Grain Handling –
Dust
Explosion
Hazards
Paul Schlumper
Georgia Tech Research Institute
404-407-6797
Dust Explosion
Requirements
Fuel
Ignition
Dispersion
Confinement
Adapted from CSB
Oxygen
Dust explosion in a work area
Dust
Dust settles on flat
surfaces
Some event
disturbs the
settled dust
into a cloud
Adapted from CSB
Dust cloud is
ignited and
explodes
Dust explosions
An initial (primary) explosion in
• processing equipment or in an area
where fugitive dust has accumulated
• may shake loose more accumulated dust, or
• damage a containment system (such as a
duct, vessel, or collector).
• The additional dust dispersed into the air may
cause one or more secondary
explosions.
• These can be far more destructive than a
primary explosion
Particles and Powders
Size
• Pellets
> 2mm diameter
• Granules
0.42mm and 2mm,
and
• dust particles
< 0.42mm
(420μm)
Hazard increases as particle size
decreases
• larger surface area for combustion
• Fine particle may have a larger role in
dust cloud ignition and explosion
propagation.
Facility Analysis Components
Carefully identify:
• Materials that can be
combustible when finely divided;
• Processes which use, consume,
or produce combustible dusts;
• Open areas where combustible
dusts may build up;
• Hidden areas where
combustible dusts may
accumulate;
• Means by which dust may be
dispersed in the air; and
• Potential ignition sources.
Facility Analysis Components
Identify and follow the applicable
federal, state, and local laws
and regulations. Some
commonly applicable mandatory
requirements
29 CFR 1910
• OSHA General Duty Clause and
Standards
• The International Code Council’s
International Fire Code®
• NFPA’s Uniform Fire Code®.
– Local building codes frequently adopt NFPA
dust standards by reference
Dust Combustibility
The primary factor in an
assessment of these
hazards is whether the
dust is in fact
combustible.
*Determine if a dust cloud will:
•
•
•
•
Detonate
Deflagrate
Present a fire hazard
Or will Not burn or ignite
Testing may be necessary
See
Explosives
regulations
Dust Combustibility
Combustible dust per NFPA 654
• Prior to 2006 - “Any finely divided solid material that is 420 microns
or smaller in diameter (material passing a U.S. No. 40 Standard Sieve)
and presents a fire or explosion hazard when dispersed and ignited in
air.”
• *2006 Edition – 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.
Agricultural Dust per NFPA 61
• Any finely divided solid agricultural material 420 microns or smaller
in diameter that presents a fire or explosion hazard when dispersed and
ignited in air.”
Dust Combustibility
*25 watt light bulb
probably can not be seen
through ten feet of a
combustible dust mixture
What
bulb
?
2 meters
40 g/m3 concentration of
comb. dust suspended in air
25 watts
Glass
Glass
What is wrong here?
Electrical classification
• OSHA Electrical standard (29
CFR Part 1910 Subpart S)
• NFPA 70, the National
Electrical Code®.
• NFPA 499, . . . Classification of
Combustible Dusts and of
Hazardous (classified)
Locations for Electrical
Installations in Chemical
Process Areas.
Electrical
Equipment
Class
Division
Division
Group
II
1
2
E
F
G
CPL 03-00-008 – National Emphasis Program
“immediate cleaning is
warranted whenever a dust
layer of 1/32-inch thickness
accumulates over a surface
area of at least 5% of the
floor area of the facility or
any given room.”
NOTE: 1910.272 stipulates
1/8 inch for Grain Dust
Dust Control
NFPA 654 - contains
comprehensive guidance
Some of its
recommendations:
 Minimize the escape of
dust from process
equipment or ventilation
systems;
 Use dust collection
systems and filters;
 Utilize surfaces that
minimize dust
accumulation and facilitate
cleaning;
Spots are
not
raindrops
Dust Control
NFPA 654 –
guidance
• Provide access
to all hidden areas
to permit
inspection;
• Inspect for dust
residues in open
and hidden areas,
at regular
intervals;
• Clean dust
residues at regular
intervals;
?
Dust Control
NFPA 654 – guidance
• Use cleaning methods
that do not generate
dust clouds, if ignition
sources are present;
• Only use vacuum
cleaners approved
for dust collection;
HAZ LOC
Classified Electrical
Ignition Control
NFPA 654, identifies
comprehensive
guidance
• Use appropriate
electrical equipment and
wiring methods;
• Control static electricity,
including bonding of
equipment to ground;
• Control smoking, open
flames, sparks;
No!
Yes!
Ignition Control
NFPA 654 - guidance
• Control mechanical
sparks and friction;
• Use separator devices
to remove foreign
materials capable of
igniting combustibles from
process materials;
• Separate heated
surfaces from dusts;
Non - Magnetic
rotating drum
Magnetic
Core
Ignition Control
Hot
work
permit
NFPA 654 - guidance
• Separate heating
systems from dusts;
_________
_________
_________
_________
• Proper use and type
of industrial trucks;
• Proper use of
cartridge activated
tools; and
• Adequately maintain
equipment.
Kaboom!
Grinder
Ignition Control
Other ignition
sources
Use appropriate Class II
Electrical equipment and
wiring methods where
required
OSHA 29 CFR 1910.178 (c)
regulates powered
industrial trucks in dust
areas
Coal handling operations
must comply with OSHA
29 CFR 1910.269
Class I & II
Group D & G
Training
Employees need to be
trained
• To recognize and
prevent hazards
associated with
combustible dust
• In taking preventative
action, and/or
• How to alert
management.
Hazardous
vertical surface
accumulation
Training
Management Responsibility
• Comply with the Hazard Communication Standard
• Have a qualified team conduct a facility analysis
(or have one done by qualified outside persons) prior to
the introduction of a hazard and
• Develop a prevention and protection scheme
tailored to the operation.
List of
Chemicals
NFPA Standards – Dust Hazards
61 Standard for the Prevention of Fires and
Dust Explosions in Agricultural and Food
Processing Facilities
68 Deflagration Venting Systems
69 Explosion Prevention Systems
70 National Electric Code
77 Static Electricity
85 Boiler and Combustion
Systems
86 Ovens and Furnaces
91 Exhaust Systems
NFPA Standards
Electrical & Systems
484 Combustible Metals
Includes Magnesium, Titanium, Zirconium, Aluminum,
Tantalum and other reactive metals
499 Classification of Combustible Dust
654 manufacturing, Processing and Handling of
Combustible Particulate Solids
655 Sulfur
664 Wood
and more
1910.272 – Grain Handling Facilities
(Promulgated in March 1988)
•
•
•
•
•
•
•
•
(a) – Scope
(b) – Application
(c) – Definitions
(d) – Emergency Action
Plan
(e) – Training
(f) – Hot Work Permit
(g) – Entry Into Grain
Storage Structures
(h) – Entry Into Flat
Storage Structures
•
•
•
•
•
•
•
•
•
(i) – Contractors
(j) – Housekeeping
(k) – Grate Openings
(l) – Filter Collectors
(m) – Preventive
Maintenance
(n) - Grain Stream
Processing Equipment
(o) – Emergency Escape
(p) – Continuous-Flow Bulk
Raw Grain Dryers
(q) – Inside Bucket
Elevators
Application of Standard
 Sections (a) – (n)
 Apply to all grain handling
operations, such as elevators,
mills, etc.
 Sections (o) – (q)
 Apply to grain elevator
operations only.
Hot Work Permit
• Hot Work Permits
•
•
•
•
Written
Authorized by Employer’s Representative
Meet requirements of 1910.252(a)
Kept on file until completion of operations
• Exceptions
• Authorizing agent is present
• Authorized welding shop
• Authorized hot work area – outside of grain facility
Contractor Information
• Fire Hazards
• Explosion Hazards
• Safety Rules of the Facility
• Emergency Action Plan
Housekeeping
• Housekeeping Program
• Written
• Establish Frequency and Methods to Reduce
Accumulations:
•
•
•
•
Ledges
Floors
Equipment
Other Exposed Surfaces
• Priority Housekeeping Areas, including at least the
following:
• Floor areas within 35 feet (10.7 m) of inside bucket elevators;
• Floors of enclosed areas containing grinding equipment;
• Floors of enclosed areas containing grain dryers located inside the
facility.
• Important: Fugitive grain dust accumulations exceeding 1/8 inch
shall be removed immediately from priority housekeeping areas.
Housekeeping
Housekeeping
• Compressed Air can be used for cleaning IF:
• Machinery in area shut-down
• All other potential ignition sources shut-down and/or removed.
Housekeeping
Housekeeping
Dust Collection Systems
• Fabric Dust Filter Collectors
•
•
•
•
Pressure drop monitoring device
Located outside of facility, OR
Protected by an Explosion Suppression System, OR
Protected by Fire-Resistant Construction
Preventive Maintenance
• Equipment:
•
•
•
•
Dryers
Grain Stream Processing Equip.
Dust Collection Equipment
Bucket Elevators
• Preventative Maintenance
• Regularly scheduled inspections
• Mechanical
• Safety Control Equipment
• 1910.272(m)(1) The employer shall implement preventive maintenance
procedures consisting of:
• Lubrication and other appropriate maintenance
• Prompt correction of:
• Malfunctioning dust collection systems
• Inside bucket elevator failures:
• Overheated bearings and/or slipping/misaligned belts
• Certified Inspection Record
• LOTO
Grain Stream Processing Equipment
• Grain stream processing equipment shall be equipped
with an effective means of removing ferrous material
from the incoming grain stream.
Continuous-Flow Bulk Raw Grain Dryers
• All direct-heat grain dryers shall be equipped with automatic
controls that:
– Will shut-off the fuel supply in case of power or flame failure or
interruption of air movement through the exhaust fan; and,
– Will stop the grain from being fed into the dryer if excessive
temperature occurs in the exhaust of the drying section.
• Direct-heat grain dryers installed after March 30, 1988 shall
be:
– Located outside the grain elevator; or
– Located in an area inside the grain elevator protected by a fire or
explosion suppression system; or
– Located in an area inside the grain elevator which is separated
from other areas of the facility by construction having at least a
one hour fire-resistance rating
Inside Bucket Elevators
• Bucket elevators shall not be jogged to free a
choked leg.
• Belts and lagging shall be conductive
• < 300 Megaohms electrical resistance rating
• Bucket elevators shall have a means of access to:
• Head pulley area
• Boot area
Inside Bucket Elevators
•Bearing are to be mounted external to leg casing
 Bearing monitoring device is required
Belt monitoring
 Motion detection device – to indicate choking condition
 Belt alignment device
Hazard Monitoring Devices
 Sample Motion Probe
Located on Tail Shaft of
Bucket Elevator
Hazard Monitoring Devices
 Bearing Temperature
Monitoring
 Sample Display
 Internal Hot Bearing Sensor
Installed Through Grease
Fitting
Hazard Monitoring Devices
 Belt Alignment Monitoring
NFPA 61 – Standard for the Prevention of
Fires and Dust Explosions in Agricultural
and Food Processing Facilities
 1-Administration
 2-Referenced Publications
 3-Definitions
 4-Construction
Requirements
 5-Ventilation and Venting
 6-Explosion Prevention,
Relief, and Venting
 7-Equipment
 8-Dryers
 9-Heat Transfer
Operations
 10-Dust Control
 11-Pneumatic Conveying
 12-Building Fire
Protection
 13-Supplemental
Requirements
QUESTIONS?