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.

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Electrochemical sensors: how long on the shelf, and how long in the field?

You might have heard the term ‘shelf life’ and ‘operational life’ before in reference to electrochemical sensors. They’re the type of terms that lots of people know, but not everybody knows the finer details of what they mean.

How long on the shelf?

For the purposes of this piece, “shelf life” is the time between manufacture of a product and initial operation.

Electrochemical sensors typically have a stated shelf life of six months from manufacture, provided they’re stored in ideal conditions at 20˚C. Inevitably, a small proportion of this period is taken up during the manufacture of the gas detector and in shipping to the customer.

With that in mind, we’d always advise that when acquiring sensors and any spare parts during its lifetime, you plan and time your purchases for minimal delay between storage and usage.

How long in the field?

Again, “operational life” in this context refers to the time from when a sensor starts being used, until it’s no longer fit for purpose.

In absolutely ideal conditions – stable temperature and humidity in the region of 20˚C and 60%RH with no incidence of contaminants – electrochemical sensors have been known to operate in excess of 4000 days (11 years)! Periodic exposure to the target gas doesn’t limit the life of these tiny fuel cells: high quality sensors have a large amount of catalyst material and robust conductors which don’t become depleted by the reaction.

However, absolutely ideal conditions don’t always exist, or stay that way, so it’s vital to err on the side of caution when it comes to gas sensors.

With that in mind, electrochemical sensors for common gases (for example carbon monoxide or hydrogen sulphide) have a typical operational life of 2-3 years. A more exotic gas sensor, such as hydrogen fluoride, may have only 12-18 months.

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Why you shouldn’t spark up

Think back to the last time you wanted to test your flammable gas detector. You’re busy; you want something quick and convenient. An obvious answer is a cigarette lighter, isn’t it? A quick squirt of gas should do the job. Shouldn’t it?

If ‘the job’ is ruining your detector’s sensor at the flick of a switch, then yes!

If you use a cigarette lighter to test your sensors, you run the risk of:

Rendering your sensor useless
Compromising your warranty – carbon deposits are a dead giveaway for manufacturers who then won’t honour your claim due to incorrect testing

Why cigarette lighters are bad news for your sensors

Pellistor-type sensors (also known as catalytic beads) are used in industrial gas detectors to detect a wide variety of gases and vapours. The sensors are made up of a matched pair of ‘beads’ which are heated to react with gases. The sensors operate in the ‘Lower Explosive Limit’ (LEL) range, so provide a warning well before a flammable level of gas concentration accumulates.

Periodic and irregular exposure to high gas concentrations is likely to compromise sensor performance, and cigarette lighters expose the sensor to 100% gas volume. Not only that, but this exposure can potentially crack the sensor beads. Cigarette lighters also leave damaging carbon deposits on the beads – leaving you with useless sensors, and potentially putting your life at risk.

How to safely test your sensors

Bump test! Or you can calibrate using 50% LEL gas – but make sure you’re using the correct gas calibration adaptor from your gas cylinder, and that your cylinder’s flow is regulated to 0.5 to 1 litre per minute.

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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.

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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.

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How much life have you got left?

When something stops working, you rarely get a heads-up. When was the last time you flipped a switch, only for your light bulb to give up the ghost? Or have you had a cold, frosty morning this winter when your car simply won’t start?

Continue reading “How much life have you got left?”

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The importance of bump testing

Bump testing is one of those topics that crops up again and again, but still not everyone gets the point. A gas detector may not respond properly to gas for many reasons. Bump testing is a quick and easy way to ensure yours does. Here is just one example of what can happen if you don’t bump test your equipment.

Continue reading “The importance of bump testing”

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Pellistor sensors – how they work

Pellistor gas sensors (or catalytic bead gas 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 gas sensor technology for flammable gases, read our comparison article on pellistors vs Infrared gas 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 file that can be downloaded.

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Minimising Exposure

The key to reducing risk – spend less time exposed to hazards! Technological advances, driven by increasing safety awareness, are providing opportunities to reduce detector maintenance and therefore also reduce the amount of time operators must spend handling detectors and transmitters in hazardous areas.

Andy, Crowcon’s Senior Product Manager, has reviewed the benefits that these developments bring.

Continue reading “Minimising Exposure”

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Cross sensitivity of toxic sensors: Chris investigates the gases that the sensor is exposed to

Working in Technical Support, one of the most common questions from customers is for bespoke configurations of toxic gas sensors. This frequently leads to an investigation into the cross sensitivity of the different gases that the sensor will be exposed to.

Cross sensitivity responses will vary from sensor type to sensor type, and suppliers often express the cross sensitivity in percentages while others will specify in actual parts-per-million (ppm) levels.

Continue reading “Cross sensitivity of toxic sensors: Chris investigates the gases that the sensor is exposed to”

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