Hydrocarbon Processing - December 2022 - 61

Plant Safety and
Environment
P. PARSONS, Baker Engineering and
Risk Consultants Inc., San Antonio, Texas
Combustible dust hazards overview
There has been a significant increase
in the use of biomass as alternative energy
or green fuel in the last two decades.
Biomass comes in many forms and is
most commonly used for industrial applications
like the fabrication of wood chips
or wood pellets for fuel. Wood chips
and wood flour are also used to produce
chipboard, medium density fiberboard
and laminate flooring. The production of
these biomass products requires milling,
pressing, grinding and other processing
techniques that produce fine particulates.
In certain configurations, such particulates
can present a fire or explosion
hazard and must be handled appropriately
to prevent catastrophic loss.
The U.S. Occupational Safety and
Health Administration (OSHA) has increased
its focus on combustible dust
hazards. It issued the Combustible Dust
National Emphasis Program (NEP) in
2008 due to the number of catastrophic
fires and explosions caused by combustible
dust over the previous two decades.
The NEP describes OSHA's policies
and procedures regarding inspecting facilities
that handle combustible dust and
the administration's expectations regarding
owner/operator compliance with
U.S. safety standards [e.g., the National
Fire Protection Agency (NFPA)].
OSHA has determined that many facilities
handling combustible dust were
unaware of the associated hazards or
were confused by the requirements of
the existing commodity-specific standards
(e.g., NFPA 61,1
484,2
654,3
and/or 6555), with the NFPA 6644
6644
standard
specifically targeting the wood processing
industries. The NFPA, therefore,
recently developed and issued the Standard
on the Fundamentals of Combustible
Dust (NFPA 6526
), which is a governing
umbrella standard that addresses
fire and explosion hazards associated
with combustible dust of all types across
all industries to promote further awareness
and reduce confusion.
A main focal point of NFPA 6526
is the
requirement for facilities that process or
handle particulate solids to perform routine
dust hazard assessments (DHAs).
While several commodity-specific NFPA
standards have required a process hazard
analysis for more than a decade, NFPA
6526
goes a step further by making this
requirement retroactive for existing installations
and establishes a deadline to
have a DHA in place. A DHA is now required
for new and existing installations
and upgrades to existing installations.
The NFPA 6526
is given to dust collection systems and
associated equipment since such systems
are typically present at most particulate
solid handling facilities.
standard, which
came into effect on September 7, 2015,
allows affected facilities 5 yr to complete
a DHA. To put the importance of
a DHA in perspective regarding regulatory
compliance, the lack of combustible
dust hazard analysis is listed as a primary
transgression.7
In addition, recently, a
jury awarded $39.7 MM to a man injured
in a fire and explosion at a wood
processing facility in 2014. Many of the
investigation's findings would likely have
been captured in a DHA and could have
prevented the incident from occurring.
There are many approaches to conducting
a DHA, and the Annex of NFPA
6526
provides one example. The Center
for Chemical Process Safety's (CCPS's)
" Guidelines for combustible dust hazard
analysis " 8
provides perhaps the most current
and comprehensive overview of the
different DHA approaches available to a
facility. The most common issues identified
during many DHAs performed by
the author over the last several years are
detailed in the following sections. Focus
The lack of defined inspection and
cleaning plan to meet NFPA housekeeping
requirements. Dust explosions
may be classified as either primary
or secondary. Primary dust explosions
typically occur within individual equipment
inside process plants or similar enclosures
(baghouse, cyclone, grinder, etc.)
and are generally controlled by pressure
relief venting through purpose-built ducting.
Secondary dust explosions, which are
disturbed, suspended and ignited by the
primary explosion, result from dust accumulations
within facilities but outside of
the equipment, resulting in a more dangerous
uncontrolled explosion inside the
workplace. Loss history shows that most
injuries and fatalities from dust explosions
result from secondary dust explosions.
Therefore, controlling fugitive dust
emissions and housekeeping outside of
equipment is a focus of all combustible
dust-related standards and is the key to
reducing the potential for a catastrophic
event. For example, NFPA 6644
(the wood
industry-specific standard) defines a hazardous
location as an area where the accumulation
of combustible dust exceeds
1/8-in. A hazardous location is deemed to
exist if the total area of dust accumulations
exceeding the layer depth criterion
is greater than 5% of the enclosure footprint
area, or if the area of any single dust
accumulation exceeding the layer depth
criterion is greater than 1,000 ft2
.
NFPA 6526 (the umbrella standard)
requires that a facility manages dust accumulations
to meet the criteria of the
relevant commodity-specific standard
Hydrocarbon Processing | DECEMBER 2022 61
Hydrocarbon Processing - December 2022

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