Combustible Wood Dust Safety

1. Combustible Wood Dust Safety
John Newquist
Draft 8 2 2015

2. History of Dust Explosions
• First recorded dust
explosion occurred in
Turin, Italy back in 1785
• 281 combustible dust
incidents in the US from
1980-2005
• Resulted in 119 deaths
and 718 injuries

3. Introduction
 Accidents in Industry caused by Combustible Dusts
For example, combustible sugar dust was the fuel for a
massive explosion and fire that occurred Feb. 7, 2008, at the
Imperial Sugar Co. plant in Port Wentworth, GA., resulting in
13 deaths and hospitalization of 40 more workers, some of
whom received severe burns.
Below is an illustration of the facility after the explosion.

4. Introduction
• Accidents in North Carolina caused by Combustible Dusts
Above: Courtesy U.S. Chemical Safety Investigation Board
Above: Aerial View of explosion and fire that occurred on Jan 29, 2003, at
West Pharmaceutical Services plant in Kinston, N.C

5. Introduction
 What Materials Can Form a Combustible Dust?
A combustible dust explosion hazard may exist in a variety
of industries, including: food (e.g., candy, sugar, spice,
starch, flour, feed), grain, tobacco, plastics, wood, paper,
pulp, rubber, furniture, textiles, pesticides,
pharmaceuticals, dyes, coal, metals (e.g., aluminum,
chromium, iron, magnesium, and zinc), and fossil fuel
power generation.
 Above: Courtesy U.S. Chemical Safety Investigation Board, November 2003, fatal accident at an automotive parts
plant explosion in the U.S. that involved aluminum dust that originated near an aluminum chip melting furnace.

6. Combustible Dust Events in US: 1980-2005
Food Products
24%
Lumber &
Wood
15%Chemical
Manufacturing
12%
Primary Metal
Industries
8%
Rubber &
Plastic
Products
8%
Electric
Services
8%
Other
7%
Fabricated
Metal Products
7%
Equipment
Manufacturing
7%
Furniture &
Fixtures
4%
Distribution of Dust Events by
Industry
Food
23%
Wood
24%Metal
20%
Plastic
14%
Coal
8%
Inorganic
4%
Other
7%
Distribution of Dust Events by
Material Type
Note: Coal mines & grain handling facilities excluded from study
(Ref. U.S. Chemical Safety Board Report No. 2006-H-1)

7. Dust Explosion by Equipment Type
Equipment Type % of Incidents
Dust Collector 52
Impact Equipment 17
Silos & Bins 13
Dryers & Ovens 9
Processing Equipment 6
Conveyor 3
Source: FM Global Property Loss Prevention Data Sheet 7-76, “Prevention and
Mitigation of Combustible Dust Explosion and Fire”, May 2008

8. NFPA Dust Standards
• Keyway Documents
Standard Industry Edition
NFPA 652 All New
NFPA 654 All – General Industry Document 2013
NFPA 61 Food/Agricultural 2013
NFPA 664 Wood 2012
NFPA 484 Metal 2012
NFPA 655 Sulfur 2012

9. NFPA Dust Standards
• How-to Documents
Standard Purpose Edition
NFPA 68 Explosion Venting 2013
NFPA 69 Suppression/Isolation/Containment/Inerting 2014
NFPA 77 Static Hazards 2014
NFPA 70 National Electric Code 2014
NFPA 499 Practical Electric Classification 2013

10. April 2014
• Corrigan TX
• Four people remain hospitalized, three in critical condition, after an
explosion and fire at a Polk County plywood mill
• a) dust collector bags impeded the venting area of the dust collector
deflagration vents.
• b) explosion vents releasing in the dust collector without taking measure
to protect employees from the fireball path
• c) dust collector vented and the deflagration traveled upstream to the
sander.
• d) responding to a fire within the sander dust collection system without
the main blower remaining in operation.
• e) responding to a fire within the sander dust collection system without a
choke between the sander dust collector and silo leading to the briquetter.

11. Chemical Safety Board
• From 2008 to 2012, The CSB board
documented, 50 combustible dust accidents
that led to 29 fatalities and 161 injuries.

12. Objectives)
• Identify the NFPA 654/664 Standards
applicable to your dust issues.
• Identify three OSHA Standards cited in
COMDUST NEP
• Identify three questions that a plant would be
asked in an OSHA COMDUST NEP inspection.

13. OSHA
• OSHA has regularly stated that NFPA standards that have not
been specifically incorporated into OSHA standards or
adopted by state or local jurisdictions should be considered by
companies as guidance.
• At the same time, however, the NEP Compliance Directive
instructs OSHA inspectors to consult the NFPA standards to
“obtain evidence of hazard recognition and feasible
abatement methods” to support a citation under the GDC.
• Consequently, companies should consult NFPAs when
evaluating and mitigating potential combustible dust hazards
at their facilities.

14. The Long and Winding Road
• History of Hazards
• OSHA Inspections
• Issues
• Citations
• Trends

15. Trend 1 – Rare Events but Still Occurring
• Two British Columbia
sawmills - 2012
• Four dead and 52
injured
• Fines of up to $652,000
• These were wood dust
explosions

16. Trend 2 – OSHA NEP continues
• Combustible Dust
National Emphasis
Program (NEP) –
revised March 2008
• CSB issues
recommendations in
2005
• Advanced Notice of
Proposed
Rulemaking
(ANPRM) –
published October
2009
• Expert panel met
May 2011

17. Possible Ignition Sources
• Possible ignition sources include:
– Open flames and sparks (welding, industrial grinding and
cutting, matches, etc.)
– Hot Surfaces (dryers, bearings, heaters, etc.)
– Heat from Mechanical Impacts
– Electrical Discharges (switch and outlet activation)
– Electrostatic Discharges (static electricity)
– Smoldering or burning dust
– Smoking materials (cigarettes, lighters, cigars, etc.)

18. OSHA Inspections
• Over 1000 COMDUST NEP
inspections since 2008
• High Violations per
inspections (Over
6.0/inspection)
Triggers are:
• Complaint or referral
• Media reports of fires and
explosions
• Inspection Targeting List
~150-300 inspections in 2014

19. Sample Accident Jan 2009
• The laminate panels pass on
a conveyor underneath a
curing UV light.
• A panel jammed up
underneath the UV light.
• The panel heated up to the
point where it charred,
smoldered and eventually
caught fire.
• The charred pieces were
sucked up into the local
exhaust system, where they
ignited the dust collector
located outside the plant.
• The dust collector blew up,
sending a shock wave back
into/through the plant.
Several overhead doors were blown
off, and one of these struck 4
employees, injuring them.

20. COMDUST NEP
• Plant history of fires
• Employer’s Dust
Management System
• MSDS’s
• Dust Accumulation
• Dust Collectors
• Ventilation Specifications
• One liter of dust sampled
• Photos
• Interviews – Employees,
Employers

21. Sample OSHA Questions
• What is the Plant’s
Housekeeping program?
• Is there dust accumulation
of 1/32 inch thick?
• Dust collectors located
inside of buildings?
• Explosion relief venting
distributed over the exterior
walls of buildings and
enclosures?

22. NFPA 654 Layer Depth Criterion Method 6.1.3
Hazard is present if dust 1/32 inches thick
covers
• 5% of room or building area up to 20,000 ft2
• Up to 1000 ft2 in a building 20,000 ft2 or larger
100
feet
200
feet
20,000 sq. ft.
Building
5% or
1000 sq.
ft.
40 feet
50 ft
1000 sq. ft.
Building or
Room
5% or 50 sq.
ft.
200
feet
200
feet
40,000 sq. ft. Building
1000
sq. ft.
22

23. How much dust is too much?
Fugitive dust outside equipment –
Permitted thickness
NFPA 654 Particulate
Solids
1/32 inch at 75 lbs/ft3 ,
adjusted for other bulk
densities
NFPA 664 Wood 1/8 inch assumes 20 lbs/ft3
bulk density
NFPA 484 Metals No accumulation – clean daily
NFPA 61 Food +
Agriculture
Remove along with operations
– references NFPA 654
OSHA
Grain
Grain
Handling
1/8 inch – program and
priority areas listed
OSHA
NEP
General
Industry
1/32 inch – Refers to NFPA
654 and FM Data Sheet 7-76
Adapted from: Application of NFPA 654 . . . Samuel A. Rogers, Process Safety, 3 - 2012
23

24. Sample OSHA Questions
• Does the facility have
isolation devices to prevent
deflagration propagation
between pieces of
equipment connected by
ductwork?
• Does the facility have an
ignition control program,
such as grounding and
bonding?
Fire through a duct is bad

25. Sample OSHA Questions
• Are Vacuum cleaners
used in dusty areas and
approved for the hazard
classification?
• Are separator devices to
remove foreign
materials used?
• Can tramp metal ignite
combustible dusts in
the dust collection
systems? Check the label for Class II

26. Sample OSHA Questions
• Is the exhaust from the
dust collectors
recycled?
• Does the dust collector
system have spark
detection and
explosion/deflagration
suppression systems?

27. Sample OSHA Questions
• Are ducts designed to maintain
sufficient velocity to ensure the
transport of both coarse and fine
particles?
• What is the design basis for the
ventilation?
• Are duct systems, dust collectors,
and dust-producing machinery
bonded and grounded to minimize
accumulation of static electrical
charge?

28. Sample OSHA Questions
• Is metal ductwork used?
• Are bulk storage containers
constructed of
noncombustible materials?
• Are employees trained in
the hazards of the
combustible dust?
• Are MSDSs for the
chemicals which could
become combustible dust
under normal operations
available to employees?

29. NEP Citations
• 1910.22, Housekeeping
• 1910.38, Emergency action plans
• 1910.94, Ventilation
• 1910.132, PPE Hazard Analysis
• 1910.146, Permit-required confined
spaces
• 1910.307, Hazardous (classified)
locations
• 1910.1000 Z table, Toxic and
hazardous substances
• 1910.1200, Hazard communication
• General duty clause
5/16/2002 Vicksburg, MS
5 fatalities, 7 injured
23 serious, 2 unclassified
$210,000
Fire in the baghouse, then rubber
dust explosion
No explosion venting or
suppression in baghouse
Poor housekeeping
88 fire reports in 13 years

30. Trend 3 – OSHA will continue to use
the General Clause Violation
• Dust collectors (Air
Material Separator)
inside
• No proper explosion
protection systems
such as explosion
venting or explosion
suppression systems
NFPA 654 – 2013
7.13.1.1.1 Where an explosion hazard
exists, air-material separators with a
dirty-side volume of 8 ft3 (0.2 m3) or
greater shall be located outside of
buildings.
There are exceptions.

31. Typical 5(a)(1) Violations
• Systems were not
provided to prevent
deflagration
propagation from
dust collectors to
other parts of the
plant.
October 29, 2003 - Hayes Lemmerz
Manufacturing Plant, IN
Shawn Boone, 33, died in the
Aluminum Dust explosion

32. Typical 5(a)(1) Violations
• No explosion relief
venting distributed
over the exterior
walls and roofs of the
buildings.
CTA Acoustics 2003 – 7 dead
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

33. Typical 5(a)(1) Violations
• Dust Collector and
ducts do not prevent
propagation to other
parts of the plant
From BS&B

34. Typical 5(a)(1) Violations
• Ducts and system were
not grounded

35. Typical 5(a)(1) Violations
• Airborne fugitive dust

36. Typical 5(a)(1) Violations
• A means of tramp metal
protection was not
provided to keep any
unwanted metal
fragments out of the
air-material separators
From Duramag

37. Typical 5(a)(1) Violations
• Excessive dust
• Not cleaning per the
appropriate NFPA
Standard

38. Typical 5(a)(1) Violations
• Compressed Air was
used for cleaning
• Tip: Clean fugitive dust
• Regular program
• Access to hidden areas
• Safe cleaning methods
• Maintain dust free as possible
• No blow down unless All
electrical power and
processes have been
shutdown and other means
cannot work.
• See NFPA

39. Typical 5(a)(1) Violations
• No PVC or
nonconductive ducts

40. Typical 5(a)(1) Violations
• Not maintaining duct
velocity
• While conditions can
vary, 4000 ft/min is
generally accepted as a
minimum conveying
velocity for wood
particulate.
• Sec 8.2.2.1.5

41. Strategy for Employers
• Test for Combustible
Dust
• Find Applicable NFPA
standards
• Implement a Safety
Management System
• Housekeeping
• Electrical Classification
• Conduct Process Hazard
Analysis for Dust
Generation Processes
• Control Ignition sources
• Develop safety
procedures for working
on dust collectors
• Investigate leaks, hot
spots, near misses
• Train Employees in
hazards of combustible
dust
• Plan for fires and
emergencies

42. Hazard Assessment & Mitigation
• Below Illustrations: Examples of Woodworking Shop area
that is kept clean, uses engineering controls (dust collection
systems), and is kept free of dust accumulation.

43. Hazard Assessment & Mitigation
• Below Illustration: An example of another Woodworking
Shop area that is kept clean and free of dust accumulation.

44. Hazard Assessment & Mitigation
• Below Illustration: An example of an overhead exhaust
ducting at Woodworking Shop area that is kept clean and free
of dust accumulation.

45. Where are Dust Sources?
• Bag Openers (Slitters)
• Blenders/Mixers
• Dryers
• Dust Collectors
• Pneumatic Conveyors
• Size Reduction Equipment (Grinders)
• Silos and Hoppers
• Hoses, Loading Spouts, Flexible Boots

46. Ignition Source Control
Electrical equipment
Hot Works
Static electricity control
Mechanical sparks & friction
Open flame control
Design of heating systems &
heated surfaces
Use of tools, & vehicles
Maintenance

47. Mitigation - Venting
Venting:
• Rupture panels to relieve
pressure preventing a vessel
failure
• Amount of vent area needed is
determined using NFPA 68
equations
• Explosion vent need to
exhaust into a safe area or a
quenching device

48. Mitigation – Suppression
Suppression:
• Detect a deflagration at early
stage and quench the event with
chemical suppressant
• Cannon/bottle consist of
pressurized gas and suppressant
chemical
• System triggers by pressure or
optical sensor
• Higher maintenance
requirements

49. Mitigation – Suppression
Factors that Impact Suppression
• Vessel Volume
• Vessel Strength
– Reduced Pressure (Pred)
• Vessel Geometry
– (L/D Ratio)
– Filter Bag/Cartridges
Factors that Impact Suppression
• Initial Pressure (+/-)
• Material (Kst)
• Activation Pressure (Pstat)

50. Isolation

51. Isolation
Isolation:
• Must be used to prevent
propagation of an event in
one vessel to
interconnected equipment
• Usually always needed in
conjunction with venting or
suppression

52. Hierarchy of Equipment Use
6.) Containment
7.) Inerting
1.) Free venting a vessel outdoors
2.) Free venting a vessel indoors next to an exterior wall using a duct
3.) Free venting a vessel indoors next to an exterior roof using a duct
4.) Flameless venting
5.) Active Suppression
Prevention

53. Maintenance
– It is also important
to ensure that all
dust-collection
systems are
operating properly
and collected dust is
recycled and/or
disposed according
to the manufacture
specifications for the
equipment.

54. Maintenance
Check dust collection
systems to make sure
all leaks are sealed
and dust is not
accumulating in the
ductwork. Check
bonding and ground
of all components in
accordance with the
manufacturer
instructions.

55. Hazard Assessment & Mitigation
• Below Illustrations: An example of an industrial dust
collection system connected to a woodworking shop exhaust
ventilation system to capture generated dust.

56. NFPA 654 - 2013
• Chapters 1 – 3
Administrative
• Chapter 4 General
Requirements
• Chapter 5 Performance-
based Design Option
• Chapter 6 Facility and
Systems Design
• Chapter 7 Process
Equipment
• Chapter 8 Fugitive Dust
Control and
Housekeeping
• Chapter 9 Ignition
Sources
• Chapter 10 Fire
Protection
• Chapter 11 Training and
Procedures
• Chapter 12 Inspection
and Maintenance

57. Seven Key NFPA 654 Changes
• 4.2 Process Hazard
Analysis (PHA)
• TREND 5 – PHA are
conducted in less than
10% of companies, but
increasing rapidly
• OSHA VPP facilities have
conducted numerous
PHAs
• 4.2.1* The design of the
fire and explosion safety
provisions shall be
based on a process
hazard analysis of the
facility, the process, and
the associated fire or
explosion hazards.

58. NFPA 654 PHA
• Examine the facility,
process, and fire and
explosion hazards
• Actual test data required to
support analysis
• Which materials are
combustible?
• If not known, but
suspected, then data are
needed
• Closed or open processes?
• Rate of generation or
release of solids to an
environment?
• Any collection methods in
place?
• Conclusion: processes
generates or handles solids
and dusts are formed in
process, potential exists

59. Seven Key NFPA 654 Changes
• 4.3 Management of
Change. Written
procedures to manage
change to process
materials, technology,
equipment, procedures,
and facilities shall be
established and
implemented.

60. Seven Key NFPA 654 Changes
• 4.4.1* Incidents
that result in a fire
or explosion of a
magnitude that
causes property
damage,
production
shutdown time, or
injury shall be
investigated.
• 4.4.3* A written report
…
• 4.4.4* A summary of
the incident
investigation report
shall be shared with
affected personnel…

61. Seven Key NFPA 654 Changes
• 6.1.1.1 Those portions of
the process and facility
interior where dust
accumulations exist
external to equipment in
sufficient depth to
prevent discerning the
underlying surface color
shall be evaluated to
determine if a dust
explosion hazard or flash
fire hazard exists.

62. Seven Key NFPA 654 Changes
• 6.1.1.3* Dust flash fire or
dust explosion hazard
areas shall additionally be
determined in accordance
with any one of the
following four methods:
 Layer depth criterion
method in 6.1.3
 Mass method A in 6.1.4
 Mass method B in 6.1.5
 Risk evaluation method in
6.1.6
The NFPA 2 day course on combustible
dust covers these assessment.

63. Seven Key NFPA 654 Changes
• 6.2 Segregation, Separation, or
Detachment of Combustible Dust
Handling and Processing Areas.
• 6.2.1 General. Areas in which
combustible dusts are produced,
processed, handled, or collected such
that combustible dust accumulation
on exposed or concealed surfaces,
external to equipment or containers,
exceeds the threshold as determined
in Section 6.1, shall be detached,
segregated, or separated from other
occupancies to minimize damage
from a fire or explosion.

64. Seven Key NFPA 654 Changes
• 7.3.2* Pneumatic Conveying,
Dust Collection, and Centralized
Vacuum Cleaning Systems.
• 7.3.2.1 The design of the system
shall be documented, and the
documentation shall include the
following information:
 Data on the range of particulate
size
 Concentration of combustible
dust in the conveyance air stream
 Potential for reaction between
the transported particulates and
the extinguishing media used to
protect process equipment
 Conductivity of the particulates
 Other physical and chemical
properties that could affect the
fire protection of the process

65. Mitigation Ignition source control
• Electrical equipment
• Class II, Division 1 and 2
• Consider equipment both inside dust handling equipment and outside
• Static electricity control
• Grounding and bonding are key
• Inspection of ground and bonding means
• Vibrating equipment (e.g., sifters) may cause fatigue failure in straps
• Mechanical sparks & friction
• Rotating equipment bearing failure can lead to very hot surfaces (above the
MIT)
• Sliding surfaces can develop charges
• Steel tools dropping onto concrete or steel
• Mechanical integrity management system/vibration analysis system
• Hot work program
• Open flames
• Design of heating systems & heated surfaces
• Use of tools & vehicles
• Maintenance
• Comfort heating equipment shall obtain combustion air from clean outside source

66. Damage Control
• Detachment (outside or other bldg.)
• Separation (distance within same room)
• Segregation (barrier)
• Pressure resistant construction
• Pressure relieving construction
• Pressure Venting
• Relief valves
• Maintenance
• Specialized detection systems
• Specialized suppression systems
• Explosion prevention systems
• Maintenance

67. Dust Collectors

68. Dust Collectors

69. Hierarchy of Equipment Use
6.) Containment
7.) Inerting
1.) Free venting a vessel outdoors
2.) Free venting a vessel indoors next to an exterior wall using a duct
3.) Free venting a vessel indoors next to an exterior roof using a duct
4.) Flameless venting
5.) Active Suppression
Prevention

70. Dust Collectors

71. Dust Collectors

72. Hierarchy of Equipment Use
6.) Containment
7.) Inerting
1.) Free venting a vessel outdoors
2.) Free venting a vessel indoors next to an exterior wall using a duct
3.) Free venting a vessel indoors next to an exterior roof using a duct
4.) Flameless venting
5.) Active Suppression
Prevention

73. Dust Collectors

74. Dust Collectors

75. Hierarchy of Equipment Use
6.) Containment
7.) Inerting
1.) Free venting a vessel outdoors
2.) Free venting a vessel indoors next to an exterior wall using a duct
3.) Free venting a vessel indoors next to an exterior roof using a duct
4.) Flameless venting
5.) Active Suppression
Prevention

76. Dust Collectors

77. Dust Collectors

78. Dust Collectors
Milton Hershey School
Location: Hershey, PA
Application: Woodworking
Model: CYLK4440
Air Flow: 8,500 CFM

79. Dust Collectors
Lincoln Middle School
Location: Passaic, NJ
Application: Woodworking
Model: DKLD48015
Air Flow: 4,800 CFM

80. Dust Collectors
William Patterson University
Location: Wayne, NJ
Application: Woodworking
Model: DKPD72015
Air Flow: 5,700 CFM

81. Dust Collectors
Gloucester HS
Location: Gloucester, MA
Application: Woodworking
Model: CYLK4450
Air Flow: 10,000 CFM

82. Dust Collectors
New Oxford Middle School
Location: New Oxford, PA
Application: Woodworking
Model: DKLD48015
Air Flow: 8,500 CFM

83. Hierarchy of Equipment Use
6.) Containment
7.) Inerting
1.) Free venting a vessel outdoors
2.) Free venting a vessel indoors next to an exterior wall using a duct
3.) Free venting a vessel indoors next to an exterior roof using a duct
4.) Flameless venting
5.) Active Suppression
Prevention

84. Multiple tasks involving exposures may involve use of
FR as normal work wear.
NFPA 2113 (2012) Recommends FR use for combustible dust
A.5.2
• Work where dust
is present on
equipment or
structure
• Changing dust
collector bags
For example, FR garments
should be required for the
following:
Per OSHA NEP
84

85. Dust depth Frequency Hsk’pg Req. Classification
Negligible
dust (color
discernable)
N/A N/A Unclassified –
general purpose
Negligible
dust to <
1/32 inch
(paper clip)
Infrequent –
Episodic release,
not > 2-3 times
yearly
Clean up
during same
shift
Unclassified –
general purpose
Negligible
dust to <
1/32 inch
Continuous to
frequent –
Continuous with
< 1/32 inch per
24 hours or
Episodic release,
> 3 times yearly
Clean as
needed –
maintain
average <
1/64 inch
(puffy little
cloud with
each step)
Unclassified –
NEMA 12 dust
entry resisting
enclosures and
/sealed non- heat
producing equip.
(For existing plants –
New to be Class II,
Div. 2)Groups F and G Dusts 85

86. 1/32 to
1/8 inch
(Two
Quarters
stacked)
Infrequent Clean up during
same shift
Unclassified – NEMA 12
dust entry resisting
enclosures and /sealed
non- heat producing
equip. (For existing
plants – New to be Class
II, Div. 2)
1/32 to
1/8 inch
Continuous
to frequent
Clean as needed –
maintain average
< 1/16 inch
Class II, Division 2
>1/8 inch Infrequent Immediately shut
down and clean
Class II, Division 2
> 1/8
inch
Continuous
to frequent
Clean frequently –
minimize
accumulation
Class II, Division 1
Groups F and G Dusts 86

87. NFPA 654 – Housekeeping 8.1,2
Fugitive dust control is
to be provided by
continuous suction
wherever dust is
liberated in normal
operations
The dust is to be
conveyed to air-
material separators
Cleaning frequency, methods and portable vacuum
cleaner requirements are RETROACTIVE for all
facilities
Continuous Suction ?
87

89. Cleaning Frequency 8.2.1
At facilities operated with LESS than the chosen threshold
dust mass/accumulation per 6.1, cleaning frequency
must ensure:
• Accumulated dust
levels do not exceed
the chosen amount
of dust
• There is a planned
inspection process
that maintains
cleaning at the
correct rate
89

90. Cleaning Frequency 8.2
For facilities operated with LESS than the chosen
threshold dust mass/accumulation
• Set specific time requirements for cleaning local and
short term spills
• The intent is to remove the excess materials quickly so
that such spills do not need to be included in the
mass calculations of 6.1
90

91. Timing of Unscheduled Cleaning
Longest Time to Complete
Unscheduled Local Cleaning
Accumulation on the worst
single square meter of
surface
Accessible
Surface
Remote
Surface
1 to 2 times threshold dust
mass/accumulation limit
(TDM/AL)
8 Hours 24 Hours
2 to 4 times TDM/AL 4 Hours 12 Hours
>4 times TDM/AL 1 Hour 3 Hours
Adapted from NFPA 654 Table A.8.2.1.3(a)
91

92. Cleaning Frequency 8.2.1
For facilities operated with MORE THAN the chosen criterion
for threshold dust mass/ accumulation per 6.1:
DUST
• FR clothing and properly
installed explosion venting
would be included
• Chapter 4 identifies some
general safety requirements
92
• Additional protective measures are necessary per
A.8.2.1.4.
• It is permitted to prepare a documented risk
assessment to determine the level of housekeeping
consistent with protection requirements

93. Cleaning Methods 8.2.2
Surfaces shall be cleaned in
a manner that minimizes the
risk of generating a fire or
explosion hazard.
Vacuuming shall be the
preferred method of
cleaning.
Where vacuuming is
impractical, permitted
cleaning
methods shall include
sweeping and water wash-down.
93

94. Cleaning Methods 8.2.2
Blow-downs are permitted for cleaning inaccessible
surfaces or surfaces where personal safety risk is less
than other methods. Use the following precautions:
Vacuuming, sweeping, or water wash-down methods are
to be used first
Dust accumulations in the
area after vacuuming,
sweeping or water
wash-down are not to
exceed the threshold
dust accumulation.
94

95. Cleaning Methods 8.2.2
NEMA 12 (resists ingress
dust of particles)
• All ignition sources and hot
surfaces capable of
igniting a dust cloud or
dust layer must be shut
down or removed from
the area
Additional requirements for dust blow-down
• Compressed air hose nozzles must be limited to 30
psi discharge pressure as per OSHA
• All electrical equipment potentially exposed to
airborne dust in the area is to meet
95

96. Housekeeping Procedures 8.2.2.5
Housekeeping
program is BIG
Must be documented (and addressed) in the dust
process hazard analysis and management of
change procedures
Housekeeping procedures should include:
• Risk analysis of the dust
• Particle size
• Moisture content
• MEC and MIE
• Other safety risks introduced
by cleaning methods
• Personal safety procedures and fall
protection
• Flame-resistant garments per NFPA
2113 96

97. Housekeeping Procedures 8.2.2.5
Procedures should also
include:
• Cleaning sequence and
methods to be used
• Equipment including:
• lifts,
• vacuum systems,
• attachments, etc.
Safety Note: Large and high velocity fans may be used to prevent dust
accumulations. Use of such fans to blow down significant dust
accumulations present the same risks as compressed air blow-downs.
97

98. Portable Vacuum cleaners 8.2.3.1
• Hoses are to be conductive or static-
dissipative – both suction and air
delivery hoses
• All conductive components including
wands and attachments must be
bonded and grounded
• Dust-laden air must not pass through
the fan or blower
Conductive or Static-
dissipative Hose
They are to meet the following:
• Generally non-combustible construction and meet
requirements for construction and static electrical hazard
controls per 9.3.2 and 7.13.2
98

99. Portable Vacuum cleaners 8.2.3.1
Additional requirements
• Electrical motors must not be in the
dust laden air stream unless listed for
Class II, Division 1 locations
• No paper filter elements for liquid or
wet pick-up
• Metal dust vacuums are to be listed for
Class II, Division 1, Group E and meet
other NFPA 484 requirements for
specific metal used
99

100. Vacuum Cleaners for Use in Hazardous Locations
8.2.3.2 And .3
• Use vacuums listed for the
location or
• Provide a fixed-pipe
suction system with
appropriate remotely located
exhauster and dust collector.
• Where flammable
vapors are present,
units are to be listed for
both Class I and Class II
locations
HAZ LOC 100

101. Spills of Large quantities of dust A.8.2.3.1
In UNCLASSIFIED areas
• Bulk material should be collected by sweeping, or
shoveling
• Listed Class II vacuums may also be used
• Vacuum cleaners per 8.3.2.1 (e.g.: compliant air driven
units) may be used afterwards for residue
Vacuum Truck See also
OSHA Fact Sheet
DSG FS-3589
10 2012
Vacuum trucks are similar to vacuum cleaners. They
require analysis with management of change (MOC)
to remove large quantity spills or releases of dust per
4.3
101

102. Concluding Remarks
• No two dust explosions are the same.
– No uniform dust laws like there are for gases
• Standards are evolving
• The dust explosion hazard exists
– Be aware of the “I’ve never had a dust explosion
before”

103. Questions?

104. Safety and Health Information Bulletin
Purpose
Background
Elements of a Dust Explosion
Facility Dust Hazard Assessment
Dust Control
Ignition Control
Damage Control
Training
References

105. Resources and Questions?
• NFPA 2-day
Combustible Dust
Seminar
• Combustible Dust
Guidebook - NFPA
• OSHA SHIB
• www.csb.gov
• LinkedIn
Combustible Dust
Forums
• Facebook Grain Mill
Accident page