Exposure to Release. Stages. Predict % affected by the exposure. Predict effects of exposure near the surface.

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Lynn Garrison
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1 Dispersion Models

2 Eposure to Release Predict effects of eposure near the surface Predict % affected b the eposure. 5 6 Stages 1. Source. Acceleration, Diffusion 3. Gravit 4. Transition 5. Surface 6. Turbulence 10/15/011 METU-N

3 Fluids Beond the Sources Effluent properties dominate near a leak Material then migrates and mies with air Ambient conditions eventuall dominate Pressure, temperature, wind velocit, humidit, sun light Transport and miing with air at a vapor cloud boundar Isopleth: constant concentration boundar of a vapor cloud 10/15/011 METU-N 3

4 Accidental Flow Prevention Mechanical integrit Predictive/preventive maintenances, inspection, testing Operator training Human factors Impact barriers Safet Levels Protection ontrol Automatic process control sstems Manual control On-line spares Backup Sstems Alarms Operator intervention Interlocks, traps Emergenc shutdown Last-resort controls Emergenc relief Ignition source control Mitigation Emergenc response Sprinkler, deluge Dike, trench Blast wall, barricade Water curtain Personal protective equipment Haard ause Deviation Accidental Event Impact Material/energ ontained and controlled during normal operation Initiating event of process upset; Start of accident event sequence Ecursion Beond design/ Operating limits Loss of containment of process material/energ Loss of containment of process material/energ Toicit Flammabilit Reactivit Elevated pressure etc. Mechanical failure Procedural error Eternal force Fouling etc. No flow High temperature Low level Impurities Wrong material Step omitted etc. Fire Eplosion Haardous material release etc. Other energ releases Illnesses/injuries/ Death Propert damage Business interruption Environmental damage etc.

5 Dispersion Modeling Needed Goals: prevent releases; mitigation Prevent Inherent safet practices: reduction, substitution, attenuation Process design and integrit PSM management; PHA Mitigation measures Emergenc response planning 10/15/011 METU-N 5

6 Haard Levels oncentration Air velocit and turbulence Time period of release; (time) following release Position of cloud relative to ground 10/15/011 METU-N 6

7 Gaussian Dispersion Pattern (0,0,0) Isopleth A: stack height B: effective height ma at center Along X u ma 10/15/011 METU-N 7

8 Dispersion Parameters loud of effluents epands, mies with air Miing dilutes the effluent: decreases Lower downwind greater area affected Dominant dispersion mechanism: turbulent dispersion horiontal and vertical movement Miing rate depends on u, atmosphere stabilit, buoanc Light winds, strong sun most unstable: rapid diffusion 10/15/011 METU-N 8

9 10/15/011 METU-N 9

10 Plume & Puff 10/15/011 METU-N 10

11 Plume Model Stead state concentration from a continuous source, e.g. smokestack Initiall increases in sie, additions from source Stead state: same amount of effluent added to plume as is mied with air; constant volume Source stopped: plume sie decreases as miing with air is dominant, plume returns to source origin, finall disappears. 10/15/011 METU-N 11

12 Puff Model loud formed from a fied amount of effluent, e.g., from a ruptured vessel Release over a short period of time that source is active Movement from source: dependent on air velocit Material mies with air, boundar diminished in sie, finall disappears 10/15/011 METU-N 1

13 t u j j j j j P. 179, 5-9 Plumes Plume 1. SS, u 0, 4. SS, u u u, j j 3. NSS, u 0, j 6. SS, u ju u,,, 9. SS, u j u u,,, 9. SS, u j u u,,, j j * j * * Plume Of Puff Source H r Source Q m Puff Puffs (r) 4 * r (r,t) Q m 4 * r erfc r * t (r) Q m u(r ) 4 * ep r * 10/15/011 METU-N 13

14 t u j j j j j P. 179, 5-9 Plumes (r,t) Plume Q m r 8( * ep 3/ t) 4 * t Plume Of Puff Puff Puffs. u 0, j j j 5. u 0,,, 7. u u u,,, j * 8. u j 0,,, Source 10/15/011 METU-N 14

15 Neutrall Buoant Dispersion No reactions; small effect of molecular diffusion Miing mechanism: air turbulence Turbulence fluctuations in, u t j (u j ) 0 u j, air velocit, concentration u j u j u j ' ' u j,, fluctuation components 10/15/011 METU-N 15

16 Edd Diffusivit, j Represent fluctuation due to turbulence u j 0; j 0 u j ' ' j j Governing equation: t u j j j j j 10/15/011 METU-N 16

17 1. Stead State, Point Release, No Wind Q m constant; independant of t, wind, u ~ 0 onstant j = * in all directions 0 Polar coordinates, integrate over r : (r) Q m 4 * r Q m, source term r 10/15/011 METU-N 17

18 . Puff Release, No Wind Wind velocit, u ~ 0 onstant j = * in all directions 1 * t Instantaneous concentration: (r,t) Q m r 8( * ep 3/ t) 4 * t METU-N 10/15/011 18

19 3. Non SS Point Release, No Wind Q m constant; wind, u ~ 0 onstant j = * in all directions 1 * t Integrate instantaneous concentration: (r,t) Q m 4 * r erfc r * t 10/15/011 METU-N 19

20 Error function & its Integration 10/15/011 METU-N 0

21 4. SS Point Source with Wind Q m constant; independent of t Wind in direction, u constant onstant j = * in all directions u * (r) Q m 4 * r u(r ) ep * enterline for + << : () Q m 4 * 10/15/011 METU-N 1

22 5. Puff with No Wind, j Varies Q* m constant; Puff release No wind(<u j > =0) j *, but constant in all directions t m t t Q t 3/ * 4 1 ep ) 8( ),,, ( 10/15/011 METU-N

23 6. SS Point Source with Wind, j Varies Q m constant; independent of t Wind in direction, u constant j *, but constant in all directions u enterline for = = 0 : m Q 4 ) ( m u Q * 4 ep 4 ),, ( 10/15/011 3 METU-N

24 7. Puff with Wind Q* m constant; Puff release Wind in direction onl( ) j *, but constant in all directions ) ( ut t m ut t t Q t 3/ * ) ( 4 1 ep ) 8( ),,, ( constant u u u j 10/15/011 4 METU-N

25 8. Puff with No Wind, Source on Ground Q* m constant; Puff release No wind(<u j > =0) j *, but constant in all directions t m t t Q t 3/ * 4 1 ep ) 4( ),,, ( Impervious boundar 10/15/011 5 METU-N

26 9. SS Point Source with Source on Ground Q m constant; independent of t Wind in direction, u constant j *, but constant in all directions u m u Q * 4 ep ),, ( Impervious boundar 10/15/011 6 METU-N

27 10. SS Point Source with Source at Height H r above the Ground Q m constant; independent of t Wind in direction, u constant j *, but constant in all directions u * 4 ep 4 ep 4 ep 4 ),, ( r r m H u H u u Q 10/15/011 7 METU-N

28 onsequence Analsis (E) /r /r Risk contour 10/15/011 METU-N 8

29 onsequence Analsis (E) 위험설비 물질정보 위험지도 50ppm 30ppm 잠재위험요소선정 100ppm 교통통제 사업장과지역사회를 연계한통합안전관리 발생확률예측피해예측가상사고시나리오비상대응전략 냉각수공급중단 냉각수공급중단 A - TRAIN 냉각수공급중단 B - TRAIN 냉각수공급중단 - TRAIN 탱크로부터공급안됨 펌프 A 고장 MOV A가 STANDBY 시닫힘 탱크에밸브 X-1 물이없음이닫힘 펌프기동실패 펌프운전전력공급펌프냉각수중고장실패공급실패인간오류 지역주민피해 소방서 경찰서 병원정보공유 10/15/011 METU-N 9

30 10/15/011 METU-N 30

31 Pasquill-Gifford Model j values difficult to measure Define: dispersion coefficient ~ st dev for i 1 (ut) n i =,, ; n, parameter j j : functions of downwind distance,, and atmospheric conditions in stabilit classes, A - F, based on sunlight and wind speed. Tab 5-1, p. 187 values for rural or urban plumes, or puffs from Figs or Tabs , pp., /15/011 METU-N 31

32 A: Etremel unstable B: Moderatel unstable : Slightl unstable D: Neutrall stable E: Slightl stable : Moderatel stable 10/15/011 METU-N 3

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38 Height Atmospheric Stabilit lasses Night Ground cold: gas dense, turbulence larger at higher u. Da Ground warm: gas light and rises, turbulence larger at lower u. Da Temperature Stabilit classes classif level of turbulance: 10/15/011 A, least stable; F, most METU-N stable (Tab. 5-1, p. 187) 38

39 11. Puff, Ground Source, u onstant (,,,t) * Q m 3/ ep 1 ut Ground concentration: = 0 Ground concentration along : = = 0 enter of moving puff, = ut: (ut,0,0,t) Q m * 3/ 10/15/011 METU-N 39

40 Total Dose D tid (,, ) (,,, t) dt 0 Puff, ground source, constant u: Ground level: D tid (,,0) * Q m u ep 1 Along : D tid (,0,0) Q m * u 10/15/011 METU-N 40

41 1. Plume, Ground Source, u onstant m u Q 1 ep ),, ( Ground (,,0) : = 0 Ground, (,0,0) along : = = 0 Isopleth concentration, * : * ),0,0, ( ln ),0,, ( ),0,0, ( ln t t t 10/15/ METU-N

42 13. Plume, Source at H r, u onstant Ground concentration: Q (,,0) m u ep 1 1 Q enterline: (,0,0) m u ep 1 Ma ground along : (,0,0) ma Q m e uh r Distance downwind for ma : H r METU-N H r H r Find 10/15/011 4

43 Model Implementation Plume ma : release position Puff ma : center of cloud If atmosphere conditions not known, assume worst case for highest. If wind speed not known, assume m/s onsider P-G model assumptions: neutral buoanc, turbulent miing, time concentrations (10 min), km distances 10/15/011 METU-N 43

44 Britter-McQuaid Dense Gas Model Ground level releases; rural, flat terrain Atmospheric stabilit effects not included Miing from drop b gravit of effluent into air Main parameters: initial buoanc, g o, initial volume flu, q o, or total initial volume,v o, wind speed at 10 m elevation, u g o g( ) / o a a a = densit of ambient air 10/15/011 METU-N 44

45 Applicabilit of B-M Model Plume g o q o u 3 D c 1/ D c q o u u R d 1/.5 Puff g o V o u D i 0.0 D i V o 1/3 u R d 0.6 Information buoanc * amnt/u source dimension R d, release duration If model criteria satisfied, use Figs 5-13, 5-14 or Tabs 5-4, 5-5 to est. or downwind distance, 10/15/011 METU-N 45

46 Implementation of B-M Model o = 1 for pure material initiall released m / o : ratio of material conc in air to pure q o q L L V V o = q o R d : initial volume, Puff Adjust conc for densit at T a : e q L : liquid volumetric discharge rate * * (1 * )(T a /T o ) e : effective conc * : unadjusted conc T o : T at release, T a : T ambient, 10/15/011 METU-N 46

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52 Toic Effect riteria Normal work hours criteria: TLV-TWA (AGIH), PEL (OSHA) Probit correlations for wide ranges of concentrations and eposure times riteria for short term eposures at higher than TLV-TWA values: available from man sources IDLH (NIOSH), 30 min eposures: SBA required for higher levels 10/15/011 METU-N 5

53 ERPG Toic Effect riteria American Industrial Hgiene Association (AIHA): Emergenc response planning guidelines (ERPG) for eposures up to 1 hour ERPG-1: mild transient effects ERPG-: reversible health effects ERPG-3: without life-threatening effects Tab 5-6, pp. 01, 0 Alternative guidelines in lieu of ERPG data: Tab 5-9, p 06 EPA Toic Endpoints based on ERPG- 10/15/011 METU-N 53

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56 EEGL Toic Effect riteria National Research ouncil (NR): Emergenc eposure guidance levels (EEGL) Acceptable eposure levels for emergenc condition tasks up to 1 or up to 4 hours Includes reversible effects that do not impair work performance Tab 5-7, p 04 10/15/011 METU-N 56

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58 Release Mitigation Part of consequence modeling, Fig 4-1, p 110. Mitigation methods, Tab 5-10, p 14 Mitigation measures depend on likelihood of a release Preventive: Inherent safet, process and mechanical integrit, training, maintenance, sensors, software Protective, reduce effect of incidents: curtains, foams, emergenc response program 10/15/011 METU-N 58

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Dispersion Model 2. Dr. AA Department of Chemical Engineering University Teknology Malaysia

Dispersion Model 2. Dr. AA Department of Chemical Engineering University Teknology Malaysia Dispersion Model Dr. AA Departent of heical Engineering Universit Teknolog Malasia Pasquill-Gifford Model Pasquill-Gifford Model ases through 0 described previousl depend on the specification of a value