9/16/2011
Ignition Control – Hazardous
Classified Locations
(NFPA-654, 499)
Samuel A.
A Rodgers,
Rodgers Honeywell
Electrical Area Classification
• Recognize a potential problem dust
- Visual evaluation initially
• Test the dust to verify it is a combustible dust
• Identify appropriate equipment surface temperature
limitation
• Classify the dust by Group E, F, G
• Identify classified areas in the field and on
equipment layouts
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2011 NFPA
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654 Combustible Dust Definitions
• 2006 Edition 3.3.4* 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.
• ROP - 3.3.4
3 3 4* Combustible Dust
Dust. A finely divided
combustible particulate solid that presents a flash
fire or explosion hazard when suspended in air or
the process specific oxidizing medium over a range
of concentrations.
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499 Combustible Dust Definition
• Finely divided solid particles that present a dust fire
or dust explosion hazard when dispersed and
ignited in air.
• The term 'solid particles' addresses particles in the
solid phase and not those in a gaseous or liquid
phase and can include hollow particles.
• Dust particles of 500 microns or smaller (material
passing a U.S. No. 35 Standard Sieve as defined in
ASTM E 11, Standard Specification for Wire Cloth
and Sieves for Testing Purposes) are considered to
present a dust fire or dust explosion hazard unless
determined otherwise.
• (See ASTM E 1226 or ISO 6184/1.)
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2011 NFPA
Material Form Testing
Yes
ASTM
E2021 –
Layer
Ignition
Ignites
Use Layer Temp
to choose
equipment
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ASTME1226 – Is
the material
form
Combustible
Dust?
Melts or Sublimes –
Apply Cloud Ignition
Explosion
Severity or
Ignition
Sensitivity
No
Hazardous
Area
Classification is
not necessary
ASTM
E1491 –
Cloud
Ignition
Ignites
Use Cloud Temp
to choose
equipment
2011 NFPA
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More Dusts are now included
• 5.7.2.5.2 Where materials being used are not listed
in Table 4.5.2 or in other reputable chemical
references, the information needed to classify the
area can be obtained by one of the following
methods:
(1) Contact the material supplier to determine if the material
has been group classified.
(2) Have the material tested to determine if the ignition
sensitivity is less than 0.2 and the explosion severity is less
than 0.5. Area classification is not considered necessary for
dusts that meet both criteria.
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499 Dust Groups
• Group E – Atmospheres containing combustible
metal dusts, including aluminum, magnesium and
their commercial alloys, or 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 (ASTM D3175)
• Group G - Atmospheres containing combustible
dusts not included in Group E or F, including flour,
grain, wood, plastic, and chemicals.
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3 Conditions for Dust Ignition
• Dust Cloud
- Ignitible mixture of dust suspended in air and present in the
vicinity of electrical equipment
- Source of thermal or electrical energy sufficient to ignite the
suspended mixture
• Dust Layer
- Dust layered thickly enough on the electrical equipment to
interfere with the dissipation of heat and allow the layer to
reach the ignition temperature of the dust
- External temperature of the electrical equipment high
enough to cause the dust to reach its ignition temperature or
to dry it out so the dust self-heats
• Group E
- Group E dust layered or in suspension as above
- Current through the dust sufficient to cause ignition
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Division 1 vs 2
• Dust Cloud
- Normal or frequent presence of dust cloud – Div 1
- Abnormal operation simultaneously causing dust cloud and
ignition source – Div 1
- Abnormal presence of dust cloud – Div 2
• Dust Layer
- Div 1 - Dust > 1/8” and less than ASTM E2021 test depth
(1/2”)
- Div 2 - Surface color not discernible and < 1/8”
• Group E
- Div 1 – Normal or abnormal presence of dust cloud
- Div 1 – Surface color not discernible and less than ASTM
E2021 test depth
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Typical Diagrams – Open or Semi-Enclosed
Groups F & G
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Group E
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2011 NFPA
Typical Diagrams – Enclosed
Groups F & G
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2011 NFPA
Additional NFPA 654 Equipment Guidance
Depth of Dust
Accumulation (in.)
Frequency
Housekeeping Requirement
Area Electrical
Classification
Negligiblea
N/A
N/A
Unclassified (general
purpose)
Infrequentc
Clean up during same shift.
Unclassified (general
purpose)
Continuous /
frequentd
Clean as necessary to
maintain an average
accumulation below 1/64 in.
in e
Clean up during same shift.
Unclassified; however,
electrical enclosures
should be dusttight
dusttight.f,g
fg
Unclassified; however,
electrical enclosures
should be dusttight.f,g
Class II, Division 2
Negligible to
<1/
32b
Negligible to <1/32b
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1/
32
to 1/8
Infrequentc
1/
32
to 1/8
Continuous /
frequentd
>1 / 8
Infrequentc
>1 / 8
Continuous /
frequentd
Clean as necessary to
maintain an average
accumulation below 1/16 in.
Immediately shut down and
clean.
Clean at frequency
appropriate to minimize
accumulation.
2011 NFPA
Class II, Division 2
Class II, Division 1
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499 Housekeeping Recommendations
Depth of Dust
Accumulation on
Equipment
Area
Release
Classification Frequency
Housekeeping Activity
Negligible and to < 1/32 in.
(1 mm)
Unclassified
Infrequent
Clean up as appropriate
Up to 1/8 in. (3 mm)
Class II,
Division 2
Infrequent
Clean as necessary to maintain
less than 1/8 in. (3 mm)
Layer up to 1/8 in. (3 mm)
or occasional cloud
formation
Class II,
Division 1 or
Division 2
Occasional
Clean at frequency appropriate
to minimize additional dust
accumulations or formation of a
cloud
Layer that [is] >1/8 in. (3
mm) to layer test value, or
presence of dust cloud
Class II,
Division 1
Continuous /
frequently
Clean at frequency appropriate
to minimize additional dust
accumulations
Exceeds layer test value,
or presence of extensive
dust cloud
Class II,
Division 1
Infrequent
Immediate shutdown and clean
equipment
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Recognize the Hazard
• Changes often occur over time
• Exhaust Systems become overextended
• Dust Accumulation becomes the Norm
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Prudent Approach for Existing Facilities
1. Clean – Housekeeping is the obvious immediate
action
2. Investigate – Determine if dust containment or
dust mitigation has failed
3 Implement – Engineered solutions to improve
3.
containment and/or mitigation
4. Re-evaluate Housekeeping – Is it achievable
5. Upgrade Electrical – Last
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Housekeeping Record
Post-Cleanup Report
Were dust clouds generated during
clean-up activities? If so, please
describe.
Any issues with
tools/equipment/access? If so,
please describe.
describe
Yes
No
Comments:
□ □
Comments:
□ □
Date: _______Manpower: ________Start Time: _______Stop Time ______
Pounds Collected (VERY IMPORTANT): ____________________________
Describe the area that you cleaned: ________________________________
Completed By: ________________________
Rodgers
Forward completed form
to Operations Leader
2011 NFPA
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Initial Evaluation
Class 2 Division 1 Group G
Class 2 Division 2 Group G
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Before Modifications
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After Modifications
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Final Evaluation
Non--classified
Non
Class 2 Division 1 Group G
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Dust now Contained in the Process Equipment
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