Hazard Risk
Analysis for Dust Collection Bins, baghouses, separators and ducts
Contributing causes for static electricity and its
discharge:
1. Bonding &
Grounding- all processes must be thoroughly grounded or bonded to a source
which is grounded. Difference in potentials
from negative to positive surfaces my lead to static discharge and arc across
the separation.
2. Conductive material usage- non-conductive material may
hold static without a normal dissipation conduit may lead to discharge in
contact with opposite potential. Do not
use material such as plastic, wood etcetera.
All metal non-sparking conductive material should be used for hazardous
atmospheres.
3. Choices for over-garments- the use of nylon,
polypropylene or other static forming material must be avoided, use only
materials which are safe for the atmosphere. (e.g. Cotton coveralls, Nomex
blended coveralls, Armid fabrics same as used in dust collection bags)
4. Humidity and temperature variations- association to
the temperature and relative humidity must be managed appropriately as certain environments
are supportive of static electrical build-up.
5. Loose or partially separated components- make sure all
components are clearly bonded, when necessary to provide a collection bin the
bin, down chute and other components must be thoroughly fasten together with no
intermittent connectivity.
6. Contaminants- when working with powder accumulations
it is important to be able to identify contaminants in the system, such as
carbon or foreign metals such as rust or iron and other metals which form other
hazardous mixtures.
7. Protective coatings- damage to protective coating
material of process units may lead to rust or accumulation and should be
avoided, where possible the parts which are damaged should be treated to
prevent corrosion.
8. Build-up of powder particulate- it is essential to
prevent build up of material in particularly on exhaust fan units and in the
duct work around elbows. The joins
should be over-lapped in the direction of flow.
Units should be inspected periodically for the build-up, electrical
connections inspected weekly. Grounding
and bonding checked at least daily by operators.
Baghouses:
Risk: Potential: Outcome: Controls:
Ungrounded High Arc/spark Operator Inspection
Daily
Bonding High Arc/spark Operator Inspection
Daily
Moisture/ Med Accumulation Operators/Maintenance weekly
low
Moisture/ High Accumulation/ Operators/Maintenance,
hazardous waste
High off-gas,
formation weekly or during
canister pick-up
Electrical High Arc/spark Maintenance/operators
weekly
Training High Injury/fatality Periodic training necessary
Maintenance Med Equipment failure Periodic maintenance, cleaning,
housekeeping
Repairs w/ High Spark/arc Unit must be thoroughly
cleaned, wiped down
hot work prior
to start up and after, cap off duct work
Cleaning High Static arc Tools, garments and
entry must be supervised,
Safety
briefing conducted and unit inspection,
Cap
off duct work
Duct work High Accumulation Periodic inspection of all
duct work must be
done
Separators:
Where necessary to use separators to extrude products
from those which will be collected and is finely grained (fines), bonding of
the process is necessary and periodic inspection and maintenance performed.
Bins:
For this purpose bins will be defined as the collection receptacles
necessary for storage of waste material.
It is necessary to have properly sealed bins when in operation and
during cleaning processes. The bins must
be thoroughly bonded to a grounded source at all times.
Ducts:
Inspection of ducts is necessary to prevent build-up and
accumulation of product in the ducts.
The duct work should always be over-lapped in the direction of flow,
limit the number of bins and kept as smooth as possible. During maintenance or repair work, the ducts
may be required to be capped to separate the processes in order to prevent
return of hazardous gas, vapor or flame back to the process facility.
Duct work within the process facilities should be periodically
inspected and cleaned as necessary to prevent build-up of fines.
New processes for metal dust collection:
Dust baghouses must be separated from the facility at sufficient
distances to allow for deflagrations, and all baghouses must meet or exceed
OSHA and NFPA recommendations for venting for deflagrations. Venting must be away from personnel and/or
the facility as to prevent propagation should an incident occur. Proper grounding of the unit must be incorporated
in the planning and implementation regardless of where the unit is
located. Risk evaluations should be made
to determine hazards and training be provided to those who shall be required to
operate or conduct maintenance on the units.
Lessons learned should be incorporated into the training process.
Aluminum powder:
Considered explosive in the air at or around 75 micron
per cubic meter, where the particulate gain size is below 500 micron.
1. The product must be combustible
2. Suspended in air
3. Fine enough to propagate sustainment of fire
4. Ignition source with enough energy to ignite
5. Concentration levels approximately 75 micron
6. Enough oxygen or another oxygen source to sustain
combustion
Moisture with aluminum powder (water) may cause
liberation of hydrogen gas and formation of aluminum hydroxide mixtures. Firefighting measures should be determined in
advance when dealing with collections of bulk aluminum powder. Whereas, the water from firefighting may
cause an undesired effect with aluminum powder, causing the rapid liberation of
hydrogen gas and is accelerated when using chlorinated products, such as found
in some dry chemical fire extinguishers.
Special cautions should be taken where the extinguishment agent shall
cause loose powder product to become airborne.
Diversion if direct stream method may be necessary with high pressure
units.
James Breedlove
CFI, CFO
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