Frequency Assessments & Ignition. Probabilities

1SEPTEMBER 8-12, 2014INOGATE PIPELINE QRA SEMINAR

PIPELINE QRA SEMINAR

SEPTEMBER 8-12, 2014INOGATE PIPELINE QRA SEMINAR

FREQUENCY ASSESSMENTS & IGNITION PROBABILITIES

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• 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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• 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 PROBABILITIESIgnition Probabilities (Liquids):


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESIgnition Probabilities (Gas Pipelines):


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESLeak rate pr year

Leak sizes in mm I tem

< 10 10 <25 25<50 50<75 75<100 >=100 N/A Compressor, Centrifugal

9.19E-03 73% 14% 5% 0% 0% 0% 9%

Compressor, Reciprocating

6.50E-02 81% 19% 0% 0% 0% 0% 0%

Heat excahnger, HC in shell

4.94E-03 75% 8% 8% 0% 0% 0% 9%

Heat excahnger, HC in tube

2.92E-03 85% 8% 0% 0% 0% 0% 8%

Instrument 5.85E-04 79% 17% 2% 0% 0% 0% 1% Piping steel, 3"< D <=11"

5.87E-05 75% 5% 2% 2% 0% 10% 6%

Piping steel, D <=3"

2.00E-04 79% 13% 6% 1% 1% 0% 1%

Piping steel, D > 11"

5.49E-05 64% 8% 0% 0% 0% 17% 11%

Pressure vessel, horizontal, separator

2.21E-03 22% 0% 0% 11% 11% 0% 56%

Pressure vessel, vertical, scrubber

1.01E-03 100% 0% 0% 0% 0% 0% 0%

Actuated Block Valve, 3” < D <= 11”

1.29E-03 87% 7% 0% 0% 7% 0% 0%

Actuated Block Valve, D <= 3”

1.29E-03 68% 9% 14% 0% 0% 0% 9%

Actuated Block Valve, D< 11”

8.04E-04 83% 17% 0% 0% 0% 0% 0%

Flanges, D <= 3” 3.95E-05 78% 10% 8% 2% 1% 1% 0% Flanges, 3” < D <= 11”

5.56E-05 84% 5% 4% 1% 0% 6% 0%

Flanges, D< 11” 9.85E-05 85% 4% 0% 4% 0% 7% 0%


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAim 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• ElectricalAgreements 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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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.

Zoning:



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Continuous grade release: A release that is continuous or nearly so, or that occurs frequently and for short periods

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

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 more than 1000 hours per year.

If it is likely to be present for between 10 to 1000 hours per year.

If it is likely to be present for 1 to 10 hours per year.


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESGrade of Release:

Continuous grade release Typically Zone 0Primary grade release Typically Zone 1Secondary grade release Typically Zone 2

“Typically” refers that it is ventilation dependent

Grade of release depends solely on frequency and duration.Grade does NOT depend on rate or quantity, ventilation or characteristics of the fluid.


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESFluid Categories:

Fluid Category

Description

A A flammable liquid that, on release, would vaporise rapidly and substantially.

B A flammable liquid, not in Category A, but at a temperature sufficient for boiling to occur on release.

C 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.

G(i) A typical methane-rich natural gas.G(ii) Refinery hydrogen.


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA CLASSIFICATION – FLUID CATEGORY

Natural gas

Unstabilized Crude

Stabilized Crude



AREA CLASSIFICATION – APPROACH

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3 Different approaches to zoning:

Based on experience and provides hazard radii fortypical installations.Open field:• Ambient temperature of max. 30°C• Wind speed 0.5 m/s – 2 m/s

• Identify sources• Determine grade• Establish zone• Determine hazard radii

• Leak size • Pressure

• Draw zone

• Risk target of 10-5 per year• Unknown leak size• Varying release size• Consequences• Exposure• Approach is similar to risk

analysis

• Direct Examples Approach

• Point Sources Approach

• Risk Based Approach


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA 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 10-2 / release source year• LEVEL II 10-2 - 10-3 / release source year• LEVEL III 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.


FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA CLASSIFICATION – POINT SOURCE: LEVEL

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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 PROBABILITIESAREA CLASSIFICATION – POINT SOURCE

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Piping:• Fully welded• Designed according to ANSI/ASME B31.3Does not require zoning.Flanges: Secondary grade release

source Broken flanges

Valves: Infrequently used Well maintained

Frequently used (Control valves)

Secondary grade

Additional Primary grade of 0.3 m

Primary grade



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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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HAZARDOUSAREA CLASSIFICATION – POINT SOURCE

Flanges & ValvesSecondary GradeLEVEL I: 10-2 / yearLEVEL II: 10-2 – 10-3 / yearLEVEL III: 10-3 – 10-4 / year

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 = 0.0112Natural Gas

IR; Occupation and ignitionPocc= 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

Calculation Example



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Pig ReceiversPig 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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26At ground level


FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA CLASSIFICATION – POINT SOURCE -VENTILATION

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• 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.


FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA CLASSIFICATION – POINT SOURCE VENTILATION – ENCLOSED AREAS

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• 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


FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESAREA CLASSIFICATION – POINT SOURCE VENTILATION – ENCLOSED AREAS

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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESEX EQUIPMENT

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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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Type Protection Functionality/concepto 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 enclosurenL: 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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For ”o”, ”d”, ”i” and ”n” there is a material subgroup division:• IIA• IIB• IIC



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Zone 0 Zone 1 Zone 2 Protection Code Category 1

(ATEX) Category 2 (ATEX)

Category 3 (ATEX)

Flame proof ’d’ Pressurized ’p’ Powder filled ’q’ Oil filled ’o’ Increased safety ’e’ Intrinsic safe , ia ’ia’ Intrinsic , ib ’ib’ Non incendive ’n’ Encapsulating ’m’

FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESEX EQUIPMENT - SUMMARY


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FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESEX EQUIPMENT –TYPICAL PRACTICE


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• 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.

FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESEX EQUIPMENT –TYPICAL PRACTICE

• 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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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

FREQUENCY ASSESSMENTS & IGNITION PROBABILITIESEX EQUIPMENT –DOCUMENTATION


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• 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.


Battery Rooms

• 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.

Non-electrical Equipment

39SEPTEMBER 8-12, 2014INOGATE PIPELINE QRA SEMINAR

END OF FREQUENCY ASSESSMENTS & IGNISTION PROBABILITIES

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Frequency Assessments & Ignition. Probabilities