7/21/2019 pslp may 2012

1/13

UNIVERSITITEKNOLOGIP ETRONAS

FINAL EXAMINATIONMAY 2012 SEMESTER

COURSE : CBB2093 PROCESS SAFEry AND LOSSPREVENTIONDATE : Sth SEPTEMBER 2012 (WEDNESDAY)TIME : 2.30 PM - 5.30 PM (3 HOURS)

INSTRUCTIONS TO CANDIDATES1. Answer ALL questions from the Questions Booklet.2. Begin EACH answer on a new page in the Answer booklet given.3. lndicate clearly answers that are cancelled, if any.4. Where applicable, show clearly steps taken in arriving at the solutions and indicateALL assumptions.5. Do not open this Question Booklet until instructed.Note : i. There are THIRTEEN (13) pages in this Question Booklet including

the cover page and Appendix.ii. ONE (1) graph paper is provided.UniversiLi Teknologri PETRONAS

7/21/2019 pslp may 2012

2/13

A. a.CBB 2IX3

List THREE (3) purgr tectmi$es ffiat cornmor$y used in prrcindustries. Discuss the adrran@es ard te disadvantages of ttre listedtechniques.

tG rnddb. A lO00Glitre tank containing air at I ar ar 30OK is to be inerH bI mol% oxygen concenfation by rue lrrogen. Defterniine ttre requir+dnumber of cycles and amount of nihogien for tfe inerting prscess usmg

the following technlques.Pressure purging at prsarre sf l8frt kPa, folkued byventing toatmosphere. Fmaffi

ii. Vacuum purging to 2 kPa abcohrte and the vacurn releases tfqenitrogen until the prssure rerns to atrnospheric condition.

[7 marl@

2

7/21/2019 pslp may 2012

3/13

CBB 2G'3

TABLE Q2 shows the efiect of explosion peak overpressure Gneardrum rupture in human.

TABLE Q2: The effect of explosion peak overpressure on eardrum

Provide and explain the significant of neralized probfrequation for exposures of major accidents such as fire,explosion and toxic release in the consequence anais.

[5 marksl

Estimate the probit conelation for the data given in TABLE Q2.fiO markslMany chemical engineers working in process industries that handetoxic materials. Explain the way of toxicants can enter the human bodyand method to control them.

[5 marksl

rupturePercentage affected Peak overpressure (kPa)2

25507595

17,40032,00044,00064,00085,000

3

7/21/2019 pslp may 2012

4/13

cBB 2093A storage tank containirry toluene (MW - 92) is confined in a dike wittldimensions of 15m x 15m. The storage is a horizontal bullet vessel with legs,raised well above the dike froor. The liquid stored at 1 atm and 3O0K. At 8riscondition, the saturated vapour prssure of toluene in the storage is very bcompared to the partial prssure of the vapour above the liquid. The effectireventilation rate for the outdoor is 15 m3/s.

Estimate the mass transfer of toluene.[5 marks

Determine the evaporation rate of the toluene from the dike if the liquidfrom the storage spilled completely and filled the floor of the dike.I markslEstimate the toluene vapour concentration near the storage in ppm.

[8 marksf

4

7/21/2019 pslp may 2012

5/13

4.CBB 2093

Toxic release and dispersion models are an important part ofconsequence modelling.i. Explain the first THREE (3) important steps in the consequence

modelling procedure.[6 marks]

i. Explain TWO (21 parameters that affect the atmosphericdispersion of toxic materials.

[4 marks]

A storage tank containing hydrogen sulphide (MW = 34) at 60 atm and300 K was located on the ground in a rural area about 1 km from aresidential place. A pipe attached to the storage tank was suddenlybroken during maintenance, and the hydrogen sulphide isinstantaneous released.

Determine the dispersion coefficient.[3 marks]

Estimate the amount of hydrogen sulphide released if theconcentration in the boundary of the residential area wasdetected to be equal to the ERPG-2 = 30 ppm for the worst-casescenario.

[7 marks]

5

7/21/2019 pslp may 2012

6/13

cBB 20935. Various safety systems are installed in the process plant to prevent accidentsfrom propagating. However, some of the safety systems may fail, which couldlead to a major accident. Event trees and fault trees analysis provide

information on how a failure can occur, and the probability of the accidentcould happen.a. Explain how the event trees analysis is used to determine failure of

initiating event and probabili of failure.[4 marksl

b. Compute the following parameters for the top event shown inFGURE Q5 (figure is on the next page).i. Failure rate

[4 marksl. Reliability

[4 marks]

i. Probability of failure [4 marks]iv. MTBF

[4 marks]

6

7/21/2019 pslp may 2012

7/13

GBB 2093

p:0.25 F - 1.0 p:0.5 $:2.0FIGURE Q5: Failure characteristics of a reactor explosion.

END OF PAPER -

7/21/2019 pslp may 2012

8/13

ffiAPPENDIX

DataUniversal gas constant, & = 8.3'14 kPa.m3 /kg-rnol.K

= O.7 &2 atm. ft3 /lb-mol.oR= O.08257 atm.m3 /kg-mol.K

Gravitational constant, g" = 1 {kg.m/s2yN = 32.174 ft{bolhrsaFor water;

DensitY,P= 1000kg/m3Mass transfer coefficient, K," = 0.83 cm/s

Unit conversionuseful unit conversion constants1 atm = 101.3 kPa I kPa = 1 kN.m-2 1 mm Hg = tr.Sf$x f-3 a1 atm = 14.7 lh/in2 I m = 3.2808 ft 1 in = 2.54 cffis1 kg - 2.21b 1 mi = 5280 ftConversion of concentration of vapours from mg.m-3 to pp;

cwn =#(*l;X',,",,,)where;Mis the molecular urelglt in g/g-mol

Zis the temperature in KelvinP is the pressure in atm

7/21/2019 pslp may 2012

9/13

cBB 2093APPEN|X (CONT',D)Vaporisation rate of a liquid

Vaporisation rate of volatile from an open vessel can be estimated using thefollowing equation; N^=WPwhere;Q, is the evaporation rateM is the molecular weight of the volatile substanceK is a mass transfer coeffcientRr is the ideal gas constantTt is the absolute temperature of the liquidtr"t is the saturation vapour pressure of the pure liquidP is the partial pressure of the vapourSaturated vapour pressure can be estimated using the Antoine equation below;

lnPsat :A- BC+Twhere;Pat is saturated vapour pressure in mm HgT is temperature in KA, B, and C are Antoine constants(For toluen , A = 16.0137, B = 3096.52 and C = 46.1 1)The concentration of a volatile in an enclosure resulting from evaporation of a liquid:

^ K{ '^ * 1guPP^ = kg"rr,where;k is the non-ideal mixing factor varies from 0.1 to 0.5 is the ventilation rateT is the enclosure temperatureP is the total pressure of the enclosure

9

7/21/2019 pslp may 2012

10/13

cBB 2093

pasquitt-Gifford dispersion modet APPENDI* (coNT'D)Puff with instantaneous point source at ground level, coordinates fixed at releasedpoint, constant wind only in x directlon wit constant velocity .

\c)(x, v, z,t) = -Jr*,?:,,,; *o{- ; [t+l . +. illPlume with continuous steady-state sou at ground rel and wind n oving in rdirection with constant velocity

(c)(x, y, ") =#"4 +l+. :)jPuff with instantaneous poin source at treight H, above ground level and acoordinate system on the ground that moves with the puff.

\c)(x, v, z,,t : 6ff *"-,[+[;)' ] " {"",1 :(+)'] . ".,1-tf+)ll

Plume with continuous steady state sou e at height, H, a ve ground level andwind moving in x direction at constant veloci u.

{c)(x, v, ") = , *",.'[ +t;J'] "l td+l' ]. ",.,1- {g)l

10

7/21/2019 pslp may 2012

11/13

cBB 2093APPENDTX (GONT'D'

TABLE A-l: Atmospheric stabilityclasses for use with ttue pasquill-Gifford dispersion model

Nglttlrl conditi ons.Surfacewind speed(n/s) Dy'Ume nsolationJStrong Moderato SfSht

Thin overto >4f8

7/21/2019 pslp may 2012

12/13

cBB 2093APPENDTX (CONT'D)

TABLE A-3: Equations for Pasquillifford dispersion coefficients for puffdispersion.

PasquillGiffordstability class , (rn)or ,(m) '(m)ABCDEF

0.18r0'e?0^140.e20.1OJIe,0.0/e?0.04l--":0.0?.role

0.60"0'is-0.53r0'0.34'?I0.15'70.10f.650.0510'61

A-F ae defined in Table 5-1.I R- F. Grifths, "Errors in the Use of the BrigS parameterization forAt-mospheric Dispersi,on Coeffcients," A tmospheric Envrorunent ll994),?8(17): 2s61-28s.2G. A. Briggs, Difresion Estnalion for Small Entjssions, ReporrATDL-10 (fVashin gton. DC: Air Resources, Atmospheric T\ubutence,and DiffusionLaboratory Environmental Research I_boratofies, 19?4).

TABLE A4: Transformation from percentages to probitsoaio010

2[304050d)7080m

3.724.164.484.755.005.255.525.&t6.28

?.673:174.t94.504.n5.035.285.555.886.34

2.953.821.234.534.805.055315.58s.926.41

3.123.874.264.564.V25.085.335.15.956.48

1.253.924.294.594.855.105.365.At5.99655

3.363.964.334.614.975.135.395.676.U6.64

3.454.014.364,&4.905.155.415:tL6.086.75

3.524.054.394.71.v_5.185.44si4.1.36.88

3.59 3.64.08 4.t24.42 4.454.69 4.724.95 4.n5.20 5.231.47 5.505.71 5.816.18 6.?37.O5 7.3309.75.3.1.0

7.65,58,51 8.(p.88J5.6.47.37.33I D. J. Finney, Prubit nalyss, (C:mbridge; Cambridge University Press, 19?1), p.25, Reprinted by permission.

12

7/21/2019 pslp may 2012

13/13

cBB 2093APPENDTX (CONT'D)

TABLE A-5: Probit conelations for a varieg of exposuresPrchitpararneters

Type of injury or damage Gausatlvevariable lA1FirerBurn deaths from flash fieBurn deaths from pool buroingExplosionlDaths frorn lun hemorrhageEardrum rupturesDeaths from impactInjures from impactInjuries from flying fragmentsStructural damage

Glass breakageToxic release2Ammonia deathsCabon monoxide deathsChlorine deathsEthylene oxide deaths3Hydrogen chlodde dealhsNtrogen dioxide deathsPhosgene deathsPropylene oxide dealhsSulfur dioxide deathsToluene

,.r"4trII0'ltlsllTdPOpotlJpo'po>c2rT> cr-orzeaT> cr0r> ct'or>'czT> Clnf> C,OT> ctiT>C2ST

-74.9-r4.9-77.t-15.6-46.t-39.1-n.l-23.8-18.1-35.9-37.98-829-6.L9-16.&5-L3,79-1927-7.42-Is.ot-619

?.562.566.9LL.934.424.454.262.v22.791.&53.7a.y21.02.01.43.690.511.00.41

.: eftective time duration (s)/. : effective radiatiol intens (Wlm2) : lime duralion of pool burnng, (s)I : radiation inlensitv frorn pool burning (-W/nr)" : peak overpressure (N/m2)/: irnpulse ( s/m'z)(l : concentation (ppm)1r= time nterEt (min)1 Seleeted from Frank P. I-ees , Loss I'reventiott in the Procs,s Indtstries {I-ondon: Buttiworths, 19S6), p. 20S.ZCCPS. Gndelircs for Consequence Analysis of Chemicol Releasas (New York: .&rnerican Institute of Chen'rical Engi-neers, 199), p.254rRichard lV. Pur8h,'Quantitative Evaluationoflnhalation Toxicity Hazards," in Pro ceedn of the2gth Loss PeventtonSytnposwn (American Insltute of Chemical Engineers, July 31. 15).

13