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DNV-OS-A101 Safety Principles and Arrangements
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SECTION 9
Special Provisions for LNG Import and
Export Terminals
(and LNG Production Units)Sec.9
A. General
Sec.9
A 100 General
Sec.9 A
101 The following requirements apply specifically to LNG terminals.
They will be applicable to both floating and fixed installations.
Sec.9 A
102 These requirements should be considered as supplementary to
the requirements given in the main body of this document.Sec.9
B. Risk Assessment
Sec.9
B 100 General
Sec.9 B
101 With reference to Sec.2 C103,
an LNG gas terminal will be regarded as a complex and non-standard installation
and therefore will require a comprehensive safety assessment as
outlined in Appendix B. Sec.9
B 200 Hazards
Sec.9 B
201 The assessment should, as a minimum, focus on hazards that
could directly, or indirectly, result in:
| — | loss of life |
| — | major fire or explosion |
| — | loss of structural integrity or control |
| — | the need for escape or evacuation |
| — | environmental impact. |
Sec.9 B
202 The following generic hazards listed in Appendix B A500 should be considered, | — | loss of well containment (for
LNG production installations) |
| — | gas release into confined space |
| — | release of toxic or other hazardous substance |
| — | collisions |
| — | helicopter crash |
| — | structural and/or foundation failure |
| — | stability and buoyancy hazards for floating installations |
| — | dropped objects |
| — | loss of mooring, propulsion, or station keeping for
floating installations |
Sec.9 B
203 In addition to the above hazards the following specific hazards
should be considered:| — | release of cryogenic liquids |
| — | leakage of LNG onto water and possible Rapid Phase Transition
effects |
| — | loss of primary LNG containment |
| — | spread of fire that may threaten storage tank integrity |
| — | relative proximity of LNG process to storage |
| — | hazards associated with venting/flaring |
| — | hazards associated with LNG transfer |
| — | hazards associated with docking of gas carriers |
| — | hazards associated with gas carrier alongside |
Sec.9 B
204 Any additional hazards identified by the assessment should
also be addressed.
Sec.9 B
205 It may be necessary to carry out additional engineering studies
in order to determine the effects of accidental loads on the installation.
(e.g. collision analysis, blast study, ventilation under fire conditions).Guidance note:
For calculation of effects of accidental loads reference is
made to DNV RP C204, Design against Accidental Loads.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.9
C. Arrangement
Sec.9
C 100 General
Sec.9 C
101 The LNG storage area, LNG processing area and the vent/flare
system shall be arranged in order to minimize the possibility of
an accidental event in one area impinging on another area or on
the Living Quarters, or of affecting escape and evacuation.
Sec.9 C
102 Safe separation may be achieved by ensuring sufficient distance
between areas or by installation of physical barriers (e.g. fire/blast
walls) to prevent escalation from one area to another.
Sec.9 C
103 Where a firewall is required to perform its function following
an explosion, it should retain its fire technical properties. Its
ability to do so should be documented by reference to test results
Sec.9 C
104 For floating installations arrangements common for gas carriers
may be used. Additional requirements due to the presence of gas
processing plant may also need to be specified.
Sec.9 C
105 For floating installations, ventilation inlets and outlets
for rooms with essential equipment shall be located in such positions
that closing devices to ensure watertight integrity will not be
necessary. This includes such rooms as: fire pump room, emergency
generator room, emergency switchboard rooms and control stations. Sec.9
C 200 Location of equipment
Sec.9 C
201 On floating installations consideration should be given to
design of equipment and control systems to accommodate vessel motions.
This may for example involve location of tall equipment close to
the centreline of the floating installation
Sec.9 C
202 Where an installation may be exposed to green seas, protection
of safety systems, safety equipment and control lines shall be considered
in addition to structural design aspects.
Sec.9 C
203 Location of equipment should take account of the predominant
wind direction and dispersion characteristics of potential leaks,
in order to safeguard areas of importance for safety.
Sec.9 C
204 Equipment should be located or oriented in such a way as to
minimize congestion and confinement that could increase potential
overpressure in the event of an explosion.
Sec.9 C
205 Equipment with potential for high energy failure (e.g. gas
turbines) should be located such that possible damage or escalation
effects will be minimized
Sec.9 C
206 Pressurised equipment for processing of gas/LNG should
normally not be located within the structure critical for floatability
of floating installations
Sec.9 C
207 If equipment is to be placed above storage tanks, the possible
hazards associated with leakage, fire, explosion, and physical collapse
as a result of an accidental event in either one of the areas should
be considered.
Sec.9 C
208 Where a process deck is provided above a storage area, sufficient
space should be provided to permit access for inspection and maintenance,
to permit access for fire fighting, and to provide for sufficient ventilation
to prevent any confinement of a gas leak. Sec.9
C 300 Location of storage tanks
Sec.9 C
301 Storage tank location should consider safety with respect
to possible accidental loads. These loads may include collision
with subsequent penetration of the external hull, or fire and explosion
elsewhere on the installation.Guidance note:
The extent of damage and penetration in the event of a collision
should be determined by a collision analysis. If collision requirements
specified in international codes (e.g. IGC) are employed these should
be justified with respect to actual traffic at the terminal location.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.9 C
302 The storage tank deck should not be used as a laydown area.
In cases where this limitation is not practicable, adequate impact
protection against dropped objects shall be provided.Sec.9
C 400 Piping
Sec.9 C
401 Where practicable, high-pressure hydrocarbon piping shall
be routed such that jet or spray fires will not impinge directly
onto the storage tank deck. Where necessary, the storage tank deck
shall be adequately protected against such fires
Sec.9 C
402 Import and export risers and pipelines shall be located to
avoid impairment from mechanical damage, fire and explosion. This
can be achieved by locating these within main structures or by provision
of protection structures, riser guide pipes etc.
Sec.9 C
403 Loading/Offloading systems shall be located at a
safe distance from accommodation spaces, air inlets, and equipment
important for safety. Special consideration shall be given to protection
of systems important for safety in the event of collision with a
shuttle tanker
Sec.9 C
404 Any piping system which may contain LNG or hydrocarbon vapour
is to be arranged so that: | — | it is segregated from other
piping systems, except where inter-connections are required for
storage related operations, such as purging, gas freeing or inerting.
In such cases precautions are to be taken to ensure that LNG or
vapour cannot enter such other piping systems through the inter-connections |
| — | it shall not normally pass through any accommodation
space, service space or control station or through a machinery space
other than a pump room or compressor space |
| — | it is connected into the LNG containment system directly
from the open deck, except that the pipes installed in a vertical
trunkway or equivalent may be used to traverse void spaces above
a containment system, and except that pipes for drainage, venting
or purging may traverse cofferdams |
Where double piping is used as a safety measure the outer
piping shall have sufficient rating to accommodate any pressure
build up.
Sec.9
C 500 Mooring of floating installations
Sec.9 C
501 Mooring systems, including winches, tensioners, chain stoppers
etc. should be located in open, non-hazardous areas. Where this
is not practicable, special precautions shall be taken to ensure
that such items do not become a source of ignition
Sec.9 C
502 Chain lockers and chain pipes should be arranged in a non-hazardous
area. Where such location is not practicable, permanent facilities
for gas freeing (e.g. flushing or purging) the chain lockers and
chain pipes shall be provided
Sec.9 C
503 The mooring system shall be arranged to minimise the potential
for damage to risers in case of failure during normal operations
or maintenance.Sec.9
D. Hazardous Area Classification
Sec.9
D 100 Codes and standards
Sec.9 D
101 Codes and standards used in the LNG onshore industry, LNG
maritime transport industry and oil and gas offshore industry may
be used. However the applicability of the selected code to an offshore
terminal should be demonstrated.
Sec.9 D
102 These codes include:| — | IEC 60079-10 |
| — | API RP 500 / 505 |
| — | NFPA 59A |
| — | IGC |
Guidance note:
In general it is not recommended to mix the requirements of
different codes on the same installation. It is not necessary to
select the most restrictive code as long as the code selected adequately
addresses the technical safety issues. ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.9 D
103 Where not adequately covered by a code, the extent of hazardous
area in connection with vents or special features should be determined
on the basis of a dispersion analysis. The 50% LEL level
may be used as a basis for determining the extent of the hazardous
area.
Sec.9 D
104 Electrical equipment in cofferdams, ballast tanks and other
spaces adjacent to gas storage tanks is to be limited to that necessary
for operational reasons only.Sec.9
D 200 Entrances and openings
Sec.9 D
201 Entrances and openings to accommodation spaces, machinery
spaces, service spaces and control stations shall be fitted with
air locks, where they are within 3 m of the storage or processing
areaGuidance note:
Restrictions on entry between storage areas and accommodation
areas are typically more stringent on gas carriers. However use
of airlocks is an accepted solution on offshore installations with
storage. A more stringent requirement may be applied by a regulatory
authority.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.9 D
202 Air intakes are normally to be located not closer than 3m
from the boundary of a hazardous area.Sec.9
E. Emergency Shutdown
Sec.9
E 100 General
Sec.9 E
101 Emergency shutdown should take account of the major functions
of the installation, i.e. LNG transfer, LNG storage, gas/LNG
processing and gas import/export.
Sec.9 E
102 The terminal emergency shutdown system should also take account
of the operation of any gas carrier which is moored to the terminal.
Sec.9 E
103 LNG transfer system controls, gas carrier systems and carrier
berthing should be integrated into the ESD system so that the carrier
may be safely disconnected and moved off location in the event of
an emergency. Guidance note:
Reference is made to publications from SIGTTO for similar
operations at land terminals.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.9 E
104 Alarms to indicate potential overfilling of tanks should be
set with sufficient margin to ensure that flow can be stopped before
maximum filling level is reached.
Sec.9 E
105 Alarm levels for gas detection should be set to give a low
level alarm and a high level alarm at 20% and 60% of
Lower Explosion Limit respectively. Reference is made to DNV-OS-D301
for actions on gas detection.Sec.9
F. Escape and Communication
Sec.9
F 100 Escape routes
Sec.9 F
101 At least one escape route shall remain available following
an accidental event in connection with LNG storage tanks, processing,
transfer or import/export.
Sec.9 F
102 Where necessary protection against spray of cryogenic material
should be provided.
Sec.9 F
103 The worst case flaring scenario shall be used in determining
radiation levels which might impair escape route availability.Guidance note:
Reference is made to Sec.3 D500 concerning
limitation on activities related to various radiation levels---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
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