Transcript Frequency Assessments & Ignition. Probabilities

PIPELINE QRA SEMINAR
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SEPTEMBER 8-12, 2014
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
• Ignition sources
• Chemical reactions
• Oil soaked lagging on hot piping
• Pyrophoric iron sulphide (H2S & metal
corrosion)
• Electrical sparks and arcs
• Electrical motors and generators
• Switches, relays and other arching
components of electrical circuits
• Electrical wiring mal functioning
• Electrical welding
• Lighting fixtures
• Impressed cathodic protection system
• Mechanical sparks
• Lightning
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
• Static electrical sparks
• Fuelling operations
• Filling containers, tanks and
pressure vessels
• High fluid exit velocities (high
pressure water sprays, gas jets)
• Drive belt operation
• Shot blasting
• Friction
• Flame
• Flaring
• Fired equipment
• Gas welding and cutting
• Hot surfaces
• Fired vessels stacks
• Engine exhaust
• Heat of compression
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• Definitions:
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Ignition Probabilities (Liquids):
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Ignition Probabilities (Gas Pipelines):
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
Item
Leak
rate pr
year
Leak sizes in mm
< 10
Compressor,
Centrifugal
Compressor,
Reciprocating
Heat excahnger, HC
in shell
Heat excahnger, HC
in tube
Instrument
Piping steel,
3"< D <=11"
Piping steel,
D <=3"
Piping steel,
D > 11"
Pressure vessel,
horizontal, separator
Pressure vessel,
vertical, scrubber
Actuated Block Valve,
3” < D <= 11”
Actuated Block Valve,
D <= 3”
Actuated Block Valve,
D< 11”
Flanges, D <= 3”
Flanges,
3” < D <= 11”
Flanges, D< 11”
10 <25
25<50
50<75
75<100
>=100
N/A
14%
5%
0%
0%
0%
9.19E-03
73%
9%
6.50E-02
81%
19%
0%
0%
0%
0%
0%
4.94E-03
75%
8%
8%
0%
0%
0%
9%
2.92E-03
85%
8%
0%
0%
0%
0%
8%
5.85E-04
5.87E-05
79%
75%
17%
5%
2%
2%
0%
2%
0%
0%
0%
10%
1%
6%
2.00E-04
79%
13%
6%
1%
1%
0%
1%
5.49E-05
64%
8%
0%
0%
0%
17%
11%
2.21E-03
22%
0%
0%
11%
11%
0%
56%
1.01E-03
100%
0%
0%
0%
0%
0%
0%
1.29E-03
87%
7%
0%
0%
7%
0%
0%
1.29E-03
68%
9%
14%
0%
0%
0%
9%
8.04E-04
83%
17%
0%
0%
0%
0%
0%
3.95E-05
5.56E-05
78%
84%
10%
5%
8%
4%
2%
1%
1%
0%
1%
6%
0%
0%
9.85E-05
85%
4%
0%
4%
0%
7%
0%
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Aim of Zoning Classification (IP 15):
Avoid ignition of those releases that may occur from time to time
• Reduce to an acceptable minimum level the probability of coincidence of flammable atmosphere and an
electrical or other source of ignition
• Risk Target is 10-5 year
• IP 15 does not concern major releases (spread of flammables more than 30 m). These shall be
minimised by design and operation to an acceptable residual risk.
Hazardous area classification requires an interdisciplinary approach:
• Process
• Safety and loss prevention
• Electrical
Agreements reached on hazardous area classification should be formally recorded in a Hazardous
Area Dossier in supplement to hazardous areas drawings.
For the majority of releases the shape profile depends primarily on angle and location of the release.
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Zoning:
Zone 0: The part of a hazardous area in which a flammable atmosphere is continuously
present or present for long periods
Zone 1: That part of a hazardous area in which a flammable atmosphere is likely to
occur in normal operation
Zone 2: That part of a hazardous area in which a flammable atmosphere is not likely
to occur in normal operation and, if it occurs, will only exist for a short period.
Non-Hazardous: areas that do not fall into any of the above.
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Continuous grade release: A release that is continuous or nearly so, or that occurs
frequently and for short periods
If it is likely to be present for more than 1000 hours per year.
Primary grade release: a release that is likely to occur periodically or occasionally in
normal operations, i.e. a release which, in operating procedures is anticipated to occur
If it is likely to be present for between 10 to 1000 hours per year.
Secondary grade release: A release that is unlikely to occur in normal operation and, in
any event, will do so only infrequently and for short periods i.e. a release which in
operating procedures is not anticipated to occur. Such release may be of unknown size
e.g. fracture of a drain or unknown size e.g. corrosion hole.
If it is likely to be present for 1 to 10 hours per year.
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Grade of Release:
Grade of release depends solely on frequency and duration.
Grade does NOT depend on rate or quantity, ventilation or characteristics of the fluid.
Continuous grade release  Typically Zone 0
Primary grade release
 Typically Zone 1
Secondary grade release  Typically Zone 2
“Typically” refers that it is ventilation dependent
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FREQUENCY ASSESSMENTS & IGNITION
PROBABILITIES
Fluid Categories:
Fluid
Category
A
B
C
G(i)
G(ii)
Description
A flammable liquid that, on release, would vaporise rapidly and
substantially.
A flammable liquid, not in Category A, but at a temperature
sufficient for boiling to occur on release.
A flammable liquid, not in Categories A or B, but which can, on
release, be at a temperature above its flash point, or form a
flammable mist or spray.
A typical methane-rich natural gas.
Refinery hydrogen.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – FLUID CATEGORY
Unstabilized Crude
Stabilized Crude
Natural gas
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – APPROACH
3 Different approaches to zoning:
• Direct Examples Approach
Based on experience and provides hazard radii for
typical installations.
Open field:
•
Ambient temperature of max. 30°C
•
Wind speed 0.5 m/s – 2 m/s
• Point Sources Approach
• Identify sources
• Determine grade
• Establish zone
• Determine hazard radii
•
Leak size
• Pressure
• Draw zone
• Risk Based Approach
•
•
•
•
•
•
Risk target of 10-5 per year
Unknown leak size
Varying release size
Consequences
Exposure
Approach is similar to risk
analysis
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – RELEASE RATES
Continuous and primary grade release rates are normally well defined as they have been
designed for.
Secondary grade release rates/ leak holes are often unknown as they occur unintentionally
e.g. breakage of a flange, corrosion hole, fracture of a drain etc.
Secondary Grades of Release operates with LEVELS:
• LEVEL I
• LEVEL II
• LEVEL III
10-2
/ release source year
-2
-3
10 - 10 / release source year
10-3 - 10-4 / release source year
The LEVEL to be used on a specific plant is based on the exposure of the most exposed
individual to flammable releases and the probability of ignition of those releases.
LEVEL frequencies are for the zone 2 boundary.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE: LEVEL
Exposure:
Exp = Pocc X Nrange
Pocc: Probability the worker is on site within the hazardous area.
Nrange: The time weighted average number of release sources which can affect the
individual during their time within the hazardous area.
Exposure is normally only calculated for the most exposed person and used for the
entire installation.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE: LEVEL
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE: LEVEL
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE
Piping:
• Fully welded
• Designed according to ANSI/ASME B31.3
Does not require zoning.
Flanges:
 Secondary grade release source
 Broken flanges
Valves:
 Infrequently used
 Well maintained
 Frequently used
(Control valves)
 Primary grade
 Secondary grade
 Additional Primary grade of 0.3 m
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE
Flanges:
• Ten or more flanges are required within close proximity to create sufficient likelihood of release to justify
classification as a secondary release.
• Fuel gas flange connection to turbine does not require classification.
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HAZARDOUS
AREA CLASSIFICATION – POINT SOURCE
Flanges & Valves
Secondary Grade
LEVEL I: 10-2 / year
LEVEL II: 10-2 – 10-3 / year
LEVEL III: 10-3 – 10-4 / year
Calculation Example
Flange d ≤ 3” :
3.95∙10-5 per year – 30 off = 0.001185
Flange 3”<d≤11”: 5.56∙10-5 per year – 10 off = 0.0112
Natural Gas
IR; Occupation and ignition
Pocc=
0.05 (Estimate)
Nrange=
5 (Table)
Exposure = 0.25 (Pocc x Nrange)
Pig =
0.03 (Table)
Pig,total =
0.00037 (0.001185+0.0112) X 0.03
From curve it is seen that we are at LEVEL 1
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE
Pig Receivers
Pig receivers are likely to opened frequently and should normally be regarded as primary
grade release. The hazardous area should be classified as zone 1.
Provided that interlock systems are in place, the release that occurs from opening the
launcher/receiver will be minor and a hazard radius of 3 m is suggested in IP 15. If the
operating procedures include purging or water washing before opening the
launcher/receiver the nominal hazard radii can be reduced to 1.5 m.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE
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HAZARDOUS
AREA CLASSIFICATION – POINT SOURCE
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HAZARDOUS
AREA CLASSIFICATION – POINT SOURCE
At ground level
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE -VENTILATION
• Natural ventilation and wind without stagnant zones.
• Typically air velocities will not be less than 0.5 m/s and will frequently be above 2 m/s.
• Where a facility is classified as an open area, the hazardous area classification of previous
slides applies without further ventilation considerations.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE VENTILATION – ENCLOSED AREAS
• Area where natural ventilation does not provide a minimum of 12 air changes per hour.
• 12 acph is defined as adequate ventilation (10 minutes persistence 2. grade release).
• Displacement ventilation.
• Dilution ventilation.
• Localised Exhaust Ventilation (LEV).
• Forced draught fan (acoustic enclosures).
• Over- and under-pressurisation
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
AREA CLASSIFICATION – POINT SOURCE VENTILATION – ENCLOSED
AREAS
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT
As a general policy, electrical equipment should not be located in a hazardous
area if it is possible to place it in a non-hazardous area, nor should it be
placed in a Zone 1 if it can be placed in Zone 2.
Correct selection of equipment requires three factors to be taken into
account:
• Zone in which the equipment will be used.
• Sensitivity to ignition of the gases or vapour likely to be present, expressed
as gas group.
• Sensitivity of the gases or vapour present to ignition by hot surfaces,
expressed as a temperature classification.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT
Type
Protection
Functionality/concept
o
Oil filled
apparatus.
The equipment is submerged in oil preventing an flammable atmosphere to occur in the area where sparks are likely to occur.
p
Pressurised
The equipment is pressurised with a protective gas to prevent ingress of flammable gasses or liquids.
The overpressure can be made with or with out constant flushing of the protective gas.
q
Powder filled
By filling the housing with a finely grained powder, an arc within the housing is unable, with correct use, to ignite the
potentially explosive atmosphere outside.
d
Flame proof
The enclosure is designed to withstand an explosion and prevent its propagation.
The enclosure shall be able to withstand an internal pressure of 12 bar.
e
Increased safety
Enclosure in which there is no spark or hot surface in normal operation.
ia
Intrinsically safe “ia”
Limit the energy within the system so that even under fault conditions a spark or thermal effects cannot occur.
ib
Intrinsically safe “ib”
Limit the energy within the system so that a spark or thermal effects cannot occur considering 1 fault.
n
Non incendive
Type n protection has several implementation types:
nA: non sparking
nC: hermetically sealed enclosure
nL: energy limited
M
Encapsulated
Parts that could ignite a potentially explosive atmosphere by means of sparks or heat are potted soas to prevent ignition of
the potentially atmosphere. This is achieved by encapsulating the components in a compound resistant to physical especially electrical, thermal and mechanical - and chemical influences.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT
For ”o”, ”d”, ”i” and ”n” there
is a material subgroup
division:
• IIA
• IIB
• IIC
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT - SUMMARY
Protection
Code
Flame proof
Pressurized
Powder filled
Oil filled
Increased safety
Intrinsic safe , ia
Intrinsic , ib
Non incendive
Encapsulating
’d’
’p’
’q’
’o’
’e’
’ia’
’ib’
’n’
’m’
Zone 0
Category 1
(ATEX)
Zone 1
Category 2
(ATEX)
Zone 2
Category 3 (ATEX)
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT –TYPICAL PRACTICE
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT –TYPICAL PRACTICE
• Instrumentation for use in hazardous areas shall be suitable for at least Zone 1
• Instrumentation for use in unclassified areas, which is required to remain
energised during an emergency, shall also be suitable for Zone 1.
• Instrument ”electrical systems” shall by preference be intrinsically safe (IS).
• Equipment shall comply with at least temperature Class T3, Group IIB.
• Instrument ”electrical systems” shall by Equipment comply with at least temperature
Class T3, Group IIB.
• All electrical apparatus located outdoor, shall be certified according to EU directive
94/9/EC (ATEX) and shall as minimum be certified for Equipment Group II Category 2G,
Explosion group IIB, temperature class T3.
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT –DOCUMENTATION
To aid maintenance and demonstrate that ignition hazards have been properly addressed,
an inventory of equipment installed in a hazardous area should be maintained, including:
• Type of protection
• Temperature class
• Subgroup of apparatus
• Location
• Marking
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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES
EX EQUIPMENT
Battery Rooms
• Battery rooms should be adequately ventilated in order to assist in the dispersion of
hydrogen.
• Electrical apparatus thus may need to be suitable for use in zone 1 hazardous areas with
apparatus of subgroup IIC T1 class suitability for hydrogen unless there is dilution by LEV.
Non-electrical Equipment
• IP 15 is designed for selection and location of fixed electrical equipment.
• However hazardous area classification is a good basis for deciding what equipment
may be used at any particular location.
• This is in accordance with the ATEX Directives, which apply equally to electrical and
non-electrical capable of causing an ignition of a flammable atmosphere.
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END OF FREQUENCY
ASSESSMENTS & IGNISTION
PROBABILITIES
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