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 21^st 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.

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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.

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What you need to be aware of when…

…zeroing your CO2 detector

Without wishing to sound accusing, where were you the last time you zeroed your CO2 detector? In your vehicle? In the office before you travelled to the location you were working in?

It might not have caused you problems so far, but the air around you can make a big difference to the performance of your CO2 detector.

What is zeroing?

Zeroing your detector means calibrating it so its ‘clean air’ gas level indication is correct.

When is zero not really zero?

Many CO2 detectors are programmed to zero at 0.04% CO2 rather than 0%, because 0.04% is the normal volume of CO2 in fresh air. In this case, when you zero your detector, it automatically sets the baseline level to 0.04%.

What happens if you zero your CO2 monitor where you shouldn’t?

If you zero your detector where you shouldn’t, the actual CO2 concentration could be much higher than the standard 0.04% – up to ten times higher, in some cases.

The end result? An inaccurate reading, and no true way of knowing how much CO2 you’re actually exposed to.

What are the dangers of CO2?

CO2 is already in the earth’s atmosphere, but it doesn’t take much for it to reach dangerous levels.

1% toxicity can cause drowsiness with prolonged exposure
2% toxicity is mildly narcotic and causes increased blood pleasure, pulse rate, and reduced hearing
5% toxicity causes dizziness, confusion, difficulty in breathing, and panic attacks
8% toxicity causes headaches, sweating and tremors. You’ll lose consciousness after five to ten minutes of exposure.

What can I do to make sure I’m safe?

Only zero your instruments if you really have to, and make sure you zero your detector in fresh air – away from buildings and CO2 emissions, and at arm’s length to make sure your own breath doesn’t affect the reading.

What if I think my zero reading is incorrect?

It’s best to test the instrument with 100% nitrogen to check the real zero point, and then with a known level of CO2 test gas. If the zero gas reading is incorrect, or any other gas reading for that matter, the detector will need a full service calibration – contact your local service provider for help.

If you have a Crowcon detector, you can use our Portables Pro software to correct its zero reading. For further information, call Crowcon customer support on +44 (0)1235 557711.

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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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Complacency – the biggest sin of all

We recently ran a series of articles under the guise of the Seven Deadly Sins of Gas Detection, which talked about gas detection and common mistakes of different kinds that could cost you your life or someone else’s life. However, the real deadly sin that sits at the root of all is complacency – not taking gases and gas hazards as a serious and present danger.

Continue reading “Complacency – the biggest sin of all”

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Deadly Sin No. 7 – Ignoring your data

Ignoring your data is Crowcon’s seventh in the series of Deadly Sins of Gas Detection. A recent news story about an oil worker found collapsed over an open hatch, dead, highlighted this all too graphically. One of the most tragic aspects of this story (tragedy being properly defined as something that could have been prevented) was that data which could have saved him was logged in his personal gas detector. Continue reading “Deadly Sin No. 7 – Ignoring your data”

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