• Establishing written management systems and procedures for operating the facility and equipment to prevent
or mitigate fires, deflagrations and explosions from combustible particulate solids.
Dust Hazard Analysis (DHA) is a systematic review to
identify and evaluate the potential fire, flash fire, and explosion hazards associated with the presence of combustible
particulate solids in a process or facility, and to determine
what safeguards could be implemented to prevent or mitigate the hazards. DHA must be conducted by someone who,
by education, certificate, professional standing, or skill and
who, by knowledge, training, and experience, has demonstrated the ability to deal with problems related to processing and managing combustible particulate solids.
A DHA does not need to comply with the Process Hazards
Analysis (PHA) requirements of the OSHA regulation, 29 CFR
1910.119 (e). NFPA 652 requires that for existing processes
that are not undergoing material modification, exceeding 25
percent of the original cost, the owner/operator shall schedule and complete dust hazards analyses (DHA) within a
three-year period of the effective date of the standard.
Additionally, the DHA should be periodically reviewed and
updated to reflect changes to the process, the equipment,
and process materials, as well as any new learnings related
to operational safety to ensure that the DHA continues to
the resulting fireball can cause significant damage and severe
injury to personnel.
The new NFPA 652 requires the owner/operator of a facility
with potentially combustible dusts to determine whether the
materials that they are handling/processing are combustible
or explosible and, if so, to characterize their ignition sensitivity and explosion severity properties, as required to support
the dust hazard assessment (DHA).
NFPA 652 further states that the evaluation of the hazard
of a combustible dust should be determined by the means
of actual test data. Where dusts are determined to be combustible or explosible, additional testing shall be performed
to acquire the data necessary to support the compliance requirements of this standard.
The testing requirements will vary depending upon the
process operations, but relevant data typically includes the
Deflagration Index (Kst), Minimum Ignition Energy (MIE),
Minimum Ignition Temperature (MIT), Minimum Explosible
Concentration (MEC) and Limiting Oxygen Concentration (LOC).
If the material is determined to be sensitive to ignition
from electrostatic sources (i.e. typically having an MIE of
less than 25 mJ), electrostatic properties such as the Volume
Resistivity and Chargeability (mass charge density) of the
powder should also be considered.
NFPA 652 allows the use of historical facility data or
published data only if it is deemed to be representative of
current materials and process conditions. However, as these
properties are strongly dependent upon specific parameters
such as particle size, moisture content, oxidant concentration
and the presence of flammable vapors, caution should be exercised in its use.
Specific particle shape and size distribution will vary from
operation to operation and can make a significant difference
in explosion properties. If a deflagration hazard is suspected,
it is recommended that a qualified laboratory determine
these explosion properties via experiments, using site-spe-cific samples.
DUST DEFLAGRATION HAZARDS IN OSD
When handling combustible solid materials, a deflagration
hazard is present whenever fine powder particles (dust)
become suspended in air. This may be intentional, for example during fluidized bed drying, or unintentional, such as
powder transfer to vessels or powder blending. NFPA 562
requires that the safety of the occupants, facility, processes,
and equipment shall be achieved by either a prescriptive approach or a performance-based design approach.
The prescriptive approach involves:
• Determination of the combustibility/explosibility charac-
teristics of process dusts and powders.
• Performing a Dust Hazard Analysis (DHA).
• Conducting a documented risk assessment to determine
the level of building design and protection features