All about Gas Monitors, Gas Detectors and Gas Detection systems

HAZOP-What does it mean?

2011-01-30T08:12:00.000-08:00

For more information about HAZOP and safety assessment, please get the HAZOP training course.
In this post we will diversify a bit away from our topic of Gas Monitors and go a bit into risk assessment techniques. One of the better known ones is the HAZOP technique.
HAZOP that started out in somewhere around the 1960s in ICI (Imperial Chemical Industries) UK when some some bright spark decided to try it out on a spanking new design of a phenol plant was on the design board.This was a phenol plant that wa sto produce phenol through the Cumene route (Benzene + Propylene-->Cumene-->Phenol)

Well, he opened a can of worms, as it were, because the study found several holes in safety aspects and the technique of HAZOP was born. Initially it was confined only to ICIs internal departments, but later on it spread via conferences and seminar papers to other organizations as well and soon became an established risk assessment and safety technique.

The Bhopal incident that happened two decades later spurred action in the global chemicals and process industries and HAZOP began to be used not only for new plants at the design stage but also for older plants, modifications, shutdowns and turnarounds and so on. The process not only improved Safety but also operational ease.

In the typical HAZOP methodology, a plant or a subsystem of the plant (called a node) is chosen for study. Then all deviations are studied against the original intentions and permutations and combinations give rise to possibilities that can result in accidents. These are then assessed to modify the design or the work flow, so that the process becomes safer. There is much more to this and it requires training in the technique plus a few real life HAZOP studies to really master the technique.

Today one cannot think of not using HAZOP in a process plant, it has become commonplace in many industries. However being subjective, the result of the HAZOP study depends greatly on the people that comprise the team carrying it out and a bad HAZOP from a bad team results in the plant being even more unsafe than had there been no HAZOP at all!
So it is very important that only trained and competent people are in charge of HAZOPs.Hence HAZOP training should be a pre-requisite for anybody wishing to take up the task.

Dangers of H2S gas-Use a personal gas monitor

2011-01-27T05:00:00.000-08:00

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Hydrogen Sulfide gas (H2S gas)is commonly encountered in many industrial facilities especially those in the Oil and Gas industry and petrochemicals production. It is commonly referred to as "Sour gas" in oilfields. Is it hazardous? You betcha! Reportedly the most deaths in the Oil and Gas industry have occurred till date are due to H2S. But if your only plan to survive it is by smelling it and running off in the other direction, then re-work your strategy!

Hydrogen Sulfide gas does have a smell, similar to eggs gone bad (rotten eggs) but the human nose can get sensitized very fast. So though one can smell it in lower concentrations, if the smell goes away, it does not mean that the gas has gone away-it simply means that the nose has stopped detecting it, though the concentration may be increasing!
Unbelievable but true- so the only great way to work in areas that may have H2S is not to trust your nose, but have a personal toxic gas monitor. If you have no idea of how to select one and use and calibrate it, then have a look at the online gas monitor training here. You will find it to be useful and a life saver!

Gas Monitors in Confined Space Entry situations

2010-04-25T09:50:00.000-07:00

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In situations that require confined space entry (for more details about what are confined spaces, please see the brief tutorial here) Gas Monitors are absolutely essential. Most dangers in confined spaces relate to either lack of breathing air (oxygen)or exposure to toxic or explosive gases and vapors. Lack of breathing air can cause asphyxiation, whereas exposure to toxic fumes can cause death or disablement, or injury. Explosive vapors and gases can of course explode, blowing people and equipment to smithereens.
But you will be surprised to know that despite there being several good, reliable and working personal gas monitors, how few are really used by workers. They are not to blame however, it is either lack of knowledge of the part of their supervisors, or a "cost cutting" mentality. This can result in needless injury, death and invitation to liabilities by the company if it can be proven that a worker got injured simply because he was not provided with a portable gas monitor.
Incidentally, here is an excellent training resource on confined safety procedures that is in an e-learning format. It means that with just one such course, you can train your workers in confined space safety procedures.

Interesting video on Gas Detector training

2009-09-21T01:01:00.000-07:00

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Industrial Safety

2009-09-19T05:06:00.003-07:00

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In this post we will have a look at some general aspects of safety in industrial plants, not just gas monitors.

How to calibrate and test a Chlorine gas monitor?

2009-09-17T10:12:00.000-07:00

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How does one test and calibrate a Chlorine gas monitor? To know it watch the video below.

For a comprehensive training program on how to select, use and maintain industrial gas monitors and gas detectors, download this excellent training program on gas monitors today!

Gas Detectors for use in Safety Instrumented Systems

2009-09-08T23:57:00.000-07:00

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I often hear/read about the following query from users and designers who have to incorporate gas detectors in their Safety Instrumented Systems, "which gas detector should I use in my SIS?". There are of course gas detectors that are rated for use in meeting SIL requirements, but the main objective of using a gas detector tends to be forgotten while splitting hairs about SIL 1 and SIL 2, PFD, demand, proof testing and other aspects about Safety Instrumented Systems-which is the actual detection of a gas by the gas detector. First the user or system designer must ensure that the selected gas detector can

Measure the target gas correctly
Respond to it in a predictable way
Is physically mounted in the plant in such a way that it WILL detect any and all gas leakages within its area
Is calibrated to the gas sought to be detected

Unless these points are considered, it is pointless to talk about SIL rating and PFD values and other aspects, isn't it?

Types of toxic gas monitors and gas detectors

2009-08-26T00:47:00.000-07:00

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There are various technologies that are used to make toxic gas detectors. Also these instruments are available in various forms, like fixed, portable or pocket types. There are different sensors used to detect different types of toxic gases. Some types of sensors can detect a variety of different gases, others can detect only one type of gas.

Fixed toxic gas detectors

These are very commonly found in large manufacturing plants and similar facilities. Each fixed gas detector is mounted at a place where it is very likely to sense the toxic gas, in case of a leak. The detector may or may not have a local display that shows the concentration of the gas. Each detector is connected via cables to a central system, that is monitored by plant personnel. In case of a leak this panel will generate alarms to warn the operators about the dangers and may also carry out any interlock actions (like triggering closure of valves or initiating a shutdown).

Portable toxic gas detectors

Portable gas monitors are used by workers to sweep a work area, to know if there is any toxic gas lurking around the area. These detectors are also called as handheld gas detectors. These detectors are normally battery powered and have a display with a buzzer and lights, to warn the operator, in case a dangerous level of toxic gas is detected. They may have their own inbuilt sampling pumps, to draw air into the sensor. Some variants also store data, to calculate time weighted average values, peak values and other important data for regulatory compliance.

Pocket toxic gas detectors

A typical personal toxic gas monitor is shown in the picture above. These are similar to the portable types, except that they are very small and meant to be carried by individual workers, by use of a belt clip, or inside a pocket. These instruments are normally throw away types and have a lifetime of about two years (lesser if they are constantly exposed to the toxic gas being detected). They also have a display, buzzer and light, but due to the small size there are no sampling pumps or data logging chips inside.

Typically, a worker carries it with him, when he enters an area that could contain such a gas (for example, he will carry a pocket H2S detector when he enters a process vessel for cleaning, if it had processed H2S previously). The vessel might still have some amount of Hydrogen Sulfide inside (or the gas may enter later through some piping that still remains connected). The worker's pocket gas detector now acts like his guardian angel, or personal bodyguard and warns him immediately, should the gas be detected. This allows him to escape or be rescued by his co-workers.

Where to get more information?

You can download a very useful e-learning course on toxic gas detectors here. This training course on gas monitors covers all types of gas detectors and gas monitors, including toxic gas monitors. It will take about three to four hours to complete and if you take an online test (optional, free of cost), you can also get a certificate of achievement, that would be a useful testimonial.

Typical design of a personal toxic gas monitors

2009-08-25T00:52:00.000-07:00

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How does a typical toxic gas monitor look like?
See picture above to get a fairly good idea.

Can one keep it in a pocket?
Of course, one can. In fact pocket type or clamp on toxic gas meters are meant for just this purpose, a gas meter that can be clamped to your dress and which continuosly monitors the air that you breathe in, 24 X 7. However these smaller sized detectors usually are meant for detection of a single gas, say Hydrogen Sulfide or Chlorine. Thus the pocket gas detector then tends to be referred to as a Hydrogen Sulfide monitor or a Chlorine monitor.

Toxic Gas Monitor fundamentals

2009-08-25T00:38:00.000-07:00

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Industrial plants that manufacture chemicals, fertilizers, petroleum products, or, facilities that produce oil & gas, have to handle various toxic chemicals in their day to day operations. Many of these toxic chemicals are in the form of gases or vapors. This article will give a brief overview of the various kinds of toxic gas detectors used to detect these poisonous materials. The example used will be a detector used to detect Hydrogen Sulfide gas, which is extremely toxic. These detectors are also called simply in industry as H2S detectors.

Why are toxic gas detectors used?

Toxic Gas detectors are mainly used for monitoring the presence harmful gases and vapors. These detectors are also referred to by many people as toxic gas monitors; both terms are interchangeable and mean the same.
These gas monitors enable a worker present in the plants that have these toxic gases, to protect himself from exposure. One of these ( commonly found harmful chemicals) is Hydrogen Sulfide. This gas that smells like rotten eggs, is even in low concentrations, extremely toxic. At lower levels of concentration the human nose can sense this as a "bad smell", however, paradoxically at higher level, there is no sense of any smell, as the human nose gets desensitized. So a worker who accidentally walks into a Hydrogen Sulfide atmosphere can get literally knocked down, without finding anything amiss! Hence, it is critical that good, working, toxic gas detectors be used in such places to protect workers from accidental exposure.

For example, consider a process vessel in a chemical processing plant that normally contains Hydrogen sulfide gas. In normal operations this vessel will be tightly sealed and no Hydrogen Sulfide can escape. However, in case the vessel sealing does not work (for example, a flange on one of the inlet pipes leaks), then, it is likely that this Hydrogen Sulfide gas can leak out and harm the workers who operate the vessel or are in the nearby area.

To prevent this from happening, a toxic gas detector that can measure Hydrogen Sulfide gas, even in small concentrations, is mounted near the vessel. Whenever it detects a dangerous level of Hydrogen Sulfide, it will give out a warning alarm. (Such a gas detector is also known as a Hydrogen Sulfide Detector).

For a detailed explanation of how gas detectors work, why don't you download the Gas Monitors training course today?

Confined Space Gas Monitors- Some basic facts

2009-05-21T04:13:00.000-07:00

For more information about Confined Space Gas Monitors, please download the Gas Monitors training course. It will help you understand all about gas monitors including Confined Space Gas Monitors

What is a confined space gas monitor?
A confined space gas monitor is an instrument that allows people to enter and work safely in confined spaces. These confined spaces are commonly found in the process industries. For example a worker who enters an empty petroleum storage tank, is entering a confined space. These confined spaces may have several hazards and a confined space gas monitor helps in reducing these hazards.

Why use one?
For starters, using a confined space gas monitor is absolutely essential to save lives of people who work in such confined spaces. Also by law it is compulsory to use certain protective equipment while working in confined spaces and one of these equipment is a gas monitor.

What does a confined space gas monitor have?
A confined space gas monitor, is any portable kind of gas monitor that can sense at least two gases- Oxygen and Explosive gas. More the gases detected, obviously the better. Also if the confined space is normally used to store or process toxic gases (like Chlorine) then this gas monitor must also include the toxic gas sensor (in this example it would be a Chlorine sensor).
There is an excellent article on basics of toxic gas detectors that you can read here).
Thus a typical 4 gas detector that has one of the sensors as oxygen, can be used as a confined space gas monitor.
The monitor must in addition be lightweight, shock and fall proof, explosion protected (if used in a hazardous area), be small enough to be carried by a worker in his pocket or on a belt clip and have an easily visible display and a loud enough hooter/buzzer.
Some newer ones may also feature a wireless communication to the control room that transmits the readings continuously as well as alarms the control room operators in case of high/low levels of the gases detected.

Calibration
The monitor must be capable of being calibrated easily with calibration gases on site. Further the plant engineer should ensure that at least bump tests of these instruments are regularly done, if not full cycle calibrations, to ensure that these instruments continue to work as desired.

That's all!
For a detailed training course on confined spaces, have a look at the course below

Total Refinery gas leak incident highlights importance of personal gas monitors

2009-05-15T01:37:00.001-07:00

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In the recent H2S gas leak at the Total refinery in Texas, contract workers were not wearing personal toxic gas monitors. There could easily have been fatalities in the incident, were it not for the alertness of some of the contract workers, who recognized the smell of Hydrogen Sulfide ( a highly toxic gas that smells somewhat like rotten eggs) and evacuated their workplaces, on their own, say news reports (Beaumont).
One of the workers was reportedly up 50 feet in the air working on a scaffolding, when he could smell the gas and clambered down, holding his breath. Apparently he was not provided any personal H2S gas monitors. Modern pocket sized gas monitors help protect workers in case of such gas leaks in the surroundings. These are available for H2S as well as for other commonly found (in industry) toxic gases like Chlorine. Even low levels of the gas trigger audio visual alarms that alert the worker to evacuate to safety. In this respect H2S gas is more dangerous because as the concentration of the gas increases, the human nose becomes desensitized and stops smelling the gas. The person usually thinks that danger has receded, when in fact it has increased. This can be easily detected by the gas monitor.
It is surprising that even large multinational companies that operate in North America (not in some forgotten third world country) can be so less equipped with these not too expensive detectors.
Investigations are still continuing into the incident. Watch this space for more information.

Importance of proper Gas Monitors proved in Bayer Cropscience incident

2009-04-24T10:15:00.000-07:00

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By now, all of those of you in industry must have heard about the Bayer Cropscience incident that took place in August 2008 in Institute, W. Va. There was an explosion in the Methomyl unit and two workers were killed. Several lapses were pointed out by the US Chemical Safety Board that led to the unfortunate incident. One issue however that was not highlighted by the board but emphasized by local investigative reporters, was the non working of several toxic gas detectors in the facility. The management claimed that the detectors were disconnected from the monitoring system due to maintenance, but this itself seems wrong. Generally only one detector is removed at a time for maintenance or calibration. The next one should be removed only when the first is in place.
Secondly there were no such toxic gas detectors placed along the western side of the plant. The wind direction unfortunately on that day was from the plant's western side to its neighbors (communities staying near the plant).
The explosion that took place was very close to a tank containing the extremely toxic chemical Methyl Isocyante (MIC), the same that caused the now infamous Bhopal disaster.
All in all it just shows how seriously companies should take the selection, installation and proper operation and maintenance of gas detectors and gas monitors in their plants. If not then disasters may be looming!

Four gas monitor or PID meter? Which one do you use?

2009-04-16T01:42:00.001-07:00

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Many people in the process industry used to use a standard "four gas" monitor for years, until the advent of PID type gas monitors. So this is just an open ended question to you all... what's your favorite meter? To the newbies, a four gas monitor is basically what it says, a portable gas monitor that can measure upto four different types of gases. These can be any mix of four sensors, or a mix of one LEL sensor (for explosive gases and vapors), an Oxygen sensor (for confined space entry) and two toxic gas sensors (say H2S and Chlorine for example). These type of four gas monitors have been used for several years and are workhorses of the plant operations and maintenance teams. However the advent of PID type meters has meant a threat to the domination of the four gas monitor. Essentially a PID meter stands for a gas monitor that uses a PID (Photoionization detector) to measure a wide range of gases. These cover most compounds found in industry such as most volatile organics and toxic gases like H2S. Many PID meters also come with a built in software and systems to automatically do datalogging and calculations of parameters like TWA, etc for regulatory compliance. Calibration is easier too, with just one gas IsoButylene being used.
So tell us what's your favorite meter- PID or four-gas?

A break from the Gas Monitors stuff-this post will be a website review

2009-03-29T23:28:00.000-07:00

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This post is something different from the posts on gas monitors and related issues that I regularly write on, it is a review on something called RSS hugger. If you are a blogger, you probably know what RSS means.
To recap RSS stands for Really Simple Syndication or Rich Site Summary, depending on whom you ask. RSS enables readers to keep in touch with numerous blogs by simply adding the feeds from the different blogs that they wish to monitor into a small piece of software that is known as an RSS reader (available for free). Once you setup an RSS reader, you simply add the feeds and hey presto, you can get all the different blogs posts into your reader automatically.

rssHugger is a unique website that aims to bring bloggers and readers together. rssHugger aims to provide blog owners with a unique easy-to-use way to promote their blogs by sending them traffic, building backlinks for search engine optimization, as well as attracting new rss subscribers if the content is interesting to the reader. rssHugger aims to help visitors be able to easily find blogs that write about subjects they are interested in. If the visitors find a blog that they had not previously heard about, they can easily add it to their RSS readers or bookmark it.

The site is promoted by Colin Lahay, who is a well known blogger in the world of new age (read- internet marketing and entrepreneurship), who always has some zany ideas on marketing.
I just added this blog to rss hugger and found the process to be fast and painless. If you have a blog, I suggest you do the same.

How to verify if a gas monitor is really working?

2009-03-26T01:11:00.000-07:00

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As you all know the reliability and accuracy of an instrument can only be verified after it is calibrated against a known standard. This is also the case with toxic gas monitors as well as other types of gas detectors.

In case of gas monitors, there are two ways to check the functioning, one is a full fledged calibration where the sensor is exposed to different concentrations of a known air-gas mixture (to calibrate it at various points from minimum to maximum) and the other is to subject it to a "bump" test. A bump test exposes the sensor to just one known concentration of the gas, to verify if it responds.

Now which amongst these two methods should you use?

There are two issues here. First, are you interested in the accuracy of measurement, or merely the functional testing? Accuracy of measurement is important in many applications, where, for example, an oxygen meter is used for confined space entry. A reading that shows 20% when the actual value is say 17% can be disastrous. Here, we require that the instrument always function at it's best accuracy and has to be thoroughly calibrated always. Also a "bump" test is simple, just check the reading in the outside air-it should Oxygen of about 21% (more or less depending on the area and the pollution levels).

However in other cases, the instrument may be used more for detecting the presence of a toxic gas rather than its exact concentration. Suppose a Chlorine gas monitor is installed on the outlet of a vent line, that carries away vent gas away from a confined Chlorine storage area-here the presence of Chlorine must be detected, rather than the exact ppm level. It does not matter whether it shows 2 ppm when the level was 1 ppm. It has to detect the presence (according to its minimum resolution). Here, instead of subjecting the Chlorine gas monitor to a full calibration, it may be simpler to bump test it once a while. As long as it responds to a bump test of the lowest concentration of Chlorine, it's fine, you need not carry out a full fledged 3 or 4 point calibration.

What are the advantages of bump testing?
1. It is simpler than a full fledged calibration
2. Less lecetrolyte is consumed in case of electrochemical sensors-this increases the life of the sensor substantially
3. Cheaper and easier-just one gas bottle per type of gas is needed.

Any other advantages? Please use the comments section below to post.

Gas Monitors-Placement is key to ensuring safety of your Industrial plant

2009-03-24T00:20:00.001-07:00

Area monitoring

Many of the fixed type toxic and combustible gas detectors in usage in industry today, are used for area monitoring. What do we mean by area monitoring? We do a strategic placement of these gas detectors in locations that will have the explosive vapor or gas present, in case of a leak. Obviously, we cannot place these gas detectors at all possible places, as this will be very costly, not only in terms of the cost of acquiring these gas detectors and their associated panels, wiring, controls, etc, but also because each gas detector has a maintenance cost associated with it.

Each gas monitor requires periodic calibration with a test gas, replacement of sensor and/or electronics and other maintenance from time to time. We cannot avoid this cost as otherwise the gas monitor will fail to function properly. Just having a gas monitor physically present in an area, may at the most satisfy a factory inspector, or insurance surveyor, it cannot actually detect anything, if not maintained well. Hence, we designate certain areas of our plant or facility as being the most vulnerable to a gas leak. We then pin point the place where the gas is most likely to be present immediately after a leak. We then ensure that vat least we have a gas detector at that point to monitor such a leak.

Placement is the key to safety at a reasonable cost

In the UK, there is a concept known as ALARP (As low as reasonably possible). This indicates that we can spend only so much on safety as to yield a benefit that is more than the cost of the spending. Thus, it is not possible to have swarms of gas detectors all over a plant, as it would cost a fortune to install and maintain them. Maybe the number of such gas detectors would be many more than the number of conventional instruments like pressure or flow transmitters in the plant! Thus strategic placement of gas monitors is the key to achieving safety under an ALARP principle. How does one therefore go about the placement?

Different strokes for different folks

As the saying goes, we employ different types of placement strategies for different types of gas detectors. Therefore, for those gases and vapors that are heavier than air, we select places that are closer to the floor or grade, for lighter gases like Hydrogen, we select higher levels where the gas is most likely to go after a leak. For a gas like Carbon Monoxide which is only slightly heavier than air, one should mount the sensor at approximately 1.6 meters above the ground level for best results.

The next step is to pinpoint potential leakage sources. These could be the outlet of a Pressure Safety relief valve, or flange joints at the inlet or outlet of a large reactor or other process vessel. All such points should be marked on a layout drawing of the plant, before we visit the site. Note that in this case, we are not targeting fugitive emissions, but only places where there can be a large amount of sudden release of a toxic or explosive gas. Other places include the inlet/outlets of blowers, gas turbines, ventilation equipment, etc.

After this study is complete, we can visit the site and actually see if our marked locations are logically correct. If it is an old site, talk to the operators or other plant personnel who can have an idea about the likely points of gas leakage. Once these are ready, we can mark these on drawings.

Next Steps

Next, select the gas detectors based on the amount of coverage for each point/area. If the area is small, a point type gas monitor will do. If the gas is expected to diffuse into the gas detector, nothing else is necessary. If however, it is felt that the gas may not easily diffuse into the detector, we may need additional forced sampling (like small vaccum pumps and collection funnels) to route the samples from the surrounding area into the gas detector. If the area is larger however, we will need an area monitor like an Infrared open path gas detector. These types of detectors cover a large open path (which is the gap between the infrared source and detector) that can cover hundreds of meters of an area. Ultimately the placement will depend on the likelihood of the gas, the type of gas monitors used and the total budget that can be allocated to the project.

Optimization

After the gas detectors have been ordered, installed and placed in the designated spots, the next stage is do a continuous performance monitoring. Are the detectors really detecting gases? Have leaks taken place that were not detected? If so, why? Were these not detected due to wrong placement or the gas detectors themselves were not functioning? Answers to these will enable you to optimize the placement further and ensure that your gas monitors do the thing that they are best at-protecting the plant, people and the environment from undesirable events.

Sam. P. Whittle is a technical expert on gas detectors and gas monitors. He is an engineer with several years of experience in various industries. At present he is on the panel of subject matter experts of Abhisam Software

Article Source: http://EzineArticles.com/?expert=Sam_P._Whittle

Safety Alert for Sperian Portable Gas Monitor issued

2009-03-22T09:00:00.000-07:00

The Safety Management Group has published a safety alert from Sperian Instruments regarding the possible malfunctioning of BioSystems PhD5 portable gas detector. The notice states that

"There is a possibility that PhD5 instruments that have the Security Beep function enabled can stop actively detecting gas while continuing to show safe readings"

The notice further states that only a "handful" of detectors may be affected but it advises users to disable the security beep in the instrument as an immediate solution to the problem. It was not clear how disabling the security beep solved the problem, perhaps it is a bug in the instruments firmware. If the security beep is enabled, apparently some instruments stop actually measuring the gas, while showing safe readings! This is a dangerous failure and users should contact Sperian Instruments to update the firmware.

More details can be found on the Safety Management Group Website.

Toxic gas monitors should be installed in all public closed spaces-not just in industrial plants!

2009-03-21T22:06:00.000-07:00

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One imagines that toxic gas monitors are necessary to be installed only in industrial plants, not in churches. Right? Well, you’re dead wrong!

AP reports that firemen and other authorities in Madison, Wisconsin said that six people — including a toddler — got sick from carbon monoxide poisoning during a Sunday church service in Madison. Paramedics were called to attend to a 2-year-old child who was reported to be groggy . The parents of the child decided to transport the child to the hospital on their own.

Fortunately, by the time a second distress call was reported to the local Fire Department, Engine Company 4 responded, bringing along monitors to check air quality at the church. The portable Carbon Monoxide toxic gas monitors showed a CO level of 3000 ppm- more than 100 times the safe limit!

The incident shows the importance of having portable toxic gas monitors handy in all places and not just industrial plants.

How do pocket H2S monitors work?

2009-03-18T02:04:00.000-07:00

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This post will give you a brief idea about how a pocket h2s monitor works. A pocket h2s monitor is a small instrument that is meant to be used by a worker who is working in an area that may get poisoned with Hydrogen Sulfide gas (referred to as h2s). The H2S monitor is a small portable toxic gas monitor that has a clamp at the back, so that it can be easily clamped to the worker's belt or clothes. Alternatively it can be carried in a pocket. Intrinsically Safe versions are also available which means that they can be use din hazardous areas.

The pocket h2s monitor consists of a sensor (mostly electrochemical), associated electronics (including an LCD display, buzzer, light/LED) and a housing with the clamp. It has to be calibrated with a known concentration of h2s gas in air using a standard calibration gas bottle. Every time a worker enters a confined space area that may later on allow some traces of h2s inside, the worker has to carry this monitor, so that whenever h2s ingress happens, the h2s monitor will go off, sounding a loud buzzer and flashing a red LED as a warning to escape at the earliest.
Some versions can even transmit this alarm wirelessly to a remote control room or to a host unit that may be mounted in the area. This enables the workman's colleagues to rescue him, should he be unable to escape on his own.
A typical unit looks like this (shown above).

Welcome to the Gas Monitors blog!

2009-03-16T22:46:00.000-07:00

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Industrial Plants, especially those that manufacture chemicals, process oil & gas or in other ways store or process flammable and/or combustible materials need various kinds of gas detectors to ensure operational safety. This blog post will give a brief overview of the various kinds of gas detectors used and the technologies behind them.

Usage of gas detectors

Gas detectors are mainly used for monitoring the presence (or in some cases, the absence) of gases and vapors. If we classify gas detectors on the basis of the gas being detected, we can classify them into three types as under.

1) Toxic Gas detectors

2) Explosive Gas Detectors

3) Oxygen detectors

Note that we can use the first two types of gas detectors to detect regular gases as well as vapors that are generated by volatile liquids. The third type is generally used to check if a restricted area (also known as a confined space-like the inside of a large storage tank) contains enough Oxygen to sustain a workman who may be present in that area. In applications where Nitrogen blanketing is used to make the vapor space above an inflammable liquid inert, an Oxygen detector can tell us if the vapor space is really inert or not. Thus in these cases, we are more interested in knowing about the absence of Oxygen, rather than its presence.

Technologies

There are a few major technologies that are in usage today for detecting gases. They are listed below.

1. Catalytic Combustion type

These detectors utilize actual combustion of the gas that is to be detected, on a hot “bead” that is part of a Wheatstone bridge network of resistors. The presence of the gas causes combustion that alters the resistance and thus can be converted into an electrical signal. This is the most common type of gas detector in usage today. The same technology is used in propane detectors.

2. Electrochemical Type

In this type of gas monitor, the sensor is an electrochemical cell with an electrolyte (which may be in the form of a gel) and two electrodes. The gas that enters this cell undergoes electrolysis and a voltage difference appears across the electrodes, thus generating an electrical signal that can indicate the amount of gas. This technology is used in toxic gas detector, h2s detector and hydrogen gas detector.

3. Infrared Type

These can be point type or continuous (also known as open path). It is well known that each chemical compound absorbs infrared light of a unique band of frequencies. Also the amount is that is absorbed is in proportion to the concentration. This principle is used in infrared type gas detection.

4. Semiconductor type

In this type of gas detector, the sensor is a doped version of Silicon or Germanium, that gets its conductivity altered by the presence of a gas. This principle is used to generate a usable electrical signal.

This is a short overview of the various kinds of gas detectors used in industries and homes today.