1. National Emphasis Program
Combustible Dust
National Emphasis Program
Combustible Dust
Oxygen in Air
Ignition Source
Dispersion
Confinement
Explosion
FIRE
Deflagration
March 10, 2008

2. Background History of Combustible Dust Incidents
Overview of Combustible Dust NEP
Hazard Mitigation Techniques
Resources

3. Catastrophic Combustible Dust Incidents since 1995

4. Combustible Dust Explosions History
Malden Mills
Methuen, MA
December 11, 1995
37 Injured
Nylon Fiber

5. Firefighting efforts following the explosion at Malden Mills (Methuen, Massachusetts, December 11, 1995).

6. Combustible Dust Explosions History
Jahn foundry
Springfield, MA
February 26, 1999
3 dead 9 Injured
Phenolic resin dust A

7. Combustible Dust Explosions History
Ford River Rouge:
Secondary
Coal Dust Explosion
February 1, 1999
Killed six workers and injured 36

8. Combustible Dust Explosions History
May 16, 2002
Rouse Polymerics
Vicksburg, Ms
5 dead, 7 injured
Rubber Dust

9. Combustible Dust Explosions History
January 29, West Pharmaceutical Services, Kinston, NC
Six deaths, dozens of injuries
Facility produced rubber stoppers and other products for medical use
Plastic powder accumulated above suspended ceiling ignited

10. West Pharmaceutical facility destroyed by polyethylene dust
Another photo of the virtual destruction of the plant
West Pharmaceutical facility destroyed by polyethylene dust

11. Combustible Dust Explosions History
February 20, 2003 – CTA Acoustics, Corbin, KY
Seven Workers died
Facility produced fiberglass insulation for automotive industry
Resin accumulated in production area that got ignited

12. Combustible Dust Explosions History
October 29, Hayes Lemmerz Manufacturing Plant
Two severely burned (one of the victims died)
Accumulated aluminum dust
Facility manufactured cast aluminum automotive wheels

13. Types of Dust Involved in incidents

14. Types of Industries Involved in Dust Incidents

15. Dust Incidents, Injuries, and Fatalities

16. What Combustible Dusts are explosible?
Metal dust such as aluminum and magnesium.
Wood dust
Coal and other carbon dusts.
Plastic dust
Biosolids
Organic dust such as sugar, paper, soap, and dried blood.
Certain textile materials

17. 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.)

18. 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) ( ) to clarify that the HCS covers combustible dusts
Communicate to the United Nations Economic Commission (UNECE) the need to amend the Globally Harmonized System (GHS) to address combustible dust hazards
Provide training through the OSHA Training Institute (OTI) on recognizing and preventing combustible dust explosions.
While a standard is being developed, implement a National Special Emphasis Program (SEP) on combustible dust hazards in general industry

19. Definitions and Terminology
Combustible Dust
Combustible Particulate Solid
Hybrid Mixture
Fugitive Grain Dust
Class II Locations
Deflagration
Detonation
Explosion
Minimum Explosible Concentration (MEC)
Lower Flammable Limit (LFL)
Upper Flammable Limit (UFL)
Minimum Ignition Temperature (MIT)
Minimum Ignition Energy (MIE)

20. Definitions and Terminology
What is Combustible Dust?
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.

21. Definitions and Terminology
What is Combustible Dust?
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

22. Particle Size of Common Materials

23. Definitions and Terminology
Class II Locations
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.

24. Deflagration Vs. Explosion
Definitions and Terminology
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.
Deflagration
Explosion
Detonation

25. How are MEC and LFL Different?
Definitions and Terminology
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.

26. Explosible Range
Source: Dust Explosions in the Process Industries, Second Edition, Rolf K Eckhoff

27. 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.

28. 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)
Dust explosion class
Kst (bar.m/s)
Characteristic
St 0
No explosion
St 1
>0 and <=200
Weak explosion
St 2
>200 and <=300
Strong explosion
St 3
>300
Very strong explosion

29. The “Typical” Explosion Event
Process
Equipment
Initial
Internal
Deflagration
Time, msec.

30. The “Typical” Explosion Event
Process
Equipment
Initial
Internal
Deflagration
Shock Wave
Time, msec.

31. The “Typical” Explosion Event
Process
Equipment
Initial
Internal
Deflagration
Elastic Rebound
Shock Waves
Time, msec.

32. The “Typical” Explosion Event
Process
Equipment
Initial
Internal
Deflagration
Dust clouds caused
by Elastic Rebound
Time, msec.

33. The “Typical” Explosion Event
Process
Equipment
Containment
Failure from Initial
Deflagration
Dust Clouds Caused
by Elastic Rebound
Time, msec.

34. The “Typical” Explosion Event
Process
Equipment
Secondary Deflagration
Initiated
Dust Clouds Caused
by Elastic Rebound
Time, msec.

35. The “Typical” Explosion Event
Process
Equipment
Secondary Deflagration
Propagates through Interior
Time, msec.

36. The “Typical” Explosion Event
Secondary Deflagration
Vents from Structure
Process
Equipment
Time, msec.

37. The “Typical” Explosion Event
Secondary Deflagration
Causes Collapse and Residual Fires
Time, msec.
Diagrams Courtesy of John M. Cholin, P.E., FSFPE, J.M. Cholin Consultants, Inc.

38. Dust Handling Equipment

39. 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

40. Equipment Involved in Dust Explosions
Source: Guidelines for Safe Handling of Powders and Bulk Solids, CCPS, AICHE

41. 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:

42. Dryers Direct-Heat Dryers Indirect–Heat Dryers
Convective Drying System
Heat provided by heated air or gas
Moisture is carried by drying medium
Indirect–Heat Dryers
Heat transfer by Conduction
Steam for Jacketed Dryers
Source:

43. Dust Collectors Cyclone Separators Electrostatic Precipitators
Fabric Filters
Wet Scrubbers

44. Dust Collectors Fabric Filters (Baghouses)
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

45. 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:

46. Pneumatic conveying systems (Cont.)
Prevention and Protection systems
Venting
Suppression
Pressure Containment
Deflagration Isolation
Spark detection and extinguishing system
Use of inert conveying gas

47. Size Reduction System
Size reduction equipment is regarded as a possible ignition source because of friction and hot surfaces arising from grinding
Entrance of metal into the equipment
Too slow feed rate can increase the possibility of fire/explosion hazard

48. 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

49. Hazard Mitigation

50. Hazard Mitigation
Dust control
Ignition source control
Damage control

51. Dust Control Design of facility & process equipment
Contain combustible dust
Clean fugitive dust
Regular program
Access to hidden areas
Safe cleaning methods
Maintenance

52. 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

53. 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

54. 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

55. Damage Control Systems
Specialized detection systems
Specialized suppression systems
Explosion prevention systems
Maintenance

56. 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.

57. 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 , Inspection of Grain Handling Facilities, 29 CFR
not intended for inspections of explosives and pyrotechnics manufacturing facilities covered by the Process Safety Management (PSM) standard ( )
does not exclude facilities that manufacture or handle other types of combustible dusts (such as ammonium perchlorate) covered under the PSM standard.

58. CSHOs Safety and Health
PPE and Nonspark Producing Clothing
Use of Cameras
Use of Safe Practices when collecting dust samples

59. Primary Applicable OSHA Standards
General – Housekeeping
Hazardous (Classified) Locations
Powered Industrial Trucks
Bakery Equipment
Sawmills
Grain Handling
General Duty Clause
General and industry-specific

60. Lab Tests and Results Percent through 40 mesh Percent moisture content
Percent combustible material
Percent combustible dust
Metal dusts will include resistivity
Minimum explosive concentration (MEC)
Minimum ignition energy (MIE)
Class II test
Sample weight
Maximum normalized rate of pressure rise (dP/dt) – Kst Test
Minimum ignition temperature

61. Laboratory Testing

62. LABORATORY TESTING OF EXPLOSIVE DUSTS

63. Initial Sample Preparation
Samples are sieved

64. Sieve stack

65. Sample Loading

67. Sieved Sample

68. At this point (if appropriate) moisture content, combustible fraction and resistivity are determined

69. Explosibility Testing Paths
Two main branches of testing are available
Class II
Kst
Note – the CSHO must pick ONE branch of testing

70. Class II Testing
Class II tests must be requested if electrical issues are in play
Testing uses an electrical arc for ignition source (2.4 joules)
Results must not be used for engineering calculations
It is much more likely to prove that a dust is explosive, than class II

71. Class II Dust Chamber

72. Dust Loaded

73. Chamber Assembled

74. Kst Testing
Unless electrical considerations exist, this is the superior test
Ignition source is a chemical igniter (2500 joules)
Chamber configuration allows for some engineering calculations
Note that the Lab uses a low turbulence chamber – results are lower than high turbulence by 4-5 X Use for rough comparisons only

75. 20 Liter Chamber

76. Loaded

77. Prepared for Firing

78. Conclusion Two basic explosibility tests run at the Lab
Class II – for electrical
Kst – to demonstrate explosiveness
CSHO must determine which test will best serve their needs, as only one or the other will be performed
Lab will always discuss options with the CSHO to help decision making

79. Resources

80. Safety and Health Information Bulletin
Purpose
Background
Elements of a Dust Explosion
Facility Dust Hazard Assessment
Dust Control
Ignition Control
Damage Control
Training
References
Purpose: hazard information & mitigation

81. NFPA Standards – Dust Hazards
654 General
664 Wood
61 Agriculture
484 Metal
480 Magnesium
481 Titanium
482 Zirconium
485 Lithium
CSB advocated specifically for NFPA 654 & 484
General Duty Clause

82. NFPA Standards – Electrical & Systems
70 National Electric Code
499 Classification of Combustible Dust
68 Deflagration Venting Systems
69 Explosion Prevention Systems
91 Exhaust Systems

83. Viewing NFPA Standards
Point to “Codes and Standards”
Click “Document List”
Click on standard desired, NFPA XXX
On bottom, click “Preview this Document”
Below disclaimer, click “I Agree”
Click “Open NFPA XXX”
After standard opens, the “1-2-3” button gives you the Table of Contents

85. Combustible Dust NEP Any Questions?
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.