W13C - Fire and Explosion(5) - Explosion Risk Analysis

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Transcript of W13C - Fire and Explosion(5) - Explosion Risk Analysis

  • Korea Advanced Institute ofScience and Technology

    OSE551 Reliability and Risk Analysis for Offshore Plants

    Daejun CHANG ([email protected])

    Division of Ocean Systems Engineering

    Fire and Explosion- Explosion Risk Analysis

  • -1- Ocean Systems EngineeringProf. Daejun CHANG

    FundamentalsFundamentals

  • -2- Ocean Systems EngineeringProf. Daejun CHANG

    Fire (Explosion) TriangleFire (Explosion) Triangle

    Fuel

    Ignition source

    Air (oxygen)

    Fire/Explosion

    Sparks, flames, static electricity, heat

    Since air always exists for open-air explosion, we focus on the coexistence of the fuel and ignition source.

  • -3- Ocean Systems EngineeringProf. Daejun CHANG

    Concept of Explosion Risk AssessmentConcept of Explosion Risk Assessment

    Risk = Consequence x FrequencyConsequence = overpressure Frequency f = fcloud x fign

    fcloud : Frequency that the cloud exists at the point.fign: Frequency that the ignition source exists at the point.

  • -4- Ocean Systems EngineeringProf. Daejun CHANG

    Some realSome real--world issuesworld issues

    The cloud size is changing with time. Leak Dispersion Cloud formation Dilution by air ESD (process isolation) and EDP (blowdown) changes the leak

    rate.

    The ignition frequency is changing with time. Ignition frequency depends on the number of equipment,

    electrical instrument, hot work etc. Upon detection of the gas, the ESD system stops the electrical

    supply to the system (electric isolation).

    In consequence, the explosion risk changes with time.

  • -5- Ocean Systems EngineeringProf. Daejun CHANG

    Time DependenceTime Dependence

  • -6- Ocean Systems EngineeringProf. Daejun CHANG

    Leak rate with timeLeak rate with time

    Time, s

    Leak rate, kg/s

    On set of leak

    Gas detection &Process isolation

    Emergency depressurization(blowdown)

  • -7- Ocean Systems EngineeringProf. Daejun CHANG

    Gas volume with timeGas volume with time

    Time, s

    Leak rate, kg/sGas volume, m3

    On set of leak

    Gas detection &Process isolation

    Emergency depressurization(blowdown)

    Dilution by ventilation

  • -8- Ocean Systems EngineeringProf. Daejun CHANG

    Ignition density with timeIgnition density with time

    Time, s

    Leak rate, kg/sGas volume, m3Ignition density

    On set of leak

    Gas detection &Process isolation

    Emergency depressurization(blowdown)

    Dilution by ventilation

  • -9- Ocean Systems EngineeringProf. Daejun CHANG

    Explosion frequency with timeExplosion frequency with time

    Time, s

    Explosion frequency Gas volume, m3Ignition density Small because of low ignition density

    Small because of low cloud size

  • -10- Ocean Systems EngineeringProf. Daejun CHANG

    Cloud Size EstimationCloud Size Estimation

  • -11- Ocean Systems EngineeringProf. Daejun CHANG

    Cloud size estimationCloud size estimation

    Do we have to estimate the cloud size for all leak rates? 8 representative leak rates by NORSOK Standard Z-013:

    0.75, 1.5, 3, 6, 12, 24, 48, 96 kg/s

    Do we have to simulate all the leak rates? Usually, some of them are simulated and the others

    interpolated Simulated: 0.75, 1.5, 3, 6, 12, 24, 48, 96 kg/s Interpolated: 0.75, 1.5, 3, 6, 12, 24, 48, 96 kg/s

    What situation do we have to simulate? All the scenarios including ESD and EDP?

    Numerous simulation cases Frozen cloud assumption!

  • -12- Ocean Systems EngineeringProf. Daejun CHANG

    Frozen cloud assumptionFrozen cloud assumption

    Time, s

    Leak rate, kg/sGas volume, m3

    On set of leak

    Leak rate

    The cloud size is just dependent on the leak rate at the moment.That implies the cloud size is independent of its history.Is it justifiable?

    Cloud size

  • -13- Ocean Systems EngineeringProf. Daejun CHANG

    Effect of Wind and Leak DirectionEffect of Wind and Leak Direction

  • -14- Ocean Systems EngineeringProf. Daejun CHANG

    Combined effects of leak direction and windCombined effects of leak direction and wind

    The leak has direction as well as rate. Leak to the inside vs. Leak to the outsideThe former is the more destructive.

    Wind has both magnitude (speed) and direction High wind speed

    - High dilution rate- Wider dispersion

    Wind direction- The effect of the wind direction depends on the leak position.

  • -15- Ocean Systems EngineeringProf. Daejun CHANG

    An approach to the combined effectsAn approach to the combined effects

    As the leak rate, we cannot simulate all the cases depending on Leak rate Leak direction Leak position Wind direction Wind speed

  • -16- Ocean Systems EngineeringProf. Daejun CHANG

    An approach to the combined effectsAn approach to the combined effects

    Approaches There are Nleak,pos leak positions. For each position, there are Nleak,dir leak directions. For each leak direction, there are Nleak,rate reference leak rates. For each rate, there are Nwind,dir wind directions. For each wind direction, there are Nwind,spd wind speed.

    For example: Total simulation cases = Nleak,pos x Nleak,dir x Nleak,rate x Nwind,dir x Nwind,spd= 4 2 8 3 5 = 960= 4 2 4 3 2 = 192

    if interpolation is used based on the frozen cloud assumption

  • -17- Ocean Systems EngineeringProf. Daejun CHANG

    An approach to the combined effectsAn approach to the combined effects

    Simulation and interpolationLeak position: Deck 1 (D)

    Leak direction: North (N)Wind Direction: North-South (NS)

    Frequency 0.071 0.0064 0.005 0.0036 0.0022 0.0008 0.0003 0.0001

    Probability Leak Rate

    Wind Speed 0.75 1.5 3 6 12 24 48 96

    0.03 1.5 DNNS11 DNNS12 DNNS13 DNNS14 DNNS15 DNNS16 DNNS17 DNNS18

    0.09 4 DNNS21 DNNS22 DNNS23 DNNS24 DNNS25 DNNS26 DNNS27 DNNS28

    0.05 6 DNNS31 DNNS32 DNNS33 DNNS34 DNNS35 DNNS36 DNNS37 DNNS38

    0.02 8 DNNS41 DNNS42 DNNS43 DNNS44 DNNS45 DNNS46 DNNS47 DNNS48

    0.01 12 DNNS51 DNNS52 DNNS53 DNNS54 DNNS55 DNNS56 DNNS57 DNNS58

  • -18- Ocean Systems EngineeringProf. Daejun CHANG

    An approach to the combined effectsAn approach to the combined effects

    Simulation and interpolationLeak position: Deck 1 (D)

    Leak direction: North (N)Wind Direction: North-South (NS)

    Frequency 0.071 0.0064 0.005 0.0036 0.0022 0.0008 0.0003 0.0001

    Probability Leak Rate

    Wind Speed 0.75 1.5 3 6 12 24 48 96

    0.03 1.5 DNNS11 DNNS12 DNNS13 DNNS14 DNNS15 DNNS16 DNNS17 DNNS18

    0.09 4 DNNS21 DNNS22 DNNS23 DNNS24 DNNS25 DNNS26 DNNS27 DNNS28

    0.05 6 DNNS31 DNNS32 DNNS33 DNNS34 DNNS35 DNNS36 DNNS37 DNNS38

    0.02 8 DNNS41 DNNS42 DNNS43 DNNS44 DNNS45 DNNS46 DNNS47 DNNS48

    0.01 12 DNNS51 DNNS52 DNNS53 DNNS54 DNNS55 DNNS56 DNNS57 DNNS58

    S: Simulated cases

    S S S S

    SSSS

  • -19- Ocean Systems EngineeringProf. Daejun CHANG

    Explosion SimulationExplosion Simulation

  • -20- Ocean Systems EngineeringProf. Daejun CHANG

    Is the cloud fixed at the position for which the dispersion analysis is done? The cloud can be moved by the wind. It can also travel on its own momentum. If the leak position is changed, the cloud position will change. The cloud position is possible at any allowable place of the

    installation.

    Position of gas cloud Small cloud (low category): 5 - 9 positions Large cloud (high category): 2 - 3 positions

    Position of gas cloudPosition of gas cloud

  • -21- Ocean Systems EngineeringProf. Daejun CHANG

    Position of gas cloudPosition of gas cloud

    Small cloud Large cloud

  • -22- Ocean Systems EngineeringProf. Daejun CHANG

    It is known that the overpressure varies with the ignition position within the cloud.

    Ignition point within the gas cloud Small cloud (low category): center Large cloud (high category): 2 - 3 positions

    Ignition position within the cloudIgnition position within the cloud

  • -23- Ocean Systems EngineeringProf. Daejun CHANG

    Continuous and Discrete IgnitionContinuous and Discrete Ignition

  • -24- Ocean Systems EngineeringProf. Daejun CHANG

    Ignition densityIgnition density

    Without ignition, there is no explosion. Ignition density determines the explosion frequency.

    Time, s

    Explosion frequency Gas volume, m3Ignition density

  • -25- Ocean Systems EngineeringProf. Daejun CHANG

    Naturally there are two types of ignition sources. Continuous: the ignition source is constantly active. Discrete: the activity of the ignition source is intermittent.

    The source can be either of the two (continuous or discrete) Both of the two (continuous and discrete at the same time)

    TDIIM Time-Dependent Internal Ignition Model Developed by a JIP program led by DNV

    Continuous and discrete ignitionContinuous and discrete ignition

  • -26- Ocean Systems EngineeringProf. Daejun CHANG

    TDIIM (TimeTDIIM (Time--Dependent Internal Ignition Model)Dependent Internal Ignition Model)

    Continuous ignition Conditional probability that the gas cloud explodes if it touches the

    continuous ignition source. Discrete ignition

    Probability that the gas cloud explodes which contains the discrete ignition source

  • -27- Ocean Systems EngineeringProf. Daejun CHANG

    Discrete ignitionDiscrete ignition

    Discrete ignition Probability that the gas cloud explodes which contains the discrete

    ignition source The ignition s