Document ID: OSHA-2009-0023-0177
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-08-04T04:00Z

Site Visits Related to Combustible Dust:
Facility J - Coal-Fired Power Plant

                                                                               
                                                                 	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 27, 2011
                               Table of Contents
                                       
1	Project Overview	1
2	Facility Description	2
3	Process Descriptions	5
3.1	Coal Receiving, Conveying, and Handling	5
3.2	Housekeeping Practices	9
3.3	Coal Size-Reduction Operations	10
3.4	Dust Collectors	13
3.5	Other	16
4	Document Review	17
4.1	Testing Data	17
4.1.1	Coal Data Provided by Facility	17
4.1.2	Test Results for Samples Collected During Site Visit	18
4.2	Material Safety Data Sheets (MSDSs)	20
4.3	Other Related Documents	21
5	Training	22
6	Safety and Health Programs	23
7	Main Findings	25
8	Feedback to OSHA	27
9	References	28

Table 1			Testing Results for Samples Collected During the Site Visit
Figure 1		Photograph of Dust Control System for a Belt Conveyor
Figure 2		Photograph of Expandable Ductwork at Pulverizer Outlet
Figure 3		Photograph of a "Dry" Dust Collector (Baghouse)
Figure 4		Photograph of a "Wet" Dust Collector (Scrubber)
Figure 5 	 	Photograph of a Dust-Tight Enclosure for Electrical Fixtures
Figure 6		Photograph Showing Evidence of Corrosion in Ductwork 

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

Acronyms and Abbreviations

CO			carbon monoxide
ERG		Eastern Research Group, Inc.
Kst			deflagration index
LOC 		limiting oxidant concentration
MSDS		Material Safety Data Sheet
NFPA		National Fire Protection Association
OSHA		Occupational Safety and Health Administration
PRB		Powder River Basin
psi			pounds per square inch

Project Overview 
On September 15 and 16, 2010, Eastern Research Group, Inc. (ERG) conducted a two-day site visit to a coal-fired electricity generating facility (hereafter referred to as "Facility J"). The site visit was conducted by an ERG employee and a consultant; three representatives from the Occupational Safety and Health Administration (OSHA) also attended. 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 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 OSHA personnel who attended the site visit are part of the team working on the agency's proposed combustible dust standard. The OSHA personnel participated in the visit strictly as observers, and their main role was to gain facility perspectives on combustible dust hazards and approaches taken to mitigate them. The OSHA personnel who participated in the visit had no inspection or enforcement authority.
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 J'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 J'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 J, 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 J'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 J 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.
    
Facility Description
Facility J is a coal-fired electricity generating facility. The facility burns approximately 10,000,000 tons of coal per year: roughly 15% of this is bituminous (or "eastern") coal, and the other 85% is sub-bituminous (or "western") coal, also known as Powder River Basin (PRB) coal. Throughout this report, the two different coal types will be referred to as bituminous coal and PRB coal. By several accounts, the facility was originally designed and constructed to process bituminous coal. Certain unit operations and dust control measures were later replaced or retrofitted when it became evident that the facility was going to be processing PRB coal. 
Both coal types arrive at Facility J by barge, where a continuous bucket unloader transfers the coal to belt conveyors that eventually drop most of the incoming coal into large storage piles. Belt conveyors also carry coal from the storage piles into the main production building, where the coal is pulverized and fed into one of the facility's two electricity generating units. The energy released from the burning coal evaporates water in a circulating system, and the steam that is formed powers large turbines that generate electricity. The combustion process also produces fly ash, which the facility collects and disposes of on site. 
The facility property spans approximately 4,000 acres, but approximately three-fourths of this land is undeveloped. The main production areas toured included coal-handling operations, which were mostly located outdoors, and two large boiler buildings that housed silos, pulverizers, boilers, turbines, and other equipment. The two electricity generating units first came online in the mid- to late-1980s. The facility operates continuously throughout the year. Facility representatives stated that the majority of their unit operations are representative of those employed by other coal-fired electricity generating facilities nationwide. However, the facility is relatively new compared to others in the industry. 
Approximately 230 employees work at Facility J, and about 75% of these work in maintenance, operations, or coal-handling positions. In addition, Facility J uses multiple contractors for security, janitorial support, housekeeping, fly ash management, and maintenance of wet dust collectors. On a typical day, roughly 25 contract employees are present at the facility. The company that owns Facility J has safety and health professionals in its corporate offices, and these individuals assist multiple electricity generating facilities (including Facility J) with combustible dust safety and health issues. 
Two full-time professionals oversee Facility J's health and safety programs. These individuals have ready access to many additional health and safety professionals employed by the company that owns Facility J, whether at corporate headquarters or at other electricity generating facilities. Facility J has its own industrial fire brigade, and approximately 12 industrial fire brigade members work during each shift. These individuals are typically the first responders to any fires or explosions, some of which are documented in Section 3.5 of this report. Smoking at Facility J is prohibited in the coal-handling area, inside any buildings, and within 10 feet of any buildings; site visitors noticed no evidence of smoking (e.g., discarded cigarettes) in the areas where smoking is not allowed.
Site visitors asked the facility's safety and health personnel to comment on the roles that outside parties play in Facility J's combustible dust safety programs. A summary of those responses follows: 
   # Facility J is located outside a small municipality that is served by a volunteer fire department. Facility representatives give site tours to the local firefighters and educate them on special considerations for addressing coal fires. However, the fire department does not require or suggest adherence to NFPA standards specific to combustible dust. 
   # The company that owns Facility J bases most of its fire protection programs on specifications in NFPA 850, "Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations." Individual facilities comply with additional requirements in state fire codes. 
   # The company that owns Facility J is self-insured. Corporate fire protection/risk management representatives previously conducted facility audits and identified action items to address potential fire and safety hazards. An outside loss prevention consultant now conducts these reviews.  
   # Corporate safety and health representatives perform periodic facility and safety and health program audits to determine effectiveness of its programs.
   # The company that owns Facility J actively participates in the PRB Coal Users' Group -- an organization that promotes the safe and efficient use of PRB coal. The PRB Coal Users' Group offers an extremely broad array of support and guidance to its member facilities. Examples include, but are not limited to:
         o Published industry/best practices guidelines on topics ranging from firefighting considerations for dust collectors to inerting systems for pulverizers; electrical hazard classifications; and a combustible dust guideline is currently being drafted. These items are only available to PRG Coal Users' Group members.
         o Publicly available webinars on specialized issues, including "Combustible Dust: Proactive Approaches to Managing Combustible Dust." 
         o Annual meetings with sessions on PRB coal fire and explosion protection and lessons learned from recent incidents. These meetings are open to any participants. 
         o Workshops on focused topics for member facilities. 
         o Multiple compact disks developed by PRB Coal Users' Group with information on combustible dust. Site visitors were given copies of two disks. One had a 65-minute presentation on "PRB Coal 101: An overview of the requirement to safely and efficiently use Powder River Basin coal" (2007), and the other had a 70-minute presentation on "Combustible Dust: Failure to control fugitive dust can yield explosive results" (2008). 
         o A website (www.prbcoals.com) with general information available to all visitors and extensive resources accessible to member companies, as well as an online discussion forum where members can share experience with combustible dust safety issues and other topics.
         o A combustible coal dust e-learning course for contractors is in development with release targeted for the summer of 2011. 
   # The company that owns Facility J is a member of various other trade associations, including the Edison Electric Institute, the American Coal Council, and the National Coal Transportation Association. While these trade associations provide the facility with valuable input on many technical and administrative topics, the PRB Coal User's Group is the facility's most trusted source of technical information on combustible dust safety hazards, especially for PRB coal.  
   # While Facility J has not consulted directly with OSHA on combustible dust safety issues, facility and corporate safety and health officials were very familiar with the agency's ongoing activities pertaining to combustible dust. For example, facility representatives frequently visit OSHA's combustible dust website; they have already read and were actively tracking the results from the National Emphasis Program, and they were aware of the agency's Advanced Notice of Proposed Rulemaking.
   # Engineering and design support is provided by engineers at Facility J, in the corporate headquarters of the company that owns Facility J, and at other electricity generating facilities owned by this company. The facility uses outside engineering and design firms for certain specialized projects (e.g., sizing and installing dust collector systems). 
   
Process Descriptions
This section describes selected process operations and production activities that site visitors viewed at Facility J. The specific issues discussed in this section were selected for more detailed summaries either: 1) because they demonstrate unique challenges faced by this facility or industry, 2) because they highlight effective engineering or administrative solutions implemented by Facility J, or 3) because they pertain to specific safety issues OSHA might be considering in its rulemaking effort. 
Coal Receiving, Conveying, and Handling 
Coal receiving and conveying at Facility J involves a sequence of material handling steps. Coal arrives at the facility by barge, where bucket elevators unload the material onto belt conveyors. A surfactant spray is used at the bucket elevators as a dust suppression agent. The type of coal being processed, wind speed, and various other factors determine the amount of foam type suppressant agent used. A series of belt conveyors then transports coal from the barge unloading stations toward the facility. Many individual belt conveyors terminate in transfer stations, where coal is dropped from one belt conveyor onto another. 
Some belt conveyors terminate at outdoor coal storage piles, where most of the coal is temporarily stored. (Some incoming coal can bypass this temporary storage, when production demands dictate.) Operators use heavy-duty equipment to move coal from the storage piles into reclaim hoppers situated above belt conveyors located in two underground tunnels. By opening motor-operated slide gates beneath the hoppers, operators manage the flow of coal from the hoppers to the belt conveyors. The preferred mixture of different coal types is achieved by controlling the loading rates on the belt conveyor and activating diversion gates for the different coal streams. 
The rest of this section documents site visitors' observations pertaining to specific unit operations in the coal receiving and conveying processes:
   # Belt conveyors. Facility J operates more than 5 miles of belt conveyors to transfer coal from barge unloading stations to transfer stations, coal storage piles, crushers, and eventually to the boiler buildings. Conveyors located above ground pass through galleys that shield the coal from the elements, and underground conveyors pass through tunnels. Belt widths range from 4 to 6 feet, and belt speeds are continuously monitored and typically range from 620 to 840 feet per minute. Limit switches monitor for belt misalignment. Head bearings are totally enclosed, automatically lubricated, and many are equipped with temperature sensors to detect overheating. However, no temperature sensors are placed on the idler roller bearings located along the conveyors, where coal dusts readily settle. 
      There are no requirements for temperature monitoring of bearings in NFPA 850, but there is a requirement to monitor conveyor belt speed and automatically shut off power if the belt slows down by more than 20 percent. Facility J conveyors are equipped with such speed monitors and associated alarms and conveyor motor emergency trips. All belt conveyors have trip wires alongside that employees can activate to automatically stop the belts. All enclosed conveyors have linear heat detectors for fire detection and alarm.
      Several conveyors use air support pressure rather than idler rollers under the conveyor belt. This has the advantage of eliminating idler rollers and bearing maintenance and potential friction ignition sources. However, some of the conveyor air enclosures are corroded and leaky. The corrosion may be due to the aqueous solution applied upstream for dust control. Furthermore, some entrances and exits to the air enclosures are locations of dust suspensions and accumulations. 
      As noted later in this section, Facility J operates continuous carbon monoxide monitors at locations throughout the facility, including inside conveyor galleys and tunnels. These monitors are highly effective at detecting burning and smoldering coal. As necessary, water deluge systems in the galleys and tunnels are used to suppress major fires. Deluge systems are interconnected to the fire detection (linear heat detection) or may be manually activated, by employees triggering manual switches placed along the conveyors or at the deluge valve itself. Employees at Facility J stated that abnormal conditions (hot) of idler roller bearings have been detected through the carbon monoxide monitoring system.
   # Transfer stations. Facility J operates several transfer stations where coal is transferred from one belt conveyor to the next. The incoming belt conveyor is on an incline and enters at the top of the transfer station, where coal drops into a chute and falls under the force of gravity to another conveyor at the foot of the transfer station. Some transfer stations are as much as 60 feet tall. This process does release coal dust, which is typically controlled with containment systems and dust collectors dedicated to each of the transfer stations. One transfer station includes a coal crusher; Section 3.4 discusses this operation in greater detail. 
      Some transfer stations are equipped with magnetic separators. The separators have two settings: "run coal" and "tramp iron discharge." In the "run coal" setting, the magnetic separators are automatically energized whenever the belt conveyor immediately upstream begins operating. Whenever the conveyor stops (e.g., between barge unloading campaigns), the separators shift into the "tramp iron discharge" setting. This setting activates diversion gates beneath the magnets and then de-energizes the magnets, allowing for collected material to drop by gravity into designated tramp metal collection areas and not onto the main process belt conveyors. These separators help ensure that tramp metal is efficiently removed from the coal process stream before it passes through crushers and pulverizers, where tramp metal would have been a potential ignition source. 
   # Coal storage piles. Facility J's outdoor coal storage piles typically contain between 1.2 and 1.4 million tons of coal, enough to support roughly 40 days of energy production. The coal is distributed into the piles and retrieved via rail mounted reversible stacker-reclaimers. Employees also operate dozers and other heavy-duty diesel-powered equipment to manage the stockpile and to move coal in the storage piles over entry doors, where coal drops by gravity through underground feeders and onto conveyor belts for further processing. These belt conveyors pass through underground tunnels before reaching the next transfer station. Consistent with the specifications of NFPA 850-2010 paragraph 7.4.6.4, which states "Consideration should be given to the installation of an automatic water spray or sprinkler system over the conveyor belt and striker plate areas within the stacker-reclaimer," Facility J's stacker-reclaimers have linear fire detection and water spray systems.
      Facility representatives noted that coal in outdoor storage piles can self heat and eventually begin burning. Operators try to avoid this situation by ensuring that coal is managed through compaction and that it does not remain in storage piles for extended periods of time. "Hot spots" occur most frequently for PRB coal and in small, localized areas generally along the base of the stockpile or in areas where it is not compacted -- one of which with visible smoke was observed during the site visit. Operators typically address this situation by wetting the coal and removing the material from the storage pile (though other procedures are used in certain circumstances). After any flames or smoldering material is extinguished, the coal can be returned to the storage piles in thin layers. 
   # Transfer chutes. In the early 1990s, Facility J conducted engineering evaluations of its transfer chutes and determined that many transfer points were not adequately sealed, presenting a source of coal spillage and fugitive coal dust. Engineers determined that fugitive dust emissions resulted in part from a so-called "trampoline effect," in which falling coal at transfer points bounces on the conveyor belt where the coal lands. The induced air flow caused by the falling coal enhances this effect. After improving the design of the transfer chute and skirt seals, fugitive coal dust emissions at transfer points were reportedly reduced but not eliminated. 
      An engineering analysis noted that fugitive dust emissions could be further reduced by use of notably higher air flow rates in the dust collection system (i.e., to account for the induced air flow from the falling coal), but the higher air flow rates would have forced the facility to redesign and replace most of its fans, ductwork, and dust collectors -- an improvement that was considered cost-prohibitive. At a minimum, the facility should consider reassessing fugitive dust releases that occur during transfer operations and implement controls accordingly. Some simple fixes, such as patching holes in ductwork and ensuring that feeder doors are fully closed prior to all transfer operations begin, might achieve notable dust reductions (see Figure 1). These evaluations could help minimize dust accumulations and the time needed for housekeeping, especially in the underground tunnels (see Section 3.2). 
   # Carbon monoxide (CO) monitoring. Facility J continuously monitors airborne CO levels at numerous places in the coal-handling areas. These monitors are viewed as highly effective at detecting the earliest signs of spontaneous coal combustion. In contrast, operators and other automated sensors typically cannot detect burning coal as quickly because the initial combustion does not generate enough heat, smoke, or odor. A common site for CO monitors is in the ductwork of blowers in dust control operations. Should CO readings exhibit a notable upward trend and exceed alarm levels, audio and visual alarm signals will be issued at nearby control rooms. Designated operators then investigate and address the situation following standard procedures (e.g., for controlling "hot coal," for dust collector fires) and document the situation in an event report. Facility representatives noted that the CO monitoring has helped facility personnel promptly identify and address any signs of burning coal well before the combustion leads to more serious or catastrophic events.  
   # Storage silos and hoppers. Facility J temporarily stores coal in numerous silos and hoppers located throughout the production processes. Site visitors briefly reviewed these operations, because enclosed storage can present explosion hazards and difficult firefighting considerations. Potential hazards can be reduced by ensuring that all silos and hoppers are equipped with CO monitors, with alarm conditions that automatically initiate some form of corrective action. Section 7.4.2 of NFPA 850 includes additional guidance on fire protection for coal silos and hoppers. Facility J's coal silos are equipped with manually operated low pressure carbon dioxide injection systems.
Housekeeping Practices 
Facility J conducts extensive housekeeping activities to remove coal dust accumulations from production areas. Site visitors focused largely on housekeeping practices employed inside the underground tunnels, given the inherently hazardous nature of this work (e.g., dust clouds form in enclosed spaces, employees have limited means for exiting the tunnels should fires or explosions occur). Facility documents acknowledged the potential hazards associated with this activity; one document states: "Enclosed conveyors and tunnels...represent the worst potential for propagating combustible dust explosions within a coal handling system." Accordingly, this section focuses entirely on housekeeping in the tunnels.  
Two employees remove coal dust accumulations from the underground tunnels, and belt conveyors are usually, but not always, idle during these housekeeping campaigns. The frequency of housekeeping varies, with one particular tunnel area cleaned every weekday, and others cleaned once or twice per week, depending on accumulations. As expected, coal dust accumulation thicknesses vary throughout the tunnels. At most places, dust layer thicknesses are reportedly less than (1/4) inch but can reach depths of 1 to 2 feet in localized areas (e.g., at some tunnel ends and some transfer stations). The method currently used to clean inside the tunnels is to wash away coal dusts using (3/4)-inch hoses emitting water streams with pressures of approximately 165 pounds per square inch (psi). The wash water containing coal dust then flows out of the tunnels through drains into onsite settling basins. However, the high-pressure spray has the undesired effect of re-suspending some settled coal dusts, forming dense brown floor-to-ceiling dust clouds inside the tunnels. While these dusts eventually settle back to the ground where employees can then wash them away, some dusts also settle on top of motors and other locations where coal dust accumulations should be avoided. During these and other housekeeping activities, the contractors wear dust masks and "rain pants." 
Site visitors encouraged facility representatives to reassess the housekeeping procedures for the tunnels, including a broader evaluation of dust control measures. Priority should be placed on strategies to reduce fugitive coal dust emissions inside the tunnels. More frequent and effective inspection and maintenance of ductwork, feeder doors, and existing hoods can identify leak points that might be a major source of the dust accumulations. Additionally, enhanced design of the dust collection system might help collect and remove a greater portion of the coal dust released inside the tunnels. Such improvements might include installing additional dust collection hoods and improving maintenance of the dust collection systems dedicated to the tunnels. Even after considering these and other engineering solutions, the current housekeeping procedures should also be evaluated, with an emphasis on adopting cleaning methods that do not form dense clouds of coal dust inside the tunnels. Facility representatives were encouraged to 1) identify preferred and prohibited cleaning methodologies, 2) communicate these methodologies to the housekeeping staff, and 3) implement a self-audit policy to ensure that housekeeping is being conducted according to facility procedures. Wearing of flash fire resistant garments (meeting NFPA 2112 requirements for flash fire resistance) during cleaning should also be considered.
Coal Size-Reduction Operations
Facility J has two types of unit operations -- pulverizers and crushers -- that are designed specifically to reduce the size of incoming coal. Other facility operations (e.g., dropping coal in transfer stations, moving coal in storage piles) also achieve some size reduction, though they were not specifically designed for this purpose. Observations of the two primary size-reduction operations follow: 
   # Pulverizers. The facility currently operates 14 coal pulverizers, with the oldest of these installed in the mid-1980s. The pulverizers are roller and table type that grind crushed coal into a powdery material. At Facility J, the pulverizers are designed to have 75% of the outlet material pass through a 200 mesh screen, with no more than 0.1% of the outlet material not able to pass through a 50 mesh screen. The feed to the pulverizers is crushed coal from large storage silos, and the output is pulverized material blown through piping (known as burner pipes). Air is supplied through expandable ductwork (see Figure 2), which assists with the movement of coal particles through the pulverizers and into the burner pipes. 
      Fires and explosions are a common safety concern for these operations throughout this industry, given that combustible dust is inside the equipment at levels far greater than the minimum explosible concentration. Near worse-case concentrations occur during startup, shutdown, or unanticipated interruptions to a steady coal flow. Site visitors provided facility representatives with a copy of a review article documenting past fires and explosion incidents in coal pulverizers (Zalosh, 1987). Facility representatives also shared documents developed by the PRB Coal User's Group on control technologies commonly employed for these systems. 
      Facility representatives noted that "puffs" (which are relatively low pressure explosions) have occurred in their pulverizers since the facility was constructed. Operators indicated that "puffs" causing minor damage occur seldomly (historically less than one per year) and "puffs" causing more extensive damage occur roughly once every ten years. These major events blew apart the weakest connections to the pulverizers, which are typically the outlet expansion joints and the inlet ductwork. When this happens, coal dust, ash, and fireballs can be emitted from these openings, causing hot coal dust and ash to coat surfaces throughout this particular production area. 
      Facility J has implemented at least two measures to reduce the frequency and potential consequences of these "puffs." First, steam inerting is routinely used during pulverizer shutdowns and when operating conditions suggest that "hot coal" might be trapped in the equipment. The steam inerting is intended to reduce oxygen concentrations in the pulverizers to levels that would not support combustion. Site visitors encouraged facility representatives to ensure that the steam inerting system meets design and operational specifications in NFPA 69. For example, Section 7.7.2 of NFPA 69 specifies the maximum oxygen concentrations that should be permitted for different types of inerting systems. In general, the oxygen concentrations should be maintained below the limiting oxidant concentration (LOC) of the mixed coal dusts, with an ample margin of safety that depends on whether or not there is continuous monitoring of oxygen concentration. Site visitors could not assess the effectiveness of the steam inerting system without testing data on the LOC for these PRB coal dusts, and they encouraged the facility to obtain testing data for this parameter. Facility contacts indicated that the LOC for PRB coal dust is 12%. 
      Second, before pulverizer startup and shutdown occurs, operators sound an audible alarm or make announcements to inform individuals in the boiler building of this activity, and people know to evacuate the area surrounding the pulverizers after hearing these announcements or alarms. The purpose of these alerts is to ensure that people are not injured during a "puff" or engulfed by the material that can be ejected into the workplace air. While such alerts appear to offer effective protection for anticipated events, they will not protect workers from unexpected "puffs" (e.g., due to a sudden interruption to coal flow). Establishing permanent exclusion zones near the pulverizers and their interconnecting ductwork can be more effective at ensuring that employees are not present during these events. Additionally, the facility should consider providing personnel who need to work around operating pulverizers with flash fire resistant garments certified to meet NFPA 2112 requirements for flash fire resistance.
   # Crusher. Facility J operates at least two coal crushers with throughput capacities of 4,000 tons of coal per hour. The crushers are located in transfer stations along the sequence of belt conveyors that carry coal from the storage piles to the pulverizers. The crushers have rotating hammer designs and are designed to reduce lumps of coal to sizes of approximately 1.25 inches in diameter. Temperature monitors on rotor bearings and motor stators are installed to detect unsafe operating conditions, and magnetic separators located immediately upstream of the crushers remove tramp metal from the incoming coal stream. The process of crushing coal generates fine coal dusts -- heavier material falls to the belt conveyor leaving the crusher, while lighter, airborne material is vented to a dedicated dust collector. 
      The crushers were not operating during the site visit, possibly due to duct corrosion damage as shown in Figure 6. Site visitors looked inside one device and noted residual crushed coal and coal dust on the interior surfaces, which presents a potential source of spontaneous combustion. Facility representatives noted that residual material is usually removed using a compressed air lance -- a procedure that generates clouds of coal dust in and around the crusher. Site visitors encouraged the facility to investigate other options for removing residual coal from this equipment. 
      Facility J's crushers are equipped with continuous CO monitors to detect the presence of burning or smoldering coal. Site visitors did not review the placement of CO monitors in this part of the facility but noted that monitor placement will affect how effectively and quickly they detect burning coal. 
Dust Collectors 
The number and design of operational dust collectors at Facility J has varied over the years. The facility was originally constructed with 33 "dry" dust collectors (baghouses). Subsequent engineering evaluations found that many of these units, particularly along belt conveyor galleys, could be removed from service without compromising compliance with environmental regulations. By the early 1990s, the facility operated 21 baghouses. Since then, the facility has removed two more baghouses, retrofitted some with enhanced engineering controls, and replaced others with "wet" systems (scrubbers). The facility invested considerable resources when retrofitting the dust collectors, including approximately $650,000 of improvements in the early 1990s. 
Currently, the facility operates 10 baghouses and nine scrubbers, and the remaining baghouses are expected to eventually be replaced with scrubbers. The site visitors viewed a subset of these systems and made the following observations:
   # "Dry" dust collectors. The 10 baghouses at Facility J control fugitive coal dust emissions from various locations in the coal handling process. Coal dust in the inlet air stream collects on filter material (i.e., the "bags") inside the baghouse, and pulsed air is periodically charged into the system to dislodge coal dust collected on the filters. The dislodged dust falls to a hopper at the base of the dust collector, passes through a rotary valve, and then is conveyed back into the main coal stream. Every baghouse vented exhaust air to the outdoor ambient environment. 
      Because PRB coal has a tendency to self heat, engineering evaluations were conducted to avoid any prolonged accumulation of coal dusts inside baghouses. In the early 1990s, an internal engineering review of the baghouses examined the design and operation of the hopper and rotary valve to ensure that coal dusts do not accumulate in the base of the baghouses. To prevent coal dusts from adhering to the hoppers' walls, this review recommended that the downward-sloping walls be coated with an epoxy resin and have a slope of at least 60 degrees. The engineering review also noted that the surface area of the filters could be increased by replacing the polyester and acrylic bags with an improved design, helping to address concerns that some baghouses might be undersized. 
      Though not originally equipped with fire suppression systems, the baghouses remaining at Facility J have since been retrofitted with these systems. Continuous CO monitoring devices were placed in the ductwork by the blowers to detect fires or smoldering coal inside the dust collectors. The fire suppression systems consisted of two types of water spray nozzles that operators could activate manually. A dry standpipe extinguishing system using "micro-fog water spray" was placed near the top of the baghouses above the bags, and a plane of larger diameter spray nozzles was placed below the bags and above the hopper. Hopper drains were installed at the base of the baghouses to prevent dust collectors from collapsing under the weight of water after fire suppression systems were activated and as a means to safely eject material (e.g., coal/fire suppression agent) without risks to people. 
      All baghouses that site visitors observed were equipped with explosion venting panels, and most had rupture diaphragm designs. In most cases, the vent panels were placed in a manner to direct explosions away from adjacent structures, but some exceptions were observed (see Figure 3). Some panels were located much closer to the tops of dust collectors (see Figure 3) than is desirable for unobstructed venting below the bag bottoms, and facility representatives were encouraged to review the NFPA 68 deflagration vent design criteria for baghouses. 
      The baghouses located at the boiler building were directly connected to storage silos containing large quantities of crushed coal, raising concerns about deflagrations propagating from the baghouse through ductwork to other process locations. The principal baghouse observed was equipped with devices that could be activated to isolate the system. These included a backdraft damper on the inlet ductwork and a rotary valve where collected dust is returned to the process. However, neither device likely qualifies as an acceptable explosion isolation device according to criteria outlined in NFPA 69. For instance, the backdraft dampers would likely not be activated quickly enough to isolate a deflagration originating in the baghouse, and may not be strong enough to withstand deflagration pressures. Facility representatives were encouraged to identify baghouses that would benefit from explosion isolation devices (i.e., baghouses where propagating explosions might be expected to lead to larger events) and install isolation devices that meet design specifications in NFPA 69. 
   # "Wet" dust extractors. In recent years, Facility J began replacing dry dust collectors with scrubbers. Most facility representatives interviewed during the site visits preferred wet systems over the dry systems, primarily because the wet extractors remove airborne coal dust into scrubber water, effectively reducing concerns of collector fires and explosions. Two other benefits were cited: 1) the wet systems are less hazardous to maintain because employees do not need to enter enclosed spaces where dry coal dusts may be present and 2) the wet systems tend to be smaller than dry systems with comparable airflow capacities. No information was available during the site visit on how dust collection efficiencies compare between the wet and dry systems. 
      The facility had purchased and installed scrubbers made by two different manufacturers. One such system is shown in Figure 4. These particular systems operate by having high-speed fans located downstream of the units draw air through the scrubbers, and they have airflow capacities ranging from 46,000 to 55,000 cubic feet per minute. Coal dust in the inlet air is collected in the scrubber water, which is eventually discharged to the facility's onsite wastewater treatment operations. Coal in the sludge can be reclaimed and returned to the process. 
      Maintenance of Facility J's scrubbers apparently presents challenges. Facility representatives noted that the slurry discharge flow on some scrubbers has plugged when water becomes saturated with coal dust, causing untreated scrubber water to leak from the devices. One of the scrubbers viewed on the site visit had extensive patchwork (including tape) on the inlet ductwork, apparently to seal holes caused by corrosion of the carbon steel housing. Water was seen dripping from this scrubber, and the cause of the leak was not known. Another scrubber was not operating due to a broken fan shaft, which employees identified more than a week prior to the site visit. Although a work order had been submitted to replace the fan shaft, facility representatives did not know when the repairs would take place. Maintenance personnel said replacement parts used to be stocked on site, but now they have to wait for purchase orders to be processed and shipments received from scrubber parts suppliers. Both problems highlighted an underlying issue that scrubber malfunctions can go undetected, in part because many of the scrubbers have no monitoring systems (e.g., level alarms on the slurry reservoir) to automatically inform operators of upset conditions, and also because the equipment is not routinely inspected. Greater oversight of the operation and maintenance of the scrubbers would help ensure that they operate correctly. Site visitors were particularly concerned about the potential for some of the scrubbers to operate dry, and thus create a fire or explosion hazard in the scrubber or ducting.
      According to facility representatives, the scrubbers cost between $200,000 and $500,000 to design, purchase, and install. This cost range applies to systems with capacities varying from 1,300 to 35,000 cubic feet per minute. Facility J hires a third-party vendor to maintain one manufacturer's scrubbers for $150 per month per unit. This monthly servicing fee does not include the vendor's travel costs or costs for purchasing replacement parts that need to be installed. 
Other
The remainder of this section documents various additional observations not summarized in the earlier discussion: 
   # Classification of hazardous locations. Facility J representatives provided site visitors with a listing of hazardous locations for the coal yard and coal-handling areas. Overall, 38 different locations are classified as "Class II, Division 2, Group F" areas. These include the barge unloading areas, certain belt conveyors, transfer stations, and bunker rooms. Some electrical fixtures in these areas are located in enclosures that are dust tight and protect against water. See Figure 5 for a photograph of a typical "NEMA 4" enclosure observed at Facility J. However, site visitors also noticed motors in the underground tunnels that were coated with coal dust and apparently not rated for Class II environments. Facility representatives acknowledged that some motors are not totally enclosed and fan cooled, in part due to the cost of replacing all motors with these systems. A full review of Facility J's electrical classifications and use of rated equipment was not conducted during the site visit. 
   # Corrosion. Some equipment in Facility J's coal-handling area showed signs of corrosion, and in recent years, some corroded decking and electrical boxes reportedly had to be replaced. Facility representatives said that the corrosion results from multiple factors, including the relatively high moisture content of PRB coal, the use of water spray for routine housekeeping, and the use of water-based dust suppression agents during barge unloading operations. Site visitors observed production areas where equipment corrosion was evident (see Figure 6) and encouraged the facility to repair or replace corroded equipment more expeditiously.
   # Past incidents. Facility J representatives shared multiple accounts of fires and explosions involving coal dust. The most serious incident occurred in the early 1990s, when employees detected evidence of coal dust burning in a baghouse dust collector. An employee responding to the issue opened an access door to the dust collector, upon which air flowed into the dust collector leading to a backdraft explosion. One employee died in the incident, and another was seriously injured. Site visitors noted numerous indications of Facility J implementing many measures to ensure that this type of incident never recurs. These measures include: installing more CO monitors to detect burning coal; replacing several dry dust collectors with wet systems; developing written fire protection guidelines for "Coal Silo, Bunker, or Hopper Fires," and updating training and other facility communications to ensure that employees never open access doors to dust collectors when coal fires are suspected. 
      Facility representatives did not provide a detailed account of other fires but noted that several fires occurred over the years along the coal conveyor lines. The fires were believed to be caused by coal dust accumulating on moving equipment (friction) and the self heating of PRB coal dust accumulations. 

Document Review
This section summarizes documents pertaining to combustible dust safety issues relevant to the site visit. 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 J's approaches for controlling them. The section also presents the testing results for samples collected during the site visit. 
Testing Data
This section summarizes chemical, physical, and explosibility testing data relevant to Facility J, whether provided by the facility (Section 4.1.1) or collected by site visitors (Section 4.1.2).
Coal Data Provided by Facility
Facility representatives were certainly well aware of coal dust combustibility -- in fact, its combustibility is the reason why the industry burns coal to generate electricity. Most employees interviewed by the site visitors were well versed in the properties of both PRB and bituminous coal. Specific properties shared by facility personnel or noted in site documents include:
   # For PRB coal, facility personnel shared data on the typical moisture content (26 - 30%), amount of fixed carbon (35 - 45%), volatile content (28-33%), and heat content (6,500 - 9,500 Btu). Information available at the facility indicated that the deflagration index (Kst) for PRB coal can range from less than 120 to more than 200 bar-meter/second (Merritt and Rahm, 2000) depending on particle size distribution and percent volatiles of the specific coal sample. Facility representatives shared several other known properties or characteristics of PRB coal, such as the potential risk for spontaneous combustion.
   # For bituminous coal, the properties differ considerably: moisture content is typically 5%; the amount of fixed carbon ranges from 45 to 80%; the heat content is approximately 13,500 Btu; and Kst values are usually between 80 and 130 bar-meter/second (Merritt and Rahm, 2000). 
Facility representatives noted that PRB coal and bituminous coal differ in many other regards that are important production considerations, such as cost and sulfur content, but these factors are not as relevant for the focus of this project. 
Test Results for Samples Collected During Site Visit
Site visitors collected four samples during the site visit, with the permission and concurrence of Facility J representatives. All samples were tested for particle-size distribution, moisture content, and low-turbulence deflagration index (Kst values). Following the OSHA laboratory's standard procedures, samples with moisture levels greater than 5% were dried prior to analysis. Attachment 1 presents copies of the original laboratory testing results and important caveats about interpreting those results, and Table 1 briefly summarizes the data. More information on the individual samples collected and the test results follows:
   # Sample #7782: fly ash. Electrostatic precipitators remove fly ash from the boilers' air exhaust stream. The collected material is stored temporarily in a series of large hoppers and is eventually disposed of in a landfill. Fly ash is typically composed almost entirely of noncombustible materials (e.g., oxides of silicon, iron, and aluminum). However, for air pollution control purposes, Facility J recently began injecting activated carbon -- a known combustible material -- into the boilers' air exhaust stream. Facility representatives requested that a fly ash sample be tested to assess whether the added activated carbon might cause fly ash to exhibit explosibility. The fly ash sample collected was a very dry and fine dust; the moisture content was 0.1%, and 91% of the material passed through a 200 mesh screen (i.e., a screen with mesh openings of 75 microns). The fly ash sample collected on the day of the site visit was found to not be explosive.
   # Coal samples. Three coal samples were collected during the site visit. While site visitors intended and attempted to sample fine coal dusts, the production area where sampling occurred had recently been cleaned. The finest coal material readily available for sampling was relatively coarse, with only 18 to 37% of the crushed coal samples (see Table 1) passing through a 20 mesh screen (i.e., a screen with mesh openings of 850 microns). Particle sizes were not reduced prior to testing, following OSHA test methodologies. This is a very important consideration when interpreting these results because finer dusts found at Facility J are expected to have higher Kst values than indicated by the test results for the coarse material, possibly by a considerable margin. Test results for the three coal samples follow:  
         o Sample #7783: Mixed coal. This material was collected from a quality control sample point in a process stream after PRB and bituminous coal had been blended and crushed, but before the mixture was pulverized. The mixed coal had a moisture content of 24%, and the dried sample was found to be explosive (Kst = 14.75 bar-meter/second). 
         o Sample #7784: PRB coal. Facility J mixes PRB coal and bituminous coal before crushing and pulverizing the mixed stream. Therefore, pure PRB coal samples could only be obtained from locations upstream of the crusher and pulverizers. This particular coal sample is material that had settled alongside an operational belt conveyor in one of the facility's underground tunnels. The original sample had a moisture content of 30%, and the dried sample was found to be explosive (Kst = 7.09 bar-meter/second). The relatively low Kst value likely reflects the coarseness of the sampled material and should not be assumed to represent the explosibility of finer dusts. 
         o Sample #7785: Bituminous coal. At the time when site visitors collected samples, Facility J was not processing pure bituminous coal, and the only place where this coal type could be sampled was from the outdoor coal storage piles. This sample is the finest material that could be located around the perimeter of one of the storage piles. The original sample had a moisture content of 11% (considerably less than the PRB coal), and the dried sample was found to be explosive (Kst = 20.65 bar-meter/second). As with the previous sample, the relatively low Kst value likely reflects the coarseness of the material and should not be assumed to represent the explosibility of finer dusts.
As noted in the testing results (see Attachment 1), the data presented above should not be used in designing or engineering protective safety equipment, and the testing results reflect the conditions of materials collected during the time of the site visit, which are not representative of the full range of combustible dusts at Facility J. The testing data shown above certainly do not represent the properties of the facility's pulverized coal.
Material Safety Data Sheets (MSDSs) 
Facility J provided site visitors with copies of 10 MSDSs for coal, coal dust, and various other materials found in the facility processes. The MSDSs varied considerably in terms of technical content pertaining to dust hazards, as described below:
   # Availability of MSDSs for coal. According to facility representatives, some coal suppliers are under the impression that MSDSs are not required for "natural products," like coal. As a result, Facility J did not have a complete set of MSDSs for the coal that it processes, nor may it be reasonable to identify specifically what coal comes from what coal seam or mine as it is processed. Site visitors reviewed all available MSDSs for coal, including those developed by the company that owns Facility J.  
   # MSDSs for PRB coal. The facility shared MSDSs provided by three different suppliers for PRB coal. Two of these MSDSs provided thorough information on potential hazards associated with the coal itself (e.g., spontaneous combustion) but did not describe or even acknowledge hazards that could result from coal dusts formed as a result of handling the coal. The third MSDS provided some qualitative insights on potential coal dust hazards: "Avoid dust generation to minimize explosive hazard. Eliminate ignition sources in areas of dust generation and accumulation to avoid explosion." However, none of these MSDSs provided quantitative information (e.g., Kst values, minimum explosible concentration) for PRB coal dust. 
   # MSDSs for bituminous coal. The facility also shared MSDSs provided by three different suppliers for bituminous coal; two of these MSDSs were for bituminous coal, and one was for bituminous coal dust. The two MSDSs for bituminous coal included qualitative precautionary language about combustible dusts: "Highly combustible and/or explosive when in dust or powder form"; "Do not permit accumulation of dust"; and "Dust/air mixtures may ignite or explode." The MSDS for bituminous coal dust included similar warnings: "It is a fire and explosion hazard when exposed to hear or flame"; "Keep source of heat and ignition, flammable materials, and strong oxidizing agents away from areas where coal dust may collect"; and "Inerting may be desirable...in a coal pulverizing machine." However, none of these MSDSs provided quantitative data on combustibility or explosibility parameters for coal dust. 
   # Other MSDSs. Site visitors reviewed four other MSDSs provided by the facility. Two of these were for surfactant solutions used for purposes of controlling fugitive coal dust emissions where the bucket unloaders scoop coal from the incoming barges. The solutions do not present combustible dust safety hazards. The third MSDS was for the coal ash generated at Facility J. This MSDS covered multiple types of ash (e.g., fly ash, bottom ash) and states, "Fly ash, bottom ash, and boiler slag are nonflammable and non-explosive...unusual fire and explosion hazards do not apply to these materials." The fourth MSDS was for activated carbon that the facility injects into the boilers' air exhaust stream for air pollution control purposes. According to the MSDS, any airborne carbon dust "...may be an explosion hazard." As Section 4.1.2 noted, site visitors collected a sample of fly ash that likely contained trace amounts of activated carbon dust, but the sample was found to not be explosive. 
Other Related Documents
Of all facilities toured to date for this project, Facility J had the most extensive written plans, policies, and procedures pertaining to combustible dust. Site visitors viewed many relevant documents during the site visit. While the extensive documentation demonstrates a strong commitment to identifying and preventing combustible dust safety hazards, site visitors also noted some instances where employee practices differed from documented policies, as explained further below. Thus, a challenge that Facility J faces is ensuring that its extensive written programs are communicated to, and fully implemented by, the appropriate facility personnel. A brief summary of selected facility documents follows: 
   # Combustible dust management procedure. In 2008, after OSHA launched its National Emphasis Program for combustible dust, the company that owns Facility J issued a written procedure on "Combustible Dust Management" designed to identify and control potential combustible dust hazards. The procedure requires facilities to use a compliance checklist to conduct "initial coal handling dust assessments." These assessments are supposed to be revisited annually or whenever the facility undergoes any major changes to its equipment, materials, or processes. 
      Safety and health officials at Facility J completed their three-page checklist in May 2009 and provided a copy of the completed checklist to site visitors. The checklist had specific questions that mirrored those listed in OSHA's National Emphasis Program. The questions fell into several categories, including electrical classification designations, ignition control, dust collectors, size-reduction equipment, fire protection, hazard communication, and housekeeping. The checklist was designed to help facility representatives identify action items for further reducing potential safety and health hazards. 
   # Housekeeping guidelines. Facility J showed site visitors a copy of its written housekeeping guidelines, which were last updated in 2009. For every production area and company-owned vehicle, the guidelines assigned specific individuals as having primary and backup cleaning responsibility. However, the document did not specify housekeeping frequencies or preferred cleaning methodologies. It was not clear if Facility J had a separate document that contained this information. 
   # Mill inerting. Facility representatives shared a copy of a document prepared by the PRB Coal Users' Group on best practices for mill inerting and associated fire suppression issues. The document is based on a survey of the industry and original equipment manufacturers and does not necessarily reflect conditions at Facility J. The survey found that approximately three-fourths of mills (i.e., pulverizers) among the respondents were equipped with some form of inerting, with the most common inerting agents being steam and carbon dioxide. After presenting background information on the design and operation of inerting systems currently in use, the document presented best inerting practices for three of the most common mill designs: ball tube mills, ball and race mills, and roller mills. While recommendations vary across these designs, best practices generally included use of mill inerting during startup, shutdown, and unanticipated interruptions to the coal flow (also known as "mill trips"). The document refers to NFPA 69 and NFPA 85 for further information on designing, operating, and maintaining inerting systems (NFPA 2007, 2008). 
   # Other. Facility representatives shared copies of several additional documents, including a corporate fire protection program and standard operating procedures to address various types of process upsets (e.g., plugged hoppers in dust collectors) or potential unsafe operating conditions (e.g., detection of "hot coal" inside dust collectors or at coal storage piles). 
   
Training 
Facility J offers numerous training courses to its employees and contractors, with these individuals' job duties determining which training courses they must take and how often. Facility representatives shared copies of training materials for a small subset of the training courses offered. Examples include: 
   # Facility safety and health representatives developed presentations to inform employees who work in the coal yard and in other coal-handling operations about combustible dust safety and health hazards. Site visitors were given copies of two of these presentations. One provided general information on combustible dust hazards, and the other addressed a broader range of topics, including hazard prevention measures, acceptable dust accumulation thicknesses (1/32" was reported for coal dust), and specific facility locations expected to have coal dust accumulations. 
   # Site visitors reviewed a presentation that facility representatives give to contractors who perform housekeeping duties in the coal-handling areas. The presentation first describes fire and explosion hazards associated with PRB coal and then reviews the preferred housekeeping strategy -- water washdown -- for removing coal dust accumulations. The training emphasizes the need to select water pressures to avoid generating airborne coal dusts but does not specify the water pressures that are preferred or those that should be avoided. This is important because the cleaning personnel often use high pressure water sprays that generate large, wet dust clouds.
   # Facility J has developed and implemented an industrial fire brigade training program. The training addresses many topics specific to combustible dust, such as firefighting procedures and precautions for incidents in pulverizers, silos, and bunkers. The training addresses numerous other topics unrelated to dust (e.g., firefighting considerations for transformers, high voltage power lines, other operations typically found at electricity generating facilities). 
   # All visitors to Facility J must watch a brief safety video, receive a facility-specific safety pamphlet, and are typically escorted by facility personnel while working on site. Contractors who work for extended durations must take additional training courses, as determined by their job duties. 

Safety and Health Programs
This section reviews the site visitors' observations of selected safety and health programs implemented at Facility J, with a focus on the extent to which combustible dust issues are factored into these programs: 
   # "Hot work" permits. Facility J defines hot work as "any work involving burning, welding, or similar operations that is capable of initiating fires and explosions." Additional examples listed in the hot work program include cutting, heat treating, grinding, riveting, and fastening. Several criteria must be met before authorized personnel can issue hot work permits. Examples include: 1) coal dust must be removed from a "safe radius" around the hot work location (but the program does not specify how this radius is determined), 2) any airborne dust must settle or be vented before hot work can begin, 3) ventilation systems should be operating prior to and during hot work activity, and 4) adequately sized fire extinguishers must be present in areas where hot work occurs. 
   # Confined space entry. Facility J shared a copy of its confined space entry program. The program defines confined spaces, describes instances requiring confined space permits, and describes the process by which these permits are issued. Combustible dust is explicitly addressed in this program -- the atmosphere within a confined space is considered hazardous when "airborne combustible dust is at a concentration that meets or exceeds its lower explosive limit" or airborne dust obscures visual perception of objects five feet away. The entry procedures do not permit smoking, open flames, or use of non-dust-proof electrical equipment when working in confined spaces with airborne coal dust. 
   # Lockout and tagout. The company that owns Facility J has a written policy, procedures, and forms for obtaining "clearance permits" to ensure that employees safely service and maintain any equipment. An appendix to this policy includes site-specific considerations for Facility J. All changes or revisions that have been made to the clearance permit program are documented at the end of the policy. The policy clearly states scenarios for which clearance permits are required and assigns responsibilities to numerous parties, from operators (both employees and contractors) to the plant manager. While the policy and procedures do not specifically mention or address combustible dust safety hazards, facility representatives said that these hazards are always considered during the permit review process.  
      During the facility tour, site visitors saw various "tagged out" equipment, confirming that facility personnel follow this corporate safety and health policy in some instances. However, some equipment had been "tagged out" for relatively long durations, raising some question about the priorities placed on timely resolution of maintenance issues. 
   # Personal protective equipment and uniforms. Employees and visitors are required to wear hard hats, eye protection with side shields, and steel-toed shoes, except when working inside offices. Hearing protection is also required in designated areas. As noted earlier, flash fire resistant personal protective equipment would provide additional protection for employees who perform housekeeping activities in underground tunnels and employees working in the immediate vicinity of operating pulverizers and pulverizer outlet ducts.
   
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 J's compliance with OSHA regulations or adherence to NFPA consensus standards. The main findings communicated to Facility J representatives are listed below, and additional findings are listed in Section 3 of this site visit report.  
   # All facility employees that site visitors met were highly aware of combustible dust safety issues. In addition, the facility's safety and health professionals seemed strongly committed to ensuring safe operations and researching and implementing proactive policies to prevent or mitigate the consequences of combustible dust incidents. Additional technical support provided by corporate safety and health officials and the PRB Coal Users' Group further enhanced Facility J's efforts to control potential combustible dust safety hazards. 
   # Facility J incorporated combustible dust safety issues into a broad array of standard operating procedures, facility policies, and employee training. However, in some instances, actual employee practices differed from those outlined in these resources. A challenge the facility faces is ensuring that employees fully understand and implement all dust-related requirements documented in the many thoroughly written safety and health programs. 
   # Over the last two decades, Facility J implemented many engineering and administrative controls to address combustible dust safety hazards associated with dust collectors. Examples include replacing some baghouses with scrubbers; retrofitting other baghouses with fire detection and suppression systems, explosion venting, and other controls; and developing standard operating procedures for detecting and extinguishing burning and smoldering coal dust. These and other improvements have likely reduced the risks of dust-related fires and explosions. Additional opportunities for further risk reduction include: reevaluating the placement and sizing of explosion panels on certain baghouses; installing explosion isolation systems on baghouses, especially those that transport collected coal dust directly to large coal storage silos; and implementing greater oversight and control on the scrubber operation (including interlocks to prevent operating without water or with a plugged outlet) and maintenance of scrubbers. Refer to Section 3.4 of this report for additional detail on these potential improvements. 
   # Coal dust accumulations varied across the facility, but were most evident along the belt conveyors that run through two underground tunnels. Employees wash away this coal dust using water pressures of approximately 165 psi sprayed through a (3/4)" hose -- a cleaning procedure that reportedly generates dense brown clouds of wet coal dust in confined spaces. Facility representatives were encouraged to investigate options to address this issue through some combination of reducing fugitive dust emissions inside the tunnels, installing additional and larger dust collection inlets and ducting in these problem areas of the tunnels, ensuring that all potential ignition sources are eliminated, implementing housekeeping procedures that minimize formation of coal dust clouds, providing additional emergency and/or improving egress paths near tunnel ends, and providing flash fire-resistant personal protective equipment (per NFPA 2112) for personnel who remove accumulated dust from the underground tunnels. Refer to Section 3.2 of this report for additional observations about Facility J's housekeeping practices. 
   # Coal pulverizers are a known source of dust fires and explosions. At Facility J, pulverizers process large quantities of fine coal powder at relatively high temperatures and in the presence of potential ignition sources (i.e., hot moving metal parts inside the mills). During startup, shutdown, and unanticipated interruptions to coal flow, airborne coal dust concentrations inside the pulverizers can be expected to reach optimal explosible concentrations. Facility J uses steam inerting during shutdown and when there are observations of burning coal to mitigate the frequency and consequences of "puffs" or explosions. While inerting is an appropriate engineering control under these circumstances, certain aspects of the inerting system could be bolstered to provide greater assurance in the system's effectiveness. NFPA 69 lists many design specifications for using inerting systems to prevent explosions. For example, Section 7.7.2 of NFPA 69 specifies the maximum allowable oxygen concentrations to provide confidence that the inerting is effective, and these concentrations depend on the LOC of the material being processed. Knowing the LOC of the mixed coal dusts typically processed, Facility J can set target oxygen concentrations and modify the steam inerting system design accordingly. Establishing employee exclusion zones near the pulverizers and connecting ductwork can help reduce safety risks associated with unanticipated "puffs." The facility can assess the effectiveness of its engineering controls on the pulverizers by documenting and tracking the frequency and severity of all "puff" events. 
   # Facility J has designated numerous production areas as "Class II, Division 2, Group F" locations. However, some equipment used in these locations apparently was not rated for this classification and showed evidence of coal dust accumulations. Motors, vacuum cleaners, and other electrical equipment should be consistent with the hazard classification in the areas where they operate. 
   # Though Facility J has inspection and maintenance programs designed to ensure that key process equipment continues to function properly, site visitors noted several examples of corroding equipment (for example, at the barge unloading station) and a delay in repairs to some malfunctioning dust collectors and dust scrubbers. Facility representatives were encouraged to evaluate the factors contributing most to the corrosion (e.g., whether the water-based dust suppression agent plays a major role) and to strive for improved upkeep, timely repairs, or replacement of the facility's problematic dust control systems.

Feedback to OSHA
At the end of the site visit, ERG asked representatives from Facility J 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, 2009] and after the agency convened its stakeholder meetings.) Facility J representatives offered the following responses:
   # Facility representatives expressed concern about the amount of resources that might be needed to comply with a new OSHA combustible dust standard. The concern included both financial resources that might be needed to upgrade equipment and personnel demands to oversee and implement all new requirements. 
   # Corporate representatives at the site visit emphasized that Facility J is relatively new compared to others in this industry. Many older coal-fired electricity generating facilities were designed and constructed in good faith according to relevant and applicable practices at the time, but could require much more extensive upgrades to adhere to current NFPA standards. These representatives encouraged OSHA to consider how potential compliance costs can vary with facility age.  
   # Facility representatives urged OSHA to ensure that its new combustible dust standard does not conflict with environmental regulations. To illustrate this concern, they noted that dust control systems are typically designed to comply with environmental regulations, with certain operating parameters required to fall within permitted limits. They encouraged OSHA to be mindful of these and other constraints when developing its combustible dust requirements. 
   # The company that owns Facility J has already communicated additional concerns to OSHA at the agency's combustible dust stakeholder meetings and through other public comment processes. 

References

ASTM, 2010. ASTM E1226: Standard Test Method for Explosibility of Dust Clouds. American Society for Testing and Materials. Current edition published in March, 2010. Originally approved in 1988.

Merritt, D and R. Rahm, 2000. Managing silo, bunker, and dust-collector fires. Power. November/December 2000. pp. 53 - 60. 

NFPA 850, "Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations," 2010 Edition.

NFPA, 2007. NFPA 85: Boiler and Combustion Systems Hazard Code. 2007 Edition.

NFPA, 2008. NFPA 69: Standard on Explosion Prevention Systems. 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.

Zalosh RG, 1987. Review of Coal Pulverizer Fire and Explosion Incidents, in "Industrial Dust Explosions, ASTM STP 958." Kenneth L. Cashdollar and Martin Hertzberg, Eds. American Society for Testing and Materials, Philadelphia, 1987. pp. 191 - 201. 
 

     Table 1. Testing Results for Samples Collected During the Site Visit
                                   Parameter
                                 Sample #7782
                                 Sample #7783
                                 Sample #7784
                                 Sample #7785
Description of material
                                    Fly ash
                                  Mixed coal
                                   PRB coal
                                Bituminous coal
Particle size data 
                                       
                                       
                                       
                                       
   % through 20 mesh
                                     100%
                                      37%
                                      29%
                                      18%
   % through 40 mesh
                                     100%
                                      21%
                                      17%
                                     0.1%
   % through 200 mesh
                                      91%
                                     5.3%
                                     1.4%
                                     0.0%
Moisture content
                                     0.1%
                                      24%
                                      30%
                                      11%
Explosive material?
                                      No
                                      Yes
                                      Yes
                                      Yes
Kst (bar-meters/second)
                                Not applicable
                                     14.75
                                     7.09
                                     20.65

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 cannot 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.
      Kst = maximum normalized rate of pressure rise (or deflagration index); values are provided only for explosive materials.
      The three coal samples were relatively coarse because finer dust accumulations had been cleaned up prior to the samples being collected (see Section 4.1). Therefore, the testing results should not be assumed to be representative of finer coal dusts.    

        Figure 1. Photograph of Dust Control System for a Belt Conveyor
                                       
                                       
Note: 	These photographs were taken in an underground tunnel where coal falls from a coal stockpile, through feeders, and onto belt conveyors, which then transport the material to crushers and ultimately to the boiler buildings. In the top photograph, the feeder is the light-colored structure atop the belt conveyor. At the time the photograph was taken, the feeder door was ajar -- a situation that would be expected to cause significant fugitive dust emissions if not addressed before the next coal loading cycle. To the right of the feeder, the belt conveyor is fully enclosed with an inlet to the dust collection system shown. The bottom photograph shows the belt conveyor downstream from the enclosure; coal dust is visible on surfaces beneath the conveyor belt. 

	

       Figure 2. Photograph of Expandable Ductwork at Pulverizer Outlet
                                       
                                       

Note: 	This photograph shows expandable ductwork that connects the pulverizer to the coal-fired boilers. During routine operations, the pulverized coal is blown through this ductwork. During larger "puffs" (or explosions) that originate in the pulverizers, the ductwork has blown apart at expandable joints, causing coal dusts and even fireballs to discharge into the workplace. 

         Figure 3. Photograph of a "Dry" Dust Collector (Baghouse)
                                       
                                       
                                       
Note: 	This photograph shows one of Facility J's baghouses. Coal dust in inlet air is collected in bags hanging from the top part of the baghouse. Pulsed air dislodges the collected dust, which then falls into the hopper at the bottom and passes through the rotary valve. Two explosion vent panels are visible in the photograph. One faces away from the boiler building structure, but the other panels face the structure. The explosion vent panels are placed relatively high on the dust collector, raising questions about whether they can effectively vent deflagrations originating in the baghouse. 
         Figure 4. Photograph of a "Wet" Dust Collector (Scrubber)
                                       
                                       
                                       
Note: 	This photograph shows one of Facility J's scrubbers, which is the blue-colored device in the middle of the picture. The dust-laden air stream enters the scrubber via the ductwork on the left-hand side of the photograph, and exhaust ("clean") air exits through the ducting on the right-hand side. Extensive tape and patchwork was located on the inlet ductwork. The water that had pooled beneath the scrubber apparently resulted from leaks in the system. 
    Figure 5. Photograph of a Dust-Tight Enclosure for Electrical Fixtures
                                       
                                       

Note: 	This photograph shows a typical "NEMA 4" dust-tight enclosure that Facility J uses in Class II areas. While the enclosures help minimize the amount of dust entering certain electrical fixtures, not all electrical equipment located in these areas is rated for this hazard classification. As one example, some motors were observed in Class II locations that were not in dust-tight and fan-cooled enclosures. 
        Figure 6. Photograph Showing Evidence of Corrosion in Ductwork
                                       
                                       

Note: 	This photograph shows a large hole in the inlet ductwork to a baghouse located at a coal crusher station. Facility representatives were encouraged to evaluate the factors contributing to this and other signs of corrosion, with one possibility being that aqueous dust suppression agents played a major role in the equipment corrosion. 

 
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 cannot 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.