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You really want to measure that H2S range??

29-Apr-2024Emissions monitoring | Fenceline | H2S | H2S monitoring | Industrial | Oil & Gas

You really want to measure that H2S range??

Requests to measure hydrogen sulphide (H2S) in ambient air at unthinkably high levels seem to be at odds with our efforts to detect and report single-figure parts per billion H2S emissions. So, why are we asked for such high ranges?

We think this may be explained by operators who are used to measuring high concentration in a gas stream – typically biogas or industrial – and then simply transferring the range across when looking at fenceline monitoring. It’s great to see the growing interest in monitoring fugitive emissions at site boundaries – including H2S – but we need to dial back the gas range expected when looking at ambient pollution.

H2S sensors for gas stream measurement are offered at parts per million ranges from 0-50ppm to 0-10,000ppm. Bear in mind that US Department of Labor guidelines say that H2S odour becomes offensive at only 3-5ppm, with prolonged exposure causing headaches, nausea and insomnia, and causes “nearly instant death” at 1,000-2,000pm. Dilution of any emission in swirling ambient air means that parts per million measurements are inappropriate, and even significant H2S leaks usually register peaks of just a few parts per billion by the time gas has reached the fence line.

That’s why the AQMesh sensor measures from 0-10,000ppb (0-10ppm), with a limit of detection of less than 1ppb. Measuring at such low levels means operators can pick up emissions much earlier and much further away from the source than would be the case with the higher range sensor typically used for measuring the gas stream. Picking up a low level at a suitable point on the industrial boundary should avoid dangerous levels of H2S building up near the source.

Monitoring in ambient air is gentler on sensors, too, so if you are used to sensor poisoning and condensate problems, that benefit does offset the ‘needle in a haystack’ challenge of picking up fugitive H2S emissions. With the potential to move an AQMesh pod from location to location, and add a wind speed and direction sensor to help with source apportionment, it is very satisfying to support our users doing just that.

Why are data centres bothered about outdoor air pollution?

05-Sep-2023Data centres | H2S

Why are data centres bothered about outdoor air pollution?

AQMesh has been used extensively in and around data centres for two main reasons: obligation to monitor emissions from back-up generators and the risk to copper components from hydrogen sulphide.

Monitoring emissions from back-up generators

Data centres accommodate core IT and computing services and infrastructure, offering businesses space and power to house their data in a secure, 24/7 supervised, temperature-controlled facility. Such facilities must have a back-up power supply to ensure data is stored securely, in case of mains electricity power failure. Back-up power is generally provided by diesel-powered generators. As diesel fumes are classed as carcinogenic by the World Health Organisation and other bodies, data centres using generators in the UK must provide information to the Environment Agency regarding pollution from their back-up generators when exceedances are identified. The key components of diesel exhaust are oxides of nitrogen – NO, NO2, NOx – and particulate matter, with PM2.5 most often measured.

AQMesh pods can monitor at any specific location, as necessary to identify and report exceedances of air pollutants, including NO2 and PM2.5. Generator fumes come from a single source and tend to be highly localised, with mixing in air affected by wind speed and direction. A network of AQMesh pods can be easily set up, using a range of power sources, depending on availability of a local power supply, including mains, battery and solar power. Alerts can be set to the required exceedance levels, with appropriate averaging of readings, to ensure compliance and minimise the risk of false alarms.

Air pollution may be produced by sources other than generators, such as nearby road traffic or construction activity. Analysis of measurements from such a network can provide information about likely pollution sources, by looking at relative concentrations of pollutants across the site. This is enhanced if wind speed and direction is used, helping to identify whether measurements are upwind or downwind of a source, with the likely scale and direction of the source identified.

One data centre using AQMesh was able to show that traffic diversions around the trading estate were causing pollutant spikes rather than their generators. This AQMesh user had installed a solar-powered pod, with the wind speed and direction option, on the roof of the facility. Wind speed and direction data is pulled into the same data stream as pollutant gases, easing the analysis process. The customer is also using a new technique to scale their AQMesh network to nearby reference stations on a six-monthly basis, to demonstrate data traceability and accuracy.

Sixteen data centres in UK and Europe are using AQMesh to detect air quality issues. Many other operations which use generators for back-up or to power core activities, such as construction sites, protect staff and nearby populations by monitoring air pollution on a 24/7 real-time basis. Readings are typically a 15-minute average but can be as short as one minute, to identify short-term spikes.

Monitoring hydrogen sulphides to prevent short-circuits

Hydrogen sulphide (H2S) in the air – which can come from a number of sources – is a particular risk to information technology, as it can damage copper circuitry. H2S, and sulphur dioxide (SO2), in the air can form a weak acid. This risk is growing worldwide, with more compact circuitry increasing the risk of short-circuits, and more data centres being located in areas with higher levels of H2S and SO2 in the air.

Airborne sulphur causes copper dendrites to form on electronic components, causing short circuits and therefore potentially data errors. H2S attacks copper, forming thin films of metallic sulphides – dendrite whiskers – which speed up corrosion, so some data centres monitor H2S outdoors, near air intakes, and internally within UPS rooms to avoid sulphur-induced degradation in power modules. These gaseous contaminants can lead to deterioration of silver solder as well as copper surfaces on computer circuit boards, leading to intermittent and hard errors, caused by either impeding the flow of electricity or forming unintended circuit paths. This ASHRAE article goes into more depth on the subject.

Data centres focus on filtration for particles and management of temperature and humidity, but gases in the air may bypass such filtration systems. One method of monitoring for potential corrosion is to expose silver and copper coupons to the air in the server centre and measure corrosion over a month. This is an effective methodology, but the results of the month-long test may arrive too late to prevent damage. Monitoring of the air coming into the building allows real-time notification of elevated levels of H2S and SO2, allowing action to be taken before polluted air enters the data centre.

AQMesh pods can be installed quickly on site, with secure data available online or by API. Pods can be shipped worldwide with a two-week manufacture and test lead time, with rental options offered.

AQMesh introduces new CO2 and H2S monitoring capability

10-Jul-2018CO2 | H2S | Performance | Product | Shipping

AQMesh introduces new CO2 and H2S monitoring capability

AQMesh is now able to offer CO2 and H2S within its range of gas options for local air pollution monitoring.

The NDIR CO2 sensor, which can be offered within a single AQMesh pod alongside five other gases out of NO, NO2, O3, CO, SO2 or H2S, as well as PM1, PM2.5, PM10, temperature, pressure and humidity, has been developed to deliver a higher performance than those typically used for indoor air quality monitoring. It has been rigorously tested against Picarro reference equipment, resulting in an R2 value of 0.93. Pod-to-pod correlation of over 20 AQMesh pods has shown R2 values of 0.98 and 0.99, and the sensor has a MAE (mean absolute error) of less than 20ppm.

In addition to monitoring deviations from ambient levels of CO2, elevated CO2 levels can indicate that monitoring is taking place in a combustion plume and levels of other gases can be interpreted accordingly. For example, the ratio of CO2 to the other pollutant gases present can indicate whether those gases were emitted by a local or distant source.

An additional electrochemical sensor has been introduced to offer H2S measurements. After integrating the sensor, measurements have been compared to readings from a Honeywell SPM Flex installed at a sewage treatment site with an R2 value of 0.87 over a measurement range of 0-150ppb. Particularly of interest to the oil and gas industry, in association with the SO2 monitoring already available on AQMesh, it can be used to measure emissions from sour gas and residual emissions from flaring operations.

AQMesh can measure up to 6 pollutant gases in various combinations, as well as particulate matter, humidity, atmospheric pressure and noise in one small, compact easy-to-install unit. There is a range of wireless power options, including lithium battery packs and solar panels, with information sent in near real-time to a secure server via cellular GPRS. Data can be accessed by a secure login or can be streamed via an API connection.

AQMesh pods are in use across the globe in a variety of indoor and outdoor air pollution monitoring applications, and are becoming increasingly popular in smart cities and networks. Pod performance has been proven through extensive testing in worldwide co-location comparison trials with reference equipment, which have delivered impressive and reliable correlation results.