Document ID: OSHA-2009-0023-0178
Agency: osha
Document Type: Supporting & Related Material
Title: 
Posted Date: 2011-08-04T04:00Z

Site Visits Related to Combustible Dust:
Facility P - Furniture 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
                                                                               
                                                                               

April 4, 2011
                               Table of Contents
                                       
1	Project Overview	1
2	Facility Description	2
3	Process Descriptions	3
3.1	Woodworking Operations	4
3.2	Wood Dust Accumulations	5
3.3	Housekeeping Practices	6
3.4	Ductwork and Controls	8
3.5	Scrap Wood Processing	11
3.6	Dust Collectors	12
3.7	Other	14
4	Document Review	15
4.1	Testing Data	16
4.2	MSDSs	17
5	Training	18
6	Safety Programs	19
7	Main Findings	20
8	Feedback to OSHA	23
9	References	24

Table 1			Testing Results for Samples Collected During the Site Visit
Figure 1		Photographs of Enclosed Woodworking Stations
Figure 2		Photograph of Non-Enclosed Woodworking Station 
Figure 3		Photographs Showing Interior of Electrical Control Panels
Figure 4		Photograph of Conveyor Feed to "Wood Hog" 
Figure 5 	 	Photograph of Overhead Wood Scrap Conveyor, Bearing, and Magnet
Figure 6		Photograph of Wood Dust Baghouse
Figure 7		Photograph of Multiple Dust Collectors
Figure 8		Photograph of an Enclosureless Dust Collector

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

Acronyms and Abbreviations

ANPR		advanced notice of proposed rulemaking
CNC		Computer Numerical Control
ERG		Eastern Research Group, Inc.
Kst			deflagration index
MSDS		Material Safety Data Sheet
NFPA		National Fire Protection Association
OSHA		Occupational Safety and Health Administration
psi			pounds per square inch
PSM		process safety management

Project Overview 
On August 31 and September 1, 2010, Eastern Research Group, Inc. (ERG) conducted a two-day site visit to a furniture production facility (hereafter referred to as "Facility P"). The site visit was conducted by two ERG employees and a consultant; two 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 P'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 P'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 P, 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 P'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 P 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 P has a standard industrial classification code for furniture manufacturing and manufactures its products from wood and particle board. Numerous woodworking operations occur at Facility P, including sawing, sanding, punching, groove cutting, boring, and clamping. Most products undergo multiple finishing operations, which typically involved spray coating using stains, sealers, and topcoats. Coated products typically pass through steam or natural gas-fired ovens to facilitate drying, while others dry under ambient conditions. Woodworking operations throughout the facility generate wood scrap, chips, and dust, and approximately 25% of this is collected and passed through a size-reduction operation ("wood hogs") before being fed to an onsite wood-fired boiler for energy recovery. Facility representatives suspected that the majority of the woodworking and finishing processes at Facility P are reasonably representative of those employed by other furniture manufacturers making similar products (e.g., cabinets, case goods, wood flooring, tables). However, due to recent downsizing, staffing levels at Facility P were believed to be lower than those at many larger furniture manufacturing companies. 
Facility P's main production areas are located in buildings with a combined total floor space of roughly 2.2 million square feet. Some of these buildings were first constructed more than 100 years ago. The main processes tend to operate four days per week throughout the year. Approximately 350 employees work at Facility P, and about 85% of these work on the various woodworking and finishing production lines. One employee (an engineer) oversees Facility P's health and safety programs. This employee splits his time between health and safety issues, environmental compliance, and other job responsibilities. 
Though Facility P representatives noted that they have never experienced an explosion resulting from combustible dusts, some fires have occurred (see Section 3.7 for more details). Local fire departments responded to the larger incidents, as Facility P does not have its own fire brigade. Smoking at Facility P is permitted only in designated outdoor areas, far from the facility's main production areas; site visitors noticed no evidence of smoking (e.g., discarded cigarettes) in the production areas.
Site visitors asked the facility's safety personnel to comment on the roles that outside parties play in Facility P's combustible dust safety programs. A summary of those responses follows: 
   # Facility P is typically visited once or twice per year by the local fire marshal. The fire marshal did not make facility personnel aware of applicable NFPA standards, including NFPA 664. 
   # For the past 10 years, Facility P's property insurance carrier has been Lumbermen's Mutual Insurance Company. Its representatives typically visit the facility four times per year and make recommendations on many safety-related topics, ranging from ergonomics assessments to fall prevention evaluations. In terms of combustible dust, these representatives made recommendations in 2003 that led to Facility P installing spark/ember detection and suppression systems and high-speed abort gates in selected ductwork locations (see Section 3.4 for more details). Facility P's annual premiums decreased after these dust controls were implemented -- a decrease that likely resulted from market conditions and, to a certain extent, facility improvements. Facility representatives noted that the insurance company is their most trusted resource for technical information on combustible dust. 
   # Facility P representatives have not consulted directly with OSHA on combustible dust issues. However, the employee responsible for safety and health programs indicated that he frequently visits OSHA's website to track emerging issues and regulatory interpretations.  
   # Facility P is a member of the Kitchen Cabinet Manufacturer's Association, which provides many services to its member facilities. In terms of combustible dust, the association has shared OSHA announcements with its member facilities and encouraged members to comment on the agency's advanced notice of proposed rulemaking (ANPR), but it has reportedly not provided its members with detailed technical guidance on identifying and controlling dust-related hazards. 
   # Facility P has previously contracted with consultants and external engineering and design firms for many activities, such as installation and maintenance of spark/ember detection and suppression systems, servicing of baghouse explosion panels, and industrial hygiene monitoring. 

Process Descriptions
This section describes selected process operations and production activities that site visitors viewed at Facility P. The specific issues discussed in this section were selected for more detailed summaries because they either: 1) demonstrate unique challenges faced by this facility or industry, 2) highlight effective engineering or administrative solutions implemented by Facility P, or 3) pertain to specific safety issues OSHA might be considering in its rulemaking effort. This section refers to relevant passages in "NFPA 664," which is NFPA's combustible dust standard for wood processing and woodworking facilities (NFPA, 2007). 
Woodworking Operations 
Facility P has several dozen individual woodworking stations where employees operate various types of equipment, such as belt sanders, disc sanders, saws, fasteners, and mills that bore holes and etch grooves into wood panels. These operations generate wood dust at varying rates, with point-to-point boring machines reportedly creating the most fugitive dust at Facility P.
Many woodworking stations at Facility P had full or partial enclosures surrounding the moving parts and dust-generating activities (see Figure 1). These enclosed stations were connected to the facility's dust control system, which collected dust-laden air generated during these operations. The enclosures appear to minimize release of fugitive dust from the woodworking operations into the workplace, provided the ductwork and air flow are properly maintained. The dust, shavings, wood chips, and other wood scrap that are not picked up by the dust control system settles onto surfaces and the floor inside the enclosures until employees remove the accumulations. 
On the other hand, several woodworking stations had no such enclosures (see Figure 2). Some stations without enclosures were equipped with flexible plastic ductwork connected to the dust control system. The air movement into the flexible ducting provided localized dust control and a means for operators to vacuum dust accumulations at their machines (i.e., by manually moving the flexible ducting near areas with settled wood dust). Nonetheless, the non-enclosed woodworking stations observed during the site visit appeared to be significant sources of fugitive wood dust, and, as Section 3.3 describes further, housekeeping procedures for removing this settled dust might be contributing to dust accumulations in other parts of the production areas. 
Some of each type of woodworking station (enclosed and non-enclosed) were interlocked with the dust control system such that employees could not conduct any woodworking operations unless the dust control system was fully operational. However, several stations were not equipped with these interlocks, and site visitors heard of instances of some employees performing small woodworking tasks during times when the dust control system was not operating (e.g., on Fridays or weekends) -- a practice that would be expected to cause increased releases of fugitive dusts to the workplace. 
Site visitors noted various opportunities Facility P could pursue to minimize the release of fugitive dusts. These include having a greater portion of woodworking stations enclosed, installing interlocks on more stations to prevent employees from operating woodworking equipment unless the dust control system is functioning, or implementing new standard operating procedures or administrative controls requiring employees to confirm that the dust control system is operating before beginning any woodworking activity. 
Wood Dust Accumulations
Overall, the general floor space throughout most of Facility P was relatively dust-free. This likely reflected the attention that operators pay to removing settled dust and accumulations at their individual woodworking stations. As to be expected, wood chips, shavings, and dust were observed at floor level in the immediate vicinity of active woodworking activities, but workers removed these accumulations at least once per shift. 
When collecting samples for laboratory testing, site visitors noted dust accumulations atop horizontal surfaces at various vertical distances above floor level. The surfaces examined included rafters in one production area and electrical control panels in various facility locations. The thickness of wood dust accumulations in these locations ranged from very fine layers to more than 1 inch. Of the materials sampled, the wood dust collected from the ceiling rafter had the finest particle size distribution, with 85% of the sample passing through a 200 mesh (i.e., smaller than 74 microns). The wood dusts in all samples had moisture contents ranging from 5.2 to 6.6%, considerably dryer than the 10 to 12% moisture contents in the wood that is received at the facility.
Site visitors also noted wood dust on internal wiring and relays inside more than one electrical control panel (see Figure 3). These accumulations likely resulted in some cases from the panel doors being open for electrical maintenance during production shifts and, in other cases, from fugitive dusts penetrating into closed panels. Some employees indicated that dust accumulations might have been interrupting relay contactors inside Computer Numerical Control (CNC) panels, but they had not seen evidence of burning dust or arcing at these locations. 
Site visitors noted that dust accumulating inside electrical control panels does, however, present a potential fire and explosion hazard and identified measures Facility P can take to prevent or limit these accumulations. Examples include implementing administrative controls to ensure that all doors on electrical panels are routinely and firmly closed, implementing preventive maintenance procedures that require designated employees (preferably electricians) to periodically inspect the electrical control panels and vacuum any wood dust observed inside, and using dust-tight electrical panels. Vacuums used for these purposes should be rated for Class II, Division 2 environments.  
Housekeeping Practices 
Facility P conducts extensive housekeeping activity to remove wood dust accumulations from production areas. The facility does not have a written housekeeping program, but interviews with multiple employees painted a consistent picture of Facility P's housekeeping practices: 
   # Daily housekeeping activities. All employees clean their workspaces throughout their shifts, as needed, and at the end of their shifts. Employees noted that they must remove dusts to ensure that woodworking equipment functions properly and to avoid dust accumulation on unfinished wood products. Employees indicated that they typically spend 15 to 30 minutes at the end of their shifts removing dust accumulations from their workstations. Employees remove wood dust accumulations from their workstations using some combination of three methods: 1) compressed air to blow dusts to the floor, 2) flexible hoses connected to the dust control system to vacuum wood dusts, and 3) sweeps, brooms, scoops, and dust pans. Supervisors reportedly inspect individual woodworking stations to confirm the effectiveness of employees' housekeeping practices. 
      Employees transfer collected wood dust and scrap items to uncovered wooden totes (see Figure 4), which are eventually rolled to another part of the facility for scrap wood processing (see Section 3.5). Site visitors encouraged facility representatives to consider using covers on these totes and to possibly use totes made from noncombustible material, such that sparks generated in the production area do not inadvertently land on and ignite large quantities of combustible dust. 
      In one production area, employees operated a propane-powered riding sweeper to remove wood dusts that had either settled onto the floor or had been swept into piles. The powered sweeping typically occurred at ends of shifts. It was unclear if the powered sweeper was approved for use in Class II, Division 1, Group G locations, as Section 11.2.1.2 of NFPA 664 requires. 
   # Periodic cleaning campaigns. The facility conducts "top-to-bottom" cleaning campaigns of entire production buildings to remove all dust accumulations, including those in hidden and inaccessible areas (e.g., atop ceiling rafters). The frequency of these cleaning campaigns depends on dust accumulation rates. In one of the larger departments, "top-to-bottom" cleaning typically occurs every three years, and the last "top-to-bottom" cleaning reportedly occurred about 3 years prior to the site visit. Facility representatives indicated that this cleaning is a major undertaking, with a crew of 20 employees working the equivalent of 12 days over the span of two months to remove the accumulated dusts. These campaigns typically occur on Fridays and Saturdays, when production is not occurring. Electrical devices are turned off during these campaigns, but lights remain on. Employees cover woodworking equipment and computers in nearby offices with cloth before performing this cleaning. 
      During these campaigns, the main approach for removing dust accumulations is blowing material down to the floor with compressed air. To facilitate clean-up efforts and prevent re-suspension of dislodged dusts, employees first spread an oil-based sweeping compound on the floors before using compressed air. A sample of this sweeping compound, known as "dust down," was sent to OSHA's laboratory for testing, and the material was not found to be explosive (see Section 4.1 and Table 1). Employees noted that dust clouds having an appearance of a "light fog" formed during the use of compressed air, but employees said they could visually discern objects through these dust clouds.
      Facility representatives noted that substantial quantities of dust are removed during these periodic cleaning campaigns. During a recent blowdown for one production building, 2.5 tons of accumulated wood dusts were reportedly removed. Some employees said the blowdowns in this particular building caused wood dust to accumulate in some electrical relays and that certain CNC equipment did not function immediately following these campaigns. 
   # Cleaning methods. As noted previously, the primary methods that facility personnel used to remove dust accumulations were using compressed air, vacuuming with flexible hoses, and manually sweeping and scooping dusts with hand-held tools. Facility representatives were not certain of the pressure of their compressed air, but thought it was 96 pounds per square inch (psi). The pressure was not down-regulated at the compressed air wands.
      After noting that facility personnel relied heavily on compressed air for removing dust accumulations, site visitors asked if Facility P had considered using vacuums for their routine or periodic housekeeping. Facility representatives said they viewed vacuuming as more time-consuming than blowing dusts with compressed air, and they also said that vacuums are difficult to use when removing accumulations from areas with limited accessibility (e.g., the interior workings in some woodworking machines, overhead rafters). Site visitors encouraged facility representatives to investigate the utility and effectiveness of vacuums, whether as standalone units or by wider use of flexible hose connections to the dust control system. This recommendation was made because vacuums do not generate clouds of combustible dusts, and their use might actually decrease the frequency needed for the labor-intensive and costly "top-to-bottom" cleaning campaigns. Another engineering control that could hold promise at Facility P is installation of overhead oscillating fans to prevent the wood dust from accumulating on rafters in the first place, thus greatly reducing the need for using compressed air to remove wood dusts from ceiling rafters. (Note: The ceiling height in some production areas was likely too low for use of these fans.) 
Overall, Facility P's current housekeeping practices appear to be somewhat effective at removing dust accumulations from individual woodworking stations in the short term, but these routine practices -- particularly the frequent use of compressed air for cleaning -- likely cause fine wood dusts to accumulate in overhead locations and inside electrical control panels over the long term. As Section 5 of this report notes, use of "NEMA 4" enclosures on electrical control panels should help prevent dust ingress. 
Other housekeeping procedures, such as greater reliance on vacuums and use of lower compressed air pressures when this technique must be used, might provide a more effective means for removing wood dust from production areas. Site visitors encouraged facility representatives to evaluate their overall housekeeping practices. They could start by measuring wood dust accumulation rates in certain production areas to assess the effectiveness of different housekeeping practices. The facility could then consider implementing new housekeeping procedures that more effectively remove settled dusts without disturbing them in a manner that leads to accumulations on overhead horizontal surfaces. Updates to Facility P's housekeeping program should be based on specifications in Section 11 of NFPA 664.
Ductwork and Controls
Facility P's dust control system conveys dust-laden airstreams from individual woodworking stations through a complex array of manifolded ductwork to dust collectors, and the collected material is eventually fed to an onsite wood-fired boiler for energy recovery. This section reviews site visitors' observations about the facility's ductwork and engineering controls that have been installed to minimize combustible dust hazards:
   # Manifolded ductwork. Many individual woodworking stations have multiple connections to Facility P's dust control system (see Figure 1). The ductwork from the individual stations is then connected to larger ducts, which eventually direct dust-laden air to one of the facility's dust collectors (see Section 3.6). To meet environmental permitting requirements, the minimum air flow rate through Facility P's duct work must be 4,500 feet per minute. The permits require facility representatives to conduct visual inspections of ductwork to evaluate structural integrity, as well as more detailed monthly, quarterly, and annual preventive maintenance evaluations. While it was unclear how frequently facility personnel directly measure air flow through the ductwork, multiple employees stated that operators would most likely notice low airflow due to unusually high accumulations of wood dust in their individual workstations.  
   # Spark/ember detection and suppression systems. In 2003, at the recommendation of its insurance underwriter, Facility P installed two infrared spark/ember detection and suppression systems on different ductwork segments. These were installed to detect and promptly suppress smoldering material before it entered dust collectors. The systems were manufactured by Clarke's International, Inc., and have been certified by Factory Mutual. The two systems have multiple zones with spark/ember detection sensors. 
      The total purchase and installation cost for both systems was approximately $130,000, which does not include ongoing maintenance costs. The company that installed the Clarke systems services them quarterly and performs more thorough annual inspections. Facility P's maintenance contract with this third-party vendor costs approximately $3,000 per year. Roughly $2,000 of this expense is paid to the vendor for its labor, and the remaining $1,000 is paid to a separate company to rent a powered lift to help the vendor access the equipment. While Facility P incurred substantial costs to purchase, install, and maintain these systems, it also received substantial reductions in insurance premiums (see footnote on page 3), which partially offset these costs. 
      The vendor that installed the Clarke systems programmed their settings, including the frequency and extent of sparking that triggers alarms. Both systems have two alarm levels. Currently, a "low alarm" is triggered when sensors inside the ductwork detect a preset sparking threshold. When this happens, an audible alarm sounds and the system issues a "short spray of water" inside the ductwork at a downstream location. The suppression continues for 5 seconds, during which 3 to 7 gallons of water are sprayed inside the ductwork (with the exact amount depending on the zone that triggers the alarm). Water used in this system is drawn from the municipal supply. 
      Employees indicated that the system downstream from the larger wood hog issues low alarms frequently, at times daily. (Note: Wood hogs are size reduction operations that shred or grind scrap wood materials; Facility P operates two wood hogs.) Burning wood embers ignited by the friction and impact forces in the shredders are believed to be the primary source of sparks that trigger these alarms. Upon hearing the audible alarms, designated operators check the process for evidence of fires or potentially unsafe conditions before deactivating the alarm and resetting the system. However, because the alarm sounds in an area that is sometimes not occupied by employees, alarms reportedly can sound for long periods of time (e.g., hours) before being deactivated. 
      A "high alarm" level is also programmed into the system. Should sparks be detected for an extended period of time and exceed a threshold that was established by the installation vendor, the higher alarm not only triggers water spray but also activates abort gates in the downstream ductwork (see next bulleted item). In the few years that these systems have been operating at Facility P, this higher alarm level has never been reached.
      Site visitors encouraged facility representatives to take advantage of the full range of hazard mitigation opportunities that the spark/ember detection and suppression systems offer. For instance, facility personnel were not aware of the spark detection settings that trigger alarms, nor had they conducted systematic evaluations to determine if alarms are linked to specific operating conditions (e.g., alarms might occur primarily after loading totes full of wood scrap into the larger wood hog). Such evaluations could be conducted if facility personnel documented the dates, times, and operating conditions during alarms or learned how to download or print the history of alarm conditions from the Clark systems. Site visitors also noted that facility representatives have the ability to program different signals for the alarm conditions. For instance, the system can be programmed to trigger flashing lights and audible alarms in more frequently occupied areas, and possibly even pages to designated facility personnel. Such changes can help ensure that alarms receive more timely responses. Finally, facility representatives should ask their maintenance vendor about recommended cleaning frequencies for the spark/ember detection sensors, because the maintenance manual for the Clarke's system indicates that certain inspection activities (e.g., ensuring the sensors are functioning properly) should be performed weekly, and not just during the quarterly servicing intervals. 
   # High-speed abort gates. At two locations in the array of ductwork and dust collectors, ducts are equipped with high-speed abort gates that are activated by "high alarm" conditions on the spark/ember detection and suppression systems. The abort gates are placed on the outlet (i.e., clean) side of selected dust collectors -- a placement that appears to be consistent with requirements listed in Chapter 8.2.2.6.2 of NFPA 664. This engineering control is designed to divert to the atmosphere air streams found to contain burning material, as opposed to directing the burning dust via the ductwork back into the production area. However, as Section 3.6 explains further, the abort gates are not suitable for diverting deflagrations that initiate within the dust collectors. Facility records indicate that the two abort gates cost approximately $60,000 to purchase, install, and interface with the spark/ember detection and suppression systems. 
Scrap Wood Processing
When manufacturing its wood and particleboard products, Facility P generates scrap wood and wood dust. Approximately 25% of the total wood waste (e.g., blocks, chunks, scrap) is collected, conveyed, or transferred to one of two "wood hogs" used for size reduction purposes and then fed to an onsite wood-fired boiler for purposes of energy recovery. The following presents the site visitors' observations regarding the two distinct scrap wood processing operations at Facility P:
   # Scrap wood processed at the "smaller" wood hog. In two large production areas, scrap wood and wood dust is conveyed to the smaller wood hog via an overhead belt conveyor. Site visitors observed only one short segment of the belt conveyor (see Figure 5). Bearings in this segment were not dust-tight and showed evidence of wood dust accumulations. 
      Before feeding material to the wood hog, the overhead belt conveyor passed beneath a magnet installed to remove tramp metal from the scrap wood and wood dust. Placement of the magnet on the inlet side of the wood hog is consistent with requirements in NFPA 664 (see Section 8.4.2.2.2), and the magnet that site visitors observed had obviously collected multiple metal items (e.g., paper clips, screws, bolts) (see Figure 5). Because the magnet does not have a self-cleaning mechanism, the collected metal material can eventually cover much of the magnet's surface, unless employees manually remove these items. The facility apparently did not have standard operating procedures specifying when inspection and maintenance of the magnet should occur, which raised concerns about the magnet becoming overloaded with metal. 
      Site visitors encouraged Facility P to consider replacing this older magnet with one of more contemporary design. For instance, self-cleaning magnetic separators that do not require manual cleaning are commercially available and might offer more effective removal of tramp metal from this scrap wood and wood dust stream, while requiring less frequent inspection and maintenance. 
   # Scrap wood processed at the "larger" wood hog. Facility P's larger wood hog was used primarily to process scrap wood and wood dust that had previously been collected into barrels, totes, and other larger containers. The feed to this hog is a short, floor-level belt conveyor (see Figure 4), onto which employees manually pour or load scrap wood and wood dust. Some employees reported that the manual loading of material onto the belt conveyor can generate dense clouds of wood dust, which gradually dissipate. This practice occurs several times per week and raised concern because dust clouds occur in close proximity to ignition sources, such as an overhead halogen lamp, a nearby electrical control panel, and stray sparks emitted from the hog itself. This potentially hazardous situation could be avoided by considering different approaches for loading the scrap wood and wood dust onto the conveyor (e.g., using enclosures or some other control that minimizes the formation of dust clouds) and by ensuring that electrical equipment in the area is rated for Class II environments. 
      The larger wood hog is equipped with a magnet to remove tramp metal from the process stream, but this magnet is placed on the outlet side of the hog. This arrangement will still remove tramp metal, but only after the metal passes through the size-reduction equipment, where it can generate sparks in the presence of wood dusts. The spark/ember detection and suppression systems placed downstream from the larger wood hog and magnet should control sparks generated by metal passing through the hog. Employees confirmed this, noting that alarm conditions were detected most frequently in this segment of ductwork, presumably due to hot metal objects not being collected by the magnet. Site visitors noted an improved design for this system would include use of self-cleaning magnetic separators or placement of a magnetic separator upstream of the hog. These upgrades would not only help reduce generation of sparks inside the hog but would also reduce the frequency of alarms sounded by the downstream spark/ember detection and suppression system. 
      (Note: Facility representatives explained that the large hog is used to grind pallets and other sub-assembled or assembled wood pieces that are held together with metal fasteners, including staples, nails, and screws. A magnet installed before the grinding would likely not remove these fasteners, because the fasteners are liberated by the grinding operation itself.)
Dust Collectors 
Facility P is currently permitted to operate seven cyclones and nine baghouses (including an enclosureless dust collector). The cyclones range in size from 4 to 12 feet in diameter, and the filter collection areas of the baghouses range from approximately 1,000 to 7,000 square feet. All of the cyclones and baghouses are located outdoors, and the enclosureless dust collector is located indoors. The site visitors viewed a subset of these systems and made the following observations:
   # Largest baghouse. The largest dust collector at Facility P is a baghouse containing approximately 450 bags offering more than 7,000 square feet of filter area. This baghouse is located outdoors (see Figure 6), over and adjacent to a flammable chemical storage area. With these operations in such close proximity, site visitors noted that major fires or explosions that start in the baghouse could rapidly spread to the chemical storage area, and vice versa -- an issue that underscores the importance of effective fire and explosion prevention measures. 
      Air exhaust from numerous woodworking stations at Facility P is vented to this baghouse via manifolded ductwork. The inlet duct is equipped with a spark/ember detection and suppression system, which is intended to prevent sparks or smoldering material from entering the dust collector (see Section 3.4 for comments on this system). 
      Wood dust in the inlet air stream collects on the filter material (i.e., the "bags") inside the baghouse. Pulsed air is periodically charged into the system to dislodge wood dust collected on the filters. The dislodged dust falls to the base of the dust collector, passes through a rotary valve, and then is conveyed via ductwork to the wood-fired boiler. Facility P's air permit requires annual internal inspections of the condition of the bag filters and continuous measurement of the pressure drop across the filters, which is performed using a magnehelic gauge. Leaking bags in the baghouses are identified either during monthly preventive maintenance campaigns or by observing visible emissions in the stack exhaust. Further, the air permit requires facility maintenance personnel to inspect the dust collector and bags whenever the pressure drop exceeds 5 inches of water, and they change the entire set of bags when elevated pressure drops persist. Changing the roughly 450 bags occurs approximately once every five years and is a labor-intensive process. The last time this task was performed in 2008, four employees worked a full day to replace all 450 bags.
      During the winter, exhaust air from the dust collector is returned via ductwork to one of the production buildings; and during the summer, dampers can be activated to discharge bag-filter exhaust air to the ambient environment. This seasonal change is used to minimize costs associated with heating and cooling production areas. (Note: As Section 3.4 explains, an abort gate is installed in the exhaust ductwork, and this is activated by "high alarm" conditions on the spark/ember detection system at the baghouse inlet.) 
      The dust collector is equipped with four explosion vent panels (two of which are visible in Figure 6). Site visitors did not attempt to assess the adequacy of the explosion panel sizing, which would require Kst data obtained per ASTM E1226 procedures as well as specifications for the vent panels. (Note: Facility representatives indicated that the bag-filters in this dust collector were originally installed more than 20 years prior to the publication of the current version of this ATSM standard.) Facility representatives noted that the explosion panels have released a few times in the past, due to degradation of the polymeric liner. When the liner degrades, the vent panel cannot withstand a baghouse pressure greater than about 5 inches of water, which is about the pressure that exists prior to bag replacement. The nominal vent deployment pressure is about four times as large. The baghouse inlet and outlet ductwork do not contain explosion isolation systems that would prevent a deflagration initiating in the baghouse from propagating back through the ductwork and toward production areas. 
   # Multiple cyclones and baghouses in series. As Section 3.5 explains, Facility P collects large quantities of scrap wood and wood dust, and a portion of the waste wood produced passes through wood hogs to pulverize the larger scrap items, and then conveys the finer material to an onsite wood-fired boiler for purposes of energy recovery. The output from both wood hogs passes through a series of cyclones and dust collectors before being stored in silos and fed to the wood-fired boiler. Figure 7 shows the arrangement of dust collectors in this part of the facility.
      The cyclones, baghouses, and interconnecting ductwork have many controls similar to those identified in the previous bulleted item and discussed in greater detail earlier in this report. For example, a spark/ember detection and suppression system with multiple detection zones is located along the main inlet duct leading from the smaller wood hog to the baghouses (see Section 3.4 for discussion). Abort gates are sited on ductwork returning filtered air from bag-filters into occupied buildings. The baghouses (but not the cyclones) are equipped with explosion panels. However, no explosion isolation systems were installed among these various interconnected equipment. 
   # Enclosureless dust collector. One department at Facility P had dust-laden air exhaust streams vented to an enclosureless dust collector consisting of four large bags (see Figure 8). This is the only dust collector at Facility P that is located indoors. Site visitors encouraged facility representatives to review the relevant requirements in NFPA 664. For instance, Section 8.2.2.5.1.4(7) lists criteria that should be met for systems that are placed indoors. The index at the end of NFPA 664 identifies all other requirements pertaining to enclosureless systems. 
Other
The remainder of this section documents various additional observations not summarized in the earlier discussion: 
   # Classification of Hazardous Locations. Facility P has assigned electrical classifications to some production areas, but only based on the presence of flammable solvents. At the time of the site visit, no electrical classifications had been designated based on the presence of wood dust. The presence of wood dust in selected production areas, particularly inside electrical control panels (see Figure 3), suggested that some areas at Facility P should be designated as Class II, Division 1 or 2, or dust control measures and housekeeping procedures should be implemented to avoid this designation. 
   # Fire History. Facility P does not keep a log of past fire incidents and "near misses." However, facility representatives shared brief accounts of two fires from the past 15 years, but it is not clear whether this included all fires that have occurred. In 1998, a part became stuck in a wide belt sander, which led to a large fire. In 2006, a maintenance contractor was cutting into a metal stack on a spray booth, igniting finishing overspray solids. The contractor performing the work did not follow the "Scope of Work," which required removal of the stacks and laying them on the roof prior to cutting; adherence to the requested work would have prevented the incident. The ensuing fire was extinguished by the local fire department and reportedly caused $400,000 in property damage. 
   # Boiler Feed Line. Saw dust from two silos is fed via auger conveyors and pneumatic lines to Facility P's wood-fired boiler. The boiler combustion chamber's pressure fluctuation (due to variations in the fine-grained and coarse-grained feed) causes puffing and the emission of burning embers into the boiler house. This is a concern to visitors because there is a possibility that a large "puff" could cause a deflagration to propagate back through the feed line to the silo. The air control in the saw dust feed line to the boiler is a manually operated control on the fan flow rate, and a "homemade" damper in the duct.

Document Review
This section summarizes documents pertaining to combustible dust safety issues relevant to the site visit. It 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 P's approaches for controlling them. The section also reviews the testing results from the samples collected during the site visit. 
Testing Data
Facility P did not have testing data for explosibility or combustibility of any materials. However, facility representatives showed awareness that wood dusts can present an explosion hazard. For quantitative information on material-specific hazards, facility representatives typically refer to Material Safety Data Sheets (MSDSs, see below) and values published in other sources. 
Site visitors collected six samples during the site visit, with the permission and concurrence of Facility P representatives. All samples were tested for particle size distribution, moisture content, and deflagration index (Kst values). Following the 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; Table 1 briefly summarizes the data. More information on the individual samples collected and the test results follows:
   # Sample #2655: Wood dust. This wood dust sample was collected from overhead rafters in Facility P's Machine Room, near the location of multiple woodworking machines (e.g., saws, punchers) where employees use compressed air to remove dust accumulations. The thickness of settled dust on these rafters varied but appeared to reach depths of 1 inch. This sample had the finest particle size of the four wood dust samples collected during the site visit. It also had the highest deflagration index (Kst = 40.84 bar-m/s), suggesting that the material could cause a more severe dust explosion compared to the other materials tested.
   # Sample #2656: Wood dust. This sawdust sample was collected from atop a wall-mounted electrical control panel near a wood-boring station ("Weeke machine"), where employees use compressed air to remove settled dusts. Dust accumulations atop the electrical panel were approximately 1 to 2 inches deep. Of the four wood dust samples collected, this sample had an intermediate particle size distribution, and it also had an intermediate deflagration index (Kst = 17.85 bar-m/s).
   # Sample #2657: "Filler" dust. This sample was collected from beneath a vacuum table, above which employees wiped down wooden panels that were previously spray-coated with fillers containing talcum powder, iron oxide, organic solvents, and various proprietary ingredients. The material collected on the day of the site visit was found to not be explosive.
   # Sample #2658: Wood dust. This sample was collected from a screw conveyor line that feeds scrap wood and wood dust from the bottom of a storage silo into Facility P's wood-fired boiler. The material is a mixed stream of scrap wood originally generated at dozens of individual woodworking stations throughout the facility. Of the four wood dust samples collected during the site visit, this sample had the most coarse particle size distribution; it also had the lowest deflagration index (Kst = 4.57 bar-m/s).
   # Sample #2659: Wood dust. This sawdust sample was collected from atop a wall-mounted electrical panel in Facility P's Panel Department, adjacent to where employees dump wood chips and dust onto a belt conveyor that feeds one of the wood hogs. Dust accumulations atop the electrical panel were approximately (1/4)-inch thick. Like Sample #2656, of the four wood dust samples collected, this material had an intermediate particle size distribution, and it also had an intermediate deflagration index (Kst = 18.50 bar-m/s). Note that this sample is likely representative of the material found in the dust clouds that routinely form when employees pour wood chips and dusts onto a belt conveyor. 
   # Sample #2660: "Dust down." This sample is an oil-based sweeping compound whose exact composition is not known due to trade secret provisions claimed on the MSDS. During periodic cleaning campaigns to remove dust accumulations from overhead structures in the Machine Room, Facility P personnel place the "dust down" compound on the floor, which helps ensure that settled dust remains on the floor and does not become re-suspended as a result of the cleaning operations. This material had the lowest proportion of finely divided particles and was not explosive. 
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 condition of materials collected during the time of the site visit. For the four wood dust samples collected, testing results are consistent with expectations: all four materials collected were found to be explosive, with explosion severity increasing with decreasing particle size. The two wood dust samples with the finest particle size distribution were collected in areas where employees use compressed air to remove dust accumulations. 
MSDSs 
Facility P provided site visitors with copies of 17 MSDSs for the wood materials processed in the greatest quantities. The MSDSs varied considerably in terms of technical content pertaining to dust hazards, as described below:
   # MSDSs for wood and wood dust. Eight of the MSDSs that Facility P shared were for wood or wood dust, primarily from maple, oak, and other hardwood trees. All eight MSDSs included qualitative warnings about fire and explosion hazards associated with the materials and their anticipated byproducts. For example: "Sawing, sanding, or machining wood products can produce wood dust which can cause a flammable or explosive hazard...wood dust is a strong to severe explosion hazard if a dust cloud contacts an ignition source...partially burned dust is especially hazardous if dispersed in air." Nearly every MSDS recommended that facilities address spills by sweeping or vacuuming the dust. While most of these MSDSs cautioned against cleanup procedures that generate dust clouds, none specifically advised against using compressed air for housekeeping purposes. 
      These MSDSs also varied in terms of quantitative information on fire and explosion hazards. All eight MSDSs presented comparable data on auto ignition temperatures for wood dust (typically 400 to 500[°]F) and lower explosive limits in air (typically 40 g/m[3]). Only one of these MSDSs provided quantitative data on additional parameters of interest: the minimum ignition energy for a dust cloud of white pine flour (40 millijoules) and the maximum pressure rise for a dust explosion (113 psig). 
   # MSDSs for particleboard and fiberboard. Nine of the MSDSs pertained to particleboard and fiberboard materials, and they presented similar language on the potential dust-related hazards. One example follows: "Particleboard is not an explosion hazard. Sawing, sanding, and/or machining particleboard could result in the by-product wood dust. Wood dust may present a strong to severe explosion hazard if a dust cloud contacts an ignition source. According to data contained in NFPA (National Fire Protection Association) standards, 40 g/m[3] (0.040 ounces/ft[3]) is the minimum explosive concentration for wood dust." Thus, these MSDSs not only characterized dust-related hazards associated with the particleboard or fiberboard, but they also acknowledged hazards that could arise from combustible dusts generated during anticipated uses of these materials.  

Training 
Facility P offers numerous training courses to its employees, and site visitors learned about a subset of these courses. All operators and maintenance employees at Facility P reportedly receive some form of initial training before starting a new position. The nature and extent of this training depends on the specific job description and the employees' experience. Facility P uses a commercial software program to ensure that all employees are up-to-date on their initial and refresher training as required by multiple regulations. They also use pre-packaged videotaped training programs developed by an outside vendor to fulfill certain training requirements. One site visitor viewed one of these videos. The outside vendor also administers training courses for procedures on workers' compensation issues, exposures during manual material handling, slip/trip/fall hazards, and various other topics. Facility P does not offer training specific to combustible dust. 

Safety Programs
This section reviews the site visitors' observations of selected safety programs implemented at Facility P, with a focus on the extent to which combustible dust issues are factored into these programs: 
   #  "Hot work" permits. Facility P has a 10-page hot work program. The program defines hot work and the conditions that require permits. It also assigns responsibilities to supervisors, cutters and welders, and fire watchers. The program includes a sample permit and lists several precautions that should be considered before issuing permits and when conducting hot work. While the document appears to cover many elements of a typical hot work program, site visitors noted that the document focuses largely on hot work in areas with combustible gases or vapors and presents no information about performing hot work in dusty environments. Facility representatives should consider revising this program to acknowledge and control potential hazards associated with performing hot work near wood dust accumulations. 
   # Personal protective equipment and uniforms. Employees at the woodworking stations are required to wear safety glasses, ear plugs, and closed-toe shoes. However, clothing worn by these operators varied greatly: some individuals wore pants with long-sleeved shirts, while others wore shorts and sleeveless shirts. (Note: The site visit occurred during very warm weather, with outdoor temperatures over 90[°]F.) Operators are not required to wear flame-resistant clothing in any area of the facility.
      Some employees who engaged in spray painting activity donned particulate dust masks. Additional personal protective equipment is required for employees when performing certain tasks. For example, maintenance personnel who change out filter media in baghouses use air purifying respirators, and employees who use compressed air to blow dust accumulations down from overhead structures wear Tyvek suits, protective eyewear, and air purifying respirators. 
   # Other programs. Site visitors inquired about other safety programs that could potentially apply to areas containing wood dusts. Facility representatives shared a copy of the facility's written lockout/tagout program. The program addresses energy control procedures, lockout procedures and sequences, startup procedures, and training. This program does not specifically mention any dust-related hazards associated with lockout/tagout (e.g., ensuring that blowers are not functioning when employees are working inside dust collectors). Site visitors also inquired about written management of change procedures specific to wood dust, but none were available. While NFPA 664 does not require facilities to develop written management of change programs, it does call for implementation of management of change procedures (see Section 10.7 of NFPA 664).  
   
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 P's compliance with OSHA regulations or adherence to NFPA consensus standards. The main findings communicated to Facility P representatives are listed below, and additional findings are listed in Section 3 of this site visit report.  
   # NFPA 664 -- "Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities" -- outlines combustible dust hazard mitigation measures developed for many operations and equipment found at Facility P. Examples include wood hogs (Section 8.12 in NFPA 664), enclosureless dust collectors (Sections 8.2.2.5 and 8.2.2.6), bearings for scrap wood conveying systems (Section 8.2.3.1), and others listed below. The standard also calls for development of written programs (e.g., for housekeeping) and evaluations (e.g., hazard analyses, incident investigations) that can further help to reduce hazards related to combustible dust. Facility representatives were encouraged to review and implement applicable specifications in the NFPA standard. 
   # Many woodworking operations at Facility P are fully or partially enclosed stations, from which wood dusts are collected and conveyed directly to the dust collection system. These enclosures and the dust collection ducting helps reduce the release of fugitive wood dust that would have otherwise occurred; more widespread use of enclosed woodworking stations is expected to further reduce wood dust accumulations. Further use of interlocks (or administrative procedures where automated interlocks are not feasible) can help ensure that employees do not operate woodworking equipment while the dust control system is down. 
   # Facility P employees remove dust accumulations both during end-of-shift cleaning of individual woodworking stations and during less frequent "top-to-bottom" cleaning of entire production buildings. Employees use various techniques to remove accumulated dusts, including the use of compressed air at a pressure of 96 psi. While use of compressed air might have the immediate benefit of quickly removing settled dusts from workplaces and hard-to-reach areas, the practice also has negative consequences. Compressed air blowdowns move finer (and more explosive) dusts to other locations, such as atop elevated horizontal surfaces, above ceiling rafters, and even inside electrical control panels where the dust has reportedly affected the performance of electrical equipment. Furthermore, removal of these overhead dust accumulations is costly, due to the labor and resources involved. Replacing the use of compressed air for housekeeping with other methodologies (e.g., enclosing more equipment, vacuuming) can help avoid these and other outcomes. Another way to prevent dust lofting to upper elevations is to install overhead oscillating ceiling fans that provide a strong downward air flow. Development and implementation of a written housekeeping program consistent with specifications in Chapter 11 of NFPA 664 should provide the safest means for addressing wood dust accumulations and reducing the likelihood and severity of secondary dust explosions, should initiating events occur. Refer to Sections 3.2 and 3.3 of this report for further details on Facility P's housekeeping procedures.
   # Dust entry into electrical cabinets and boxes creates both operational and safety issues. These cabinets, which currently allow dust entry, should be upgraded to more effective dust-tight designs with either a NEMA rating or "Ingress Protection" rating that would prevent wood dust entry, especially during times when employees use compressed air to remove dust accumulations.
   # Dust control at Facility P is accomplished by collecting wood dusts from individual woodworking stations through a complex array of manifolded ductwork to dust collectors. Facility P's environmental permit requires ongoing inspection and maintenance of the dust collection system. Adherence to these requirements and those in Chapter 8.2 of NFPA 664 should help ensure that the dust collection system effectively removes combustible dusts from the individual woodworking operations.
   # The facility has implemented engineering controls to prevent or reduce the severity of combustible dust incidents associated with the dust control system. These controls include spark/ember detection and suppression systems at the inlets of two large dust collectors, explosion vent panels on the main facility dust collectors, and abort gates on the outlet side of selected dust collectors. Opportunities for minimizing hazards in the dust control system include: 1) developing a better understanding for operating and maintaining the spark/ember detection and suppression systems (see Section 3.4 for further details) and 2) installing explosion isolation systems in ductwork locations found to present the greatest risk for deflagrations propagating from dust collectors back through manifolded ductwork. Annex D of NFPA 664 and NFPA 69 provide additional information on the design of explosion isolation systems (e.g., diverter valves, back blast dampers). Without explosion isolation systems on the baghouse inlet lines, there is a potential for widespread dust explosion propagation back through the various manifolded ducting leading to the baghouses.
   # Operations in which wood dust clouds are expected to be routinely present should also be evaluated for hazard mitigation options. One example is the airborne wood dust clouds that reportedly occur during the manual loading of wood scrap material onto the belt conveyor that feeds the larger wood hog. These dust clouds occur in the presence of potential ignition sources (e.g., halogen lamps, two electrical panels). Facility representatives can minimize potential hazards from such operations by implementing various engineering controls (e.g., designing an enclosed loading system that does not generate the dust clouds, ensuring that electrical fixtures in this area are rated for Class II, Division 2 environments) and administrative controls (e.g., implementing operating procedures that limit loading quantities and therefore reduce dust cloud formation, requiring employees to wear flame-retardant clothing when performing this duty). In addition, consideration should be given to installing an explosion suppression system in the inlet hood for the wood hog.
   # The occurrence of puffing and burning ember emissions during operation of the boiler is a  concern that should be addressed through a) review of requirements for fuel feed control and startup in NFPA 85: Boiler and Combustion Systems Hazard Code, 2007 Edition.  The threat of deflagration propagation from the boiler to the saw dust silo can be mitigated by acquiring and installing a dust explosion isolation system in the pneumatic feed line carrying saw dust to the boiler.

Feedback to OSHA
At the end of the site visit, ERG asked representatives from Facility P 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 P representatives offered the following responses:
   # Some facility representatives voiced concern about OSHA specifying minimum educational and professional certification requirements for individuals who develop and implement combustible dust safety programs. One employee noted that numerous individuals at Facility P do not have college degrees but have many years of professional experience that likely qualifies them to help develop dust safety programs. The employee felt that minimum educational requirements could force the facility to hire external consultants to accomplish certain tasks that qualified facility personnel could handle on their own. The employee acknowledged, however, that some tasks (e.g., engineering design of dust control technologies) should be conducted by highly qualified individuals. 
   # Facility representatives voiced concern about the potential costs associated with complying with a new combustible dust standard. One employee, for instance, voiced concern about any future requirement that certain employees attend combustible dust training courses, due to the cost of these courses. Given resource constraints, the facility encouraged OSHA to allow facilities time to comply with any new combustible dust requirements, rather than requiring immediate compliance. 
   # Facility representatives encouraged OSHA to develop multiple compliance assistance products to help employers understand and comply with the combustible dust standard. For example, the facility recommend that OSHA consider publishing guidance documents on several topics: 
         o A compilation of explosibility data for dusts commonly encountered in industry. This compilation would present data as a function of dust particle size, which employers could then use to characterize hazard potential without unnecessarily investing resources in material testing. 
         o Guidance on housekeeping procedures, which would document existing requirements from other OSHA standards, considerations for identifying vacuum cleaners rated for different electrical classification areas, and other topics. 
         o Information on continuous air monitoring systems that facilities could use to determine if airborne dust concentrations reach potentially hazardous levels. 
   # Finding OSHA's PSM standard onerous to implement, some facility representatives encouraged OSHA to not model its combustible dust standard after the PSM standard. Facility representatives did not indicate the specific PSM requirements that they found burdensome. 
 
References

NFPA, 2007. NFPA 664: Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities. 2007 Edition. 

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

     Table 1. Testing Results for Samples Collected During the Site Visit
                                   Parameter
                                 Sample #2655
                                 Sample #2656
                                 Sample #2657
                                 Sample #2658
                                 Sample #2659
                                 Sample #2660
Description of material
                                   Wood dust
                                   Wood dust
                               "Filler" dust
                                   Wood dust
                                   Wood dust
                                "Dust Down"
Particle size data 
                                       
                                       
                                       
                                       
                                       
                                       
   % through 20 mesh
                                      98%
                                     100%
                                      84%
                                      32%
                                      40%
                                      63%
   % through 40 mesh
                                      96%
                                      98%
                                      78%
                                      21%
                                      69%
                                      23%
   % through 200 mesh
                                      85%
                                      29%
                                      64%
                                      6%
                                      23%
                                     0.2%
Moisture content
                                     6.0%
                                     6.6%
                                     5.4%
                                     6.0%
                                     5.2%
                                     41% 
Explosive material?
                                      Yes
                                      Yes
                                      No
                                      Yes
                                      Yes
                                      No
Kst (bar-meters/second)
                                     40.84
                                     17.85
                                      N/A
                                     4.57
                                     18.50
                                      N/A

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 moisture content reported for the "dust down" sample likely reflects water in the sample and hydrocarbon liquid with a low boiling point.    

            Figure 1. Photographs of Enclosed Woodworking Stations
                                       
                                       
Note: 	This photograph shows two enclosed (or partially enclosed) woodworking stations at Facility P. Dust-laden air generated in both stations is vented through flexible hosing connectors to the facility's dust control system, which helps reduce fugitive dust releases. Ductwork from multiple stations is manifolded into larger ducts at the dust collector inlets.

          Figure 2. Photograph of a Non-Enclosed Woodworking Station
                                       
                                       

Note: 	This photograph shows a machine used to bore holes in wood. The machine is not enclosed, and wood dusts are visible on the machine's horizontal surfaces and on the floor. The photograph was taken during operations, but before end-of-shift cleaning. Several inches of wood dust collected on the floor around the base of the machine. Operators cleaned the area using compressed air (96 psi), sweeps and scoops, and flexible hosing connected to the dust control system (i.e., vacuum). Sample #2656 was collected from atop an electrical panel located on the wall adjacent to this machine but not visible in the photograph. Refer to Section 4.1 and Table 1 for the sample results. 

      Figure 3. Photographs Showing Interior of Electrical Control Panels
                                       
                                       
                                       
                                       

Note: 	This photograph shows the interior of two electrical control panels where site visitors saw wood dust accumulations. In the top photograph, a layer of wood dust can be seen along the bundled wires at the bottom of the panel. In the bottom photograph, wood dust can be seen along the horizontal surface near the base of the panel.
            Figure 4. Photograph of Conveyor Feed to "Wood Hog"
                                       
                                       
                                       
 Note: 	The top photograph shows the belt conveyor that feeds to the larger wood hog. Employees poured totes and containers of wood scrap and wood dust (see smaller photograph for an example) directly onto the belt -- a procedure that led to dense clouds of wood dusts that gradually dissipated. Potential ignition sources were also identified in the area, including a ceiling-mounted halogen lamp, a wall-mounted electrical panel, and sparks from the wood hog itself. Sample #2659 was collected from atop the electrical panel located on the wall to the left of the belt conveyor. Refer to Section 4.1 and Table 1 for the sample results. 

   Figure 5. Photograph of Overhead Wood Scrap Conveyor, Bearing, and Magnet
                                       
                                       

Note: 	This photograph shows an overhead belt conveyor that carried wood scrap material from multiple process locations to the smaller wood hog. For purposes of orientation, the belt conveyor was located about 8 feet above the floor. The side of the belt loaded with wood scrap is behind the red-colored barrier and therefore not visible in the photograph. The magnet located above the belt was intended to remove tramp metal found in the wood scrap and had collected numerous paper clips, bolts, nails, and screws. Bearings for the belt conveyor (see left-hand side of the photograph for one example) showed signs of wood dust accumulations. 
                  Figure 6. Photograph of Wood Dust Baghouse
                                       
                                       

Note: 	This photograph shows Facility P's largest dust collector, in terms of area of filter media. Dusts from multiple woodworking stations in different departments are vented to this baghouse, which is equipped with roughly 450 bags that offer a combined total of approximately 7,000 square feet of filter area. The dust collector has multiple hazard control measures, including four explosion panels (two are visible in the photograph), an abort gate on the outlet ductwork (visible in the photograph), and a spark/ember detection and suppression system on the inlet ductwork (not visible in the photograph). The white structure beneath and adjacent to the dust collector is a chemical storage area. 

                Figure 7. Photograph of Multiple Dust Collectors
                                       
                                       
                                       

Note: 	This photograph shows an array of multiple cyclones and baghouses in series. This sequence of dust handling and collection steps occurred after material passed through wood hogs. Fine wood chips and dusts removed from the airstream are stored in two large silos (not visible in the photograph) before being fed to the wood-fired boiler (also not visible in the photograph). The dust collector has multiple hazard control measures, including explosion panels on the baghouses (but not on the cyclones), an abort gate at the outlet of one baghouse (visible in the photograph), and a spark/ember detection and suppression system with multiple detection zones on the inlet ductwork (not visible in the photograph). 
            Figure 8. Photograph of an Enclosureless Dust Collector
                                       
                                       

Note: 	This photograph shows the collection media for an enclosureless dust collector, located inside one of Facility P's production buildings. The enclosureless system had four bags for collecting dust. 

 
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.