Document ID: OSHA-2009-0023-0162
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-08-23T04:00Z

Site Visits Related to Combustible Dust:

Facility K–Sweetener Manufacturer

	Prepared for:

U.S. Department of Labor

	Occupational Safety and Health 

Administration

	Directorate of Standards and Guidance

	

	Prepared by:

	Eastern Research Group, Inc.

Lexington, MA 02421

(October 5, 2009)

Table of Contents

  TOC \o "1-5" \h \z \u    HYPERLINK \l "_Toc243113392"  1	Project
Overview	  PAGEREF _Toc243113392 \h  1  

  HYPERLINK \l "_Toc243113393"  2	Facility Description	  PAGEREF
_Toc243113393 \h  2  

  HYPERLINK \l "_Toc243113394"  3	Process Descriptions	  PAGEREF
_Toc243113394 \h  3  

  HYPERLINK \l "_Toc243113395"  3.1.	Sweetener Manufacturing	  PAGEREF
_Toc243113395 \h  3  

  HYPERLINK \l "_Toc243113396"  3.2.	Sweetener Packaging and Milling	 
PAGEREF _Toc243113396 \h  9  

  HYPERLINK \l "_Toc243113397"  3.3.	Sweetener Warehousing	  PAGEREF
_Toc243113397 \h  11  

  HYPERLINK \l "_Toc243113398"  4	Document Review	  PAGEREF
_Toc243113398 \h  11  

  HYPERLINK \l "_Toc243113399"  4.1.	Testing Data	  PAGEREF
_Toc243113399 \h  11  

  HYPERLINK \l "_Toc243113400"  4.2.	Material Safety Data Sheets (MSDSs)
  PAGEREF _Toc243113400 \h  12  

  HYPERLINK \l "_Toc243113401"  4.3.	Housekeeping Checklists	  PAGEREF
_Toc243113401 \h  13  

  HYPERLINK \l "_Toc243113402"  4.4.	Process Hazard Analyses	  PAGEREF
_Toc243113402 \h  13  

  HYPERLINK \l "_Toc243113403"  5	Training and Employee Awareness	 
PAGEREF _Toc243113403 \h  14  

  HYPERLINK \l "_Toc243113404"  5.1.	Operator Training	  PAGEREF
_Toc243113404 \h  15  

  HYPERLINK \l "_Toc243113405"  5.2.	Contractor Training	  PAGEREF
_Toc243113405 \h  15  

  HYPERLINK \l "_Toc243113406"  5.3.	Safety Video for Facility Visitors	
 PAGEREF _Toc243113406 \h  15  

  HYPERLINK \l "_Toc243113407"  5.4.	Employee Interviews	  PAGEREF
_Toc243113407 \h  16  

  HYPERLINK \l "_Toc243113408"  6	Safety Programs	  PAGEREF
_Toc243113408 \h  16  

  HYPERLINK \l "_Toc243113409"  6.1.	Emergency Response	  PAGEREF
_Toc243113409 \h  16  

  HYPERLINK \l "_Toc243113410"  6.2.	Confined Space Entry	  PAGEREF
_Toc243113410 \h  16  

  HYPERLINK \l "_Toc243113411"  6.3.	“Hot Work” Permits	  PAGEREF
_Toc243113411 \h  17  

  HYPERLINK \l "_Toc243113412"  6.4.	Management of Change	  PAGEREF
_Toc243113412 \h  18  

  HYPERLINK \l "_Toc243113413"  6.5.	Personal Protective Equipment (PPE)
and Uniforms	  PAGEREF _Toc243113413 \h  18  

  HYPERLINK \l "_Toc243113414"  6.6.	Fire Protection	  PAGEREF
_Toc243113414 \h  18  

  HYPERLINK \l "_Toc243113415"  7	Main Findings	  PAGEREF _Toc243113415
\h  18  

  HYPERLINK \l "_Toc243113416"  8	Feedback to OSHA	  PAGEREF
_Toc243113416 \h  20  

  HYPERLINK \l "_Toc243113417"  9	References	  PAGEREF _Toc243113417 \h 
21  

 

Table 1			Overview of Facility K’s Dust Collectors

Table 2			Testing Parameters Reported for Three Milled Products and Two
Reference Materials

Figure 1		Photograph of a Rotary Dryer

Figure 2		Photograph of Dust Accumulation Due to Leaking Fitting on a
Sifter

Figure 3		Photograph of Building Exterior Showing Outlets from Two
Explosion Vents

Figure 4		Photograph of Explosion Venting Ductwork from a Baghouse 

Figure 5		Photograph of Product Storage Bag

Figure 6		Photograph of Explosion Vent Outlet

Attachment 1	Housekeeping Checklist for Sweetener Production Line #1

Attachment 2	Housekeeping Checklist for Sweetener Production Line #2

Attachment 3 	Housekeeping Checklist for Milling Room

Abbreviations

ERG		Eastern Research Group, Inc.

GMP		Good Manufacturing Practice

MEC		minimum explosible concentration

MIE		minimum ignition energy

MSDS		Material Safety Data Sheet

NFPA		National Fire Protection Association

OHSAS	Occupational Health and Safety Assessment Series

OSHA		Occupational Safety and Health Administration

PPE		personal protective equipment

SCFM		stan慤摲挠扵捩映敥⁴数⁲業畮整

μm			micron (or micrometer) 

Project Overview 

On April 14 and 15, 2009, Eastern Research Group, Inc. (ERG) conducted a
2-day site visit to a sweetener manufacturer (hereafter referred to as
“Facility K”). The site visitors included two ERG employees (a
chemical engineer and a safety engineer) and one consultant (a
combustible dust expert). The purpose of this site visit was to obtain
facility-specific information on combustible dust recognition,
prevention, and protection programs, and to relay notable findings and
other facility feedback to the Occupational Safety and Health
Administration (OSHA). Site visit activities included touring facility
operations, reviewing relevant documentation, and interviewing employees
who work in areas with combustible dust. No samples were collected
during this site visit. 

The purpose of this report is strictly to document observations made
during the site visit, which may not reflect facility conditions at
other times. The site visit was not designed to assess Facility K’s
compliance with OSHA regulations or adherence to National Fire
Protection Association (NFPA) consensus standards, and should not be
used to make such assessments. The site visit focused on safety issues
pertaining to combustible dust and was not intended to be a
facility-wide evaluation of all OSHA regulations (e.g., means of egress,
fire protection, powered platforms, process safety management, etc.).
The remainder of this report is organized into the following sections:

Table 1. Organization of Report

Section	Title	Contents

2	Facility Description	General information about Facility K, such as its
main products, operational history, and number of employees.

3	Process Descriptions	Descriptions of the production processes that ERG
toured, with a focus on combustible dust safety issues; section includes
information on process-specific controls, housekeeping practices, and
equipment cleaning procedures. 

4	Document Review	Summary of various facility documents pertaining to
combustible dust safety issues.

5	Training	Review of Facility K’s training programs.

6	Safety Programs	Summary of the extent to which combustible dust
factors into emergency response, confined space entry, and other safety
programs.

7	Main Findings	Key observations made by the site visit team. 

8	Feedback to OSHA	Feedback that Facility K representatives wished to
communicate to OSHA as it decides how to pursue combustible dust issues.

9	References	Full references for documents cited throughout the report. 

 

Facility Description

Facility K has three main production lines that manufacture different
sweetener products. The first production line has been operating since
1980; the second since 1998; and the third since 2000. ERG only toured
the first two production lines, given that they accounted for the
majority of facility-wide production. These production lines operate
continuously (except for process down times) and make chemically-similar
sweetener products primarily from a “hydrolysate” feedstock. 

Facility K’s property covers 130 acres, with developed areas spanning
approximately 40 acres. The facility is located in a rural area served
by a volunteer fire department, which conducts annual inspections of
Facility K’s operations and fire protection measures. Facility K’s
main production areas are located in buildings with a combined total
floor space of approximately 100,000 square feet. Roughly 80 employees
work at Facility K. Process operators typically work 12-hour shifts, and
eight operators are needed to oversee the main production lines during
any particular shift. Smoking is not allowed at Facility K, except in
isolated shelters located outside and separate from the main production
lines; no evidence of smoking (e.g., discarded cigarettes) was observed
in the production areas. The smoking areas were well-marked, and “no
smoking” signs were posted at various locations throughout Facility K.

Although multiple employees at Facility K contribute to health and
safety programs, only one employee works exclusively on health and
safety issues. This employee handles most of Facility K’s safety
requirements, except for some specialized topics (e.g., fire protection
training) that outside contractors address. This employee estimated that
she spends approximately 1% of her time addressing combustible dust
safety issues, with the bulk of her time spent addressing other health
and safety issues and ensuring compliance with existing OSHA standards
(e.g., especially process safety management requirements for the
facility’s hydrogen use). Facility K representatives noted that they
have never experienced an explosion or fire resulting from combustible
dusts. 

ERG asked facility representatives to comment on the roles that outside
parties play in Facility K’s combustible dust safety programs. A
summary of those responses follows: 

The facility is located in a sparsely populated area served by a
volunteer fire fighting force. The local fire marshal provides the
facility virtually no information or unique insights on combustible dust
and does not require or suggest adherence to NFPA standards specific to
combustible dust.

Facility K has previously contracted with external engineering and
design firms to characterize various materials (see Section 4.1) and to
design dust controls. 

Facility representatives have obtained insights on design considerations
from corporate officials who work at similar manufacturing facilities in
the United States and abroad. 

Facility representatives have not consulted directly with OSHA on
combustible dust issues, and they were not aware of OSHA’s Combustible
Dust National Emphasis Program. 

Facility K’s insurance underwriter conducts risk analyses annually,
but the focus of these analyses has typically been on fire protection
and other safety issues, without necessarily considering explosion
hazards pertaining to combustible dust. 

Facility K was aware of informational courses on combustible dust
offered by a state Safety Council, but had not attended these courses. 

Process Descriptions

This section describes the process operations that the ERG site visitors
viewed at Facility K: sweetener manufacturing (Section 3.1) addresses
the two production lines that manufactured the facility’s two primary
sweetener products; sweetener packaging and milling (Section 3.2)
addresses a production area that included a milling operation that
generated a finer product and some packaging operations; and sweetener
warehousing (Section 3.3) addresses the facility’s warehousing
operations. Each section presents information on the sequence of unit
operations, controls implemented to prevent fires and explosions from
handling combustible dusts, presence of hazardous locations, and general
housekeeping and cleaning procedures. 

Sweetener Manufacturing

As noted previously, ERG toured two of Facility K’s sweetener
production lines. Though the two production lines make different
products, both lines are summarized in this one section because they
have a similar sequence of unit operations and associated combustible
dust safety issues. 

a moisture content of approximately 1% and a particle size of roughly
500 microns (μm). This output is then collected on an enclosed conveyor
system and screw-fed into a rotary dryer designed to reduce the moisture
content to 0.1%. Site visitors focused on all operations starting at the
dryer and continuing through the end of the production line, as these
operations appeared to have the greatest concerns regarding combustible
dusts.	

Facility K has multiple rotating drum dryers, which operate in the
temperature range of approximately 150–212 oF, with material having a
residence time of 40 to 90 minutes. (See Figure 1 for a photograph of
one of the dryers.) Drying occurs due to contact with a hot air stream,
which is fed counter-current to the sweetener flow. The main dryers are
approximately 8 feet in diameter and 60 feet long, and gently sloped.
Output air from the dryer is conveyed to a cyclone which removes larger
particles, after which this air stream passes through a baghouse where
final filtration occurs before the exhaust is vented through a stack to
the ambient environment; this baghouse is located in the center of the
production building, as discussed later in this report. The solid
material (i.e., the product) from the dryer passes through a screen
separator to remove oversized material and is then collected in a
storage silo, until it is pneumatically conveyed to the warehouse
building for packaging, and sometimes milling. 

is typically on the order of 500 microns (μm) (see Section 4.1). The
end product from these two lines has a moisture content of 0.1%. The
facility did not believe either product presents a combustible dust
hazard possibly due to the particle size upper limit of 420 microns that
NFPA 61 has used to define combustible agricultural dusts, though no
explosibility testing for the main products were available to support
this judgment. More specifically, Facility K’s testing data clearly
demonstrates that its milled products (see Section 3.2 and 4.1) are
combustible powders, but no testing data were available to make similar
judgments about the un-milled sweetener products. 

Dust accumulations. ERG site visitors looked for evidence of dust
accumulation, considering both visible and concealed areas. In
production areas covered by OSHA’s “Housekeeping Standard” (29 CFR
1910.22), virtually no dust accumulation was observed. In areas not
covered by the Housekeeping Standard (e.g., beneath production
equipment, atop elevated horizontal surfaces), some isolated floor areas
had local dust accumulations, with the greatest accumulation observed
beneath a leaking fitting near a screener. (See Figure 2 for a
photograph of this mound.) Minimal dust accumulation was noted along the
rafters, catwalks, tops of processing equipment, and other elevated
surfaces that the site visitors observed. 

Housekeeping practices. In the main production building, three different
cleaning procedures were cited for removing dust accumulations on floors
and surfaces of equipment. The safety managers at Facility K described
these procedures, which operators later confirmed during employee
interviews:

Larger and localized dust accumulations (e.g., the mound of sweetener
noted beneath the leaking fitting) are usually associated with process
upsets. These accumulations are removed immediately, typically through
use of plastic shovels, brushes, sweeps, and dust bins. This “bulk”
material that is collected is recycled in the process. Compressed air is
not used to clean up this material. Note that the detection of leaking
equipment triggers submission of a work request to repair the leak.
Facility personnel indicated that leaks are typically repaired within a
few hours, unless repair requires shutdown, in which case repair occurs
at the end of the production run.

Smaller accumulations over broader areas are cleaned daily during every
shift (though some specific tasks are conducted on a weekly basis),
without the need for process interruptions or shut-downs. Operators use
water hoses to perform this cleaning—an effective strategy due to the
solubility of the sweetener, the fact that the wash water is not
hazardous, and the presence of floor drains throughout these production
areas. Operators interviewed by ERG indicated that they spend between 10
and 60 minutes per shift on routine cleaning of settled dust in
production areas. The operators are supposed to fill out “cleaning
check lists” (see Attachments 1 and 2 of this report) following their
routine cleaning activities. 

More extensive “top-to-bottom” cleaning of the two main production
lines occurs at least once per year when the processes are shut down.
This cleaning is essentially a major water wash-down that targets all
horizontal and vertical surfaces in the production buildings where
accumulations may occur (e.g., ducts, pipes, ledges, cat-walks). Dust
collectors are also cleaned during these shutdowns. 

The plant manager and process supervisors both conduct unannounced
inspections of production areas to ensure that housekeeping practices
are followed; the frequency of these inspections varies from monthly to
quarterly. These inspections attempt to identify any dust accumulations,
whether in open work spaces, in hidden areas, and in other non-work
areas. 

Dust collectors. Several dust collectors captured particles and dusts
generated during the sweetener production processes, primarily from the
dryers and subsequent materials handling steps. Every dust collector was
constructed of non-combustible materials and was located inside the main
production building with exhaust air vented to the ambient (outdoor)
environment and typically to rooftop stacks, away from locations where
workers might be exposed. With one exception, the dust collectors were
located in close proximity to walls; however, a large dust collector was
located near the center of the main production building, approximately
50 feet from the nearest wall. 

Facility K had approximately a dozen functioning dust collectors
(excluding cyclones located upstream of these collectors). These dust
collectors were typically referred to as either baghouses or bin vents,
which varied in size and construction. Refer to Table 1 for selected
design parameters and other details for Facility K’s dust collectors
that were made available during the site visit. The baghouses varied
considerably in size, containing between 9 and 100 bags, with the total
filter media area ranging from approximately 50 to 1,900 square feet.
Nearly every dust collector was originally designed (rather than
retrofit) with explosion venting via ductwork (as long as 50 feet, in
one case) to the outdoors. (Figure 3 is a photograph showing the outlet
of the explosion vents from two baghouses.) However, some dust
collectors were not equipped with explosion vents. 

Collected dust in the baghouses were removed periodically according to
change-out schedules, and almost all of the dust collectors employed
automated shaking, vibration, or other mechanical mechanisms to dislodge
collected material. For most of the dust collection systems, there was
no evidence of significant leaks or fugitive air emissions within
production buildings.

When originally designing the dust collectors, Facility K provided
materials testing data (see Section 4.1) to an external engineering
company, which then designed and installed the dust collector explosion
venting accordingly. While most explosion vents were relatively short
(10 feet or less), one of the larger baghouses had an explosion vent
that was approximately 50 feet long and included a 90-degree bend.
(Figure 4 is a photograph of this ductwork.) The dust collectors were
not equipped with measures (e.g., spark and ember detection systems)
that would help detect small fires inside equipment/ducts and extinguish
them before reaching the collector. Further, the dust collectors (and
interconnecting ductwork) were not equipped with explosion isolation
devices, raising concern about explosions propagating from the collector
back to the process equipment. 

Much of Facility K’s explosion venting design work was completed in
the early to mid 1990s. Detailed cost data for the design and
installation of dust collectors was not readily available during the
site visit, in part because much of this work had been completed roughly
20 years ago. Further, Facility K personnel were not aware why the
outside engineering firm recommended installation of explosion venting
over other protection options such as explosion suppression, although
explosion suppression systems are often more expensive than explosion
vents. 

None of the ductwork for the dust collectors was grounded or bonded, but
it is unclear if such electrostatic controls are necessary without
having material-specific minimum ignition energy (MIE) data. Similarly,
the bags used in the dust collectors do not offer the highest protection
against dissipation of static electricity, but the site visit team could
not assess the need for greater protection given the lack of MIE data. 

Ductwork. Facility K operators noted that they clean ductwork as part of
their broader housekeeping efforts. For instance, when cleaning out
dryers, operators also look for evidence of dust accumulation in the
connecting ductwork. However, operators also acknowledged that they tend
to identify dust accumulation in ductwork only following signs of
restricted air flow (e.g., increased pressure drop). Some operators bang
mallets on the exterior of ductwork when seeking evidence of dust
accumulations, which can be inferred by the noise made during this
activity. As necessary, pressure washing is used to clean dust
accumulations in ductwork. The ductwork throughout this process was not
grounded or bonded, and is not equipped with any means for preventing
deflagration propagation between various operations. 

Maintenance and equipment cleaning. During employee interviews, site
visitors learned of maintenance and equipment cleaning procedures for
certain operations. The dryers, for instance, were washed a few times
per year, typically during process shutdowns that occurred between
campaigns of different product formulations. After obtaining a confined
space entry permit (see Section 6.2), operators followed standard
operating procedures to clean the dryers. In general, the operators
washed the dryer using water from hoses, which effectively removed all
build-up of dusts from the “blades” and “spokes” along the dryer
interior. The operators said they had never seen smoldering or smoking
material during these designated cleaning times. 

When cleaning dust collectors, operators said they employed several
approaches to cleaning, depending on access restrictions:

For some dust collectors, operators could clean the equipment without
entering it. For instance, operators cleaned certain cyclones and
hoppers simply by opening doors or lids and using hoses to wash away
accumulated material.

For other dust collectors, particularly the largest baghouses, operators
had to enter the equipment. The procedures for changing filter material
and cleaning baghouses follows. First, employees followed all lockout
and confined space entry procedures (see Section 6.2) before entering
the units, after which they opened baghouse doors to access the
“cages” from which the filter material (referred to as “socks”)
were hanging. Operators would manually shake cages, which were not
grounded, to dislodge excess accumulation of sweetener product and then
remove the cages using pneumatic wrenches and screwdrivers.  The spent
“socks” were then removed from their cages and then manually removed
any additional excess accumulation of sweetener from the “socks,”
either by hand (brushing the sweetener from the filter material) or
using a brush. Dirty socks were placed in laundry sacks and sent
off-site for cleaning. Operators noted that these procedures led to
formation of small dust clouds that rapidly dissipated. The extent to
which this presents a hazard was difficult to assess from the available
testing data, because some testing results suggested that the average
sweetener particle size in this part of the facility were greater than
500 µm—larger than the 420 µm cut-off cited in NFPA 61 for
“agricultural dust” (NFPA, 2008). After completing these tasks, all
sweetener material that fell to the floor was removed using the standard
housekeeping approaches. 

Hazardous locations. Facility K did not designate any areas in the main
sweetener production lines as Class II hazardous locations. However,
these classifications were made more than 10 years ago and based on
testing data that may not characterize the full range of parameters
needed for a more rigorous determination. Based on observations made
during the site visit and experience with similar materials, site
visitors suspected that Facility K’s milled products and un-milled
fines are likely Class II materials. 

Sweetener Packaging and Milling 

Section 3.1 describes how Facility K manufactures most of its sweetener
products, which again have particle diameters typically greater than 500
µm. This section describes activities in a separate building, where
some sweetener products are packaged as produced and others are milled
before packaging to provide finer product for certain customers. All
products from the two main sweetener lines are pneumatically conveyed to
the packaging and milling area and loaded into silos. The majority of
this material is packaged as is, into various sizes drums and bags. 

Some of the product is further milled. In the milling operation,
sweetener product from the holding silos is fed to a pin mill. The pin
mill appears to be the only unit operation in this building with the
potential for causing mechanical sparks. The owner’s manual for the
pin mill (Model 60 Mikro “ACM” Pulverizer) recommends that “all
metallic scrap (tramp) must be positively separated from the feed
material before it enters the mill grinding chamber…which can be
accomplished by use of scalping screens, magnetic separators, etc.”
Process operators noted that they have seen evidence of damaged (bent)
pins and rub marks in the mill enclosure when they clean the mill. There
are screens at the inlet and outlet of the pin mill to prevent transport
of metal parts into and outside the mill, but there is no magnetic
separator or other device to detect and remove broken screens or pins. 

The milled product settles into another silo, from which product is
collected into bulk bags, 25-kilogram bags, and fiber drums (with
capacity of approximately 30 gallons). The side exterior walls of the
milling room were equipped with explosion vent panels, and both silos
located in the milling room had explosion venting. Additional
information on the milling operation follows:

Testing. According to Facility K representatives, the two main milled
products have an average particle diameter in the range of 50 to 170
µm, which is in the particle size range that NFPA 61 considers as
combustible agricultural dusts. Refer to Section 4.1 for information on
testing of milled products for explosibility parameters. 

Dust accumulations. The passageways and floors were relatively clean,
and minimal accumulations of fine sweetener product were observed on
stairs and catwalks. However, the pin mill was not operating at the time
that the site visitors toured this part of the facility.  

Housekeeping practices. The housekeeping practices employed in the
milling room were similar to those employed in the two main sweetener
production lines, with one major exception. Because the building in
which the milling room is located does not have floor drains, operators
typically do not use hoses to wash away dust accumulations. Instead,
most housekeeping in the milling room is conducted using vacuums,
brushes, dust pans, and wet mops. In comparison to the water wash-downs
in the other building, use of these “dry” techniques was more likely
to generate airborne dust. The vacuums used in this area were not rated
for Class II areas, even though the milling room was considered a Class
II area (see below). Employees noted that their daily housekeeping
activities take approximately 1 hour to complete. The milling room
operators are supposed to fill out a cleaning check list (see Attachment
3 of this report) following their daily cleaning activities. 

According to the housekeeping procedures for the milling room, operators
sweep accumulations on floors and vacuum accumulations beneath equipment
daily. Wet cleaning with mops occurs every other day in some areas, and
weekly in others. All of the previous cleaning activities can occur
while the processes operate. More extensive “top-to-bottom” cleaning
occurs a few times per year, and only during process shut-downs. 

Dust collectors. The milling room contains several silos and baghouses,
all of which are located inside the building and vent exhaust outdoors
to ambient air. These dust collectors all have explosion panels that
vent outdoors, though the pin mill does not. None of these devices is
equipped with measures (e.g., spark and ember detection systems) that
would help detect fires inside equipment and extinguish them, nor do
they have isolation devices to prevent events from propagating into
other operations, raising concern about explosions or fires propagating
from one unit operation to another. 

Site visitors noted that the outlet of an explosion vent was “blown
out” and awaiting replacement (see Figure 6). Facility personnel
stated that the “blow out” most likely resulted from a recent
pressure boost in the pneumatic conveyor system to ensure efficient
transport of a material with a higher moisture content. However, site
visitors noted that this would have required an anomalously high
pressure because most of the vents have set pressures in the range 0.75
psig to 1.25 psig.

Ductwork. All ductwork in the milling room is metal, but is not grounded
or bonded. The facility does not have routine procedures for looking for
dust accumulations within duct work. This is typically done annually, or
when operators detect evidence of potential accumulation (e.g., poor
flow of material through ductwork). 

Hazardous locations. Facility K classified the entire milling room as a
Class II location, based on evaluations conducted more than 20 years
ago. Site visitors encouraged Facility K to reevaluate this
classification based on more recent data and NFPA 499 evaluations. Light
fixtures, electrical boxes, and motors in the milling room appeared to
conform to requirements for Class II, Division 1, Group G atmospheres.
However, operators used equipment in the milling room (e.g.,
propane-powered fork lifts, vacuum cleaners) that is not designed for
Class II locations, and the room did not include warning signs about the
presence of combustible dusts. 

Sweetener Warehousing 

All product packaged in the milling area (and its adjacent room) is
ultimately transported to a large warehousing area. The ceiling in the
warehouse building is 35 feet high, and product storage occurs in tiers
of racks equipped with in-rack sprinklers. Products are shipped in bulk
bags of varying sizes, so-called “super sacks,” and fiber drums
before being transported off-site via truck. The amount of material in
the individual product items ranges from 25 to 1,000 kilograms. 

Figure 5 is a photograph of a typical bag of Facility K sweetener
product. As the figure shows, Facility K used “Type C” bags and
sacks for packaging many products. These Type C “super sacks” are
conductive and can prevent electrostatic discharges providing they are
effectively grounded (the label specifies a resistance to ground of less
than 10 ohms) during loading and unloading.  ERG observers did not see
the filling of the Type C “super sacks” during the visit. 

Document Review

This section summarizes documents pertaining to combustible dust safety
issues that Facility K made available to site visitors.  

Testing Data

In the early 1990s, Facility K contracted with a laboratory and
associated consulting organization to analyze three of its milled
products and make recommendations on mitigating potential fire and
explosion hazards. Original documentation of the testing was not
available, most likely because the testing occurred nearly 20 years ago.
Testing results were available in summary tabulations only, which are
reproduced here in Table 2. As the table shows, the three milled
products were tested for the minimum explosible concentration (MEC), the
maximum explosion pressure (pmax), and the maximum normalized rate of
pressure rise [(dp/dt)max]. However, ASTM standard test procedures
apparently were not used.  The table also presents test results from two
reference material samples, sugar and fructose. No further information
on this testing (e.g., methods used, analytical costs) was available
during the site visit. Further, Facility K apparently does not have
comparable testing results for the un-milled sweeteners.

Facility K also shared with the site visitors particle size distribution
data for two main products. For the first product, the mean particle
size was 517 μm, and approximately 20% of the sample (by volume) had
particle sizes less than 420 µm; for the second product, the mean
particle size was 530 μm, and approximately 25% of the sample (by
volume) had particle sizes less than 420 µm. While these testing
results confirm statements made throughout the site visit about the main
sweetener products tending to be “larger than 500 μm,” it should be
noted that the testing was apparently conducted on bulk product and may
not be representative of material found throughout the production areas.
For instance, material in certain dust collectors and dust accumulations
on surfaces would not necessarily have the same particle size
distribution as the bulk product.

Facility K also shared more recent (2008) explosibility testing results
for five of its specialty products. Those results are not presented
here, because the site visitors did not tour these operations and these
products account for a very small portion of Facility K’s production. 

Material Safety Data Sheets (MSDSs) 

Site visitors reviewed copies of MSDSs for four of Facility K’s main
sweetener products. All four of these MSDSs were last modified in 2008.
The following paragraphs quote information specific to potential
combustible dust hazards from these four documents:

Products #1, #2, and #3. These three materials had identical information
on the MSDSs related to potential combustible dust hazards.
Specifically, Section 5 of these MSDSs (“Fire-Fighting Measures”)
indicates that “dust-air mixtures may ignite or explode” and
instructs to “not scatter spilled material with high-pressure water
streams,” and Section 10 (“Stability and Reactivity”) cautions to
“avoid contact with excessive heat, sparks, or open flame.” The
MSDSs do not present information on particle size, minimum ignition
energy, and other explosibility parameters (which are particle size
dependent) that might inform users about potential combustible dust
hazards. 

Product #4. This material’s MSDS included more detailed information on
potential hazards. For instance, Section 5 (“Fire-Fighting
Measures”) notes that “…in high concentrations, dust may form
explosive mixtures in air, classified as a Class ST-1 dust explosion
hazard (ASTM E1226).” Further, Section 6 (“Accidental Release
Measures”) provides the following instruction for addressing leaks and
spills: “Sweep up and place in an appropriate waste container; avoid
raising dust…” Section 9 “Physical and Chemical Properties” has
an entry for “Explosive Properties” that echoes the same warning
that appears in Section 5. 

Housekeeping Checklists 

Facility K does not have a single, comprehensive housekeeping plan.
However, the facility has multiple “good manufacturing practice”
(GMP) documents that specify housekeeping procedures for the various
processing and packaging areas. These GMPs included roles and
responsibilities, preferred practices for removing dust accumulations,
and checklists. The checklists (see Attachments 1, 2, and 3) do not have
a maximum tolerable thickness of dust accumulation or any other
quantitative measure of what is considered a “clean” surface;
rather, the overarching strategy is to clean any accumulations upon
sight. The plant manager conducts quarterly GMP audits, which include
inspecting areas for dust accumulations, and the production manager
conducts more frequent informal GMP audits. 

One motivating factor for Facility K’s emphasis on cleanliness is the
need for a clean workspace for manufacturing food products, especially
considering that Facility K’s customers occasionally tour the process
operations. Additional process-specific details on housekeeping follow:

For the two main production lines, Facility K has cleaning checklists
that are completed daily. Operators fill out these checklists after
completing the required cleaning, which include brushing dust
accumulations off equipment surfaces and vacuuming or washing dust on
the floors. This routine cleaning does not require process shutdowns. As
noted previously, “top-to-bottom” cleaning also occurs at least once
per year for the two main production lines. This cleaning, which occurs
during process shut-downs, involves water wash-downs of accumulations on
all surfaces from the ceiling to the floor. 

The cleaning procedures in the warehousing area are similar, with one
exception. Because the warehouse building (which includes the milling
room) does not have floor drains, wash-downs do not occur and surfaces
are instead cleaned using vacuums, brooms, and limited mopping. 

Several employees noted that they were explicitly instructed to not use
compressed air when removing dust accumulations, and site visitors saw
no evidence of employees using compressed air for housekeeping purposes.

Process Hazard Analyses 

When conducting the site visit, ERG asked to view any process hazard
analyses that Facility K may have conducted specific to combustible
dust. Facility K representatives did not have any such analyses, perhaps
because controls were installed more than 20 years ago, but they shared
a document on the facility’s “Environmental, Health & Safety
Aspects.” The document was prepared pursuant to “Occupational Health
and Safety Assessment Series (OHSAS) 18001”—standards developed by
the British Standards Institute for occupational health and safety
management systems. The hazard analysis ranks potential hazards at the
facility, which Facility K uses to assign priorities for mitigating
hazards.

In this “hazard analysis” document, Facility K lists dozens of
employee activities and processes (including potential for combustible
dust explosions) and then assigns each item a “significance of
impact” score. Scores were provided for several categories, including
severity or intensity of potential hazards, likelihood of occurrence,
frequency of occurrence, area of impact, and community visibility and
impacts. While this exercise was not specific to combustible dust, the
hazard analysis gave some of the highest possible “significance of
impact” scores to combustible dust issues associated with the milling
and packaging operations. The individual scores appear to be based on
professional judgment. 

Training and Employee Awareness

This section describes various safety training courses that Facility K
offers to its employees and to contractors, focusing on the extent to
which combustible dust concepts are covered in the course content.
Overall, Facility K offers numerous safety training courses to
employees, and those were typically developed in fulfillment of specific
OSHA requirements. These courses discuss combustible dust issues to
varying degrees, as described below. 

The employees at Facility K exhibited different levels of awareness of
combustible dust safety hazards. Some employees seemed quite aware of
potential hazards, but these employees also acknowledged that part of
this awareness stemmed from previous employment at facilities that
handled combustible dust. Most operators seemed aware of a “rule of
thumb” used at Facility K to assess potentially hazardous conditions
that should be avoided: employees cited the facility’s suggestion to
avoid working in areas with airborne dust accumulations that obscure
objects more than 10 feet away. Facility K representatives were not
aware of the origin of this recommendation and (see Section 8) sought
feedback from OSHA on characterizing what airborne concentrations of
combustible dusts are hazardous.  

Operator Training

Facility K offers multiple safety training courses to operators, mostly
in fulfillment of other OSHA standards. For instance, operators receive
annual confined space entry training (an hour-long course), annual
training on hazard communication (an hour-long course), annual emergency
response training, respirator training (for employees whose job
descriptions require use of respirators), and lockout-tagout training.
Additionally, operators receive initial training for specific job
classifications that involve detailed reviews of operating procedures,
with follow-up training provided when changes are made to work
instructions. 

Facility K’s safety training courses apparently provided limited
information on combustible dust hazards, with exceptions noted in
Sections 6.2 and 6.3 of this report. When asked about this, some
Facility K representatives explained that many of their training courses
are developed to meet specific requirements in OSHA standards, and the
lack of training material on combustible dust results, in part, from
OSHA not having promulgated a combustible dust standard. 

Contractor Training

Facility K developed a high-quality electronic training course that all
contractors must take and pass before they can be issued a work permit.
The training course has more than 80 slides and proficiency testing
throughout. The course covers many general safety topics including, but
not limited to, emergency procedures, security, use of motor vehicles,
hazard communication, confined space entry, and hot work permits. While
the training course acknowledges the unique hazards posed by the highly
hazardous chemicals (hydrogen gas) that triggered process safety
management requirements at Facility K, the course includes no content
describing unique hazards posed by combustible dusts. 

Safety Video for Facility Visitors

All visitors to Facility K who will be entering production areas are
required to watch a 10-minute informational video on general safety
concepts. The three ERG site visitors viewed this video at the beginning
of the site visit. The video covers many topics, including hazard
communication, personal protective equipment, and emergency response.
The video introduces visitors to some potential health and safety
hazards and mentions that Facility K has processes containing flammable
and explosive materials (mostly in reference to hydrogen), but makes no
specific mention of sweetener products that are combustible dusts. 

Employee Interviews

ERG site visitors interviewed five of Facility K’s operators and
maintenance personnel to learn their perspectives on combustible dust
issues. These employees had worked at Facility K between 7 years and 27
years. The 20-minute interviews revealed several notable observations,
which are incorporated into the discussion presented throughout this
report. Overall, employee feedback regarding housekeeping procedures,
cleaning methods, and cleaning frequencies were generally consistent
with Facility K’s process-specific procedures. Further, the employees
exhibited a strong understanding of the facility’s requirements for
lockout-tagout, “hot work” permits, and confined space entry. 

Safety Programs

This section reviews the site visitors’ observations of selected
safety programs implemented at Facility K, with a focus on the extent to
which combustible dust factored into these programs. 

Emergency Response

Facility K has a 14-page emergency response procedure, and employees
receive training on this annually. The procedure lists a wide range of
possible emergency events, including “dust explosions.” Most of the
specifications in the procedure are general, except for the following
passage specific to combustible dust events: “Dust explosions and
subsequent fires should be contained to the vessel. Do not allow
personnel near the vessel until a water spray is directed on the vessel
for cooling. Without water, the metal will fatigue and fail [and the
structural steel will weaken]. Be careful of the water weight added to
the silo under these conditions. While the silo should be able to
support the entire water weight, fatiguing during the explosion and fire
often compromise this.” 

Confined Space Entry

Information on confined space entry programs was obtained through
employee interviews and review of Facility K’s “work
instructions,” which apply to both facility personnel and contractors.
ERG site visitors noted that confined spaces at Facility K appeared to
be well labeled. The facility’s confined space entry procedures
require employees to follow several steps before entering confined
spaces (e.g., dryers, silos, baghouses). Employees are required to
conduct at least the following sequence of activities before entering
confined spaces:

Prepare a confined space entry permit that must be reviewed and approved
by a department manager.

Open door to confined space.

Measure oxygen concentrations with a monitor.

Visually check for evidence of suspended dust. Specifically, the
confined space entry permit has a field in which employees respond
(Yes/No) to the following question: “Dust visibility greater than 10
feet?” Meaning, entry to confined space is denied if suspended dust
levels impair visibility at a distance of 10 feet. Another condition of
entry is that “…the vessel must be clear of residual product if
deemed harmful.”

Don safety harness, tag line, and dust mask.

Facility K’s “work instruction” on confined space entry
specifically acknowledges the potential hazards of combustible dusts:
“Special Precautions and Considerations: …Dust explosions: Grinding
operations in a vessel can create a dust cloud and ignite it.”
Therefore, the confined space entry program accounts for combustible
dust to a certain extent. 

If requested by OSHA and approved by Facility K, ERG will provide a copy
of the facility’s confined space entry “work instruction” and a
blank confined space entry permit, though the preceding text describes
the full extent to which those resources address combustible dust. 

“Hot Work” Permits

Facility K has a “hot work” program that requires special permits to
be obtained before any work that involves a “…spark or heat
producing activity.” Facility K has a written work instruction that
defines “hot work” as activities that include “…cutting,
welding, boring holes, drilling, grinding, smoldering, open flames, and
others.” In order to obtain a “hot work” permit, the applicant
(which can be an operator or supervisor) “…should take all necessary
provisions to protect the surrounding area against fire or burn damage;
this may include covering cable trays with weld tarps, cleaning built up
sugar dust from I-beams or floors, or wetting down potentially flammable
materials” (emphasis added). Therefore, even though the “hot work”
program is largely general, it does include some acknowledgment of the
unique hazards posed by the potential presence of combustible dust. All
operators interviewed during the site visit were aware of the “hot
work” program and its general requirements, which apply to both
facility personnel and contractors.

If requested by OSHA and approved by Facility K, ERG will provide a copy
of the facility’s “work instruction” for “hot work” and a
blank permit for this activity, though the preceding text describes the
full extent to which those resources address combustible dust. 

Management of Change

Facility K had several written procedures outlining special requirements
for managing various types of change to processes. The specific
procedures are titled “New Product/Project Planning” and “Change
Control and Deviations.” For process changes beyond
replacements-in-kind, the procedures outline a series of requirements
(e.g., impact review, pre-start-up safety review, reviews and approvals)
that must be met before changes can be implemented. Development of the
procedures was apparently motivated by general safety concerns, process
safety management requirements for processes using hydrogen gas and
other covered materials, and OHSAS specifications. More information can
be provided on these procedures, if requested; however, the procedures
included no requirements to address unique hazards potentially posed by
combustible dusts. 

Personal Protective Equipment (PPE) and Uniforms

Operators are required to wear uniforms, hard hats, safety goggles, hair
and beard nets, and steel-toed shoes in most production areas. Some of
these requirements are motivated by safety reasons and others by hygiene
demands common for food production facilities. Operators are not
required to wear flame-resistant clothing anywhere at the facility. 

Fire Protection

Site visitors noted several aspects of Facility K’s fire protection
strategies. The facility’s warehousing operation, milling operation,
and one of the two main production lines are located in buildings
equipped with sprinkler systems. However, the other main production line
is located in a building with no sprinklers. In addition, the dust
collectors do not contain smoke or fire detection equipment or automatic
fire suppression systems.

Main Findings

During the closing meeting of the site visit, the ERG site visitors
shared several key findings. These represent observations raised by
three independent engineers, and should not be viewed as a judgment on
Facility K’s compliance with OSHA regulations or adherence to National
Fire Protection Association (NFPA) consensus standards. The main
findings communicated to facility representatives include: 

Dust accumulations at Facility K were generally minimal, with few
exceptions in isolated areas. The facility’s housekeeping efforts,
which included both routine removal of spot accumulations and periodic
“top-to-bottom” wash-downs of selected production areas, appeared to
be effective in addressing potential dust accumulations. Continued
effort to minimize dust accumulations should help reduce the likelihood
and severity of secondary explosions, should an initiating event occur.

The adequacy of Facility K’s engineering controls could not be fully
evaluated due to the lack of detailed material explosibility testing
data for its main products. While Facility K had some materials analyzed
for explosibility parameters, the available data had several
limitations: (1) some testing data were about 20 years old and were
probably not conducted with ASTM or ISO standardized methods; (2) the
data addressed some but not all of the facility’s current products,
and testing of bulk product material may not reflect the hazards
associated with material collected in dust collectors or found in dust
accumulations; and (3) the laboratory testing for the main products did
not include minimum ignition temperatures and minimum ignition energies.
The ignitability data would be needed to do a comprehensive hazard
analysis for the key process equipment such as the dryers and mill. 
This finding was based on the material made available during the site
visit, and site visitors acknowledged that Facility K, or its external
engineering and design contractor, may have additional documentation of
testing results that address some of the concerns expressed above.  

For certain processes and unit operations, site visitors expressed
concern about the adequacy of controls for detecting and controlling
combustible dust safety hazards. For instance, many interconnected unit
operations lacked explosion isolation devices, raising concern about
explosions or fires propagating from one unit operation to another
(e.g., from the sugar milling operation to the downstream baghouses and
packaging operations). In addition, one dust collection system had
explosion venting ductwork that spanned approximately 50 feet, including
a 90-degree bend, before reaching the building exterior, raising
questions about the efficacy of the venting. Finally, some unit
operations lacked process controls (e.g., excess temperature sensors,
inlet moisture readings) and spark or ember detection systems that could
be used to identify and prevent unsafe operating conditions. The
significance of these issues is difficult to assess without access to
more detailed material testing data for selected products and
intermediates and original design specifications (and hazard analyses)
for individual processes. 

Facility K’s diagram of hazardous area classifications is more than 20
years old and may not reflect current conditions. It is possible that
some areas currently designated as Class II (e.g., the entire milling
room) may actually not need to be Class II areas, while other areas
currently not designated as Class II (e.g., inside selected dust
collection systems) should have this designation. Some of the equipment
currently used in the Class II area (e.g., propane-powered forklifts,
vacuum cleaners) is not rated for such environments. 

Facility K’s safety personnel focused their time largely on issues
other than combustible dust. This situation seemed to reflect the
current regulatory framework, in which the facility invested more time
and resources complying with existing OSHA standards (particularly
process safety management). 

The training for contractors thoroughly covers many important safety
topics, but presents no information on combustible dusts. If contractors
work in the main production areas, Facility K should ensure that they
are adequately informed of potential combustible dust safety hazards and
how they can be avoided. 

Facility K apparently does not have an inspection and maintenance
program for its explosion venting systems. One explosion vent panel was
partially “blown out” (see Figure 6), and facility personnel
mentioned that they typically only become aware of damaged or partially
actuated vent panels when dust is observed blowing through the outlet
exhausts to the building exterior. 

Feedback to OSHA

At the end of the site visit, ERG asked representatives from Facility K
if they had any specific feedback to OSHA on combustible dust safety
issues. (Note: This site visit occurred before OSHA publicly announced
its intention to initiate a rulemaking on combustible dust (OSHA,
2009)). Facility K representatives offered the following responses:

When asked about the possibility of a new combustible dust standard,
Facility K representatives recommended that OSHA place lesser emphasis
on regulation and enforcement, and greater emphasis on guidance,
compliance assistance, and other proactive measures to help facilities
avoid combustible dust hazards. One suggestion was for OSHA technical
staff to work cooperatively with facilities in a consultative manner
(e.g., through voluntary site visit programs), rather than interact with
facilities largely through inspections. Another specific suggestion was
for OSHA to develop industry- or material-specific guidance on
combustible dust safety issues, similar to guidance that the U.S.
Environmental Protection Agency has developed as part of its Risk
Management Plan requirements (see:   HYPERLINK
"http://www.epa.gov/emergencies/guidance.htm#rmp" 
http://www.epa.gov/emergencies/guidance.htm#rmp ). 

Facility K representatives listed several questions they were hoping
OSHA guidance might address, such as: How much dust (whether expressed
as a thickness or a mass over a specified area) is considered an
“unsafe” accumulation? What airborne concentration of combustible
dust is considered safe? What specific analytical methods and testing
parameters should be considered when designing combustible dust
engineering controls? How should facilities interpret different types of
testing data (e.g., what actions should be triggered when testing
parameters reach certain levels)?  Facility managers were not familiar
with the various NFPA standards that address these issues.

Facility K representatives noted that, because combustible dust safety
is a highly specialized topic, and because they have limited internal
resources and expertise, the facility would likely have to hire
consultants and engineering firms to implement additional engineering
controls, if required by a new combustible dust standard. More
generally, they suspected that many other small to mid-sized
manufacturing facilities, especially those that are not part of a larger
companies, would also lack internal resources on combustible dust safety
issues and may need detailed guidance on how to comply with any standard
that OSHA might implement. 

References

NFPA, 2008. NFPA 61: Standard for the Prevention of Fires and Dust
Explosions in Agricultural and Food Processing Facilities. 2008 Edition.
National Fire Protection Association. 

NFPA 499 Recommended Practice for the Classification of Combustible
Dusts and of Hazardous (Classified) Locations for Electrical
Installations in Chemical Process Areas, 2008 Edition

OSHA, 2009. U.S. Department of Labor’s OSHA announces rulemaking on
combustible dust hazards. U.S. Department of Labor, OSHA, Office of
Communications. National News Release: 09-475-NAT. April 29, 2009.

Table 1. Overview of Facility K’s Dust Collectors

Reference Number	Equipment Description

S-5210	A pulse jet baghouse manufactured by Micropole (model #69835)
with 69 bags that provide 650 square feet of filter area; flow rates are
typically 3,000 standard cubic feet per minute (SCFM); the baghouse is
equipped with explosion venting.

S-5220	A pulse jet baghouse manufactured by Flexclean (model #58BV9)
with an estimated 9 bags that provide 65 square feet of filter area; the
baghouse is equipped with explosion venting.

F-1518	A pulse jet baghouse manufactured by “DCE” with 1,900 square
feet of filter area; the baghouse is equipped with explosion venting.

F-1537	A pulse jet baghouse with 129 square feet of filter area.

F-1539	A pulse jet baghouse with 129 square feet of filter area.

F-1105	A baghouse at the outlet of one of the process dryers. 

F-1115	A baghouse in the packaging department.

F-1116	A bin vent in the packaging department. 

F-4614	A baghouse manufactured by Sweco (model #S10-120) with 100 bags.

V-4605	A baghouse in one of the production lines.

V-4603	Referred to as the “holding hopper.” 

F-4612	A baghouse manufactured by Flexclean (model #58BV-9) with 9 bags
that provide 58 square feet of filter area; the baghouse is not equipped
with explosion venting.

F-4615	A bin vent manufactured by Flexclean (mode #46BV-9) with 9 bags
that provide 49 square feet of filter area; the bin vent is equipped
with explosion venting.

Note: 	The table documents all information that was readily available
during the site visit. The table does not document information on
cyclones that were located upstream of baghouses.  

Table 2. Testing Parameters Reported for Three Milled Products and Two
Reference Materials

Parameter (Units)	Milled Products	Reference Materials

	#1	#2	#3	Sugar	Fructose

MEC (oz/ft3)	0.188	0.1-0.2	0.136	0.2	0.5-0.75

Pmax (psig)	102	87	93	123	87

Kst (bar-m/sec)	188	NA	98	138	NA

Notes:	MEC = minimum explosible concentration

Pmax = maximum explosion pressure

Kst = deflagration index; normalized maximum-rate-of-pressure-rise =
(dp/dt)maxV1/3

(dp/dt)max = maximum rate of pressure rise for worst-case concentration
in a particular test vessel

Full documentation of the testing and the sample particle sizes and
moisture contents were not available during the site visit.

This table presents testing parameters available for the main products
reviewed during the site visit. Testing data were also available for
specialty products manufactured in a production line that site visitors
did not tour. The specialty products that were tested had Kst values in
the range 54 to 105 bar-m/sec and minimum ignition energies in the range
37 to 1,046 mJ.

Figure 1. Photograph of a Rotary Dryer

 

Note:	This photograph shows the rotary drum dryer, which is the large,
grey cylinder. The “wet” (1% moisture) sweetener enters the dryer at
the inlet, which is on the left-hand side of the photograph, and the
sweetener product (0.1% moisture) exits the dryer at the outlet, which
is not visible in this photograph. The hot air used to dry the sweetener
material enters the dryer at the outlet side. 

Figure 2. Photograph of Dust Accumulation Due to Leaking Fitting on a
Sifter

Note:	As this site visit report notes, site visitors saw minimal
evidence of dust accumulations throughout Facility K. This photograph is
included to depict the worst-case accumulation that was observed. Note
that operators and maintenance personnel promptly remove accumulations
(like that shown in this photograph) using brooms and dust pans, and not
using means (e.g., compressed air) that could generate airborne
dispersions of potentially combustible dust. 

Figure 3. Photograph of Building Exterior Showing Outlets from Two
Explosion Vents

 

Note:	All of Facility K’s dust collectors are located indoors, and
most have explosion panels to vent deflagrations. Every explosion
venting system has ductwork leading to the outdoors. This photograph
depicts two outlets from explosion vents. 

Figure 4. Photograph of Explosion Venting Ductwork from a Baghouse

 

Note:	The explosion venting from most baghouses at Facility K vented
short distances—typically 10 feet or less—to the outdoors. As the
exception, one baghouse had explosion venting ductwork that vented
approximately 50 feet to the outdoors. This is a photograph of the
ductwork from that baghouse. Due to the length of the ductwork, it was
impossible to have the baghouse and explosion vent ductwork appear in a
single photograph. Not shown in the photograph is a 90-degree bend in
the ductwork. 

	This photograph illustrates challenges that facilities face when
implementing controls. For some processes, equipment is located in parts
of buildings that complicate efforts to install explosion venting. In
this case, the only way that conventional explosion vents could be used
was to have lengthy ductwork to the outdoors. It was unclear why other
control options were not pursued. 

Figure 5. Photograph of Product Storage Bag

Note:	The product storage bag is reported as being electrostatically
dissipative (Type C). Without having MIE data for sweetener products,
site visitors could not assess whether this selection of bag material
was sufficiently protective. However, Facility K had not observed any
fires or other evidence of electrostatic dissipation in its warehousing
area. 

Figure 6. Photograph of Explosion Vent Outlet

 

Note:	Photograph shows a “blown out” outlet of an explosion venting
system. Facility personnel stated that the “blow out” was most
likely caused by a pressure increase in the pneumatic conveying system
to transport material with a high moisture content. The damaged outlet
raised concern about Facility K’s inspection and maintenance practices
for their explosion venting ductwork.

Attachment 1. Housekeeping Checklist for Sweetener Production Line #1

Attachment 2. Housekeeping Checklist for Sweetener Production Line #2

Attachment 3. Housekeeping Checklist for Milling Room

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ttributes of the dryers, without commenting on how design varies among
them. 

 Facility K representatives acknowledged that the pin mill and its
downstream dust collector would likely remain a Class II location,
though other parts of the pin mill room may no longer need to be Class
II. 

 This threshold is used because it is the size cut-off cited in NFPA 61
for “agricultural dust” (NFPA, 2008).

 When asked about the origin of this requirement, Facility K
representatives said they were aware that certain work activities in
confined spaces can cause combustible dust safety hazards. However, they
were unsure how to quantify objectively the precise conditions that must
be avoided (e.g., is there a specific airborne dust concentration that
should be avoided when working in confined spaces?). Without specific
guidance on this matter, Facility K representatives developed the
10-foot visibility requirement listed above as a “rule of thumb.”
Refer to Section 8 of this report for Facility K’s feedback to OSHA on
this issue. 

 During this discussion, facility representatives explained that
interpreting air concentrations of explosive gases is relatively
straightforward, based on comparisons to the lower and/or upper
explosive limits. They wondered what specific parameters could be used
to specify “safe thresholds” for airborne concentrations of
combustible dusts. 

 PAGE   

Site Visits Related to Combustible Dust – Facility K 

 PAGE   33 

Site Visits Related to Combustible Dust – Facility K