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Consequences on port facilities of
a tanker explosion
P. L. Metropolo1 & A. E. P. Brown2
1Rhodia, Technology Research Centre, Brazil
2Polytechnic College, University of Sao Paulo, Brazil
Abstract
The explosion scenario of a 30,000 m3 naphtha tanker that lay at anchor in port is
simulated. The tanker geometry is enforced by a double steel plate, with the
hazardous gas storage in the middle tanker containment. Baker’s method was
used to determine overpressures levels and damage distance from a potential
confined vapour cloud explosion. The people vulnerability study at the port
facility vicinity is also elaborated by using Probit equations. The explosion can
be started by a simple electrostatic spark, human error, by sabotage or by acto of
terrorism. Safety measures are recommended.
Keywords: risk analysis, fire, explosion, hazardous materials transportation,
safety.
1 Introduction
Globalization has promoted an increase in the amount of hazardous materials
transportation by road, air or sea. Great tankers transporting oil, petrochemical
products and flammable gases, discharge these products in ports all over the
world. At peace time this is a normal activity, but in conflict areas this simple
activity may represent a great danger to port facility activities, its vicinity and
materials that can result in a catastrophe. Besides process safety procedures, port
security activities have also to be enforced in order to guarantee port safety. In
Brazil, the International Ship and Port Security (ISPS) code regulations are
attended to enhance maritime security, according to the International Maritime
Organization (IMO) Diplomatic Conference of December 2002.
As accidents can happen, prevention studies can be performed to figure out
fire or explosion damages extension. Risk analysis is a strong tool to help port
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©2006 WIT Press
WIT Transactions on The Built Environment, Vol 87,
Structures Under Shock and Impact IX 279
doi:10.2495/SU060281
safety and security. Consequence and vulnerability analyses are part of the risk
analysis methodology [1, 2]. Baker’s method [3] was applied to define physical
impacts of the potential confined vapour cloud explosion. A vulnerability study
was performed by using Probit [4] calculations to define the impact to port
facility employees and to the near-by community. Finally, mitigation actions are
recommended.
2 Risk analysis
Risk analysis methods are used to evaluate the confined explosion severity of
naphtha reservoir installed inside a tanker. For confined vapour cloud explosions
(CVCE) calculations model, we used Baker’s method [3], which is a
conservative approach, with added elements of the TNO multi-energy method
[3]. Details of the method will not be described here. The method present
results of the overpressure and impulse estimates due to the blast waves from the
cylindrical reservoir rupture from pressurized gas, located at ground level. A
ground level correction is also performed for the case studied. The method
depends on the phase of the reservoir contents, its boiling point at ambient
pressure, its explosion scenario critical and local temperatures and assumes that
the flammable product combustion is complete.
2.1 Explosion scenario description
For the confined explosion scenario, it is assumed that the explosion will occur
when the naphtha concentration inside the reservoir reaches the low flammable
limit of 1.4% v/v. To the calculations, naphtha is considered as n-pentane. The
maximum explosion pressure of n-pentane in air of 8.7 bar gauge [5] is
considered in the calculations. The naphtha reservoir geometry is 12 m high
with a squared bottom of 10 m. The gaseous phase volume of the naphtha
reservoir is 1,200 m3.
2.2 Calculation of the explosion energy
To calculate the explosion pressure attenuation of the naphtha reservoir, it is
considered the naphtha combustion reaction presented in equation 1:
C5H12 + 8O2 + N2 -----Æ 5CO2 +
6H20 + N2 (1)
1 8 (0,79/0,21) x 8 5 6 (0,79/0,21) x 8
The naphtha combustion heat (
∆
H
) is 10,750 kcal/kg. The internal energy
varies according to equation 2:
UHPV
∆
=∆ −∆ (2)
The moles number variation before and after the combustion is 2. The naphtha
mass inside the reservoir will be calculated when it reaches the low flammable
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280 Structures Under Shock and Impact IX
limit of 1.4% v/v (40,570 mg/m3). For a reservoir of 1,200 m3 this corresponds
to 48.7 kg of naphtha. The internal energy variation corresponds to the liberated
energy from the explosion, which is shown in equation 3.
()
()()
89
10, 750 48.7 1, 000 1.987 373 2
5.23 10 2.2 10
kcal cal
Ukg
kg kcal
xcal xJ
∆=− − =
=
(3)
The explosion energy must be corrected to the ground reflection effect, because
the naphtha reservoir is not above ground level. For this reason, the explosion
energy must be duplicated, resulting in 4.4 x 10
9
J. The input data to the Baker’s
method is shown in Table 1.
Table 1: Input data1.
Description Value
Flammable substance Naphtha ( n-pentane )
Local temperature (
o
C) 22.7
Tanker gaseous volume (m
3
) 1,200
3 Results
The Baker’s method calculation results are shown in Table 2. The resulting
explosion overpressure attenuation is presented in Figure 1.
Table 2: Explosion overpressure results.
Physical Impact Description Value
Naphtha Flammable Mass (kg) 48.7
Distance to 3.84 kgf/cm
2
20 m
Vapour Cloud Explosion Distance to 0.53 kgf/cm
2
40 m
(VCE) Distance to 0.3 kgf/cm
2
60 m
Distance to 0.16 kgf/cm
2
100 m
Distance to 0.07 kgf/cm
2
160 m
1 kgf/cm
2
= 10
5
Pascal.
3.1 Vulnerability results
Eisenberg et al. [4] report the following Probit equations to:
Lung haemorrhage: Pr = -77.1 + 6.91 x ln ( P ) (4)
Eardrum rupture in humans: Pr = -15.6 + 1.93 x ln ( P ) (5)
where: P = peak overpressure, in Pascal or kgf/cm
2
.
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©2006 WIT Press
WIT Transactions on The Built Environment, Vol 87,
Structures Under Shock and Impact IX 281
0
50000
100000
150000
200000
250000
300000
350000
400000
450000
0 50 100 150 200
Distance to the Centre of the Explosion ( m )
Overpressure (Pascal
)
Figure 1: Overpressure attenuation graphic.
Table 3: Vulnerability results.
Effect Overpressure
(kPa)
Probability
(%)
Distance
(m)
Lung haemorrhage 100 1 36
Eardrum rupture 100 95 36
Eardrum rupture 13.8 1 130
4 Mitigation and conclusions
The port facility supervision work is very important to avoid security violations
such as acts of terrorism or sabotage. Closed circuit TV (TVCC) with backup
installed on port facility as well as intrusion supervision system are reliable
systems against undesirable actions. On the process side, static electricity
represents a hazard. Equipment must be earthed and the area of the tanker
discharge must be electrically classified according to IEC norm 60079-10 [6].
To enhance port facility safety, the following documents must be prepared:
risk analysis, security assessment, security plan and to appoint the port facility
security officer.
The physical impact of the naphtha tanker explosion on port facility is
equivalent to the mass of 940 kg TNT.
From Figure 1, it is concluded that the safe distance is normally considered at
the overpressure peak of ca. 0.02 kgf/cm2. At this level, the probability 95% of
no serious damage is 320 m from the tanker. At overpressure levels of
0.16 kgf/cm2 reparable damages to structures occur. Above this level,
overpressure peaks results in the total destruction of buildings. With regards to
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WIT Transactions on The Built Environment, Vol 87,
282 Structures Under Shock and Impact IX
human safety, the probability of lethality of 1% or 95% eardrum rupture from
direct blast are reached at 36 m from the tanker and up to the distance of 130 m
from the tanker, people can be thrown down to the ground that can cause
secondary injuries.
References
[1] Lees, F.P. (1996) Loss Prevention in the Process Industries, 2nd ed, v.1/2,
Butterworth, Oxford, UK.
[2] Brown, A.E.P. (2004) Risk Analysis Study, S. Paulo/SP, Brazil.
[3] Yellow Book (1997) Methods for the Calculation of Physical Effects,
Committee for the Prevention of Disasters, CPR 14E, TNO, 3rd ed, The
Hague, Netherlands.
[4] Eisenberg, N.A., C.J. Lynch and R.J. Breeding (1979) Vulnerability
Model: A Simulation System for Assessing Damage Resulting from
Marine Spills, Dept. of Transportation, Washington DC, USA.
[5] NFPA 68, (2002) Guide for Venting of Deflagrations, National Fire
Protection Association, Quincy, MA, USA.
[6] IEC 60079-10 (2002) Electrical apparatus for explosive atmospheres -
Classification of hazardous areas, 4th ed, EC.
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©2006 WIT Press
WIT Transactions on The Built Environment, Vol 87,
Structures Under Shock and Impact IX 283
