruction
CPL 02-01-004, Inspection of Grain Handling Facilities, 29 CFR
1910.272.
not intended for inspections of explosives and pyrotechnics
manufacturing facilities covered by the Process Safety Management
(PSM) standard (1910.119)
does not exclude facilities that manufacture or handle other types of
combustible dusts (such as ammonium perchlorate) covered under
the PSM standard.
70. CSHOs Safety and Health
• PPE and Nonspark Producing Clothing
• Use of Cameras
• Use of Safe Practices when collecting dust
samples
73. Safety and Health Information
Bulletin
Purpose
Background
Elements of a Dust Explosion
Facility Dust Hazard Assessment
Dust Control
Ignition Control
Damage Control
Training
References
75. NFPA Standards – Electrical & Systems
70 National Electric Code
499 Classification of Combustible
Dust
68 Deflagration Venting Systems
69 Explosion Prevention Systems
91 Exhaust Systems
The employer manufacturers various types of textile products for upholstery and clothing. One production process for an upholstery product is known as flocking. During this process, small chemically-treated nylon fibers are applied to a fabric backing using an electrical field. Three of the company&apos;s five flock lines are located on the first through third floors and were in operation. A sudden explosion/deflagration occurred on the first floor, originating at the beginning of the production lines where some employees were cleaning. The explosion/deflagration moved throughout the entire first floor of the building with great force, leaving only small incidental fires. Employees #1 through #13 were injured. Employees located closest to the explosion suffered multiple burns. Employees further away sustained less severe burns. Some injured employees were located on the second floor directly above the explosion point. They sustained minor injuries, smoke inhalation, bruise and contusions. Some of the employees who helped with a search and rescue were treated for smoke inhalation. The explosion was caused by an electrical spark which ignited a combustible nylon fiber dust cloud in the hopper room at the beginning of a production line. The hopper room is where the nylon fibers are applied to the cloth backing.
37 people were injured in an explosion of nylon fibers. Even though the facility was completely destroyed, the owner of the company kept the employees on the payroll long after the explosion.
The Malden Mills explosion was likely ignited by the static electricity used to make the fibers stand on end, where they could be glued to fabric to make fleece.
A
Employees #1 through #12 were in the shell mold department when there was a large explosion. All twelve sustained burns, from which Employees #6, #8, and #12 died. Employees #1 through #5, #7, and #9 through #11 were hospitalized.
OSHA and fire investigators determined that the damage was caused by secondary explosions of accumulated resin within exhaust ductwork throughout the building.
He noted that the investigation determined that an initiating fire event in one of the Shell Mold stations in the Shell Mold Building was pulled into the exhaust ventilation system. The interior of the ductwork of that system was heavily loaded with deposits of phenol formaldehyde resin, an explosive organic dust. The ignition of this dust caused a turbulent fire and explosion(s) which traveled through the interior ductwork and in turn shook down explosive concentrations of combustible resin dust that had collected on surfaces throughout the Shell Mold Building. When the fire exploded out from the ductwork, it ignited these airborne concentrations of combustible dust, causing a catastrophic dust explosion which lifted the building&apos;s roof and blew out its walls.
The report notes that, although it was not possible to conclusively determine the initiating event which caused the resultant dust explosion, a number of plausible scenarios were developed from the physical and testimonial evidence. Of these, the following two were determined to be the most probable:
Dust Scenario: Heavy deposits of resin dust were found in the flexible exhaust ducts serving the ovens in the shell molding stations. The open ends of the ducts were placed adjacent to the ovens, at approximately head level, and in an area where employees must present themselves to deal with the ovens. Jarring of the duct readily dislodged the deposits of dust. In this scenario, jarring of the duct caused dust to fall down onto the oven and be ignited. The resulting fireball was then pulled back into the flexible duct where it started the turbulent fire and explosions in the exhaust ventilation system.
Gas Scenario: The fuel trains to the ovens in the shell molding stations were found to be in very bad condition. The internal mechanisms of the valves controlling the flow of combustion air and natural gas to the ovens were found to be massively contaminated with resin and sand. The proper functioning of these valves was critical for providing air and gas to the ovens in the correct ratio to support combustion. Oven flameouts were a recurrent problem. The ovens were not provided with a flame-sensing device to prevent the flow of gas to the oven in the absence of main flame. Although a switch and thermocouple prevented the flow of gas to the oven in the absence of a pilot flame, the pilot flame was not able to light the burners. Thus, in the absence of a main flame, gas could continue to flow to the oven. In this scenario, gas was flowing to an oven that was not lit. The unburned gas collected in sufficient quantities to finally be ignited by the pilot or other ignition source, and the resulting fireball was pulled into the flexible duct where it started the turbulent fire and explosions in the exhaust ventilation system.
The report found that inadequate housekeeping, ventilation, maintenance practices and equipment were all causal factors for the initiating and catastrophic events.
On February 1, 1999 a natural gas explosion at the power plant for the Ford River Rouge facility near Dearborn, Michigan, triggered subsequent secondary explosions of coal dust that had accumulated on surfaces in the plant. Six people died and another 30 were injured. The power plant had to be completely rebuilt.
Six employees were taking a boiler off-line for maintenance. A natural gas valve was inadvertently left open. When a secondary butterfly valve was opened for purging, gas entered the unfired boiler which was still hot. This resulted in an explosion in the boiler and that explosion caused secondary explosions from coal dust that had accumulated on building and equipment surfaces. All six employees were killed in the explosion.
Combustible dust was ignited by some ignition source causing an initial explosion in the Milling Room, which dislodged ceiling tiles, steel beams, and wall panels, and also putting a large quantity of combustible dust from these areas into suspension, which was added fuel to the blast wave from the first explosion, creating a second and larger explosion, that exited through the roof of the Northeast tower section of the building, in the ACS area. Three workers were killed from this explosion on 1/29/03 and three other workers died later (1/31/03 to 3/03/03), in the UNC Burn Center in Chapel Hill, NC.
85/86 Citations were deleted. $602K to $100k was the final serious penalty for a single general duty violation.
Another photo of the virtual destruction of the plant
Only three weeks after the explosion in North Carolina, another deadly blast occurred in Corbin, Kentucky, at the CTA Acoustics facility. Thirty-seven people were injured, and seven workers died, some weeks after the explosion from severe burn injuries. This photo shows one of the many production areas where workers were caught in secondary dust explosions that traveled from one production line to the next.
On February 20, 2003, at approximately 7:30am an explosion occurred at CTA Acoustics, Inc. in Corbin, KY. The explosion and subsequent fires resulted in the injury of 45 employees, 18 of which were hospitalized. Of the 18 employees hospitalized, six later succumbed to their injuries. Most injuries consisted of 1st, 2nd and 3rd degree burns. Other injuries included lacerations, smoke inhalation, and one knee fracture. The explosion occurred in the area of the facility&apos;s production lines known as Lines 405, 403, 402 and 401, which produce a fiberglass/resin blend automotive insulation. The explosion damaged all lines with the most significant damage on Lines 405 and 403. Damage to the facility included blown out roof decking, fire and blast damage to the dust collection system on the equipment. At the time of the explosion, employees were beginning their shift and the four lines were being prepared to run product. All of the seriously injured were working on or near the four lines when the explosion occurred as supervisors, machine or oven operators, or product inspectors. two of the injured line employees were working on the roof performing maintenance duties on the dust collection system for line 405.
Hayes Lemmerz aluminum foundry in Huntington, Indiana. Two workers were engulfed in flames from an aluminum dust explosion. One of those workers died later that evening; another spent weeks in the burn unit.
Hayes remelted scrap aluminum in their automotive wheel casting plant. A dust collector attached to the recycling equipment exploded. The explosion propagated through piping to a furnace where the burned employees were working.
On 10-29-2003 at about 8:25 PM the facility experienced a major explosion and fire in the number 5 furnace area that killed one employee and severely burned another. 5 others were transported to emergency care facilities and released after treatment, these included 3 Hayes Lemmerz employees and two contract employees doing foundry stack testing. The day of the explosion at about 3:00 P M a fire was reported in the number 5 furnace chip melt side well exhaust duct. The maintenance department was sent to evaluated the fire and shut the exhaust ventilation system down to allow the fire in the pipe to self extinguish as this was the plant policy for aluminum dust fires in the pipe. About 8:10 or 8:15 the employees started the system up after the pipe had cooled and been cleaned out by the employees. An employee who was working in the area that evening states in his statement in part the night of the event we had to wait for a smoldering in the multi clone pipe to go out then we cleaned the ash out of the pipe started multiclone blower checked for proper operation turned on the dry chip blower #3 then the auger checked multiclone for proper operation we were starting to leave when a big flash came out of the well where the chips feed in this moved the dust off of the ceiling & ignited it causing a ball of fire to move through the room it also destroyed equipment outside the building & started many small fires inside the building in that area.
CSB advocated specifically for NFPA 654 & 484
General Duty Clause
The draft directive has been reviewed by both National and Regional Offices. Comments received during the review process have been addressed.
Additionally, OSHA received extensive input from the Office of the Solicitors , along with their final concurrence.
The directive was reviewed by the PPB and we received Secretarial approval in the last week of September and It was approved on October 18th.