Focus on Sensor Technology - Gas Detection 33
An introduction to setting workplace
exposure limits At the 81st Gas Analysis and Sensing Group Colloquium, which focussed on exposure limits, toxicology and human health, Kate Jones from the Health and Safety Executive discussed the setting and revising of workplace exposure limits – our reporter went along to fi nd out more.
It’s important to state at the outset that the process of setting and revising workplace exposure limits (or WELs, if you’re really pressed for time) is slow and resource-intensive, so there’s really no substitute for robust control measures and continuous monitoring when it comes to occupational safety.
With those preliminaries out of the way, then, let’s start right at the beginning of the process, which, paradoxically, is an endpoint. In the toxicology community, studies to determine the relative toxicity of a substance are called toxicological endpoints. It’s at this earliest stage that we encounter our fi rst roadblock.
Depending on the literature available for a substance, the relative toxicity may have been determined only in relation to non- human sample-groups – this is where relative toxicity takes on its full meaning. Further, the experiments may have avoided organisms entirely, opting instead to test the substance in vitro (literally, ‘in glass’ but refers specifi cally to a test-tube) or in silico (by computerised simulation). So, the uncertainty of your workplace exposure limit really depends upon what types of studies have been conducted and peer-reviewed.
From an endpoint, you can establish the important dimensions of relative toxicity. Most important is the benchmark dose (BMD), which is a certain amount of the substance that produces a known rate of adverse change in the organism. Establishing this predictability is absolutely essential, as WELs are established in relation to 8-hour days and 40-hour weeks over a working-life of 40 years. Beyond this is the lowest-observed-adverse-effect level (LOAEL), which, somewhat obviously, is the smallest amount of a substance required to produce a harmful effect. Just below this level, you’ll have the no-observed adverse-effect level (NOAEL), the largest amount of the substance that produces no negative effects.
However, it’s important to remember that as only a very limited number of doses are tested, both the LOAEL and NOAEL should be regarded as coarse estimates.
After all these measures have been established, compliance with workplace exposure limits is then ascertained in a two-part process. Firstly, you’ll need to conduct an analysis of various possible exposures. Then, using this knowledge, it will be time to get somewhere between 3 and 6 representative measurements for each group of employees likely to be exposed to the same substances. If less than 5% exceed the workplace exposure limit, congratulations! You’ve (probably) just demonstrated compliance with the guideline.
Of course, it’s important not to then close the book on exposures until the worst happens. Whenever there’s a change of location, new machinery and technology or some form of renovation, it’s best to go through this process again. And as we’ve already discussed, keep monitoring! It’ll make sure that you’re as responsive as possible to changes in the concentration of toxic substances.
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Digital pyroelectric detector extends gas detection portfolio built over 3 decades
InfraTec, exhibitors at this year’s SENSOR + TEST exhibition in Nuremberg, has been developing and producing pyroelectric detectors for over 30 years. They have been tried and proven in numerous demanding customer applications in recent decades. However, to reduce expenditure for customers and to facilitate the system integration of a detector, InfraTec has developed the digital pyroelectric detector (LRD).
Like all detectors from InfraTec, the digital detector is based on lithium tantalate (LiTaO3) and is used in the fi eld of gas analysis and fl ame detection. It enables complete fl exibility in the confi guration of the detector parameters and therefore variable signal processing. In addition, it offers improved electromagnetic compatibility (EMC), as the entire signal conversion of the detector is spatially concentrated and shielded.
The digital detector offers a wide range of further benefi ts. It is equipped with a clock input (pin) to synchronise the radiator and the detector clock. This means that a time signal with a highly precise sampling rate can be generated. An additional, special feature is the “fast recovery after saturation “. This function detects the override due to a defective operating status and automatically resets the analogue input stage.
The digital detector converts the analogue signal with a 16-Bit resolution directly into a digital signal. The analogue signals can be multistage adjustably fi ltered and strengthened. The complete signal processing is performed via an ASIC (application-specifi c integrated circuit) with integrated A/D-converter, whereby the analogue input stage acts like a transimpedance amplifi er. Users receive a digital measurement signal, which can be read out via a standard communication interface and processed immediately.
The digital detector will expand the portfolio comprising analogue detectors in the future. Which of the two variants is used, depends mainly on the complexity of the measuring tasks. Both detectors have their strengths and offer different benefi ts.
Figaro’s New Battery Operable Methane Sensor, the TGS 8410, Featured with High Selectivity and Durability
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Figaro Engineering Inc. is pleased to announce its latest offering – the methane gas sensor TGS8410 with the lowest power consumption among its combustible gas sensors.
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Combining the advanced Micro-Electro-Mechanical Systems (MEMS) technology with Figaro’s 50+ years of extensive experience in MOS type gas sensors, Figaro has developed a new methane gas sensor that has the lowest power consumption among its current product lineups. This low power consumption is less than 0.1mW on average, which will enable a methane gas detector to work as long as for 5 years with just a single lithium battery (2.8V/2400mAH).
The TGS 8410 has fi lter material in its housing for eliminating the infl uence of interference gases such as alcohol, resulting in a highly sensitive and selective response to methane gas.
Featured with excellent durability and stability, TGS8410 is ideal for applications such as portable gas detectors, wireless residential gas detectors, leak detection for natural gas vehicles, gas pipelines, etc.
Where Safety excels, Figaro dwells
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