Key Safety Issues for Combustible Dust Handling. By Molly R. Myers, P.E. Senior Safety and Risk Management Consultant

Transcription

1 Key Safety Issues for Combustible Dust Handling By Molly R. Myers, P.E. Senior Safety and Risk Management Consultant Summary For the past few years OSHA has been conducting focused inspections at facilities which generate or handle combustible dusts as part of a Combustible Dust National Emphasis Program (NEP). Some of these facilities were not even aware that they were handling combustible dusts and may not be familiar with the necessary safeguards to safely handle these materials. This paper will review the background for this NEP, some of the common findings, and some suggestions on how to safely deal with combustible dusts and minimize the likelihood of a citation should OSHA visit your facility. Background for OSHA Dust NEP In November 2006 the U.S. Chemical Safety and Hazard Investigation Board (CSB) issued an Investigation Report on combustible dusts i. The CSB identified 281 combustible dust incidents between 1980 and 2005 that killed 119 workers and injured 718, and extensively damaged industrial facilities. This report concluded that combustible dust explosions are a serious hazard in American industry and that existing efforts inadequately address this hazard. In response to this CSB report, OSHA issued a National Emphasis Program for Combustible Dusts in late However, after the catastrophic incident at the Imperial Sugar Refinery in Port Wentworth, Georgia, the directive was reissued in March 2008 ii. OSHA wanted to intensify its focus on the combustible dust hazards as a result of the Imperial Sugar explosion. This NEP applies to all facilities covered by OSHA which generate or handle combustible dusts. Basis for Citations One of the recommendations from the 2006 CSB combustible dust report was for OSHA to issue a standard designed to prevent combustible dust fires and explosions in general industry. OSHA has begun the process of drafting such a standard, but they still have a long way to go before it can be finalized. In the interim, OSHA has continued the practice of citing companies with combustible dust hazards for non-compliance with the General Duty Clause. iii A portion of this requirement is stated as follows: (a) Each employer

2 (1) shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees; Although OSHA doesn t have a standard for safely handling combustible dusts, the National Fire Protection Association (NFPA) does have several thorough standards available for various types of combustible dust facilities. OSHA s combustible dust NEP specifically references several of these NFPA standards as possible citations. Some of the main NFPA standards which are applicable include the following: NFPA 484 Standard for Combustible Metals iv which covers all metals and alloys in a form that is capable of combustion or explosion. NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities v which covers facilities that process wood or manufacture wood products, using wood or other cellulosic fiber as a substitute for or an additive to wood fiber, and that process wood, creating wood chips, particles, or dust. NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids vi which covers combustible dust handling which is not specifically covered by the other two standards. This paper will take a look at several common types of citations which have been issued by OSHA against the General Duty Clause for combustible dust violations. For each of these areas, the basis for the citations will be identified along with key steps to take to ensure compliance with the applicable NFPA standard. Dust Collector Location One of the two most frequently cited problems is related to the location of dust collectors. Ideally these should be located outdoors, although many are located indoors. This is an easy citation for OSHA since a cursory field tour will identify which dust collectors are located indoors. Here are some example citations for reference. OSHA citation to Toll Compaction Group, LLC on 1/25/2010 stated, dust collection systems located inside the production area were not designed to prevent or minimize damage that would occur in the event of a dust explosion The penalty for this citation was $1,500. OSHA citation to Fred Knapp Engraving Company, Inc. on 1/4/2011 stated, The Torit dust collector was inside the building and did not have explosion protection systems The penalty for this citation was $3,430.

3 NFPA 654 does provide some conditions under which dust collectors can be safely located indoors. According to NFPA 654, the requirement to locate air-material separators (i.e. dust collectors) outside does not apply in the following situations: (1) Air-material separators that are protected in accordance with [oxidant concentration reduction, deflagration pressure containment, deflagration suppression system, dilution with a noncombustible dust, or deflagration venting through a listed dust retention and flame-arresting device]. (2) Air-material separators that meet all of the following criteria: (a) They are equipped with deflagration vents that are vented through ducts to the outside (b) The reduced venting efficiency due to the duct has been taken into account (c) The ducts are designed to withstand the effects of the deflagration. (3) Air-material separators that have a volume of less than 8 ft 3 (0.2 m 3 ). [NFPA 654 Section ] There are also other NFPA documents which have additional restrictions on the locations for dust collectors, which have all been referenced in OSHA citations. One 11/13/2009 OSHA issued the following citation ( ) to Probuild, East LLC, a) enclosureless dust collector was located within 20' of an area routinely occupied by employees. b) enclosureless dust collector was located within 20' of an area routinely occupied by employees The penalty for this citation was $2,000. NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, has several requirements which must all be met in order to locate an enclosureless dust collector indoors. One of those requirements is the following: The collector is located at least 6.1 m (25 ft) from any means of egress or area routinely occupied by personnel [NFPA 664 Section ] The most obvious solution to the location of a dust collector is to move it outdoors. However, the cost for that change can be prohibitively expensive for many facilities. Therefore, it is important to review the NFPA standard that applies to your facility and investigate whether there are any explicit conditions which if met the dust collector can remain indoors. It may be easier to make modifications to adhere to these conditions than to relocate the dust collector outdoors. Additionally, NFPA 654 and NFPA 664 allow provisions for a performance based option under which a risk analysis can be done to determine the appropriate safeguards required for your particular installation. This option may be utilized to support the decision to leave the dust collectors indoors if there are sufficient other safeguards to bring the risk down to an acceptable level.

4 Explosion Protection NFPA 654 requires that the design of explosion protection for equipment incorporate one or more of the following options: (1) Oxidant concentration reduction in accordance with NFPA 69 (2) Deflagration venting (3) Deflagration pressure containment in accordance with NFPA 69 (4) Deflagration suppression systems in accordance with NFPA 69 (5) Dilution with a noncombustible dust to render the mixture noncombustible (6) Deflagration venting through a listed dust retention and flame-arresting device [NFPA 654 Section ] Once again, this is a relatively easy thing for OSHA to check for all equipment handling combustible dusts. The simplicity of verification probably explains why this is one of the most cited problems for combustible dust facilities. Here are a few example citations related to a lack of explosion protection. OSHA citation to Kard Welding, Inc. on 9/2/2009 stated, On or about June 17, 2009 the employer did not ensure that the Wheelabrator (Machine No. 6, Model 112-AC; Serial A ) shot-blast unit was equipped with explosion prevention systems to prevent the deflagration of combustible dust generated by the shot-blast process The penalty for this citation was $2,500. OSHA citation to Cooper Tire and Rubber Company on 6/3/2011 stated, (a)the pneumatic/vacuum duct system used to transfer carbon black from the tank railcars and tank trailers was not provided with deflagration and explosion protection. (b)the eight (8) main storage silos located outside and away from the building were not provided with deflagration and explosion protection. (c)the eight (8) inch diameter pneumatic/vacuum conveying duct that transfers carbon black from the silos to the day bins on the roof of the building above the banbury mixers was not provided with deflagration and explosion protection. (d)the two day bins, "E" Day Bin for banbury mixer #4 and "D" Day Bin for banbury mixer 3 were four (4) compartment silos located on top of the roof above the master batch mixers. They were not provided with deflagration and explosion protection The penalty for this citation was $7,000. Although deflagration venting (relief panels) is a very common method for explosion protection, as noted above that is only one of six acceptable methods. For each piece of equipment which handles a combustible dust, the selected option for explosion protection should be clearly

5 documented. If this information for the entire facility can by summarized in a single document, then this will simplify the process of providing this information in the event of an audit or OSHA site visit. No matter which option is selected, the instruments and equipment necessary to implement the option must be properly designed, documented and maintained. Bonding and Grounding Although not all combustible dusts are sensitive enough to be ignited by static discharge, the practice of providing bonding and grounding for all equipment and transfer pipe/duct which handle combustible dusts is considered a common best practice or RAGAGEP (Recognized and Generally Accepted Good Engineering Practice). This is also relatively easy to verify visually during a field tour of a facility, which is probably why it appears so frequently in OSHA General Duty Clause citations. Here are a few citations for reference: OSHA citation to Forbo Siegling, LLC on 1/15/2010 stated, production area, hopper was not interconnected and grounded to the metal drum used to collect the dust The penalty for this citation was $5,600. OSHA citation to Specialty Metal Processing, Inc. on 3/5/2010 stated, All components of the dust collection system were not bonded and grounded The penalty for this citation was $1,300. OSHA citation to H & H Woodworking, Inc. on 4/15/2010 stated, The segments of duct work for the dust collection system were neither grounded, nor bonded to each other The penalty for this citation was $1,500. In addition to being a RAGAGEP, there are several references to the requirement for bonding and grounding within the NFPA standards. In NFPA 654 there are specific requirements for bonding and grounding of access doors in general and on air-material separators specifically. NFPA 654 also requires bonding and grounding for all conductive components with a resistance of less than 1.0 x 10 6 ohms to ground. NFPA 664 requires that equipment which could be subjected to the accumulation of static charge have the static electric charge controlled by some form of bonding and grounding. NFPA 484 is the most specific of all in terms of requirements for bonding and grounding. It states that, All process equipment and all building steel shall be bonded and grounded in accordance with NFPA 70 [NFPA 484 Section ] It further requires that a continuity check of the bonding and grounding system be conducted as part of the routine system maintenance program. To meet these requirements, all process equipment which handles combustible dust should have a permanent grounding wire attached between the equipment and an earth ground or piece of grounded building steel. All interconnecting piping, drums, and other accessories should be bonded to these pieces of equipment with wires making electrical contact from metal to metal along the length of the pipe or duct. If there are any non-conductive components in the system,

6 there should be a metal bonding wire connected across this between the two closest conductive components. All of this bonding and grounding system should be periodically tested for the resistance to ground to ensure that all connections are still in place and making electrical contact. Typical test frequencies are annual, but may need to be adjusted depending on local conditions. Fugitive Dust Fugitive dust can lead to very dangerous situations. Fugitive dust is any dust which has escaped the containment of the equipment or conveying system and has settled on some surface within the facility. Accumulations of fugitive dust can change a small fire or limited overpressure event into a catastrophe. In these situations the initial event acts to dislodge the fugitive dust from surfaces, creating dust clouds which can be ignited by the primary event or another ignition source. It doesn t take a lot of fugitive dust to provide enough fuel in the form of a dust cloud to destroy entire buildings. This type of event is frequently referred to as a secondary dust explosion and it is what makes the news. Examples of these secondary dust explosions are the incidents at Imperial Sugar Refinery in Port Wentworth, GA in 2008 and the West Pharmaceutical Services in Kingston, NC in The 2006 edition of NFPA 654 included some guidance on the amount of fugitive dust accumulations which would require the use of a separation between hazardous areas. This has been widely used as a general rule of thumb in determining when there is enough dust in the area to be a hazard. NFPA clarified the use of this fugitive dust determination in the Tentative Interim Amendment (TIA) issued in 2011 vii. In this TIA the use of the fugitive dust determination was broadened to be used to determine which, if any, parts of the facility may be subject to a dust explosion hazard and therefore subject to all of the general provisions of the standard. In general there may be a dust explosion hazard if the dust accumulations exceed 1/32 over more than 5% of the floor area. There are many adjustments and considerations to be made for these determinations, which are clearly spelled out in the TIA for NFPA 654. However, if there is enough dust present on surfaces to obscure the paint colors or you can write your name in it, then the facility should be carefully examined for possible fugitive dust problems. Here are a few example OSHA citations related to fugitive dust. OSHA citation to Flex Pack on 10/26/2009 stated, The horizontal and vertical surfaces around the silos had a buildup of more than 1/4-inch to 3/4-inches of a Class 2 combustible sugar dust, as observed on or about 07/09/2009. The surfaces included the beams, joists, equipment, west wall, and slightly on the floor. No explosion relief panels were distributed along the exterior walls and roof of the area The penalty for this citation was $750. OSHA citation to Noranda Aluminum, Inc. on 8/24/2010 stated, employees were exposed to dust explosion, deflagration, or other fire hazards because bucket elevators were not

7 dust tight. At the time of the inspection, explosive dust clouds were generated in the Green Mill around leaking boot sections of bucket elevators The penalty for this citation was $1,875. OSHA citation to Valley Proteins, Inc. on 5/2/2011 stated, no methods were used to control the escape of fugitive combustible dust during the loading of trucks The penalty for this citation was $6,300. OSHA citation to Stratton Equity Cooperative Co. on 5/24/2011 stated, Stratton Equity Cooperative Company did not ensure employees were protected from fire/explosion hazards by sufficiently removing fugitive grain dust that accumulated beyond 1/8th inch (.32 cm) inside the rail car loading scale The penalty for this citation was $2,103. The best way to control fugitive dust at the facility is to ensure that the dust is properly contained within the equipment or conveying system through good design and maintenance programs. If the dust is allowed to escape, then a good housekeeping plan is the primary means to prevent these accumulations from becoming dangerous. Deflagration Isolation Deflagration isolation is an important safeguard to limit the extent of damage in the event a fire or explosion happens inside a piece of process equipment. In particular, dust collectors are notorious for fires and explosions and it would be quite unfortunate to have such a fire propagate through the connecting duct work to injure someone or damage equipment upstream. Many of the key NFPA documents have several specific requirements for isolation devices. NFPA 654 requires the following for equipment, Where an explosion hazard exists, isolation devices shall be provided to prevent deflagration propagation between pieces or equipment connected by ductwork. [NFPA 654 Section ] NFPA 664 includes the following requirement for conveying systems, Conveying systems with fire and deflagration hazards shall be isolated to prevent propagation of fire and deflagration both upstream and downstream into occupied areas or other critical process equipment. [NFPA 664 Section ] There are a variety of options for providing this isolation. NFPA 654 lists a few common types including chokes, rotary valves, automatic fast-acting valve systems, and chemical isolation systems. NFPA 664 includes a table in the reference section which breaks the choices into two groups, diversion devices and blocking devices. For each of these options, you must carefully review all of the specific requirements and limitations in order to properly protect your system. Here are some examples of OSHA citations in this category: OSHA citation to Dye-Chem International, Inc. on 3/31/2010 stated, piping and ductwork that was connected to the Sly dust collector that was not protected by deflagration isolation systems The penalty for this citation was $1,000.

8 OSHA citation to Walk-On Products, Inc. on 6/10/2010 stated, enclosed screw conveyors used to transport shredded/ground polyurethane to material storage hoppers did not have equipment to vent and isolate a dust deflagration The penalty for this citation was $2,100. Duct Construction Duct construction is another commonly cited problem with combustible dust handling facilities. Most of the standards require ductwork to be constructed of non-combustible materials. There are also requirements for balancing, minimum flow velocities, orientation of seams and reducers, and dead legs. Here are some examples of problems that OSHA has found with duct construction: OSHA citation to Broward Casting Foundry on 10/16/2009 stated, the aluminum dust collection system for the Wheelabrator polishing machine used an exhaust duct constructed of PVC, thereby exposing the employees to a fire/explosion hazard The penalty for this citation was $1,000. OSHA citation to Metal Improvement Company, Inc. on 12/9/2009 stated, production area - DC8, ductwork design was changed by placing two cardboard squares to close branches where the duct was removed production area DC1, DC4, DC5, DC8, and DC10, ductwork design was changed; fire and explosion hazards existed due to the ductwork being open at the end and some areas downstream when ductwork was removed. Branches were left open, in order to allow for make-up air to keep combustible dust from settling in the ductwork The penalty for this citation was $2,000. OSHA citation to Aleris Rolled Products on 6/11/2010 stated, The dust collector ductwork had irregularities related to flexible ductwork use and the multiple "bends and turns" orientation of the ductwork pipe. Additionally a section of the ductwork pipe is unused and capped to create a "dead-end" section. These conditions can interrupt free airflow and allow for the build-up of material in these sections of the collection system ductwork The penalty for this citation was $3,000. It is important to review all of the ductwork in your facility and ensure that it is properly designed and installed. The first step is to ensure that all of it is constructed with noncombustible materials. If flex joints are required, try to utilize steel braided, or other conductive hoses. If there is any history of solids plugging the ductwork, then the system design should be reviewed to ensure there is adequate air flow throughout the system to minimize the potential for dust settling out. Changes to the ductwork should be carefully reviewed to ensure that they do not introduce any problems into the system.

9 Other Potential Concerns Although not as common, there are a few other citation topics which are worth mentioning. The first of these is the use of compressed air for cleaning combustible dust deposits. This is a very dangerous practice which can easily generate significant dust clouds, which are just waiting for an ignition source in order to become a disaster. NFPA 654 and NFPA 664 only allow the use of compressed air for cleaning if several precautionary conditions are met. NFPA 484 is a little more explicit in their warnings, Compressed air blowdown shall not be permitted, except in certain areas that are otherwise impossible to clean and, where permitted, shall be performed under carefully controlled conditions with all potential ignition sources prohibited in or near the area and with all equipment shut down. [NFPA 484 Section 6.4.4] Here is an example of an OSHA citation regarding the use of compressed air. OSHA citation to Taylor Lumber, Inc. on 6/14/2010 stated, (a) In the Little Saw Mill Building, compressed air was used to blow combustible wood dust off of the End Trimmer Saw, and the floor surrounding it, roughly hourly, while potential ignition sources such as the nearby standard motor and wall fan, lighting, equipment, etc. were not eliminated; (b) In the Big Saw Mill Building, compressed air was used roughly every other day to blow off saws, equipment and floors without eliminating all potential ignition sources, such as standard lighting, wiring, outlets, motors, saws and fork lift trucks throughout the Big Saw Mill Building The penalty for this citation was $700. Another issue that has come up a few times in recent citations is the need for a Process Hazard Analysis (PHA). NFPA 654 and NFPA 664 require a hazard analysis as the basis for the applicability of the prescriptive design criteria itemized in the standard. NFPA 484 also requires a hazard analysis for avoiding certain requirements within the standard. Here is an example of a citation related to not having a PHA. OSHA citation to Industrial Container Services Nc, LLC on 6/16/2011 stated, combustible dust collection systems, a documented Risk Evaluation was not conducted to determine the level of explosion protection to be provided for a dust collection system. (Reference NFPA 484, ); a process hazard analysis for the design of the fire and explosion safety provisions was not based on a process hazard analysis of the facility, the process, and the associated fire or explosion hazards. (Reference NFPA 654, 4.2.1) The penalty for this citation was $5,600. One last item to highlight relates specifically to combustible metals and wood processing and woodworking facilities. Due to the unique hazards, NFPA 484 and NFPA 664 have specific requirements to empty the collection bins from dust collectors and other waste bins on a daily

10 basis, at a minimum. Once again, this is a relatively easy thing for an inspector to verify, so it lends itself to inclusion as a citation. Here are a couple of examples of such citations: OSHA citation to Woodmill Products, Inc. on 10/8/2009 stated, The enclosureless dust collectors in the production department were located inside the building, were used for dust collection with sanders and planers that had mechanical material feeds, and collected dust was not removed daily or more frequently if necessary The penalty for this citation was $1,250. OSHA citation to Specialty Metal Processing Inc. on 3/5/2010 stated, Aluminum dust was not removed from the dust collector daily The penalty for this citation was $1,300. Conclusion Although OSHA doesn t currently have its own standard for combustible dust handling, that isn t slowing them down in their effort to enforce safe handling of combustible dusts. OSHA is conducting numerous inspections under their Combustible Dust NEP and issuing citations against the General Duty Clause. If you handle dust or particulates, you should first determine if the material is a combustible dust. If it is, then use this listing of frequent OSHA citations as a starting point for compliance, but don t limit your efforts to these issues. Instead, familiarize yourself with the applicable NFPA standards and ensure that you comply with all of the requirements which are applicable to your facility. i U.S. Chemical Safety and Hazard Investigation Board, Investigation Report, Combustible Dust Hazard Study, Report No H-1, November 2006 ii OSHA Directive CPL , Combustible Dust National Emphasis Program (Reissued), 3/11/2008.

11 iii OSH Act of 1970, Section 5, Duties iv NFPA 484 Standard for Combustible Metals, National Fire Protection Association, 2009 Edition v NFPA 664 Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, National Fire Protection Association, 2007 Edition vi NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of combustible Particulate Solids, National Fire Protection Association, 2006 Edition vii TIA 06-1, Tentative Interim Amendment to NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of combustible Particulate Solids 2006 Edition, National Fire Protection Association, Issue Date: March 1, 2011