Identifying Leaks from Natural Gas pipelines at a Safe Distance

The use of natural gas, of which methane is the principle component, is increasing worldwide. It also has many industrial uses, such as the manufacture of chemicals like ammonia, methanol, butane, ethane, propane and acetic acid; it is also an ingredient in products as diverse as fertilizer, antifreeze, plastics, pharmaceuticals and fabrics.

Natural gas is transported in several ways: through pipelines in gaseous form; as liquefied natural gas (LNG) or compressed natural gas (CNG). LNG is the normal method for transporting the gas over very long distances, such as across oceans, while CNG is usually carried by tanker trucks over short distances. Pipelines are the preferred transport choice for long distances over land (and sometimes offshore), such as between Russia and central Europe. Local distribution companies also deliver natural gas to commercial and domestic users across utility networks within countries, regions and municipalities.

Regular maintenance of gas distribution systems is essential. Identifying and rectifying gas leaks is also an integral part of any maintenance programme, but it is notoriously difficult in many urban and industrial environments, as the gas pipes may be located underground, overhead, in ceilings, behind walls and bulkheads or in otherwise inaccessible locations such as locked buildings. Until recently, suspected leaks from these pipelines could lead to whole areas being cordoned off until the location of the leak was found.

Precisely because conventional gas detectors – such as those utilising catalytic combustion, flame ionisation or semiconductor technology – are not capable of remote gas detection and are therefore unable to detect gas leaks in hard to access pipelines, there has been a lot of recent research into ways of detecting methane gas remotely.

Remote Detection

Cutting edge technologies are now becoming available which allow the remote detection and identification of leaks with pinpoint accuracy. Hand-held units, for example, can now detect methane at distances of up to 100 metres, while aircraft-mounted systems can identify leaks half a kilometre away. These new technologies are transforming the way natural gas leaks are detected and dealt with.

Remote sensing is achieved using infrared laser absorption spectroscopy. Because methane absorbs a specific wavelength of infrared light, these instruments emit infrared lasers. The laser beam is directed to wherever the leak is suspected, such as a gas pipe or a ceiling. Because some of the light is absorbed by the methane, the light received back provides a measurement of absorption by the gas. A useful feature of these systems is the fact that the laser beam can penetrate transparent surfaces, such as glass or perspex, so it may be possible to test an enclosed space prior to entering it. The detectors measure the average methane gas density between the detector and target. Readings on the handheld units are given in ppm-m (a product of the concentration of methane cloud (ppm) and path length (m)). In this way, methane leaks can be quickly confirmed by pointing a laser beam towards the suspected leak or along a survey line, for example.

An important difference between the new technology and conventional methane detectors is that the new systems measure average methane concentration, rather than detecting methane at a single point – this gives a more accurate indication of the severity of the leak.

Applications for hand-held devices include:

  • Pipeline surveys
  • Gas plant
  • Industrial and commercial property surveys
  • Emergency call out
  • Landfill gas monitoring
  • Road surface survey

Municipal Distribution Networks

The benefits of remote technology for monitoring pipelines in urban settings are now being realised.

The ability of remote detection devices to monitor gas leaks from a distance makes them extremely useful tools in emergencies. Operators can stay away from potentially dangerous leak sources when checking the presence of gas in closed premises or confined spaces as the technology allows them to monitor the situation without actually gaining access. Not only is this process easier and quicker, but it is also safe. Moreover, it is not affected by other gases present in the atmosphere since the detectors are calibrated to only detect methane – therefore there is no danger of getting false signals, which is important in emergency situations.

The principle of remote detection is also applied when inspecting risers (the above-ground pipes carrying gas to the customers’ premises and normally running along the building outside walls). In this case, the operators point the device towards the pipe, following its route; they can do this from ground level, without having to use ladders or access the customers’ properties.

Hazardous Areas

In addition to detecting gas leaks from municipal distribution networks, explosion-proof, ATEX approved devices can be used in Zone 1 hazardous areas such as petrochemical plants, oil refineries, LNG terminals and vessels, as well as certain mining applications.

When inspecting an LNG/LPG underground tank, for example, an explosion-proof device would be required within 7.5 metres of the tank itself and one metre around the safety valve. Operators therefore need to be fully aware of these restrictions and equipped with the appropriate equipment type.

GPS Coordination

Some instruments now allow spot methane readings to be taken at various points around a site – such as an LNG terminal – automatically generating GPS tracking of the measurement readings and locations. This makes return trips for additional investigations far more efficient, while also providing a bona-fide record of confirmed inspection activity – often a prerequisite for regulatory compliance.

Aerial Detection

Moving beyond hand-held devices, there are also remote methane detectors which can be fitted to aircraft and which detect leaks from gas pipelines over hundreds of kilometres. These systems can detect methane levels at concentrations as small as 0.5ppm up to 500 metres away and include a real-time moving map display of gas concentrations as the survey is conducted.

The way these systems work is relatively simple. A remote detector is attached beneath the aircraft’s fuselage (usually a helicopter). As with the handheld device, the unit produces an infrared laser signal, which is deflected by any methane leakage within its path; higher methane levels result in more beam deflection. These systems also utilise GPS, so the pilot can follow a real-time moving map GPS route display of the pipeline, with a real-time display of aircraft path, gas leaks and concentration (in ppm) presented to the crew at all times. An audible alarm can be set for a desired gas concentration, allowing the pilot to approach for closer investigation.

Conclusion

The range of remote methane detection systems is increasing rapidly, with new technologies being developed all the time. All these devices, whether hand-held or fitted to aircraft, allow quick, safe and highly targeted identification of leaks – whether beneath the pavement, in a city or across hundreds of kilometres of Alaskan tundra. This not only helps prevent wasteful and costly emissions – it also ensures personnel working on or near the pipelines are not exposed to unnecessary danger.

Because the use of natural gas is increasing worldwide we foresee rapid technological advances in remote gas detection in applications as diverse as leak survey, transmission integrity, plant and facilities management, agriculture and waste management, as well as process engineering applications such as coke and steel production. Each of these areas have situations where access may be difficult, combined with the need to put personnel protection at the top of the agenda. Opportunities for remote methane detectors are therefore growing all the time.

 

Identifying Leaks from Natural Gas pipelines at a Safe Distance

The use of natural gas, of which methane is the principle component, is increasing worldwide. It also has many industrial uses, such as the manufacture of chemicals like ammonia, methanol, butane, ethane, propane and acetic acid; it is also an ingredient in products as diverse as fertilizer, antifreeze, plastics, pharmaceuticals and fabrics.

Natural gas is transported in several ways: through pipelines in gaseous form; as liquefied natural gas (LNG) or compressed natural gas (CNG). LNG is the normal method for transporting the gas over very long distances, such as across oceans, while CNG is usually carried by tanker trucks over short distances. Pipelines are the preferred transport choice for long distances over land (and sometimes offshore), such as between Russia and central Europe. Local distribution companies also deliver natural gas to commercial and domestic users across utility networks within countries, regions and municipalities.

Regular maintenance of gas distribution systems is essential. Identifying and rectifying gas leaks is also an integral part of any maintenance programme, but it is notoriously difficult in many urban and industrial environments, as the gas pipes may be located underground, overhead, in ceilings, behind walls and bulkheads or in otherwise inaccessible locations such as locked buildings. Until recently, suspected leaks from these pipelines could lead to whole areas being cordoned off until the location of the leak was found.

Precisely because conventional gas detectors – such as those utilising catalytic combustion, flame ionisation or semiconductor technology – are not capable of remote gas detection and are therefore unable to detect gas leaks in hard to access pipelines, there has been a lot of recent research into ways of detecting methane gas remotely.

Remote Detection

Cutting edge technologies are now becoming available which allow the remote detection and identification of leaks with pinpoint accuracy. Hand-held units, for example, can now detect methane at distances of up to 100 metres, while aircraft-mounted systems can identify leaks half a kilometre away. These new technologies are transforming the way natural gas leaks are detected and dealt with.

Remote sensing is achieved using infrared laser absorption spectroscopy. Because methane absorbs a specific wavelength of infrared light, these instruments emit infrared lasers. The laser beam is directed to wherever the leak is suspected, such as a gas pipe or a ceiling. Because some of the light is absorbed by the methane, the light received back provides a measurement of absorption by the gas. A useful feature of these systems is the fact that the laser beam can penetrate transparent surfaces, such as glass or perspex, so it may be possible to test an enclosed space prior to entering it. The detectors measure the average methane gas density between the detector and target. Readings on the handheld units are given in ppm-m (a product of the concentration of methane cloud (ppm) and path length (m)). In this way, methane leaks can be quickly confirmed by pointing a laser beam towards the suspected leak or along a survey line, for example.

An important difference between the new technology and conventional methane detectors is that the new systems measure average methane concentration, rather than detecting methane at a single point – this gives a more accurate indication of the severity of the leak.

Applications for hand-held devices include:

  • Pipeline surveys
  • Gas plant
  • Industrial and commercial property surveys
  • Emergency call out
  • Landfill gas monitoring
  • Road surface survey

Municipal Distribution Networks

The benefits of remote technology for monitoring pipelines in urban settings are now being realised.

The ability of remote detection devices to monitor gas leaks from a distance makes them extremely useful tools in emergencies. Operators can stay away from potentially dangerous leak sources when checking the presence of gas in closed premises or confined spaces as the technology allows them to monitor the situation without actually gaining access. Not only is this process easier and quicker, but it is also safe. Moreover, it is not affected by other gases present in the atmosphere since the detectors are calibrated to only detect methane – therefore there is no danger of getting false signals, which is important in emergency situations.

The principle of remote detection is also applied when inspecting risers (the above-ground pipes carrying gas to the customers’ premises and normally running along the building outside walls). In this case, the operators point the device towards the pipe, following its route; they can do this from ground level, without having to use ladders or access the customers’ properties.

Hazardous Areas

In addition to detecting gas leaks from municipal distribution networks, explosion-proof, ATEX approved devices can be used in Zone 1 hazardous areas such as petrochemical plants, oil refineries, LNG terminals and vessels, as well as certain mining applications.

When inspecting an LNG/LPG underground tank, for example, an explosion-proof device would be required within 7.5 metres of the tank itself and one metre around the safety valve. Operators therefore need to be fully aware of these restrictions and equipped with the appropriate equipment type.

GPS Coordination

Some instruments now allow spot methane readings to be taken at various points around a site – such as an LNG terminal – automatically generating GPS tracking of the measurement readings and locations. This makes return trips for additional investigations far more efficient, while also providing a bona-fide record of confirmed inspection activity – often a prerequisite for regulatory compliance.

Aerial Detection

Moving beyond hand-held devices, there are also remote methane detectors which can be fitted to aircraft and which detect leaks from gas pipelines over hundreds of kilometres. These systems can detect methane levels at concentrations as small as 0.5ppm up to 500 metres away and include a real-time moving map display of gas concentrations as the survey is conducted.

The way these systems work is relatively simple. A remote detector is attached beneath the aircraft’s fuselage (usually a helicopter). As with the handheld device, the unit produces an infrared laser signal, which is deflected by any methane leakage within its path; higher methane levels result in more beam deflection. These systems also utilise GPS, so the pilot can follow a real-time moving map GPS route display of the pipeline, with a real-time display of aircraft path, gas leaks and concentration (in ppm) presented to the crew at all times. An audible alarm can be set for a desired gas concentration, allowing the pilot to approach for closer investigation.

Conclusion

The range of remote methane detection systems is increasing rapidly, with new technologies being developed all the time. All these devices, whether hand-held or fitted to aircraft, allow quick, safe and highly targeted identification of leaks – whether beneath the pavement, in a city or across hundreds of kilometres of Alaskan tundra. This not only helps prevent wasteful and costly emissions – it also ensures personnel working on or near the pipelines are not exposed to unnecessary danger.

Because the use of natural gas is increasing worldwide we foresee rapid technological advances in remote gas detection in applications as diverse as leak survey, transmission integrity, plant and facilities management, agriculture and waste management, as well as process engineering applications such as coke and steel production. Each of these areas have situations where access may be difficult, combined with the need to put personnel protection at the top of the agenda. Opportunities for remote methane detectors are therefore growing all the time.

 

Explosion hazards in inerted tanks and how to avoid them

Hydrogen sulphide (H2S) is known for being extremely toxic, as well as highly corrosive. In an inerted tank environment, it poses an additional and serious hazard combustion which, it is suspected, has been the cause of serious explosions in the past.

Hydrogen sulphide can be present in %vol levels in “sour” oil or gas. Fuel can also be turned ‘sour’ by the action of sulphate-reducing bacteria found in sea water, often present in cargo holds of tankers. It is therefore important to continue to monitor the level of H2S, as it can change, particularly at sea. This H2S can increase the likelihood of a fire if the situation is not properly managed.

Tanks are generally lined with iron (sometimes zinc-coated). Iron rusts, creating iron oxide (FeO). In an inerted headspace of a tank, iron oxide can react with H2S to form iron sulphide (FeS). Iron sulphide is a pyrophore; which means that it can spontaneously ignite in the presence of oxygen

Excluding the elements of fire

A tank full of oil or gas is an obvious fire hazard under the right circumstances. The three elements of fire are fuel, oxygen and an ignition source. Without these three things, a fire can’t start. Air is around 21% oxygen. Therefore, a common means to control the risk of a fire in a tank is to remove as much air as possible by flushing the air out of the tank with an inert gas, such as nitrogen or carbon dioxide. During tank unloading, care is taken that fuel is replaced with inert gas rather than air. This removes the oxygen and prevents fire starting.

By definition, there is not enough oxygen in an inerted environment for a fire to start. But at some point, air will have to be let into the tank – for maintenance staff to safety enter, for example. There is now the chance for the three elements of fire coming together. How is it to be controlled?

  • Oxygen has to be allowed in
  • There may be present FeS, which the oxygen will cause to spark
  • The element that can be controlled is fuel.

If all the fuel has been removed and the combination of air and FeS causes a spark, it can’t do any harm.

Monitoring the elements

From the above, it is obvious how important it is to keep track of all the elements that could cause a fire in these fuel tanks. Oxygen and fuel can be directly monitored using an appropriate gas detector, like Gas-Pro TK. Designed for these specialist environments, Gas-Pro TK automatically copes with measuring a tank full of gas (measured in %vol) and a tank nearly empty of gas (measured in %LEL). Gas-Pro TK can tell you when oxygen levels are low enough to be safe to load fuel or high enough for staff to safely enter the tank. Another important use for Gas-Pro TK is to monitor for H2S, to allow you judge the likely presence of the pryophore, iron sulphide.

Servicing for safety… A visit to the oil refinery

Working in the office makes it easy to focus on the individual tasks and get detached from how our products are making a difference to people’s lives. One of our customers was kind enough to facilitate an onsite visit so that Andrea (our Halma Future Leader on a marketing placement) could see first-hand how our products are used and who the end users are. This meant a visit to an oil refinery to see where our Crowcon portable gas detectors are used.


“The main thing that surprised me was the sheer size of the site. The oil refinery was very spaced out and it took us 10 minutes to walk from the entrance of the site to where the Crowcon engineer’s based. The engineers and employees around different parts of the refinery wore Hi Vis jackets, big safety boots, hard hats and all appeared to have personal gas detectors. During a quick site tour, I learned the products of the oil refinery are not limited to gas or petrol, but also tar, asphalt, lubricants, washing up liquid, paraffin wax and much more.

The products are all stored in big containers with pipes all over the site. Most of the products are highly flammable which explains the big focus on safety. In the distance, there were a few dome shaped containers which are pressurised vessels. If one of them were to explode, it would have a 10 mile blast radius. Suddenly I had the urge to leave and drive about 10 miles.

Crowcon’s engineer base was full of orange T4s, Gas-Pros as well as an army of “Daleks”, I mean Detectives, awaiting calibration and service. While the harshness of this industrial environment was evident from their appearance, they were otherwise in good working order, and the service engineer worked through the devices quickly.

The end users think of them as a simple device they have to wear to do their job, and they like the simplicity and reliability of Crowcon devices. The Detectives get thrown around and Gas-Pros are almost black is comparison to the usual orange, which just showcases how important the robustness of our devices is. The dangers of this working environment are not generally a big concern to the users, this is everyday life to them. Our devices help ensure they go home after a tough shift. Ensuring the devices are functioning properly is down to the service engineers, and they need to think for the users to ensure that the devices are being used properly.

Seeing Crowcon’s devices being used and the number of times someone enquired if the devices are calibrated and ready to go back into action, highlighted just how important use of portables as part of the safety regime  is considered. “Quality” and “robust” is how users describe Crowcon products and even though they may now treat them like the life saving devices they are, the devices are regularly used and valued. They make a very flammable and dangerous environment a safer place to be.”

Changes to Workplace Exposure Limits (WELs)

What Are Work Place Exposure Limits?

Workplace exposure limits (WELs) provide a legal maximum level for harmful substances in order to control working conditions.

Directive and National Standards

The EU Directive 2017/164 establishes new ‘indicative occupational exposure limit values’ (IOELVs) for a number of toxic substances. The UK Health & Safety Executive (HSE) has decided to change UK statutory limits to reflect the new IOELVs. This decision by the HSE has been taken to comply with Articles 2 and 7 of the Directive requiring Member States to establish the new occupational exposure limit values within national standards by August 21st 2018.

Gas Detector Alarm Thresholds

The exposure limits defined in this Directive 2017/164 are based on the risks of personal exposure: a workers’ exposure to toxic substances over time. The limits (configured into gas detectors as ‘TWA alarm levels’) are expressed over two time periods:

  • STEL (short-term exposure limit): a 15 minute limit
  • LTEL (long-term exposure limit): an 8-hour limit

Portable (personal) monitors are intended to be worn by the user near to their breathing zone so that the instrument can measure their exposure to gas. The instruments TWA (time-weighted) alarms will therefore alert the user when their exposure exceeds the limits set within the national standards.

Portable monitors can also be configured with ‘instantaneous’ alarms which activate immediately when the gas concentration exceeds the threshold. There are no standards to define alarm levels for instantaneous alarms, and so we have these generally set at the same thresholds as the TWA alarms. Some of the new TWA thresholds are low enough to make frequent false alarms a significant problem if they were also adopted for the instantaneous alarm setting. Therefore, new portable instruments will retain the current instantaneous alarm thresholds.

Fixed gas detectors only utilise ‘instantaneous’ alarms as they are not worn by the user and therefore cannot measure an individuals’ exposure to gas over time. Alarm levels for fixed detectors are often based on the TWA alarms as these are the only published guidelines. HSE document RR973 (Review of alarm setting for toxic gas and oxygen detectors) provides guidance on setting appropriate alarm levels for fixed detectors in consideration of site conditions and risk assessment. In some applications where there may be a background of gas it may be appropriate for fixed detector alarm levels to be set higher than those listed in EH40 to prevent repeated false alarms.

Re-configuration of Gas Detector Alarm Thresholds

Users of portable gas detectors who choose to adjust their instrument alarm thresholds to align with the Directive can easily do-so using a variety of accessories available from Crowcon. For full details of calibration and configuration accessories visit the product pages at www.crowcon.com.

Other documents you may find useful:

http://www.hse.gov.uk/pubns/priced/eh40.pdf

http://www.hse.gov.uk/research/rrhtm/rr973.html

 

Working together for safety at sea

Crowcon Detection Instruments is working together with Solent University’s Warsash School of Maritime Science and Engineering – all in the name of teaching engineering cadets, senior Merchant Navy officers, and Superyacht crews.

Solent delivers world-renowned yacht and powerboat design degree programmes, a suite of international maritime studies courses and a wide range of specialist support services for the maritime industry. It is also conducting a large number of research studies that make a real impact on industry thought leadership.

Their partnership with Crowcon makes good sense!  The marine environment is a dangerous one – and not just the more obvious hazards like high seas, storms, or rocks and coral reefs.  Confined spaces on ships, high-risk cargo, and on-ship processes all present potential gas hazards.

To keep mariners safe, gas monitoring equipment is essential.  Gas detection equipment requires specific marine environment testing and certification to ensure suitability to the extreme environments it operates in.  The European Marine Equipment Directive (MED) approval is internationally recognised. Gas detectors used by mariners onboard a vessel registered in an EU country must hold MED approval, and show the wheel mark to demonstrate compliance.

Crowcon has provided the university with demonstration T4 portable multi gas detectors.  T4 provides effective protection against the four most common gas hazards experienced in the marine industry, and is robust and tough enough to deal with the demanding marine environments.  T4 is ideally suited to help vessels comply with multiple SOLAS requirements which dictate the need for gas detection onboard vessels.

John Gouch, lecturer at  Solent University, said: “I have used Crowcon instruments in industry for many years, and know how reliable and trustworthy their gas detectors are. Since joining Warsash 18 months ago, I have been keen to ensure students understand the important part gas detection plays within the on-board safety system.”

“By using demo units of these detectors within our marine engineering courses, we can show the importance of gas detection in a marine environment to hundreds of seafarers and mariners, keeping as many people as possible aware and safe.”

Louise Early, Head of Marketing at Crowcon, said: “We’re really pleased with our partnership with Solent University.  By developing our relationship with training establishments, our safety message gets out to the people who will benefit most. We are always keen to learn from industry and this programme also offers Crowcon further insight into the way in which our equipment is used.”

For more information, visit the Solent University website, or the marine section of our industries page.

What you need to be aware of when…

…putting your portable gas detector into storage

Do you use your portable gas detector every day?  Or perhaps you get it out of storage as and when you need it?  Either way, there are things to consider if you’re putting your detector into storage – and the conditions they’re kept in can have a real impact.

Batteries

Your portable detector contains a battery – and it doesn’t entirely switch off the moment your detector does.  Internal processes, like the date and time clock, are running all the time.  If your battery runs flat when in storage, you might have to reset the date and time when you start the detector back up again.  This is easy to do if you have the right accessories, but it could otherwise lead to an inconvenient trip to your service centre.

Larger detectors, like Detective+, contain lead-acid batteries (like a car battery).  Like their vehicular relatives, these batteries don’t like being left to go flat during storage, which can also adversely affect the battery life.  Give them a boost before putting them away, and keep them topped up periodically.

Generally, it’s good practice to charge your detector fully before storing, and refer to the user manual for particular advice about charging before and during storage periods.  Typical storage times obviously vary from case to case, but in our examples we’re working to a four week storage period.

Environment

Both batteries and detectors are sensitive to their storage environment.  Avoid extremes of temperature and humidity, and keep your detectors away from any chemicals that could affect the sensors.  Things like high concentrations of solvents or silicone compounds can poison catalytic flammable sensors, for example – and there are plenty more examples in our blog on the subject.

Coming out of hibernation

When using your detector for the first time after a period of storage, make sure it’s fully operational and within calibration periods.  For more information on how to check and recalibrate your detectors, take a look at our blog on detector calibration.

Any questions?  Call Crowcon Customer Support on +44 (0)1235 557711.

Just what are Intrinsic Safety Barriers?

In your industry, you may have heard of Intrinsic Safety barriers, commonly known as I.S. barriers.  But what are they, exactly?

I.S. barriers are protection devices for electrical equipment such as gas detectors, fire detectors, alarms etc mounted in a hazardous area.  They protect equipment from current surges, which would otherwise run the risk of turning the equipment into an ignition source – disastrous when the detector is in an area where there may be explosive gases.

A good analogy is a steam engine with a pressure relief whistle – when the engine is under too much pressure, it’s relieved through the whistle by literally letting off steam.

How do they work?

I.S. barriers work by limiting the energy available to the I.S. device.  Here at Crowcon, we use two types of I.S. barriers – zener barriers and galvanic isolators.

Zener barriers contain zener diodes which divert any excess energy to earth – so you need to make sure that there’s an intrinsically safe earth point available.  When you don’t have an earth point, you can use a galvanic isolator, which provides electrical isolation between the hazardous area and the safe area circuits via a transformer.

When do you need to use them?

Basically, when you’re using certified devices that use the I.S. protection method.  If your device uses this method, you’ll see the following in their ATEX and IECEx certificates:

  • ‘ia’ or ‘ib’ in their certification classification
  • For example – Ex ia IIC T4 Ga (the classification for our Xgard Type 1 fixed detector)

Some products might use more than one protection method – a common example is I.S. and flameproof protection.  In these cases, the product is unlikely to require the use of an external I.S. barrier.  However, as always, we recommend that you consult your product manual for guidance.

How do you use them?

I.S. barriers should be located between the devices in the hazardous area and the control equipment (installed in a safe area).  The I.S. barrier needs to be within the safe area.

The ATEX certificate for the I.S. device will stipulate acceptable parameters for the I.S. barrier.

When should they be avoided?

Detectors which don’t use the ‘intrinsic safety’ method of protection shouldn’t be used with  an I.S. barrier.

For example, the Xgard type 5 uses the flameproof (Exd) method of protection – so it doesn’t need an I.S. barrier.  However, not all versions of the Xgard have flameproof protection, so do need an I.S. barrier – it all boils down to the product you’re using.

When your detector and control equipment are both installed in the safe area, you don’t need I.S. barriers.

One thing you should remember – using an I.S. barrier with a detector that doesn’t use the intrinsic safety method of protection doesn’t make the detector intrinsically safe.

Your sensor is more sensitive than you think

 

We all know that pellistor sensors are one of the primary technologies for detecting hydrocarbons.  In most circumstances, they’re a reliable, cost-effective means of monitoring flammable levels of combustible gases.

As with any technology, there are some circumstances in which pellistors shouldn’t be relied on, and other sensors, like infrared (IR) technology, should be considered.

Problems with pellistors

Pellistors are generally extremely reliable at detecting flammable gases.  However, every type of technology has its limits, and there are a few occasions where pellistors shouldn’t be assumed to be most suitable.

Perhaps the biggest drawback of pellistors is that they’re susceptible to poisoning (irreversible loss of sensitivity) or inhibition (reversible loss of sensitivity) by many chemicals found in related industries.

What happens when a pellistor is poisoned?

Basically, a poisoned pellistor produces no output when exposed to flammable gas. This means a detector would not go into alarm, giving the impression that the environment was safe.

Compounds containing silicon, lead, sulphur, and phosphates at just a few parts per million (ppm) can impair pellistor performance.  So whether it’s something in your general working environment, or something as innocuous as cleaning equipment or hand cream, you could be compromising your sensor’s effectiveness without even realising it.

What’s so bad about silicons?

Silicons have their virtues, but they may be more prevalent than you think; including sealants, adhesives, lubricants, and thermal and electrical insulation. They can poison pellistor sensors at extremely low levels.  For example, there was an incident where a company replaced a window pane in a room where they stored their gas detection equipment.  A standard silicon-based sealant was used in the process, and as a result all of their pellistor sensors failed their subsequent testing.  Fortunately this company tested their equipment regularly; it would have been a very different and more tragic story had they not done so.

Situations like this ably demonstrate the importance of bump testing (we’re written about it previously – take a look), which highlights poisoned or inhibited sensors.

What can I do to avoid poisoning my sensor?

Be aware, in essence –bump-test your equipment regularly, and make sure your detectors are suited to the environment you’re working in.

Find out more about infra-red technology in our previous blog.

  

Pellistor sensors – all you need to know

We’ve written about pellistor sensors before, but the information still remains vital and useful.  Here’s all you need to know…

Pellistor sensors (or catalytic bead sensors) have been the primary technology for detecting flammable gases since the ‘60s. Despite having discussed a number of issues relating to the detection of flammable gases and VOC, we have not yet looked at how pellistors work. To make up for this, we are including a video explanation, which we hope you will download and use as part of any training you are conducting:

A pellistor is based on a Wheatstone bridge circuit, and includes two “beads”, both of which encase platinum coils.  One of the beads (the ‘active’ bead) is treated with a catalyst, which lowers the temperature at which the gas around it ignites. This bead becomes hot from the combustion, resulting in a temperature difference between this active and the other ‘reference’ bead.  This causes a difference in resistance, which is measured; the amount of gas present is directly proportional to it, so gas concentration as a percentage of its lower explosive limit (%LEL*) can be accurately determined.

The hot bead and electrical circuitry are contained in flameproof sensor housing, behind the sintered metal flame arrestor (or sinter) through which the gas passes. Confined within this sensor housing, which maintains an internal temperature of 500°C, controlled combustion can occur, isolated from the outside environment. In high gas concentrations, the combustion process can be incomplete, resulting in a layer of soot on the active bead. This will partially or completely impair performance. Care needs to be taken in environments where gas levels over 70% LEL may be encountered.

For more information about sensor technology for flammable gases, read our comparison article on pellistors vs Infrared sensor technology: Are silicone implants degrading your gas detection?.

*Lower Explosive Limit – Learn more

 Click in the top right hand corner of the video to access a downloadable file.