International Journal
on Marine Navigation
and Safety of Sea Transportation
Volume 1
Number 4
December 2007
421
Safety and Environmental Concern Analysis for
LNG Carriers
I. D. Er
Istanbul Technical University, Maritime Faculty, Istanbul, Turkey
ABSTRACT: The main attempt of this study is to overview and to discuss occupational safety and
environmental conciseness for the transportation of LNG with gas carriers. LNG is transported by a fleet of
157 LNG tankers of varying sizes from 18,500 m3 to 140,000 m3. This study investigates the technological
development and innovation in LNG transportation while considering safety and environmental standards and
regulations for LNG shipping. It is also originally contributing the process safety for decision making process
for the MET institutions while planning the further needs of LNG industry during the planning of their related
curricula. The further research activities could also be concentrated on quantitative risk evaluations of LNG
equipment, based on risk maintenance and reliability concepts.
1 INTRODUCTION
1.1 LNG Definition
LNG is the common acronym for “Liquefied Natural
Gas”. Natural gas is a mixture of gases that is
produced with or without oil in gas and/or oil fields
and consists primarily of methane. Liquefaction of
methane is achieved by cooling the gas to below
minus 160°C under normal atmospheric pressure.
Natural gas in liquid form is some 600-620 times
less in volume than its gaseous equivalent. The
actual percentage of methane in the natural gas
depends on the characteristics of the oil field where
it is produced.
1.2 World Energy Demand and Supply
World energy production relative with the demand
and supply intention has a great significance on the
determination of usage and transportation. Therefore
Figure 1 illustrates the world energy production in
2005 to give an idea on the change of energy
supply-demand and how the LNG takes a significant
portion in the world total energy production (BP,
2006). When the world energy production in 1990’s
analyzed, similar distribution among the different
kinds of energy production still remains with only
slight differences and increase in: oil 40%, gas 23%,
coal 28%, nuclear 7% and hydroelectric 2% (U.S.
Energy Information Administration, 2005).
It would seem that production share changes in 15
years have been quite insignificant. However,
considering the very large figures involved in the
total world produced energy, even a variation of 1 %
percent is noticeable. The above data clearly indicate
that there is a clear trend of increase of the “clean”
sources of energy (gas and water) and a decrease of
the “dirty” sources (oil and coal), while the nuclear
remains almost constant (U.S. Energy Information
Administration, 2005). This trend appears more
evident comparing the rate of increase of the world
energy consumption with the rate of increase of the
various types of fuels for the 15 years period
between 1991 and 2005 (BP, 2006).
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WORLD ENERGY PRODUCTION ON 2005
37%
23%
28%
6%
6%
Oil
Natural Gas
Coal
Nuclear Energy
Hydro-electricity
Fig. 1. Energy source production rates (BP, 2006)
1.3 LNG Supply and Demand
Up to 1970, almost all natural gas was transported
from the producing countries to the consuming
countries via pipelines. Pipelines are still used to
transport the majority of natural gas today,
particularly in Europe and United States. Figure 2
respectively illustrates LNG Trade by Exporting
Country (BP, 2006). This figure is also useful to give
an idea of the dimensions, the trends, the routes of
gas and LNG in the world.
Fig. 2. LNG trade depending upon the demand of exporting
countries
Fig. 3. World LNG trade expansion
Figure 3 indicates how the transportation of LNG
has increased for the last ten years, since 1996 and
continuing up to the end of 2006 comparing with the
existing pipelines and the maritime transportation
(BP, 2006).
2 WORLD LNG SHIPPING CAPACITY
According to LNG Shipping Solutions, number of
LNG tankers were in operation worldwide as of End
2006 shown in Figure 4,: 16 ships with a capacity of
less than 50,000 cubic meters, 21 in the 50,000 to
120,000 cubic meters range, and 120 larger than
120,000 cubic meters (BP, 2006). Fifty-five ships are
under construction, of which 46 are designed to
carry at least 138,000 cubic meters of LNG
(equivalent to 2.9 Bcf of natural gas). Much larger
ships with 250,000 cubic meters of capacity
(equivalent to 5.3 Bcf of natural gas) are under
consideration, but may not be compatible with all
existing LNG terminals. The addition of new ships
to the fleet will raise total fleet capacity 44 percent
from 17.4 million cubic meters of liquid (equivalent
to 366 Bcf of natural gas) in October 2003 to 25.1
million cubic meters of liquid (equivalent to 527 Bcf
of natural gas) in 2006.
Shipping accounts for 10 to 30 percent of the
delivered value of LNG (depending on the distance
from the reserves to the market), compared with less
than 10 percent for oil, because of the relatively high
cost of manufacturing LNG tankers. Tankers
currently cost $150 to $160 million for a 138,000-
cubic-meter ship, more than double the price of a
very large crude oil tanker which carries 4 to 5 times
as much energy. One reason for this high cost is that
LNG ships require expensive, insulated cryogenic
containment for the cargo.
Fig. 4. LNG fleet expansion statistics
Only thirteen shipyards in the world currently
build LNG tankers: five in Japan; four in Korea,
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three in Europe and one in China. However, India,
and Poland are planning to develop LNG tanker
construction capabilities in their shipyards (U.S.
Energy Information Administration, 2005).
3 SAFETY AND ENVIRONMENTAL
PROTECTION FOR LNG OPERATIONS
3.1 LNG Hazardous and Mitigation
The potential hazards of most concern to operators
of LNG facilities and surrounding communities flow
from the basic properties of natural gas. LNG
hazardous and its consequences to assure safety and
to prevent environmental pollution are subdivided
into four categories. These are the primary
containment; secondary containment, safeguard
systems, and separation distance provide multiple
layers of protection (American Bureau of Shipping,
2000). These measures provide protection against
most hazards associated with LNG.
Primary containment is the first and most
important requirement for containing the LNG
product. This first layer of protection involves the
use of appropriate materials for LNG facilities as
well as proper engineering design of LNG containers
onshore, offshore, and on LNG ships. LNG storage
containers are specially designed, constructed,
installed, and tested to minimize the potential for
failure. The containers are designed to: safely
contain the liquid at cryogenic temperatures, permit
the safe filling and removal of LNG, permit boil-off
gas to be safely removed, prevent the ingress of air,
reduce the rate of heat input consistent with
operational requirements, and prevent frost heave,
withstand the damage leading to loss of containment
arising from credible factors, operate safely between
the design maximum and minimum pressures,
withstand the number of filling and emptying cycles
and the number of cool-down and warming
operations that are planned during the design life
(ABSG Consulting Inc., 2004).
Secondary containment ensures that if leaks or
spills occur at the LNG facility, the LNG can be
fully contained and isolated. In many installations, a
second tank is used to surround the LNG container
and serves as the secondary containment. Secondary
containment systems are designed to exceed
the volume of the LNG container for onshore
installations; dikes surround the LNG container to
capture the product in case of a spill. Secondary
containment should be designed to minimize the
possibility of accidental spills and leaks endangering
structures, equipment, adjoining property, or
adjacent waterways. NFPA 59A requires that LNG
containers be provided with a natural barrier, dike
impounding wall, or combination to contain a leak
or spill of LNG (National Federal Protection
Agency, 2001). Additionally, a drainage system can
be used to remove the LNG to a holding area where
the LNG can vaporize safely. NFPA 59A provides
guidance on the location and sitting of LNG
containers from adjacent property lines, equipment,
and other facilities at terminals. EN 1473 is
performance based in its approach to sitting and
location. The outcomes of a risk assessment can be
used to justify the distance and locations specified
(EN 1473, 1996). On offshore facilities, trenches are
used to channel LNG flow to a safe location where
the LNG can vaporize under controlled conditions.
Safeguards’ goal is to minimize the frequency
and size of LNG releases both onshore and offshore
and prevent harm from potential associated hazards,
such as fire. For this level of safety protection, LNG
operations use technologies such as high level
alarms and multiple backup safety systems, which
include Emergency Shutdown (ESD) systems.
Fire and gas detection and fire fighting systems
all combine to limit effects if there is a release.
The LNG facility or ship operator then takes action
by establishing necessary operating procedures,
training, emergency response systems, and regular
maintenance to protect people, property, and the
environment from any release (SIGTTO, 2003).
There are many safeguards required by
regulations. These can be summarized in terms of
detection, emergency shutdown and fire protection.
The ability to detect a leak of LNG or natural gas is
important for emergency response actions to begin.
Hydrocarbon gas detectors can be used to detect a
natural gas leak if properly located. Hydrocarbon
detectors need to be located higher than suspected
leak points and placed where natural gas can be
expected. Hydrocarbon detectors are generally
located over vaporizers, in metering stations, and
in cargo tanks where natural gas is stored and
processed. Hydrocarbon detectors will not detect
a LNG spill because vapors are insufficient.
Temperature detection is used to sense a spill of
LNG. The set point for the alarm is set low enough
that ambient freezing conditions do not cause a fault
trip. Temperature detection is located where spills
can occur. In some instances, the temperature
detection is used to activate a high expansion foam
system that helps control vaporization.
ESD Systems are required to shut off operations
in the event certain specified fault conditions or
equipment failures occur. They should be designed
to prevent or limit significantly the amount of LNG
and natural gas that could be released. The ESD
systems should be designed such that a spill or leak
does not add to or sustain an emergency condition.
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The ESD systems should fail to a safe condition.
NFPA 59A is pseudo–performance based when it
comes to fire protection. Because of the wide range
in size, design, and location of LNG facilities, NFPA
59A does not identify specific details of fire
protection. The extent of fire protection should be
determined by an evaluation based on sound fire
protection engineering principles, analysis of local
conditions, hazards within the facility, and exposure
to or from other property. The evaluation should, as
a minimum, consider (Mizner & Eyer, 1983):
The type, quantity, and location of equipment
necessary for the detection and control of fires,
leaks, and spills of LNG, flammable refrigerants,
or flammable gases.
The type, quantity, and location of equipment
necessary for the detection and control of
potential non-process and electrical fires.
The methods necessary for protection of the
equipment and structures from the effects of fire
exposure.
Fire protection water systems.
Fire extinguishing and other fire control
equipment.
All LNG terminals are required to be provided
with a fire water system. The amount of water will
be determined by the number of fire protection
systems and demand for these systems. The duration
of water supply is typically not a problem because
LNG terminals are generally located next to water.
Fire protection systems for LNG facilities consist
of water spray, high expansion foam, dry chemical,
or a combination of these. Water spray is used to
control radiant heat exposure on equipment and
structures. LNG pool fires are neither controlled nor
extinguished by water. In fact, the application of
water on the LNG surface will increase the
vaporization rate, and thus there is the potential
to increase burning rate with negative consequences
on fire control. The use of water spray systems
should be carefully considered in the design.
High expansion foam can be used to control
the vaporization rate on the surface of an LNG spill.
The foam works by warming the LNG vapors and
reducing the fire thermal radiation back to the LNG
pool, thereby reducing the LNG burning rate.
High expansion foam is generally provided for
impounding areas or where a LNG pool can form.
Dry chemical extinguishing systems are used to
extinguish an LNG fire. The dry chemical should be
applied such that the surface is not agitated, which
will allow additional vaporization. Dry chemical
systems have been installed at unloading area, LNG
pumps, boil-off compressors, and LNG vaporizers.
Separation (Safety Excursion Zones) LNG facility
designs are required to maintain separation distances
to separate land-based facilities from communities
and other public areas. National regulations have
always required that LNG facilities be sited at a safe
distance from adjacent industries, communities, and
other public areas. Also, safety zones are established
around LNG ships while underway in territorial
waters of a nation and while moored. The safe
distances or exclusion zones are based on LNG
vapor dispersion data, thermal radiation contours,
and other considerations as specified in regulations
(Paik et al. 2001). Most hazard analyses for
LNG terminals and shipping depend on computer
models to approximate the effects of hypothetical
accidents. Regardless of the cause, the formation of
a methane/ air mixture and its movement depends on
the quantity of the spill, whether on land or water,
atmospheric stability, wind direction and velocity,
and temperature of the atmosphere and water.
3.2 Emergency Procedures for Low Temperature
Effects and Pressure
Spillage of LNG may lead to the following dangers:
Fire starting from the vapor, which is generated
during the spillage, brittle fractures of the ship
structures, which are in contact with the spilled
LNG, accidental contact of LNG or its vapor with
ship personnel. However, should a spillage be
detected on a LNG ship the measures to be taken are
the following: Stopping the flow, avoiding contacts
with liquid and vapor, extinguish all possible
sources of ignition, flooding the area where the
spillage happened with a large amount of water in
order to disperse the spilled LNG and to prevent the
risk of brittle fracture.
As liquefied gas cargoes are often shipped at low
temperatures it is important that temperature sensing
equipment is well maintained and accurately
calibrated. Hazards associated with low temperatures
include (Bainbridge, 2003):
Brittle Fracture: Most metals and alloys become
stronger but less ductile at low temperatures (i.e. the
tensile and yield strengths increase but the material
becomes brittle and the impact resistance decreases)
because the reduction in temperature changes the
material’s crystal structure. Normal ship building
steels rapidly lose their ductility and impact-strength
below 0°C. For this reason, care should be taken to
prevent cold cargo from coming into contact with
such steels, as the resultant rapid cooling would
make the metal brittle and would cause stress due to
contraction. In this condition the metal would be
liable to crack. The phenomenon occurs suddenly
and is called ‘brittle fracture’. However, the ductility
and impact resistance of materials such as
aluminum, austenitic and special alloy steels and
nickel improve at low temperatures and these metals
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are used where direct contact with cargoes at
temperatures below -55° C is involved.
Spillage: Care should be taken to prevent spillage
of low temperature cargo because of the hazard to