You won’t find Crowcon sensors sleeping on the job

MOS (metal oxide semiconductor) sensors have been seen as one of the most recent solutions for tackling detection of hydrogen sulphide (H2S) in fluctuating temperatures from up to 50°C down to the mid-twenties, as well as humid climates such as the Middle East.

However, users and gas detection professionals have realised MOS sensors are not the most reliable detection technology. This blog covers why this technology can prove difficult to maintain and what issues users can face.

One of the major drawbacks of the technology is the liability of the sensor “going to sleep” when it doesn’t encounter gas for a period of time. Of course, this is a huge safety risk for workers in the area… no-one wants to face a gas detector that ultimately doesn’t detect gas.

MOS sensors require a heater to equalise, enabling them to produce a consistent reading. However, when initially switched on, the heater takes time to warm up, causing a significant delay between turning on the sensors and it responding to hazardous gas. MOS manufacturers therefore recommend users to allow the sensor to equilibrate for 24-48 hours before calibration. Some users may find this a hinderance for production, as well as extended time for servicing and maintenance.

The heater delay isn’t the only problem. It uses a lot of power which poses an additional issue of dramatic changes of temperature in the DC power cable, causing changes in voltage as the detector head and inaccuracies in gas level reading. 

As its metal oxide semiconductor name suggests, the sensors are based around semiconductors which are recognised to drift with changes in humidity- something that is not ideal for the humid Middle Eastern climate. In other industries, semiconductors are often encased in epoxy resin to avoid this, however in a gas sensor this coating would the gas detection mechanism as the gas couldn’t reach the semiconductor. The device is also open to the acidic environment created by the local sand in the Middle East, effecting conductivity and accuracy of gas read-out.

Another significant safety implication of a MOS sensor is that with output at near-zero levels of H2S can be false alarms. Often the sensor is used with a level of “zero suppression” at the control panel. This means that the control panel may show a zero read-out for some time after levels of H2S have begun to rise. This late registering of low-level gas presence can then delay the warning of a serious gas leak, opportunity for evacuation and the extreme risk of lives.

MOS sensors excel in reacting quickly to H2S, therefore the need for a sinter counteracts this benefit. Due to H2S being a “sticky” gas, it is able to be adsorbed onto surfaces including those of sinters, in result slowing down the rate at which gas reaches the detection surface.

To tackle the drawbacks of MOS sensors, we’ve revisited and improved on the electrochemical technology with our new High Temperature (HT) H2S sensor for XgardIQ. The new developments of our sensor allow operation of up to 70°C at 0-95%rh- a significant difference against other manufacturers claiming detection of up to 60°C, especially under the harsh Middle Eastern environments.

Our new HT H2S sensor has been proven to be a reliable and resilient solution for the detection of H2S at high temperatures- a solution that doesn’t fall asleep on the job!

Click here for more information on our new High Temperature (HT) H2S sensor for XgardIQ.

An ingenious solution to the problem of high temperature H2S

Due to extreme heat in the Middle East climbing up to 50°C in the height of summer, the necessity for reliable gas detection is critical. In this blog, we’re focusing on the requirement for detection of hydrogen sulphide (H2S)- a long running challenge for the Middle East’s gas detection industry.

By combining a new trick with old technology, we’ve got the answer to reliable gas detection for environments in the harsh Middle Eastern climate. Our new High Temperature (HT) H2S sensor for XgardIQ has been revisited and improved by our team of Crowcon experts by using a combination of two ingenious adaptations to its original design.

In traditional H2S sensors, detection is based on electrochemical technology, where electrodes are used to detect changes induced in an electrolyte by the presence of the target gas. However, high temperatures combined with low humidity causes the electrolyte to dry out, impairing sensor performance so that the sensor has to be replaced regularly; meaning high replacement costs, time and efforts.

Making the new sensor so advanced from its predecessor is its ability to retain the moisture levels within the sensor, preventing evaporation even in high temperature climates. The updated sensor is based on electrolytic gel, adapted to make it more hygroscopic and avoiding dehydration for longer.

As well as this, the pore in the sensor housing has been reduced, limiting the moisture from escaping. This chart indicated weight loss which is indicative of moisture loss. When stored at 55°C or 65°C for a year just 3% of weight is lost. Another typical sensor would lose 50% of its weight in 100 days in the same conditions.

For optimal leak detection, our remarkable new sensor also features an optional remote sensor housing, while the transmitter’s displays screen and push-button controls are positioned for safe and easy access for operators up to 15metres away.

 

The results of our new HT H2S sensor for XgardIQ speak for themselves, with an operating environment of up to 70°C at 0-95%rh, as well featuring a 0-200ppm and T90 response time of less than 30 seconds. Unlike other sensors for detecting H2S, it offers a life expectancy of over 24 months, even in tough climates like the Middle East.

The answer to the Middle East’s gas detection challenges fall in the hands of our new sensor, providing its users with cost-effective and reliable performance.

Click here for more information about the Crowcon HT H2S sensor.

Have you ever thought about the dangers behind your favourite beverage?

Beer Production

It’s only natural for us to associate the need for gas detection in the oil and gas, and steel industries, but have you thought about the need to detect hazardous gases such as carbon dioxide and nitrogen in the brewing and beverage industry?

Maybe it’s because nitrogen (N2) and carbon dioxide (CO2) are naturally present in the atmosphere. It could be that CO2 is still under-valued as a hazardous gas. Although in the atmosphere CO2 remains at very low concentrations – around 400 parts per million (ppm), greater care is needed in brewery and cellar environments where in confined spaces, the risk of gas canisters or associated equipment leaking could lead to elevated levels. As little as 0.5% volume (5000ppm) of CO2 is a toxic health hazard. Nitrogen on the other hand, can displace oxygen.

CO2 is colourless, odourless and has a density which is heavier than air, meaning pockets of CO2 gather low on the ground gradually increasing in size. CO2 is generated in huge amounts during fermentation and can pose a risk in confined spaces such as vats, cellars or cylinder storage areas, this can be fatal to workers in the surrounding environment, therefore Health & Safety managers must ensure the correct equipment and detectors are in place.

Brewers often use nitrogen in multiple phases of the brewing and dispensing process to put bubbles into beer, particularly stouts, pale ales and porters, it also ensures the beer doesn’t oxidise or pollute the next batch with harsh flavours. Nitrogen helps push the liquid from one tank to another, as well as offer the potential to be injected into kegs or barrels, pressurising them ready for storage and shipment. This gas is not toxic, but does displace oxygen in the atmosphere, which can be a danger if there is a gas leak which is why accurate gas detection is critical.

Gas detection can be provided in the form of both fixed and portable. Installation of a fixed gas detector can benefit a larger space such as plant rooms to provide continuous area and staff protection 24 hours a day. However, for worker safety in and around cylinder storage area and in spaces designated as a confined space, a portable detector can be more suited. This is especially true for pubs and beverage dispensing outlets for the safety of workers and those who are unfamiliar in the environment such as delivery drivers, sales teams or equipment technicians. The portable unit can easily be clipped to belts or clothing and will detect pockets of CO2 using alarms and visual signals, indicating that the user should immediately vacate the area.

At Crowcon, we’re dedicated in growing a safer, cleaner, healthier future for everyone, every day by providing best in class gas safety solutions. It’s vital that once gas detectors are deployed, employees should not get complacent, and should be making the necessary checks an essential part of each working day as early detection can be the difference between life and death.

Quick facts and tips about gas detection in breweries:

  • Nitrogen and CO2 are both colourless and odourless. CO2 being 5 times heavier than air, making it a silent and deadly gas.
  • Anyone entering a tank or other confined space must be equipped with a suitable gas detector.
  • Early detection can be the difference between life and death.

Once again, Gas-Pro is ‘detector of choice’ for volcano environmental expedition

We are all familiar with the term global warming and often see statistics about the potential effects this could have on our planet.  One such prediction is by the end of this century the globe will increase in temperature by between 0.8 and 4 degrees.

What many of us may not know is that volcanoes, which are a completely natural phenomenon, contribute a significant amount of gases into our atmosphere. And these gases are currently not considered in the world’s climate models, which means there is potentially a large margin of error.

However, this could be about to change as Yves Moussallam, an inspiring French Volcanologist, who with the support of Rolex and the 2019 Rolex Awards for Enterprise, has made it his mission to understand volcanos and how they impact on our planet.  He ventures into these dramatic and dangerous environments to take measurements which are used by scientists and climatologists to improve their prediction models.

By observing volcanos, and gathering this vitally important data, he is helping the world understand the impact volcanos are having on climate change.

Yves is no stranger to volcanic expeditions. In 2015, he led a small team to the Nazca subduction zone in South America. Their mission was to provide the first accurate and large-scale estimate of the flux of several volatile gas species.

To keep the team safe, Yves selected Crowcon detection equipment and was delighted with Gas man and Gas-Pro’s lightweight, clean and safe functionality.

Now Yves is back with a new expedition and has turned to Crowcon once again. This time, Yves is heading to the region of Melanesia in Italy.  Satellites, which are used to track volcanic behaviour, have shown that this region is responsible for approximately a third of global volcanic gas emissions.

His expedition will climb these volcanoes and take measurements directly in the volcanic plume.

There are two main methods to measure gases in volcanoes.  The first is via satellite which takes images from space.  The second is to go directly into the field and measure gas released at its source.

Experts believe the method of working directly in the field is the most accurate as it is positioned far closer to the source so there is a reduced risk of error.

To conduct these measurements requires tried, tested and trusted equipment and with Crowcon’s proven track record, Yves turned again to Gas-Pro.

Crowcon’s Gas-Pro includes an onboard datalogging feature which will provide an extra line of data and an idea of average exposure, which is important for expeditions that span longer periods.  It is also lightweight which is hugely beneficial when carrying bulky equipment.

Everyone at Crowcon wishes Yves a safe and successful expedition and we hope the data he gathers will help us understand the impact volcanos have on our world.

#Rolex #RolexAwards #PerpetualPlanet #Perpetual

Helping you stay safe during the BBQ season

Who doesn’t love a summer BBQ? Come rain or shine we light up our BBQs with usually the only worries being whether it will rain, or the sausages are fully cooked through.

While these are important, (especially making sure the sausages are cooked!) many of us are completely unaware of the potential risks.

Carbon monoxide is a gas that has received its fair share of publicity with many of us installing detectors in our homes and businesses, but completely unaware carbon monoxide is associated with our BBQs.

If the weather is poor, we may decide to barbeque in the garage doorway or under a tent or canopy. Some of us may even bring our BBQs into the tent after use.  These can all be potentially fatal as the carbon monoxide collects in these confined areas.

Equally with a propane or butane gas canister, we store in our garages, sheds and even our homes unaware that there is a risk of a potentially deadly combination of an enclosed space, a gas leak and a spark from an electrical device.  All of which could cause an explosion.

All of that said, BBQs are here to stay and if we use them safely, are a great way to spend a summer afternoon.  So, here is a selection of facts and tips from our safety team at Crowcon which we hope will help you enjoy a safe and delicious summer ahead!

 

Quick facts and tips about BBQ charcoals:

  • Carbon monoxide is a colourless and odourless gas so just because we can’t smell or see it, doesn’t mean it’s not there
  • Carbon monoxide is a by-product of burning fossil fuels, which include charcoal and BBQ gas
  • Always use your BBQ in a well-ventilated open area as it can accumulate to toxic levels in enclosed spaces
  • Never bring a charcoal into a tent, even if it seems cold. Remember a smouldering BBQ will still give off carbon monoxide
  • Be aware and act quickly if someone experiences the symptoms of carbon monoxide poisoning which include headaches, dizziness, breathlessness, nausea, confusion, collapse and unconsciousness. These symptoms can be potentially fatal

 

Quick facts and tips about gas cannisters:

  • Gas barbecues tend to use propane, butane or LPG (which is a mixture of the two)
  • Gas BBQs have holes in the bottom to prevent a build-up of gas. This is because gas is heavier than air so will accumulate in low areas or fill a space from the bottom up
  • To avoid the accumulation of gas, cannisters should always be stored outside, upright, in a well-ventilated area, away from heat sources, and away from enclosed low spaces
  • If you store your BBQ in the garage, make sure you disconnect the gas cannister and keep this outside
  • When you are using your BBQ, keep the cannister to one side so it isn’t underneath and close to the heat source and position the BBQ in an open space
  • Always keep the cannister away from ignition sources when changing cannisters
  • Always make sure you turn off the gas at the BBQ as well as on the regulator on the cannister, after use

 

Chernobyl – a powerful safety message to the world

The recent Sky Atlantic TV series Chernobyl sent out a powerful message about the catastrophic and far reaching consequences of radiation gases, both to people and the environment.

The series is based on true events from the 1986 nuclear disaster in the then USSR; the largest uncontrolled radioactive release into the environment ever recorded. The accident resulted in an untold number of fatalities, as well as serious social and economic disruption for large populations within the USSR and beyond.

The Chernobyl explosion resulted in a radioactive gas cloud which travelled across Europe, including the UK; falling to the ground in the form of ‘nuclear rain’.

There are many disturbing facts we read about. Not least that according to the British Ministry of Health, 369 farms and 190,000 sheep in Britain still contain traces of radioactive fallout from the Chernobyl disaster.

Both human and mechanical error contributed to the disaster and thankfully safety standards, regulations, awareness and new technologies have significantly improved since the disaster.

The principal of safety, whether a huge nuclear facility or small manufacturing plant, must remain the same. Here at Crowcon we are dedicated to keeping people and the environment protected. Our technologies support organisations across multiple industries, including nuclear plants, improving plant and personal safety. Our technologies help our customers be protected from the dangers of gases.

At Crowcon, we welcome shows such as Chernobyl which document historical disasters such as this and highlight in a dramatic but real way, the importance of ensuring companies understand the need for safety measures, however big or small, are in place.  Protecting their people, the environment and the world.

#DetectingGasSavingLives

#SaferCleanerHealthier

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