Gas-Pro TK: Dual readings of LEL and Vol

Gas-Pro TK (re-branded from Tank-Pro) dual range portable monitor measures the concentration of flammable gas in inerted tanks. Available for methane, butane and propane, Gas-Pro TK uses a dual IR flammable gas sensor – the best technology for this specialist environment. Gas-Pro TK dual IR features auto-range switching between %vol. and %LEL measurement, to ensure operation at the correct measurement range. This technology isn’t damaged by high hydrocarbon concentrations and does not need oxygen concentrations to work, as are the limiting factors of catalytic bead/ pellistors in such environments. 

What problem is Gas-Pro TK specifically designed to overcome? 

When you wish to enter a fuel storage tank for inspection or maintenance, you may start with it full of flammable gas. You can’t just start pumping air in to displace the flammable gas because at some point in the transition from only fuel present to only air present, there would be an explosive mixture of fuel and air. Instead, you must pump in an inert gas, usually nitrogen to displace the fuel without introducing oxygen. The transition from 100% flammable gas and 0% volume nitrogen, to 0% volume flammable gas and 100% nitrogen enables a safe transition from 100% nitrogen to air. Using this two-step process enables a safe transition from fuel to air without risking an explosion. 

During this process there is no air or oxygen present, so catalytic bead / pellistor sensors will not work properly and will also be poisoned by the high levels of flammable gas. The dual range IR sensor used by Gas-Pro TK does not require any air or oxygen to function, so it is ideal to monitor the whole of the process, from %volume to %LEL concentrations, while also monitoring oxygen levels in the same environment. 

What is LEL? 

The Lower Explosive Limit (LEL) is the lowest concentration of a gas or vapour that will burn in air. Readings are a percentage of that, with 100%LEL the minimum amount of gas needed to combust. LEL varies from gas to gas, but for most flammable gases it is less than 5% by volume. This means that it takes a relatively low concentration of gas or vapour to produce a high risk of explosion.
Three things must be present for an explosion to occur: combustible gas (the fuel), air and a source of ignition (as shown in the diagram). In addition, the fuel must be present at the right concentration, between the Lower Explosive Limit (LEL), below which the gas/air mixture is too lean to burn, and the Upper Explosive Limit (UEL), above which the mixture is too rich and there is not enough of a supply of oxygen to sustain a flame. 

Safety procedures are generally concerned with detecting flammable gas well before it reaches an explosive concentration, so gas detection systems and portable monitors are designed to initiate alarms before gases or vapours reach the Lower Explosive Limit. Specific thresholds vary according to the application, but the first alarm is typically set at 20% LEL and a further alarm is commonly set to 40% LEL. LEL levels are defined in the following standards: ISO10156 (also referenced in EN50054, which has since been superseded) and IEC60079. 

What is %Volume? 

The percent by volume scale is used to give the concentration of one gas type in a mixture of gases as a percentage of the volume of gas present. It is just a different scale with, for example the methane lower explosive limit concentration is displayed at 4.4% volume instead of 100% LEL or 44000ppm, which are all equivalent. If there was 5% or more methane present in air, we would have a highly dangerous situation where any spark or hot surface could cause an explosion where air (specifically oxygen) is present. If there is 100%volume reading, it means that there is no other gas present in the gas mix. 

Gas-Pro TK 

Our Gas-Pro TK has been designed for use in specialist inerted tank environments to monitor levels of flammable gases and oxygen, as standard gas detectors will not work. In ‘Tank Check Mode’ Our Gas-Pro TK device is suitable for specialist application of monitoring inerted tank spaces during purging or gas freeing, as well as doubles as a regular personal gas safety monitor in normal operation. It enables users to monitor the gas mix in tanks carrying flammable gas during transport at sea (as it is marine approved) or on shore, such as oil tankers and oil storage terminals. At 340g, Gas-Pro TK is up to six times lighter than other monitors for this application; a boon if you have to carry it with you all day. 

In Tank Check mode, the Crowcon Gas-Pro TK, monitors concentrations of flammable gas and oxygen, checking that an unsafe mixture is not developing. The device auto-ranges, switching between %vol and %LEL as gas concentration demands, without manual intervention, and notifies the user as it happens. Gas-Pro TK has real-time oxygen concentrations from within the tank on its display, so users can track the oxygen levels, either for when the oxygen levels are low enough to safely load and store fuel, or high enough for safe tank entry during maintenance. 

The Gas-Pro TK is available calibrated to methane, propane or butane.  With IP65 and IP67 ingress protection, Gas-Pro TK meets the demands of most industrial environments. With optional MED certifications, it is a valuable tool for tank monitoring on-board vessels. The optional High H₂S Sensor addition allows users to analyse possible risk if gases vent during purging. With this option, users can monitor over the 0-100 or 0-1000ppm range. 

Please note: if the fuel in the tank is hydrogen or ammonia, a different gas detection technique is required – and you should contact Crowcon. 

For more information on our Gas-Pro TK visit our product page or get in contact with our team.