The challenge of detecting hydrogen gas
08 November 2022
Hydrogen (H2) is set to play a vital role in producing cleaner energy. Specifically, within the UK where the government has set a target to create a thriving hydrogen economy by 2030. Seen as a greener way of living, countries such as Japan, South Korea and China are also on course to make significant progress in H2 development. The European Commission has also presented a hydrogen strategy in which H2 could provide for 24% of the world’s energy by 2050.
(Click here to view article in digital edition)
With the shift to hydrogen as a clean fuel, and the emphasis on its usage globally, it is important for the relevant people, within industries that utilise hydrogen, to gain a full awareness of the dangers and impact of this shift. There is a collective global sustainability focus on decarbonising the fuel we use by 2050. To achieve this, decarbonising the production of a significant fuel source like hydrogen, giving rise to green hydrogen, is one of the key strategies. This is because the production of non-green hydrogen is currently responsible for more than 2% of total global carbon dioxide (CO2) emissions.
During combustion, chemical bonds are broken, and constituent elements combined with oxygen. Traditionally, methane gas has been the natural gas of choice with 85% of homes and 40% of the UK’s electricity depending on natural gas. Methane is a cleaner fuel than coal, although when burnt CO2 is produced as a waste product which, on entering the atmosphere, contributes to CO2 emissions. Hydrogen gas when burnt only produces water vapour as a waste product, thereby not contributing to global warming.
Dangers of hydrogen
Although it is a cleaner fuel source, there are still dangers inherent with the use of hydrogen. All relevant personnel who encounter it should therefore be aware of these dangers and how to protect themselves.
Hydrogen is non-toxic, but in indoor environments like battery storage rooms, hydrogen can accumulate and theoretically cause asphyxiation by displacing oxygen. Colourless, odourless gases can build up without those in the environment knowing about it. This danger can be offset to some extent by adding odorants to hydrogen fuel which provide an artificial smell to alert users in the case of a leak.
Hydrogen is also a highly flammable and volatile substance which combusts at low concentrations. Explosions can happen from a single spark or increased heat. Its reactivity and flammability mean it can be highly dangerous if not managed, stored and measured correctly.
The ISO 22734-1:2019 regulations govern the use of hydrogen generators using water electrolysis across industrial, commercial, and residential applications. Generators that use aqueous bases and acids, solid polymeric materials with proton exchange membrane (PEM) and anion exchange membrane (AEM) are referred to here. The legislation also covers the management of generators used in outdoor residential spaces including in sheltered areas, such as carports, garages, utility rooms and similar areas of a residence.
In the UK, the Gas Safety (Management) Regulations 1996 state that the concentration of hydrogen that can be injected onto the UK gas network is 0.1%. Although this is currently being tested to increase the hydrogen up to 20% in a blend with natural gas.
Elsewhere in the UK, hydrogen is legislated for within the definition of “gas” in the Gas Act 1986 (the “Gas Act”) and regulated as part of the gas network. In the UK the gas market is regulated by the Gas and Electricity Markets authority, operating through the Office of Gas and Electricity Markets, commonly known as Ofgem.
Therefore, anyone supplying, shipping or transporting gas, participating in the operation of gas interconnectors, or providing smart metering needs a licence as required by the Gas Act. These licences govern the measures relating to the safe operation of the gas network and provisions relating to price controls.
As created and defined by OSHA, the PHMSA regulates almost 700 miles of hydrogen pipelines under the 49 C.F.R. Part 192 in the USA. These regulations focus on natural gas, but also cover hydrogen due to the inclusion of “flammable gas”.
Importance of detection technology
As hydrogen is a colourless, odourless and tasteless gas this makes the utilisation of detection technology paramount in order to trace it within working environments. With hydrogen starting to play an important role in energy production, the implementation of robust detection infrastructure is vital to minimise the risk of a small leak becoming an insurmountable incident. Hydrogen is highly mobile and capable of exiting breaks in damaged infrastructure far faster than traditional natural gas.
Detection technology is required for personnel and environmental safety, as well as to ensure compliance with regulations, however there are also best practice processes that can be undertaken when working with hydrogen. Workers should remain alert and listen for the sound of high-pressure gas escaping, as well listen and watch for alarms. The use of portable hydrogen detectors is recommended, as are routine checks for small leaks by applying soap bubble solutions on the surface of areas where leaks are suspected, or use of metal oxide (non-IR based) leak sensors.
Types of technology and products for detection
Awareness of the different types of detection technology available enables those making decisions about the safety of their staff working with hydrogen to make informed choices.
Pellistor detectors, or catalytic bead gas sensors, have been the primary technology for detecting flammable gases since the 1960s. Detection of Hydrogen has been restricted to pellistor sensor technology due to infrared (IR) sensors’ inability to detect hydrogen.
Paul Basham, Crowcon
Electrochemical sensors are 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 detectable concentration range.
Electrochemical sensors can be specific to a particular gas or vapour in the parts-per-million range. The degree of selectivity depends on the type of sensor, the target gas and the concentration of gas the sensor is designed to detect. They have a high repeatability and accuracy rate, and once they are calibrated to a known concentration, the sensor provides an accurate reading to a target gas that is repeatable. It is also not susceptible to poisoning by other gases and is less expensive than most other gas detection technologies, such as IR or PID technologies.
IR sensors use infrared emitters within the sensor with each generating beams of IR light. Each beam is of equal intensity and is deflected by a mirror within the sensor onto a photo-receiver, which measures the level of IR received. The “measuring” beam, with a frequency of around 3.3µm for hydrocarbon measurement, is absorbed by hydrocarbon gas molecules, so the beam intensity is reduced. The “reference” beam (around 3.0µm) is not absorbed, so arrives at the receiver at full strength. The %LEL of hydrocarbon gas present is determined by the difference in intensity between the beams measured by the photo-receiver. However, this technology is unable to detect hydrogen which does not absorb light at either 3.3µm or 3.0µm.
Fortunately, there is gas detection technology available that is suitable for varied environments within the hydrogen industry. The technologies already described detect lighter than air gases, catalytic sensors and IR sensors detect hydrocarbon gases with similar densities to air, and PID products detect heavy gases and liquid-based fuels once airborne, as either hydrocarbons on dust particles or solvent vapours.
Full coverage can be arranged by judicious use and placement of the safety technologies available. This equipment, including multi-gas, pumped portable products and fixed products, each have the capability of detecting all the gases mentioned. Meeting sustainability goals and being a part of the drive towards cleaner energy is important globally. However, keeping teams working with hydrogen safe is also vitally important, as the risks can be high if left unmonitored and undetected.
About the author:
Paul Basham is the company scientist at Crowcon. His career has been in instrumentation, focused mostly on safety products for fire and gas detection, but also infrared spectrometers. Paul focuses on the physics and chemistry of gas flows and sensing technologies and matching them to applications and industrial practices.
Contact Details and Archive...