Chemical Engineering May 2016 - 77

Figure 3. While housekeeping is important, facilities should focus on containing and collecting potentially
flammable or explosive dust from the processes that handle or generate fine powdered materials.
These include such common, seemingly innocuous materials, such as sugar, flour and sawdust
standards that would apply to different
facilities. Over time these earlier,
industry-specific standards will become
more aligned with NFPA 652.
The primary focus of NFPA 652 is
to help all facilities to identify where
hazards exist due to the presence
or handling of combustible or potentially
explosive materials. In order to
do this, a qualified person will need
to conduct a dust hazard analysis
(DHA). To conduct a DHA, a facility
will need to develop a sampling
plan to coordinate the collection and
analysis of dust samples throughout
the facility. This will allow the facility
to identify and evaluate areas where
combustible dust hazards exist.
Once all potentially hazardous
areas and process equipment have
been identified and a DHA has been
completed, the facility should work
to reduce the likelihood of a flash
fire or explosion from occurring. It
should also implement procedures
or equipment to mitigate the hazards
associated with a combustible dust
fire or explosion.
If possible, the facility should work
to contain and collect combustible
dust, by both preventing fugitive
dust from being discharged from
equipment and by installing an effective
dust-collection system throughout
the process areas that handle
combustible dust. The facility should
develop a management system that
monitors how hazards relating to
combustible dust are being controlled.
Facilities
should also provide train76
ing
to employees and contractors.
Such training should focus on both
general safety regarding the hazards
associated with combustible dusts,
and on any job-specific training
relating to their specific work
environments.
Hazard identification and DHA
NFPA 652 includes procedures that
all facilities can follow in order to
identify areas where potential combustible-dust
hazards exist. Dust
samples should be collected from
throughout the facility (Figure 2), in
order to determine the combustible
or potentially explosive qualities of
the dust. To carry out such sampling,
all facilities are required to create a
plan that should include the following
[1]:
* Identification of locations where
fine particulate materials and dusts
are present
* Collection of representative
samples
* Methods to ensure preservation of
sample integrity
* Communication with the test laboratory
regarding proper samplehandling
procedures
* Documentation of samples taken
* Safe sample-collection practices
Following a rigorous sampling plan
will help facility operators to ensure
that the dust samples are accurately
analyzed to determine if they are
combustible or potentially explosive.
Once dust samples have been
collected and tested, if any of the
materials are identified as being
combustible or potentially explosive,
the facility should then complete a
DHA, to identify and evaluate the potential
hazards associated with a fire
or explosion due to the combustible
materials handled throughout the
facility. Inspections of areas where
combustible dust is handled also
allow facility operators to develop
recommendations to minimize the
risks of a combustible-dust incident.
Specifically, a DHA should include
the following [1]:
* Identification and evaluation of locations
or processes throughout
the facility where hazards resulting
from a potential fire, flash fire or
explosion exist
* Identification and evaluation of
specific fire and deflagration scenarios
where fire and explosion
hazards exist
* Identification of safe operating
ranges
* Identification of any safeguards
that are in place to mitigate the
hazards of a fire or explosion
* Recommendations for additional
safeguards, where needed
The DHA must be completed or led
by a qualified person who has demonstrated
the ability to understand
combustible dust and associated
hazards through education or experience
[1]. This qualified person
should inspect all buildings and processes
to determine the potential
likelihood of a fire or explosion due
to the presence of combustible dust.
This is determined by understanding
the properties associated with
the potentially combustible dusts
that are handled in the building or
process, identifying all potential ignition
sources, and evaluating the effectiveness
of any deflagration-suppression
or protection systems that
are currently in place.
Mitigating hazards
Once a DHA has been completed by
a qualified person, the facility should
begin to implement any recommendations
made, to prevent or minimize
the hazards. Often times, updated
housekeeping procedures are the
first actions facilities can take - for
instance, to remove excessive dust
accumulation in rooms and buildings
(Figure 3). However, this requires
extra labor and is often not as effective
as expected.
For example, certain inaccessible
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