Page 1 of 64. First Revision No. 30-NFPA [ Global Input ] Submitter Information Verification. Committee Statement 3/22/ :02 AM

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1 of 50 3/22/ :02 AM First Revision No. 30-NFPA [ Global Input ] Change pressure units "bar" to "bar-g" and "psi" to "psig" throughout the standard, unless specified as "bar-abs" or "psia". This does not apply to Annex G or units for change in pressure ( P). Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Wed Feb 10 10:53:57 EST 2016 Committee Statement Committee Statement: Response Message: Section 1.8 specifies that all pressures are gauge pressure unless otherwise specified. However, this is not apparent to some users. This revision will aid in the application of the standard. Page 1 of 64

2 of 50 3/22/ :02 AM First Revision No. 26-NFPA [ Section No. 1.6 ] Page 2 of 64

3 of 50 3/22/ :02 AM 1.6 Conversion Factors. Page 3 of 64

4 of 50 3/22/ :02 AM The conversion factors in Table 1.6 are useful for understanding the data presented in this standard. Table 1.6 Conversion Factors Length Parameter Unit Equivalent 1 m 3.28 ft 39.4 in. 1 in mm 1 ft 305 mm 1 μm m Area 1 m ft 2 1 in cm 2 Volume 1 L 61.0 in. 3 1 ft U.S. gal 1 m ft U.S. gal 1 U.S. gal 3.78 L 231 in ft 3 Pressure 1 atm 760 mm Hg 101 kpa 14.7 psi 1.01 bar 1 psi 6.89 kpa 1 N/m Pa 1 bar 100 kpa 14.5 psi atm 1 kg/cm psi 1 kg/m lb/ft 2 (psf) Energy 1 J 1.00 W-s 1 Btu 1055 J 1 J ft-lb KStK G and 1 bar-m/s 47.6 psi-ft/s conversion 1 psi-ft/s bar-m/s Concentration 1 oz avoirdupois/ft g/m 3 Key to abbreviations: atm = atmosphere Btu = British thermal unit cm = centimeter ft = foot g = gram gal = gallon Hg = mercury Page 4 of 64

5 of 50 3/22/ :02 AM in. = inch J = joule kg = kilogram kpa = kilopascal L = liter lb = pound m = meter mm = millimeter N = newton oz = ounce Pa = pascal psf = pounds per square foot psi = pounds per square inch s = second W = watt μm = micron (micrometer) Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 09 17:12:44 EST 2016 Committee Statement Committee Statement: As of the 2013 edition, K_G is no longer used in this standard. Response Message: Page 5 of 64

6 of 50 3/22/ :02 AM First Revision No. 25-NFPA [ Section No. 1.7 ] 1.7 Symbols. The following symbols are defined for the purpose of this standard: A = area (m 2, ft 2, or in. 2 ) AS = internal surface area of enclosure (m 2 or ft 2 ) Av = vent area (m 2 or ft 2 ) C = constant used in venting equations as defined in each specific use dp/dt = rate of pressure rise (bar/s or psi/s) Fr K G KSt = reaction force constant (lb) = deflagration index for gases (bar-m/s) = deflagration index for dusts (bar-m/s) Ln = linear dimension of enclosure [m or ft (n = 1, 2, 3)] Lx L/D LFL = distance between adjacent vents = length to diameter ratio (dimensionless) = lower flammable limit (percent by volume for gases, weight per volume for dusts and mists) MEC = minimum explosible concentration (g/m 3 or oz/ft 3 ) MIE p = minimum ignition energy (mj) = perimeter of duct cross-section (m or ft) P = pressure (bar bar-g or psi psig ) Pes = enclosure strength (bar bar-g or psi psig ) Pex = explosion pressure (bar bar-g or psi psig ) Pmax = maximum pressure developed in an unvented vessel (bar bar-g or psi psig ) P0 = initial pressure (bar bar-g or psi psig ) Pred = reduced pressure [i.e., maximum pressure actually developed during a vented deflagration (bar bar-g or psi psig )] Pstat = static activation pressure (bar bar-g or psi psig ) dp Su Sf tf UFL = pressure differential (bar or psi) = fundamental burning velocity (cm/s) = flame speed (cm/s) = duration of pressure pulse (s) = upper flammable limit (percent by volume) V = volume (m 3 or ft 3 ) Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Page 6 of 64

7 of 50 3/22/ :02 AM Zip: Submittal Date: Tue Feb 09 17:11:25 EST 2016 Committee Statement Committee Statement: As of the 2013 edition, K_G is no longer used in this standard. Response Message: Page 7 of 64

8 of 50 3/22/ :02 AM First Revision No. 4-NFPA [ Chapter 2 ] Chapter 2 Referenced Publications 2.1 General. The documents or portions thereof listed in this chapter are referenced within this standard and shall be considered part of the requirements of this document. 2.2 NFPA Publications. National Fire Protection Association, 1 Batterymarch Park, Quincy, MA NFPA 69, Standard on Explosion Prevention Systems, edition. NFPA 70, National Electrical Code, edition. NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, edition. NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response, edition. 2.3 Other Publications API Publications. American Petroleum Institute, 1220 L Street, NW, Washington, DC API STD 650, Welded Steel Tanks for Oil Storage, , Errata, ASME Publications. American Society of Mechanical Engineers ASME International, Two Park Avenue, New York, NY ASME Boiler and Pressure Vessel Code, ASTM Publications. ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA ASTM E1226, Standard Test Method for Explosibility of Dust Clouds, A ISO Publications. International Organization for Standardization, 1, rue de Varembè, Case postale 56, CH-1211 Geneve 20 ISO Central Secretariat, BIBC II, 8, Chemin de Blandonnet, CP 401, 1214 Vernier, Geneva, Switzerland. ISO 6184/ - 1, Explosion Protection Systems Part 1: Determination of Explosion Indices of Combustible Dust in Air, Other Publications. Merriam-Webster s Collegiate Dictionary, 11th edition, Merriam-Webster, Inc., Springfield, MA, References for Extracts in Mandatory Sections. NFPA 53, Recommended Practice on Materials, Equipment, and Systems Used in Oxygen-Enriched Atmospheres, edition. NFPA 484, Standard for Combustible Metals, 2012 edition. NFPA 652, Standard on the Fundamentals of Combustible Dust, 2016 edition. NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, edition. Submitter Information Verification Page 8 of 64

9 of 50 3/22/ :02 AM Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Mon Feb 01 08:27:03 EST 2016 Committee Statement Committee Statement: Response Message: Referenced current standards development organization names, addresses, standard names, numbers, and editions. Public Input No. 1-NFPA [Chapter 2] Page 9 of 64

10 0 of 50 3/22/ :02 AM First Revision No. 27-NFPA [ Section No ] Deflagration Index. Value indicated by the use of the variable, K. (See , K G, and , KSt.) Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 09 17:14:43 EST 2016 Committee Statement Committee Statement: As of the 2013 edition, K_G is no longer used in this standard. Response Message: Page 10 of 64

11 1 of 50 3/22/ :02 AM First Revision No. 28-NFPA [ Section No ] K G. The deflagration index of a gas cloud. Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 09 17:15:30 EST 2016 Committee Statement Committee Statement: As of the 2013 edition, K_G is no longer used in this standard. A is also deleted. Response Message: Page 11 of 64

12 2 of 50 3/22/ :02 AM First Revision No. 2-NFPA [ Section No ] Replacement-in-Kind. A replacement that satisfies the design specifications. [484, , 2016 ] Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Fri Jan 29 16:43:07 EST 2016 Committee Statement Committee Statement: Response Message: Updating extract reference. NFPA 484 was revised in 2015 to extract the definition for Replacement-in-Kind from NFPA 652. Page 12 of 64

13 3 of 50 3/22/ :02 AM First Revision No. 17-NFPA [ New Section after ] * For aluminum, hafnium, magnesium, tantalum, and titanium, unless K St and P max are determined in nominal 1 m 3 or larger calibrated test vessels, the K St value shall be multiplied by a factor of 2 for application of the design methods. Supplemental Information File Name NFPA_68_FR_17_New_annex.doc Description Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 02 14:40:16 EST 2016 Committee Statement Committee Statement: Response Message: Additional research and testing demonstrated the degree of change in KSt between 20 L and 1 m3 test results for a number of metal dusts and the associated change in experimental results during vented deflagration tests. Iron, zinc, silicon and aluminum dusts were recently compared in both standard test vessels along with a control cornstarch. While the cornstarch KSt remained essentially constant, as intended, iron and zinc exhibited 30-40% increase in KSt, silicon a 60% decrease, and aluminum a 100% increase when comparing 1 m3 results with 20 L results. Page 13 of 64

14 A Recent testing has shown that certain metal dusts exhibit KSt values that are significantly larger in 1 m 3 tests than in 20 L tests. There is evidence of nonconservative vent area predictions for aluminum, when based on 20 L tests, while silicon vent area is overpredicted. It is currently hypothesized that flame temperature is a significant related parameter and it is therefore considered appropriate to require either testing in the larger 1 m 3 vessel or application of a safety factor to 20 L results for aluminum, hafnium, magnesium, tantalum, and titanium. These metals all have maximum adiabatic flame temperatures higher than 3300 C. Until more information is available, KSt results for aluminum, hafnium, magnesium, tantalum, and titanium in smaller test vessels are adjusted to provide additional confidence in application of the design methods. It is possible that the adjusted 20 L value will exceed the actual KSt when measured in the 1 m 3 vessel and, where available, the measured KSt should be used. If the adjusted KSt value exceeds 800 bar-m/s, testing in a 1 m 3 vessel is recommended because this exceeds the limitations of the dust venting equations. (See Table A ) Table A Determining Kst and Pmax for Aluminum, Hafnium, Magnesium, Tantalum, and Titanium Multiply KSt from 20 L sphere tests by a factor of 2 AND use Pmax from 20 L sphere tests OR Use KSt/Pmax from 1 m 3 vessel tests Page 14 of 64

15 4 of 50 3/22/ :02 AM First Revision No. 29-NFPA [ Section No ] The most accurate value of K G shall be determined directly by test, as outlined in Annex C For gases, P max shall be determined in approximately spherical calibrated test vessels of at least 5 L (1.3 gal) capacity with initially quiescent mixture with low energy ignition source (i.e., less than 100 J) If testing cannot be done to determine K G for a particular gas, K G shall be permitted to be approximated by ratioing from the K G of propane (100 bar-m/s) on the basis of the corresponding fundamental burning velocity (see Annex D ) of propane (46 cm/s) and the fundamental burning velocity of the gas in question For gases, P max shall be determined in approximately spherical calibrated test vessels of at least 5 L (1.3 gal) capacity with initially quiescent mixture with low energy ignition source (less than 100 J). Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 09 17:17:44 EST 2016 Committee Statement Committee Statement: As of the 2013 edition, K_G is no longer used in this standard. Response Message: Page 15 of 64

16 First Revision No. 20-NFPA [ Section No ] The baseline value, λ0, of λ shall be calculated from Equations a through f: ( [ a) ] ( [ b) ] ( [ c) ] ( [ d) ] ( [ e) ] ( [ f) ] where: ρu = mass density of unburned gas-air mixture (kg/m 3 ) = 1.2 for flammable gases with stoichiometric concentrations less than 5 vol%, and an initial temperature of 20 C Su = fundamental burning velocity of gas-air mixture (m/s) Dhe = the enclosure hydraulic equivalent diameter as determined in Chapter 6 (m) µu = the unburned gas-air mixture dynamic velocity = kg/m-s for gas concentrations less than 5 vol% at ambient temperatures β 1 = 1.23 β 2 = m/s m/s Dv = the vent diameter as determined through iterative calculation (m) u v = maximum velocity through vent (m/s) Pred = the maximum pressure developed in a vented enclosure during a vented deflagration (bar-g) au = the unburned gas-air mixture sound speed = 343 m/s for gas concentrations less than 5 vol% at ambient temperatures θ = 0.39 Supplemental Information Page 16 of 64 5 of 50 3/22/ :02 AM

17 6 of 50 3/22/ :02 AM File Name FR_20_replace_equation_ _e_.docx Description Equation to replace e. For staff use. Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 02 15:32:28 EST 2016 Committee Statement Committee Statement: Application of the gas equation for Phi_2 for low burning velocity materials was found to inappropriately result in unrealistic results. The correlation c was adjusted consistent with the original range of test data to produce a more appropriately bounded vent area as Su approaches zero. The original equation e was valid for venting of air at near ambient conditions but did not include the possibility of higher initial temperatures, and thus the velocity could have been calculated as greater than the speed of sound. This revision also adds a definition for uv. Page 17 of 64

18 7 of 50 3/22/ :02 AM First Revision No. 16-NFPA [ Sections , ] When Aobs < AS, λ1 shall be equal to λ0 as determined in When Aobs > AS, λ1 shall be determined as follows: ( [ ) ] Supplemental Information File Name FR_16_replace_equation_ docx FR_16_obstructed_enclosure_gas_venting_example.jpg Description For staff use. The committee is working on an example of applying these equations to this arrangement. Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 02 12:00:33 EST 2016 Committee Statement Committee Statement: Response Message: This revision is based on further review of large scale test data with obstructed enclosures. The threshold criteria for accounting for obstructions was revised and the equation to represent the effect of those obstructions was revised to be more consistent with test data. The committee is working on an example of applying these equations to the arrangement in the attached figure. Page 18 of 64

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20 8 of 50 3/22/ :02 AM First Revision No. 22-NFPA [ Section No ] For M > MT, the required vent area, Av2, shall be calculated as follows: ( [ 7.3.3) ] where: M = mass of vent panel (kg/m 2 ) Av1 = vent area determined in (m 2 ) FSH = vent closure shape factor as defined in Chapter 8 1 for translating panels or 1.1 for hinged panels Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 02 16:18:55 EST 2016 Committee Statement Committee Statement: Response Message: This revision eliminates confusion between F_SH used in Chapters 7 and 8 and shape factor,c_s, used in Annex G. Page 20 of 64

21 9 of 50 3/22/ :02 AM First Revision No. 31-NFPA [ Sections 8.1, 8.2, 8.3, 8.4 ] 8.1 Introduction This chapter shall apply to all enclosures with L/Dless than or equal tosix 6 handling combustible dusts or hybrid mixtures This chapter shall be used with the information contained in the rest of this standard In particular, Chapters 6, 7, 10, and 11 shall be reviewed before the information in this chapter is applied This chapter provides a number of equations and calculation procedures that shall be used to treat a variety of vent sizing applications. Page 21 of 64

22 0 of 50 3/22/ :02 AM Page 33 of 64

23 1 of 50 3/22/ :02 AM The general flowchart given in Figure shall be used to select applicable vent sizing methods. Figure Dust Explosion Vent Sizing Calculation Flowchart. Page 34 of 64

24 2 of 50 3/22/ :02 AM 8.1.2* Where actual material is not available for test, vent sizing shall be permitted to be based on KSt values for similar composition materials of particle size no greater than the specified particle size range per the chosen standard: ASTM E1226, Standard Test Method for Explosibility of Dust Clouds, or ISO , Explosion Protection Systems Part 1: Determination of Explosion Indices of Combustible Dust in Air Where the actual material intended to be produced is smaller than the size determined by 8.1.2, tests shall be performed near the intended particle size When the actual material is available, the KSt shall be verified by test. 8.2 Venting by Means of Low-Inertia Vent Closures Minimum Vent Area Requirement Global FR-30 Page 35 of 64

25 3 of 50 3/22/ :02 AM Equation shall be used to calculate the minimum necessary vent area, Av0: [ ] where: A v 0 = vent area (m 2 ) Pstat = nominal static burst pressure of the vent (bar-g) KSt = deflagration index (bar-m/s) V = enclosure volume (m 3 ) Pmax = maximum pressure of a deflagration (bar-g) Pred = reduced pressure after deflagration venting (bar-g) [115] Equation shall apply to initial pressures before ignition of 1 bar-abs ± 0.2 bar The following limitations shall be applicable to Equation : ) 5 bar bar-g Pmax 12 bar bar-g ) 10 bar-m/s KSt 800 bar-m/s ) 0.1 m 3 V 10,000 m 3 ) Pstat 0.75 bar bar-g The L/D of the enclosure shall be determined according to Section Effects of Elevated L/D The L/D of the enclosure shall be determined according to Section When L/Dis less than or equal to 2, Av1 shall be set equal to Av For L/D values greater than 2 and less than or equal to 6 For 2 < L/D 6, the required vent area, Av1, shall be calculated as follows (where exp (A) = e A, e is the base of the natural logarithm [114]): ( [ ) ] where: A v0 = vent area as calculated by Equation L/D = length-to-diameter ratio P red * = reduced pressure after deflagration venting (bar-g) It shall be permitted to extend Equation to values of L/D of 8 for top-fed bins, hoppers, and silos, provided the calculated required vent area, after application of all correction factors, does not exceed the enclosure cross-sectional area. Page 36 of 64

26 4 of 50 3/22/ :02 AM For situations where vents can be distributed along the major axis of the enclosure, Equation and Equation shall be permitted to be applied where L is the spacing between vents along the major axis For L/D values greater than 2 and less than or equal to 6, the required vent area, A v 1, shall be calculated as follows (where exp( A ) = e A, e is the base of the natural logarithm [114]): (8.2.3) where: A v0 = vent area as calculated by Equation L/D = length-to-diameter ratio P red = reduced pressure after deflagration venting (bar-g) * It shall be permitted to extend Equation to values of L/D of 8 for top-fed bins, hoppers, and silos, provided the calculated required vent area, after application of all correction factors, does not exceed the enclosure cross-sectional area Effects of Initially Elevated or Subatmospheric Pressure When the initial pressure is between 0.2 bar bar-g and 0.2 bar bar-g, Avep shall be set equal to Av * When enclosure pressure is initially greater than > 0.2 bar bar-g (20 kpa) or less than < 0.2 bar bar-g ( 20 kpa), Avep/Av0 shall be determined from the following equation: (8.4.1) [ where: Avep = vent area (m 2 ) A v 1 = vent area as calculated by or Equation Pstat = static burst pressure of the vent (bar bar-g ) Pinitial = enclosure pressure at moment of ignition (bar bar-g ) Peffective =1 / 3Pinitial (bar bar-g ) Πeffective = (P red Peffective)/(P E max Peffective) Pred = reduced pressure P E max =[(P max + 1) (Pinitial + 1)/(1 bar-abs) 1] maximum pressure of the unvented deflagration at pressure (bar bar-g ) Pmax = maximum pressure of an unvented deflagration initially at atmospheric pressure (bar bar-g ) Page 37 of 64

27 5 of 50 3/22/ :02 AM * When enclosure pressure is initially less than < 0.2 bar bar-g, the vent area correction in Equation shall be evaluated over the range between operating pressure and atmospheric pressure and the largest vent area correction applied When enclosure pressure is initially less than < 0.2 bar bar-g, it shall be permitted to use a value of 1.1 as the vent area correction for this section When enclosure pressure is initially greater than > 0.2 bar bar-g, deflagration vents shall be permitted only when the following conditions are met: (1) Vent duct length L/D 1 (2) Panel density M MT and 40 kg/m 2 (3) vaxial and vtan < 20 m/s (4) No allowance for partial volume (5) Equation used to calculate the necessary vent area adjustment Effects of Additional Turbulence * For this application, average air axial velocity shall be calculated according to the following equation: ( [ ) ] where: v = average axial gas velocity (m/s) Q = volumetric air flow rate (m 3 /s) A = average cross-sectional area of the flow path (m 2 ) [118, 119] * If a circumferential (i.e., tangential) air velocity is in the equipment, vtan shall be given by 0.5 vtan_max, where vtan_max is the maximum tangential air velocity in the equipment Values of Q, vaxial, vtan_max, and vtan shall be measured or calculated by engineers familiar with the equipment design and operation The measurements or calculations shall be documented and made available to vent designers and the authority having jurisdiction When the maximum values derived for vaxial and vtan are less than 20 m/s, Av2 shall be set equal to Avep. Page 38 of 64

28 * When either vaxial or vtan is larger than 20 m/s, Av2 shall be determined from the following equation where max (A, B) = maximum value of either A or B [118, 119]: ( [ ) ] where: v axial v tan = axial air velocity (m/s) = tangential air velocity (m/s) A vep = vent area calculated by or Equation * Vent areas for buildings in which there is a dust explosion hazard shall be determined from Equation [118, 119]: where: A vep = vent area calculated by or Equation The required vent areas for these buildings shall be permitted to be reduced through use of the partial volume Equation Three different general equations (Equations 8.2.3, , and ) shall be applied to the determination of dust deflagration minimum required vent areas Equation 8.2.3, which produces the smallest required vent areas, shall apply to dust handling and storage equipment within which the average air axial velocity, v axial, and the tangential velocity, v tan, are both less than 20 m/s during all operating conditions. 8.3* Effects of Panel Inertia ( [ ) ] When the mass of the vent panel is less than or equal to 40 kg/m 2, Equation shall be used to determine whether an incremental increase in vent area is needed and the requirements of shall be used to determine the value of that increase The vent area shall be adjusted for vent mass where the vent mass exceeds MT as calculated in Equation : Global FR-30 ( [ ) ] where: MT = threshold mass (kg/m 2 ) Pred = reduced pressure after deflagration venting (bar bar-g) n = number of panels V = volume (m 3 ) K St = deflagration index (bar-m/s) Page 39 of 64 6 of 50 3/22/ :02 AM

29 7 of 50 3/22/ :02 AM Where Mis greater than > 40 kg/m 2, it shall be permitted to use the procedure provided in Annex G. Global FR For M > MT, the required vent area A v3, shall be calculated as follows: ( [ ) ] where: FSH = 1 for translating panels or 1.1 for hinged panels M = mass of vent panel (kg/m 2 ) K St = deflagration index (bar-m/s) n = number of panels V = volume (m 2 ) P red = Reduced pressure after deflagration venting (bar-g) A v 2 = vent area calculated by , Equation , or Equation , as applicable If KSt < 75 bar-m/s, KSt = 75 shall be used in Equation Where M MT, Av3 shall be set equal to Av2. 8.4* Effects of Partial Volume When the volume fill fraction, Xr, can be determined for a worst-case explosion scenario, the minimum required vent area shall be permitted to be calculated from the following equation: ( [ ) ] where: A v4 = vent area for partial volume deflagration A v3 = vent area for full volume deflagration as determined from Equation or from Xr = fill fraction > Π Π = Pred/Pmax * If Xr Π, deflagration venting shall not be required Where partial volume is not applied, Av4 shall be set equal to Av * Process Equipment Partial Volumes. Process equipment involving nonsolvent drying shall be permitted to use partial volume venting in accordance with Equation In applications involving dryers with recirculation of dry product, the fill fraction shall be taken as 1.0. Page 40 of 64

30 Furthermore, if If the solvent is flammable, hybrid deflagration KSt values shall be determined In applications such as a spray dryer or fluidized bed dryer, the specific fill fraction to be used for vent design shall be based on measurements with representative equipment and process materials In applications involving spray dryers where a partial volume venting is calculated in accordance with Equation , the vent shall be mounted within the chosen partial volume zone of the dryer that contains the driest fraction of material In these applications, the determination of Xr shall be documented and submitted to the authority having jurisdiction for review and concurrence Building Partial Volumes. (See Annex I.) This subsection shall apply to large process buildings in which a dust explosion hazard is associated with combustible material deposits on the floor and other surfaces, and with the material contained in process equipment. Page 41 of 64 8 of 50 3/22/ :02 AM

31 9 of 50 3/22/ :02 AM The minimum required deflagration vent area for the building dust explosion hazard shall be based either on the full building volume or on a partial volume determined as follows: (1) Collect at least three representative samples of the floor dust from either the actual building or a facility with similar process equipment and materials. The samples shall be obtained from measured (2) floor areas, Afs, that are each 0.37 m 2 (4 ft 2 ) or larger. Weigh each sample and calculate the average mass, (grams), of the floor samples. (3) Collect at least two representative samples from measured sample areas, Ass, on other surfaces with dust deposits. These surfaces on any plane could include beams, shelves, and external surfaces of process equipment and structures. Calculate the total area, Asur, of these surfaces with dust deposits. (4) Weigh each sample and calculate the average mass, (grams), of the surface samples. (5) Determine the total mass, Me, of combustible dust that could be released from the process equipment in the building. (6) Test the dust samples per ASTM E1226, Standard Test Method for Explosibility of Dust Clouds, to determine Pmax, KSt, and the worst-case concentration, cw, corresponding to the largest value of KSt. (7) Using the highest values of Pmax and KSt, the building volume, V, and Π = Pred/Pmax, use Equation or to calculate the vent area, Av3, needed if the full building volume were filled with combustible dust. (8) Calculate the worst-case building partial volume fraction, Xr, in accordance with (9) If the calculated Xr > 1, the minimum required vent area is equal to Av3. (a) (b) If Xr Π, no deflagration venting is needed. If 1 > Xr > Π, the minimum required vent area, Av4, is calculated from Equation as follows: ( [ ) where: A v 4 = vent area for partial volume deflagration A v 3 = vent area for full volume deflagration as determined from Equation or from X r = fill fraction > Π Π = P red / P max Page 42 of 64

32 0 of 50 3/22/ :02 AM The worst-case building partial volume fraction, Xr, shall be calculated from the following equation: ( [ ) where: Xr = worst-case building partial fraction = average mass of floor samples (g) Af-dusty = total area of floor with dust deposits (m 2 ) ηdfloor = entrainment factor for floor accumulations Afs = measured floor areas (m 2 ) V = building volume (m 3 ) cw = worst-case dust concentration (g/m 3 ) = average mass of surface samples (g) Asur = total area of surfaces with dust deposits (m 3 ) ηdsur = entrainment factor for surface accumulations Ass = measured sample areas of surfaces with dust deposits (m 2 ) Me = total mass of combustible dust that could be released from the process equipment in the building (g) If a measured value of cw is available, the lowest value of cw for the various samples shall be used in Equation If a measured value of cw is not available, a value of 200 g/m 3 shall be permitted to be used in Equation * If measured values of and are not available, and if the facility is to be maintained with dust layer thickness in accordance with NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, an approximate value for these ratios shall be permitted to be used, based on a dust layer bulk density of 1200 kg/m 3 and a layer thickness of 0.8 mm ( 1 32 in.) over the entire floor area and other surfaces defined in The total mass of dust that could be released from process equipment in the building/room Me, shall be determined as follows: (1) Evaluate equipment with exposed dust accumulations, such as but not limited to screeners, open-top conveyors or conveyor belts, open packaging or shipping containers, and enclosureless dust collectors. (2) Evaluate anticipated episodic spills from equipment in light of current housekeeping procedures and practices. (3) Do not include material in closed packaging or shipping containers, material in enclosed silos or storage bins, or in otherwise explosion-protected equipment. Page 43 of 64

33 The entrainment factor, ηd for each representative area shall be determined by one of the following methods: (1) Assume an entrainment factor of 1. (2) Calculate the entrainment factor as follows: (a) (b) Determine the average particle density, ρp for each sampled dust layer. Determine the entrainment threshold velocity using the following equation: [ (2)(b where: Ut = threshold velocity (m/s) ρp = particle density (kg/m 3 ) (c) (d) Assume a maximum free-stream velocity, U, of 50 m/s or establish a different free-stream velocity calculated from a maximum credible initiating event. Determine a maximum entrainment rate using the following equation: [ (2)(d where: m" = entrained mass flux (kg/m 2 -s) ρ = gas density (kg/m 3 ) U = free-stream velocity (m/s) > Ut Ut = threshold velocity (m/s) (e) (f) Determine initiating event time, t, by dividing the building or enclosure building s or enclosure s longest dimension by 1 2 the maximum free-stream velocity. Using the appropriate surface area, A, determine the maximum mass, Mmax, from the presumed initiating event using the following equation: [ (2)(f where: m" = entrained mass flux (kg/m 2 -s) A = surface area (m 2 ) t = initiating event time (s) (g) Determine the entrainment factor using the following equation: [ (2)(g where: M = average mass of the sample (g) Supplemental Information File Name FR_31_Chapter_8_Reorganization.docx Description Page 44 of 64 1 of 50 3/22/ :02 AM

34 2 of 50 3/22/ :02 AM Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Wed Feb 10 14:23:47 EST 2016 Committee Statement Committee Statement: Response Message: Though Figure is intended to guide the user through the vent sizing process, the text and order of equations make it quite difficult to navigate the actual calculation procedure. By organizing the sections by order of intended execution, the user will be able to follow the flow of section 8.2 without needing to jump through the chapter. Public Input No. 7-NFPA [Chapter 8] Page 45 of 64

35 Draft copy for NFPA 68 Committee work only Chapter 8 Venting of Deflagrations of Dusts and Hybrid Mixtures 8.1 Introduction This chapter shall apply to all enclosures with L/D less than or equal to six handling combustible dusts or hybrid mixtures This chapter shall be used with the information contained in the rest of this standard In particular, Chapters 6, 7, 10, and 11 shall be reviewed before the information in this chapter is applied This chapter provides a number of equations and calculation procedures that shall be used to treat a variety of vent sizing applications The general flowchart given in Figure shall be used to select applicable vent sizing methods. Figure Dust Explosion Vent Sizing Calculation Flowchart. Commented [ML1]: This will need to be renumbered based on new section numbers

36 Draft copy for NFPA 68 Committee work only The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.

37 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only 8.1.2* Where actual material is not available for test, vent sizing shall be permitted to be based on KSt values for similar composition materials of particle size no greater than the specified particle size range per the chosen standard: ASTM E 1226, Standard Test Method for Explosibility of Dust Clouds, or ISO , Explosion Protection Systems Part 1: Determination of Explosion Indices of Combustible Dust in Air Where the actual material intended to be produced is smaller than the size determined by 8.1.2, tests shall be performed near the intended particle size When the actual material is available, the KSt shall be verified by test. 8.2 Venting by Means of Low-Inertia Vent Closures The L/D of the enclosure shall be determined according to Section Minimum Vent Area Requirement Commented [ML2]: This is moving above current section Equation shall be used to calculate the minimum necessary vent area, Av0: (8.2.2) where: Av0 = vent area (m 2 ) Pstat = nominal static burst pressure of the vent (bar) KSt = deflagration index (bar-m/s) V = enclosure volume (m 3 ) Pmax = maximum pressure of a deflagration (bar-g) Pred = reduced pressure after deflagration venting (bar) [115] Equation shall apply to initial pressures before ignition of 1 bar-abs ± 0.2 bar The following limitations shall be applicable to Equation : (1) 5 bar Pmax 12 bar (2) 10 bar-m/s KSt 800 bar-m/s (3) 0.1 m 3 V 10,000 m 3 (4) Pstat 0.75 bar Commented [ML3]: deleted

38 . The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only Effects of Elevated L/D The L/D of the enclosure shall be determined according to Section 6.4. Commented [ML4]: Came from When L/D is less than or equal to 2, Av1 shall be set equal to Av For L/D values greater than 2 and less than or equal to 6, the required vent area, Av1, shall be calculated as follows (where exp(a) = e A, e is the base of the natural logarithm [114]): ( ) * It shall be permitted to extend Equation to values of L/D of 8 for top-fed bins, hoppers, and silos, provided the calculated required vent area, after application of all correction factors, does not exceed the enclosure cross-sectional area For situations where vents can be distributed along the major axis of the enclosure, Equation and Equation shall be permitted to be applied where L is the spacing between vents along the major axis Effects of Initially Elevated or Subatmospheric Pressure. Commented [ML5]: This section and all underneath are moving here from When the initial pressure is between -0.2 bar and 0.2 bar, Avep shall be set equal to Av * When enclosure pressure is initially greater than 0.2 bar-g (20 kpa) or less than -0.2 bar-g (-20 kpa), Avep shall be determined from the following equation: Commented [ML6]: /Av0 is being deleted here where: Avep = vent area (m 2 ) (8.4.1) Pstat = static burst pressure of the vent (bar-g) Pinitial = enclosure pressure at moment of ignition (bar-g) Peffective = 1 /3Pinitial (bar-g)

39 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only Πeffective = (Pred - Peffective)/(P E max - Peffective) Pred = reduced pressure (bar-g) P E max = [(Pmax + 1) (Pinitial + 1)/(1 bar-abs) - 1] maximum pressure of the unvented deflagration at pressure (bar-g) Pmax = maximum pressure of an unvented deflagration initially at atmospheric pressure (bar-g) * When enclosure pressure is initially less than -0.2 bar-g, the vent area correction in Equation shall be evaluated over the range between operating pressure and atmospheric pressure and the largest vent area correction applied When enclosure pressure is initially less than -0.2 bar-g, it shall be permitted to use a value of 1.1 as the vent area correction for this section When enclosure pressure is initially greater than 0.2 bar-g, deflagration vents shall be permitted only when the following conditions are met: (1) Vent duct length L/D 1 (2) Panel density M MT and 40 kg/m 2 (3) vaxial and vtan < 20 m/s (4) No allowance for partial volume (5) Equation used to calculate the necessary vent area adjustment When the initial pressure is between -0.2 bar and 0.2 bar, Avep shall be set equal to Av1. Commented [ML7]: This requirement is moving up to Effects of Additional Turbulence Three different general equations (Equations 8.2.3, , and ) shall be applied to the determination of dust deflagration minimum required vent areas Equation 8.2.3, which produces the smallest required vent areas, shall apply to dust handling and storage equipment within which the average air axial velocity, vaxial, and the tangential velocity, vtan, are both less than 20 m/s during all operating conditions * For this application, average air axial velocity shall be calculated according to the following equation: ( ) where: v = average axial gas velocity (m/s) Q = volumetric air flow rate (m 3 /s) A = average cross-sectional area of the flow path (m 2 ) [118,119] * If a circumferential (tangential) air velocity is in the equipment, vtan shall be given by 0.5 vtan_max, where vtan_max is the maximum tangential air velocity in the equipment.

40 . The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only Values of Q, vaxial, vtan_max, and vtan shall be measured or calculated by engineers familiar with the equipment design and operation The measurements or calculations shall be documented and made available to vent designers and the authority having jurisdiction When the maximum values derived for vaxial and vtan are less than 20 m/s, Av2 shall be set equal to Avep * When either vaxial or vtan is larger than 20 m/s, Av2 shall be determined from the following equation where max (A, B) = maximum value of either A or B [118,119]: ( ) * Vent areas for buildings in which there is a dust explosion hazard shall be determined from Equation [118,119]: ( ) The required vent areas for these buildings shall be permitted to be reduced through use of the partial volume Equation * Effects of Panel Inertia When the mass of the vent panel is less than or equal to 40 kg/m 2, Equation shall be used to determine whether an incremental increase in vent area is needed and the requirements of shall be used to determine the value of that increase The vent area shall be adjusted for vent mass where the vent mass exceeds MT as calculated in Equation : where: ( ) MT = threshold mass (kg/m 2 ) Pred = reduced pressure after deflagration venting (bar) n = number of panels V = volume (m 3 ) Where M is greater than 40 kg/m 2, it shall be permitted to use the procedure provided in Annex G For M > MT, the required vent area Av3, shall be calculated as follows:

41 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only Commented [ML8]: Change N to lowercase n where: FSH = 1 for translating panels or 1.1 for hinged panels (8.2.7) M = mass of vent panel (kg/m 2 ) n = number of panels Av2 = vent area calculated by , Equation , or Equation , as applicable If KSt < 75 bar-m/s, KSt = 75 shall be used in Equation Where M MT, Av3 shall be set equal to Av * Effects of Partial Volume When the volume fill fraction, Xr, can be determined for a worst-case explosion scenario, the minimum required vent area shall be permitted to be calculated from the following equation: (8.3.1) where: A v4 = vent area for partial volume deflagration A v3 = vent area for full volume deflagration as determined from Equation or from Xr = fill fraction > Π Π = Pred/Pmax * If Xr Π, deflagration venting shall not be required Where partial volume is not applied, Av4 shall be set equal to Av * Process Equipment Partial Volumes. Process equipment involving nonsolvent drying shall be permitted to use partial volume venting in accordance with Equation In applications involving dryers with recirculation of dry product, the fill fraction shall be taken as Furthermore, if the solvent is flammable, hybrid deflagration KSt values shall be determined In applications such as a spray dryer or fluidized bed dryer, the specific fill fraction to be used for vent design shall be based on measurements with representative equipment and process materials

42 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only In applications involving spray dryers where a partial volume venting is calculated in accordance with Equation 8.3.1, the vent shall be mounted within the chosen partial volume zone of the dryer that contains the driest fraction of material In these applications, the determination of Xr shall be documented and submitted to the authority having jurisdiction for review and concurrence Building Partial Volumes. (See Annex I.) This subsection shall apply to large process buildings in which a dust explosion hazard is associated with combustible material deposits on the floor and other surfaces, and with the material contained in process equipment The minimum required deflagration vent area for the building dust explosion hazard shall be based either on the full building volume or on a partial volume determined as follows: (1) Collect at least three representative samples of the floor dust from either the actual building or a facility with similar process equipment and materials. The samples shall be obtained from measured floor areas, Afs, that are each 0.37 m 2 (4 ft 2 ) or larger. (2) Weigh each sample and calculate the average mass, (grams), of the floor samples. (3) Collect at least two representative samples from measured sample areas, Ass, on other surfaces with dust deposits. These surfaces on any plane could include beams, shelves, and external surfaces of process equipment and structures. Calculate the total area, Asur, of these surfaces with dust deposits. (4) Weigh each sample and calculate the average mass, (grams), of the surface samples. (5) Determine the total mass, Me, of combustible dust that could be released from the process equipment in the building. (6) Test the dust samples per ASTM E 1226, Standard Test Method for Explosibility of Dust Clouds, to determine Pmax, KSt, and the worst-case concentration, cw, corresponding to the largest value of KSt. (7) Using the highest values of Pmax and KSt, the building volume, V, and Π = Pred/Pmax, use Equation or to calculate the vent area, Av3, needed if the full building volume were filled with combustible dust. (8) Calculate the worst-case building partial volume fraction, Xr, in accordance with (9) If the calculated Xr > 1, the minimum required vent area is equal to Av3. (a) If Xr Π, no deflagration venting is needed. (b) If 1 > Xr > Π, the minimum required vent area, Av4, is calculated from Equation as follows: ( ) The worst-case building partial volume fraction, Xr, shall be calculated from the following equation: where: ( )

43 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only Xr = worst-case building partial fraction = average mass of floor samples (g) = total area of floor with dust deposits (m 2 ) Afdusty ηdfloor = entrainment factor for floor accumulations Afs = measured floor areas (m 2 ) V = building volume (m 3 ) cw = worst-case dust concentration (g/m 3 ) = average mass of surface samples (g) Asur = total area of surfaces with dust deposits (m 3 ) ηdsur = entrainment factor for surface accumulations Ass = measured sample areas of surfaces with dust deposits (m 2 ) Me = total mass of combustible dust that could be released from the process equipment in the building (g) If a measured value of cw is available, the lowest value of cw for the various samples shall be used in Equation If a measured value of cw is not available, a value of 200 g/m 3 shall be permitted to be used in Equation * If measured values of and are not available, and if the facility is to be maintained with dust layer thickness in accordance with NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, an approximate value for these ratios shall be permitted to be used, based on a dust layer bulk density of 1200 kg/m 3 and a layer thickness of 0.8 mm (1 32 in.) over the entire floor area and other surfaces defined in The total mass of dust that could be released from process equipment in the building/room Me, shall be determined as follows: (1) Evaluate equipment with exposed dust accumulations, such as but not limited to screeners, open-top conveyors or conveyor belts, open packaging or shipping containers, and enclosureless dust collectors. (2) Evaluate anticipated episodic spills from equipment in light of current housekeeping procedures and practices. (3) Do not include material in closed packaging or shipping containers, material in enclosed silos or storage bins, or in otherwise explosion-protected equipment

44 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only The entrainment factor, ηd for each representative area shall be determined by one of the following methods: (1) Assume an entrainment factor of 1. (2) Calculate the entrainment factor as follows: (a) Determine the average particle density, ρp for each sampled dust layer. (b) Determine the entrainment threshold velocity using the following equation: where: Ut = threshold velocity (m/s) [ (2)(b)] ρp = particle density (kg/m 3 ) (c) Assume a maximum free-stream velocity, U, of 50 m/s or establish a different free-stream velocity calculated from a maximum credible initiating event. (d) Determine a maximum entrainment rate using the following equation: where: m" = entrained mass flux (kg/m 2 -s) [ (2)(d)] ρ = gas density (kg/m 3 ) U = free-stream velocity (m/s) > Ut Ut = threshold velocity (m/s) (e) Determine initiating event time, t, by dividing the building or enclosure longest dimension by 1 2 the maximum free-stream velocity. (f) Using the appropriate surface area, A, determine the maximum mass, Mmax, from the presumed initiating event using the following equation: [ (2)(f)] (g) Determine the entrainment factor using the following equation: where: M = average mass of the sample (g) [ (2)(g)] 8.4 Effects of Initially Elevated or Subatmospheric Pressure * When enclosure pressure is initially greater than 0.2 bar (20 kpa) or less than -0.2 bar (-20 kpa), Avep/Av0 shall be determined from the following equation: Commented [ML9]: Moved to 8.2.3

45 The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. Draft copy for NFPA 68 Committee work only where: Avep = vent area (m 2 ) (8.4.1) Pstat = static burst pressure of the vent (bar) Pinitial = enclosure pressure at moment of ignition (bar) Peffective = 1 /3Pinitial (bar) Πeffective = (Pred - Peffective)/(P E max - Peffective) Pred = reduced pressure P E max = [(Pmax + 1) (Pinitial + 1)/(1 bar-abs) - 1] maximum pressure of the unvented deflagration at pressure (bar) Pmax = maximum pressure of an unvented deflagration initially at atmospheric pressure (bar) 8.4.2* When enclosure pressure is initially less than -0.2 bar, the vent area correction in Equation shall be evaluated over the range between operating pressure and atmospheric pressure and the largest vent area correction applied When enclosure pressure is initially less than -0.2 bar, it shall be permitted to use a value of 1.1 as the vent area correction for this section When enclosure pressure is initially greater than 0.2 bar, deflagration vents shall be permitted only when the following conditions are met: (1) Vent duct length L/D 1 (2) Panel density M MT and 40 kg/m 2 (3) vaxial and vtan < 20 m/s (4) No allowance for partial volume (5) Equation used to calculate the necessary vent area adjustment When the initial pressure is between -0.2 bar and 0.2 bar, Avep shall be set equal to Av1.

46 3 of 50 3/22/ :02 AM First Revision No. 9-NFPA [ Section No ] Equation 8.5.1a shall not be used if the initial pressure exceeds ± 0.2 bar-g. Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Mon Feb 01 16:22:42 EST 2016 Committee Statement Committee Statement: Response Message: The limitation given in incorrectly included both positive and negative pressure limitations where the limitation indicated in Table is only relevant for positive pressures above 0.2 bar. Equation 8.5.1a can be used for vacuum conditions. Public Input No. 10-NFPA [Section No ] Page 46 of 64

47 4 of 50 3/22/ :02 AM First Revision No. 6-NFPA [ Sections , , ] Global FR The owner/operator shall be permitted to choose a design strength based on a P red of either 0.2, 0.5, or 1.0 bar bar-g The casing(s), head, and boot shall all be designed for the same Pred chosen from Additional vents shall be installed in each casing at center-to-center spacing distance along the elevator axis based on the bucket elevator classification, the KSt of the material being handled, and the design strength based on Pred, as given in Table Table Additional Vent Spacing Spacing (m) Global FR-30 Bucket Elevator Classification K St (bar-m/s) P red 0.2 bar bar-g P red 0.5 bar bar-g P red 1.0 bar bar-g Double-casing (twin leg) <100 6 None required None required N/A N/A 3 4 >200 N/A N/A 3 Single-casing (single leg) <100 N/A* None required None required N/A N/A N/A 3 4 >200 N/A N/A 3 N/A: Not allowed. *For Pred = 0.3 bar bar-g, vent spacing of 6 m is appropriate. Source: [120] Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Mon Feb 01 14:38:08 EST 2016 Page 47 of 64

48 5 of 50 3/22/ :02 AM Committee Statement Committee Statement: This revision clarifies that the values in the table are reduced pressure values, not enclosure strength pressures. The headings of each column were revised to show that the given spacing and Kst values will produce no more than the listed Pred values. The information from A is being moved to and A See FR 8. Public Input No. 13-NFPA [Section No ] Page 48 of 64

49 6 of 50 3/22/ :02 AM First Revision No. 8-NFPA [ New Section after ] * Where plastic buckets are used, the corresponding elevator design P red of 0.2, 0.5, or 1.0 bar-g shall be increased by the factors given in Table Table Design P red Adjustment for Plastic Buckets K St (bar-m/s) Percent Increase <100 20% % % Source : [120]. Supplemental Information File Name NFPA_68_FR_8_New_annex.doc Description New Annex and new table Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Mon Feb 01 15:41:24 EST 2016 Committee Statement Committee Statement: Response Message: Information on plastic buckets was not readily apparent to the user, and due to the increasing use of plastic buckets, this information was relocated from the Annex to the body of the standard. The Technical Committee is asking for Public Comments on the use of plastic buckets including any testing to support the provision on plastic buckets in VDI Page 49 of 64

50 . Table Design Pred Adjustment for Plastic Buckets KSt (bar-m/s) Percent Increase <100 20% % % Source: [120]. A Changing from metal to plastic buckets has been demonstrated to increase the explosion pressures. For example, if designing a double-casing bucket elevator with plastic buckets for a KSt of bar-m/s, and intending to space vents at no more than 10 m, then the enclosure strength should be based on a Pred of 0.5 x 1.35 = 0.68 bar. Page 50 of 64

51 7 of 50 3/22/ :02 AM First Revision No. 10-NFPA [ Sections A , A ] A This is also referred to as explosion pressure shock resistant design in European documents, such as EN 14460, Explosion Resistant Equipment. A If the enclosure is intended to be reused following an event, the owner or operator should design the system to prevent permanent deformation of the enclosure. This is also referred to as explosion pressure resistant design in European documents such as VDI 3673, Pressure Venting of Dust Explosions, and EN 13237, Potentially explosive atmospheres Terms and definitions for equipment and protective systems intended for use in potentially explosive atmospheres. Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Mon Feb 01 16:56:16 EST 2016 Committee Statement Committee Statement: Response Message: The descriptions given in A and A are reversed when referencing the standard text in sections and describes a design scenario allowing deformation, not rupture. The description in is equivalent to "Explosion pressure shock resistant" design in the EU harmonized standards such as EN "Explosion Resistant Equipment." A should describe the design scenario where no deformation is allowed, which is equivalent to "explosion pressure resistant" design as defined in EU harmonized standard EN 14460, "Explosion Resistant Equipment." Public Input No. 6-NFPA [Section No. A ] Public Input No. 5-NFPA [Section No. A ] Page 51 of 64

52 8 of 50 3/22/ :02 AM First Revision No. 15-NFPA [ Section No. A.8.7.1(2) ] Page 52 of 64

53 9 of 50 3/22/ :02 AM A.8.7.1(2) Page 53 of 64

54 0 of 50 3/22/ :02 AM Another approach to provide a clear path is to provide a flow area equivalent to the vent area immediately adjacent to the vent. Figure A.8.7.1(2)(a) and Figure A.8.7.1(2)(b) show a side view and a plan view, respectively, for vertical elements. Figure A.8.7.1(2)(c) and Figure A.8.7.1(2)(d) show an end view and a side view, respectively, for Version 1 of the horizontal elements, while Figure A.8.7.1(2)(e) shows an end view for Version 2 of the horizontal elements. Figure A.8.7.1(2)(a) Free Area Normal to Vent for Vertical Filter Elements Side View. Figure A.8.7.1(2)(b) Free Area Normal to Vent for Vertical Filter Elements Plan View. Figure A.8.7.1(2)(c) Free Area Normal to Vent for Horizontal Elements Version 1, End View. Page 54 of 64

55 1 of 50 3/22/ :02 AM Figure A.8.7.1(2)(d) Free Area Normal to Vent for Horizontal Filter Elements Version 1, Side View. Page 55 of 64

56 2 of 50 3/22/ :02 AM Figure A.8.7.1(2)(e) Free Area Normal to Vent for Horizontal Filter Elements Version 2, End View. Supplemental Information File Name FR_15_A.8.7.1_2_d_.png Description change figure as shown- the black bar should be shortened to the height of the vent (D) Page 56 of 64

57 3 of 50 3/22/ :02 AM Submitter Information Verification Submitter Full Name: Laura Montville Organization: [ Not Specified ] Street Address: City: State: Zip: Submittal Date: Tue Feb 02 10:24:43 EST 2016 Committee Statement Committee Statement: Figure A.8.7.1(2)(d) is being edited to clarify the restraint of full-length cartridges. Response Message: Public Input No. 12-NFPA [Sections A.8.7.1(1), A.8.7.1(2)] Page 57 of 64

58 4 of 50 3/22/ :02 AM First Revision No. 14-NFPA [ Section No. A ] A Figure A.8.7.3, in comparison to Figure A.8.7.1(1)(a) and Figure A.8.7.1(2)(a), shows a situation situations for vertical and horizontal elements in which neither separation nor a clear path is provided. A similar situation can exist for horizontal elements. Figure A Insufficient Separation for Vertical and Horizontal Filter Elements. Supplemental Information File Name FR_14_new_images.png Description Replace current figure with the three arrangements shown in the attached file. Submitter Information Verification Submitter Full Name: Laura Montville Page 58 of 64