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DNV-OS-A101 Safety Principles and Arrangements
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Sec.7
B. Arrangement
Sec.7
B 100 General
Sec.7 B
101 The unit shall be oriented to provide efficient natural ventilation
of hazardous areas, and safeguard areas important to safety.
Sec.7 B
102 The production plant shall be located and protected such that
an incident within the process area will not escalate to the product
storage tanks, e.g. located outside the storage tank area, or on
a deck elevated above the cargo tank deck.
Sec.7 B
103 Pressurised processing plant shall normally not be located
within the main hull.
Sec.7 B
104 Requirements given in IMO instruments applicable for oil tankers,
gas carriers etc. may be applied to special designs or issues that
are not addressed in these standards.
Sec.7 B
105 Design and location of structures, equipment and controls
shall take account of the motion of the unit and the possibility
of green sea.
Sec.7 B
106 To ensure satisfactory operation in all weather conditions,
ventilation inlets and outlets for rooms with essential equipment
shall be located in such positions that closing appliances will
not be necessary. Such rooms are machinery spaces, emergency generator
room, switchboard rooms and control stations.Guidance note:
Basis for determining acceptable locations for ventilators
as mentioned above should be an examination of the extent green
sea for the unit. For areas clearly not affected by green sea, e.g.
at the top of the bridge, documentation for location of the inlets
and outlets will not be necessary.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.7 B
107 If hydrocarbon containment, and connections to such are located
in the lower hull of a unit or installation, the design shall be
examined by a safety assessment.Guidance note:
Typical methods would include HAZOP, FMEA, SWIFT (Structured
What If Technique), or similar. Standard fuel oil and lube oil storage
need not be subject to special assessment.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.7
B 200 Process and storage tank decks
Sec.7 B
201 The space between process deck and storage tank deck shall
be designed to allow easy access for operation, inspection and maintenance,
and shall be sufficiently open to allow efficient natural ventilation
and possibility of fire fighting. This normally implies an elevation
of 3 m or more above storage tank deck.
Sec.7 B
202 The process deck shall be provided with suitable process drainage
and bunding for operational and accidental spillage collection.
Drainage shall prevent large oil spills and firewater from impairing
escape routes or spreading to storage tank deck.
Sec.7 B
203 The storage tank deck should not be used as a laydown area.
In cases where this limitation is not practicable, the tank deck
shall be provided with adequate impact protection against dropped
objects. Precautions shall also be taken to avoid spark generation
in gas hazardous area.Sec.7
B 300 Risers and piping
Sec.7 B
301 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.7 B
302 Risers shall be located to avoid impairment from mechanical
damage, fire and explosion. This can be achieved by locating risers
within main structures or by provision of protection structures,
riser guide pipes etc.
Sec.7 B
303 Pig launchers and receivers shall be located in open, well-ventilated
areas with the opening directed outboard, away from pressurised
or other critical equipment, where practicable.Guidance note:
Special consideration must be given where design involves
a submerged turret production (STP) type solution, where pig launcher
or receiver and ESD valves may be located in an enclosed space.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.7 B
304 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 shuttle tanker.Sec.7
B 400 Entrances and openings
Sec.7 B
401 Entrances and openings to accommodation spaces, machinery
spaces, service spaces and control stations shall be fitted with
air locks, where they are on the bulkhead facing the hazardous area,
an adjacent bulkhead within 3 m of a facing bulkhead, or within
hazardous area.
Sec.7 B
402 The following apply to boundaries facing the tank area:- Gas tight, bolted plates for
removal of machinery may be fitted in such boundaries. Signboards
giving instruction that such plates shall be kept closed unless
the unit is gas-free shall be posted nearby.
- Windows in the navigation bridge may be accepted on
the conditions that the windows are of non-opening type and provided
with inner steel covers, or alternatively rated to the same fire
and explosion rating as the boundary.
Sec.7
B 500 Crude oil storage area and cofferdams
Sec.7 B
501 Crude oil storage tanks shall not have a common boundary with
machinery spaces.
Sec.7 B
502 Cofferdams shall be provided between crude oil tanks, slop
tanks and adjacent non-hazardous areas (e.g. machinery spaces and
accommodation spaces). Cargo and ballast pump rooms and ballast
tanks can be accepted as cofferdams. Access to the pump room entrances
shall be from open deck.
Sec.7 B
503 Cofferdams shall be of sufficient size for easy access and
shall cover the entire adjacent tank bulkhead. Minimum distance
between bulkheads shall be 600 mm.
Sec.7 B
504 Crude oil tanks, slop tanks and enclosed spaces adjacent to
these tanks shall be arranged with suitable access for inspection
of structural elements.
Sec.7 B
505 Where a non-hazardous space and a crude oil tank meet in a "corner
to corner" configuration, a diagonal plate or an angle
across the corner may be accepted as cofferdam. Such cofferdams
shall be:| — | ventilated if accessible |
| — | filled with a suitable compound if not accessible. |
Sec.7 B
506 Fuel oil bunker tanks shall not normally be located within
the cargo tank area. Such tanks may, however, be located at forward
and aft end of tank area instead of cofferdams. Fuel oil bunker
in double bottom tanks situated under crude oil tanks is not permitted.
Sec.7 B
507 Hatches, openings for ventilation, ullage plugs or other deck
openings for crude oil tanks shall not be arranged in enclosed compartments.
Sec.7 B
508 The closing of deck openings for scaffolding wire connections
may be done by use of screwed plugs of metal or a suitable synthetic
material.
Sec.7 B
509 Anodes, tank washing machines and other permanently attached
equipment units in tanks and cofferdams shall be securely fastened
to the structure. The units and their supports shall be able to
withstand sloshing in the tanks, vibration and other operational
loads
Sec.7 B
510 Selection of materials for moving parts or attachments in
tanks and cofferdams shall include due consideration to avoiding
spark-production in case of impact.Sec.7
B 600 Slop tanks
Sec.7 B
601 At least two slop tanks shall be provided for collection of
oil contaminated water, primarily from water washing of oil storage
tanks.
Sec.7 B
602 Slop tanks shall be designed particularly with respect to
separation of water, oil and solids. Inlets, outlets, baffles or
weirs shall be arranged to avoid excessive turbulence and entrainment
of oil or emulsion with the water.
Sec.7 B
603 The slop tanks may be used as drain tanks for open and closed
hazardous drains from the processing area. The liquids shall be
collected in an intermediate tank and pumped in closed piping to
the slop tanks. Where an intermediate tank is not practicable, vent
systems shall be designed to accommodate the maximum gas release rate.
Sec.7 B
604 Back flow of inert gas from slop tanks to open hazardous drain
boxes shall be prevented by effective and reliable means (e.g. double
barriers including a water seal and level alarm).
Sec.7 B
605 Slop tanks or intermediate collection tanks shall be designed
to collect the maximum volume of liquid in any process segment that
may be encountered by open or closed drain system.Sec.7
B 700 Crude oil pump rooms and pipe
tunnels
Sec.7 B
701 Submerged (deep well) crude pumps shall be used where practicable,
in order to limit risk of hydrocarbon leaks in confined spaces.
The requirements in 702 to 705 apply where use of deep well pumps
is not practicable.
Sec.7 B
702 The lower portion of the pump room may be recessed into machinery
and boiler spaces to accommodate the pumps. Deck head of the recess
is, in general, not to exceed one-third of the moulded depth above
the keel. In ship shaped units of less than 25 000 tons deadweight,
where it can be demonstrated that this height does not allow satisfactory
access and piping arrangements, a recess up to one half of the moulded
depth above the keel may be acceptable.
Sec.7 B
703 Pipe tunnels are to have ample space for inspection of the
pipes.
Sec.7 B
704 The pipes in pipe tunnels shall be situated as high as possible
above the unit bottom. There shall be no connection between a pipe
tunnel and the engine room (e.g. through pipes or manholes).
Sec.7 B
705 Access to pipe tunnels is normally to be arranged from the
pump room, a similar hazardous space or from open deck. Access opening
from the cargo pump room shall be provided with watertight closures.Sec.7
B 800 Mooring systems
Sec.7 B
801 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.7 B
802 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.7 B
803 The mooring system shall be arranged to minimise the potential
for damage to risers in case of failure during normal operations
or maintenance.
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