Hydrogen Gas Detection – Crowcon portable and fixed gas detection solutions
Hydrogen sulphide (H2S) is a naturally occurring gas and can be found in many of the worlds crude oils. The gas is colourless and has a distinctive rotten egg odour at low levels however at high concentrations the gas will numb the human sense of smell which can be fatal.
Heavy oils such as crude oil, residual fuel and gas oil tend to have large concentrations of hydrogen sulphide and this can become a concern if the oils are to be stored over extended time periods.
This Blog looks at the dangers of hydrogen sulphide gas in the oil refining industry and the working areas that may have H2S present and the gas detection solutions available.
Image: Valero
Working in and around an oil refinery is naturally fraught with dangers and potentially hazardous areas. One of the most common and most underestimated problems faced by personnel is the presence of toxic gases and particularly hydrogen sulphide (H2S) gas.
H2S is a colourless gas and therefore invisible. The gas does have a distinctive rotten egg smell that can only be smelt at low concentrations as at higher and more dangerous levels, peoples sense of smell is significantly numbed and therefore without adequate fixed or portable gas detectors, they can succumb to the harmful effects of the gas.
Inhalation of hydrogen sulphide gas can lead to acute poisoning and death by suffocation occurs extremely fast. This Blog looks at where hydrogen sulphide gas can occur within refineries and which situations are particularly dangerous including hazardous areas.
The above case studies highlight just how dangerous this gas can be and how essential it is to install effective, working gas detection systems.
Valero St. Charles Refinery’s major process units were built or substantially reconstructed in the late 1990s, making the refinery one of the newest in the USA.
Hydrogen Sulphide – H2S Fact Card
Hydrogen sulphide gas is colourless and at certain low concentrations it has a distinctive rotten egg odour which is instantly recognisable and as a result of this smell, H2S is commonly know as sewer gas, digester gas or marsh gas.
However, at higher concentrations the gas numbs olfactory nerves and starting at a concentration of 100ppm. People are therefore no longer able to smell the gas – concentrations higher than 1000ppm can be instantly fatal.
in addition to the numbing of senses, H2S gas is heavier than air and therefore will often collect in low-lying areas and working sites near ground level. The gas will ignite itself at a temperature of 270°C and due to its highly inflammable properties an explosive atmosphere may occur when combined with air.
Strong reactions are possible that can trigger spontaneous combustion, explosions and detonations. In addition, H2S gas combined with air and humidity or moisture can corrode metals through the formation of sulphuric acid.
90% of hydrogen occurs naturally in the environment for example in hot sulphur springs and rock masses, however there are many areas within the oil and gas industry in which the presence and bi-production of H2S gas is a common occurrence.
The refining process commonly produces H2S as a bi-product however the gas also occurs at wellheads, oil and water tanks, pumps, piping systems and flare heads.
The most common locations for the presence of hydrogen sulphide within refineries are:
Storage – The crude oil is transported via either a pipeline or barge and is stored waiting to be processed. Hydrogen sulphide can be found in the head space of the tank and can corrode the tank reducing it’s product lifespan and as the tank fills the headspace concentration increases.
Distillation Columns – The crude oil is separated into various components in the distillation columns based on boiling points. The lightest components are used for gas with the heaviest elements used for asphalt. Hazards occur even though this is a closed system and the gas can be present in the heat exchanger, furnace, tower flash column, vacuum furnace and bottom exhcanger.
Hydrotreater & Hydrocracker – The hydrotreater is used to remove the sulphur and the hydro cracker breaks long hydrocarbon chains into shorter chains in order to create more efficient petroleum products. These actions are performed over a catalyst at high pressure and temperature with excess hydrogen. Hydrogen and sulphur combine and create H2S which is then sent to a recovery unit to create water and sulphur. H2S content in the feedstock must be monitored along with any leaks.
Blending – This is the physical mixing of various hydrocarbons in order to produce an end product with desired characteristics. H2S hazards can occur during sampling, inspection, maintenance and turnaround.
Solution: Safety considerations to undertake include fixed and portable gas detectors to be installed in and around maintenance equipment and on turnaround equipment.
Chemical Treatment Process – This process removes contaminants such as sulphur, nitrogen, oxygen, dissolved metals and salts. This in turn improves the odour, colour and oxidation stability. Hydrogen sulphide is commonly used during the recovery of sulphur and the hydrogen sulphur scrubbing process.
Gas hazards will occur during sampling, inspection, maintenance and turnaround.
Solution: Portable and fixed gas detector solutions should be used in and around maintenance and inspection equipment to ensure gas detection safety.
Power Generation – Oil refineries have many other operations including electric generation, steam generation, cooling towers, wastewater treatment and flaring systems. The potential for H2S hazards to occur are around cooling towers and contaminated wastewater. Caution should always be taken during sampling, inspection and maintenance.
Solution: Portable gas detectors should be used along with respirators and air purifiers.
Hydrogen sulphide gas is a so called ‘nitrogen’ gas and causes damage to the lungs, central nervous system and can also cause skin and mucous membrane irritation. Typical symptoms of poisoning include headaches, dizziness, fatigue, dry mouth, anxiety, confusion and lack of coordination.
Even in low concentrations and a low dose, H2S can be harmful if exposure is continuous over several hours or days. High concentrations can lead to unconsciousness almost instantly and a coma followed by death in just a few short breaths – these effects show exactly how dangerous this gas is and highlights the need for effective gas detection.
There are a number of gas detection solutions available from Thorne & Derrick including fixed, portable and transportable suitable for use in safe and hazardous areas. Each working area and gas hazard requires a different gas detection solution in order to provide the proper, effective protection for personnel and buildings.
Typically, smaller confined spaces require personal and portable gas detection solutions to be carried by workers.
Fixed point gas detectors provide constant, 24 hour gas monitoring 365 days a years which is important for the detection of random gas release. T&D are distributors for the Crowcon ranges of gas detection equipment. Our gas detection specialists can help you determine exactly the correct product for your requirements.
The ever-present safety protection provided by Crowcon fixed gas detectors means personnel working in areas such as distillation columns and chemical treatment plants are able to work freely – improving safety figures and increasing productivity.
Fixed gas detection systems are favoured in many oil and gas areas for their constant gas safety protection, monitoring of any gas leaks and providing both audible and visual warnings when there are no personnel on site.
Portable gas detectors provide an excellent solution for the detection and monitoring of hydrogen sulphide among other hazardous gases. There are many benefits of using portable gas detection and differences compared to the use of fixed point detection systems.
The use of portable gas detection allows personnel the freedom to move between working areas safe in the knowledge that they are carrying their safety devices with them to detect and alert the presence of hazardous gases.
The difference between portable gas detectors and fixed is the length and continuity of detection – portable detection equipment must be tested, re-charged and have its own power supply whereas a fixed point detection system is hard wired and will provide constant, 24/7 detection however the flexibility and portability is compromised
Hazardous areas can occur when the presence of hazardous vapours, dusts or mists exist in a high enough volume. There are three categories of risk that must be identified reliably in order to protect human life and assets:
Without the use of auxiliary tools, people are often unable to recognise these dangers early enough to take action and prevent a serious incident or accident occurring.
Any equipment to be used in hazardous areas for gas monitoring purposes must fulfill the Essential Health And Safety Requirements (EHSR). In addition, as gas detection systems are products of safety technology, it is important not to misinterpret their role within oil refinery safety.
They are not simply a handful of detectors spread across and manufacturing plant, they are and should be considered a bespoke solution developed to fulfill the requirements of individual protection objectives.
Hazardous Area Gas Detectors Certified To International Classifications
All equipment to be used in zone 1 and zone 2 hazardous areas must be explosion proof and certified for use under the relevant local hazardous areas classifications such as ATEX and IECEx.
Hydrogen sulphide gas is extremely corrosive and causes metals to become brittle when exposed. All oil well drilling sites and areas within oil refineries must be classified according to areas of potential or actual exposure to H2S gas.
The four hazard levels are:
In any working area where there is the potential for exposure to hydrogen sulphide, a gas monitoring strategy is recommended to ensure exposure levels are kept below acceptable levels and that the appropriate action is taken if there is ever exposure above these levels.
In order to protect workers from exposure to harmful levels of hydrogen sulphide, the American Conference Of Governmental Industrial Hygienists (ACGIH) modified the Threshold Limit Value (TLV) for H2S in 2010.
From 1976 to 2009, the 8 hour time weighted average TLV (TLV-TWA) was 10 parts per million (PPM) and the 15 minute short-term exposure limit TLV (TLV-STEL) was 15 PPM. In 2010 a TLV-TWA of 1 PPM was adopted along with a TLV-STEL of 5 PPM for H2S.
The ACGIH is a globally recognised authority on the establishing of exposure limits for chemical agents including toxic gases, and the changes to the H2S limits followed a five year review period during which industry experts had the chance to express any concerns they had.
The best protection would be an electronic instrument that could measure and store both the 1 PPM TWA and 5 PPM STEL H2S levels and also provide and alarm when concentrations reached 5 PPM.
A portable gas detector is ideal for users who want to accurately and reliably measure H2S levels. It provides a noticeable visual, audible and vibration alarm notification to alert the user to dangers levels of hydrogen sulphide gas that is present.
The detector features an easy-to-use intuitive interface and also features data logging which records the entire history of the monitor for complete analytical and safety uses.
Thorne & Derrick are Specialist Distributors of Hazardous Area & Explosion Proof Equipment with IECEx & ATEX Certifications to the onshore and offshore oil, gas, petrochemicals and process industries.
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T&D – Suppliers of Crowcon Gas Detectors
T&D, the specialist distributor of Gas Detection, Detectors & Monitoring Equipment for H2S gas detection.
Watch, listen and learn how Crowcon, H2S gas detection specialists, protect people and plant from the gas risks posed by flammable and toxic gas.
Hydrogen sulphide gas is considered a broad-spectrum poison, meaning that it can poison several different systems in the body, although the nervous and respiratory systems are most severely affected. Besides being highly toxic H2S is a flammable gas – heavier than air and hence tending to accumulate in low-lying areas.
H2S is pungent but rapidly destroys the sense of smell.
H2S gas is toxic at breathable concentrations between 500-1000 ppm, but death is not instantaneous. However, at concentrations of greater than 1000 ppm, H2S is lethal.
Industry practice is to recognise that fatality from H2S exposure can occur over a wide concentration band but at around 500–1000 ppm exposure for a short period, the fatal exposure levels would be significant. 800 ppm is the generally accepted lethal concentration for 50% of an exposed human population for 5 minutes exposure.
T&D are Crowcon distributors – market leading fixed and portable gas detectors and monitors for flammable and toxic gases, including ATEX Certified equipm
H2S Gas Detection : Crowcon are market leading manufacturers of Portable and Fixed Gas Detection Equipment
The UK HSE (Health & Safety Executive) have provided guidance to duty holders for detecting and managing hydrogen sulphide (H2S) hazards in hydrocarbon processing systems. As reservoirs begin to water out, hydrogen sulphide can become an issue when processing returning fluids. The gas is toxic in relatively low concentrations and the risks to the workforce need to be safely addressed once the presence of hydrogen sulphide has been detected.
H2S presence in reservoir streams tends to increase with time and it is important therefore that duty holders ensure that if the concentration levels in modules begin to increase the toxicity status of the areas are revised accordingly. The recommended strategy for fixed and portable detection is based on accepted management practice for confined space entry, and normally accessible process modules.
On an offshore installation, the standards recommend a 3-tier approach to H2S gas detection; similar to the flammable hazardous area classification arrangements:-
Fixed H2S detection is not recommended in areas where H2S is known to be present at high concentrations during normal operations. The argument is that if the presence of the toxic gas is known and known to be unacceptably high, there is no reason for installing detection.
Access is controlled by special precautions, confined space entry management, that starts with the removal of H2S and initial entry is by specifically trained personnel with portable H2S detection equipment wearing breathing apparatus (BA) and other protective equipment.
Entry is only allowed with portable toxic detection equipment and fixed detection is recommended for these areas to maintain a risk history, but should not be used for making safety-related decisions.
For ‘open access modules’, where H2S is not normally present but could be following a leak, fixed detection is recommended in certain scenarios. This is based on a concentration of 500 ppm H2S in the ‘carrier’ stream of process fluids. If the H2S concentration is below 500 ppm, in the carrier stream, the areas may be classified as “2A” and H2S detection is via the standard hydrocarbon detection instruments. At concentrations greater than 500 ppm, in the carrier stream, the area is designated “2B”, and requires a H2S specific detection system because the hydrocarbon detection systems cannot provide a timely response to the more harmful, higher H2S concentrations levels.
This argument is based on an assumption in the standard (unsubstantiated) that process hydrocarbon carrier gas on release is diluted to 1% by air entrainment. Hence if the hydrocarbon gas contained 500 ppm H2S, the toxic component would be diluted to 5 ppm; the occupational exposure limit (OEL) for the gas. However, there is no supporting argument in the standard that a 100:1 dilution will be achieved if a hydrocarbon gas stream is released to atmosphere.
Na Kika Project : involves the production of hydrocarbons from five small- to medium-sized discoveries in the Mississippi Canyon area of the Gulf of Mexico. Shell already has an extensive range of offshore hydrocarbon operations in the Gulf of Mexico. The map shows the oil projects operated by Shell, the gas projects operated by Shell and the many offshore hydrocarbons project in which Shell has an interest. Image Courtesy : Hydrocarbon Technology
The offshore industry employs about 28,000 personnel in the UK involved in a wide range of activities.
Since the Piper Alpha disaster in 1988, health and safety issues concerning offshore platforms have vastly reduced, however, the work practices involved are not risk free and still have the potential to cause considerable loss of life when things go wrong.
A falling oil price, declining reserves and an ageing infrastructure have resulted in increased drilling activity around marginal fields. Operators have looked for new ways in which to cut costs, which could affect the health and safety of the workforce.
In recent years there has been an increase in the number of major and significant hydrocarbon releases on offshore platforms that require investigation. – the following report aims to identify the immediate cause of hydrocarbon leaks and determine if there are discernable reasons for the increasing trends.
Hydrogen sulphide is a colourless gas that is known by its characteristic rotten egg like odour appearing naturally as a by-product of decomposition. A drawback to trusting the senses (olfactory) for protection against hydrogen sulphide is that prolonged exposure to the gas renders the sense of smell inoperative.
H2S reacts with the enzymes in the blood stream which inhibit cell respiration.
Put simply, high concentrations of hydrogen sulphide can shut off the lungs. Low concentration exposure to the gas can burn the respiratory tract and cause swelling around the eyes.
Symptoms of acute H2S gas exposure include nausea, headaches, delirium, tremors, convulsions, skin and eye irritation
The following table provides an overview of the Crowcon Gas Detectors available for detecting hydrogen sulphide – for expert technical support and product selection guidance please call T&D Sales Engineers.
 Crowcon Xgard INFO |
 Crowcon TXgard-IS+ INFO |
 Crowcon Clip INFO |
 Crowcon TXgard Plus INFO |
 Crowcon Gasman INFO |
 Crowcon Tetra 3 INFO |
 Crowcon GasPro INFO |
 Crowcon Tetra INFO |
 Crowcon Triple Plus+ INFO |
 Crowcon Detective+ INFO |
 Crowcon Detective INFO |
 Crowcon XgardIQ INFO |
 Crowcon T4 INFO |
 Crowcon Gas-Pro PID INFO |
Crowcon Hazardous Area Gas Detectors (ATEX Certified) Zone 1 & Zone 2. Contact T&D for with your enquiry.
See 3 more Crowcon Factoids ➡
Detecting Hydrogen Sulphide, Methane, Oxygen & Carbon Monoxide Gas Using Crowcon Detectors
Hazardous area industries including offshore oil/gas platforms and FPSOs, onshore oil refineries, processing plants, pipelines, storage farms and LPG/LNG plants all utilise or produce a wide range of hazardous flammable liquids and gases that can be detected using correctly specified flame and gas detectors.
Detecting toxic and flammable gases requires the detectors to be classified and certified according to the specific IECEx or ATEX standard – we distribute flame and fire detectors manufactured by Spectrex to operate in the harshest environmental conditions including self-contained stand-alone devices designed for direct connection to control and alarm systems or automatic fire extinguishing systems.
Our range of Hazardous Area Fire & Gas Detection System products also includes Explosion Proof Warning Systems & Hazardous Area Lighting – comprehensive range of intrinsically safe, flameproof and explosion proof alarm sounders, sirens, bells and horns, loudspeakers and beacons.
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