AIHA Professional Development Conference by Daniel Brechko, Managing Consultant

Transcription

1 AIHA Professional Development Conference by Daniel Brechko, Managing Consultant

2 Basics: Fire vs. Explosion OSHA NEP and NFPA 654 What is a combustible dust? Hazard Assessment Hazard Mitigation Strategies Management Q & A

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4 all three components necessary for a fire

5 all three components necessary for an explosion

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7 Nov 2006 CSB report described the occurrence of nearly 280 fires and explosions in US industrial facilities over the past 25 years, resulting in approximately 119 fatalities and over 700 injuries. Oct 18, 2007 OSHA initiates Combustible Dust National Emphasis Program (NEP) to inspect facilities that generate or handle combustible dusts that pose a deflagration/explosion or other fire hazard.

8 Feb 7, 2008 Imperial Sugar, Port Wentworth GA 14 deaths, 38 injured, 14 with serious burns

9 Mar 11, 2008 OSHA Combustible Dust NEP - Reissued Narrowed focus : 64 industries by SIC/NAICS codes Since 2007: > 1000 inspections > 4900 violations (not all dust related)

10 Dust explosions have been happening since before the industrial revolution with the first documented event in 1785 in Turin, Italy NFPA 61 Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities 1930s NFPA Originated practices for woodworking dusts 1943 NFPA 654 (initially only for plastics industry) In 1982 expanded NFPA to include chemical, dye, and pharmaceutical dusts In 1997 revised to reflect all industries not separately covered by specific standards

11 NFPA Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids Scope: This Standard shall apply to all phases of the manufacturing, processing, blending, pneumatic conveying, repackaging, and handling of combustible particulate solids or hybrid mixtures, regardless of concentration or particle size, where the materials present a fire or explosion hazard.

12 Becomes the catch all standard for managing combustible dust hazards with references to other NFPA Standards for specifics: NFPA 68 - Explosion Protection by Deflagration Venting NFPA 69 - Explosion Prevention Systems NFPA 70 - National Electric Code NFPA 77 - Static Electricity NFPA Classification of Combustible Dusts and of (Classified) Locations for Electrical Installations in Chemical Process Areas Note separate standards exist for specific industries and unique hazards

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14 from the dictionary... combustible capable of combustion, a usually rapid chemical process (such as oxidation) dust fine particles, the particles into which something disintegrates

15 current definitions used in NFPA and OSHA... 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 combustible particulate solid any combustible solid material, composed of distinct particles, or pieces, regardless of size, shape, or chemical composition

16 old NFPA definition: Any finely divided solid material that is 420 microns or smaller in diameter(material passing a US no 40 standard sieve) and presents a fire or explosion hazard when dispersed and ignited in air. Why the change? Ratio of surface area to mass ratio is determinant eg. agglomerates, flakes, and fibers and flakes will not pass through sieve but still a deflagration hazard

17 From Dust Explosions in the Process Industries, Third Edition, by Rolf K. Eckhoff, 2003 Elsevier

18 Metal dust such as aluminum and magnesium Wood dust Coal and other carbon dusts Plastic dust and additives Biosolids Other organic dust such as sugar, flour, paper, soap Certain textile materials Source: OSHA NEP CPL

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20 Information gathering phase: Examine your facility, equipment, and operations to determine where particulate solids are or may be List all particulate materials identified Compile information for each material: MSDS Technical data sheets Research material

21 Check all aspects of your operations? Raw materials Intermediate Materials Finished products Waste streams Debris or residue in/on equipment or facility

22 Determine whether dusts are combustible: Start with qualitative analysis based on the chemistry of the material Review published data to see if your dusts are combustible Unless materials are inert testing is necessary Develop a prioritized action plan for testing Begin correcting deficiencies for known hazards immediately

23 Many factors contribute to explosibility Particle size distribution Shape (sphere, flake, needle, etc.) Surface characteristics Porosity Contaminants / impurities Current consensus is that every dust get tested.

24 The particle size and moisture content significantly impact the dust test results: Moisture content, < 5% Particle size, less than 40 mesh (420 um) Particle size, less than 75 mesh (200 um) Some debate over whether Kst should be tested as received, or sieved, risk of being too conservative.

25 Which particulates are combustible? Go / No-go How severe of a deflagration is produced? ASTM E 1226 Explosibility of Dust Clouds What is the ignition sensitivity? ASTM E 2019 Minimum Ignition Energy of Dust Cloud in Air, MIE

26 Measure rate of pressure rise, dp / dt for various particulate concentrations to determine: Deflagration Index, Kst Maximum Pressure, Pmax

27 From Dust Explosions in the Process Industries, Third Edition, by Rolf K. Eckhoff, 2003 Elsevier

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29 Kst index normalized to 1 m 3 test sphere: Kst = (dp/dt)max V 1/3 Kst = (825) (0.02) 1/3 = 224 bar m/s Ranked deflagration severity indexes from OSHA NEP

30 Measure energy required to ignite particulate dispersed in a vessel: Minimum Ignition Energy, MIE Electrostatic sensitivity MIE less than mj

31 From Dust Explosions in the Process Industries, Third Edition, by Rolf K. Eckhoff, 2003 Elsevier

32 For specific mitigation strategies: ASTM E 1515 Minimum Explosible Concentration, MEC ASTM WK 1680 Limiting Oxygen Concentration, LOC Other ignition sensitivity tests: ASTM E 2021 Hot Surface Ignition Temperature of Dust Layer ASTM E 1491 Minimum Autoignition Temperature of Dust Cloud For understanding electrostatic ignition hazards: Volume resistivity Charge relaxation time

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34 Review particulate hazards and where they occur Determine degree of hazard Establish preventative and protective measures Develop prioritized action plan for corrective actions

35 from Guidelines for Safe Handling of Powders and Bulk Solids, AIChE Center for Chemical Process Safety, 2005

36 NFPA 654 states that must provide one or more: Prevention Dilution with non-combustible dusts Oxidant Concentration Reduction Protection Deflagration Venting Deflagration Pressure Containment Deflagration Suppression Systems Deflagration Venting through dust retention device and flamearresting device

37 Prevention by eliminating the potential for explosion, keeping concentrations below MEC Primary application is housekeeping Confine hazard to equipment Prevent devastating secondary explosion Difficult for to apply to processes dusts don t distribute evenly like vapors

38 From Dust Explosions in the Process Industries, Third Edition, by Rolf K. Eckhoff, 2003 Elsevier

39 Prevention by reducing oxygen concentration below MOC required for combustion Applied inside enclosed volumes Use nitrogen or carbon dioxide as inert gas to displace oxygen from Neutronics, NTRON

40 Protection by deflagration venting, allowing the deflagration to occur but enlarges volume to reduce pressures from MGH Engineering and Control from NFPA 654

41 Provide protection by designing equipment strong enough to contain deflagrations inside equipment.

42 Provide explosion protection by detecting incipient explosion and interrupting it with suppressing agent. from NFPA 654 from NFPA 654

43 Provide explosion protection by venting equipment through a dust rentation and flame-arresting device. from Rembe Inc from Rembe Inc

44 For mitigation strategies that allow explosion to occur, isolation is paramount. Must prevent explosion from spreading Pressures increase in subsequent enclosures Options for passive or active isolation from NFPA 654

45 Use dust tight separations in facility to segregate areas Design surfaces to prevent dust accumulations Avoid drop ceilings Avoid flat surfaces, ie use round ductwork Local exhaust ventilation Avoid cleaning with compressed air, use central vacuum Pneumatic conveying use vacuum, not pressure Electrical installations

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47 Hazard Communication and Process Safety Fire and explosion hazards in the workplace Process description and safe operation Explosion protection systems Warning Signs Explosion vent areas No smoking, No ignition sources

48 Electrostatic Dissipative Shoes (ESD) For static sensitive dusts Floors must have static dissipative coatings Fire Resistant (FR) Clothing Required where a flash fire hazard exists

49 Hot Work Program Prevent ignition sources from welding, cutting brazing Powered Industrial Trucks Rated for areas with combustible dusts Electrical devices Approved for Class II areas, Division 1 + 2, Class Dust tight Low temperature

50 Management of Change Changes to facilities, processes and equipment New raw materials, intermediates, finished products New waste streams Inspections and Audits to check your systems Employee training Grounding and bonding Management of Change Maintenance of safety devices

51 References: Know what combustible dusts you have at your facility Have dust explosibility information for your dusts Use appropriate hazard mitigation strategies Housekeeping!! (make processes dust tight) Train employees Maintain systems, equipment, and documentation Questions? Daniel Brechko, Managing Consultant Sangwin Solutions