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1
Protecting Worker Health
Welcome Introduction to Combustible Dust Hazards and Mitigation for IHs
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Protecting Worker Health
Webinar
Introduction to Combustible Dust Hazards and Mitigation for IHs
2
Protecting Worker Health
Accreditation Information
• Board of Certified Safety Professionals (BCSP)
• American Board of Industrial Hygiene (ABIH)
Protecting Worker Health
Certification Maintenance
Individual participants seeking CM and COC credit MUST:
• participate in the live Webinar or review the archive
• complete an online evaluation and submit a *processing fee post-Webinar
To access the fee and evaluation post-Webinar visit:
http://www.aiha.org/education/CourseCalendar/eLearning/Pages/13DEC1WB-Welcome.aspx
*Fee does not apply to 2013 eLearning Subscription participants
3
Protecting Worker Health
Certification Maintenance cont’d *The deadline for participants to submit the processing fee and online
evaluation for the LIVE WEBINAR is *March 10, 2014
• Sites participating in Archive Group Training have *90 DAYS from the date of viewing the archive to submit an exam.
• CM and COC credit will not be awarded and may not be claimed by individuals who have not submitted the processing fee and evaluation.
• Access and instructions for submitting the processing fee and evaluation can be found at: http://www.aiha.org/education/CourseCalendar/eLearning/Pages/13DEC1WB-Welcome.aspx
• Allow 2-4 weeks after submitting the required materials to gain access to your education transcript, which will reflect course completion and CM and COC credits awarded.
*Fee and deadline does not apply to 2013 eLearning Subscription participants.
Introduction to Combustible Dust Hazards and Mitigation
for Industrial Hygienists
Gary Q. Johnson, P.E.
Workplace Exposure Solutions LLC
December 10, 2013
4
Agenda
Conditions for dust deflagrations
Combustible dust tests
Explosion protection equipment
Dust collection equipment
Combustible dust procedures
Summary
7 Combustible Dust Hazards and
Mitigation
8
What Dusts Are Combustible?
OSHA Website general description (www.osha.gov/dts/shib/shib073105.html)
“The vast majority of natural and synthetic organic materials, as well as some metals, can form combustible dusts.”
“A combustible dust explosion hazard may exist in a variety of industries, including: food (e.g., candy, starch, flour, feed,) plastics, wood, rubber, furniture, textiles, pesticides, pharmaceuticals, dyes, coal, metals (Al, Cr, Fe, Mg, Zn,) and fossil fuel power generation.”
Combustible Dust Hazards and Mitigation
5
9
Dust Explosion Pentagon
Oxidant (Air)
Heat or Ignition
Fuel
Chemical Chain Reaction
New Fire Triangle
“Fire Triangle” plus Two
Combustible Dust Hazards and Mitigation
Animation of Dust Explosion Hayes Lemnertz Incident
10 US Chemical Safety Board
Combustible Dust Hazards and Mitigation
6
11
FLASH FIRE SEQUENCE WITH FLAMMABLE VAPORS ~ 3 SECONDS DURATION
SERIOUS BURNS BECAUSE CLOTHES IGNITE (~500 F) FROM FLASH FIRE (>1500 F)
Combustible Dust Hazards and Mitigation
Combustible Dust Hierarchy of Controls
Design it out – substitution? Not likely
Engineering controls – explosion protection and dust collection equipment
Administrative controls – housekeeping, hot work, equipment maintenance, Management of Change, emergency response, training
PPE – flame resistant garments
12 Combustible Dust Hazards and
Mitigation
7
13
Light weight Flame Resistant Garments
Protection comes from preventing ignition of clothing in a flash fire – undergarments should also be flame resistant so the elastic will not melt into your skin from the heat
Work with vendors to determine what heat flux rating (ie, kcal/sq.cm.) FRG is appropriate. FRG after fire – fabric did not
support burning
Courtesy Bulwark Protective Apparel
Combustible Dust Testing Defines These Hazards
Ease of ignition of dust cloud
Minimum Explosible Concentration
Minimum Ignition Energy
Minimum Ignition Temperature, Layer, Cloud
Pressure consequences of a dust deflagration
Kst, deflagration index (Pmax, dP/dt)
14 Combustible Dust Hazards and
Mitigation
8
15
Hazard Class
Kst
(bar-m/sec)
Pmax
(bar)
Some examples
ST-1 <200 Moderate (?)
explosion
10
powdered milk, charcoal, sulfur,
zinc
ST-2 200-300 Strong
explosion
10 cellulose, wood flour, methyl acrylate
ST-3 >300 Very strong explosion
12
anthraquinone, aluminum, magnesium
Example combustible dusts (NFPA 68) (higher number higher pressure explosion)
20 liter sphere
Greater hazard? Small qty ST-3 or Large qty ST-1
Courtesy Fauske Assoc.
Combustible Dust Hazards and Mitigation
16
Source: Dust Explosions in the Process Industries, Second Edition, Rolf K Eckhoff
Minimum Explosible Concentration The minimum concentration of combustible dust suspended in air, measured in mass per unit volume that will support a deflagration.
(lower concentration higher hazard)
Dust
Deposit Explosible
Range
IH
Range
10-3 10-2 10-1 1 10 101 102 103 104 105 106
MASS OF POWDER/DUST PER UNIT VOLUME [g/m3]
Dust MEC Dust MEC
Sugar 200 Aluminum 30
Cellulose 80 Magnesium 30
Combustible Dust Hazards and Mitigation
9
17
Static Electrical Ignition Potential? (lower MIE easier ignition)
Minimum Ignition Energy range, mJ
Example materials
25 - 50 ABS resin, aluminum, cellulose, cinnamon, coal, corn flour, paper dust, sugar, wheat starch
10 - 25 Aluminum stearate, epoxy resin, sulfur
< 10 Bisphenol-A, red phosphorus, polyethylene, thorium, zirconium
MIE Tester, Mike 3 apparatus
Courtesy Fauske Assoc.
Combustible Dust Hazards and Mitigation
Minimum Ignition Energy (MIE) (mJ)
Predicts the ease and likelihood of ignition of a dispersed dust cloud. Lower number is greater risk of ignition.
MIE (mJ) Recommended Precaution per BS 5958
500 Low sensitivity to ignition. Ground plant below this level.
100 Consider grounding personnel below this level.
25 The majority of ignition incidents occur below this level.
10 High sensitivity to ignition. Consider restrictions on the use of high resistivity non-conductors below this level.
1 Extremely sensitive to ignition at this level. Handling operations should be such that they minimize the possibility of suspending the powder in air. Dissipate or discourage charge operations.
18 Combustible Dust Hazards and
Mitigation
10
Layer and Dust Cloud Ignition Temperature (ºC) Examples (Lower Temp Easier ignition)
Layer
Cloud Page 19
Courtesy Fauske Assoc.
Combustible Dust Hazards and Mitigation
Measured Properties of Combustible Dusts and how the data is used – sample sizes 0.5 -2.0 kg
Property Definition ASTM Test Method
Application
KSt Dust deflagration index, bar-m/sec
ASTM E 1226 Measures the relative explosion severity & pressure compared to other dusts.
Pmax Maximum explosion overpressure generated in the test chamber
ASTM E 1226 Used to predict the severity of the explosion consequences and to design explosion protection for enclosures
(dp/dt)max Maximum rate of pressure rise
ASTM E 1226 Predicts the violence of an explosion. Used to calculate Kst
MIE Minimum ignition energy, milli-Joules
ASTM E 2019 Predicts the ease and likelihood of ignition of a dispersed dust cloud.
MEC Minimum explosible concentration, gm/m3
ASTM E 1515 Measures the minimum amount of dust, dispersed in air, required to spread an explosion. Analogous to the lower flammability limit (LFL) for gas/air mixtures but there is no UFL test for dusts.
MIT-Layer Minimum Ignition Temperature – Dust layer
ASTM E 2021 Measures surface temperature that will ignite a layer of dust
MIT-CLoud Minimum Ignition Temperature - Cloud
ASTM E 1491 Measures surface temperature that will ignite a dispersed dust cloud.
Page 20 Combustible Dust Hazards and
Mitigation
11
21
Sieved Sample – As received, through 40 mesh screen (420 um)
Material larger than 20 mesh
Material passing through 20 mesh but not through 40 mesh screen
Material passing through 40 mesh but not through 200 mesh screen
Material passing through 200 mesh screen
Combustible Dust Hazards and Mitigation
Factors that Change Dust Ignitability
Property & Change Risk increases as the value:
Kst
MIE
Particle size distribution DECREASES
Dust chemistry (ie, PVC vs polyethylene)
Dust moisture content INCREASES
Dust concentration optimal range
Dust cloud turbulence INCREASES
Oxygen content INCREASES
Dust cloud temperature INCREASES
Initial dust cloud pressure INCREASES
Hybrid mixtures dust cloud with flammable vapors or gases
22 Combustible Dust Hazards and
Mitigation
12
Combustible Dust Hazards and Mitigation 23
Questions – CD Hazards, Testing
OSHA CD Inspections & Violations Issued Oct. 2007-Oct. 2012
24
7625
2356
14321827
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Serious Other Than Serious
Federal
State
2272
653
0
500
1000
1500
2000
2500
Federal State
INSPECTIONS
VIOLATIONS
Combustible Dust Hazards and Mitigation
13
Distribution of Federal Violations
25 Combustible Dust Hazards and
Mitigation
Some Combustible Dust NEP Findings
1. Hazardous dust accumulations
2. Unrated electrical equipment and Powered Industrial Trucks
3. Dust collectors inside buildings - no explosion protection systems.
4. Deflagration isolation systems not provided
5. The horizontal surfaces not minimized to prevent accumulation of dust on surfaces.
26
Combustible Dust Hazards and Mitigation
14
27
Explosion Vent Problems
Combustible Dust Hazards and Mitigation
Some Combustible Dust NEP Findings 6. Dust collector exhaust recycled through duct work back
into the work area without protection.
7. Magnetic separators and tramp metal separators not installed or not functioning to prevent foreign material entering into process stream.
8. Explosion vents on bucket elevator(s) and dust collectors were directed into work areas and not vented to a safe, outside location.
9. Equipment (such as grinders and shakers) not designed to minimize escape of dust into the surrounding work area.
10. Ductworks used in transporting combustible dust were not constructed of metal, not bonded or grounded.
28 Combustible Dust Hazards and Mitigation
15
Some Combustible Dust NEP Findings
11. Hot work performed in the combustible dust handling areas without hot work procedures.
12. Silos, legs of bucket elevators were not equipped with explosion relief venting.
13. Enclosureless dust collection systems were allowed indoors where they were connected to sanders having mechanical feeds and did not follow other reqmts.
14. Compressed air used to clean up the combustible dust accumulation in the presence of ignition sources.
15. Portable Vacuum Cleaners were not approved for Class II locations.
29 Combustible Dust Hazards and
Mitigation
Welding on Outside
of Duct Wall
Dust Deposit on
Inside of Duct Wall
30
Set Explosion Control Strategy Process Hazard Analysis NFPA 654
Based on hazardous characteristics of dust
PHA-documented, thorough analysis and risk mitigation strategy for:
The facility
The process
Associated fire and explosion hazards
Retain PHA for life of process
Update PHA every 5 years
Other NFPA Stds: 664 Wood, 484 Metal, 61 Agriculture & Food Combustible Dust Hazards and
Mitigation
16
31
Accident Scenarios to Assess Explosion within process equipment
Ignition sources (frictional heating, smoldering dust layers, electrostatic sparks)
Equipment with dust clouds > MEC (blenders, driers, size reduction) Dust collectors have dust clouds > MEC (> 40% of incidents))
Explosion propagation – interconnected equipment (spark or deflagration)
Secondary explosions (fuel in dust accumulations, often more significant than primary explosion)
{Zalosh, et al, “Safely Handle Powdered Solids,” Chemical Engineering Progress Magazine, Dec. 2005}
NEW: ADD FLASH FIRE SCENARIO AND DETERMINING OPERATOR PROTECTION
Combustible Dust Hazards and Mitigation
NFPA 654-2013 Key Definition Changes (Ch.3) Flash Fire. A fire that spreads rapidly through a diffuse fuel,
such as dust, gas, or the vapors of an ignitable liquid, without the production of damaging pressure.
Dust Explosion Hazard Area. A room or building volume where an unvented deflagration of the entrainable dust mass can result in a pressure exceeding the strength of the weakest structural element not intended to fail.
Dust Flash Fire Hazard Area. An area where combustible dust accumulation on exposed or concealed surfaces, outside of equipment or containers, can result in personnel injury from thermal dose during a dust deflagration, as well as any areas where dust clouds of a hazardous concentration exist during normal operation. A propagating deflagration yields a flash fire through the hazard area.
32
Combustible Dust Hazards and Mitigation
17
33
Dust overhead, over an ignition source Dust MEC = 30
grams/cubic meter
Dust cloud 2 meters diameter, 5 meters long
Mass of dust in perfectly distributed dust cloud? V =pi x D2/4 x
L=3.14 x 22/4 x 5= 15.7m3
Mass =15.7 m3 x 30 gr/m3=471 gm x 1#/454gm= 1.04 pounds
How Little Dust for an Explosion?
Combustible Dust Hazards and Mitigation
34
Dust Explosion Pentagon: Multiple Strategies to Reduce Risk
Heat or ignition source:
prevent flames static
electricity, sparks,
smolders
Confinement of dust
cloud: building &
equipment designed
to safely contain or
vent
Oxidizer (oxygen
in air): reduce O2
with inert gas
Combustible dust
(fuel): prevent
accumulation –
design,
housekeeping
Dispersion of
dust particles:
prevent dust
layer getting
airborne – relief
device vent path
Combustible Dust Hazards and Mitigation
18
Ignition Sources
Stronger Open flame Welding arc Gas or dust
explosion Electrical short or
arc Friction Mechanical spark
(tramp metal)
35 Combustible Dust Hazards and
Mitigation
Static Electricity Types
36
Spark discharge Brush discharge
Corona discharge
Propagating brush discharge
Bulk brush discharge
Courtesy Crohmiq Co.
Up to 1000 mJ Up to 40 mJ
Up to 1000 mJ
Up to 1000 mJ
Up to 1 mJ Combustible Dust Hazards and
Mitigation
19
Ignition Sources Less strong
Static sparks
Cigarettes
Hot surfaces – internal combustion engines
Smoldering embers
Overheated electrical equipment
©Sierra Pacific Infrared Thermography
37 Combustible Dust Hazards and
Mitigation
38
Grounding , Bonding-Dissipate Static Electrical Charges
Metal strip under rubber Courtesy Morris Coupling Co.
Jumper Wire – Courtesy J.O.A.
Clamp together Courtesy Jacob Tubing
Flanges and bolts on metal ducts < 106 ohms – British study
Dust drum bonding cable with alligator clip
Combustible Dust Hazards and Mitigation
20
Big Bags or Flexible Intermediate Bulk Containers (FIBC) Applications (consider contents, environment)
Type FIBC Comb. Solids?
Flam. Vapors?
MIE, mJ Exclusions
A OK No > 1000 Conductive solids
B OK NO > 3 Conductive solids
C (grounding tab, < 108 Ω)
OK, conductive solids OK
OK if present > 0.14 Ground resist. < 25 Ω
D (static dissipating construction)
OK OK flammable atmospheres
> 0.14 Conductive solids
39
TYPES B, C, & D: tested & verfied safe for intended use by recognized organization in accordance with IEC 61340-4-4, Electrostatics Part 4-4, Standard Test Methods for Specific Applications – Electrostatic Classification of FIBC’s
Combustible Dust Hazards and Mitigation
40
Electrical Classification – Class II for Combustible Dusts
Class II Group
Type Dust Temp. Lim., Normal Opns, oF/oC
Temp. Lim., F, Abnormal Opns, oF/oC
E Metal 392/200 392/200
F Carbonaceous 302/150 392/200
G Flour, grain, wood, plastics, chemicals
248/120 329/165
Division 1: combustible dust normally present that could product explosive or ignitable mixtures, mechanical failure might cause mixtures, electrically conductive dusts
Division 2: airborne combustible dust not normally present, comb.dust layer on electrical equipment may interfere with heat dissipation
Combustible Dust Hazards and Mitigation
21
Class II Electrical Equipment Enclosures
41
Division 1 – dust incendive proof? (NEMA 12) Courtesy Crouse Hinds Division 2 –
dust tight?
Div. 1 or 2 – purge retrofit as per NFPA 496? Courtesy Pepprl-Fuchs
TEFC-courtesy wegelectrical motors
Cour. Thomas.net
Combustible Dust Hazards and Mitigation
Combustible Dust Hazards and Mitigation 42
Questions – Regulatory, Ignition Sources
22
43
Dust Explosion Pentagon: Multiple Strategies to Reduce Risk
Heat or ignition source:
prevent flames static
electricity, sparks,
smolders
Confinement of dust
cloud: building &
equipment designed
to safely contain or
vent
Oxidizer (oxygen
in air): reduce O2
with inert gas
Combustible dust
(fuel): prevent
accumulation –
design,
housekeeping
Dispersion of
dust particles:
prevent dust
layer getting
airborne – relief
device vent path
Combustible Dust Hazards and Mitigation
44
Explosion Pressure Profile
Explosion pressure rapidly builds beyond typical vessel yield strength
Vent or suppress –pressure less than Preduced to 2/3 yield strength –
no deformation
Yield strength - allow deformation
Pre
ssu
re
Time
Pmax
Vessel strength
Vent too small
Preduced
Pstat
Correct Vent
Unvented
Combustible Dust Hazards and Mitigation
23
Important to Get the Design Right the First Time!
45 Courtesy Rembe Co. Combustible Dust Hazards and
Mitigation
46
Explosion Containment
Pressure CONTAINMENT 10-12 bar (150-180 psig) Pros
no additional protection on vessel
indoor applications
Cons still need to isolate
connected equipment with high pressure design to isolation device
ASME pressure vessel & high capital costs
Courtesy Glatt Air Techniques Combustible Dust Hazards and
Mitigation
24
47
Venting - Explosion Doors
door safety cage if near walkway
Door weight = 2.5 #/sq.ft (NFPA 68) so its mass does not impede venting
Adv: Does not need to be replaced after venting
Disadv: Door sizes maybe larger than panels/membranes
Courtesy Philadelphia Safety Door Combustible Dust Hazards and
Mitigation
48
Venting – Explosion Panels, Rupture Disks
Domed panel, courtesy Fenwal
Rupture discs, courtesy Fike
Domed panels resist pressure cycling better than flat panels – 4-20x longer
Courtesy BS&B Safety Systems
Combustible Dust Hazards and Mitigation
25
Vented Explosions Are Violent!
49 Courtesy Rembe Co. Combustible Dust Hazards and
Mitigation
50
Explosion Vent Design – Safe Discharge Zone
D = K(V/n)1/3
D – dist. in front, m K – flame length factor, K=10
(metal dust), K=8 (chem., agric. dusts)
V – volume vented enclosure, m3
n – number of vents Flame width = ½ D
Example: 2 vents V= 60 m3 (1980 ft3) Chemical dust, K = 8 D=24.5 m = 80 ft in front of
vent Courtesy Fenwal Combustible Dust Hazards and Mitigation
26
51
Indoors Venting Considerations Prevent ice & snow from adding weight to vent – vendor options
Max vent duct length as per NFPA 68, (<10 ft)
Blast Deflector Plate Design (NFPA 68, section 6.6)
-size: 175% vent area
-45-60o angle , centered on vent
-Distance, 1.5x vent diameter
-Strong mounting
-Limited to enclosures smaller than 20 m3 (706 ft3)
Combustible Dust Hazards and Mitigation
Safe Vent Discharge Location?
Page 52
Explosion Venting
Emergency Exit Doors
Rotate dust collectors, blast deflector plates
Combustible Dust Hazards and Mitigation
27
Don’t Make Your Own Explosion Vent Panels! (Plastic bags too strong)
53 Courtesy Rembe Co. Combustible Dust Hazards and
Mitigation
Building Damage Limiting Construction – Wall Vent Panels
54
Courtesy BS&B Safety Systems
Combustible Dust Hazards and Mitigation
28
55
Flameless Vent
Two parts of device
• Rupture disk to relieve pressure
• Mesh screen to contain and quench flame front
Advantages:
• Indoor protection
Disadvantages:
•capital cost
•may not be suitable for high Kst dusts
• building pressure impact?
• hot gases safety zone 6-12 ft
Courtesy Fenwal
Combustible Dust Hazards and Mitigation
Flameless Vent Operation
56
Courtesy Rembe Co.
Combustible Dust Hazards and Mitigation
29
57
Fire Sprinklers in Dust Collector
Risk decision – puts out fire without operator intervention
Collector rated for 20”w.c. – filled with sprinkler water it would collapse!
Water dump valves to drain water
Challenge – getting an air tight dump valve
Courtesy Donaldson Corporation
3” dia. check valve
Combustible Dust Hazards and Mitigation
58
Active Protection – requires sensors & high speed control to initiate
Advantages:
• Indoor applications
• Prevents growth of explosion and aftermath
Disadvantages:
• Product contamination (perhaps moot with fire)
•Ongoing vendor inspection and maintenance costs -Quarterly -2 hr downtime -$800-1000/day
Explosion Chemical Suppression
Interlock suppression controls with equipment protected – permissive on
Courtesy Fenwal
Combustible Dust Hazards and Mitigation
30
Reinforce Mounting for Suppression Canisters
59 Combustible Dust Hazards and
Mitigation Courtesy Fenwal
60
Chemical Suppression Lockout
- Remove permissive insert – magnetic switch
- Install lockout blank flange
- Install lockout cable and locks
Courtesy Fenwal
Combustible Dust Hazards and Mitigation
31
Explosion Suppression vs. Venting
Equipment indoors vent duct not practical
Not enough vent area on equipment High Kst or hybrid dust
Low Preduced
No safe place to vent
Toxic dusts cannot be discharged to atmosphere via a vent
Flame propagation through interconnection suppression on equipment -
isolation suppression controlled by same controls
61
Courtesy Fike
Combustible Dust Hazards and Mitigation
62
Spark Detection & Extinguishing
Courtesy BS&B Wide belt sanders generate sparks
Combustible Dust Hazards and Mitigation
32
Abort Gates
63 Courtesy Imperial Systems Combustible Dust Hazards and
Mitigation
64 Combustible Dust Hazards and Mitigation
33
65
Equipment DEFLAGRATION ISOLATION Isolation devices
needed:
To protect workers working near dust controlled equipment
To prevent pressure piling on upstream equipment such as a cyclone before a baghouse
One of the most common gaps in explosion protection equipment
Courtesy Fenwal Combustible Dust Hazards and Mitigation
66
Passive ISOLATION: Flame Front Diverter
Passive device
-Locate close to collector
-Vent to safe location
Advantages:
-Passive
-Self closing possible
Disadvantages:
-Directional
-System d/p
-Kst < 200
-Not tight seal
Courtesy J.O.A.
Combustible Dust Hazards and Mitigation
34
67
Passive ISOLATION: Back Draft Damper
Normal flow direction (conceptually a check valve)
Tested for up to Kst = 300 dusts (ST-2 class) depending on duct diameter
Heavy duty damper slams shut with deflagration pressure wave – normally hangs open 60o against 25o valve seat
Routinely inspect for cleanliness – potential for dust fouling
Courtesy Rembe
Combustible Dust Hazards and Mitigation
Backdraft Damper Operation
68
Courtesy Rembe Combustible Dust Hazards and Mitigation
35
69
Passive Isolation: Mechanical Path
Rotary airlock valve (tight construction, 6 vanes or more)
Screw conveyors
Powder chokes
Rotary Air Lock Valve Combustible Dust Hazards and
Mitigation
70
Isolation – Fast Acting Valves
Gate valve – full opening design Located far enough from collector
to allow for time delay between sensing an explosion and sending a signal to close the valve.
Advantage Full isolation of flame front Prevent product cross contamination
Disadvantage Capital cost ($1200-1400/inch
diameter) – MAX SIZE 24” Stronger duct between valve and
collector (3-8 meters) Routine test cycling of valve may
require replacement parts
Courtesy Fenwal
Combustible Dust Hazards and Mitigation
36
71
Active Isolation: Pinch Valves
Courtesy CV Technologies
How it works 1. Housing installed into ductwork. 2. Inflatable bladder rapidly activates to close the line. 3. Air receiver tank provides inflation energy. 4. Controller manages and monitors valve operation. 5. Sensor (not shown) triggers activation of valve closing. - Clean side application - Lower differential pressure rating than float valve
Courtesy Rembe Combustible Dust Hazards and
Mitigation
Explosion Protection Design Standards
NFPA 68-2012
Explosion vent doors, vent panels, flame arresting vents, flame front diverters
NFPA 69-2008
Explosion prevention: chemical suppression, limiting oxidants (inerting)
Explosion isolation: high speed valves, rotary airlock valves
Fire prevention: spark detection and extinguishing, abort gates
72 Combustible Dust Hazards and
Mitigation
37
73
Dust Explosion Pentagon: Multiple Strategies to Reduce Risk
Heat or ignition source:
prevent flames static
electricity, sparks,
smolders
Confinement of dust
cloud: building &
equipment designed
to safely contain or
vent
Oxidizer (oxygen
in air): reduce O2
with inert gas
Combustible dust
(fuel): prevent
accumulation –
design,
housekeeping
Dispersion of
dust particles:
prevent dust
layer getting
airborne – relief
device vent path
Combustible Dust Hazards and Mitigation
74
Oxidant Concentration Reduction (NFPA 69: Explosion Prevention)
Inerting gases to reduce oxygen from normal 19.5% to 8-10% (actual value depends on dust Limiting Oxidant Concentration test)
Nitrogen most common, some use of carbon dioxide
Requires oxygen monitor and controls to ensure continual low oxygen level
Advantages Preventive technique
Avoids product contamination
Disadvantages
Asphyxiation hazard next to inerted equipment if it goes positive– adequate alarms and controls?
Nitrogen use operating expense if no recycling possible
Nitrogen molecule
Combustible Dust Hazards and Mitigation
38
Combustible Dust Hazards and Mitigation 75
Questions – Explosion Protection Equipment
Jahn Foundry – Phenolic Resin
76
Dust Explosion Pentagon: Multiple Strategies to Reduce Risk
Heat or ignition source:
prevent flames static
electricity, sparks,
smolders
Confinement of dust
cloud: building &
equipment designed
to safely contain or
vent
Oxidizer (oxygen
in air): reduce O2
with inert gas
Combustible dust
(fuel): prevent
accumulation –
design,
housekeeping
Dispersion of
dust particles:
prevent dust
layer getting
airborne – relief
device vent path
Combustible Dust Hazards and Mitigation
39
Housekeeping Blowdowns for inaccessible or
unsafe locations (precautions to prevent flash fire)
Clean accessible areas with vacuum, etc. so dust accum. < threshold dust accum.
Compressed air hoses – pressure relief nozzles 30 psig max pressure
All energized electrical equipment NEMA 12
Ignition sources, hot surfaces shutdown or removed from area
Housekeeping procedures documented
77 Courtesy Rembe Co.
Combustible Dust Hazards and Mitigation
78
Safe sweeping
Sweep gently to minimize airborne dust
Natural bristles (no synthetic)
Aluminum or conductive polymer dust pans
Courtesy Rembe Co.
Combustible Dust Hazards and Mitigation
40
79
Static dissipating features -Drum grounding cable -Conductive vacuum and air hoses -Conductive wheels
Courtesy Vac-U-Max
Combustible Dust Hazards and Mitigation
Electric with Explosion Proof blower and control switches
Portable Vacuum Cleaners with Combustible Dust Protection
courtesy Ruwac
80
Central Vacuum Cleaning Systems
System components -High vacuum producer (6-12”Hg = 82-164” w.c.) -Filter/receiver -Pre-separator (optional) -Tubing branches to use zones -Hoses and tools
Courtesy Gardner Denver
Combustible Dust Hazards and Mitigation
41
Housekeeping Procedures
Layer Depth Criterion (LDC) – dust thickness (density x area)
Hazard if > 5% of floor area of confined area – include overhead horizontal surfaces – up to 1,000 sq.ft.
Survey – dust deposition rates
Written procedure
Responsibilities
Safe methods
Routine and special cleanup
Recordkeeping
81 Combustible Dust Hazards and
Mitigation
Dust collection system design 1 – Minimize fugitive dust
Open hoods have lowest collection efficiency
Better - Enclosed process under dust collection
Design as though OEL < 1 mg/m3
Control smaller dust sources – discarding bags at bag dump 82
Combustible Dust Hazards and Mitigation
42
83
Dust collection system design 2-adequate conveying velocity
Dust Control Systems: 3500 to 4500 fpm (higher for some dusts.)
Aerosol or other small particle Control Systems: 2500 to 3500 fpm.
(ft/min)duct in airstream of velocity V
min)/(ft lumeexhaust vo Q
(inches)diameter duct D
)(ftduct of area sectional-crossA
: where ) 576/*_(/
3
2
2
DAAQV
Hayes – Lemnertz ducts
Combustible Dust Hazards and Mitigation
84
1) Duct does not get larger after branch entry
2) Unneeded ducts blanked
3) Poor duct transitions or merges
4) Excessive use of flexible ducts
5) High dust collector d/p
6) Blast gates changed
7) No system technical documentation
8) No system monitoring
8 visible clues of inadequate duct conveying or transport velocity
Combustible Dust Hazards and Mitigation
43
85
Complete Dust Collection System Explosion Protection Overview
Static grounding
Conveying velocity
Static grounding
Internal, external
Inlet
isolation
Explosion
vent,
suppress,
or contain
Spark
resistant?
Recirculation?
return air isolation
Hood
design
Housekeeping to prevent
dust accumulations
Electrical
Classification
Combustible Dust Hazards and Mitigation
86
Review - Can a Dust Collector Be Indoors?
YES IF ONE OF THESE IN PLACE
Pressure containment
Short explosion vent duct to outdoors
Flameless vent
Chemical or Water Suppression
Volume < 8 cubic feet with no explosion protection – carefully considered risk decision
Sources: NFPA 654, 68, 69
Combustible Dust Hazards and Mitigation
44
Combustible Dust Procedures
Ignition Control: enhanced hot work permits, static grounding integrity, electrical enclosures
Housekeeping
Equipment maintenance: explosion protection, dust collection, vacuum cleaning
Emergency response: fighting dust fires
Management of Change: internal design standards, Process Hazard Analyses, change procedures
Flame Resistant Garments
Employee training
87 Combustible Dust Hazards and
Mitigation
Summary Treat dust as guilty of being combustible unless
proven innocent
Conduct PHA’s for your process – “live” as long as your process
Apply hierarchy of controls where a deflagration hazard exists as per NFPA stds.
Maintain explosion protection and dust collection equipment as per NFPA stds.
Implement a Combustible Dust Program
Use Management of Change
Reference materials follow 88 Combustible Dust Hazards and Mitigation
Copyright Gary Q. Johnson 2013
45
Combustible Dust Hazards and Mitigation 89
Final Questions
Gary Q. Johnson
December 2013
Reference: Other Combustible Dust Regulations, Standards, Guidelines
46
Literature to ID Comb. Dusts (Use for setting direction, not design)
OSHA CD Safety Poster
NFPA 61 (Food, Agric.) table A.6.2.1
NFPA 68 (Expl.Vent) Annex F
NFPA 484 (Metals) in Annexes
NFPA 499 (Haz. Area Elec.) Table 4.5.2
BGIA (Europe – table of ~ 4600 matls.) http://www.dguv.de/ifa/Gefahrstoffdatenbanken/GESTIS-STAUB-EX/index-2.jsp
91 Combustible Dust Hazards and
Mitigation
US Chemical Safety Board (http://www.csb.gov/combustible-dust-hazard-investigation/)
Combustible Dust Hazard Investigations Hayes Lemnertz (aluminum dust) CTA Acoustics (auto insulation – phenolic resin) West Pharmaceutical (polyethylene) Jahn Foundry (phenolic resin) Rouse Polymerics (rubber) Ford River Rouge Coal Explosion
Imperial Sugar Company Dust Explosion and Fire (sugar dust)
Hoeganaes Corporation Fatal Flash Fires (iron dust)
Page 92 Combustible Dust Hazards and
Mitigation
47
Page 93
OSHA Technical Manual Section III: Chapter 3 - Ventilation Investigation
(http://www.osha.gov/dts/osta/otm/otm_toc.html)
Contents: I. Introduction II. Health Effects III. Standards and Codes IV. Investigation Guidelines V. Prevention and Control VI. Bibliography Apdx III:3-1. Ventilation Primer Apdx III:3-2. Glossary Apdx III:3-3. OSHA, Consensus Standards Apdx III:3-4. Troubleshooting an Exhaust System
Combustible Dust Hazards and Mitigation
OSHA Ventilation Regulations
29 CFR 1910.94
A) – Abrasive Blasting
B) – Grinding, Polishing, and Buffing
C) - Spray Finishing
29 CFR 1910.106 – Flammable and Combustible Liquids
29 CFR 1910.1450 – Laboratory Chemical Safety
Page 94 Combustible Dust Hazards and
Mitigation
48
OSHA Resources
Website: http://www.osha.gov/dsg/combustibledust/index.html
Combustible Dust National Emphasis Program
Status Report on Combustible Dust National Emphasis Program, October 2009
Other useful documents – see last slides of presentation – copies of complete document in web posting
Advanced Notice of Proposed Rule Making Combustible Dust Postings: Docket # 2009-0023 (178 postings)
http://www.regulations.gov/ - search on “Combustible Dust” and there are over 1700 postings
95 Combustible Dust Hazards and
Mitigation
Safety and Health Information Bulletin www.osha.gov
Purpose Background Elements of a Dust Explosion Facility Dust Hazard Assessment Dust Control Ignition Control Damage Control Training References 9 pages
Issued 7/2005
96 Combustible Dust Hazards and
Mitigation
49
OSHA Combustible Dust Safety Poster
97
1 page Issued 2008
Combustible Dust Hazards and Mitigation
OSHA Fact Sheet
Explosions overview
Prevention
Dust Control
Ignition Control
Injury and Damage Control
2 pages
Issued 3/2008
98 Combustible Dust Hazards and
Mitigation
50
Combustible Dust Hazard Communication
99
Introduction OSHA’s Hazard Communication Standard Identifying and Controlling the Potential for Dust Explosions MSDS Preparation Product Labels Training & Information References OSHA Assistance Regional Offices 21 ½ size pages
Issued 2009 Combustible Dust Hazards and
Mitigation
OSHA Guidance Combustible Dust Fire Fighting (2013)
100
Inform firefighters of hazards from Combustible Dust fires Useful tool for site emergency planning and fire department interaction
Combustible Dust Hazards and Mitigation
51
Page 101
National Fire Protection Association (NFPA) Standards GENERAL: 68: Guide for Venting of Deflagrations 69: Std. on Explosion Prevention Systems 91: Std. for Exhaust Systems for Air Conveying of
Vapors, Gases, Mists, and Noncombustible Particulate Solids (incorporated by reference into NFPA 61, 484, 654, 655, 664)
499: Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
Combustible Dust Hazards and Mitigation
Page 102
INDUSTRY SPECIFIC 61: Standard for the Prevention of Fires and Dust Explosion
in Agricultural and Food Processing Facilities 85: Boiler and Combustion Systems Hazards Code 86: Standard for Ovens and Furnaces 484: Standard for Combustible Metals 654: Std. for the Prevention of Fire and Dust Explosions
from the Manufacturing, Processing, and Handling of Combustible Particulate Solids
655: Standard for Prevention of Sulfur Fires and Explosions 664: Standard for the Prevention of Fires and Explosions in
Wood Processing and Woodworking Facilities
National Fire Protection Association (NFPA) Standards
Combustible Dust Hazards and Mitigation
52
Standards – Combustible Dust • NFPA 652 (NEW) –
Fundamentals (in development)
• NFPA 61 – Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities.
• NFPA 484 – Standard for Combustible Metals
• NFPA 654 – Standard for the Prevention of Fire and Dust Explosions from Manufacturing, Processing, and Handling of Combustible Particulate Solids
• NFPA 655 – Standard for Prevention of Sulfur Fires and Explosions
• NFPA 664 – Standard for the Prevention of Fire and Explosions in Wood Processing and Woodworking Facilities. 103
NFPA 652
NFPA 664
NFPA 61
NFPA 484
NFPA 655
NFPA 654
Combustible Dust Hazards and Mitigation
Page 104
ANSI/AIHA Z9 Standards (http://www.asse.org/shoponline/standards.php)
Z9.1 – Open Surface Tanks Ventilation and Operation
Z9.2 - Fundamentals Governing the Design and Operation of Local Exhaust Systems
Z9.3 - Standard for Spray Finishing Operations — Safety Code for Design, Construction, and Ventilation
Z9.4 - Abrasive-Blasting Operations — Ventilation and Safe Practices for Fixed Location Enclosures
Z9.5 - Standard for Laboratory Ventilation
Z9.6 - Exhaust Systems for Grinding, Polishing, and Buffing
Z9.7 - Recirculation of Air from Industrial Process Exhaust Systems Combustible Dust Hazards and
Mitigation
53
ANSI/AIHA Z9 Standards (http://www.asse.org/shoponline/standards.php)
Z9.9 BSR/AIHA (Draft) Portable Ventilation Systems
Z9.10 ANSI/AIHA -2008 Fundamentals Governing the Design and Operation of Dilution Ventilation Systems in Industrial Occupancies
Z9.11 ANSI/AIHA 2008 Laboratory Decommissioning Standard
Z9.12 BSR/AIHA Design, Operation, and Maintenance of Combustible Dust Collection Systems (in process)
Z9.13 BSR/AIHA Design, Operation, Testing, and Maintenance of Laminar Flow Fume Hoods
Z9.14 BSR/AIHA Methodology for Certification of a Biosafety Level - 3 (BSL-3) Lab
Page 105 Combustible Dust Hazards and
Mitigation
Industrial Ventilation, A Manual of
Recommended Design, 28th Edition, ACGIH,
2013 (Now in Imperial and SI Units)
Page 106
1. Exposure Assessment
2. Preliminary Design
3. Principles of Ventilation
4. General Industrial Ventilation
5. Design Issues – Systems
6. Design Issues - Hoods
7. Fans
8. Air Cleaning Devices
9. LEV System Design Calculation Procedures
10. Supply Air Systems
11. Energy Considerations
12. Cost Estimating
13. Specific Operations
Combustible Dust Hazards and Mitigation
54
Page 107
ACGIH Industrial Ventilation Manual Chapter 13 – Specific Operations
13.05-Battery Charging
13.10-Clean Rooms
13.15-Filling Operations
13.20-Foundry Operations
13.25-Gas Treatment
13.30-Kitchen Equipment
13.35-Laboratory Ventilation
13.40-Low Volume-High Velocity Exhaust Systems
13.45-Machining
13.50-Material Transport
13.55-Metal Melting Furnaces
13.60-Mixing
13.65-Moveable Exhaust Hoods
13.70-Open Surface Tanks
13.72 Push-Pull Ventilation
13.75-Painting Operations
13.80-Mech.Surface Cleaning and Finishing
13.85-Vehicle Ventilation
13.90-Welding and Cutting
13.95-Woodworking
13.99-Miscellaneous
Combustible Dust Hazards and Mitigation
Industrial Ventilation, A Manual of Recommended Practice for Operation & Maintenance, 1st Edit., ACGIH, 2007
Page 108
1. Construction & Project Management Phase
2. Commissioning and Proof of Performance
3. Testing and Measurement of Ventilation Systems
4. Balancing Duct Systems with Dampers
5. Ventilation System Monitoring & Maintenance
6. Monitoring & Maintenance – Air Cleaning Devices
7. Troubleshooting Ventilation Systems
8. Modifying Industrial Ventilation Systems
9. Operator Skills and Training
Combustible Dust Hazards and Mitigation
55
Page 109
Air Movement and Control Association (AMCA)
200: Air Systems
201: Fans and Systems
202: Troubleshooting
203: Field Performance Measurements of Fan Systems
410: Recommended Safety Practices for Air Moving Devices
Combustible Dust Hazards and Mitigation
Factory Mutual Global Property Loss Prevention Data Sheets
110
Insurance company guidance, not a standard. (Referenced in CD NEP.) Available for free download at: http://www.fmglobal.com/fmglobalregistration/
PLPDS pertinent to combustible dusts No. 7-76, Prevention and Mitigation of Combustible
Dusts and Explosions (2006) No.7-73, Dust Collectors and Collection Systems (2008) No. 10-3, Hot Work Management
Combustible Dust Hazards and
Mitigation
56
Page 111
National Institute for Occupational Safety and Health (NIOSH) Publications
Occupational Health Guidelines for Chemical Hazards http://www.cdc.gov/niosh/81-123.html
Hazard Control http://www.cdc.gov/niosh/hazcommn.html
Hazards Identification http://www.cdc.gov/niosh/hidlist.html
Site Index http://www.cdc.gov/niosh/siteindx.html#alpha
Combustible Dust Hazards and Mitigation
Page 112
Industrial Ventilation Design Guidebook
(1600 pgs,$200) (http://www.invent.hut.fi/)
1. INDUSTRIAL AIR TECHNOLOGY
2. TERMINOLOGY 3. DESIGN METHODOLOGY
OF INDUSTRIAL AIR TECHNOLOGY
4. PHYSICAL FUNDAMENTALS 5. PHYSIOLOGICAL AND
TOXICOLOGICAL CONSIDERATIONS
6. TARGET LEVELS 7. PRINCIPLES OF AIR AND
CONTAMINANT MOVEMENT INSIDE AND AROUND BUILDINGS
8. ROOM AIR CONDITIONING
9. AIR-HANDLING PROCESSES 10. LOCAL VENTILATION 11. DESIGN WITH MODELING
TECHNIQUES 12. EXPERIMENTAL
TECHNIQUES 13. GAS-CLEANING
TECHNOLOGY 14. PNEUMATIC CONVEYING 15. ENVIRONMENTAL
ASSESSMENT 16. ECONOMIC ASPECTS
Combustible Dust Hazards and Mitigation
57
Page 113
U.S.EPA Hazardous Air Pollutants
http://www.epa.gov/ttn/atw/hapindex.html
Maximum Achievable Control Technology (MACT) Rules Status http://www.epa.gov/ttn/atw/112j/info/112(j)-table2.html
Integrated Risk Information System http://www.epa.gov/iris/index.html
Pollution Prevention http://www.epa.gov/opptintr/p2home/
Pollutants/Toxics http://www.epa.gov/ebtpages/pollutants.html
Treatment/Control http://www.epa.gov/ebtpages/treatmentcontrol.html
EPA Method 204 – Criteria For and Verification of a Permanent or Temporary Total Enclosure
Combustible Dust Hazards and Mitigation
Protecting Worker Health
Thank you!
Upcoming AIHA Webinar
ISO 45001 – A Global OH&S Management System Standard
Monday, December 16, 2013
2:00 PM ET - 3:30 PM ET
This session will begin promptly at the scheduled start time. We appreciate your patience.