Petroleum Development Oman L.L.C.
Document title: H2S and SO2 Management
The Basics, Classification & Sour Contracts
Document ID
SP-1190-1
Document Type
Specification
Security
Unrestricted
Discipline
Owner
Issue Date
Version
Technical Safety Engineering
MSE/4 – CFDH Technical Safety Engineering
December 2018
5.0
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Document Authorisation
Authorised For Issue
Document Authorisation
Document Owner
Document Custodian
Document Controller
Lucien Van Ham (MSE4)
(CFDH)
Lesley Tallentire (MSE47)
Lesley Tallentire (MSE47)
Van Ham, Lucien MSE4
Date : 13-01-2019 1:54 PM
Page 3
Kesanakurthy, Vijay MSE47
Date : 13-01-2019 1:53 PM
SP-1190 – 1
Tallentire, Lesley MSE47
Date : 07-10-2019 9:38 AM
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ii Revision History
The following is a brief summary of the 4 most recent revisions to this document. Details of all revisions
prior to these are held on file by the issuing department.
Version No.
5.0
Date
Dec-18
Author
Lesley
MSE47
4.0
Aug-15
Lesley
MSE47
Tallentire,
Tallentire,
Scope / Remarks
Removal of the Classification Examples and include
Classification Responsibilities.
Updated to split the existing SP-1190 into sections.
This section 1190-1 is aimed at providing information
on the following:
the impact of H2S & SO2 on humans,
to provide a simpler facility classification
structure and,
to detail the additional requirements in
contracts for sour facilities.
3.0
Sep-11
Ian Jewitt, MSE4
2.0
Nov-04
A.C. Sluijterman, UEP1
Updated to (i) align with Shell DEP “Very Toxic”
terminology, (ii) reflect learning from Kashagan and
Harweel 2A/B projects, (iii) provide guidance on partial
classification and zoning of facilities, and (iv) address
over-conservatism for souring in high percentage
water cut reservoirs.
Revalidated and updated references.
iii Related Corporate Management System (CMS) Documents
The related CMS Documents can be retrieved from the Corporate Management Portal (CMS).
Code
SP-1125
CMS Document
Isolation of Process Equipment Specification
SP-1231
HSE Specification – Occupational Health
SP-1258
HSE Specification – Quantified Risk Assessment (QRA)
PR-1078
Hydrogen Sulphide Management Procedure (withdrawn &
incorporated within the SP-1190 – 4 structure)
PR-1080
Well Testing, Scheduling, Sampling and Validation
PR-1096
Sampling of Oilfield Liquids and Gases Procedure
PR-1172
Permit to Work Procedure
PR-2219
Procedure for Conducting QRA, PEM and Related Studies
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TABLE OF CONTENTS
i Document Authorisation .......................................................................................................................... 3
ii Revision History....................................................................................................................................... 4
iii
Related Corporate Management System (CMS) Documents ............................................................ 4
1
Introduction ......................................................................................................................................... 7
1.1
Hydrogen Sulphide (H2S) – The Basics.............................................................................................. 8
2
2.1
3
4
5
Changes to the Specification .................................................................................................... 7
H2S Limits ................................................................................................................................. 8
2.1.1
Unpleasant Odour ........................................................................................................... 9
2.1.2
Eight (8) Hour Time Weighted Average (TWA)............................................................... 9
2.1.3
15 Minute Short Term Exposure Limit (STEL) ................................................................ 9
2.1.4
Emergency Planning ..................................................................................................... 10
2.1.5
Onset of Significant Health Effects ............................................................................... 10
2.1.6
Onset of Worker Fatalities ............................................................................................. 11
Sulphur Dioxide (SO2) - The Basics ...................................................................................................... 12
3.1.1
Unpleasant Odour ......................................................................................................... 13
3.1.2
8 Hour Time Weighted Average (TWA) ........................................................................ 13
3.1.3
15 Minute Short Term Exposure Limit (STEL) .............................................................. 13
3.1.4
Emergency Planning ..................................................................................................... 13
3.1.5
Onset of significant Health Effects ................................................................................ 13
3.1.6
Onset of worker Fatalities ............................................................................................. 14
H2S Facilities Classification ................................................................................................................... 15
4.1
H2S Classification Definitions – Sweet, Sour, Critical Sour .................................................... 15
4.2
Facility Classification entirety or part of facility ....................................................................... 18
4.3
SO2 or CO2 Classification ....................................................................................................... 19
Zoning of Sour & Critical Sour Facilities ................................................................................................ 20
5.1
Red and Yellow Zoning........................................................................................................... 20
5.2
Emergency Planning Zone (EPZ) Classification .................................................................... 20
5.3
SIMOPS Zoning (Simultaneous Operations) Classification ................................................... 20
5.4
Well Test Flaring Zoning ......................................................................................................... 21
6
Critical Sour & Sour Contract HSE Requirements ................................................................................ 22
7
Appendix A Glossary of Definitions, Terms and Abbreviations ............................................................. 23
Page 5
7.1
General Definitions ................................................................................................................. 23
7.2
Key Terminology ..................................................................................................................... 23
7.3
Abbreviations .......................................................................................................................... 24
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8
Appendix B, Classification Changes ..................................................................................................... 25
9
Appendix C, Classification Dispersion Graphs ...................................................................................... 26
10 Appendix D User Comment Form ......................................................................................................... 30
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1 Introduction
This document provides PDO with the basis required to understand the hazards associated with
encountering H2S and SO2 within its operations. It provides details of how PDO facilities are
classified with respect to the H2S levels, which then determines how the risks are managed.
There are special requirements for contracts which are let within Critical Sour and Sour facilities, and
these are included herein.
SP-1190 has been modified to standardise the approach taken to H2S and SO2 management within
the company, across the assets and directorates. This document SP-1190-1, fits into the structure
as noted below:
1190- 1
The Basics, Classification and Sour Contracts
Well Engineering
Engineering Design
Operations
H2S PPE and Training
The other documents in the series shall be consulted and applied where appropriate.
The development of this standard is based on a series of workshops which were conducted within
Petroleum Development Oman (PDO). These workshops were conducted to canvas the opinions of
those individuals who have a wide experience of working / designing for oil and gas infrastructure
which contains high levels of H2S, SO2 or other toxic substances. The output of the workshops is
summarised in SP-1190 Workshop Summary Technical Note, (PDO201408100001). The technical
note and earlier interviews are the basis for the update of this document.
1.1 Changes to the Specification
The notable changes for this Revision 5.0 of SP-1190 are :
SP-1190-2 Wells is issued.
SP-1190-5 Respiratory Protective Equipment and Training is issued.
Documents updated to take account of project and operational learnings.
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2 Hydrogen Sulphide (H2S) – The Basics
Hydrogen Sulphide (H2S) is a colourless, flammable and very toxic gas with a strong odour of rotten
eggs that is found in many reservoir fluids and aquifers in the PDO concession area.
Exposure can result in significant impact on health and potential loss of life. Health impacts include
irritation to the eyes and skin. Through inhalation it affects the respiratory system; resulting in
stopping or disturbing breathing, coma, convulsions; conjunctivitis, eye pain, discharge of tears,
abnormal visual intolerance to light, blistering of the cornea; dizziness, headache, weakness &
exhaustion, irritability, insomnia; and gastrointestinal disturbance (NIOSH 2005-149).
2.1
H2S Limits
Table 2-1 identifies the limits which are put in place to understand and manage the associated
hazards. Further explanation of these limits is provided in the subsequent sections.
The impact of H2S on humans is a function of both the H2S concentration in air and the time
persons are exposed.
Table 2-1
H2S Limits
Level of Concern
Hydrogen
Sulphide
Immediate Impact on Health & Work
Unpleasant Odour
0.13 ppm
Nuisance smell only; no adverse health
effect.
Unless H2S levels are expected, persons
should remove themselves from the area
and advise the operations team.
8 Hour TWA (Threshold Limit
Value)
5 ppm
15 Minute STEL (Short Term
Exposure Limit)
10 ppm
No adverse health effects.
Persons should remove themselves from
the area and advise the operations team.
No adverse health effects for short term
exposure.
Alarm level for personal and plant fixed
detectors. Persons don RPE & proceed
to muster.
Emergency
Response
Planning Guideline ERPG-3
(AIHA) for 60 minutes
100 ppm
Onset of Significant Health
Effects at 30 minutes
300 ppm
Eye irritation, coughing and loss of sense of
smell.
Personal detectors indication limit is
100ppm. Persons don RPE & proceed to
muster.
Conjunctivitis and build up of fluid in lungs,
leading to respiratory problems.
Personal detectors indication limit is
100ppm, so if reading is 100ppm, actual
concentration may be greater. Persons
don RPE & proceed to muster.
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Level of Concern
Hydrogen
Sulphide
Immediate Impact on Health & Work
Onset of Worker Fatalities at
10 minutes
650 ppm
Increased breathing rate leading to severe
breathing difficulties and collapse.
Personal detectors indication limit is
100ppm, so if reading is 100ppm, actual
concentration may be greater. Persons
don RPE & proceed to muster.
2.1.1 Unpleasant Odour
Hydrogen Sulphide has an obvious and unpleasant odour at 0.13 ppm and is quite noticeable at 4.6
ppm (API RP 55). These levels of H2S are considered as nuisance only, and there is no impact on
health. However if low levels of H2S are not anticipated, then persons should remove themselves
from the area and advise the operations team.
2.1.2 Eight (8) Hour Time Weighted Average (TWA)
The UK Health and Safety Commission sets Workplace Exposure Limits (WEL) under COSHH, in
order to protect the health of workers. WELs are concentrations of hazardous substances in the
air, averaged over a specified period of time referred to as a time-weighted average (TWA). Two
time periods are used: long term (8 hours) and short term (15 minutes). The long-term (8 Hour
TWA) exposure limit is intended to control such effects by restricting the total intake by inhalation
over one or more work shifts, depending on the length of the shift. The Health and Safety
Executive document EH40/2005 defines the 8 Hour TWA for Hydrogen Sulphide as 5 ppm.
In addition, SP-1231 ‘HSE Specification for Occupational Health’ defines the use of the
occupational exposure limits (OELs) for all chemical and physical agents to be the Threshold Limit
Values (TLVs). Typically, these are as defined in the latest annual edition of the American
Conference of Governmental Industrial Hygienists (ACGIH) and Biological Exposures Indices (BEI)
booklet. Where a different OEL is defined by local legislation or by PDO, the Corporate Industrial
Hygienists will publish this within SP-1231. For H2S exposure, PDO use 5ppm for an 8 hour
exposure.
No significant adverse health effects are expected at the specified H 2S concentration and time, i.e.
the dose.
If persons read 5ppm or above on their personal H2S monitor, they should remove
themselves from the area and advise the operations team.
2.1.3 15 Minute Short Term Exposure Limit (STEL)
As 2.1.2, the UK Health and Safety Commission sets WELs for short term exposures (15 minutes).
Short-term exposure limits (STELs) are set to help prevent effects, such as eye irritation, which may
occur following exposure for a few minutes. The Health and Safety Executive document EH40/2005
defines the 15 Minute STEL for Hydrogen Sulphide as 10 ppm.
As above, SP-1231 defines the use of the occupational exposure limits (OELs) for H2S exposure.
PDO use 10ppm for 15 minutes STEL.
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No significant adverse health effects are expected at the specified H2S concentration and time, i.e.
the dose.
Personal detectors in use within PDO, will track the H2S levels in the air and are set to alarm at
10ppm.
The fixed plant H2S detection system should also alarm at 10ppm, in line with DEP32.30.20.11 Fire
& Gas Detection.
If personal detector alarms, persons hold breath, don RPE & proceed to muster.
2.1.4 Emergency Planning
An average concentration of 100 ppm of Hydrogen Sulphide over an exposure time of 60 minutes is
used by the American Industrial Hygiene Association (AIHA) (ERPG-3) and the Canadian
regulatory body ERCB for defining the extent of the Emergency Planning Zone.
Exposure to 100 ppm of Hydrogen Sulphide has been associated with coughing, eye irritation, and
loss of sense of smell after 3 to 15 minutes. Altered respiration, pain in the eyes, and drowsiness
after 15 to 20 minutes, followed by throat irritation after one hour. Prolonged exposure results in
gradual increase in the severity of these symptoms (API RP 55).
ERPG tiers in use in PDO are defined as follows:
ERPG-3 is the maximum airborne concentration below which it is believed that nearly all
individuals could be exposed for up to 1 hour without experiencing or developing lifethreatening health effects.
ERPG-2 is the maximum airborne concentration below which it is believed that nearly all
individuals could be exposed for up to 1 hour without experiencing or developing
irreversible or other serious health effects or symptoms which could impair an individual’s
ability to take protective action.
Table 2-2
ERPG Limits in use in PDO for H2S AIHA (2014)
Contaminant ERPG Level
ERPG-3
ERPG-2
H2S (ppm)
100
30
PDO uses ERPG-2 as the internal concentration for defining Control Room impairment, and
calculation of Protection Factors for RPE..
2.1.5 Onset of Significant Health Effects
The UK Health and Safety Executive suggest a 30 minute long term exposure of 400 ppm (i.e. in
excess of 300 ppm) as the maximum exposure (dose) that may be received with a negligible
statistical probability of fatality and without impairment of an individual’s ability to escape
(SPC/Tech/OSD/30).
Marked conjunctivitis and respiratory tract irritation may occur when exposed to Hydrogen Sulphide
concentrations at 300 ppm (API RP 55).
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PDO uses 300 ppm as the level of concern for the Onset of Significant Health Effects for Hydrogen
Sulphide. This is the value used in determining the Simultaneous Operations (SIMOPS) zone.
2.1.6 Onset of Worker Fatalities
For PDO / Contractor personnel with suitable respiratory protective equipment and knowledge to
self-escape, the onset of immediate fatality due to exposure to Hydrogen Sulphide (or the
concentration that is lethal to 1% of the population is 650ppm) based on Shell advice on UK Health
and Safety Executive Specified Level of Toxicity (SLOT).
For use in QRA, PDO has adopted the following concentrations of H2S in air:
Page 11
1% probability of fatality
650ppm
50% probability of fatality
1000ppm
100% probability of fatality
1320ppm
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3 Sulphur Dioxide (SO2) - The Basics
Describe the process owners responsibilities, relating this to a defined job description where
possible.
Combustion of fluids containing H2S produces Sulphur Dioxide (SO2). SO2 is a colourless gas which
is very toxic. It has a characteristic, irritating, pungent odour. Through inhalation, skin and/or eye
contact SO2 affects the eyes, skin and respiratory system. Exposure can result in irritation to eyes,
nose and throat; discharge of thin mucus; choking, cough; and narrowing of air passages (NIOSH
2005-149).
Table 3-1 identifies the limits which are put in place to understand and manage the associated
hazards. Further explanation of these limits is provided in the subsequent sections.
Table 3-1
SO2 Levels of Concern
Level of Concern
Sulphur
Dioxide
(Concentration, Time)
Immediate Impact on Health & Work
Unpleasant Odour
0.35 ppm
Nuisance smell only; no adverse health
effect.
Unless SO2 levels are expected, persons
should remove themselves from the area
and advise the operations team.
8 Hour TWA (Threshold Limit
Value)
None quoted by ACGIH
(see 3.1.2)
15 Minute STEL (Short Term
Exposure Limit) ACGIH
0.25 ppm, 15 minutes
No adverse health effects for short term
exposure.
Alarm level for personal SO2 detectors.
Persons don RPE & proceed to muster.
Emergency
Planning ERPG-
Response
25 ppm, 60 minutes
Eye
irritation,
symptoms.
chronic
respiratory
Persons don RPE & proceed to muster.
3
Onset of Significant Health
Effects
400ppm
Increased breathing rate leading to
severe breathing difficulties and collapse.
Persons don RPE & proceed to muster.
Onset of worker Fatalities
965ppm (5 mins)
Severe respiratory distress & collapse
Persons don RPE & proceed to muster.
SP-1231 ‘HSE Specification for Occupational Health’ defines the use of the occupational exposure
limits (OELs) for all chemical and physical agents to be the Threshold Limit Values (TLVs). These
are defined in the latest annual edition of the American Conference of Governmental Industrial
Hygienists (ACGIH) and Biological Exposures Indices (BEI) booklet. Where a more stringent OEL
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is defined by local legislation or by PDO, the Corporate Industrial Hygienists will publish this within
SP-1231. For SO2, PDO use the ACGIH concentrations.
It should be noted that SO2 detectors, fixed / personal, shall be provided in the event that SO2
streams are processed on the facility.
3.1.1 Unpleasant Odour
SO2 can be detected by smell at concentrations of 0.35-1.05 ppm and has a pungent, irritating
odour with an odour threshold of 0.67-4.75 ppm. (Acute Exposure Guideline Levels for Selected
Airborne Chemicals: Volume 8, Committee on Acute Exposure Guideline Levels).
3.1.2 8 Hour Time Weighted Average (TWA)
PDO follows the American Conference of Governmental Industrial Hygienists (ACGIH). No 8 hour
exposure concentration is quoted in the latest version of the BEI.
For information only, the NIOSH Recommended Exposure Limit (REL), Time Weighted Average for
8 hours is 2ppm, which in compliance with the F&G DEP (32.30.20.11) for the alarm set point 1;
AL1, for fixed plant SO2 detection.
3.1.3 15 Minute Short Term Exposure Limit (STEL)
PDO follows the American Conference of Governmental Industrial Hygienists (ACGIH) 15 Minute
STEL for Sulphur Dioxide, which is 0.25 ppm. This is the limit where personal SO2 detectors alarm.
3.1.4 Emergency Planning
ERPG levels are defined for SO2. An average concentration of 25ppm of Sulphur Dioxide over an
exposure time of 60 minutes is used by the AIHA (ERPG-3) to define “the maximum airborne
concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour
without experiencing or developing life-threatening health effects.”
Therefore, should SO2 be the dominant hazard:
ERPG-3 level should be used to define the zone in which Emergency Planning
Requirement s / Contingency Plan shall be functional.
ERPG-2 is used within PDO as the internal concentration for Control Room Impairment.
Table 3-2
ERPG Limits in use in PDO for SO2 AIHA (2014)
Contaminant ERPG Level
ERPG-3 (ppm)
ERPG-2 (ppm)
SO2
25
3
3.1.5 Onset of significant Health Effects
The 400 ppm should be used as a basis for the onset of significant health effects (Health effects of
Project Shad Chemical agent: Sulfur dioxide [CAS 7446-09-5], Prepared for the National
Academies by The Center for Research Information, Inc, 2004).
If SO2 is the dominant hazard, then this is the value to be used in determining the SIMOPS zone.
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3.1.6 Onset of worker Fatalities
For PDO / Contractor personnel with suitable equipment and knowledge to self-escape, the onset
of immediate fatalities due to exposure to Sulphur Dioxide is approximately 965 ppm; 5 minute
time-weighted average dose, based on the UK Health and Safety Executive SLOT dangerous toxic
load, “Indicative human vulnerability to the hazardous agents present offshore for application in risk
assessment of major accidents” (SPC/Tech/OSD/30).
For use in QRA, PDO has adopted the following concentrations of SO2 in air:
Page 14
1% probability of fatality
965ppm
50% probability of fatality
2400ppm
100% probability of fatality
3860ppm
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4 H2S Facilities Classification
4.1
H2S Classification Definitions – Sweet, Sour, Critical Sour
The following classification applies to all PDO Hydrocarbon Facilities:
Table 4-1
Facility Classification for Gas Streams
Sweet
≥ 100ppm
Sour
Critical Sour
<100ppm H2S in gas phase
<approaching 5 bar(a) H2S
partial pressure (PP)
Examples of 5 bar (a)PP
Pressure
(bara)
H2S % (ppm)
20
25% (250,000)
50
10% (100,000)
100
5%
400
1.25% (12,500)
(50,000)
Approaching & >5 bar(a)
H2S partial pressure
The classification is based on the worst case process stream. A thorough review of the Heat &
Material balances should be conducted, to ensure that they are complete and accurate. The most
onerous H&MB composition, with respect to H2S partial pressure shall be used to determine the
classification of the facility. In addition see Section 4.2 and SP-1190-3.
Facilities which are predicted to become more sour over the facility lifetime, shall select the most
onerous composition for design as sour design requirements are extremely difficult, complicated
and high in personnel risk to retrofit.
Classification of the well fluids / process streams on the facilities shall be conducted once sampling
of the fluids has been conducted in accordance with PR-1080, and PR-1096.
The operational pressure and the composition of the process stream will determine the likely
distance to which the H2S hazard can extend. The H2S partial pressure for the gas stream is simply
calculated by multiplying the % H2S in the stream by the operating pressure in bar(a).
Non-gaseous streams are classified based on the mg/l of H2S contained within the liquid phase.
An earlier study was carried out on the Main Oil Line (MOL) in 2012, which assessed the likely
dispersion characteristics of a release from the line, taking account of the 27 different entry points
for fluids into the MOL.
This was based on a 22mm release resulting in a dispersed cloud having a concentration of less
than 300ppm at 2m, which is in line with the previous version of this standard. The results of the
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study are currently applied to the MOL. This revision of SP-1190, shall follow those requirements,
with respect to non gaseous fluids classification.
Table 4-2
Facility Classification for Non - Gaseous Streams
Dispersion modelling results
In the absence of H2S
dispersion modelling
Sweet
H2S 300ppm contour < 2m
from release point
<20 mg/l
Sour
H2S 300ppm contour ≥ 2m
from release point
≥20mg/l
The work carried out for the MOL classification, identified that the likely dispersion of the gas
remaining within the liquids is based on a number of variables, such as TVP, temperature, and H 2S
concentration in the composition. Therefore each stream is likely to disperse different amounts of
gas, and this can be extremely difficult to model, especially at pressures close to atmospheric.
Closed samples shall be taken of the liquid streams, which contain H2S in order to demonstrate
compliance with the classification requirements.
Assets where the classification is based on the H2S concentration of the non-gaseous systems, and
where concern over H2S levels exist, such as samples recording levels close to 20mg/l, shall take
account of the likely error bands in the Garret Gas Train (GGT) sampling mechanism.
The temperature and the volatility of the fluids will impact the potential dispersion characteristics.
This can be significant especially in the case of pipelines, carrying export fluids, and therefore
dispersion calculations shall be the basis for classification.
The dispersion calculations are based on the following:
a 22mm release size with an endpoint of 300ppm,
All dispersion calculations shall typically be conducted in compliance with the guidance provided in
SP-1258, QRA using Shell FRED and PR-2219. The calculations shall be based on the F2
meterological conditions, and an appropriate surface roughness for the site. In this particular case,
and only for the classification of facilities, in a variation from the SP-1258, Instantaneous sampling
should be used for these mixed fluids releases. Using instantaneous sampling is more
conservative, and shall be used for both on-plot and off-plot classification.
To summarise the facility shall be classified based on what is carried through its pipes & equipment,
rather than what the pipes and equipment are made of. The classification shall be recorded within
the relevant HSE Case. The Classification should also be provided to the Geomatics department
(XGG), to allow them to input it into PDO Earth.
The classification of a facility shall determine the level of controls which are required for a facility as
a whole.
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H2S Classification Decision Flow chart
The Responsibilities for H2S Classification of the Assets are as noted in
Table 4-3
H2S Classification Responsibilities
Input / Activity
Discipline
1. Provide TA2 Approved Input Data
a) PVT, or / and
Reservoir Engineer
b) H&MB
Concept / Process Engineer
2. Conduct dispersion for multiphase fluids
Technical Safety Engineer
3. Assign Classification
Technical Safety Engineer
4. Add Classification to HSE Case and provide input to XGG for
inclusion in PDO Earth
Technical Safety Engineer
5. Approve the H2S Classification
Asset DTL
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If a facility is classified as SWEET, no further application of this standard is required. However, the
classification exercise shall be formally recorded and levels of H2S shall be monitored, by site
sampling. The classification exercise should be re-assessed every 4 years, or in the event of a
significant fluid change.
The frequency of the sampling regime will be commensurate with the perceived risk, based on the
likely consequences of an increase in H2S concentrations to the facility materials of construction,
and the impact of a release at that location. It shall also be based on the management of historical
sampling data to measure any trends. Any increase in H2S levels, which result in a change in the
classification of the facility shall be fully evaluated. The evaluation shall take account of the
consequences on risks and management of such at the facility, in compliance with the Management
of Change Code of Practice (CP-206). The existing PR-1080 identifies that H2S measurements
should be taken as part of any well test.
A summary of the changes in the classification basis is noted in Section 8, Appendix B.
As noted in 2.1.4, 100ppm H2S is the Emergency Planning Requirement for concentration of H2S in
air. This is considered a level where personnel will be able to remove themselves from any incident
without additional measures, such as breathing apparatus. If there is less than 100ppm in the
process stream then any leak from the equipment to the atmosphere will be dispersed and will
result in concentrations much less than 100ppm, irrespective of the pressure of the contained fluids.
The pressure of the fluid will determine how far the dispersed components may travel, but it will
remain below the 100ppm level.
For the purpose of the design of new piping and equipment, or during a Management of Change
process, the design process fluid composition shall address the range of H 2S concentrations over
the lifetime of the facility.
Many facilities are operated worldwide with high concentrations of H 2S, however these are typically
operated at low pressure. As part of the Enhanced Oil Recovery (EOR) requirements for extracting
oil in Oman, PDO now operates facilities which have well fluids, process systems and gas injection
which have high levels of H2S, measured in terms of percentages, and very high operating pressures,
typically above 400 bar. Recent QRA’s conducted for PDO facilities, such as Birba, Al Noor and
Harweel have indicated that the risks to individuals for high H 2S partial pressure plants are at the
upper limit of tolerability (SP-1258 for further details). Therefore, a second tier of sour classification;
Critical Sour is required to capture the operational and design requirements, which leads to a step
change in the way that risks are managed due to the inherently high nature of the risk posed by
these operations.
4.2
Facility Classification entirety or part of facility
The entire facility shall be given a single classification. The classification process shall apply to all
facilities, both new and existing, to both on plot and off plot infrastructure, including subsurface
pipelines, flange pits etc.
An exception to the above statement is for facilities where the areas of differently classified
equipment’s are located such that they are an H2S Classification Distance from each other. The
H2S Classification Distance is based on partial pressure of the fluids and the dispersion
characteristics of the release. Further details are provided within SP-1190-3 Design Engineering.
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SO2 or CO2 Classification
The requirement to classify a facility due to the presence of SO2 and CO2 is not addressed within
this SP-1190, but guidance to be sought from the CFDH Technical Safety (TA1), in the event that
the process streams have a higher toxic concentration of SO2 & CO2 than the H2S concentration.
Historically within PDO, H2S has been the bounding case.
For information, the current IDLH for SO2 is 100ppm and & 40,000ppm for CO2. For updates of
IDLH values refer to www.cdc.gov/niosh/idlh.
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5 Zoning of Sour & Critical Sour Facilities
Facilities which are classified as either Sour or Critical Sour are further zoned, within and outside of
the facility to manage the effects of the hazards. The zoning of the facility drives which controls
shall be provided within these specific areas. Further details are provided of the zoning
requirements for design, i.e. sizing of the zones, in SP-1190-3. The operational requirements for
working within the zones are noted within SP-1190-4.
5.1
Red and Yellow Zoning
Red Zones are established in specific areas within Critical Sour facilities where the concentrations
and pressures of H2S in process fluids requires additional precautions to be taken, such as donning
or carrying breathing air.
Yellow Zones are implemented in both Critical Sour and Sour facilities where a 22mm release from
the process can result in a toxic atmosphere which has the potential to cause fatalities.
5.2
Emergency Planning Zone (EPZ) Classification
The Emergency Planning Zone is an area where given a worst case release, there may be levels of
H2S present in the air of 100ppm, or greater for 60 minutes. The EPZ is in place to inform persons
of the potential hazards, to recognise and minimise the consequences of an H2S event and to allow
PDO to manage the risks to As Low As Reasonably Practicable (ALARP).
Critical Sour facilities shall apply the Emergency Planning Zone (EPZ) concept.
Sour Facilities shall initially screen and review their H2S release scenarios for pipelines entering
and exiting the facility using Shell FRED, to determine the extent of the 100ppm contour. Further
details are found in SP-1190-3.
5.3
SIMOPS Zoning (Simultaneous Operations) Classification
Activities involving large maintenance and construction workforces, at Sour or Critical Sour facilities
shall be subject to Quantitative Risk Assessment (QRA), in accordance with PDO specification SP1258. An ALARP demonstration, in accordance with PDO specification SP-2062 shall be prepared
to show that the risks to the construction workforce are identified, understood and are tolerable
taking account the duration of the works. The SIMOPS Zones are based on the sphere of influence
from toxic operations taking account of the dispersed 300 ppm H2S contour, at a certain frequency
(Shell SHEPHERD).
In practice within PDO, inner and outer SIMOPS Zones have been established, based on the
SIMOPS QRA models. These SIMOPS zones apply for both on plot and off plot facilities. In the
case of well works being conducted exclusion zones shall apply for the period of the intervention.
Further details are found in SP-1190–3.
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Well Test Flaring Zoning
Well fluids with H2S in the composition will release SO2 if a well test unit (WTU) is flaring.
Preferentially WTU should be provided with a route to minimise flaring, however, if flaring cannot be
avoided then precautions must be taken to limit the effect of the SO2. In the event that the flare
was to be extinguished, there is also the potential for H2S to impact persons in the area.
Well test flaring zoning shall be implemented when the H2S levels in the composition result in
dispersion distances for 5ppm SO2 (ignited flare), or 300ppm H2S (flame-out) at distances which
are greater than the controlling thermal radiation hazard. Further details are found in SP-1190–2.
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6 Critical Sour & Sour Contract HSE Requirements
All projects which are conducted by contractors of behalf of PDO, follow the GU-140 Standard
Contract format.
Section C4 provides details of the scope and the required deliverables for the project phase.
Projects which are classified as Critical Sour shall have the deliverables list enhanced as noted in
SP-1190-3, to ensure the sour hazards are captured early in the design.
The HSE Section, C9 is typically dominated by the HEMP and HSE training requirements. Critical
Sour and Sour projects shall provide the following additional information in C9.
Details of any existing or new/ associated Emergency Planning Zones, and the principles
to be satisfied.
For existing site and project interfaces, any SIMOPS Zones, their requirements and the
existing MOPO.
Details of any Red / Yellow Zones and their requirements.
Requirements for emergency drills & rescue provision (in construction phase).
Compliance with the SP-1190 series of standards.
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7 Appendix A Glossary of Definitions, Terms and Abbreviations
7.1
General Definitions
The lower-case word shall indicates a mandatory requirement.
The word should indicates a recommendation.
7.2
Key Terminology
Table 7-1
Key Terminology
Term
Explanation
Sweet Facility
The classification given to a facility or wellhead containing fluids with Hydrogen
Sulphide concentrations below 100ppm in the gas phase and less than 20mg/l in
the non-gaseous phase.
Sour Facility
The classification given to a facility or wellhead containing fluids with
concentrations of Hydrogen Sulphide above 100ppm in the gas stream and more
than 20mg/l in the non-gaseous phase.
Critical Sour Facility
A facility which operates with partial pressures of H2S approaching or above 5
bar(a).
The definition is purposefully worded, as approaching 5 bar(a), such that facilities
which process 4.9bar(a), and those which process 5 bar(a) are not afforded
different risk reduction measures without due consideration to the whole risk
picture.
Where facilities operate with partial pressures of H2S above 4 bar(a), but under 5
bar(a), an assessment of the conditions shall be made to determine whether the
additional controls in place for the defined Critical Sour Facilities, are required in
this case. The assessment shall be recorded and form part of the facility ALARP
justification, and shall be included in the facility HSE Case.
Critical Sour classification is required to capture the operational and design
requirements, which lead to a step change in the way that risks are managed,
due to inherently high residual individual risk levels.
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Abbreviations
ACGIH
American
Conference
of
Governmental Industrial Hygienists
NIOSH
National Institute for Occupational Safety and
Health
AEGL
Acute Exposure Guideline Levels
OEL
Occupational Exposure Limit
AIHA
American
Association
PPM
Parts Per Million
BEI
Biological Exposures Indices
RPE
Respiratory Protective Equipment
COSHH
Control of Substances Hazardous
to Health Regulations
SCBA
Self Contained Breathing Apparatus
EPA
Environmental Protection Agency
(US)
SLOT
Specified Level of Toxicity
EPZ
Emergency Planning Zone
STEL
Short Term Exposure Limit
ERCB
Energy Resources Conservation
Board
TLV
Threshold Limit Values
ERPG
Emergency
Guidelines
TVP
True Vapour Pressure
GGT
Garret Gas Train
TWA
Time Weighted Average
IDLH
Immediately Dangerous to Life &
Health
WEL
Workplace Exposure Limit
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8 Appendix B, Classification Changes
This Appendix highlights the change in the classification requirements from Rev 3 to Rev4.
There is no change in Classification basis from Revision 4 to Revision 5.
8-1
Classification Difference on Gas Streams
SP-1190 Revision 3
SP-1190 Revision 4 & 5
Class
H2S concentration
Class
H2S concentration
Sweet (inferred)
< 50ppm
Sweet
<100ppm
Low Risk Sour
50ppm<
Low Risk Sour
<500ppm
High Risk Sour
≥500ppm
Critical High Risk
Sour
As High Risk Sour +
EPZ greater than
50m
8-2
100ppm ≤
Sour
Sour
<approaching 5 bar H2S
partial pressure
Critical Sour
Approaching & > 5 bar
H2S partial pressure
Classification Difference on Non-Gaseous Streams
SP-1190 Revision 3
SP-1190 Revision 4 & 5
Class
H2S concentration
Class
H2S concentration
Sweet (inferred)
--
Sweet
Dispersed H2S <300pm
@ 2m,
Or <20mg/l
Low Risk Sour
<0.03 wt%
Sour
Dispersed H2S ≥ 300pm
@ 2m,
Or ≥20mg/l
Page 25
High Risk Sour
≥0.03wt% &
dispersion model
Critical High Risk
Sour
As High Risk Sour +
EPZ greater than
50m
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9 Appendix C, Classification Dispersion Graphs
This appendix provides details of the likely H2S dispersion characteristics associated with different
pressures and temperatures which may be encountered within the PDO facilities.
Figure 9-1 illustrates the potential contour distances for a 22mm release from a methane stream
with 100ppm H2S. This is included to show that a Sweet Facility may still see low levels of H2S.
Dispersion Contours for a 100 bara, 22mm release at H2S concentration of
100ppm
3.5
3
95ppm
release height (m)
2.5
80ppm
70ppm
2
50ppm
40ppm
1.5
30ppm
20ppm
10ppm
1
5ppm
0.5
0
0
Figure 9-1
2
4
6
8
10
12
Release Distance (m)
14
16
18
Dispersion Contours for a 22mm release from a 100 bara system, with
internal H2S Concentration of 100ppm in methane
FRED dispersion calculations have been run to determine the likely level of H2S in air due to a 2mm
and 22mm release event from a 100ppm H2S concentration in a methane stream.
Figure 9-2 indicates the likely release distances to 5ppm and 10ppm contours based on the stream
release pressure.
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Dispersion Distances to 5ppm & 10ppm from 100ppm H2S Stream
700
600
system pressure (bar)
500
2mm 5ppm
2mm 10ppm
400
22mm 5ppm
300
22mm 10ppm
200
100
0
0
Figure 9-2
10
20
distance (m)
30
40
Dispersion Distances of 100ppm H2S stream to 5ppm & 10ppm from 2mm &
22mm release size
Figure 9-3 and Figure 9-4 illustrate the distance which H2S can travel at low concentrations,
assuming a release from a 1% (10,000ppm) H2S stream, with varying operational pressure.
For example in Figure 9-3, a 2mm release of methane containing 10,000 ppm H2S, from a 100
bar(a) system, will disperse 5 ppm H2S to approximately 200m, while a 22mm release (as noted
Figure 9-4) with the same conditions will disperse 5ppmH2S to 5000 m distance.
It should be noted that for lower concentrations of H2S (such as 5ppm), and distances beyond 2-3
km, the dispersion should be reviewed using the ADMS tool.
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Dispersion Distances to 5ppm & 10ppm from a 1% H2S Gas Release
(2mm)
450
400
system pressure (bar)
350
300
250
2mm 5ppm
200
2mm 10ppm
150
100
50
0
0
Figure 9-3
100
200
distance (m)
300
400
Dispersion Distances of 1% H2S gas stream to 5ppm & 10ppm from 2mm
release
Dispersion Distances to 5ppm & 10ppm from a 1% H2S Gas Release
(22mm)
450
400
system pressure (bar)
350
300
250
22mm 5ppm
200
22mm 10ppm
150
100
50
0
0
5000
10000
15000
distance (m)
Figure 9-4
Page 28
Dispersion Distances of 1% H2S gas stream to 5ppm & 10ppm from 22mm
release
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Figure 9-5 shows the impact of increasing partial pressure on dispersion distances to the 1,320ppm H 2S
contour. PDO assumes a 100% probability of fatality, when a concentration of 1,320ppm H 2S in air is
attained.
Distance to 1320ppm H2S based on increasing H2S Partial Pressure
(Constant composition, varying pressure)
12
Release Height (m)
10
8
1 bara
2 bara
6
3bara
4bara
4
5bara
2
6bara
0
0
50
100
150
200
250
300
350
Distance(m) to 1320ppm H2S (100% Fatality Level)
400
450
Figure 9-5 Figure illustrating the influence of increasing partial pressure on
dispersion distances
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10 Appendix D User Comment Form
User Comment Form
If you find something that is incorrect, ambiguous or could be better in this Specification, write
your comments and suggestions on this form. Send the form to the Document Custodian.
Procedure Details
Number:
Title:
Page Number:
Issue Date:
Heading Number:
Figure Number:
Comments:
Suggestions:
User’s personal details
Name:
Ref.
Ind.:
Signature:
Date:
Phone:
Document Control Section Actions
Comment
Number:
CFDH
Ref. Ind.:
Date:
Recd.:
CFDH Actions
Decision:
Recd.
Date:
To CFDH:
Ref.
Ind.:
Inits.:
Reject:
Accept, revise at next issue:
Accept, issue temporary amendment



Date:
Comments:
Originator
Advised:
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