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

 

Why enter into an apprenticeship at Crowcon?

“Working at Crowcon provides me with all the necessary skills required to become a competent engineer within the industry.” Noah Fisher

Apprenticeships are more than just a qualification. They allow you to become a professional in your chosen trade area, earning a wage whilst making a real impact in the business.

Whilst building your engineering career through an apprenticeship scheme at Crowcon, you’ll get experience in a work environment day-to-day in parallel with also gaining the benefits from experienced colleagues and mentors who can help you build your skills and take them straight into the workplace.

Key benefits to an apprenticeship:

 

  • Learn and earn money at the same time
  • Gain a nationally recognised qualification
  • Get relevant and practical experiences
  • Have full support, guidance and training
  • Broaden your knowledge and skillset
  • Network and collaborate with colleagues
  • Future career prospects

There is great scope to earn good rates of pay working as an engineer – across a variety of specialisms as your career develops.

Hear what some of our current apprentices have to say:

“For anyone looking to start an apprenticeship I would say go for it, as it has been a great experience for me because you get to carry out practical activities on site at Crowcon and the theory side at college on a day release type format. This is vital as it gives me the knowledge behind carrying out certain activities and it all links together with my everyday work.” Ryan Jones

 

“For someone who was interested in technology and how things work in different industries, it was inevitable that engineering would be sector in which I chose to pursue a career. However, I am also a person who wouldn’t prefer to be learning in a classroom every day. Therefore, apprenticeships allow you to work in real world environments giving the options to gain the essential experience needed for future careers choices.

Working for an established company like Crowcon provided a clear training programme, both in and out of the workplace that would provide me with the skills and knowledge to progress further within the engineering industry. Given the support provided by the company I have been able to push myself in the classroom to achieve the very best. This was reflected in being awarded a variety of accolades on both local and national levels during my time here at Crowcon.”  Vikesh Patel

We’re always looking at recruiting apprentices and graduate engineers to support in achieving recognised qualifications from NVQs at Level 2 to BTECs, HNC and in some disciplines, such as finance or purchasing, post graduate or professional certificates.

Home grown talent will be the differentiator of the future. The cost of higher education is making many re-think the automatic study routes. It is no longer necessary to become burdened with a large debt, via full time study, to achieve your potential in the work place. Vocational career paths are finally becoming more widely available, with a multitude of opportunities and development routes.

People Development is at the heart of our business success and working collaboratively to release the wider potential within our business is how Crowcon will continue to go from strength to strength.

Following a successful completion of the 3 year apprenticeship, you could follow a similar path to previous apprenticeships with scope to move into an engineering role after a few years in the Line Technician position. Previous apprentices have taken roles in Test & Verification, Quality Engineering, and Manufacturing Engineering.

After all, why would you take a job, when you can have a career?

Don’t get caught in a tight space!

OSHA (Occupational Safety and Health Administration) has released a factsheet (29 CFR 1926 Subpart AA) on all the rules and regulations of residential workers in confined spaces. OSHA works to assure the safety and health of all of America’s working people.

This blog highlights what we think are the key points.

Well, how is a confined space defined?

OSHA defines these as

  • has limited entry and exits
  • larger enough for workers to enter
  • not intended for regular occupancy

Confined space sites could be drains, manholes, water mains, sewer systems, crawl spaces, attics, heating, ventilation, and air-conditioning systems.

There are two different variants on confined spaces. Those that contain hazardous conditions and those that do not contain a physical hazard to the individual.

A confined space that contains hazardous conditions could be considered a permit-required space under the new regulations (PRCS). These spaces might be dangerous to the life of the worker if the space hasn’t been investigated, tested and controlled.

Spaces that tend not to be permit-required confined spaces generally do not contain life threatening hazards. Attics, basements and crawl spaces have a smaller risks but still fall into new regulations.

I’m an employer. What do I need to do?

  • Evaluate the space! If hazardous conditions are present, a permit specifying safety measures and names of those permitted in the space must be written before any work can take place.
  • Inform employees! Let your employees know all the facts. Does a workplace contain a confined space? Is this a permit-required space? All workers should be informed of these hazards – these only needs to be a signpost for entry and exit points if required.
  • Protection! Attempt to remove or isolate any hazards that may be present in the space.
  • Have the right equipment! Check out our range of Portables that would help protect your employees from hazardous gases.
  • Train your staff! Workers should be aware of the dangers and understand any hazards in places permits are required.

Still not clear? Don’t worry, the factsheet offers insight and obligations for all kinds of employers.

Under the new standards, the obligation of the employer will depend on what type of employer they are. The controlling contractor is the main point of contact for any information about PRCS on site.

  • Host employer: The employer who owns or manages the property where the construction work is taking place.
  • Controlling contractor: The employer who has overall responsibility for construction at the worksite.
  • Entry employer or Sub Contractor: Any employer who decides that an employee it directs will enter a permit-required confined space.

How are the new regulations different to the previously applied rules?

The guidelines require employers to figure out what confined spaces their employees are working in, what hazards there are and how these can be made safer, develop rescue plans and ensuring staff training.

For all the facts, visit https://www.osha.gov/Publications/OSHA3914.pdf

 

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.

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.

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.

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.

You can read more about sensor life in our HazardEx article.