2010 Sfpe Cpd On Explosion Venting

4,604 views

Published on

0 Comments
3 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
4,604
On SlideShare
0
From Embeds
0
Number of Embeds
10
Actions
Shares
0
Downloads
154
Comments
0
Likes
3
Embeds 0
No embeds

No notes for slide

2010 Sfpe Cpd On Explosion Venting

  1. 1. Andrew W. Wong MBA, CFIFireE, CFEI, CFII, CCFI April 13, 2010 Explosion Venting for Low & High-Strength Enclosures Toronto Chapter
  2. 2. Applicable Law <ul><li>2007 Fire Code, Division B, Part 4 “Flammable and Combustible Liquids” </li></ul><ul><li>Section 22 of R.R.O. 1990, Reg. 851 as amended “Industrial establishments” </li></ul><ul><li>Section 98 to 102 of O. Reg. 67/93 “Health care and residential facilities” </li></ul>
  3. 3. Changes to NFPA 68 - 2007 <ul><li>From a “guideline” to a “standard”. </li></ul><ul><li>Need to determine whether the dust in question is explosive (has a K St value). </li></ul><ul><li>Need to commission a hazard analysis of the proposed dust collection system. </li></ul><ul><li>Need to maintain extensive documentation. </li></ul><ul><li>Need to perform annual inspection of the dust collection system’s explosion venting equipment. </li></ul>
  4. 4. Low Strength Enclosures <ul><li>NFPA 68 – 2007 </li></ul><ul><ul><li>Enclosures that are capable of withstanding reduced pressures, P red , of not more than 0.1 bar (1.5 psi). </li></ul></ul>
  5. 6. Enclosure Strength [P es ] <ul><li>Up to two-thirds the ultimate strength for low-strength enclosures. </li></ul><ul><ul><li>2/3 x 1.5 psi (215 psf) </li></ul></ul><ul><ul><li>= 1 psi (144 psf) </li></ul></ul><ul><ul><li>0.5 psi (72 psf) safety margin </li></ul></ul>
  6. 7. Enclosure Strength [P es ] <ul><li>For high-strength enclosure, the enclosure design pressure sufficient to resist P red . </li></ul><ul><li>P es  P red </li></ul>
  7. 8. Deflagration Index <ul><li>K G (bar-m/sec) for a gas cloud. </li></ul><ul><ul><li>Propane = 100 </li></ul></ul><ul><ul><li>Toluene = 94 </li></ul></ul><ul><ul><li>Ethyl alcohol = 78 </li></ul></ul><ul><ul><li>Hydrogen = 550 </li></ul></ul><ul><ul><li>Acetylene = 1415 </li></ul></ul>
  8. 9. Maximum Pressure [P max ] <ul><li>The maximum pressure developed in a contained deflagration of an optimum mixture. </li></ul>
  9. 10. Reduced Pressure [P red ] <ul><li>The maximum pressure developed in a vented enclosure during a vented deflagration. </li></ul>
  10. 11. Static Activation Pressure [P stat ] <ul><li>Pressure that activates a vent closure when the pressure is increased slowly (with a rate of pressure rise less than 0.1 bar/min (0.15 psi/min or 1.6 psf/min) </li></ul>
  11. 12. Explosion Vents Explo-vent ®
  12. 13. Pressure Relief Panel
  13. 14. Reduced-shank machine bolt installed to fail in shear.
  14. 15. Collapsing washer used with a single-layer panel.
  15. 16. Collapsing washer installed.
  16. 17. Collapsing washer in action.
  17. 18. Explosion Venting
  18. 19. Fire Rated Blast-Resistant Door
  19. 20. Ministry of Labour Engineering Data Sheet #4-01 <ul><li>Explosion venting to outdoors at a minimum ratio of 656 cm 2 /m 3 </li></ul><ul><li>(1 ft 2 /50 ft 3 ) of room volume. </li></ul>
  20. 21. Ministry of Labour Engineering Data Sheet #4-01 <ul><li>Explosion venting may be provided by means of open areas, outwardly opening sash or panels with explosion venting catches or clear glass diagonally scored on the outside surface. </li></ul>
  21. 22. Ministry of Labour Engineering Data Sheet #4-01 <ul><li>The walls of the room shall be made explosion resistant by the use of reinforcing steel in masonry or other means. </li></ul>
  22. 23. Problem #1 <ul><li>Using the MoL guideline, calculate the size of explosion vent for a dispensing room measuring 30’ x 10’ x 12’ high. </li></ul><ul><li>Substance being dispensed is Toluene. </li></ul>
  23. 24. Answer to Problem #1 <ul><li>Room volume = (30 x 10 x 12) cu.ft. </li></ul><ul><li>Room volume = 3600 cu.ft. </li></ul><ul><li>Vent size = (3600 / 50) sq.ft. </li></ul><ul><li>Vent size = 72 sq.ft. </li></ul>
  24. 25. Factory Mutual Global Property Loss Prevention Data Sheet #1-44 <ul><li>Use Table 4 for Toluene, & Figure 1 for damage-limiting construction. </li></ul><ul><li>Ratio of A s to A v should not exceed 7.25. </li></ul><ul><li>Vent panel weight should be limited to about 3 lb/ft 2 . </li></ul><ul><li>Vent ratio of 1 ft 2 /15 ft 3 of room volume. </li></ul>
  25. 26. Problem #2 <ul><li>Using the site information given in Problem #1, determine the following performance criteria using FM guidelines: </li></ul><ul><li>A v (Vent size) </li></ul><ul><li>P v (Static Vent Opening Pressure) </li></ul><ul><li>P r (Resistant Design Pressure) </li></ul>
  26. 27. Answer to Problem #2 <ul><li>Using situation of Problem #1 </li></ul><ul><li>Room Volume = 3600 cu.ft. </li></ul><ul><li>Vent area = (3600 / 15) sq.ft. </li></ul><ul><li>Vent area = 240 sq.ft. </li></ul>
  27. 28. Answer to Problem #2 (cont’d) <ul><li>A s = [2 (30 x 10) + 2 ( 10 x 12) + 2 (30 x 12)] sq.ft. </li></ul><ul><li>A s = 1560 sq.ft. </li></ul><ul><li>A s / A v = 1560 / 240 = 6.5 </li></ul><ul><li>Using P v = 20 psf (0.14 psi) (Static Vent Opening Pressure) </li></ul><ul><li>P r = 125 psf (0.87 psi) (Resistant Design Pressure) </li></ul>
  28. 29. NFPA 68 <ul><li>Recommended venting equation for low strength structures (P es < 1.5 psi): </li></ul>C (A s ) --------------- P red 1/2 A v =
  29. 30. NFPA 68 C (A s ) --------------- P red 1/2 A v = C = Venting equation constant P red = Maximum pressure developed in a vented enclosure during a vented deflagration
  30. 31. Assumptions of Equation <ul><li>C = 0.17 (for gases with fundamental burning velocity less than 1.3 times that of propane) </li></ul><ul><ul><li>Propane – 46 cm/sec [1.3 ft/sec] </li></ul></ul><ul><li>Masonry wall [8” brick or concrete block, 10’ high] cannot withstand a pressure difference from one side to the other of much more than 0.5 psi. </li></ul>
  31. 32. Problem #3 <ul><li>Using given conditions in Problem #1, calculate the vent size with the following assumptions: </li></ul><ul><li>P red = 0.50 psi </li></ul><ul><li>C = 0.17 </li></ul>
  32. 33. --------------- P red 1/2 A v = C (A s ) A v = (0.17) (1560) / 0.5 ½ A v = 375 sq.ft.
  33. 34. NFPA 68 - Other design criteria <ul><li>Individual venting panel size should not exceed 33 sq.ft. </li></ul><ul><li>P red should always exceed P stat by at least 0.35 psi. </li></ul><ul><li>Vent closure weight < 2.5 lb/sq.ft. </li></ul>
  34. 36. Ontario Fire Code, O.Reg. 213/07 made under the Fire Protection and Prevention Act, 1997, as amended. High Strength Enclosures
  35. 37. Fire Code Requirements <ul><li>Division B, 3.2.1.2. </li></ul><ul><ul><li>Every machine that produces wood dust, particles or shavings shall be provided with a blower and exhaust system installed in conformance with NFPA 91 – 2004* edition. </li></ul></ul><ul><ul><li>* Any amendments up to and including June1, 2007. </li></ul></ul>
  36. 38. Combustible Dust Producing Process <ul><li>Division B, 5.10.1.1.(2) </li></ul><ul><ul><li>Machinery that produces, agitates or conveys combustible dusts shall have or be connected to a mechanical exhaust system to the outside atmosphere and dust-tight casings or enclosures. </li></ul></ul>
  37. 41. Origin of Requirement
  38. 42. Verification of Data - P stat <ul><li>Static activation pressure – pressure that activates a vent closure when the pressure is increased slowly (with a rate of pressure rise less than 0.1 bar/min = 1.5 psi/min) </li></ul><ul><ul><li>from product specification of explosion panel </li></ul></ul>
  39. 43. Verification of Data – P max & K St <ul><li>The deflagration index of the dust cloud. Varies with test samples. </li></ul>100 9.0 Wood Grinding dust 144 8.9 Wood Chips/dust 149 8.9 Sawdust K St bar m/s P max bar Dust Type
  40. 44. Verification of Data - K St <ul><li>Dust Explosion Class - Dust explosion causes a pressure increase in a closed vessel. Dust is classified into dust explosion classes based on the (d p /d t ) max in a volume of 1 m3 (the so-called K St value): </li></ul><ul><ul><li>K St value in bar · m · s -1 </li></ul></ul><ul><ul><li>St 1> 0 to 200 </li></ul></ul><ul><ul><li>St 2> 200 to 300 </li></ul></ul><ul><ul><li>St 3> 300 </li></ul></ul>
  41. 45. Verification of Data - P red <ul><li>Reduced pressure – the maximum pressure developed in a vented enclosure during a vented deflagration. </li></ul><ul><ul><li>Data from design engineer </li></ul></ul>
  42. 46. Verification of Volume <ul><li>Volume calculation shall be in conformance with NFPA 68 – 2007. </li></ul><ul><ul><li>Design engineer to show details and method of calculation </li></ul></ul><ul><ul><li>Configuration of dust collector affects calculation </li></ul></ul>
  43. 48. Alternative Vent Area Methodology for Dusts <ul><li>Annex H of NFPA 68 – 2007 edition </li></ul><ul><li>As a primary means for determining vent area of dust collectors </li></ul><ul><li>As a backup to verify the vent area calculation by Equation 8.2.2. of NFPA 68 – 2007 edition. </li></ul>
  44. 49. Vent size calculation <ul><li>A v (m 2 ) = Factor A x Factor B x </li></ul><ul><li>Factor C x Factor D </li></ul>
  45. 61. Example Problem <ul><li>P max = 10 bar (145 psig) </li></ul><ul><li>K St = 350 bar-m/sec </li></ul><ul><li>P stat = 0.2 bar (2.9 psig) </li></ul><ul><li>P red = 0.6 bar (8.7 psig) </li></ul><ul><li>V = 25 m 3 </li></ul><ul><li>L/D = 3 </li></ul>
  46. 62. Model Answer <ul><li>From Figure H.2(b), Factor A = 0.041 </li></ul><ul><li>From Figure H.2(d), Factor B = 11 </li></ul><ul><li>P red / P max = 0.6/10 = 0.06 </li></ul><ul><li>From Figure H.2(h), Factor C = 4.0 </li></ul><ul><li>From Figure H.2(j), Factor D = 1.4 </li></ul><ul><li>Av = 0.041 x 11 x 4 x 1.4 = 2.5 m 2 </li></ul>
  47. 63. Other Considerations 1. Classification of Hazardous Locations 2. Explosion Venting and Size of Fireball 3. Warning sign on Vent Closures 4. Automatic Sprinkler System
  48. 64. Existing Explosion Venting to the Outdoors <ul><li>Fire Code, Division B, 5.10.1.5.(4) </li></ul><ul><li>“ Existing” is not a defined term </li></ul><ul><ul><li>Literal meaning: Prior to June 1, 2007 </li></ul></ul><ul><li>Acceptable Vent Area </li></ul><ul><li>= 0.1 m 2 /m 3 of collector volume </li></ul><ul><li> (1 sq.ft./35 cu.ft.) </li></ul>
  49. 65. Discharge of Deflagration (End slideshow to play wmv file)
  50. 66. Dust Explosion Inside Dust Collector Flame discharged from explosion vent Diameter of Fire Ball
  51. 67. Flame Front of the Fire Ball
  52. 68. <ul><li>where: </li></ul><ul><li>D = axial distance (front) from the vent (m) </li></ul><ul><li>K = flame length factor </li></ul><ul><ul><li>K = 10 for metal dusts, K = 8 for chemical and </li></ul></ul><ul><ul><li>agricultural dusts </li></ul></ul><ul><li>V = volume of vented enclosure (m 3 ) </li></ul><ul><li>n = number of evenly distributed vents </li></ul>Fireball Diameter Calculation for Dust Explosion
  53. 69. Scenario <ul><li>Wood dust </li></ul><ul><li>Volume of vented enclosure = 25 m 3 </li></ul><ul><li>Number of vents = 6 </li></ul><ul><li>Diameter of fire ball </li></ul><ul><ul><li>= 8 x (25/6) 1/3 </li></ul></ul><ul><ul><li>= 8 x 1.6 = 12.8m (42 ft) </li></ul></ul>
  54. 70. <ul><li>where: </li></ul><ul><li>D = axial distance (front) from the vent (m) </li></ul><ul><li>3.1 = formula constant </li></ul><ul><li>V = volume of vented enclosure (m 3 ) </li></ul><ul><li>n = number of evenly distributed vents </li></ul><ul><ul><ul><li>Maximum individual vent panel should not exceed 33 sq.ft. </li></ul></ul></ul>Fireball Diameter Calculation for Gas Explosion
  55. 71. Scenario <ul><li>Toluene </li></ul><ul><li>Volume of vented enclosure = 3600 m 3 </li></ul><ul><li>Number of vents = 12 </li></ul><ul><li>Axial distance of fire ball </li></ul><ul><ul><li>= 3.1 x (3600/12) 0.402 </li></ul></ul><ul><ul><li>= 3.1 x 9.9 = 30.7m (100 ft) </li></ul></ul><ul><li>Hazard zone to the sides = 15m (50 ft) </li></ul>
  56. 72. Mitigating Exposure Risk
  57. 73. Warning Sign on Vent Closure WARNING: Explosion relief device. or As per ANSI Z535 Product Safety Signs and Symbols

×