What is Purge Testing and when should I be doing it?

Purge testing is vital when installing, replacing or maintaining a natural gas pipeline or storage tank, or filling new pipework with flammable gas. This process uses an inert gas to clear the enclosed environment of flammable gases prior to air being introduced thereby preventing air and flammable gas mixing. Such mixtures could of course lead to explosive combustion.

What is Purge Testing? 

Purge testing is a key part of the process of making a working environment safe prior to entering it to carry out work. Analysis of the atmosphere in the pipe or enclosure shows the starting point – usually 100% flammable gas. Purge testing is the measurement and reporting of the atmosphere as an inert gas is introduced. As the flammable gas declines to a safe level well below concentrations that would be dangerous in air, the atmosphere is continually analysed, and the flammable gas concentration reported. Once a low concentration has been achieved, air may be introduced. During this phase the flammable gas concentration is analysed to check it remains low, and oxygen concentration is measured to indicate when the atmosphere becomes breathable. Work may then commence – all the while protected by the measurement of flammable gas and oxygen concentration. If, as is likely, the purge testing is being carried out via suction of atmosphere through a sample tube, then this sample tube must at all times and all along its length be held above the flash point of the flammable gas in the tank. This is vital to both your safety and the safety of those working with you.  

Purging removes or displaces hazardous gases from the tank or pipework to prevent them from mixing with the air you need to introduce into the tank to carry out the inspection or maintenance task. The most used and preferred purge gas is Nitrogen, due to its inert properties. After conducting the inspection or maintenance task the reverse process is carried out, reintroducing the inert gas and reducing the oxygen level to near zero prior to allowing natural gas to re-enter. Often a service valve on the line with a standpipe or diffuser attached is cracked to release the venting gas or nitrogen. Purging systems are generally designed to redirect additional gases away from the work area preventing them from remixing with the gas within the tank or pipework. 

Why Conventional Gas Detection isn’t enough 

Traditional gas detection systems are not designed to work in oxygen-deprived environments. This is because they are primarily designed as safety equipment with the specific purpose to detect small traces of target gases in otherwise normal breathable environments. Gas detection equipment designed for use in purge testing activities must be able to function in low oxygen environments and with all contaminants likely to be found in tanks and pipes being purge tested. If sensors can be poisoned by the contaminants present or if there isn’t enough oxygen in the air to enable the selected sensor technology to be used, it may lead to the sensors on the device producing inaccurate results, posing a threat to those working within that environment. An additional point to note to note is that certain gas combinations, concentrations and corrosive liquids may damage the gas detection equipment, rendering it useless. For these reasons, Infrared technology or thermal conductivity is usually chosen as the measurement technology of choice for purge tests. Crowcon uses infrared technology in these applications. A fortunate by-product of that design decision is better accuracy than required over the full sensing range. 

More about Purge testing 

Purge Testing is essential for workers as some may be breathing in toxic gases without even realising it if the sensors on their detection equipment have become defective, don’t measure the required gas type or don’t measure over the required gas range, or environmental range present. Toxic or asphyxiant gas exposure can lead to respiratory issues, significant injury, even death. 

Workers cannot merely rely on a standard confined space gas detection instrument to adequately test for safe conditions during this process, as the high gas level may overwhelm or damage an LEL (Lower Explosive Limit) sensor depending upon type. Or the sensor may not function in an oxygen-depleted atmosphere leading to an unreported dangerous condition. 

What products do we offer? 

Our Gas-Pro TK is a specialised tank monitor that is perfect for customers who want to purge, free, or maintain storage and transportation tanks due to its integrated auto switching dual range IR sensor technology. Other sensors in the product, for example the H2S (Hydrogen Sulphide) sensor option cover other potential risks if gases vent during purging. 

How Long will my Gas Sensor Last?

Gas detectors are used extensively within many industries (such as water treatment, refinery, petrochemical, steel and construction to name a few) to protect personnel and equipment from dangerous gases and their effects. Users of portable and fixed devices will be familiar with the potentially significant costs of keeping their instruments operating safely over their operational life. Gas sensors are understood to provide a measurement of the concentration of some analyte of interest, such as CO (carbon monoxide), CO2 (carbon dioxide), or NOx (nitrogen oxide). There are two most used gas sensors within industrial applications: electrochemical for toxic gases and oxygen measurement, and pellistors (or catalytic beads) for flammable gases. In recent years, the introduction of both Oxygen and MPS (Molecular Property Spectrometer) sensors have allowed for improved safety.  

How do I know when my sensor has failed? 

There have been several patents and techniques applied to gas detectors over the past few decades which claim to be able to determine when an electrochemical sensor has failed. Most of these however, only infer that the sensor is operating through some form of electrode stimulation and might provide a false sense of security. The only sure method of demonstrating that a sensor is working is to apply test gas and measure the response: a bump test or full calibration. 

Electrochemical Sensor  

Electrochemical sensors are the most used in diffusion mode in which gas in the ambient environment enters through a hole in the face of the cell. Some instruments use a pump to supply air or gas samples to the sensor. A PTFE membrane is fitted over the hole to prevent water or oils from entering the cell. Sensor ranges and sensitivities can be varied in design by using different size holes. Larger holes provide higher sensitivity and resolution, whereas smaller holes reduce sensitivity and resolution but increase the range. 

Factors affecting Electrochemical Sensor Life 

There are three main factors that affect the sensor life including temperature, exposure to extremely high gas concentrations and humidity. Other factors include sensor electrodes and extreme vibration and mechanical shocks.  

Temperature extremes can affect sensor life. The manufacturer will state an operating temperature range for the instrument: typically -30˚C to +50˚C. High quality sensors will, however, be able to withstand temporary excursions beyond these limits. Short (1-2 hours) exposure to 60-65˚C for H2S or CO sensors (for example) is acceptable, but repeated incidents will result in evaporation of the electrolyte and shifts in the baseline (zero) reading and slower response. 

Exposure to extremely high gas concentrations can also compromise sensor performance. Electrochemical sensors are typically tested by exposure to as much as ten-times their design limit. Sensors constructed using high quality catalyst material should be able to withstand such exposures without changes to chemistry or long-term performance loss. Sensors with lower catalyst loading may suffer damage.  

The most considerable influence on sensor life is humidity. The ideal environmental condition for electrochemical sensors is 20˚Celsius and 60% RH (relative humidity). When the ambient humidity increases beyond 60%RH water will be absorbed into the electrolyte causing dilution. In extreme cases the liquid content can increase by 2-3 times, potentially resulting in leakage from the sensor body, and then through the pins. Below 60%RH water in the electrolyte will begin to de-hydrate. The response time may be significantly extended as the electrolyte or dehydrated. Sensor electrodes can in unusual conditions be poisoned by interfering gases that adsorb onto the catalyst or react with it creating by-products which inhibit the catalyst.  

Extreme vibration and mechanical shocks can also harm sensors by fracturing the welds that bond the platinum electrodes, connecting strips (or wires in some sensors) and pins together.  

‘Normal’ Life Expectancy of Electrochemical Sensor 

Electrochemical sensors for common gases such as carbon monoxide or hydrogen sulphide have an operational life typically stated at 2-3 years. More exotic gas sensor such as hydrogen fluoride may have a life of only 12-18 months. In 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 more than 4000 days (11 years). Periodic exposure to the target gas does not limit the life of these tiny fuel cells: high quality sensors have a large amount of catalyst material and robust conductors which do not become depleted by the reaction. 

Pellistor Sensor 

Pellistor sensors consist of two matched wire coils, each embedded in a ceramic bead. Current is passed through the coils, heating the beads to approximately 500˚C. Flammable gas burns on the bead and the additional heat generated produces an increase in coil resistance which is measured by the instrument to indicate gas concentration. 

Factors affecting Pellistor Sensor Life 

The two main factors that affect the sensor life include exposure to high gas concentration and poising or inhibition of the sensor. Extreme mechanical shock or vibration can also affect the sensor life. The capacity of the catalyst surface to oxidise the gas reduces when it has been poisoned or inhibited. Sensor life more than ten years is common in applications where inhibiting or poisoning compounds are not present. Higher power pellistors have greater catalytic activity and are less vulnerable to poisoning. More porous beads also have greater catalytic activity as their surface volume in increased. Skilled initial design and sophisticated manufacturing processes ensure maximum bead porosity. Exposure to high gas concentrations (>100%LEL) may also compromise sensor performance and create an offset in the zero/base-line signal. Incomplete combustion results in carbon deposits on the bead: the carbon ‘grows’ in the pores and creates mechanical damage. The carbon may however be burned off over time to re-reveal catalytic sites. Extreme mechanical shock or vibration can in rare cases also cause a break in the pellistor coils. This issue is more prevalent on portable rather than fixed-point gas detectors as they are more likely to be dropped, and the pellistors used are lower power (to maximise battery life) and thus use more delicate thinner wire coils. 

How do I know when my sensor has failed? 

A pellistor that has been poisoned remains electrically operational but may fail to respond to gas. Hence the gas detector and control system may appear to be in a healthy state, but a flammable gas leak may not be detected. 

Oxygen Sensor 

Long Life 02 Icon

Our new lead-free, long-lasting oxygen sensor does not have compressed strands of lead the electrolyte has to penetrate, allowing a thick electrolyte to be used which means no leaks, no leak induced corrosion, and improved safety. The additional robustness of this sensor allows us to confidently offer a 5-year warranty for added piece of mind. 

Long life-oxygen sensors have an extensive lifespan of 5-years, with less downtime, lower cost of ownership, and reduced environmental impact. They accurately measure oxygen over a broad range of concentrations from 0 to 30% volume and are the next generation of O2 gas detection. 

MPS Sensor  

MPS sensor provides advanced technology that removes the need to calibrate and provides a ‘True LEL (lower explosive limit)’ for reading for fifteen flammable gases but can detect all flammable gases in a multi-species environment, resulting in lower ongoing maintenance costs and reduced interaction with the unit. This reduces risk to personnel and avoids costly downtime. The MPS sensor is also immune to sensor poisoning.  

Sensor failure due to poisoning can be a frustrating and costly experience. The technology in the MPS™ sensor is not affected by contaminates in the environment. Processes that have contaminates now have access to a solution that operates reliably with fail safe design to alert operator to offer a peace of mind for personnel and assets located in hazardous environment. It is now possible to detect multiple flammable gases, even in harsh environments, using just one sensor that does not require calibration and has an expected lifespan of at least 5 years. 

What is a Flame Detector and How Does it Work?

What is a Flame Detector? 

A flame detector is a type of sensor that can detect and respond to the presence of a flame. These detectors have the ability to identify smokeless liquid and smoke that can create open fire. For example, in boiler furnaces flame detectors are widely used, as a flame detector can detect heat, smoke, and fire. These devices can also detect fire according to the air temperature and air movement. The flame detectors use Ultraviolet (UV) or Infra-Red (IR) technology to identify flames meaning they can alert to flames in less than a second. The flame detector would respond to the detection of a flame according to its installation, it could for example sound an alarm, deactivate the fuel line, or even activate a fire suppression system. 

Where would you find these Detectors? 

  • Industrial warehouses
  • Chemical production plants 
  • Chemical stores 
  • Petrol storage and pump stations 
  • Arc welding workshops 
  • Power plants 
  • Transformer stations 
  • Underground tunnels 
  • Motor testbeds 
  • Wood stores 

What are the Components of a Flame Monitoring System and does it work?

The major component of a flame detector system is the detector itself. It comprises of photoelectric detective circuits, signal conditioning circuits, microprocessor systems, I/O circuits, and wind cooling systems. The sensors in the flame detector will detect the radiation that is sent by the flame, the photoelectric converts the radiant intensity signal of the flame to a relevant voltage signal and this signal would be processed in a single chip microcomputer and converted into a desired output. 

How many types of Flame Detectors are there and how do they work? 

There are 3 different types of flame detector: Ultra-Violet, Infra-Red and a combination of them both Ultra-Violet-Infra-Red 

Ultra-Violet (UV) 

This type of flame detector works by detecting the UV radiation at the point of ignition. Almost entirely all fires emit UV radiations, so in case of the flame, the sensor would become aware of it and produce a series of the pulses that are converted by detector electronics into an alarm output.  

There are advantages and disadvantages of a UV detector. Advantages of UV detector include High-speed response, the ability to respond to hydrocarbon, hydrogen, and metal fires. On the other hand, the disadvantages of UV detectors include responding to welding at long range, and they may also respond to lightning, sparks, etc. 

Infra-Red (IR) 

The infra-red flame detector works by checking the infrared spectral band for certain ornamentation that hot gases release. However, this type of device requires a flickering motion of the flame. The IR radiation may not only be emitted by flames, but may also be radiated from ovens, lamps, etc. Therefore, there is a higher risk for a false alarm 

UV-IR 

This type of detector is capable to detect both the UV and IR radiations, so it possesses both the UV and IR sensor. The two sensors individually operate the same as those described, but supplementary both circuitry processes signals are present due to there being both sensors. Consequently, the combined detector has better false alarm rejection capability than the individual UV or IR detector. 

Although there are advantages and disadvantages of UV/IR flame detector. Advantages include High-speed response and are immune to the false alarm. On the other hand, the disadvantages of UV/IR flame detector include the issue that it cannot be used for non-carbon fires as well as only being able to detect fires that emits both the UV/IR radiation not individually.  

Are any products available? 

The FGard IR3 delivers superior performance in the detection of hydrocarbon fires. The device utilises the latest IR flame detection algorithms to ensure maximum false alarm immunity. The detector has been independently tested to demonstrate it can detect a hydrocarbon fuel pan fire at nearly 200 feet in less than 5 seconds. The FGuard IR3 has a multi spectrum IR allowing for 60 metre flame detection range. That can detect all Hydrocarbon fires with no condensation forming on the window, improving reliability and performance across temperature. This product has fast detection time responding in less than 5 seconds to 0.1m² fire at 60 metres.  

Crowcon offers a range of infra-red (IR) and ultra-violet (UV) based flame detectors for quickly detecting flames at a distance. Depending on model, this includes a variety of gas and fuel fires including those generated from hydrocarbons, hydrogen, metals, inorganic and hydroxyl sources.

What’s so Important about my Monitors Measuring Range?

What is a Monitor Measuring Range?

Gas monitoring is usually measured in PPM range (parts per million), percentage volume or percentage of LEL (lower explosive limit) this enables Safety Managers, to ensure that their operators are not being exposed to any potentially harmful levels of gases or chemicals. Gas monitoring can be done remotely to ensure that the area is clean before a worker enters the area as well as monitoring gas through a permanently fixed device or body worn portable device to detect any potentially leaks or hazardous areas during the course of the working shift.  

Why are Gas Monitors essential and what are the Ranges of deficiencies or enrichments?

There are three main reasons why monitors are needed; it is essential to detect oxygen deficiencies or enrichment as too little oxygen can prevent the human body from functioning leading to the worker losing consciousness. Unless the oxygen level can be restored to a normal level the worker is at risk of potential death. An atmosphere is considered to be deficient when the concentration of O2 is less than 19.5%. Consequently, an environment that has too much oxygen in it is equally dangerous as this constitutes a greatly increased risk of fire and explosion, this is considered when the concentration level of O2 is over 23.5%. 

Monitors are required when Toxic Gases are present of which can cause considerable harm to the human body. Hydrogen Sulphide (H2S) is a classic example of this. H2S is given off by bacteria when it breaks down organic matter, due to this gas being heavier than air, it can displace air leading to potential harm to persons present and is also a broad-spectrum toxic poison.  

Additionally, gas monitors have the ability to detect flammable gases. Dangers that can be prevented through using a gas monitor are not only though inhaling but they are a potential hazard due to combustion. gas monitors with an LEL range sensor detects and alert against flammable gases.  

Why are they important and how do they work?

Measurement or Measuring Range is the total range that the device can measure in normal conditions. The term normal meaning no overpressure limits (OPL) and within maximum working pressure (MWP).  These values are usually found on the product website or specification datasheet. The measuring range can also be calculated by identifying the difference between the Upper Range Limit (URL) and the Lower Range Limit (LRL) of the device. When trying to determine the range of the detector it is not identifying the area of square footage or within a fixed radius of the detector but instead is identifying the yielding or diffusion of the area being monitored. The process happens as the sensors respond to the gases that penetrate through the monitor’s membranes. Therefore, the devices have the ability to detect gas that is in immediate contact with the monitor. This  highlights the significance of understanding the measuring range of gas detectors and highlight their importance for the safety of the workers present in these environments.   

Are there any products that are available?

Crowcon offer a range of portable monitors; The Gas-Pro portable multi gas detector offers detection of up to 5 gases in a compact and rugged solution. It has an easy-to-read top mount display making it easy to use and optimal for confined space gas detection. An optional internal pump, activated with the flow plate, takes the pain out of pre-entry testing and allows Gas-Pro to be worn either in pumped or diffusion modes. 

The T4 portable 4-in-1 gas detector provides effective protection against 4 common gas hazards: carbon monoxide, hydrogen sulphide, flammable gases and oxygen depletion. The T4 multi gas detector now comes with improved detection of pentane, hexane and other long chain hydrocarbons. Offering you compliance, robustness and low cost of ownership in a simple to use solution. T4 contains a wide range of powerful features to make everyday use easier and safer. 

The Gasman portable single gas detector is compact and lightweight yet is fully ruggedised for the toughest of industrial environments. Featuring simple single button operation, it has a large easy-to-read display of gas concentration, and audible, visual and vibrating alarms.  

Crowcon also offer a flexible range of fixed gas detection products that can detect flammable, toxic and oxygen gases, report their presence and activate alarms or associated equipment. We use a variety of measurement, protection and communications technologies and our fixed detectors have been proven in many arduous environments, including oil and gas exploration, water treatment, chemical plants and steel mills. These fixed gas detectors are used in many applications where reliability, dependability and lack of false alarms are instrumental to efficient and effective gas detection. These include within the automotive and aerospace manufacturing sectors, on scientific and research facilities and in high-utilisation medical, civil or commercial plants. 

Detecting VOCs with PID – how it works

Having recently shared our video on pellistors and how they work, we thought it would make sense to also post our video about PID (photo-ionisation detection). This is the technology of choice for monitoring exposure to toxic levels of another group of important gases – volatile organic compounds (VOCs).

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Pellistor sensors – how they work

Pellistor gas sensors (or catalytic bead gas sensors) have been the primary technology for detecting flammable gases since the ‘60s. Despite having discussed a number of issues relating to the detection of flammable gases and VOC, we have not yet looked at how pellistors work. To make up for this, we are including a video explanation, which we hope you will download and use as part of any training you are conducting

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Onshore oil not new, but is it the future?

The onshore oil industry is often overlooked and the latest news that there could be up to 100 billion barrels of oil beneath the South of England has surprised many. However, on-shore production is more prevalent worldwide than people realise.

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Are Silicone Implants Degrading your Gas Detection?

In gas detection terms, pellistors have been the primary technology for detecting flammable gases since the 60s.  In most circumstances, with correct maintenance, pellistors are a reliable, cost-effective means of monitoring for combustible levels of flammable gases.  However, there circumstances under which this technology may not be the best choice, and infrared (IR) technology should be considered instead.

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The Characteristics of Flammable Gas Detection

We often get questions on flammable gases and whether we can detect them, therefore this week’s blog looks at some of the characteristics that are important to understand and know before you can consider if it can be detected.

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