strength at the receiver indicates a gas cloud in the range. If this signal drops below a certain level, the device will warn that its beam is becoming blocked. Equally if the signal sent from the transmitter falls below a certain level, the device will interpret this as possible dirty optics and warn of the fact that work will need to be carried out in due course, thus minimising unforeseen failures.


Conversely, a catalytic bead device has undetected failure modes. For example, if someone has accidentally painted over a catalytic bead device and blocked its sinter, or a poison such as silicone kills the sensor, the detector will not indicate a fault and will appear to be capable of detecting gas; it will just show a zero reading as if no gas is present. Not only does this compromise potential safety, it means that more frequent checks need to be made.


In a petrochemical plant where known catalytic bead poisons are present, this bump testing might need to be as frequent as every three months, equating to an increased maintenance labour requirement of 400% when compared to an Open Path IR device’s ongoing requirements; and this does not account for additional savings that can be made from a reduction in points needed (one Open Path device can typically


replace fi ve points of detection), and the subsequent reduction in cabling. These additional dimensions make the migration from point to Open Path one that can potentially deliver huge savings.


It is important to clarify that many factors impact upon whether a fail-to-safety device is more applicable than a solution with undetected failures. For example, many petrochemical applications choose to fi t catalytic bead devices because they are less likely to be affected by the potential failure modes. When considering the impact of maintenance, an individual site’s philosophy should be considered, including the available resource to undertake necessary work, and also any additional process equipment in the area where gas detection is situated that also requires ongoing maintenance.


The maintenance of portable devices is something that is evolving; the new EN 60079-29-2:2007 regulation which was released in November 2010, advises the bump testing of portable gas detectors each day before use. Naturally, this kind of safety introduction can impact upon a site’s maintenance costs. Devices like MicroDock II from BW Technologies by Honeywell help to simplify bump testing, limiting the adverse impact that this type of compliance can have.


Bump testing a portable device using MicroDock II is as simple as docking the unit in the station, pressing a single button and waiting for less than two minutes. This not only helps to save time on bump testing using the manual method but also provides operators with a simple system that requires minimal training; another appealing aspect as the new regulation states that that bump testing should ideally be carried out by the person using the equipment. This helps to make compliance with daily bump testing guidelines less costly and easier to integrate into a site.


A case by case approach


Local factors and individual plant set up will have a massive impact on whether one device is more suitable than another in terms of providing cash savings. In reality there are a wide variety of factors that can impact upon the selection of gas detection solutions capable of reducing the ongoing cost of gas detection. It’s important to work with a supplier who can provide multiple technologies and specifi cation variance, as this will enable them to give impartial guidance on choosing the right solution that is truly fi t for purpose, based on your individual variables.


GasDetector | Winter 2011 | Page 7


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