Document ID: OSHA-2009-0023-0163
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2010-08-23T04:00Z

Site Visits Related to Combustible Dust:

Facility B–Paper 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

 (June 15, 2010)

Table of Contents

  TOC \o "1-5" \h \z \u    HYPERLINK \l "_Toc264360795"  1	Project
Overview	  PAGEREF _Toc264360795 \h  1  

  HYPERLINK \l "_Toc264360796"  2	Facility Description	  PAGEREF
_Toc264360796 \h  2  

  HYPERLINK \l "_Toc264360797"  3	Process Descriptions	  PAGEREF
_Toc264360797 \h  3  

  HYPERLINK \l "_Toc264360798"  3.1	Overview of Common Operations	 
PAGEREF _Toc264360798 \h  4  

  HYPERLINK \l "_Toc264360799"  3.1.1	Wood Chip Processing	  PAGEREF
_Toc264360799 \h  4  

  HYPERLINK \l "_Toc264360800"  3.1.2	Paper Making	  PAGEREF
_Toc264360800 \h  5  

  HYPERLINK \l "_Toc264360801"  3.1.3	Paper Converting	  PAGEREF
_Toc264360801 \h  6  

  HYPERLINK \l "_Toc264360802"  3.2	Specific Issues Pertaining to
Combustible Dust	  PAGEREF _Toc264360802 \h  6  

  HYPERLINK \l "_Toc264360803"  3.2.1	Dust Accumulations	  PAGEREF
_Toc264360803 \h  6  

  HYPERLINK \l "_Toc264360804"  3.2.2	Equipment Cleaning	  PAGEREF
_Toc264360804 \h  7  

  HYPERLINK \l "_Toc264360805"  3.2.3	Housekeeping Practices	  PAGEREF
_Toc264360805 \h  9  

  HYPERLINK \l "_Toc264360806"  3.2.4	Dust Collectors	  PAGEREF
_Toc264360806 \h  10  

  HYPERLINK \l "_Toc264360807"  3.2.5	Automated Fire Suppression Systems
  PAGEREF _Toc264360807 \h  11  

  HYPERLINK \l "_Toc264360808"  3.2.6	Classification of Hazardous
Locations	  PAGEREF _Toc264360808 \h  12  

  HYPERLINK \l "_Toc264360809"  3.2.7	Fire History	  PAGEREF
_Toc264360809 \h  12  

  HYPERLINK \l "_Toc264360810"  4	Document Review	  PAGEREF
_Toc264360810 \h  12  

  HYPERLINK \l "_Toc264360811"  4.1	Testing Data	  PAGEREF _Toc264360811
\h  13  

  HYPERLINK \l "_Toc264360812"  4.1.1	Facility B’s Testing Data	 
PAGEREF _Toc264360812 \h  13  

  HYPERLINK \l "_Toc264360813"  4.1.2	OSHA’s Test Data for Samples
Collected During the Site Visit	  PAGEREF _Toc264360813 \h  15  

  HYPERLINK \l "_Toc264360814"  4.1.3	Micrographs of Settled Paper Dust	
 PAGEREF _Toc264360814 \h  16  

  HYPERLINK \l "_Toc264360815"  4.2	Material Safety Data Sheets (MSDSs)	
 PAGEREF _Toc264360815 \h  16  

  HYPERLINK \l "_Toc264360816"  4.3	Housekeeping Guidance Document	 
PAGEREF _Toc264360816 \h  17  

  HYPERLINK \l "_Toc264360817"  4.4	Quote for Installing a Wet Dust
Collector	  PAGEREF _Toc264360817 \h  18  

  HYPERLINK \l "_Toc264360818"  4.5	Combustible Dust Fire and Explosions
Hazard Assessment	  PAGEREF _Toc264360818 \h  18  

  HYPERLINK \l "_Toc264360819"  4.6	Analysis of Costs to Comply with
NFPA Combustible Dust Standards	  PAGEREF _Toc264360819 \h  19  

  HYPERLINK \l "_Toc264360820"  5	Training	  PAGEREF _Toc264360820 \h 
20  

  HYPERLINK \l "_Toc264360821"  6	Safety Programs	  PAGEREF
_Toc264360821 \h  21  

  HYPERLINK \l "_Toc264360822"  7	Main Findings	  PAGEREF _Toc264360822
\h  22  

  HYPERLINK \l "_Toc264360823"  8	Feedback to OSHA	  PAGEREF
_Toc264360823 \h  23  

  HYPERLINK \l "_Toc264360824"  9	References	  PAGEREF _Toc264360824 \h 
25  

 

Table 1			Testing Results for Samples Collected During the Site Visit

Table 2			Effect of Moisture Content on Paper Dust Testing Results

Table 3			Estimated Costs for Updating Operations Involving Paper Dust
to Comply with NFPA 654

Figure 1		Photograph of Sawdust Accumulation on Screener in Wood
Processing Room

Figure 2		Photograph of “Blow Down” of Paper Machine

Figure 3 	 	Photograph of Dust Accumulations in a Paper Winding
Enclosure

Figure 4		Photograph of Paper Dust Accumulation on Top of a Yankee Dryer

Figure 5		Photograph of Tiger Vac on a Scissor Lift

Figure 6		Photograph of Dust Collector (1)

Figure 7		Photograph of Dust Collector (2)

Figure 8		Photograph of Dust Accumulation in the Sawdust Press Building

Figure 9		Micrographs of Settled Paper Dust

Attachment 1	Copy of Testing Results Provided by OSHA’s Analytical
Laboratory

Attachment 2	Facility B’s Procedure for “Settled Bulk Density and
Maximum Accumulation Determination”

Acronyms and Abbreviations

cfm			cubic feet per minute

CO2		carbon dioxide

ERG		Eastern Research Group, Inc.

MSDS		Material Safety Data Sheet

NFPA		National Fire Protection Association

OSHA		Occupational Safety and Health Administration

Project Overview 

On September 1 and 2, 2009, Eastern Research Group, Inc. (ERG) conducted
a two-day site visit to a paper mill (hereafter referred to as
“Facility B”). The site visit was conducted by an ERG employee and a
consultant. 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, collecting samples for
analysis by OSHA’s analytical laboratory, and interviewing employees
who work in areas with combustible dust. 

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 B’s
compliance with OSHA regulations or adherence to National Fire
Protection Association (NFPA) consensus standards and therefore, 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
facilitywide evaluation of all OSHA regulations (e.g., means of egress,
fire protection, powered platforms). This report should not be viewed as
a comprehensive review of Facility B’s operations, because site
visitors toured only a subset of the facility’s processes, and not all
of the site visitors’ observations are documented in this report. The
remainder of this report is organized into the following sections:

Organization of Report

Section	Title	Contents

2	Facility Description	General information about Facility B, 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 B’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 B representatives wished to
communicate to OSHA as it proceeds with its combustible dust rulemaking
effort.

9	References	Full references for documents cited throughout the report. 

Attachments	Testing results provided by OSHA’s analytical laboratory
and Facility B’s Procedure for “Settled Bulk Density and Maximum
Accumulation Determination”

 

Facility Description

Facility B is an integrated paper mill that manufactures multiple
household paper products, including toilet paper, tissue paper, and
paper towels. Facility B receives various types of wood in the form of
chips, which are further sized and digested on site to form pulp. Paper
products are then made by feeding the pulp through paper machines.
Facility B representatives suspected that their potential combustible
dust hazards are likely reasonably representative of those experienced
by other companies in this industry manufacturing similar products
(i.e., “lighter” paper products). 

Facility B operates multiple paper machines; ERG site visitors toured a
representative subset of these processes, including the facility’s
older and newer paper machines. Most of Facility B’s production lines
operate continuously, except for scheduled process down times. The
oldest paper machines still operating at Facility B are approximately 45
years old, and the newest paper machine was installed within the last
five years. 

Facility B’s main production areas are located in buildings with a
combined total floor space of roughly 1.8 million square feet.
Approximately 1,000 employees work at Facility B. The facility hires
contractors for security, office cleaning, and other tasks unrelated to
production. During scheduled process shut downs (“outages”), which
can last more than 10 days, Facility B hires contractors to assist with
the more thorough cleaning of production lines. 

Facility B has its own fire brigade with three paid members and roughly
50 volunteers. The facility also has a fire station, fire engine truck,
hazardous materials response van, and other equipment needed to respond
to fires and other emergency events. Though Facility B representatives
noted that they have never experienced an explosion resulting from
combustible dusts, minor fires have occurred (see Section 3.2.7 for more
details). Smoking is not allowed in or near Facility B’s production
areas; site visitors noticed no evidence of smoking (e.g., discarded
cigarettes) in the production areas.

Six full-time employees work in Facility B’s safety department, and
two additional employees work full time implementing the facility’s
process safety management requirements. In addition, the company that
owns Facility B has a corporate safety group and a corporate process
safety group, which provide support and guidance to Facility B. One of
the corporate safety officials devotes approximately 90% of his time to
researching, evaluating, and addressing combustible dust safety hazards
applicable to paper manufacturing operations. 

Site visitors asked the facility’s safety personnel to comment on the
roles that outside parties play in Facility B’s combustible dust
safety programs. A summary of those responses follows: 

Facility B is visited annually by the local fire marshal. The local fire
fighting force, however, reportedly has limited specialized experience
with combustible dust safety issues and does not require or suggest
adherence to NFPA standards specific to combustible dust. 

Facility B has previously contracted with consultants and external
engineering and design firms to characterize various materials (see
Section 4.1) and assist with designing and installing dust controls
during facility expansions, process upgrades, and other changes to
production equipment. 

Facility B representatives have not consulted directly with OSHA on
combustible dust issues. However, the corporate safety representative
actively tracks OSHA’s ongoing activities pertaining to combustible
dust. For instance, he had already obtained and reviewed OSHA’s
Combustible Dust National Emphasis Program, and he periodically visits
the agency’s combustible dust Web site. Both he and selected Facility
B personnel have obtained and reviewed NFPA standards for further
insight on combustible dust safety issues. 

The company that owns Facility B is a member of a trade association
(American Forest and Paper Association [AF&PA]) that is very actively
engaged in tracking combustible dust safety issues and safety and
environmental rulemaking efforts. Representatives of the Facility B
corporate safety department have communicated with this trade
association and owners of other paper manufacturing companies to discuss
specific issues pertaining to combustible dust recognition,
housekeeping, and hazard prevention. 

Process Descriptions

This section describes the process operations that the site visitors
viewed at Facility B. Section 3.1 provides a very general overview of
Facility B’s production processes, and Section 3.2 summarizes site
visitors’ specific observations pertaining to dust accumulations,
housekeeping practices, presence of hazardous locations, control
technologies, and other related issues. All photographs referred to in
this section appear at the end of this report. 

Overview of Common Operations

This section presents a very general overview of the activities involved
in the production lines that the site visitors toured. Housekeeping
procedures are described here and discussed in greater detail in Section
3.2. Many additional operations occur at Facility B other than those
listed below. 

Wood Chip Processing

Facility B manufactures its paper products from wood chips, which are
stored on site in multiple piles. The wood chips are fed to a sizing
process consisting of a series of vibrating screens to remove chips that
are either smaller or larger than the optimal size for the digester. The
tertiary screen is not covered. The chips that pass the screening
process are fed via conveyor to digesters. Air exhaust from the
vibrating screens is vented to dry dust collectors located inside the
wood processing building, and fugitive dust not captured and vented to
the dust collectors eventually either settles on horizontal surfaces or
adheres to vertical surfaces. The wood dusts in this area typically have
a moisture content of approximately 15%. Although the wood screening
building was originally designated as a Class II location for specifying
electrical equipment and wiring, the replacement equipment and wiring
are no longer rated for Class II hazardous locations.

Fines from the wood screening building are blown to a nearby silo. The
silo does not have fire or explosion protection. However, a sample
collected during the site visit of settled dusts near the base of the
silo indicates that these fines have a high moisture content (50%) and
relatively large particle size distribution (see testing results for
Sample #1985 in Table 1). 

Settled dusts in the wood screening building are removed both during
routine cleaning activities and less frequent “top-to-bottom”
cleaning campaigns. As part of the routine cleaning, which typically
occurs once every few days, dusts on horizontal surfaces in the vicinity
of the primary and secondary screens are swept into chutes that lead to
a storage bunker outdoors; near the uncovered tertiary screen, employees
use plastic shovels and brooms to remove settled dusts. The purpose of
the “top-to-bottom” cleaning is to remove accumulated dusts from all
horizontal and vertical surfaces, and this is typically accomplished
using various techniques (e.g., vacuums, compressed air). Facility
personnel indicated that fires are rare inside the wood processing
building, with none occurring in at least the last five years. The high
moisture content of the wood chips and sawdust probably best explains
why fires occur so infrequently in this production area.

Paper Making

Facility B has multiple paper machines that manufacture paper rolls for
the subsequent paper converting operations that produce consumer paper
products. The two oldest paper machines are 1960s vintage, while the
newest is about six years old. Nearly every machine is located in
separate large buildings. Though the individual machines vary in many
regards, they share some common operating principles. At each machine,
pulp slurry is fed to the “wet end,” where a 12-foot-wide paper
sheet is formed. At this stage, the paper web has a moisture content of
approximately 50%, but the sheet is continuously passed through pressing
and drying operations that reduce the moisture content to 5%. The output
from the paper machine is finished paper that is wound on large 12-foot
reels to be sent to the converting area (see Section 3.1.3) for further
processing.

Paper machines generate dusts as they move and dry massive quantities of
paper. Most of Facility B’s machines have dust collection systems that
vent these airborne paper dusts to wet scrubbers and to wet pits leading
back to the pulping operations. Though the dust collection systems
capture a large volume of airborne dusts, paper dusts do settle on
surfaces throughout the large paper machine, especially toward its
“dry end.” Dust collection on the newest paper machine seemed to be
significantly more effective than on the older machines. 

For the paper machines that operate continuously, the machines’ doctor
blades have to be changed up to three times per day. During these daily
blade change-outs, operators perform “blow downs” during which they
use compressed air to remove settled dust from the internal workings of
the paper machine and the surrounding areas. The paper machine continues
to run during these blow downs (i.e., the machine is not shut off or
de-energized, heated surfaces have not cooled), but no paper is being
made or spooled during this time. The routine blow downs typically take
less than 15 minutes to complete. Operators also conduct more extensive
blow downs on a weekly basis, with the main differences from the routine
blow downs being 1) the extent of the blow down (i.e., walls and
overhead structures are cleaned) and 2) the paper machine does not
continue to run during these activities. 

Facility B personnel familiar with the blow downs noted that operators
have encountered smoldering material and observed fires during this
activity. According to multiple employee accounts, compressed air blow
downs of paper machines and other major equipment at paper mills is
commonplace in this industry. Section 3.2.2 presents more detailed
information on the challenges that paper mills face when removing
settled dusts from paper machines. 

Paper Converting

The final production operation is converting, where several machines
unwind paper from the 12-foot-wide reels and rewind the paper onto
smaller cardboard rolls (for tissue paper and paper towels); these rolls
are subsequently cut by log saws and packaged. All log saws are in
enclosures. Some winding and packaging operations also occur in
enclosures, but others do not. Like paper making, paper converting
operations take place in large warehouse-style buildings. One of these
areas at Facility B spanned 350,000 square feet and had ceilings
approximately 30 feet high. 

During the conversion process, paper dust is liberated as large rolls
are unwound, as smaller rolls are wound and cut, and during packaging.
The dust in this part of the facility has the lowest moisture content
(typically 5% or less). Several large dry dust collectors, situated
outside the buildings, control the dusts generated in the converting
areas. However, some dusts liberated in the process settle on horizontal
surfaces and overhead structures. In recent years, Facility B has
employed and investigated a wide range of housekeeping techniques to
minimize dust accumulations while not creating a dust nuisance to
operators. Section 3.2.3 revisits this issue. 

Specific Issues Pertaining to Combustible Dust 

This section summarizes site visitors’ observations on several
specific issues regarding potential combustible dust hazards at Facility
B. These specific issues were selected for more detailed summaries
because they either 1) demonstrate unique challenges faced by this
industry, 2) highlight effective engineering solutions implemented by
Facility B, or 3) point to areas where improved combustible dust control
measures could be implemented. 

Dust Accumulations

The nature and extent of dust accumulations at Facility B varied across
the different production areas:

In the wood chip processing building, the settled sawdust was relatively
coarse in the vicinity of the primary and secondary vibrating screens
and finer near the tertiary screen. The settled dust on horizontal
surfaces near the tertiary screen—floors and ledges of equipment (see
Figure 1)—was more likely to be re-suspended. The material that
adhered to walls and windows was not easily dislodged, however.

In the vicinity of the paper machines, the paper dusts were present in
various forms. During blow downs, for example, use of compressed air
generated a finely dispersed cloud of paper dust (see Figure 2) that
remained airborne for several minutes. The compressed air used during
the blow downs appeared to effectively remove settled dust from the
paper machines; however, much of this dust eventually settled on
surfaces throughout the building (e.g., floors, ductwork, overhead
surfaces, rooftop exhaust fans). Once settled, many of the dust
particles tended to agglomerate and clump together, eventually forming a
“fluff” that would likely not disperse in air unless physically
disturbed. The extent of agglomeration appeared to vary with moisture
content. Equipment cleaning operations (see Section 3.2.2) were
established to minimize dust accumulations in the paper machines. The
operators also washed down dust accumulations that settled onto floors
after the blow downs.

In the converting areas, finely divided dust particles also tended to
agglomerate and clump after settling on horizontal surfaces, forming a
“fluff” material (see Figure 3). This material was observed inside
enclosures where converting operations occurred (e.g., winding, cutting)
and in the general production area. Facility B conducted extensive
evaluations of housekeeping procedures (see Section 3.2.3) to identify
cost-effective measures for removing accumulations. 

Equipment Cleaning

Facility B’s blow downs of paper machines (see Figure 2) illustrate a
difficult challenge this industry faces in dust control: How might
facilities remove dust accumulations from crevices and other surfaces
that are difficult (if not impossible) to clean effectively by means
other than compressed air blow downs? 

When discussing this issue, facility representatives first noted that
most paper machines operating in industry were originally designed with
a projected lifetime of approximately 40 years, but many
machines—especially older ones—were not originally designed to
optimize dust control. Therefore, across the industry, older paper
machines without optimal dust control are still expected to operate for
decades before being replaced with more modern designs. The paper
machines also represent a significant capital investment. With design,
purchase, and installation of a new machine likely costing more than
$250 million, replacing or significantly retrofitting existing machines
just to enhance dust control to prevent the need for blow downs is not
an attractive option. 

Facility representatives explained that cleaning during blade
change-outs is a necessity, because excessive dust accumulations in the
paper machines not only pose a potential fire hazard, but also may
compromise the integrity of paper manufactured during subsequent
operations. Vacuuming techniques were investigated but found to be
ineffective for removing dusts from the inner workings of the paper
machines. Moreover, vacuuming would likely present personnel safety
risks when vacuuming inside components of paper machines and take
substantially longer than conducting a compressed air blow down, which
would therefore increase the duration of production down-time. 

Site visitors inquired about opportunities for conducting the blow downs
in a manner that minimizes risks for fires and explosions:

Dusts generated by the paper machines can settle on heated surfaces,
including the tops of Yankee dryers (see Figure 4). During the site
tour, site visitors noted that some of the dust that settled on
dryers’ welds and seams showed evidence of charring. This observation
raised concern that employees conducting blow downs might inadvertently
suspend smoldering or burning material into air containing high
concentrations of combustible dust—a concern reinforced by the fact
that fires have already occurred on and near the Yankee dryers (see
Section 3.2.7). These observations suggest the need to consider
engineering solutions to prevent accumulation of combustible dust on
these and other heated surfaces, which might be accomplished by using
overhead oscillating fans or sealing off areas above the Yankee dryers. 

During blow downs, facility personnel reportedly deactivated the dust
collection system, though the reasons for this practice were not
entirely clear. Obviously, the dust collection system is not designed to
control dust clouds generated during the blow downs, but operation of
the system during the blow down would vent at least some of the airborne
dusts to the wet scrubber and reduce the amount of time that large dust
clouds are present during and after blow downs. Further, while
installation of additional hoods would likely not eliminate dust clouds
formed during the blow downs, installing hoods near heated surfaces
might reduce accumulations near areas of potential concern. 

Employees who operate the compressed air lines during blow downs work
for short time periods directly inside clouds of combustible dust, and
some areas in the paper machines are confined spaces where dust clouds
can linger. This practice likely does not pose a health hazard, given
employees’ use of respiratory protection, but it may pose a fire or
explosion risk. Installation of additional fire detection and
suppression systems in confined areas of the paper machines can minimize
the risk of damage and injury in the event that dust clouds in these
areas ignite. 

Housekeeping Practices

In recent years, Facility B has launched several improvements to its
housekeeping practices, including innovative and cost-effective
engineering solutions. Examples of three such improvements follow: 

The company that owns Facility B recently developed a corporate
combustible dust housekeeping guidance document (see Section 4.3). Once
employed, this guidance should lead to a more systematic and coordinated
effort to minimize dust accumulations and identify problem areas
requiring further evaluation.

Facility B has purchased new vacuums for removing accumulations of
combustible dust in the paper converting areas. The new “Tiger vacs”
(see Figure 5) are certified for operating in Class II environments.
According to specification sheets provided by the manufacturer, these
devices have a collection capacity of 16 gallons and are dust ignition
proof, static-dissipative with conductive hoses and attachments, and
grounded with a resistivity of less than 10 ohms. While the new vacuums
appear suitable for the intended application, older vacuums not rated
for Class II environments have not been removed from the paper
converting areas, and some employees continue to use them. 

Housekeeping approaches for removing dust accumulations from overhead
structures in the paper converting areas have proven to be an
interesting case study. Facility B’s original practice was to have
employees use compressed air to dislodge the “fluff” from the
overhead structures and then sweep and vacuum the material that fell to
the floor. While this practice effectively removed settled dust from
overhead structures, some of the material dislodged by the compressed
air would simply accumulate in other locations. Additionally, some
employees working in the area expressed concern about being exposed to
airborne dust during the blow downs, which led Facility B to halt this
practice and consider other housekeeping options (e.g., contractor or
employee vacuuming with approved dust ignition proof equipment and
overhead oscillating fans). 

The next approach adopted by Facility B was to remove overhead
accumulations using Tiger vacs placed on scissor lifts. This practice
was very effective at removing accumulations without exposing workers to
dust, but the practice was relatively slow and labor intensive.
Specifically, the practice required teams of two employees: one employee
worked on the ground and operated and moved the scissor lift, and the
other employee worked on the lift and operated the Tiger vac. These
teams of two would work nearly full time for several weeks to vacuum all
overhead structures in just one part of the paper converting areas. 

Facility B recently investigated an engineering solution: installing
overhead oscillating fans that consistently blow air over and near
overhead surfaces to prevent dusts from accumulating at these
elevations. The fans were recently pilot tested at Facility B, where
each fan proved to be highly effective at minimizing dust accumulations
within a 35-foot radius. They also dramatically reduced, though did not
eliminate, the need for vacuuming accumulated dusts. Operating the fans
had the added benefit of not requiring employees to work in elevated
areas, which was necessary when they operated Tiger vacs from the
scissor lifts. As an added safety measure, emergency stop (e-stop)
buttons were placed in production areas beneath the fans. Employees were
instructed to promptly activate these e-stops in the event of a fire,
thus preventing the fans from interfering with ceiling sprinkler
actuation and discharge, and possibly preventing re-suspending
smoldering or burning material. Industrial hygiene evaluations verified
that operation of the fans did not lead to excess noise exposure (i.e.,
0-2 dBA increase, depending on location in relation to floor), increased
exposure to airborne dust, or excessive temperatures that would affect
employee comfort. 

Facility B shared data confirming that use of the overhead oscillating
fans was cost-effective. The facility recently installed 71 permanent
fans at a cost of approximately $450,000. Once installed, the amount of
time that employees would have to spend vacuuming dusts from overhead
structures will decrease considerably. Facility representatives have
estimated that installation of the fans will translate into a labor cost
savings of $88,000 per year. Therefore, the upfront costs associated
with purchasing and installing the fans will be fully recovered in
approximately five years. 

Dust Collectors 

Facility B operates various types of dry and wet dust collectors.
However, the facility is gradually phasing out the dry systems and
replacing them with wet dust collectors, which should greatly reduce the
risks of fires or explosions originating in dust control operations. The
remainder of this section focuses on the dry dust collectors operating
in the paper converting areas, which control dusts having the lowest
moisture content and thus appear to present the greatest risk for fires
and explosions. 

The dust collectors observed in the paper converting areas shared
several design features: they were all located outdoors; they all
returned treated air to the workplace; they were equipped with dry pipe
sprinkler systems and explosion vents; and they were not equipped with
explosion isolation systems. However, they differed in basic design
(e.g., some employed mechanical shaking to remove dust from the
collection media, others used reverse pulsed air) and other factors.
Observations from two specific dust collectors are used to illustrate
the variability in design and operation: 

A newer dust collector (see Figure 6) controlled paper dusts generated
in parts of the converting areas and returned treated air to the
workplace. The explosion panels on the dust collector vent away from the
production building. No evidence of fugitive dust releases were observed
at the dust collector, which appeared to be well maintained.

An older dust collector (see Figure 7) controlled paper dusts generated
in other sections of the paper converting areas. A complex array of
ductwork directed the air streams to the dust collector, with treated
air returned to the workplace. Explosion vent panels were placed on the
side of the dust collector facing the production building, which would
therefore vent a deflagration toward (instead of away from) the building
and employees. 

All surfaces in the vicinity of this dust collector were coated with
settled paper dust, which had agglomerated and clumped into a
“fluff.” This material had settled on the ground, all components of
the dust collector, and the overhead electrical wires. The accumulations
at this particular dust collector likely resulted from some combination
of fugitive leaks and poor maintenance, though the exact source of the
settled dust could not be pinpointed. Employees in the converting area
controlled by this dust collector noted that effectiveness of dust
control in their workplace seemed to deteriorate in recent years—a
trend that might be linked to this particular dust collector’s
performance. 

Automated Fire Suppression Systems

In Facility B’s converting areas, several log saws cut 12-foot-long
wound rolls of paper towels and tissue paper into the smaller sizes used
for the finished consumer products. All log saws were placed in full
enclosures. Facility representatives appreciated the fire and explosion
risks for this operation, given the release of combustible dusts and the
friction of the saw (from self-sharpening) and bearings. To control
these hazards, log saw enclosures were equipped with automated carbon
dioxide (CO2) fire suppression systems triggered by the detection of
excessive heat or fire. The suppression systems are serviced annually,
and facility maintenance personnel replace the CO2 cylinders after they
discharge or otherwise indicate loss of pressure. The systems have been
activated several times, and they effectively suppressed fires in all
instances. 

Classification of Hazardous Locations

It was unclear to site visitors if Facility B had systematically
classified its hazardous locations per the National Electrical Code
Article 502 and NFPA 499. Testing data collected during the site visit
(see Table 1) and the facility tour suggested that some areas were
likely Class II locations due to the accumulation or suspension of Class
II combustible dust particulates.

Site visitors confirmed that some equipment (e.g., Tiger vacs) used in
the converting areas were rated for operation in Class II locations; but
site visitors did not review ratings for a broader range of equipment
(e.g., motors, blowers, forklifts) used throughout the facility. Site
visitors learned during employee interviews that some electrical boxes
and other installations in the converting areas were reportedly “dust
tight” or “dust ignition proof,” but paper dusts had been observed
inside some of these reportedly dust-tight electrical installations. One
employee said the accumulated dusts, in some cases, had enough moisture
to cause short circuits. Employees used vacuums and compressed air to
remove accumulated dusts from the electrical boxes and installations. 

Fire History

According to a log maintained by the facility, 91 fire events occurred
between January and August 2009; however, many of these events did not
involve combustible dusts. Examples of fires that occurred due to, or in
the presence of, combustible dusts included forklift fires (e.g., caused
by accumulation of dust and paper near exhaust pipes and other heated
surfaces on the vehicles), fires atop Yankee dryers that were
extinguished manually, and fires in enclosed log saw rooms that were
extinguished automatically by CO2 suppression systems. During employee
interviews, site visitors learned of additional fires that occurred
prior to 2009, such as a smoldering fire in the hog fuel mounds (which
are located outdoors and away from main production areas); smoldering
material during blow downs of paper machines; fires due to accumulation
of paper dusts on overhead beams and roof exhaust ceiling fans in rooms
housing paper machines; and some accounts of flash fires during deep
blow downs. 

 

Document Review

This section summarizes documents pertaining to combustible dust safety
issues that Facility B made available to site visitors. This section
does not review every document that site visitors evaluated, but rather
focuses on documents that offered unique insights into combustible dust
safety issues and Facility B’s approaches for controlling them. 

Testing Data

Testing data for materials that Facility B handles and produces were
available from two sources: Facility B representatives let site visitors
review some testing data that they had recently collected, and site
visitors collected five samples that were sent to OSHA’s laboratory
for testing. This section summarizes both data sets. It also includes
micrographs of settled paper dust generated by one of the site visitors.
Refer to Section 4.2 for facility representatives’ concerns regarding
potential testing costs and the availability of combustibility and
explosibility data from suppliers of particulate materials used in
Facility B. 

Facility B’s Testing Data

Facility B and the company that owns it have compiled extensive testing
data on numerous materials that the facility uses and produces. The
facility shared two sets of testing data during the site visit, and
these data sets illustrate two broader points: 

Density and allowable dust accumulation thickness. The 2006 edition of
NFPA 654 has an equation for “allowable thickness” of combustible
dusts. This equation includes a correction factor for the material’s
settled bulk density. Facility B representatives provided several
insights on the implications of this equation for paper mills and
general industry and noted where some allowable thickness calculations
generate counter-intuitive results:

Facility B shared results from over 150 paper dust samples that were
analyzed for settled bulk density. All samples were collected from paper
converting areas, where dust moisture content is typically between 5%
and 8%. On average, these samples had a settled bulk density of 1.5
lb/ft3—a density that would suggest an allowable thickness of 1.6
inches according to NFPA 654 (see equation in Section 6.2.3.2 of the
standard). Some materials had settled bulk densities less than 0.5
lb/ft3, which would translate into an allowable thickness (using
NFPA’s equation) of nearly 5 inches. Note that for any material with a
settled bulk density less than 2 lb/ft3, Facility B set its own “alarm
level” for dust accumulations to be 1.25 inches (considered maximum
dust accumulation allowance for tissue dust), even though the NFPA
equation suggests that a greater thickness may be acceptable. 

Facility B representatives also noted that ASTM and other organizations
have not published standard methods for measuring settled bulk density,
which is a parameter that future editions of NFPA 654 might include in
its equation for allowable dust thicknesses. Without standard
methodologies, industry must determine the most appropriate approach for
measuring this parameter—something that Facility B has already done.
(Note: The facility’s written procedure for “Settled Bulk Density
and Maximum Accumulation Determination” is included in this report as
Attachment 2.) 

Facility representatives emphasized that tapped bulk density can far
exceed settled bulk density for paper dust and other low-density fibrous
material. Thus, any future definitions or equations for allowable
combustible dust thickness should clearly state which form of bulk
density should be considered (i.e., settled or tapped) and provide
guidance on testing methodologies if settled bulk density factors into
the equation. Facility B representatives indicated that settled bulk
density is more relevant from a risk perspective than tapped bulk
density as a result of paper fibers “collapsing” onto themselves
when handled, collected, and measured in a collection device such as a
vial or bottle which is required for “tapped bulk density”
measurements, thereby not providing the “true” bulk density of the
dust from a risk perspective as it lays on horizontal surfaces (i.e.,
the tapped bulk density provides a greater value than settled bulk
density).

Facility B representatives also shared density testing results for wood
dusts from the mill’s screen room. These dusts had settled bulk
densities on the order of 6 lb/ft3—a density that would suggest a
maximum allowable accumulation thickness of 0.4 inches. Thus, by the
current NFPA 654 equation, the wood dust would have a lower maximum
accumulation thickness than the paper dust, even though wood dust’s
moisture content (approximately 15%) suggests that it may pose less of
an explosion risk than the paper dust. Facility B representatives were
also well aware that NFPA 664 has requirements applicable to combustible
wood dusts (e.g., a 1/8 inch accumulation allowance).

Moisture content and testing data. Facility B also shared with site
visitors testing results that were conducted to evaluate the impact of
moisture content on combustibility and explosibility parameters.
Specifically, paper dust from a converting area was collected and split
into two samples; one was tested “as received,” and the other was
dried before testing. Table 2 compares the results from these two
samples. For most parameters, the testing results for the “as
received” sample (4.8% moisture) and the dried sample (0% moisture)
differed by less than 25%; for the minimum ignition energy, however, the
measured values for this particular split sample differed by a factor of
three—a difference illustrating the significance of moisture content
for evaluating combustible dust ignition sensitivity. 

After the site visit, Facility B representatives shared additional
testing results demonstrating the effect that moisture content can have
on certain parameters. Specifically, an “as received” paper dust
sample (7.9% moisture) was found to have a minimum ignition energy of
1,600 mJ. However, a dried sample (<0.5% moisture) of the same material
was found to have a minimum ignition energy of 40 mJ. In this case, the
minimum ignition energy increased by a factor of 40 once the moisture in
the sample was removed. 

OSHA’s Test Data for Samples Collected During the Site Visit

As noted previously, site visitors collected five samples during the
site visit, with the permission and concurrence of Facility B
representatives. Per discussion with Facility B representatives, four
samples were subject to a “Class II test” at OSHA’s laboratory. In
some cases, Facility B representatives were interested in testing
results for “as received” samples; however, following the
laboratory’s standard procedures, samples with moisture levels greater
than 5% were dried prior to analysis. Copies of the laboratory testing
results appear in this report as Attachment 1; Table 1 summarizes the
results. More information on the samples collected and the test results
follows:

Sample #1985: Sawdust. This sample is sawdust that had accumulated
around the base of a storage silo that was not equipped with fire or
explosion protection. Though a Class II test was requested, the
laboratory could not perform this test on the sample because the
material was too coarse. The laboratory instead tested the sample for
explosibility and concluded that the material tested was not explosive. 

Sample #1986: Sawdust. This sawdust sample was collected from a ledge on
the exterior of the tertiary screening device in the wood processing
building (see Figure 1). The original sample had a moisture content of
13%. The laboratory concluded that the dried sample was a Class II dust.

Sample #1987: Sludge (biosolids). This sludge sample consisted of
biosolids collected near the hog fuel storage piles. The original sample
had a moisture content of 64% and was dried to below 5% moisture for
testing. The laboratory concluded that the dried material was not a
Class II dust. Note, however, that this sample exhibited signs of
biological decay from the time it was collected to the time it was
analyzed. 

Sample #1988: Paper dust. This paper dust sample was collected from the
top of a Yankee dryer in one of the papermaking operations (see Figure
2). Of the five samples collected, this sample had the lowest moisture
content (4.1%) and did not require further drying before testing. The
laboratory concluded that the sample, as received, was a Class II dust. 

Sample #1989: Sawdust. This sawdust sample was collected from a pit in
the sawdust press building (see Figure 3). After drying, which brought
the moisture content from 17% to below 5%, the sample was found to be a
Class II dust. 

As noted in the testing results (see Attachment 1), the data presented
above should not be used in designing or engineering protective safety
equipment.

Micrographs of Settled Paper Dust

The consultant who participated in the site visit generated micrographs
of settled paper dust from the top of a Yankee dryer (Sample #1988).
Figure 9 presents these micrographs, which include one image at a
magnification of 50x (see Figure 9A) and three images at a magnification
of 200x (see Figure 9B). It is clear from the micrographs that paper
“dust” is composed primarily of fibrous material as opposed to
particles. The fiber lengths ranged from approximately 120 to 790
microns, with an average aspect ratio of 12. Some paper fibers were
curved or bent, which appears to allow fibers to become entangled and
form agglomerates. Some fiber agglomerates were observed in the
micrographs (see lower left-hand corner of Figure 9A). These
agglomerates would need to be dispersed in order for the settled
material to burn as a suspended dust cloud. Dispersal appears to be
possible with a sufficient disturbance, such as the high pressure
compressed air source used during blow downs.  

Material Safety Data Sheets (MSDSs) 

Facility B’s division within its company uses roughly 150 materials
that are combustible dusts or have the potential to form them during
processing. To ensure that these materials’ hazards are fully
understood and prevented, corporate safety officials have asked
suppliers to provide quantitative testing data for these parameters
(e.g., minimum explosible concentration, minimum ignition energy,
deflagration index). To date, the company has received quantitative
explosivity testing data for approximately 35% of these materials.
Facility B representatives felt that suppliers were obligated to provide
this quantitative testing data, whether on an MSDS or upon request.
Should suppliers refuse to provide these data, Facility B might have to
conduct its own testing at costs between $3,000 and $12,000 per
material—the actual costs will depend on the parameters for which
testing is required. 

Most of the products generated by Facility B are consumer products for
which MSDSs are not required, but the facility did share copies of two
MSDSs: one prepared by a supplier of “cellulose dust” and one
prepared by Facility B for “paper dust.” Neither MSDS included
quantitative data on combustibility or explosibility, but both MSDSs
included the following qualitative information about the potential
explosion risks: 

High concentrations of airborne dust may create an explosion
hazard…Finely divided cellulose dust presents an explosion hazard in
the presence of an ignition source…Do not handle near open flames,
heat, sparks, or other sources of ignition…Avoid creating airborne
dust; dust at sufficient concentration can form explosive mixtures in
air.

Note: 	The company that owns Facility B has since updated MSDSs for wood
and cellulose dust that contain more quantitative data (e.g., ranges of
minimum explosible concentrations). 

Housekeeping Guidance Document

Corporate safety personnel recently prepared a 24-page housekeeping
guidance document for all facilities companywide that manufacture
consumer products. A draft of this document was made available to site
visitors. (Note: The facility’s final Combustible Dust Housekeeping
Guidance Document was issued earlier this year.) Examples of noteworthy
topics addressed in the guidance document include: 

Identifying roles, responsibilities, and training requirements for
operators, supervisors, management, and other individuals. 

Designating a “facility combustible dust leader” who would assume
responsibility for implementing the housekeeping requirements and
monitoring compliance. 

Requiring each facility to develop a written housekeeping program
consistent with the general requirements outlined in the corporate
guidance.

Listing best practices to minimize dust accumulations, such as using
overhead oscillating fans, sealing off areas prone to dust accumulation,
sloping horizontal surfaces, inspecting ductwork for evidence of leaks
or buildup, and investigating all incidents.  

Specifying preferred cleaning methods, which were water wash down, wet
wiping, vacuuming, and nonvigorous sweeping. Use of compressed air is
permitted for cleaning inaccessible surfaces or surfaces that could only
be accessed by means that would otherwise present a greater physical
safety hazard. Additional specifications are documented for blow downs
using compressed air (e.g., using lowest air pressure possible,
prohibiting “hot work” during blow downs, requiring electrical
equipment to be shut down, using 30 psi “dead head” protection on
air wands), though site visitors noted that some of these proposed
measures for blow downs have not been fully implemented at Facility B.

Quote for Installing a Wet Dust Collector 

To illustrate the costs associated with upgrading equipment, Facility B
shared a vendor quote, prepared within the last five years, for
purchasing and installing a new dust collection system to control dusts
generated in a “rewinding” section of the converter areas. This
quote was sought to replace the existing dry dust collection system with
a wet dust collection system (a venturi scrubber). The detailed cost
estimate from the vendor amounted to $550,000. The dust collection
system quoted by the vendor included many components: seven 8-foot-wide
dust capture hoods that have exhaust rates of 2,000 to 4,000 cubic feet
per minute (cfm); a stainless steel venturi scrubber with an air flow
capacity of 27,000 cfm; a water circulation pump; multiple fans; and
various other peripherals. The vendor estimated that it would take four
months to install the new wet dust collection system. 

Note that the quote reviewed in this section only accounts for the costs
that Facility B would pay the vendor for the new dust collection system;
it does not include internal costs associated with machine down time.
Further, this one new dust collection system would serve only a portion
of the converting processes employed at Facility B. To upgrade dust
collection systems throughout the converting areas would cost
considerably higher than implied by this one cost estimate. (Note:
Section 4.6 presents additional estimates for upgrading Facility B’s
equipment to be compliant with NFPA 654.)

Combustible Dust Fire and Explosions Hazard Assessment

Approximately six months before the site visit, corporate safety
officials coordinated with Facility B to conduct a facility-wide hazard
assessment for combustible dusts. The team that conducted this hazard
assessment reported several findings, some of which already led to
changes in facility practices (e.g., installation of more overhead
fans); others are being considered for further improvements. Examples of
conclusions include:

Designate an individual to lead Facility B’s combustible dust hazard
and risk mitigation program.

Develop a written facilitywide housekeeping program, which should also
include area- and building-specific housekeeping plans.

Conduct a risk assessment to determine the need for fire and explosion
protection on paper machines and their dust collectors. Evaluate dust
control options for two machines that currently are not equipped with
dust collectors. 

Incorporate “management of change” into the review of any dust
handling or generating system to ensure risks associated with the
changes are addressed. 

Ensure all dust collection systems are balanced and operated and
maintained according to design criteria and manufacturer specifications;
establish an engineering approval authority to approve all future
modifications to dust collectors. 

Install overhead oscillating fans in areas with high dust accumulation
rates to control accumulated dusts and ease housekeeping burden. 

Perform and document grounding and bonding checks for all equipment
handling combustible dusts.

Document all housekeeping activities following the Corporate Combustible
Dust Housekeeping Guidance document. 

Analysis of Costs to Comply with NFPA Combustible Dust Standards

Facility B representatives conducted an internal assessment of the costs
to bring the facility’s operations involving paper dust into
compliance with the current (2006) edition of NFPA 654. This assessment
considered costs associated with bringing operations involving paper
dust into compliance, but did not consider costs associated with other
types of dusts (e.g., coal dust). Table 3 presents an itemized
accounting of Facility B’s projected costs for upgrading operations
involving paper dust to comply with NFPA 654.

As Table 3 shows, Facility B’s anticipated total costs are $17.8
million, with 86 percent of this total attributed to upgrades to dust
collection systems dedicated to paper machines or converting operations.
The remaining 14 percent of the costs are comprised of safety
engineering controls, environmental compliance costs, instrumentation
for performance monitoring, and purchases to support the facility’s
housekeeping program.

Note that the company that owns Facility B has conducted similar cost
assessments at 11 other paper mills. These mills vary in size,
geographical location, and other aspects, but all make consumer paper
products. The estimated costs associated with bringing these individual
facilities into compliance ranged from $2.0 million to $26.5 million,
depending on the nature and extent of upgrades required. At most of
these facilities, upgrades to dust collection systems were the most
expensive item. Between Facility B and the 11 other mills that
manufacture consumer paper products, the company that owns Facility B
estimated that its company-wide upgrades will cost $183 million.

Training 

Facility B offers numerous training courses to its employees and
contractors. This section presents observations on the content of only
those training courses that facility personnel mentioned during the site
visit. Therefore, this is just a partial list of the training that
Facility B offers to its employees. 

New employee safety orientation. Site visitors scanned through training
materials (87 slides) used to introduce new employees to Facility B and
its safety programs. The course addresses many general topics, including
a segment on combustible dust safety. This segment describes the
required elements of a combustible dust explosion, dust control
strategies, and ignition control measures. 

Combustible dust training course. Corporate safety officials developed a
training module to teach operators important safety considerations for
working near combustible dust. The module was developed to be used by
individual facilities as part of their Hazard Communication trainings. 

Site visitor informational video. All visitors to Facility B are
required to view a 15-minute video on facility-specific safety
practices. The video addressed emergency response, motor vehicle safety,
lockout, and other general safety issues. 

Fire brigade training. Every member of Facility B’s fire brigade was
trained in accordance with NFPA 600 requirements. 

Contractor training. All contractor employees review a CD and take a
test on dust hazards before working at Facility B. These tests are
retained for the duration of the contractor’s work period for
reference.

 Dust Collection System Operation, Maintenance, Troubleshooting, and
Combustible Dust Requirements training. Three of these training courses
have been provided to paper mill engineers, paper machine optimizers,
paper machine maintenance personnel, and safety and health professionals
between February and May, 2010. A fourth course is planned for October,
2010. The facility plans to continue providing this course in 2011 and
beyond.

Safety Programs

This section reviews the site visitors’ observations of selected
safety programs implemented at Facility B, with a focus on the extent to
which combustible dust issues are factored into these programs. The site
visitors’ observations about the various programs follow: 

Confined space entry. Facility B’s confined space entry policy
prevents entry into confined spaces when the following condition is met:
“…a concentration of airborne combustible dust that obscures vision
at a distance of 5 feet (1.52 meters) or less.” The origin of this
condition is believed to be based on guidelines in a previous scientific
publication (Eckhoff, 2003). 

“Hot work” permits. Facility B’s hot work policy defines hot work
as “any work that contributes a direct source of ignition.” Specific
examples listed in the policy include welding, grinding, use of torches,
electric or battery heating elements, sandblasting, drilling, sawing,
and use of jack hammers. In order to obtain a hot work permit, an
employee must demonstrate that “no flammable or explosive materials
are present,” and floors must be swept clean of combustible material
within a 35-foot radius of where hot work is to take place. 

Lockout/tagout. Facility B has lockout/tagout procedures and training to
ensure that employees do not inadvertently activate or energize
equipment that can place themselves or other employees at risk. Facility
B also has implemented numerous safety interlocks to prevent employees
from entering certain enclosures (e.g., log saw rooms) while potentially
hazardous operations are taking place. 

Personal protective equipment and uniforms. Operators at Facility B are
required to wear hard hats, safety goggles, and steel-toed shoes in most
production areas. Employees donned respiratory protection (air purifying
respirators) when conducting blow downs. Operators are not required to
wear flame-resistant clothing anywhere at the facility. 

Main Findings

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

Facility B’s safety staff exhibited a high level of awareness of
combustible dust safety issues, and the added support provided by
corporate safety personnel enhanced this awareness. Both facility and
corporate staff appeared to be very knowledgeable of existing NFPA
standards and pending revisions. As testament to this knowledge and
awareness, Facility B implemented—or was in the process of
implementing—many proactive programs and policies (e.g., corporate
housekeeping guidance, extensive effort to characterize materials,
combustible dust training courses). 

In recent years, Facility B implemented many effective and innovative
engineering solutions to control dusts and prevent fires and explosions.
Examples include installation of overhead oscillating fans to reduce
dust accumulations on overhead structures in the paper converting areas;
gradual shift from dry dust collection systems to wet scrubbers;
installation of CO2 fire suppression systems to control fires in log saw
enclosures; and use of Tiger vacs in locations most likely to have
combustible dust atmospheres. Review of fire logs and other
prioritization methods can help identify opportunities for future
improvements in dust control.  

Sawdust and paper dust accumulations were evident in the wood processing
operations, paper machines, and paper converting areas. Facility
representatives seemed well aware of the production areas that had the
greatest accumulations and were in the process of considering
engineering solutions and administrative controls to minimize or control
dust releases for some of these areas. Specific areas that may require
further attention include dust accumulations on heated surfaces, in
“dust tight” electrical boxes, and in some enclosed areas. Dust
collection improvements to prevent dust suspensions in a few specific
areas (e.g., log saw rooms, areas around doctor blades on paper
machines) would also be beneficial.

Compressed air blow downs of paper machines are an obvious source of
airborne combustible dust; however, this practice is reportedly
commonplace in industry and is the most effective and fastest means for
removing dust accumulations from paper machines. Replacing older paper
machines with newer machines with dust control fully integrated into
equipment design does not appear to be a cost-effective solution in the
near term, and does not appear to eliminate the need for blow downs
(even though it can reduce the duration and extent of the blow downs).
Facility B is encouraged to examine additional measures for ensuring
that removing dust accumulations from paper machines is conducted as
safely as possible. Examples of such measures include preventing dust
accumulations on heated surfaces (e.g., by sealing them off, using
oscillating overhead fans, installing additional dust control hoods),
considering the installation of local fire detection and suppression
systems in confined areas of the paper machines, and possibly providing
fire resistant personal protective equipment (per NFPA 2112) for
personnel doing blow downs in these confined areas. 

Facility B has taken proactive measures to replace dry dust collection
systems with wet systems, which should greatly reduce risks of fires or
explosions in these devices. The existing dry dust collection systems
vary considerably in terms of design and maintenance. Opportunities for
minimizing hazards in dry dust collectors include installing explosion
isolation systems, interlocking the clean air returns to shutdown upon
sprinkler actuation, ensuring that dust collectors have no fugitive
releases, and maintaining all systems according to manufacturer
specifications. Priority should be given to dust collectors exhibiting
signs of poor performance and those judged to present the greatest
potential hazard (e.g., those that handle dusts with the lowest moisture
content). 

Forklifts, motors, vacuum cleaners, and other equipment should be
approved for the hazard classification in the areas where they operate.
Measures should be taken to prevent dust from entering and accumulating
in “dust tight” enclosures. 

Feedback to OSHA

At the end of the site visit, ERG asked representatives from Facility B
if they had any specific feedback for OSHA on combustible dust safety
issues. (Note: This site visit occurred after OSHA publicly announced
its intention to initiate a rulemaking on combustible dust [OSHA,
2009b], but before the agency convened its stakeholder meetings).
Facility B representatives offered the following responses:

Facility B noted that paper mills have some operations that are major
capital investments. A new paper machine, for instance, can cost more
than $250 million to purchase and install. These facilities will
experience severe economic burden should OSHA’s combustible dust
rulemaking effectively require replacement of, or significant retrofit
to, this equipment. 

Facility B representatives expressed concern that OSHA’s combustible
dust standard would prohibit or severely limit the use of compressed air
to remove dust accumulations. For reasons stated earlier in this report
(see Section 3.2.2), Facility B representatives stated that blow downs
using compressed air are currently the only effective means to remove
dust accumulations from the paper machines, particularly their inner
components. Facility representatives also voiced concern about OSHA
adopting NFPA requirements that allow for use of compressed air but
limit gauge pressures to levels too low to allow for effective cleaning
of paper machines. While setting maximum allowable gauge pressures for
compressed air would limit the formation of dust clouds during equipment
cleaning, setting gauge pressures too low would require operators to
enter poorly accessible parts of paper machines to remove all
accumulated material, thus creating a potential physical hazard and
risks to operators.

Citing recent pending changes to NFPA 654 that could have significant
implications on combustible dust definitions and controls, facility
representatives voiced concern about maintaining compliance with NFPA
standards that are reviewed and amended every few years with no
cost-benefit analyses performed or considered

Facility B representatives urged OSHA to consider material-specific
properties when developing its standard, given that paper and wood dusts
differ considerably from other types of dusts (e.g., coal, metal) that
necessitate more stringent controls. They referred to NFPA 654’s
proposed changes to allowable accumulation thicknesses to emphasize how
material density and moisture content should factor into hazard
assessment. Another specific concern was whether OSHA’s rule would
apply to dusts that have a tendency to agglomerate: finely dispersed
airborne paper dust has a tendency to form a “fluff” after settling
onto a surface. 

Facilities need information on combustibility and explosibility
parameters to fully assess the hazard potential of certain materials.
However, Facility B indicated that many of its suppliers are not
including quantitative testing data for these parameters on their MSDSs,
nor are they providing this information after it is requested. Facility
B representatives urged OSHA to require suppliers to provide this
information. If that is not done, they asked that OSHA consider the
economic burden of material testing in its regulatory impact analyses. 

The company that owns Facility B is actively engaged in the ongoing
review of NFPA standards that apply to its facilities. Many technical
issues are being debated leading up to the release of the next edition
of NFPA 654. Facility representatives indicated that some of the new
mass equations replacing density equations planned for the 2001 edition
of NFPA 654 are troublesome due to being overly conservative and lumping
all combustible dusts (e.g. plastics, coal, paper, starch) into one
category for the two simple mass equations and too complex and costly
for the two more complex equations that have not been validated in
practice, have not been peer reviewed, and have factors (e.g., the
entrainment factor) whose methodologies have not yet been developed or
substantiated. Additionally, Facility B representatives noted that there
is no loss history indicating that the present settled bulk density
allowance equation used in the 2006 edition has not provided appropriate
protection, as opposed to the new equations proposed for the 2011
edition. Facility B representatives added that the new equations
proposed for the 2011 edition are impractical for industry for
determining compliance with mass allowances (e.g. all dust in an
affected building or area would have to be collected, bagged, and
weighed to determine compliance with the mass allowance established to
determine compliance or non-compliance and would have to be repeated any
time a process change occurs). OSHA can track these issues, which
underscore facility concerns about the scope and applicability of
proposed dust control measures, by monitoring the proposed changes to
selected NFPA standards, in particular the proposed 2011 edition of NFPA
654. 

References

Eckhoff, 2003. Dust Explosions in the Process Industries (3rd Edition).
R.K. Eckhoff. Gulf Professional Publishing, Elsevier Science:
Burlington, MA.

OSHA, 2009b. 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. Testing Results for Samples Collected During the Site Visit

Parameter	Sample #1985	Sample #1986	Sample #1987	Sample #1988	Sample
#1989

Description of material	Sawdust silo	Sawdust	Sludge (biosolids)	Paper
dust	Sawdust

Particle size data 

	   % through 20 mesh	21%	100%	8.7%	93%	90%

   % through 40 mesh	5%	97%	1.9%	83%	64%

   % through 200 mesh	0%	4.5%	0%	17%	2.8%

Moisture content	50%	13%	64%	4.1%	17%

Explosive material?	No	Not tested	No	Not tested	Not tested

Class II dust?	Not tested	Yes	No	Yes	Yes

Notes:	See Section 4.1 for a more detailed description of the sampled
materials and where they were collected.

Refer to Attachment 1 for the original reports from OSHA’s analytical
laboratory and important disclaimers about use of these data (e.g.,
“it is possible that the material is hazardous under different
conditions; the results obtained from this equipment can not be used in
designing or engineering protective safety equipment”).

Samples with moisture content greater than 5% were dried prior to
testing, following the laboratory’s standard protocols. 

Table 2. Effect of Moisture Content on Paper Dust Testing Results  

Parameter	Testing Result

	Sample “As Received”	Dried Sample

Moisture content	4.8%	0%

Pmax (bar)	8.2	8.4

Maximum rate of pressure rise (bar/s)	467	411

Kst (bar-m/s)	127	112

Minimum ignition energy (mJ)	124	40

Minimum explosive concentration (g/cm3)	75	60

Explosion severity (--)	1.46	1.36

Class II dust?	Yes	Yes

Particle size distribution

	     % on #40 screen	7.6%	48.0%

     % on #70 screen	25.6%	24.8%

     % on #100 screen	15.6%	7.2%

     % on #200 screen	23.6%	10.8%

     % in pan	27.6%	9.2%

Notes: 	Data provided to site visitors by Facility B representatives.
Both samples represent a composite of paper dust collected from one of
the paper converting areas. Paper dust was collected from multiple
horizontal surfaces. The composite sample was split for testing. 

	It is unclear if the lower Kst value for the dried sample reflects
test-to-test variability or the presence of smaller particles in the
dried sample. 

		The laboratory used standard ASTM testing methods for most parameters.

 

Table 3. Estimated Costs for Updating Operations Involving Paper Dust
to Comply with NFPA 654

Category	Specific Upgrade Activity	Estimated Cost

Improvements to Dust Collection Systems	Dust collection system upgrade
for paper machine #1	$1,903,000

	Dust collection system upgrade for paper machine #2	$2,000,000

	Dust collection system upgrade for paper machine #5	$1,980,000

	Miscellaneous upgrades to dust collection systems for the paper
machines	$500,000

	Dust collection system upgrade for tissue converting operations
$3,000,000

	Miscellaneous upgrades to dust collection systems in converting
operations	$6,000,000

	Subtotal for category	$15,383,000

Safety Engineering Controls	Fire detection systems in the supply air for
dust collectors	$125,000

	Fire suppression (chemical) in dust collectors	$125,000

	Fire suppression and mechanical isolation for return air ductwork
$125,000

	Bonding and grounding	$25,000

	Protection of electrical equipment	$250,000

	Subtotal for category	$650,000

Environmental Compliance Controls	Monitoring of particulate matter
emissions from wet scrubbers (for EPA)	$648,000

	Monitoring of dry fabric filters (not for EPA)	$150,000

	Subtotal for category	$798,000

Instrumentation for Performance Monitoring	Systems to monitor scrubber
water flow control, static/differential pressure, etc.	$700,000

	Subtotal for category	$700,000

Houskeeping	Purchase and installation of overhead oscillating fans
$255,000

	Purchase of industrial vacuum cleaners	$25,000

	Subtotal for category	$280,000

Total Estimated Costs for Upgrading Operations Involving Paper Dust
$17,811,000

Note: 	Table includes costs for complying with requirements only for
paper dusts. The facility is in the process of estimating compliance
costs for other types of combustible dusts (e.g., coal, wood).

 Figure 1. Photograph of Sawdust Accumulation on Screener in Wood
Processing Room 

Note: 	This photograph shows the tertiary screening equipment found in
the wood processing building. The screening device separates wood chips
of different sizes prior to further processing (i.e., digesting,
pulping). A fine wood dust is visible in this photograph along the
ledges of the screening equipment. Some of this material was collected
and tested in OSHA’s laboratory (sample #1986). The wood dust was
found to have a moisture content of 13%, and the dried sample was a
Class II dust. 

Figure 2. Photograph of “Blow Down” of Paper Machine

Note: 	This photograph was taken while employees conducted a blow down
of a paper machine. Blow down of this machine typically occurred three
times a day and coincided with the time when employees had to exchange
the doctor blade on the paper machine. During the blow downs, which
lasted up to 15 minutes, several employees used compressed air wands to
remove dust accumulations from inner workings of the paper machines
(i.e., areas that could not be efficiently cleaned by other means).
Dusts were blown off the machines and to the side and back of the room.
The large dust clouds generated by the compressed air largely dissipated
by the time the blow down was finished.

Figure 3. Photograph of Dust Accumulations in a Paper Winding Enclosure

Note: 	This photograph shows equipment located inside one of the
enclosed re-winder machines in the paper converting area. Settled paper
dust, which has a “fluff” consistency, is visible on the floor and
horizontal surfaces. The dust also settled atop a motor and other
mechanical equipment. Paper dusts were removed from these enclosures
using various techniques during periodic cleaning campaigns. 

Figure 4. Photograph of Paper Dust Accumulation on Top of a Yankee
Dryer

Note: 	This photograph shows the top of a Yankee dryer in one of the
paper making rooms. A thin layer of paper dust had deposited on the
dryer; these settled dusts compacted and covered the dryer. A quarter
was placed in the layer (see top photograph) for an indication of its
thickness. Some of the accumulated dust, particularly along the
dryer’s welds and seams, showed evidence of charring. The lower
photograph shows some potentially charred material a site visitor
removed from the top of the dryer. Some of this accumulated material was
collected and tested in OSHA’s laboratory (sample #1988). The material
had a moisture content of 4.1% and was found to be a Class II dust.

 

Figure 5. Photograph of Tiger Vac on a Scissor Lift

Note: 	This photograph shows a vacuum listed for Class II hazardous
locations (a Tiger Vac) placed on top of a scissor lift. A team of two
employees used this Tiger Vac to remove paper dust accumulations from
overhead structures throughout the paper converting area. As Section
3.2.3 notes, this cleaning approach was effective at safely removing
overhead dust accumulations without causing workers below to be exposed
to dust; however, this approach was also labor intensive and therefore
not cost-efficient. In some areas of the facility, installation of
overhead oscillating fans has nearly eliminated the need for cleaning
with the Tiger vacs. 

 

 Figure 6. Photograph of Dust Collector (1)

Note: 	This photograph shows a dust collector that controlled airborne
dusts generated in one of the paper converting areas. The dust collector
is equipped with fire detection and suppression (sprinklers) and
explosion panels that vent away from the production building. The
exhaust air from the dust collectors is returned to the production
building, but the dust collector is not equipped with an explosion
isolation system. No evidence was observed of significant fugitive dust
emissions from this operation. 

 Figure 7. Photograph of Dust Collector (2)

Note: 	This photograph shows another dust collector that controlled
airborne dusts generated in two different processes in one of the paper
converting areas. Paper dust (or “fluff”) was visible on most of the
horizontal surfaces at this dust collector, including the ductwork, the
ground, and the overhead electric wires. The dust collector was equipped
with fire suppression (sprinklers) and explosion vent panels, but these
panels were on the dust collector wall that faces the production
building. The dust collector is not equipped with explosion isolation
devices. Exhaust air from this dust collector returns to the paper
converting area.

Figure 8. Photograph of Dust Accumulation in the Sawdust Press Building

Note: 	This photograph shows a pit in the sawdust press building. The
sawdust visible at the base of the pit was wet (i.e., the darker
material in the photograph). Sawdust accumulations on ledges and on top
of mechanical equipment were collected and tested in OSHA’s laboratory
(sample #1988). The material had a moisture content of 17%, and the
dried sample was found to be a Class II dust. Sawdust in this and other
parts of the wood processing operations had accumulated on motors,
blowers, and other electrically powered devices, but it was not clear if
these devices were rated for Class II locations. 

Figure 9. Micrographs of Settled Paper Dust

A) 50x magnification image

B) Selected images at 200x magnification

Note: 	Micrographs generated by the consultant who participated in the
site visit. The micrographs indicate that the settled paper “dust”
was largely composed of paper fibers, some of which tended to
agglomerate. Section 4.1.3 discusses these micrographs in greater
detail. Attachment 1. Copy of Testing Results Provided by OSHA’s
Analytical Laboratory

Notes: 

Refer to Section 4.1.2 for information on the materials sampled and how
they were collected. 

Table 1 summarizes the sampling results; note that the “Sample
Numbers” across the top of the table correspond to the “Submission
Numbers” in this attachment. 

As acknowledged in OSHA’s testing results presented throughout this
attachment: “The results obtained from this equipment can not be used
in designing or engineering protective safety equipment.” Further, it
is possible that some materials that were tested exhibit lesser or
greater explosion hazards under different conditions. 

Attachment 2. Facility B’s Procedure for “Settled Bulk Density and
Maximum Accumulation Determination”

[Note: This attachment is a copy of Facility B’s written procedure,
except that any information that would identify Facility B has been
removed.]

COMBUSTIBLE DUST DENSITY

and

MAXIMUM ALLOWABLE ACCUMULATION DEPTH DETERMINATION

DENSITY DETERMINATION – MAXIMUM ALLOWABLE ACCUMULATION DEPTH

DENSITY RANGE  (LBS / FT3)	MAXIMUM ACCUMULATION DEPTH

(ALARM LEVEL)

INCHES

> 37	1/32

18.9  -  37	1/16

9.3  -  18.8	1/8

4.7  -  9.3	1/4

3.2  -  4.6	1/2

2.5  - 3.1	3/4

2.0  -  2.4	1

< 2.0	1 1/4

Tools needed:  neoprene or other similar plastic type gloves, ruler, two
natural bristle brushes (4” width), scales (that measures grams),
pre-weighed container (weighed in grams to nearest tenth of a gram),
digital camera, three hole punched 8’ x 11” paper.

Procedures:

Pre-weigh container.  Record weights.

Locate horizontal surface area where dust is present in the department
or processing area and is evenly distributed across the surface (i.e.
having relatively flat top layer).  Take photo of horizontal dust layer.

Don gloves.  Using a ruler mark off a 1 x 1 square foot area (It is
easier if one of the four sides is the horizontal surface ledge).  If
one square foot is not available due to size of surface use 1/2’ x
2’; ¼’ x 4’, etc.

Using the ruler as a guide, carefully scrape the other dust surrounding
the marked 1 x1 square foot area (or other established one square foot
dimension) back away from the dust square (or rectangle) to at least 8
– 12 inches.  Use the first brush if needed to clean away dust away
from the 1 x 1 square foot area selected for density measurement
(ensuring that the 1’ x 1’ area does not receive any of the dust
being brushed away).  Take photo of dust square.

Measure and record the height (to the nearest 1/32 inch) of the dust
layer as it sits on the horizontal layer.  Take a minimum of three to
five measurements along the edge of the dust layer to establish an
average height (to the nearest 1/32 inch) of the dust layer.  Take photo
showing one of the height measurements.

Take the second, clean natural bristle brush and carefully brush the
dust contained inside the 1 x 1 square foot area into the pre-weighed
container.  Weigh the dust and the container together and record the
weight in grams.  Record the weight in grams.

Subtract the dust and container weight from the pre-weighed container
weight to determine the weight of the dust in grams.  Record dust weight
in grams.

Calculate volume of dust layer using height measured (in inches) x
length (12 inches) x height (12 inches) etc. to get cubic inches of
volume.  (Record calculations and volume determined)

Convert cubic inches to cubic feet.  (Record conversion calculations.)

Convert grams of dust measured to pounds (Note: 453.6 grams = 1 pound)
(Record conversion calculations.)

Divide pounds of dust by cubic feet to establish estimated density in
pounds per cubic feet (lbs/ft3).

Record all conversions/calculations and maintain all records and
associated photos indefinitely in easily retrievable format in the
facility Safety Office for historical documentation)

Example:

container pre-weight is 500 grams.

dust height measured is 2 1/32 inches.

container plus dust weight is 660 grams.

Dust Volume Determination in cubic feet (ft3):

2 1/32 inch = 65/32 inches or 2.03125 inches

Volume (in3) = L x W x H = 12” x 12” x 2.03125” =  292.5 cubic
inches (in3)

Convert cubic inches to cubic feet:  There are 1728 in3 in 1 ft3.

Volume (ft3) = Volume (in3) / 1728  =  292.5 / 1728 = 0.169 ft3

Dust Weight Determination in pounds (lbs):

To obtain the weight of the dust, subtract container weight in grams
from dust + container weight in grams:

660 grams – 500 grams = 160 grams

Convert grams to pounds:  There are 453.6 grams in one pound. 
Therefore,

160 grams / 453.6 grams per pound  =  0.353 pounds (of dust)

Dust Density Determination:

Divide pounds of dust by volume of dust in cubic feet:

0.353 lbs / 0.169 ft3 =  2.087 lbs/ft3 or rounding off to nearest tenth
of a pound = 2.1 lbs/ft3

Maximum Accumulation Depth (Alarm Level) Determination:

From the Density Range - Maximum Accumulation Depth (Alarm Level) table
2.1 lbs/ft3 is between 2.0 lbs/ft3 and 2.4 lbs/ft3, therefore, the
maximum accumulation depth that serves as an alarm level for immediate
cleaning is 1 inch for this department or processing area.

Dust Density Determination Records Retention and Submission:

Maintain all records including the location, date, time, name and title
of person collecting the data, the procedure, and all calculations,
conversions and photos for each dust density determination in the Safety
Department for easy retrieval.  These records will be maintained for
historical purposes and for substantiation for regulatory purposes.

Submit a copy of density and maximum allowable accumulation data and
location(s) electronically your business unit leader – safety and to
XXXXXXX..

 The OSHA state program recently inspected Facility B in response to an
employee complaint about exposure to airborne dust. This complaint
resulted from Facility B’s housekeeping efforts to keep paper dust
from accumulating on overhead structures. Section 3.2.3 of this report
provides further information on the various housekeeping strategies and
engineering and administrative solutions that Facility B has considered
to address accumulations of paper dust. 

 For a sense of the size of these buildings and the paper machines, one
of Facility B’s paper machines was located in a 150,000-square-foot
building with ceiling heights ranging from 43 feet to 70 feet. The paper
machine itself occupied a large portion of the space within this
building.

 The company that owns Facility B plans to install overhead oscillating
fans at several of the company’s paper mills. Over the next 2 years,
the company plans to purchase and install 715 fans at 12 locations at an
estimated cost of $6.3 million. 

 While the 2006 edition of NFPA 654 is still the most current, proposed
revisions to the standard include different approaches for calculating
the maximum allowable dust accumulations without a need for explosion
protection. The proposed revisions were discussed during the site visit,
but are not described further here. 

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Site Visits Related to Combustible Dust – Facility B 

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Site Visits Related to Combustible Dust – Facility B