1

Assessment of Hydrocarbon Explosion and Fire Risks

by

Professor Jeom Paik

The LRET Research CollegiumSouthampton, 11 July – 2 September 2011

Assessment of Hydrocarbon Explosion and Fire Risksin Offshore Installations:

Recent Advances and Future Trends

Prof. Jeom Kee Paik, DirectorThe LRET Research Center of Excellence

at Pusan National University, Korea

New Paradigm for Robust Design of Ships and Offshore …

Design Formula

Experimental InvestigationExperimental Investigation

Past Experience First PrinciplesFirst Principles

Deterministic ProbabilisticProbabilistic

Mathematical Algorithm

( )21 1

!lim! !

m n

xi j

nr n rx x

ζφαβγε η→∞

= = −− +∑∑

Limit States/RiskLimit States/RiskAllowable Stress

EngineeringEngineering

Various Ocean Environmental Phenomena

Traditional Future

Trend in Offshore Oil & Gas Production Systems• Fixed type in shallow waters Floating type in deep waters• Ship-shaped offshore unit, Semi-sub, Spar, TLP• Pipeline infrastructure Multiple functions such as

production, storage and offloading

Vessel (hull), topsides (process facility), mooring, risers/flow lines, subsea, and export system

FPSO for Oil and Gas Production

Oil/Gas Leak Resulting in Explosion and Fire

Source: HSE

• 6th July 1988, UK• 167 people killed• Property damage of 1.4billion US$• Risk based engineering became mandatory since the Pipe Alpha accident

Pipe Alpha Accident

• 20th April 2010, Gulf of Mexico• 11 people killed, 17 people wounded• Environmental damage of approx. 30 billion US$

Deepwater Horizon Accident

Oil spill

• Hydrocarbons can explode through ignition when combined with an oxidiser (usually air). Thus, when the temperature rises to the pointat which hydrocarbon molecules react spontaneously to an oxidiser,combustion takes place. This hydrocarbon explosion causes a blastand a rapid increase in overpressure.• Fire is a combustible vapour or gas that combines with an oxidiser in a combustion process that is manifested by the evolution of light, heat,and flame.• The impact of overpressure from explosions and that of elevatedtemperature from fire are the primary concern in terms of the actions thatresult from hazards within the risk assessment and managementframework.

Hydrocarbon Explosions and Fires

Gas burns

Volume increases

Gas flow increases

Turbulence

Gas expands

Larger volume pushes unburnt gas ahead

Unburnt gas pushed around obstacles

Flame front wrinkled, burning surface greater, increased mixing, faster burning

BLAST

CONGESTION? CONFINEMENT?

Mechanism of Gas Explosion – Depending on Topology and Geometry

Factors Affecting Explosions and Fires

· Wind direction· Wind speed· Leak rate· Leak direction· Leak duration· Leak position (x)· Leak position (y)· Leak position (z)· Type of oil or gas (molecules)· Concentration ratio· Temperature of oil or gas(LNG Cryogenic -163 degree C)

Risk Based Design Process

Hazard identification (Step1)

Riskassessment (Step2)

Decision makingrecommendations (Step5)

Risk control options (Step3)

Cost benefit assessment (Step4)

What is Risk? How to Manage Risk?

i ii

R F C= ×∑• Asset risk

- Damage to structures and equipment- Duration of production delay (downtime)

• Environmental risk- Amount of oil that spills out of the offshore installation

• Personnel risk- Loss of life

Trends in Risk Assessment

Qualitative Quantitative

Past Experience Simulation

Experiment,

Deterministic Probabilistic

Specific Scenarios All Possible Scenarios

API Procedure for Risk-based Design

Doesthe facility

meet screeningcriteria?

Establish performancecriteria

Implement measures toreduce fire and blast risk

Arenominal load cases

applicable?

Assess impact on safetycritical elements

Areperformancecriteria met?

Assessment completefor the facility

Consider fire and blast riskEvent-by-Event

Risk matrix

Reconsideror modify concept

or reassess risk withmore rigorous

approach

Modify or select newconcept or reassess risk

Implement measures toreduce fire and blast risk

Risk matrix

Assess load andresponse for the event

Areperformancecriteria met?

Are furtherrisk reduction options

available?

Assessment completefor the event

Assessment completeensure good practice

Redesign

Yes

No

Yes

No

Yes

Yes

No

Low

Low

Yes

No

NoYes

Medium or Higher

Medium or Higher

Method 1Design

according toguidances is

sufficient if lowconsequencesare expected

Method 2Possibility to

omit load assessmentin certain cases

Method 3Scenario based

load andconsequenceassessment

Simulation-based Procedure for Risk-based Design

Dead and live loads Nominal loads Design guidance

System description

Definition of scenarios

Loads assessment

Design load

Consequence Frequency

Risk evaluation

Risk acceptable Risk unacceptable

Design complete

Mitigation

Redesign

Performanceacceptance

criteria

Riskacceptance

criteria

A

B

A: Limit states based designB: Risk based design

Joint Industry Projects

EFEF JIP - 27th JIP in the WorldExplosion and Fire Engineering of FPSOs

Coordinators:- Pusan National University, Korea- Nowatec AS, Norway

Partners:- DSME, SHI, HHI, ABS, KR, LR- Gexcon, CompuIT, USFOS, UK HSE, NTUA

Quantitative Gas Explosion Risk Assessment and Management (1/2)

Selection of credible scenarios involving PDF parameters of

leak and environment conditions

Selection of credible scenarios involving PDF parameters of

gas cloud conditionE

xplo

sion

freq

uenc

y of

exc

ceda

nce

(per

FPS

O y

ear)

Overpressure (MPa)0 0.02 0.04 0.06 0.08 0.1

0.00001

0.0001

0.001

0.01Large cylindrical vessels (Point 171 )

CAD modelCFD model

Gas dispersion analysis

Explosion CFD simulation Design loads with exceedance curve Nonlinear consequenceanalysis under explosion

EFEF JIP Procedure for Explosion Risk Assessment and Management (2/2)

Latin hypercube sampling technique

EFEF JIP Fire Risk Assessment and Management (1/2)

Selection of credible scenarios involving PDF parameters of

leak and environment conditions

EFEF JIP Procedure for Fire Risk Assessment and Management (2/2)

CAD modelCFD model

Fire CFD simulationDesign loads with exceedance curve

Nonlinear consequenceanalysis under fire

Temperature(K)

Exc

eeda

nce

fire

freq

uenc

y(pe

rFP

SO y

ear)

200 400 600 800 1000 1200

0.00001

0.0001

0.001

0.01

0.1

Mean temperature (Point20 and Point31)

Mean temperature (Point41 and Point52)

Latin hypercube sampling technique

Applied Example: VLCC Class FPSO Topsides

Effect of Gas Cloud Volume on Maximum Overpressure – Comparison between EFEF JIPand Existing FPSO Practices

Ove

rpre

ssur

e (M

Pa)

Equivalent volume (m3)0 2000 4000 6000 8000 10000 12000

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

FPSO AFPSO B

EFEF JIP

Exp

losi

on fr

eque

ncy

of e

xcee

danc

e(p

er F

PSO

yea

r)

Overpressure (MPa)0 0.02 0.04 0.06 0.08 0.1 0.12

0.00001

0.0001

0.001

0.01

Top process deck(Point 226 & 274)

Solid process deck(Point 76 & 124)

Above the middle process deck(Point 161)

Process decks

Design Explosion Loads with Exceedance Curves

0 0.02 0.04 0.06 0.08 0.10 0.12 0.14

0

0.02

0.04

0.06

0.08

0. 10

0.12

0.14R

isk

acce

pted

load

FPSO

C, D

(MPa

)

Risk accepted loadEFEF JIP (MPa)

EFEF JIP vs. FPSO CEFEF JIP vs. FPSO D

Design Explosion Loads – Comparison between EFEF JIP and Existing FPSO Practices

Temperature(K)

Exc

eeda

nce

fire

freq

uenc

y(pe

rFP

SO y

ear)

280 300 320 340 360 380

0.0001

0.001

0.01

0.1

0.00001

Separation train 2(Point 77)

Oil inlet(Point 96)

Gas compressor(Point 75)

Surrounding separation train1

Design Fire Loads with Exceedance Curves

Nonlinear Structural Consequence Analysis – Escape Route

Trends in Risk Assessment

Qualitative Quantitative

Past Experience Simulation

Experiment

Deterministic Probabilistic

Specific Scenarios All Possible Scenarios

CFD Explosion Simulations

(barg)

Gas Explosion Tests with or without Water Sprays (1/2)- Importance of Risk Management

Source: © The Steel Construction Institute, Fire and Blast Information Group

Without water sprays With water sprays

0.0

2.0

1.5

1.0

0.5

700100 200 300 400 500 600

Time (ms)

TNO PI-10, Test 10, LDN NozzlesTNO PI-10, Test 11, MV57 NozzlesTNO PI-10, Test 12, No Deluge

Source: © The Steel Construction Institute, Fire and Blast Information Group

Gas Explosion Tests with or without Water Sprays (2/2)- Importance of Risk Management

Explosion and Fire Test Facilities under Construction in Korea