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NFPA 68-2007

NFPA 68-2002. NFPA 68-2007. Guide for Venting of Deflagrations. Updated/Revised to:. Standard on Explosion Protection by Deflagration Venting. Two main directives and codes recognized for the use of explosion protection. ATEX

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NFPA 68-2007

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  1. NFPA 68-2002 NFPA 68-2007 Guide for Venting of Deflagrations Updated/Revised to: Standard on Explosion Protection by Deflagration Venting

  2. Two main directives and codes recognized for the use of explosion protection ATEX • Atex is the European equivalent to NFPA except it is the law, not a guideline • Global companies may request compliance to Atex regardless of location National Fire Protection Agency (NFPA) • NFPA is an international organization charged with creating and maintaining minimum standards and requirements from fire prevention, building codes, and personnel protective equipment, numbering over 300.

  3. NFPA 68 - 2007 EditionGuide to Explosion Venting Applies to the design, location, installation and maintenance, and use of devices and systems that vent the combustion gases and pressure resulting from a deflagration within an enclosure.

  4. General Organization – Changes and focus

  5. Summary of Major Changes • Standard • Hazard Analysis and Design Options • Vessel L/D Determination • Revised general correlations for dusts • Basic equation • Initial pressure • L/D • Turbulence • Panel inertia • Partial volume • Vent ducts • Inspection and Maintenance

  6. Additional Minor Changes • Dust collector volumes for sizing • Kst Data • Hydraulic diameter • Fireball dimension • FlamQuench building volume

  7. Standard on Explosion Protection by Deflagration Venting • Mandatory requirements for the • design, • location, • installation, • maintenance and • use of devices and systems • More power, authority to the Authority Having Jurisdiction (OSHA, FM, Company Official)

  8. Hazard Analysis(part of new Chapter on General Requirements) • 4.2.3 Hazard Analysis. • 4.2.3.1 The design basis deflagration hazard scenario shall be identified and documented. • 4.2.3.2 A documented risk evaluation acceptable to the authority having jurisdiction shall be permitted to be conducted to determine the level of protection to be provided.

  9. Compliance Options(New in 2007 Standard) • 4.3.2 Performance-Based Design. A performance-based design shall be in accordance with Chapter 5 of this standard. • 4.3.3 Prescriptive-Based Design. A prescriptive-based design shall be in accordance with Chapter 6 through Chapter 11 of this standard.

  10. Explicit Procedure for L/D Calculation(now specifically defined by NFPA) • H = maximum flame travel • Veff based on distance H • Aeff = Veff/H • Dhe = hydraulic diameter 4x[Aeff/p] • where p = perimeter • Deff = [4xAeff/π]0.5 (round) • L/D = H/Deff H Additional Examples

  11. Revised General Correlations • Flow Chart- information input in sequence, as one will now affect others • Combination Rule Chart • New Equations • Basic equation • Initial pressure • L/D • Turbulence • Panel inertia • Partial volume • Vent ducts

  12. Revised General Correlations For Dusts NFPA-68 2007 Edition Determine appropriate input parameters (e.g. Kst, Pmax, Pstat, Pinitial, enclosure volume and L/D, vent cover area density, etc. • 6.1.2* For dusts, KSt and Pmax shall be determined in approximately spherical calibrated test vessels of at least 20 L capacity per ASTM E 1226, Standard Test Method for Pressure and Rate of Pressure Rise for Combustible Dusts. • 6.1.2.1 It shall be permitted to determine KSt and Pmax per ISO 6184/1, Explosion Protection Systems - Part 1: Determination of Explosion Indices of Combustible Dusts in Air. • 6.1.2.2* It shall be permitted for the owner/user to test the dust with moisture content and particle size that deviates from the recommended conditions established by the method described in 6.1.2 or 6.1.2.1(new) provided a documented assessment acceptable to the authority having jurisdiction has been performed prior to using these KSt and Pmax values to determine vent sizing. • .2.2.1 Where the hazard consists of a dust mixture, the vent size shall be based on the KSt and Pmax of the mixture. • 6.2.2.2 Where the dust mixture composition is not certain, the vent size shall be based on the highest KSt of all components and the highest Pmax of all components

  13. Chapter 11. Inspection and Maintenance **Critical for Owner/Operators“Inspected annually - can be increased or decreased based on documented operating experience” 11.2 Design Parameters and Documentation. Data sheets, installation details, and design calculations shall be developed and maintained for each vent closure application, suitable for review by an authority having jurisdiction that verifies a vent area is sufficient to prevent deflagration pressure from exceeding the enclosure strength and identifies areas exposed to potential overpressure, event propagation, and fireball effects during venting.

  14. Manufacturer’s data sheets and instruction manuals Design calculations – (VentCalc) General specifications Vent closure specifications End user inspection/maintenance forms User documentation of conformity with applicable standards Vent closure identification Combustible material properties test report – (Kst Testing) Copy of vent identification label Process plan view Process elevation view Vent relief (pressure and fireball) path – (Fireball dimension) Proximity of personnel to vent relief path – (Safe Placement of vents) Mechanical installation details Electrical supervision (if provided) installation details Vent restraint installation and design documentation (if required) Process interlocks (if provided) Event deflagration isolation requirements (if required) Employee training requirements 11.2 Design Parameters and Documentation Documentation shall include all of the following:

  15. Dust Collector Vent Placement – 8.7.1(1) If all vent area is below the filters; And The spacing between bags is less than the radius; Then Calculate the volume “below the bags only”

  16. Dust Collector Vent Placement– 8.7.1(1) All vent area is below the filters; And The spacing between bags is greater than the radius; Then Use entire volume below the tube sheet minus the bag volume

  17. Vent Diameter, D Dust Collector Vent Placement – 8.7.1(2) If the bags extend below the vent and are modified… .i.e. the bags are either completely removed or shortened so that they do not extend below the top of the vent for a distance of one vent diameter from the vent. Then The bags immediately adjacent to the vent shall be removed and the remaining bags shall be restrained from passing through the vent Calculate The entire volume below the tube sheet minus the bag volume Full Length Bag D Shortened or Removed Bag Bag Restraint for Full Length Bags D

  18. Dust Collector Vent Placement– 8.7.1(3) If the bottom of vent is at or above the bottom of the bags; Then you must Restrain the row closest to the vent And Calculate the total volume below the tube sheet (vent size is larger)

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