Combustible Dust Hazards


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Dated 2/2/2009 - Overview for the kinds of industries where Combustible Dust Hazards are an issue. Also, recommendations for prevention and mitigation along with how to test to see if a specific manufacturing facility has a problem with either their raw ingredients, byproducts/scrap, and/or finished goods.

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Albert V. Condello III
Univ of Houston Downtown

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  • At least 281 combustible dust fires and explosions occurred in general industry between 1980 and 2005, which caused at least 119 fatalities and 718 injuries in the United States; included seven catastrophic dust explosions in the past decade, involving multiple fatalities and significant community economic impact; and occurred in a wide range of industries and involved many types of combustible dusts.
  • On January 29, 2003, a massive dust explosion at the West Pharmaceutical Services facility in Kinston, North Carolina, killed six workers and destroyed the facility (Figure 4). The explosion involved a part of the building used to compound rubber. West produced rubber syringe plungers and other pharmaceutical devices at the facility. In the rubber compounding process, freshly milled rubber strips were dipped into a slurry of polyethylene, water, and surfactant to cool the rubber and provide an anti-tack coating. As the rubber dried, fine polyethylene powder drifted on air currents to the space above a suspended ceiling. Polyethylene powder accumulated on surfaces above the suspended ceiling, providing fuel for a devastating secondary explosion. While the visible production areas were kept extremely clean, few employees were aware of the dust accumulation hidden above the suspended ceiling, and the MSDS for the polyethylene slurry included no dust explosion warning. Even those employees who were aware of the dust accumulation had not been trained about the hazards of combustible dust. West did use a safety review process when the compounding system was designed and modified, but the dust explosion hazard was not addressed during the reviews. OSHA, the local fire department, an insurance underwriter, and an industrial hygienist had inspected the facility, but none had identified the potential for a dust explosion. In addition, the electrical equipment above the suspended ceiling in the rubber compounding section was not rated for use around combustible dust, as the National Electric Code (NEC) requires (for areas where combustible dust can accumulate). The CSB determined that if West had adhered to NFPA standards for combustible dust,14 the explosion could have been prevented or minimized.
  • The CSB identified an average of 10 dust explosion incidents per year from 1980 to 2005. Although incidents increased in later years, this may be due to limitations in the data, including the possibility that earlier incidents were under-reported. The CSB identified 119 fatalities in 78 of the 281 incidents. Injuries totaled 718, and the data show an average of nearly five fatalities and 29 injuries per year. Injuries or fatalities occurred in 71 percent of the incidents..
  • Dust deflagration, other fire, and explosion hazards in the industries noted in Section I, Purpose, are covered by several OSHA standards and the general duty clause. A chemical dust deflagration occurs when the right concentration of finely divided chemical dust suspended in air is exposed to a sufficient source of ignition to cause ignition (combustion) of the dust. If the deflagration is in a confined area, an explosion potential exists. These materials can also cause other fires. Combustible dust is often either organic or metal dust that is finely ground into very small particles. The actual quantity of dust that may accumulate in an affected area may vary, depending upon air movement, particle size, or any number of other factors.
  • On February 20, 2003, a series of dust explosions at the CTA Acoustics (CTA) facility in Corbin, Kentucky, claimed the lives of seven workers, injured 37, and destroyed the manufacturing facility(Figure 5). This facility primarily made acoustic insulation for automobiles. The manufacturing process began by impregnating a fiberglass mat with phenolic resin, and then used air to draw the resin into the fiberglass webs. On the day of the explosion, a curing oven that had been left open because of a temperature control problem likely ignited the combustible resin dust stirred up by workers cleaning the area near the oven. The CSB also found that plant design, work practices, and housekeeping problems contributed to causing the explosions. The CTA building was not designed to prevent or minimize secondary dust explosions (minimizing flat surfaces where dust can accumulate and using fire walls to separate production lines). Although management was aware of dust explosion hazards associated with the materials being used, dust had accumulated in dangerous amounts throughout the production areas, in vent ducting, and in dust collector housings, due to inadequate housekeeping and maintenance. In addition, employees routinely used compressed air and brooms to clean production lines, creating clouds of resin dust. The MSDS for the resin used at CTA did not adequately communicate that the material posed a dust explosion hazard. In addition, the resin supplier, Borden Chemical (Borden), had not communicated to CTA the safety lessons from the 1999 Jahn Foundry resin dust explosion, even though documents obtained by the CSB indicated that Borden was aware of the explosion, which involved a resin similar to the one used at CTA. The Kentucky Office of Occupational Safety and Health (KYOSHA) had inspected the facility, but had not issued citations regarding combustible dust hazards. In addition, the CTA facility had never been inspected by the Kentucky State Fire Marshal’s Office, and frequent inspections by CTA’s insurer had failed to identify phenolic resin as an explosion hazard. The CSB determined that if CTA had adhered to NFPA16 standards for housekeeping and fire/explosion barriers, the explosions could have been prevented or minimized.
  • OSHA is initiating this National Emphasis Program (NEP) to address the deflagration, other fire, and explosion hazards that may exist at facilities handling combustible dust. A combustible dust hazard study conducted by the U.S. Chemical Safety and Hazard Investigation Board (CSB) found that nearly 280 dust fires and explosions have occurred in U.S. industrial facilities over the past 25 years, resulting in 119 fatalities and over 700 injuries. The purpose of this NEP is to inspect facilities that generate or handle combustible dusts which pose a deflagration or other fire hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape; deflagrations can lead to explosions. Combustible dusts are often either organic or metal dusts that are finely ground into very small particles, fibers, fines, chips, chunks, flakes, or a small mixture of these. Types of dusts include, but are not limited to: metal dust, such as aluminum and magnesium; wood dust; plastic dust; biosolids; organic dust, such as sugar, paper, soap, and dried blood; and dusts from certain textiles. Some industries that handle combustible dusts include: agriculture, chemicals, textiles, forest and furniture products, wastewater treatment, metal processing, paper products, pharmaceuticals, and recycling operations (metal, paper, and plastic). In situations where the facility being inspected is not a grain handling facility, the lab results indicate that the dust is combustible, and the combustible dust accumulations not contained within dust control systems or other containers, such as storage bins, are extensive enough to pose a deflagration, explosion, or other fire hazard, then citations under 29 CFR 1910.22 (housekeeping) or, where appropriate, 29 CFR 1910.176(c) (housekeeping in storage areas) may generally be issued. Combustible dusts found in grain handling facilities are covered by 29 CFR 1910.272.
  • Most solid organic materials, as well as many metals and some nonmetallic inorganic materials, will burn or explode if finely divided and dispersed in sufficient concentrations.1 Combustible dusts can be intentionally manufactured powders, such as corn starch or aluminum powder coatings, or may be generated by handling and processing solid combustible materials such as wood and plastic pellets. For example, polishing, grinding, transporting, and shaping many of these materials can produce very small particles, which can easily become airborne and settle on surfaces, crevices, dust collectors, and other equipment. When disturbed, they can generate potentially explosive dust clouds. Like all fires, a dust fire occurs when fuel (the combustible dust) is exposed to heat (an ignition source) in the presence of oxygen (air). Removing any one of these elements of the classic fire triangle (Figure 1) eliminates the possibility of a fire.
  • Further, the concentration of suspended dust must be within an explosible range3 for an explosion to occur. This is analogous to the flammability range commonly used for vapors (such as natural gas and propane). Dust explosions can be very energetic, creating powerful waves of pressure that can destroy buildings and hurl people across a room.4 People caught in dust explosions are often either burned by the intense heat within the burning dust cloud or injured by flying objects or falling structures.
  • Annex D is an idealized approach based on certain assumptions, including uniformity of the dust layer covering the surfaces, a bulk density of 75 lb/ ft3, a dust concentration of 0.35 oz/ ft 3, and a dust cloud height of 10 ft. Additionally, FM Data Sheet 7-76 contains a formula to determine the dust thickness that may create an explosion hazard in a room, when some of these variables differ.
  • Combustible Dust Hazards

    1. 1. Explosions ENGR 4355 – Industrial Safety Course 21994 (Spring, 2009) Albert V. Condello, III Professor, Safety Mgmt & Fire Protection Engineering Department of Engineering Technology
    2. 2. Source <ul><li>Chapter 11 </li></ul><ul><li>Safety Engineering , 3 rd Edition (ASSE)Gilbert Marshall, 2000 </li></ul><ul><li>pp. 233-243 </li></ul>
    3. 3. Aftermath – Effect of Explosions
    4. 4. Average 10 Explosions Per Year from 1980 to 2005
    5. 5. Learning Objectives <ul><li>Know the underline conditions require to have an explosion. </li></ul><ul><li>Comprehend that Combustible Dust Explosions do exist and are a challenge for many industries </li></ul><ul><li>Apply the recommendations to design performance-based fire protection systems. </li></ul><ul><li>Analyze the 5 necessary components for Dust Explosions & recognize ways to mitigate. </li></ul><ul><li>Synthesize recommendations for innovative approach. </li></ul><ul><li>Evaluate whether or not a particular industrial situation has this as a hazard. </li></ul><ul><li>Interpret consensus standards from NFPA and others for recommendations </li></ul><ul><li>Extrapolate the amount of effort necessary to protect lives and ensure the health of the workers. </li></ul>
    6. 6. Definitions <ul><li>Deflagration – a flame spread rate of less than the speed of sound.(subsonic) </li></ul><ul><li>Explosion – a rapid release of high pressure gas into the environment. </li></ul><ul><li>Detonation – a flame spread rate that is above the speed of sound.(supersonic) </li></ul><ul><li>Combustible Dust - A combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape. </li></ul><ul><li>Explosive material/substance – those capable of causing an explosion influenced by confinement. </li></ul><ul><li>Hybrid Mixture - A mixture of a flammable gas with either a combustible dust or a combustible mist. </li></ul><ul><li>Minimum Explosive Concentration (MEC) - The minimum concentration of combustible dust suspended in air, measured in mass per unit volume that will support a deflagration. </li></ul>
    7. 7. Definitions – Con’t. <ul><li>Minimum Ignition Energy (MIE) - The minimum ignition energy (MIE) of the sample is determined by suspending the sample in a Hartmann Lucite explosion chamber. To determine the MIE, the energy of the electrical spark used to ignite the dust is varied until the MIE is determined. </li></ul><ul><li>Minimum Ignition Temperature (MIT) - Minimum ignition temperature (MIT) is determined by using the Godbert-Greenwald furnace. Dust is discharged through this furnace at various temperatures. The lowest temperature that ignites the dust is considered to be the MIT. </li></ul><ul><li>Minimum Explosible Concentration - Minimum explosible concentration (MEC) of the sample is determined by suspending the sample in a 20-liter explosibility testing chamber and ignited with a 2500-joule chemical igniter. MEC is the lower concentration limit of explosibility for the dust. This limit is determined using test material that has been sieved through a 40-mesh sieve (425 μm particle size), dried, suspended in a 20-liter explosibility testing chamber. Approximately 200 grams of material with a particle size of 425 μm or less are needed for the MEC tests. </li></ul><ul><li>Dust Deflagration Index (K st ) - test results provide an indication of the severity of a dust explosion. </li></ul>
    8. 8. Characteristics of an Explosion <ul><li>Commonly begins with the ignition of a fuel that burns very rapidly. </li></ul><ul><li>Produces a large and sudden release of gas </li></ul><ul><li>An explosion need not involve a fire. </li></ul><ul><li>When a container bursts from increased internal pressure, sudden release also called an explosion. </li></ul>
    9. 9. NFPA 69 – Standard on Explosion Prevention Systems <ul><li>Defines an explosion as: </li></ul><ul><li>“ the bursting or rupture of an enclosure or container due to the development of internal pressure from a deflagration.” </li></ul>
    10. 10. NFPA Fire Protection Handbook <ul><li>Defines an Explosion as: </li></ul><ul><li>“ a rapid release of high pressure gas into the environment.” </li></ul>
    11. 11. Commonality between definitions <ul><li>In either definition, </li></ul><ul><li>The key word, “pressure” </li></ul><ul><li>And its effects on the surrounding environment. </li></ul>
    12. 12. Other Situations - Explosion <ul><li>Explosions might result from a chemical reaction (combustion of a flammable gas mixture) </li></ul><ul><li>From over-pressurization of an structure or enclosed container/vessel </li></ul><ul><li>By physical means (bursting of a tank) </li></ul><ul><li>By physical/chemical means (boiler explosion) </li></ul>
    13. 13. Reactive Hazard Definitions
    14. 14. Designing Facilities for Use of Explosive Materials <ul><li>Pressure rate-of-rise detectors can activate a device or system to extinguish a potential explosion before it reaches an explosive stage. </li></ul><ul><li>Controlling ventilation & humidity level above 25% </li></ul><ul><li>Fixed monitoring for mass and size fraction using light-scattering laser photometers providing real-time aerosol mass readings. </li></ul><ul><li>Inerting – purging supply of oxygen when flammable atmospheres are detected with care being taken for those workers in the area – (BA available for Emergency Donning) </li></ul>
    15. 15. Design of Buildings <ul><li>Relief of overpressure – break away & blow out walls and window openings to minimize destructiveness (explosion release panel) </li></ul><ul><li>Shielding personnel and equipment – deflection of shock wave so as not to pass unobstructived into another work area. </li></ul><ul><li>Explosive proof wall or barrier </li></ul><ul><li>Burst vessel/container disk – venting away to transmit pressure wave harmlessly to outside atmosphere </li></ul>
    16. 16. Explosives <ul><li>Ammonium nitrate </li></ul><ul><li>Aluminum and other metal powders </li></ul><ul><li>Tovex, water gels instead of Dynamite – used for quarry operations </li></ul><ul><li>Magazines – special buildings to storage lockers (OSHA 1910.109) </li></ul><ul><ul><ul><li>Class I – not to exceed 50 pounds </li></ul></ul></ul><ul><ul><ul><li>Class II – 23 kilograms or greater </li></ul></ul></ul>
    17. 17. Dust Explosions <ul><li>Smaller the particles, the greater the potential for an explosion to occur. </li></ul><ul><li>Primary areas in process industries inside process equipment such as conveyors, dryers, mills, mixers, and storage silos. </li></ul><ul><li>Many materials can explode it they come in contact with an ignition source, when air dispersed in the right concentration. </li></ul><ul><li>Combustible powders (metals) difficult to avoid danger of dust explosions in processes where being handled. </li></ul>
    18. 18. CTA Acoustics – Corbin, KY
    19. 19. Comparison of Foodstuff Silo Storage <ul><li>OSHA’s Grain Facilities Standard has successfully reduced the risk of dust explosions in the grain industry </li></ul>
    20. 20. OSHA Directive – Combustible Dust National Emphasis Program <ul><li>CPL-03-000-006 (Effective Oct. 2007) </li></ul><ul><li>Contains policies and procedures for inspecting workplaces that create or handle combustible dusts. </li></ul><ul><li>In some circumstances these dusts may cause a deflagration, other fires, or an explosion. These dusts include, but are not limited to: </li></ul><ul><ul><ul><li>• Metal dust such as aluminum and magnesium. </li></ul></ul></ul><ul><ul><ul><li>• Wood dust </li></ul></ul></ul><ul><ul><ul><li>• Coal and other carbon dusts. </li></ul></ul></ul><ul><ul><ul><li>• Plastic dust and additives </li></ul></ul></ul><ul><ul><ul><li>• Biosolids </li></ul></ul></ul><ul><ul><ul><li>• Other organic dust such as sugar, paper, soap, and dried blood. </li></ul></ul></ul><ul><ul><ul><li>• Certain textile materials </li></ul></ul></ul>
    21. 21. Excludes for OSHA Directive <ul><li>This directive does not replace the grain handling facility directive, OSHA Instruction CPL 02-01-004, Inspection of Grain Handling Facilities, 29 CFR 1910.272. </li></ul><ul><li>In addition, this directive is not intended for inspections of explosives and pyrotechnics manufacturing facilities covered by the Process Safety Management (PSM) standard (1910.119). </li></ul><ul><li>However, it does not exclude facilities that manufacture or handle other types of combustible dusts (such as ammonium perchlorate) covered under the PSM standard. </li></ul>
    22. 22. Criteria that must be met before a Dust Deflagration can occur <ul><li>The dust has to be combustible. </li></ul><ul><li>The dust has to be dispersed in air or another oxidant, and the concentration of this dispersed dust is at or above the minimum explosible concentration (MEC). </li></ul><ul><li>There is an ignition source, such as an electrostatic discharge, spark, glowing ember, hot surface, friction heat, or a flame that can ignite the dispersed combustible mixture that is at or above the MEC. </li></ul>
    23. 23. Dust Explosion Pentagon
    24. 24. What is required <ul><li>A dust explosion requires the simultaneous presence of two additional elements—dust suspension and confinement (Figure 2). </li></ul><ul><li>Suspended dust burns more rapidly, and confinement allows for pressure buildup. </li></ul><ul><li>Removal of either the suspension or the confinement elements prevents an explosion, although a fire may still occur. </li></ul>
    25. 25. Train Effect – Subsequent Explosions as Dust Disturbed <ul><li>Secondary dust explosions, due to inadequate housekeeping and excessive dust accumulations, caused much of the damage and casualties in recent catastrophic incidents. </li></ul>
    26. 26. Criteria that must be met for an Dust Explosion to occur <ul><li>The above criteria for deflagration must be present. </li></ul><ul><li>The combustible mixture is dispersed within a confined enclosure (and the confined enclosure does not contain sufficient deflagration venting capacity to safely release the pressures) such as a vessel, storage bin, ductwork, room or building. It must be noted that a small deflagration can disturb and suspend the combustible dust, which could then serve as the fuel for a secondary (and often more damaging) deflagration or explosion. </li></ul>
    27. 27. OSHA Poster
    28. 28. Industries that handle Combustible Dusts <ul><ul><ul><ul><ul><li>• Agriculture </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Chemicals </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Textiles </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Forest and furniture products </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Metal processing </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Tire and rubber manufacturing plants </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Paper products </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Pharmaceuticals </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Wastewater treatment </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Recycling operations (metal, paper, and plastic.) </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>• Coal dust in coal handling and processing facilities </li></ul></ul></ul></ul></ul>
    29. 29. Current Best Practices <ul><li>To prevent Dust Explosions: </li></ul><ul><li>1. Methods of explosion containment </li></ul><ul><li>2. Explosion suppression </li></ul><ul><li>3. Explosion venting </li></ul><ul><li>4. Suitable sitting of plant – minimize effects </li></ul><ul><li>5. Control of ignition sources or inerting </li></ul>
    30. 30. Dust Control Measures <ul><li>The dust-containing systems (ducts and dust collectors) are designed in a manner (i.e., no leaking) that fugitive dusts are not allowed to accumulate in the work area. </li></ul><ul><li>The facility has a housekeeping program with regular cleaning frequencies established for floors and horizontal surfaces, such as ducts, pipes, hoods, ledges, and beams, to minimize dust accumulations within operating areas of the facility. </li></ul><ul><li>The working surfaces are designed in a manner to minimize dust accumulation and facilitate cleaning. </li></ul>
    31. 31. NFPA 654 – Guidance on Dust Layer Characterizations & Precautions <ul><li>Indicates that immediate cleaning is warranted whenever a dust layer of 1/32-inch thickness accumulates over a surface area of at least 5% of the floor area of the facility or any given room. </li></ul><ul><li>The 5% factor should not be used if the floor area exceeds 20,000 ft 2 , in which case a 1,000 ft 2 layer of dust is the upper limit. </li></ul><ul><li>Accumulations on overhead beams, joists, ducts, the tops of equipment, and other surfaces should be included when determining the dust coverage area. </li></ul><ul><li>Even vertical surfaces should be included if the dust is adhering to them. Rough calculations show that the available surface area of bar joists is approximately 5 % of the floor area and the equivalent surface area for steel beams can be as high as 10%. </li></ul>
    32. 32. What is 1/32 of an inch? <ul><li>When observe areas of the plant for dust accumulations of greater than 1/32 of an inch… </li></ul><ul><li>It is the approximately equal to the thickness of a typical paper clip. </li></ul>
    33. 33. Likely Areas for Dust Accumulations <ul><li>Within a plant are: </li></ul><ul><ul><ul><li>• structural members </li></ul></ul></ul><ul><ul><ul><li>• conduit and pipe racks </li></ul></ul></ul><ul><ul><ul><li>• cable trays </li></ul></ul></ul><ul><ul><ul><li>• floors </li></ul></ul></ul><ul><ul><ul><li>• above ceiling </li></ul></ul></ul><ul><ul><ul><li>• on and around equipment </li></ul></ul></ul><ul><ul><ul><li>(leaks around dust collectors and ductwork.) </li></ul></ul></ul>
    34. 34. Ignition Control Measures <ul><li>Electrically-powered cleaning devices such as vacuum cleaners, and electrical equipment are approved for the hazard classification for Class II locations. </li></ul><ul><li>The facility has an ignition control program, such as grounding and bonding and other methods, for dissipating any electrostatic charge that could be generated while transporting the dust through the ductwork. </li></ul><ul><li>The facility has a Hot Work permit program. </li></ul><ul><li>Areas where smoking is prohibited are posted with “No Smoking” signs. </li></ul><ul><li>Duct systems, dust collectors, and dust-producing machinery are bonded and grounded to minimize accumulation of static electrical charge. </li></ul><ul><li>The facility selects and uses industrial trucks that are approved for the combustible dust locations. </li></ul>
    35. 35. Prevention Measures <ul><li>The facility has separator devices to remove foreign materials capable of igniting combustible dusts. </li></ul><ul><li>MSDSs for the chemicals which could become combustible dust under normal operations are available to employees. </li></ul><ul><li>Employees are trained on the explosion hazards of combustible dusts. </li></ul>
    36. 36. Protection Measures <ul><li>The facility has an emergency action plan. </li></ul><ul><li>Dust collectors are not located inside of buildings. (Some exceptions) </li></ul><ul><li>Rooms, buildings, or other enclosures (dust collectors) have explosion relief venting distributed over the exterior wall of buildings and enclosures. </li></ul><ul><li>Explosion venting is directed to a safe location away from employees. </li></ul><ul><li>The facility has isolation devices to prevent deflagration propagation between pieces of equipment connected by ductwork. </li></ul><ul><li>The dust collector systems have spark detection and explosion/ deflagration suppression systems. </li></ul><ul><li>Emergency exit routes are maintained properly. </li></ul>
    37. 37. Equipment used when sampling <ul><li>Equipment for collecting dust samples may include the following: </li></ul><ul><ul><li>• Natural bristle hand brushes for collecting settled dust. </li></ul></ul><ul><ul><li>• Non-sparking, conductive dust pans (aluminum), for collecting settled dust. </li></ul></ul><ul><ul><li>• Non-spark producing sample container. </li></ul></ul><ul><ul><li>• Non-spark producing funnel for filling sample containers. </li></ul></ul><ul><ul><li>• Non-spark producing scoops for removing dust from cyclone containers or other ventilation equipment. </li></ul></ul>
    38. 38. OSHA - Salt Lake Technical Center <ul><li>Dust Samples are analysis to determine the explosibility and combustibility parameters of the dust samples submitted </li></ul><ul><li>Percent through 40 mesh </li></ul><ul><li>Percent moisture content </li></ul><ul><li>Percent combustible material </li></ul><ul><li>Percent combustible dust </li></ul><ul><li>Metal dusts will include resistivity </li></ul><ul><li>Minimum explosive concentration (MEC) </li></ul><ul><li>Minimum ignition energy (MIE) </li></ul><ul><li>Class II test </li></ul><ul><li>Sample weight </li></ul><ul><li>Maximum normalized rate of pressure rise (dP/dt) – Kst Test </li></ul><ul><li>Minimum ignition temperature </li></ul>
    39. 39. Lab Results <ul><li>Lab results may contain some of the results listed below, but not all, depending on particular tests that are performed: </li></ul><ul><ul><ul><ul><li>Mesh size </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Moisture content </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Percent combustible dust </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Sample weight </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Explosion severity </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Kst Value </li></ul></ul></ul></ul><ul><ul><ul><ul><li>MEC </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Resistivity for metal dusts </li></ul></ul></ul></ul>
    40. 40. Max Normalized Rate of Pressure Rise (dP/dT) – K st Test <ul><li>K st is the Deflagration Index for dusts, and the Kst test results provide an indication of the severity of a dust explosion. The larger the value for Kst, the more severe is the explosion. </li></ul><ul><li>K st is essentially the maximum rate of pressure rise generated when dust is tested in a confined enclosure. Kst provides the best “single number” estimate of the anticipated behavior of a dust deflagration. </li></ul><ul><li>Approximately 300 grams of &quot;as received&quot; sample material are needed for the Kst test. In this test, dust is suspended in the 20-liter explosibility testing chamber and is ignited using a chemical igniter. The 20-liter explosibility testing chamber determines maximum pressure and rate of pressure rise if the sample explodes. </li></ul><ul><li>These parameters are used to determine the maximum normalized rate of pressure rise (K st ). </li></ul>
    41. 41. K st best “Single Number” Estimate – Anticipated Behavior
    42. 42. K st Calculation
    43. 43. Reactive Hazard Mgmt Process
    44. 44. Summary <ul><li>Need to know your operations and what are the raw ingredients being used as well as any byproducts and scrap. </li></ul><ul><li>Need to test the physical and chemical properties to determine if the hazardous substances are reactive. </li></ul><ul><li>Utilize available guidance for hazard control and incorporate performance-based design for fire protection systems. </li></ul><ul><li>Important that you as a safety professional become knowledgeable in recognition and control of combustible dust hazards and familiar with NFPA provisions </li></ul>
    45. 45. Discussion Questions <ul><li>How is an explosive distinguished from an explosive material? </li></ul><ul><li>What is a forbidden or unacceptable explosive material? </li></ul><ul><li>If you learn that explosive material was being used in your plant, what is the first thing you would do to correct the hazard? </li></ul><ul><li>Why should explosive materials be stored and carried in small containers? </li></ul><ul><li>Why should a plastic container not be used for explosive liquid dispensing? </li></ul>
    46. 46. Discussion Questions <ul><li>6. Why is it necessary to ground a metal container prior to pouring a explosive liquid? </li></ul><ul><li>7. What would you incorporate in a design for a system that will force an inert gas into a container as explosive liquid is being drawn out of the container? </li></ul><ul><li>8. Explain how you would design the four rivets that are used to hold a 1 m x 1 m explosion-release panel in place if the panel is to release at an overpressure of 3.5 kP(0.5 psi) </li></ul><ul><li>9. How can we evaluate the explosion potential of a substance by using the NFPA 704M Hazard Symbol? </li></ul><ul><li>10. Give an example of an explosion occurring without combustion. </li></ul>
    47. 47. References <ul><li>Eckhoff, Rolf K. - Dust Explosions in the Process Industries, 3 rd ed. Gulf Professional Publishing, 2003 ISBN 0-7506-7602-7 </li></ul><ul><li>Barton, John – Dust Explosion: Prevention and Protection, A Practical Guide, 1 st Ed., Gulf Professional Publishing, 2002 ISBN 0-7506-7519-5 </li></ul><ul><li>NFPA 654 Standard for the Prevention of Fires and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids (2006 Edition) </li></ul><ul><li>NFPA 68 Guide for Venting of Deflagrations (2002 Edition) </li></ul><ul><li>NFPA 69 Standard on Explosion Prevention Systems </li></ul><ul><li>Explosive Identification Guide, Mike Pickett, Delmar 1999, </li></ul><ul><li>FM Global, Data Sheet No. 7-76, Prevention and Mitigation of Combustible Dust Explosions and Fire (2006 ed.) </li></ul>
    48. 48. NFPA Publications Relevant to Combustible Dust Hazard Controls
    49. 49. Industries that may have Combustible Dusts
    50. 50. Industries – Con’t.
    51. 51. Industries – Con’t.
    52. 52. Measured Properties of Combustible Dust
    53. 53. For Additional Information <ul><li>Email: [email_address] </li></ul><ul><li>Office Phone: (713-221-8089) </li></ul><ul><li>Fax: (713-221-2712) </li></ul><ul><li>Professor Albert V. Condello, III FSI-III, TCFP Master Instructor </li></ul><ul><li>University of Houston Downtown </li></ul><ul><li>College of Science and Technology </li></ul><ul><li>Department of Engineering Technology </li></ul><ul><li>One Main Street, Suite N-717 </li></ul><ul><li>Houston, TX 77002-1001 </li></ul><ul><li>Websites: </li></ul><ul><li> </li></ul>