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Gas sampling standard
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Table of Contents
1 Introduction 3
2 Objective 3
3 Scope 3
4 Philosophy 4
5 Workplace assessments: 4
6 Competency and Training 5
7 pre job MEETING 6
8 Selecting the correct measurement method 6
9 Gas detection intrumentation 7
10 gas sampling area 8
11 Defining gas concentration 8
12 Gas dispertion calculation 8
13 Breaking containment 9
14 Precautions While well-Testing 9
15 sampling procedure with manual detection instrumentation 10
16 Gas or liquid containers and bags 10
17 gas monitors 11
18 Manual gas sample procedure 14
19 Manual DLE gas sample procedure 16
20 Contamination of the Sample 17
21 Responsibilities 17
22 Reporting of unintended gas release Incidents: 17
23 References 18
23.1 Internal References 18
23.2 External References 18
24 requirements 18
25 Terms, Abbreviations & acronyms 19
25.1 Abbreviations & Acronyms 19
The purpose of this document is to provide knowledge and understanding of the types of equipment and instrumentation available for use for gas reading and gas sampling. The information is not a comprehensive resource for specific different types of instruments, nor is it intended to replace the individual manuals for different instrumentation. End users shall always follow the specific instrumentations manual and manufacturer recommendations in relation to the specific operation and maintenance of the equipment being used.
There are several acknowledged industry standards related to gas sampling that in detail discuss the potential causes of sample distortion, procedures and sampling techniques
The generally refereed standards for gas sampling in the oil and gas industry are among others:
American Petroleum Institute (API), Manual of Petroleum Measurement Standards, Chapter 14 – Natural Gas Fluids Measurement, Section 1- Collecting and Handling of Natural Gas Samples for Custody Transfer (API 14.1), Gas Processors Association (GPA) Obtaining Natural Gas Samples for Analysis by Gas Chromatography (GPA 2166) and NIOSH Manual of Analytical Methods.
This standard does not seek to go above and beyond these standards but merely state best practice of how to obtain a gas sample. The latest industrial standard should always be referred to if any discrepancies are encountered.
This document aims to deliver guidance on the best practice for gas sampling with electronic or manual gas detecting systems. For the purpose of this document, any reference to gas detectors shall be to the manufacturer’s guidelines. This document is subject to yearly revision and shall refer to the latest international and local regulations where applicable (e.g. the Gas Act 1995, the Utilities Act 2000 in the UK and the API 14.1 in the USA)
This document covers the procedure for taking gas reading and/or samples on locations where MHSS have contractual duties. The document shall discuss various types of instrumentation, calibration and maintenance for direct-reading instruments used for assessing chemical contaminants in air.
The document covers operations performed on or within any asset to which MHSS operates as a contractor or 3rd party operator. Legal requirements and national codes and standards shall be complied with at all times. Where Maersk H2S Safety Services standards are more stringent than national codes and standards, then the Maersk H2S Safety Services requirements shall take precedence. Where a Maersk H2S Safety Services standard appears to be less stringent, then the applicable legal and regulatory requirements shall always be followed and the discrepancy shall be brought to the attention of the relevant department.
The standard will present, in details, a uniform procedure of how to understand and act during gas sampling in areas that can contain potential volatile or toxic gases. Included in the standard is information on:
Toxic gas properties
Gases in relation to personnel
Muster procedure during gas alarms
Requirements for personnel competence and training
Gas detection equipment
Procedure for taking gas samples
Personal protective equipment against toxic gases
Maersk H2S Safety Services strongly believes that Health, Safety, Environment and Quality are of the utmost importance to the employees of the Company. Maersk H2S Safety Services is committed to having an effective HSEQ Management System in place with the commitment and active participation of management and all staff involved at all levels. This is to ensure the safety of all involved personnel.
The aim is to actively incorporate the APMM values to guide our behaviour and ensure that we make decisions that are aligned with our Company culture.
Our policy is to:
Advocate a safe working environment in areas where toxic gases may be present.
Prevent accidents in our workplace that could have been avoided by forward thinking, planning and execution of work in high risk areas.
Uphold a culture that promotes safety in compliance applicable to laws and internal policies and procedures in respect to people, equipment and the environment.
Employ best practices that are practically implementable in striving towards a safe working environment.
Preserve the good health and wellbeing of all employees.
A workplace assessment must be prepared for any operations that involve gas reading or gas sampling operations.
It must include:
A review of essential working conditions (health and safety related risks present in the working environment including the potential risk of volatile and poisonous gases, including any psycho-social issues that can be related to the work offshore.
A description of any health and safety related risks and the extent including:
- A prioritisation of the risks
- A plan for their resolution
- A plan for following up on the work
Competency and Training
All personnel working in or visiting an area where H2S or other volatile gases which could present the risk of exposure shall be provided with the minimum safety training stipulated by the authorities.
The competency and training matrix applies to all personnel within the Restricted Area Zone (RAZ).
No personnel shall be allowed to work or stay within the RAZ until they have been briefed and trained according to this standard.
Personnel working OUTSIDE the designated RAZ and NOT involved in the gas sampling
Personnel performing Watch duties OUTSIDE the designated RAZ
Personnel performing gas-reading with a multi-gas detector or a manual hand-pump
Authorised Gas Tester Level 1
Personnel assigned supervising responsibilities at the site shall have received additional training in the following elements:
Supervisor responsibilities in relation to the contingency plan.
Effects of volatile toxic gases on the human organism.
The importance of personal safety.
Personnel shall receive training on where and when to remove breathing apparatus after completing a job as there may still be gases present. They should be informed to remove the breathing apparatus at a remote location or test the atmosphere adjacent to the job site before doffing the set.
Personnel's medical evaluation and fit test should be taken into account prior to commencing work in areas were volatile or toxic gases may be present.
Any and all employees that have the duty of performing a gas reading or sampling shall have been trained according to the specific task and towards their respective roles.
A minimum requirement of training is the accepted industrial standard training for working in gaseous atmospheres and gas sampling e.g. Authorized Gas Tester level 1-3.
The employer shall retain documentation of all training records for a minimum of five (5) years.
pre job MEETING
Prior to commencement of an operation involving gas sampling, a pre job meeting with special attention to the potential danger of accidental release of volatile gases shall be completed and documented. All involved parties shall participate in the meeting.
The following topics must be discussed and clarified:
Actual work to be carried out
Restricted area definitions and location of barriers
Organisation and line of responsibility
First aid assistance
Action in case of an unintended gas release
Location and position of breathing equipment
Safe muster location(s)
Wind speed and direction
Setting up a system where newly arrived personnel are informed and briefed on the contingency system
Can the area be abandoned immediately?
Precautions in case of installation alarm, general FG alarm or abandon
Precautions in case of power cut.
The above mentioned are not exhaustive and shall be modified according to specific job conditions.
Selecting the correct measurement method
Selecting the correct measurement method is essential when detecting hazardous gases. Each type of measuring principle has its own advantages and disadvantages, and each is more suitable for particular groups of gases (flammable/toxic gases and oxygen). For this reason, it is important to ask which gases/vapours occur in the gas flow being tested.
Normally, following difference between gas risks are used:
Risk of explosion
– Wherever flammable gases and vapours can occur, there is an increased risk of explosion or ignition. Typical areas for this can be confined spaces, mining, refineries, petrochemical industry. Infrared and catalytic bead sensors are used to detect this type of gases and vapours. These sensors usually detect gas concentrations in the LEL (lower Exposure Level) range. Most types of catalytic sensors are depending on a minimum amount of oxygen to be present in the test gas in order to have a chemical reaction occurring in the sensor housing. Lack of oxygen can result in an incorrect gas reading for LEL
Lack or excess of oxygen
Lack of oxygen is life-threatening and can pose a build-up of explosive gases. An excess of oxygen can affect the flammability of certain materials and can cause an auto-ignition. Electrochemical sensors are used to measure oxygen.
Poisonous or toxic gases and substances can be present in a variety of industrial processes offshore and onshore. In tank toxic gases can develop as a result of decomposing organic material e.g. mud that contains bacterial can create H2S if not agitated thoroughly. Electrochemical and PID sensors are normally used to detect toxic gases.
Gas detection intrumentation
Gas detection is conducted with either electronic devices or manual hand-pumps and extraction systems.
Manual gas extraction instruments
Manual gas sample or gas extraction instruments referred to in this document measure gas in ambient air mixture with gases.
In general, two systems are in use:
Direct reading instruments with tubes that chemically react with one or more gases in the test gas flow. E.g. Dräger Manual hand pump, Kitigawa hand pump or GasTec hand pump.
Indirect gas reading instruments that release the gases from a liquid sample enabling the gases to be interpreted with a manual tube system. E.g. Dräger Liquid Extraction Kit.
The manufacturer’s manual shall always be referred to prior to any gas test.
All manual gas detection shall be inspected according to the manufacturers standards prior to use. As a minimum the following checks shall be performed;
Inspect the instrument for any damage.
Inspect that the correct sample tubes are available in the ranges/sequences required.
Perform a leak test for a minimum of one (1) minute.
Correct PPE is ready and tested for the gas sample operation (SCBA, personal detector).
Electronic gas detection instruments
Electronic gas detection instruments referred to in this document measure gas in ambient air mixture with gases. Gas detectors are multi gas detectors with pumps.
Upon activating the instrument, the user shall observe the start-up sequence of the apparatus to ensure all values are set correct for installed sensors and that they are calibrated within the manufacturer’s recommended interval.
If any abnormities are encountered during the instrument start-up sequence they shall be corrected and logged in the gas reading log. If the user is unable to resolve the encountered malfunction or discrepancy, then the apparatus must be red-tagged for further maintenance.
Note that some CH4 sensors require longer warm-up time than electrochemical sensors.
Prior to any gas sample operation, the multi gas detector used shall be inspected according to the manufacturer’s standards. As a minimum the following checks shall be performed;
Inspect the instrument for damages.
Ensure that calibration of apparatus and sensors are in date (e.g. 6(six) months interval).
Inspect that the correct probes and adaptors are selected (if applicable)
Perform a leak test for a minimum of the pump-unit.
gas sampling area
Restricted Area Zone
A Restricted Area Zone (RAZ) shall be defined by a barrier and signs indicating the operation ongoing, contact person/department and the owner of the operation. Only trained personnel shall have access to the RAZ.
General access to restricted area
In general, all employees that have been trained according to the specific task and towards their respective roles have access to the restricted area at all times. The area shall be confined to authorized personnel only.
To ensure a uniform procedure under any operation/work within the RAZ, all personnel working in the area shall be in possession of relevant additional PPE e.g. SCBA, EEBD or escape mask and personal detector. In case of any type of unexpected alarm they are required to follow the general alarm procedure.
All personnel involved in gas sample operations shall as a minimum be able to use safe systems of work processes (SJA or JSA) to identify hazards and mitigate or reduce risks to as low as reasonably practicable (ALARP). Further they shall be able to select, use and care for PPE (to include detectors, filter-masks and respirators).
Defining gas concentration
When measuring harmful gases or substances in air, the quantity of that substance is defined in terms of a concentration in relation to the air. Depending on the volatile nature of the substance different units are used to define the concentration.
High concentration is usually specified as Vol.-% – in other words, one part of a substance to 100 parts of air. Air, for example, consists of 21% Vol.-% oxygen, which means that 100 parts of air contain 21 parts of oxygen.
Lower concentration levels are measured in ppm = parts per million (mL/m3), or ppb = parts per billion (μL/m3). A concentration of one ppm means there is one part of a substance or gas in one million parts of air. E.g. most humans lose their sense of smell with 100 ppm of H2S in air. Converting low concentrations into Vol.-% can be performed following this relationship: 1 Vol.-% = 10,000 ppm = 10,000,000 ppb
Gas dispertion calculation
An operation that involves a potential volatile or toxic gas should have a dispersion model available for contingency purposes. The dispersion model should as a minimum include a Radius of Exposure Calculation that indicates possible low and high risk areas within the installations safety zone with potential exposure levels calculated from estimated average gas volumes that can be expected.
The dispersion and plume model should include the different seasonal changes present at the installations specific location. The calculation shall be included in risk assessment for all contingency plans during all operations within the installations safety zone.
The specific dispersion or plume model selected can be Gaussian, Puff or similar that are recognised within the oil and gas industry. The dispersion models calculate a single event release of gases in a centreline from a user specified steady state meteorically condition and downwind distances.
Rupture Exposure Radius (RER)
For toxic effects, the rupture exposure radius refers to the horizontal distance from a leak source to a specified level of hydrogen sulphide concentration in parts per million at 10 ppm.
For a flammable gas hazard, the rupture exposure radius refers to the horizontal distance from a leak source to a reduction to 50% of LEL.
Determination of Rupture Exposure Radius (RER)
The radius shall be determined in three concentric circles representing the three rupture exposure radii - e.g. 10 ppm, 100 ppm hydrogen sulphide and 50 % of the lower explosion limit (LEL). These must be plotted from the well's proposed surface location to the furthest extend of the rupture Radius.
If any operation involves any form of breaching or breaking the containment (e.g. dismantling or installing equipment or similar on any oil/gas bearing system) to any suspected volatile or toxic gas system, then a risk-assessment, HAZOP and/or HAZID shall be completed in advance and a PWT issued and approved by the offshore Platform Manager, Master or OIM.
As both volatile and toxic gases are a hazard to humans and equipment, the utmost caution and care should be taken during working on systems that are suspected to have been affected with H2S or other volatile toxic gases.
A fire hazard is to be expected if any systems have been in contact with gases. A plan for containing a potential fire shall be implemented in the job description and made known to all involved personnel.
Prior to breaking the containment, the following steps should be completed:
The area shall be restricted with a barrier to prevent unauthorized access.
PA announcement of the ongoing operation shall be performed prior and during the operation with intervals.
All personnel shall be trained in self rescue from the area.
A designated watchman shall be assigned to the operation with sufficient fire-fighting and breathing equipment available to be able to contain a locally developed fire as a result of a pyrolysis ignition of entrapped H2S and other gases.
If breaking any process lines in connection with well-heads, choke manifolds etc., these shall have been flushed prior to dismantling.
All equipment used shall be classified for use in ATEX zone 0, due to the probability of gases being present within the area.
Personnel performing the actual breaking/opening/venting of closed systems shall wear SCBA until gas levels have been determined safe below the WEA guideline at any time.
Resuscitator and/ or equivalent other rescue equipment shall be present in the vicinity of the worker and rescuers to facilitate an efficient rescue and minimize a possible exposure to personnel.
Upon breaching the containment, an authorized gas tester shall measure for possible contaminant gases. (Refer to gas testing section for this).
The list should be considered as minimum requirements but is not exhaustive and shall be tailored to the specific tasks. See section “Dismantling or loosening of bolts in flange and clamp joints” for further details.
Precautions While well-Testing
When testing wells containing volatile or toxic gases, no gas, shall be released to the atmosphere unless it is flared on location according to procedure. Further precautions during testing can be the following best practice statements but is not limited to this:
Always open up a well slowly, using the upper master valve.
A surface shut down system shall be installed in any well-test hook-up.
Steel hammers should be replaced with brass hammers when the test is ongoing.
Never allow open flame or naked light inside the safety perimeters. All hot work shall be suspended.
Always pressure test the installation prior to well opening.
When rigging up a well-testing set-up, make sure the equipment used can safely withstand and handle the maximum wellhead pressure for the portion which may be exposed to such pressure.
Wind direction should be considered when blowing gas into the atmosphere. Total lack of wind currents may also create hazardous conditions.
Chain and stake all flow lines and install safety wires on connections.
All units must be properly grounded to prevent risks of ignition by static electricity.
sampling procedure with manual detection instrumentation
The procedure for performing a sample with a manual gas detection instrument (e.g. DLE or pump system) is considered best practice and shall be considered a minimum procedure for all MHSS personnel or personnel working under the supervision of any MHSS personnel. If a more stringent procedure is available, then this takes precedence over MHSS procedure. If this scenario is encountered, then it shall be noted in the gas test log.
All employees that are involved directly in the gas sample operation shall have been trained according to the specific task and towards their respective roles. The area shall be confined to authorized personnel only.
Preparing for a gas sampling on a wellhead, X-mas tree, seperator or any other similar sample point, the following equipment shall be rigged up and checked:
Minimum two WEBA for use by the essential personnel are required to be present at the well site and ready for use with a minimum of working pressure +/- 10%.
A local or temporary cascade system including manifolds and hoses shall be installed and tested ready for use with a minimum of the cylinders working pressure +/- 10%.
Minimum two SCBA for use by the rescue personnel are required to be avaiable for the rescue team and ready for use with a minimum of the cylinders working pressure +/- 10%.
Detection equipment tested and ready for use.
Sample containers, probes, tubes, log papers etc. ready for use.
All personnel have the required PPE for working within the restricted area (e.g. confined space, test site) and be trained according to their individual duties.
Prior to starting the job, a pre-job safety meeting shall be held in order to explain emergency response and location of lifesaving equipment.
The pre-job meeting shall also cover the personnel’s individual duties in case of a contingency involving the release of gases.
On any operation involving pressure at surface only the minimum number of people necessary to perform the task shall be exposed to the equipment under pressure.
Gas or liquid containers and bags
For air sampling at which the enrichment of substances is neither possible, nor necessary, gas storage containers (e.g., plastic bottle) or gas sample bags should be used.
Any ordinary sealable container or rubber bag can be used as a displacement sampler under the circumstances that the container or rubber bag has been cleaned and is free from contaminants. Original air is replaced by the sample air by aspirating it through the container with a double acting rubber bulb aspirator or a battery or electrically operated vacuum pump. The volume of air/gas mixture passed through the container should be 10-15 times the container volume to achieve an efficient sample.
Portable gas detection instruments are subject to multiple requirements depending of their application areas. It is generally possible to distinguish between the following application areas:
Personal and portable monitoring
– Contains electronic devices that are designed to warn the user of a gas risk in the immediate vicinity.
For this reason, they are carried on the work clothing. The basic requirements that these units therefore have to fulfil are wearing comfort, durability, and reliability. Continuously measuring single-gas and multi-gas instruments are suitable for this kind of work.
– If the purpose is to monitor an area in which one or more workers are active a unit can be placed within the work site enabling the unit to monitor the working area as effectively as possible. The basic requirements in this case are durability, stability, and an alarm, that is easy to perceive (both visually and acoustic). Continuously measuring multi-gas instruments are used in these areas.
When several work areas are simultaneously being monitored and these individual areas are not visible from one central point, a wireless alarm connected with an area monitoring device can provide the adequate warning capabilities.
ATEX stands for ATmospheres EXplosibles. All electronic gas detectors that are to be operated within a gaseous atmosphere must be approved to the latest ATEX standard. The standard describes the minimum requirements for the protection of employees’ health and safety in areas at risk of explosion.
The ATEX for atmospheres containing gases at risk of explosion are divided into the following zones according to the likelihood of an explosive atmosphere forming there:
Zone 0 Area in which explosive atmospheres comprising mixtures of air and flammable gases, vapours, and aerosols are present constantly, frequently, or over long periods of time.
Zone 1 Area in which, under normal operation, an explosive atmosphere can occasionally form as a mixture of air and flammable gases, vapours, or aerosols.
Zone 2 Area in which, under normal operation, an explosive atmosphere consisting of a mixture of air and flammable gases, vapours, or aerosols normally does not form – or only briefly.
For atmospheres containing dust the prefix 2 is added:
Zone 20 Area in which explosive atmospheres in the form of clouds of combustible dust in the air are present constantly, frequently, or over long periods of time.
Zone 21 Area in which, under normal operation, an explosive atmosphere can occasionally form as clouds of combustible dust in the air.
Zone 22 Area in which, under normal operation, an explosive atmosphere in the form of a cloud of combustible dust in the air normally does not form – or only briefly.
Working principle for electronic detectors
Electrochemical-type gas sensors are aerometric fuel cells fitted with two electrodes. The basic components of two electrode gas sensors are a working (sensing) electrode and a counter electrode with an ion conductor in between them.
When toxic gas such as hydrogen sulphide (H2S) diffuses through a permeable membrane, the volume of H2S increases in the air inside the chamber and an oxidation or reduction reaction occurs at one of the electrodes, and as a result, a change of current occurs as the gas comes in contact with the working electrode through chemical reaction with water molecules in the air.
The difference in the current between the two electrodes is a direct answer of the amount of H2S in air calculated by the loss of current.
A disadvantage of the electrochemical sensor is the somewhat long response time to reach T90, which explained is 90% reading of the actual concentration of gas in air. Some sensors require above 30 seconds to reach this level, therefore a sample conducted with an electrochemical sensor shall take into account the extended response time.
Direct gas sample procedure
Direct gas samples are drawn directly out of the air at the given sample point e.g. needle valve etc.
Prior to braking any tubes or opening any valves it shall be confirmed that all barriers are in place, SCBA tested and ready.
In the following example a Dräger X-Am 2500 multi gas detector is used. Any other similar multi gas detector with a pump and probe installed.
Getting the detector ready
The unit shall be started in a clean and gas free area. During the start-up sequence the user should observe the relevant data on the gas detector display. The unit shall be within the manufacturers recommended calibration interval. The unit shall further be inspected for damages and a leak test performed.
Once the multi-gas detector is active and the warm up sequence completed for the CH4 sensor (this is indicated by an exclamation mark disappearing next to the CH4 gas reading in the display) the detector is ready for use.
If a pump with probe is used the unit is inserted in the pump adaptor. The adaptor indicates activation with audible and visible alarms. A pump test is compulsory to complete the adaptor setup.
A red light will indicate that a pump test is required. With the probe inserted into the adaptor the air flow is blocked. A successful test will be indicated by a long beep and a green light appears. Release the blockage and prepare for taking a gas sample.
Taking the sample
Fully masked up with an appropriate SCBA and a stand-by person observing the operation in an upwind position the valve controlling the gas flow can be opened. The sample gas shall be allowed to flow through the needle valve for 30 seconds to allow a uniform gas flow.
Align the probe next to the outlet of the needle valve no further away than 0-1 centimetres as the gas otherwise will disperse to the surrounding air. The multi gas detector now draws the gas flow through the sampling hose and probe into the sensors. This phase is referred to as the flushing phase and is required during EACH gas sample.
A flushing phase is necessary to eliminate or minimise all effects associated with the use of a sampling hose or a probe, e.g. memory effects, dead volume or pockets of air in the sampling hose or probe. The extent of the flushing phase depends on different factors such as type and concentration of the gas or vapour that are being measured. The material, length, diameter, and age of the sampling hose are also to be taken into account when calculating the flushing time.
You have a new probe and sampling hose with a length of 10 m and are using an electrochemical XXS H2S-LC sensor and a Catalytic Ex CH4 sensor installed
Sampling hose flush is approximately 30 seconds
The sensor response time is ≤17 seconds for CH4 and ≤18 seconds for H2S.
In addition, flow-rate alarm is delayed by 10 to 30 seconds
The total minimum flushing time is sampling hose length + sensor reaction time, therefore the calculation is 10 x 3 seconds + 18 seconds +30 seconds = approximately 90 seconds.
Once the multi gas sensors reacts on the test gas they should be given time to stabilize. Once a given mean value has been achieved, normally within 1-2 minutes, the valve can be closed again and the test system secured. When back in a safe area and no toxic or harmful gases have been confirmed in the area and PPE (coverall) ventilated, the SCBA can be removed.
Peak value of the different measured gases should be noted on the gas test papers following the specific job and the AGT shall sign it.
Gas sampling on flowlines or similar
When performing a gas sampling on a flowline, mud pit, open reservoirs or similar conditions with lager open spaces or surfaces, the subsequent shall be followed:
Procedure for direct gas sampling with electronic devices shall be followed. During sampling the test probe shall not be further away from the surface than 0-2 centimetres in order to draw most gases into the probe and hose as possible without contaminating the sample.
Alternatively, a liquid sample can be taken into a glass or plastic container. The sample should then be sealed, shaken or stirred to release the gases prior to lowering the probe or hose into the container for sampling. This procedure can have high potential of contaminating the sample if air is let in the container. To avoid air and contaminants in liquid sampling the DLE procedure can be followed.
Manual gas sample procedure
Natural, ambient air is chemically a mixture of gases that consists of 78 % nitrogen, 21 % oxygen, 0.03% carbon dioxide and 0.97% other gases such as argon, helium and other rare gases. Any concentrations that differ significantly from this is considered a hazardous atmosphere. Tubes, sensors electrochemical or not react to the different substances in air.
For determining hazardous substances in a gas mixture using test tubes, a chemical reaction of a substance in the tube is occurring with the test gas. The effect will lead to a change in colour of the test tube and can be used for verifying concentration.
The sampling is basically performed drawing a defined volume through a test tube by using a hand pump. The length of coloured layer is proportional to the concentration of the substance (or substance class) under investigation.
The advantage of using test tubes is that the measured concentration is obtained quickly and directly after sampling.
Using test tubes, the Authorized Gas Tester shall take into consideration the following:
Possible reactions of tube chemicals with accompanying substances
Problems in reading or interpreting the coloration
Error in determining correct temperature and pressure for calculating gas concentration
Usually, tubes are possible to interpreted due to indication of the substance conversion as a length-of-stain indication.
When measuring with tubes it is important to verify the correct tube for the given gas reading as some tubes require a certain amount of humidity to react with gases.
For H2S tubes the basis reaction pattern is the chemical reactions of metal salts. Metal salts react with hydrogen sulphide and form slightly soluble metal sulphides. This is a fast ion reaction which is nearly independent of the flow rate through the tube. In order to make this reaction occur, a small amount of water, i.e. humidity, is necessary:
H2S + Cu2+ 2 H+ + CuS
The selected equipment for this tutorial as a Gastec hand pump. Other hand pump systems such as Kitigawa or Dräger Accuro can be used as well.
Getting the detector tube ready
After selecting the appropriate gas detector tube for the target gas, the tips on both ends are broken off.
Break off the tips on both ends using the tip-breaker holder or the built-in tip breaker
Make sure the pump handle is fully pushed. Then insert the detector tube into the rubber inlet of the pump with the arrow on the tube pointing towards the pump
A glass or plastic container with a sealed inlet and an unsealed outlet are the recommended gas dispersion container to be used when taking a gas sample from a needle-valve with a hand pump as there is no overpressure in the container.
Fully masked up with an appropriate SCBA and a stand-by person observing the operation in an upwind position the valve controlling the gas flow can be opened. The sample gas shall be allowed to flow through the sample container for a minimum of 30 seconds to ensure a uniform gas mix. No personnel should be allowed any operations downwind of the RAZ during this part of the procedure.
Align the guide mark (red line) on the back of the cylinder and the guide mark on the handle. At start, the handle must be fully retracted (pushed in).
Point the tube end towards the desired sampling target area with a minimum of distance to the gas dispersion area (preferably 0-0,5 cm.) and pull out the handle fully (for 100mL sampling) or halfway (for 50mL sampling) in one thrust until it locks in place.
Keep the tube (and pump) pointed towards the target area with no greater distance than 0,5 cm. until the prescribed amount of time has elapsed.
The number of sampling strokes and the sampling time and the sampling time differs for the individual detector tube types. Be sure to always consult the respective instruction sheet. The following procedures should be used to ensure that the correct volume has been aspirated.
Turn the handle 90 degrees and let go; it should remain in place without retracting. Wait until the sampling time has elapsed. Completion of 100mL or 50mL sampling can be verified using the flow finish indicator in the handle.
Reading the measurement
After sampling (the time allowed to measure the presence of target gas) has been completed, the colour change layer in the calibrated tube is interpreted to determine the correct concentration.
When the end of the colour change layer is flat, simply read the value at the end.
When the end of the colour change layer is slanted, read the value in the middle of the slant.
When the demarcation of the colour change layer is pale, the mean value between the dark and the pale layer ends is taken.
In all the above sampling cases the reading would be 5%.
Manual DLE gas sample procedure
The Dräger Liquid Extraction method (DLE) is used for the determination of volatile contaminants in water (Liquids). The measurement basically consists of two steps:
The extraction of the contaminant
The DLE Method is designed for the rapid analysis of water, waste water, oil sludge, soil, drilling fluid and multiphase samples by using Dräger-Tubes.
An activated charcoal tube is attached to the inlet of the bottle to prevent any airborne contaminants from entering the water (liquid) during the test.
The Dräger-Tube is attached to the outlet of the bottle and a specific volume of air is drawn through the water (liquid) sample.
The porous frit in the bottle produces a high number of small air bubbles in the water (Liquid) which extract the contaminant as they break at the surface.
The extracted contaminant is measured from the headspace of the bottle in the Dräger-Tube. Glass cylinders shall not be exposed to pressure.
DLE Measurement Steps
Grab the sample in the Drager beaker and put it in the Drager cylinder to determined level.
You have to prepare two Drager tubes:
Carbon pre- An activated charcoal tube attached to one inlet of the connector to prevent any airborne contaminants from entering the system during the test.
Contaminant detection tube (Dräger tube) e.g. H2S or SO2 tubes. You have to know a range for the contaminant you face to determine tube to be used
Break off both tips of both tubes using the Drager tube opener.
Begin constructing the system by inserting the gas measuring tube in the Dräger pump; arrow points towards the pump.
Complete setting up the system by putting the connector inside the sample cylinder, connecting rubber hose to each tip of the connecter, and inserting the tubes in the rubber hoses.
When stroking the pump, squeeze it as far as possible & allow it to open again fully, according to the number of strokes published by the Dräger tube manual.
Reset the pump counter to zero using the reset button.
After Finishing the measuring process, the chemical in the tube will change color (Ex. In case of H2S from white to brown). See examples of different collorations of tubes on the picture.
Contamination of the Sample
Commen errors in gas reading results are an outcome of poor sample container cleanliness, incorrect air in the sample container or lack of calibrated equipment.
Prior to a sample container is to be used, it should be entirely clean and free of any contaminants that may contaminate the analysis of the flowing gas stream. Sample containers or cylinders, must be cleaned and entirely purged after each use. This can be performed by either steam cleaning or flushing the unit. After steam cleaning the cylinders are dried and purged and prepared for the next collection period.
Another contamination issue is allowing air contamination of the collection system and consequently the sample. This is typically a result of either not sealing the sample container/cylinder to the extraction point or improper handling of the sample container/cylinder.
During sampling the Authorized Gas Tester should avoid to:
Open the valve on the sample point too quick.
Allow a flow of gas mixture to fill the sample container/cylinder sufficiently prior to taking the sample.
If using manual detector tubes; Ensure a complete seal between gas test tube and sample container/cylinder.
If using multi gas detector; Ensure a complete seal between probe and sample container/cylinder.
Measuring in an over-pressured sample container/cylinder.
All personnel are responsible for sounding the alarm upon detecting volatile or toxic gases either on their personal detector or otherwise. General actions shall be to don personal escape equipment, warn others in the area and proceed to their primary muster area as stated in the local contingency plan.
All personnel shall be trained according to their respective roles and responsibilities. Personal who have not been trained accordingly have the obligation to inform their line manager of this.
All personnel shall:
Have a personal detector in their possession while working within the RAZ. Personal detectors will be issued during the briefing for the specific operation. Personnel detectors shall be returned upon completion of the operation.
Listen for announcements such as voice and audible alarms or otherwise watch the visible warning system.
Know the location of the Safe Briefing Area (SBA).
Know the location of the protective breathing apparatus (SCBA).
Inform your working partner or team of an alert or an emergency situation.
Do not enter a suspicious area without breathing apparatus until the concentration of volatile or toxic gas has been checked and the area declared clear.
Reporting of unintended gas release Incidents:
When volatile or toxic gases have been detected released unintentionally within the RAZ and appropriate actions have been taken, a report on the incident must be immediately forwarded to the relevant authorities onshore. The platform manager, OIM and/or area responsible supervisor is responsible for implementing this as soon as possible or upon resuming normal operational conditions.
Confined Space Entry Procedure
General work routines for H2S Supervisors
Safe Job Analysis
This section is mandatory and shall describe the requirements established by the document.
Terms, Abbreviations & acronyms
Terms, abbreviations and acronyms included in this document are specific to the contents of the same terms
Used to indicate statements of possibility and capability.
Advance permission to deviate from a stated requirement.
Used to indicate that direct involvement is required.
Must be followed or implemented.
Verbal form used to indicate a course of action permissible within the limits of the procedure. Designates a Permissive Statement – an option that is neither mandatory nor specifically recommended.
Not necessary to comply with stated requirements.
Necessary to comply with stated requirements.
Indicates the requirements strictly to be followed in order to conform to this procedure. Deviations from shall requirements shall be subject to waiver approval.
Indicates that among several possibilities, one is recommended as particularly suitable, without mentioning or excluding others or that a certain course of action is preferred but not necessarily required. Other possibilities may be applied subject to agreement.
Abbreviations & Acronyms
As Low As Reasonably Practicable
Authorized Gas Tester
American Petroleum Institute
Bottom Hole Assembly
Central Control Room
WEBA for connecting to a cascade manifold
Hazards and Operability Analysis
Immediately Dangerous to Health and Life
Lower Explosive Limit
Lower Master Valve
Lost Time Incident
Maersk Oil Design Standard
Mobile Offshore Drilling Unit
Includes any platform, drilling rigs, production units, vessels etc. that is used for performing operations offshore
Oxygen, concentrated sources of oxygen can contribute to ignition
Potential Loss of Life
Public Announcement system
Person in Charge. (Normally OIM)
Production Operational Procedures
Parts per million
Used as an extension of a gas extraction instrument.
Permit to Work
Quantitative Risk Assessment
Rupture Exposure Radius
A container for collecting the gas sample during indirect gas sampling
A device used to distribute gas from a gas sample point to a gas detector
A point in a gas stream where a representative sample can be obtained
Safe Briefing Area. Also known as the muster area. The Safe Briefing Area will be located upwind in regards to the prevailing wind. An alternative Safe Briefing Area should also be appointed.
Self-Contained Breathing Apparatus
Safety Of Life At Sea
Sulphur Dioxide, A non-flammable and colourless toxic gas
Standard Operational Procedure
Sulphate Reducing Bacteria
Sulphide Stress Corrosion
Surface Safety Valve, an automated spring-assisted fail-safe valve installed on a wellhead to automatically shut in flow during an abnormal condition. E.g. upper master valve, a wing valve or a production valve
Subsurface Safety Valve, an automated valve installed below surface level in the tubing string of an oil or gas well
Time Weighted Average. The allowable average concentration of H2S over a period of 8 hours.
Upper Explosive Level
United Nations Law Convention on the Law of the Sea
Uninterrupted Power Supply
Danish Working Environment Authority
Work & Escape Breathing Apparatus
The valve manifold directly at the top of the well bore
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Safe Briefing Area. Also known as the muster area. The Safe Briefing Area will be located upwind in regards to the prevailing wind. An alternative Safe Briefing