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DNV-OS-A101 Safety Principles and Arrangements
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SECTION 3
ArrangementSec.3
A. General
Sec.3
A 100 Objective
Sec.3 A
101 The provisions of this section aim to avoid or reduce the
effects of hazards on the unit or installation, by means of safe
general arrangement of structures, plants and facilities.Sec.3
A 200 Application
Sec.3 A
201 The requirements of this section shall be applied to all units
and installations. Additional, specific requirements for arrangement
of different unit types are given as indicated in Table A1.
Sec.3 A
| Table A1 Additional
requirements |
| Reference | Unit type | Sec.7 | Special provisions for floating production
and/or storage units | | Sec.8 | Special provisions for drilling units | | Sec.9 | Special Provisions for LNG Import and Export
Terminals (and LNG Production Units) | |
Sec.3
B. Segregation of Areas
Sec.3
B 100 General
Sec.3 B
101 The unit or installation shall be divided into different areas
according to the type of activities that will be carried out and
the associated hazard potential.
Sec.3 B
102 Areas of high risk potential shall be segregated from areas
of low risk potential, and from areas containing important safety
functions. Incident escalation between areas shall be avoided.
Sec.3 B
103 Accommodation and other areas important for safety, such as
control stations, shall be located in areas classified as non-hazardous
by location, and as far as practicable away from hazardous areas
for hydrocarbon processing, hydrocarbon storage, wellheads, risers
and drilling. The effect of prevailing winds and potential for segregation
by less hazardous areas shall also be considered for area protection.
Sec.3 B
104 Use of firewalls, blast walls, cofferdams etc. shall be considered
in cases where segregation by physical distance is not sufficient.
Sec.3 B
105 Where control stations or control functions are located in
LER/LIRs outside the accommodation block/safe
area special precautions against gas ignition related to gas detection,
ventilation and shutdown will need to be provided.Sec.3
C. General Arrangement
Sec.3
C 100 General
Sec.3 C
101 Where practicable, the orientation of the unit or installation,
with respect to wind direction, shall aim to avoid smoke or gas
impairment of escape, muster and evacuation areas.
Sec.3 C
102 Equipment shall be arranged with a view to providing:| — | safe escape from working areas |
| — | efficient ventilation of hazardous areas |
| — | minimal explosion overpressure in case of ignited gas
release |
| — | access for fire fighting and emergency response |
| — | prevention of serious consequences from dropped objects |
| — | facilitation of well operations and control in normal
and emergency situations |
| — | minimal possibility for escalation of fires and other
failures or accidents |
| — | safe containment of accidental release of hazardous
liquids |
| — | planned simultaneous operations. |
Guidance note:
ISO 13702 section 13 and Annex B provides useful principles
to minimise the effect of explosions.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3
D. Location of Plants and Equipment
Sec.3
D 100 Location of safety systems
Sec.3 D
101 Important safety systems and controls shall be located such
that they can remain operational during the defined accidental events.
Controls for safety systems shall be located where they are accessible
and available for safe, simultaneous use during an emergency.
Sec.3 D
102 Where redundant safety equipment is used in meeting 101, this
shall not be vulnerable to the same accidental events as the main
system.
Sec.3 D
103 The emergency and UPS systems and associated controls etc.
shall be self-contained, and located such that they are not vulnerable
to events that affect main power supply.
Sec.3 D
104 The bridge of mobile installations intended for self propelled
transit shall be located and arranged to provide sufficient field
of vision for safe navigation and manoeuvring. The requirements
in SOLAS Regulation V/22 or MODU Code 14.7 apply.
Sec.3 D
105 Field control panels and energy or actuation sources for well
control equipment, pipeline and riser ESD valves shall be protected
from dimensioning accidental events such as fire, explosion and
mechanical impact, to ensure emergency operation of the barrier
as necessary.Sec.3
D 200 Location of risers and ESD valves
Sec.3 D
201 Risers shall be located to avoid damage e.g. by fire, explosion
or impact from dropped objects.
Sec.3 D
202 Riser ESD valves shall be located in easily accessible, open,
well-ventilated areas, to avoid damage from wave impact and dimensioning
accidental events such as fire, explosion and mechanical impact.Sec.3
D 300 Location of air intakes and other
openings
Sec.3 D
301 Intakes for ventilation and combustion air shall be located
to avoid ingress of hazardous substances. Such intakes shall be
outside hazardous area.
Sec.3 D
302 Exhausts from combustion equipment and ventilation systems
shall be located to avoid cross contamination of air inlets.
Sec.3 D
303 Openings, such as windows, doors, and ventilation ducts, shall
normally be avoided in boundaries between main areas. In particular
this applies to openings in accommodation spaces, control stations
and other areas important for safety which face areas for hydrocarbon
processing, hydrocarbon storage, wellheads, risers or drilling.
Sec.3 D
304 External entrances to areas important for safety shall be
provided with air locks if located where smoke or gas ingress is
possible during an emergency.
Sec.3 D
305 Requirements for freeboard to prevent uncontrolled flooding
through openings in watertight barriers are given in DNV-OS-C301.Sec.3
D 400 Fired heaters, combustion engines
and hot surfaces
Sec.3 D
401 Fired heaters and combustion engines shall normally be located
at a safe distance from hazardous areas. Special precautions shall
be taken where such items could cause ignition of accidental gas
or liquid release. This could include use of gas tight enclosures,
overpressure ventilation, gas detection and automatic isolation, insulation
or cooling of hot surfaces etc.Guidance note:
See recognised standards such as EEMUA publication 107 for
protection of diesel engines for use in zone 2 hazardous area or
API RP 14J, paragraphs 5.5 and 5.6.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3 D
402 Other requirements for protection of hot surfaces are presented
in DNV-OS-D101.
Sec.3 D
403 Where fired heaters and combustion engines are located in
the vicinity of hazardous areas, the potential for an incident to
escalate from such equipment to the hazardous area shall be minimised,
e.g. through use of segregation and/or fire barriers.
Sec.3 D
404 The potential consequences of high-energy missiles from gas
turbines shall be considered in relation to location of equipment.
Damage to safety functions and associated controls shall be avoided.Sec.3
D 500 Location of flares and vents
Sec.3 D
501 Flares, burner booms, engine exhausts and other similar ignition
sources shall be located to avoid ignition of normal or accidental
gas releases. Use of dispersion calculations should be considered.
Sec.3 D
502 The flare and vent systems shall comply with API RP 521 or
equivalent. The radiant heat intensities or emissions from flares
and vent systems shall not exceed the following limits:| — | 6.3 kW/m2 (2000 Btu/hr/ft2) in areas where emergency
actions lasting up to one minute may be required by personnel without
shielding but with appropriate clothing |
| — | 4.7 kW/m2 (1500
Btu/hr/ft2 in
areas where emergency actions lasting several minutes may be required
by personnel without shielding but with appropriate clothing |
| — | 1.6 kW/m2 (500
Btu/hr/ft2)
at any location where personnel are continuously exposed |
| — | temperature rating of electrical and mechanical equipment |
| — | 50% LEL at any point on the installation where
the gas plume from a vent could be ignited or personnel could get
into contact with the gas. The most unfavourable weather and process
conditions have to be taken into consideration when calculating
heat radiation and dispersion. |
The limits above also apply to abnormal conditions (e.g. flame
out of flare system and accidental ignition of vent).
Sec.3
E. Storage of Hazardous Substances
and Cryogenic Liquids
Sec.3
E 100 General
Sec.3 E
101 Stores for hazardous substances shall be segregated from,
and located at a safe distance from accommodation spaces and control
stations. Indoor storage areas are to have access from open deck
and have efficient ventilation.
Sec.3 E
102 Equipment for storage and handling of cryogenic liquids (e.g.
liquid nitrogen) shall be located in open areas with efficient natural
ventilation. Equipment with potential for significant leakage shall
be located in a bunded area, which is constructed of materials suitable
for sustaining low temperatures. Reference also Sec.9 dealing with LNG terminalsGuidance note:
Evaporating cryogenic gases will be heavier than air and care
should be taken to ensure that such gases do not contaminate lower
modules.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.3
F. Cranes and Lay Down Areas
Sec.3
F 100 General
Sec.3 F
101 Cranes and lay down areas shall be located so as to minimise
the risk of load handling or dropped object damage to systems and
structures.
Sec.3 F
102 The need for load handling above pressurised hydrocarbon equipment,
hazardous inventories, and equipment important for safety shall
be avoided as far as possible. Suitable impact protection shall
be provided where such lifting cannot be avoided.
Sec.3 F
103 Lay down areas shall normally be located in non-hazardous
areas and provided with heavy-duty barriers to prevent damage to
adjacent equipment. On floating installations, necessary points
for securing of deck loading shall be provided.Sec.3
G. Other Requirements
Sec.3
G 100 General
Sec.3 G
101 The helicopter deck shall be located with a view to minimising
hazards from obstructions, turbulence, gas vents or exhaust plumes,
whilst providing a good approach path during prevailing weather
conditions. The helicopter shall not be required to cross the unit
or installation during such approaches.
Sec.3 G
102 Major hydrocarbon inventory areas, e.g. wellhead, drill floor,
riser and tank deck areas shall be arranged to allow efficient external
fire fighting assistance.
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