Leading Trends in Chemical Processing Assessment of Dust Explosion Hazards Practical Facts to Consider Presented by: Ashok Ghose Dastidar, PhD MBA, Vice President, Dust & Flammability Testing and Consulting Services 16W070 83 rd Street Burr Ridge, Illinois 60527 (877) Fauske1 or (630) 323-8750 Fax: (630) 986-5481 E-mail: Info@Fauske.com
Ashok Ghose Dastidar B.Sc. Chemistry Dalhousie University MBA Saint Mary s University Master of Applied Science Technical University of Nova Scotia Ph.D. Chemical Engineering Dalhousie University 24 years research in the field of dust & gas/vapor explosions Safety Consulting Engineers, Inc. 2001-2007 Fauske & Associates, LLC 2007- Memberships AIChE, ASTM, NFPA Editorial Advisory Board of Powder/Bulk Solids and Journal of Loss Prevention in the Process Industries Chairperson of the ASTM E27.05 Subcommittee on Dust Explosion Test Methods NFPA Technical Committee 654, 655, 91, 61, 664, & 484 2
Fundamentals of Dust Explosions
Dust Fires & Explosions 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 eliminates the possibility of a fire 4
Dust Fires & Explosions (continued) Dust explosions require the presence of two additional elements dust dispersion and confinement Suspended dust burns more rapidly and confinement allows for pressure buildup; removal of either the suspension or the confinement elements prevents an explosion, although a fire may still occur 5
Overview of NFPA 652
Who is the NFPA? Founded in 1896 Independent body - Not-for-profit Mission Driven - We help save lives and reduce loss with information, knowledge, and passion. 60,000 members, 118 countries Voluntary Codes and Standards Developer ANSI Accredited Organization Internationally Recognized 7
NFPA Standards Voluntary Consensus Standards Development - Adopted by state and local fire and building codes - 50 states use either ICC IFC or NFPA 1 - Referenced in federal regulations as well No federal dust standards Codes developed by over 5000 volunteers Open process anyone can attend meetings and propose changes 8
The Five W s & an H What? NFPA 652 Standard on the Fundamentals of Combustible Dust - Aims to provide basic principles and requirements for identifying and managing fire and explosion hazards associated with combustible dusts - Directs users to the appropriate industry specific or commodity specific NFPA standard 9
The Five W s & an H What? What are the Objectives of NFPA 652 - Life Safety Ensure that occupants of the facility are reasonably protected Ensure that adjacent properties and the public are reasonably protected - Mission Continuity Limit damage levels and ensure the ongoing mission, production, or operating capability of the facility - Mitigation of Fire Spread and Explosions Ensure that the facility and processes are designed to prevent or mitigate fires and explosions from causing failure to adjacent buildings, properties, or the facilities structural elements 10
The Five W s & an H Where? Where does NFPA 652 apply? - All industries - Applies to facilities and operations manufacturing, processing, blending, conveying, repackaging, generating, or handling combustible dusts 11
The Five W s & an H Who? Who has the responsibility - The owner/operator of a facility with potential combustible dust is responsible for: Determining combustibility and explosibility hazards of the materials handled at the facility Identifying and assessing any fire, flash fire, and explosion hazards Managing the identified hazards Communicating the hazards to affected personnel 12
The Five W s & an H Why? Why was NFPA 652 Created - There are multiple commodity specific NFPA standards NFPA 61, Agricultural and food processing NFPA 484, Combustible metals NFPA 654, Combustible Particulate Solids NFPA 655, Sulfur NFPA 664, Wood processing & Woodworking - Requirements are sometimes inconsistent between industry sectors and dust types - Defines the relationship between this standard and others to address gaps or conflicts with requirements - Aims to simplify OSHA compliance and enforcement Combustible Dust National Emphasis Program 2007 13
Framework NFPA 652 NFPA 68, 69, 70 etc. ASTM NFPA 61 NFPA 484 NFPA 664 NFPA 654 14
The Five W s & an H When? When does this take effect? - Unless otherwise specified, the provisions of this standard shall not apply to facilities, equipment, structures, or installations that existed or were approved for construction or installation prior to the effective date of the standard - What is retroactive? Dust Hazard Analysis Chapter 7 Housekeeping Section 8.4 Ignition Source Control Section 8.5 Management Chapter 9 15
The Five W s & an H How? Compliance begins with an understanding of the rules - Requires knowledge of the standard(s) - Shall indicates a requirement - Should indicates a recommendation Understand your materials Evaluate your process Manage your Risk - Administrative controls - Engineering controls Maintain documentation 16
Hazard Identification
Characterize the Explosion Potential of a Material Explosion severity violence of the explosion - KSt Dust deflagration index - Pmax Maximum explosion overpressure - (dp/dt)max Maximum rate of pressure rise Ignition sensitivity ease of ignition - MIE Minimum ignition energy - MEC Minimum explosible concentration 18
Risk Factors Dust properties: - type - particle size - moisture content Sensitivity to oxidizer Ignition sensitivity and sources Quantity of material (fuel) Dispersion mechanisms Confinement Source: U.S. Chemical Safety Board (U.S. CSB) Report #2003-09-I-KY 19
Sampling Strategy Consider material handling from receipt of raw materials to end product packaging - Dust deposits - Dust in cloud Test material with finest particle size - Baghouse or dust collector - Elevated horizontal surfaces Enclosed equipment - Hoppers, bins, dryers Locations where properties of the material could change Source: Hughes Environmental 20
The Role Of Testing
Screening Tests Is My Material Combustible? Two main tests - Determination of Combustibility UN Test N.1 (4.1) Test Method for Readily Combustible Solids Identifies if the material presents a fire hazard - Determination of Explosibility ASTM E1226 Go/No Go Methodology ASTM E1515 Minimum Explosible Concentration 22
Commonly Measured Properties of Combustible Dusts Property Definition ASTM Test Method Application K St Dust deflagration index ASTM E 1226 P max (dp/dt) max Maximum explosion overpressure generated in the test chamber Maximum rate of pressure rise ASTM E 1226 ASTM E 1226 MIE Minimum Ignition Energy ASTM E 2019 MEC LOC ECT Minimum Explosible Concentration Limiting Oxygen Concentration Electrostatic Charging Tendency ASTM E 1515 ASTM E 2931 No ASTM standard Measures the relative explosion severity compared to other dusts Used to design enclosures and predict the severity of the consequence Predicts the violence of an explosion. Used to calculate K st Predicts the ease and likelihood of ignition of a dispersed dust cloud Measures the minimum amount of dust dispersed in air, required to spread an explosion Analogous to the lower flammability limit (LFL) for gas/air mixtures Determines the least amount of oxygen required for explosion propagation through the dust cloud Predicts the likelihood of the material to develop and discharge sufficient static electricity to ignite a dispersed dust cloud 23
Explosion Severity (P max & K St ) ASTM E1226 Determined in a 20-L or 1-m³ chamber Indication of the severity of an explosion Data used in the design of explosion protection devices - Pmax = maximum pressure - K St = (dp/dt)max V ⅓ New addition of Go/No Go explosibility screening test 24
20-L Siwek Test Chamber 10 kj ignition source 25
1-m³ FAI Chamber 26
P max Maximum Explosion Overpressure Generated in the Test Chamber Used to design enclosures and predict the severity of the consequence - The higher the number the more severe the dust deflagration will be If an enclosure is constructed to withstand this pressure failure, explosion venting or suppression is not required 27
Hazard Classes of Dust Deflagration Based on K St Hazard Class K St (bar-m/sec) St-1 < 200 St-2 200-300 St-3 >300 Example Bronze 31 Bituminous Coal 129 Sugar 138 Cork 202 Cellulose 229 Phenolic Resin 269 Aluminum Dust 415 Magnesium 508 28
Data Interpretation Tips Identify what apparatus is being used. - 20L Vessel has potential for under-driving & over-driving - Bureau of Mines Chamber only adequate for determining if a material is explosible If over-driving is suspected consider 1m³ Challenge Test - Low K St <50 bar-m/s - Low P max <3 bar 29
Minimum Explosible Concentration (MEC) ASTM E1515 Lowest dust concentration that will propagate an explosion - Analogous to the Lower Flammability Limit (LFL) for gas/air mixtures - The lower the number, the less dispersed dust required for a dust deflagration Dust MEC (g/m³) Dust MEC (g/m³) Sugar 200 Aluminum 30 Cellulose 80 Magnesium 30 30
Limiting Oxygen Concentration (LOC) ASTM E2931 Minimum quantity of oxygen required to propagate an explosion - Dust concentration independent - Data can be used to develop an inerting strategy - Start at optimal concentration - Once established, test several other concentrations to verify Limiting the oxygen concentration of the air surrounding the dust is a method of explosion control Dust Diameter (μm) LOC (%) Aluminum 22 5 Anthracite coal 17 14 Sulfur 30 7 Wood 27 10 31
Minimum Ignition Energy (MIE) ASTM E2019 Predicts the ease and likelihood of ignition of a dispersed dust cloud MIE of a flammable dust is the minimum spark energy needed to ignite an ideal concentration under lab conditions - A capacitive discharge spark is used for this test - Test can be run with or without inductance - Compared to typical ES ignition sources Examples: sugar (powdered) 30 mj, paper dust 20-60 mj, aluminum 50 mj, magnesium 40 mj 32
Minimum Autoignition Temperature of a Dust Cloud (MIT) ASTM E 1491 Measures the sensitivity to hot surfaces and environments - Hot surfaces in dryers, bearings and mechanical parts - Friction spark ignition with MIE data - Maximum exposure temperature 33
Autoignition Temperature of a Dust Layer (LIT) ASTM E2021 Sensitivity to ignition on hot surfaces - Other side room temperature Longer exposure time (1-2 hr) - LIT is typically lower than MIT Some materials melt before reacting - Not a true minimum since layer thickness affects results 34
Combustible Dust Hazard Analysis (DHA)
Dust Hazard Analysis (DHA) Defined as a systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of one or more combustible particulate solids in a process or facility. The purpose is to identify hazards in the process and document how those hazards are being managed. 36
DHA Requirements Qualifications - Must be performed or led by a qualified person Documentation - Results of DHA Should classify areas into three general categories Not a Hazard Maybe a Hazard Deflagration Hazard - Any necessary action items Process material changes Physical process changes Process operation changes Facility changes
DHA Requirements (continued) Methodology - Must identify and evaluate the process or facility areas where fire, flash fire, and explosion hazards exist. - Must include: Identification of safe operating ranges Identification of safeguards in place Recommendation of additional safeguards where warranted
DHA Requirements (continued) Methodology (continued) - Acceptable methods may include, but are not limited to: What-if analysis Checklist & What-if analysis Failure Modes and Effects Analysis (FMEA) Fault Tree Analysis HAZOP 39
Hazard Assessment Strategy Process and Material Characterization Identify the Process Hazards / Hazardous Conditions Understand the Consequences Reduce, Eliminate, Substitute, Prevent or Mitigate the Hazard Document, Train and Manage Change 40
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