Effective: May-12
Petroleum Development Oman L.L.C.
Document Title: Hydrogen Sulphide (H2S) Management
Document ID / PR-1078Document Type / Procedure
Security / Unrestricted
Discipline / Engineering and Operations
Owner / UOP – Functional Operations Manager
Issue Date / May 2012
Revision / 4.1
This document is the property of Petroleum Development Oman, LLC. Neither the whole nor any part of this document may be disclosed to others or reproduced, stored in a retrieval system, or transmitted in any form by any means (electronic, mechanical, reprographic recording or otherwise) without prior written consent of the owner.
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i Document Authorisation
Authorised For Issue – May 2011
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.
Revision No. / Date / Author / Scope / Remarks4.1 / May-12 / Robin Norman UOP61 / See Interim Amendment 1078_0512_01
4.0 / Apr-11 / Tom Moffat UOP95 / Update, revise, reformat in conjunction with UOP, HSE, UEP
3.0 / Jul-07 / Robin Norman UOP6 / Reformat and revision in conjunction with HSE Engineers.
2.0 / Feb-01 / UOP1 / Minor Revision of 2.2.5 & 2.8 to incorporate user feedback comments
1.0 / Sep-98 / UOP1 / SI-02 rewritten to new format and merged with SI-10.
iii Related Business Processes
Code / Business Process (EPBM 4.0)EP.71 / Produce Hydrocarbons
EP.72 / Maintain & Assure facilities Integrity
iv Related Corporate Management Frame Work (CMF) Documents
The related CMF Documents can be retrieved from the CMF Business Control Portal.
Refer to Appendix 2
TABLE OF CONTENTS
i Document Authorisation 3
ii Revision History 4
iii Related Business Processes 4
iv Related Corporate Management Frame Work (CMF) Documents 4
1 Introduction 7
1.1 Background 7
1.2 Purpose 7
1.3 Key Rules regarding H2S 7
1.4 Changes to the Document 8
1.5 Step-out Approval 8
2 H2S Hazards, Classification and Access Control 9
2.1 Physiological Properties 9
2.2 Physical Properties of H2S 9
2.3 Facility Classification and Area Controls 10
2.4 Area H2S Classification within a Sour Facility 11
2.5 Access Prerequisites 11
2.6 Numbers Permitted to Enter (at any one instance) 12
2.7 Departure 13
2.8 Work Outside of Facility Perimeter Fences 13
2.9 Formal H2S Training Courses 14
3 H2S Safety and Emergency Response 15
3.1 Activities requiring BA 15
3.2 H2S Detection 15
3.3 Alarms and Mustering 16
3.4 Rescue 16
3.5 Emergency Procedures and Drills 16
4 Safe Worksite Practices in H2S Facilities 17
4.1 Job Planning, Hazard Identification and Assessment 17
4.2 Permit to Work 18
4.3 Isolation Procedures 18
4.4 Purging and Returning Equipment to Service 18
4.5 Sample Points and Safe Sampling 18
Appendix 1 - Abbreviations 19
Appendix 2 – Reference Material 20
Appendix 3 - User Feedback Page 21
Interim Amendment 1078_0512_01 22
1 Introduction
1.1 Background
Hydrogen Sulphide (H2S) is an extremely dangerous substance and can cause fatalities if not managed properly. H2S is present in more of PDO’s operations as existing fields begin to sour and as high sour developments are brought on stream. This procedure deals with the identification and assessment of the hazards and the management of the associated risk for “sour gas”, or gas containing H2S.
H2S in the upstream oil and gas industry comes from:
· the original reservoir, as a result of the hydrocarbon source material and the conditions under which it was converted to oil and gas. If this is the case then H2S will be produced with the fluids
· the reservoir after prolonged injection of water with oxygen (brackish or formation water) which may result in 'souring' of the fluids within it due to the action of sulphate reducing bacteria (SRB) introduced during the injection process. Any H2S will be subsequently produced with fluids.
1.2 Purpose
The purpose of this procedure is to outlines the hazards associated with H2S and the steps required to assess and manage the associated risk, and protect personnel within Production Operations.
1.3 Key Rules regarding H2S
a) Facilities are classified as either sweet, low sour, high sour or critical sour (refer to Section 2 - Classification). Unless facilities are classified as sweet, H2S management procedures shall be followed at all times. Additional rules apply to high or critical sour facilities.
b) When dealing with sour gas, the primary focus should be on the controls that prevent release or exposure, and a secondary but also important focus should be on the recovery measures. These are illustrated in the bow-tie diagram below:
c) Strict access control requirements are mandated for sour facilities
d) Personnel shall have specific training to work in or visit sour facilities
e) Breathing apparatus shall be worn for specific activities
f) Emergency response plans are established for all facilities, and sour facilities shall have Emergency Response Procedures (ERP’s) which specifically address the sour aspects of the operation. Drills shall be conducted regularly to keep personnel trained on the ERP’s.
g) A combination of fixed and portable H2S detection systems shall be used to provide warning of the presence of H2S in the atmosphere.
h) Risk assessments shall be done for sour activities, and the job procedures, hazards and controls shall be identified to ensure the work is done safely
i) Sour equipment shall be properly isolated, gas freed and made safe prior to breaking of containment. When returning to service, proper assembly, tightening, purging and leak testing shall be carried out to ensure integrity.
j) Sampling of sour fluids will be strictly controlled and managed, using engineered sample points, breathing apparatus and the buddy system.
1.4 Changes to the Document
Responsibility for the upkeep of the Document shall be with Functional Operations Manager UOP, the Owner. Changes to this document shall only be authorised and approved by the Owner.
Users of the Document who identify inaccuracy or ambiguity can notify the Custodian or his/her delegate and request changes be initiated.
The Document Owner and the Document Custodian should ensure review and re-verification of this procedure every 3 years.
1.5 Step-out Approval
This procedure is mandatory and shall be complied with at all times. Should compliance with the procedure be considered inappropriate or the intended activity cannot be effectively completed or safely performed, then step out authorisation and approval shall be obtained in accordance with PR-1001e – Operations Procedure Temporary Variance, prior to any changes or activities associated with the procedure being carried out.
2 H2S Hazards, Classification and Access Control
2.1 Physiological Properties
H2S has acute effects on people, as follows:
Level of Concern / H2S concentration in air /Unpleasant Odour / 0.13 ppm
8 Hour Threshold Limit Value (TLV) / 5 ppm
Immediately Dangerous to Life and Health (IDLH) / 100 ppm
Onset of significant health effects / 300 ppm
Immediate unconsciousness, onset of worker fatalities / 650 ppm
NOTE: 1% H2S equates to 10,000 ppm
2.2 Physical Properties of H2S
· H2S is extremely toxic and can cause death at very low concentrations
· H2S, also known as sour gas, is a colourless toxic, corrosive and flammable gas, which is heavier than air and tends to collect in low-lying areas such as trenches, sumps and confined spaces.
· H2S reacts with the internal surfaces of carbon steel vessels in the absence of oxygen to form pyrophoric iron sulphide. Pyrophoric iron sulphide can auto-ignite when exposed to air.
Property / CharacteristicColour / Colourless
Odour / H2S concentration, when:
<100 ppm - has a distinctive, offensive smell – similar to rotten eggs
>100 ppm - impairs the sense of smell; therefore, the nose cannot be relied upon to detect the presence of H2S
Vapour Density / 1.189 – heavier than air
Explosive limits and flammability / 4.3 to 46 percent – by volume in air
H2S explodes over a very wide range, when:
· mixed in the right proportions with air (oxygen), and
· there is a source of ignition.
Burns readily (with a distinctive blue flame)
Produces Sulphur Dioxide (SO2) – another toxic gas
Auto Ignition Temperature / 260ºC
Reactivity / Can react with carbon steel, in the absence of oxygen – forming Pyrophoric Iron Sulphide (on the internal surfaces of vessels), which in turn can react upon contact with air (oxygen) – auto igniting
Water Solubility / H2S is:
· Readily dissolved in both water and hydrocarbons
· Dependent on temperature and pressure to be soluble
· Quickly released, by simply agitating the fluid
Corrosives / H2S forms a corrosive mixture with water
Boiling Point / · 60ºC at normal pressure
· Liquefied H2S boils at a very low temperature and is normally found as a gas
2.3 Facility Classification and Area Controls
Facilities in PDO are classified as follows:
1. Sweet
2. Low Risk Sour
3. High Risk Sour
4. Critical Sour (currently only applies to Harweel 2AB, Birba and Al Noor facilities)
Each facility in PDO is classified according to criteria set out in SP-1190 - Design For Sour Service Specification. Operations staff at each facility shall understand the classification of their facility and the appropriate level of controls that apply:
Facility Classification / Basic RequirementsSweet / No additional requirement to base standards
Low Risk Sour / · Company/Contractor personnel shall be made aware of the hazard and the appropriate actions to escape or shelter from a credible release of the hazard.
· Competencies in H2S, breathing apparatus, and sour work practices
High Risk Sour And Critical Sour / As stated above plus:
· Company/Contractor personnel shall be provided with suitable equipment and knowledge to self-escape to a place of safety in case of a credible release.
· Work (or rest) that could reasonably be completed further from the hazard source shall not take place.
· Activities requiring large maintenance or construction work forces shall be subject to Quantitative Risk Assessment and Bow-Tie assessment.
· A SIMOPs plan should be in force for simultaneous operations under different lines of command.
· Emergency Planning Zone (based on toxic risk) and Emergency Response Plans to be established
2.4 Area H2S Classification within a Sour Facility
Within a sour facility, some facilities are zoned on the level of toxic gas risk present in accordance with SP-1190 - Design For Sour Service Specification. This is typically determined by quantitative risk assessment considering the partial pressure of H2S in the process units, the layout/spacing of the unit, and the nature of the work activities there. Sour facilities shall have the zones identified in consultation with Corporate MSE and marked by Operations, and personnel shall be trained accordingly. Rules which apply to the zones are as follows:
Zone / Description / ControlsGreen / Low toxic H2S gas hazard / No additional controls
Yellow / A credible release of H2S could result in a concentration in air above IDLH levels in the vicinity of the process units or in the vicinity of the well. / As High Risk Sour Facility Classification plus:
· The number of persons present shall be actively minimised (reference Section 2.6)
Red / H2S is expected to be present in the breathing zone for an area (confined space, ground level or elevated working platform) as part of normal operations at a concentration in air above the 8 hour TLV.
OR
A credible release of H2S could result in a concentration in air above 650 ppm in the process units or in the vicinity of the well.
AND
The perceived operational risk is higher than in normal operations e.g. operational risk may be perceived to be higher during start up or during periods when a facility is operating with uncertain static integrity, and therefore Red Zone operating rules may be enforced. / As Yellow Zone plus:
· Area / activity specific sour operating procedures including wearing Respiratory Protective Equipment at all times.
· Specific area access control.
2.5 Access Prerequisites
Access to H2S designated areas shall only be allowed provided the following have been adhered to:
· Area Authority or Approved Gas Tester has completed a gas test of the area at the start of the shift and after scheduled breaks, and the recorded results indicate < 5 ppm of H2S in air.
· Valid Permit to Work has been issued, authorised by the Responsible Supervisor, validated by the Area Authority and specifying clearly the reasons for entry.
· Valid H2S Entry Permits are held by all persons entering the sour classified facility and that they have been hung on the numbered slot board in the Control Room.
· Persons entering the restricted area have the correct safety equipment for that area which shall include personal H2S monitors.
· All persons entering the restricted area are fully conversant with the ‘Buddy’ system and are aware of the escape routes and Area Muster Points.
· All persons entering the restricted area have completed and signed the Station Entry logbook i.e. Name, Department, Entry Pass Number and Time In.
Mandatory requirements for personnel entry to sour facilities are shown below.
Facility H2S CategoryLow Risk Sour / High Risk Sour and Critical Sour
Required for Entry / Permit to Work
Or
Access Authorisation Form
Or
Asset Holder Exemption
And
H2S Entry Permit / As for Low Risk Sour
And
Buddy System to be in force (PR-1081 – The Buddy System)
Training Required / Safety Induction.
And
H2S Awareness and Escape Course. / As for Low Risk Sour
Safety Equipment Required / Personal H2S Gas Detector (PDO Approved) / As for Low Risk Sour
And
Respiratory Protective (Escape) Equipment (RPE).
2.6 Numbers Permitted to Enter (at any one instance)
As a general rule the numbers of personnel that shall be allowed to be in a high risk sour facility at any one instance shall be limited to 20. However this shall be governed by the number of personal monitors and escape sets held at site.
Where the work is classed as ‘non-routine work’ i.e. major overhaul of equipment, additional personnel may be permitted on site provided the following criteria are met: