While hydrogen has advantages that explain its ongoing use as a putative green replacement for many other fuels, it does present a quite distinct set of safety challenges. But it seems the risks can be mitigated with sufficient awareness, and the deployment of appropriate technologies and best practices, as Envirotec discovered in conversation with industrial safety and gas detection expert Dräger. The firm assists organisations to work safely with hydrogen, and to equip their sites accordingly. Gas detection systems are a key ingredient.
Hydrogen’s particular strength is with its versatility as a means to store, transport and distribute energy over large distances and between sectors – indeed, it’s the only at-scale technology able to do so. It can be produced wherever renewable energy such as wind or solar is generated, and then transported to where it is required. This is the ideal, at least.
There are certainly similarities between hydrogen and methane, and some of the existing infrastructure for natural gas can be repurposed for it. Both are explosive, for one thing. But there are key differences in terms of their properties and the specific risks they present. Adam Pope, Marketing Manager and Gas Detection Lead with Dräger suggests this is not always apparent to operators and staff who have worked with natural gas or LPG. “They’ll maybe have some idea about the Hindenburg disaster,” he muses, referencing the 1937 calamity that drew a line under an earlier era’s exploration of hydrogen as a fuel, but they’ll often be unfamiliar with hydrogen’s special challenges, and the necessary risk-mitigation strategies.
For one thing, hydrogen’s flame characteristics are quite distinct from other common fuels, in that it is difficult to detect with the naked eye in daylight (although it can be seen in darker conditions). It also emits very little heat – so you can’t feel it until you are in very close proximity.
One way it can be detected is by the electromagnetic radiation emitted when it burns – a signature that can be picked up by certain classes of detector.
Some of the key risk factors specific to hydrogen are listed in the side panel (“Hydrogen risk factors”, see end of article). Its flammability and propensity to leak from structures place a premium on high-integrity storage. And leak detection is a vital element of safeguarding.
These risk factors will obviously be unfamiliar where hydrogen is a recent add-on to an organisation’s core expertise. For example, at a wind or solar energy site where the operators have opted to produce hydrogen via electrolysis.
Points of vulnerability in the value chain are explored in an ebook from Dräger.1 Even where existing infrastructure can be adapted there will be vital new ideas to grasp. For example, existing gas pipelines, where suitable, will require new monitoring and maintenance regimes.
The ebook explains that “the probability of safety incidents increases when people are involved”. The document adds: “When heavy machines such as trucks are moved around, even minor bumps need to be taken seriously as they increase the risk of leakage.”
Profiling a site
Gaining a full picture of a site’s risks is a vital precursor to designing mitigation measures – and requires an individualised risk assessment, something Dräger’s literature recommends “before joining the hydrogen economy”. There is no standard risk profile, seemingly, and the risks manifest in different ways in each site.
Fire and gas mapping is one service the group introduces at this early stage, says Adam Pope, which will result in a colour-coded 3d map of a site intended to afford a clear understanding of the different risks, and of where leaked gases will travel in different circumstances.
Fixed gas and flame detection is the primary means to protect a site from explosion risk, by alerting operators to the presence of a leak, so that premises can be evacuated and processes can potentially be shut down.
A range of different technologies is used here, each with different strengths and weaknesses. Best practice involves a mix of technologies, as Adam explains.
Three layers of protection
Point detectors are the core technology for gas detection and form the foundation of most safety systems, he says. These will be located anywhere there is a danger that gas can accumulate, such as in confined spaces. The downside is that the gas must be able to make contact with the detector or it might be missed.
The choice of sensor technology is crucial here. As Adam points out, the infrared sensors used to detect hydrocarbons are completely blind to hydrogen. Instead, catalytic bead (CatEx) sensors, or electrochemical (EC) sensors, can be used here. CatEx sensors offer a robust way to detect hydrogen up to the explosive limit (i.e., below 100% LEL, the Lower Explosion Level), providing a fast response time. EC sensors are typically used where lower (ppm) concentration levels of hydrogen are to be detected, and also offer a fast response time and high accuracy.
An earlier warning of leakage is available with ultrasonic detectors, to be deployed as an additional layer of detection where appropriate. These exploit the fact that hydrogen’s small molecule size results in a high-frequency noise, wherever there’s a leak. The acoustic sensor can detect leaks occurring up to 7 – 15 m away from the leak source, and deliver an on/off signal that can be used to trigger an alarm or automatic shutdown of equipment.
Ultrasonic detectors are good for outdoor locations, where the wind might otherwise carry hydrogen away from point detectors.
The relative invisibility of hydrogen flames means an additional layer of detection can sometimes be appropriate for a site, in the form of hydrogen flame detectors. Two technologies appear to stand out: UV/IR detectors, and 3IR.2 A traditional option for detecting hydrocarbon fires is a UV/IR detector, employing one ultraviolet and one infrared sensor, and providing a swift response time but with some potential for false alarms, particularly when trying to detect hydrogen.
To assist with hydrogen detection specifically, Dräger has adopted a technology called “3IR” – so-named for its use of three separate IR sensors, and this is incorporated in the company’s Flame 1750 H₂ detector. The 3IR technology produces a low rate of false alarms and a fast response – as Adam says, it can detect a 1m flame at a distance of up to 40m, within 5 seconds. It also provides a wide field of detection in comparison to UV/IR. A case study explores the details of these claims, which is also the focus of a recent white paper.
Dräger’s flame-detection technology partner Micropack conducted the analysis and used HazMap3D software to model a complex industrial installation, and to indicate the detection coverage available with ten Dräger Flame 1750 H2 detectors. A colour-coded analysis displayed the detected fire-risk areas in green, and blind spots in red. And this seemingly showed that it provided 64% coverage, with 36% of the target areas remaining outside the flame detector’s range or obstructed. In comparison, twenty UV/IR flame detectors in the same installation achieved only 44% coverage, leaving 56% unprotected. The conclusion? 3IR technology reduces cost and increases coverage.
Multichannel approach
Unlike hydrocarbon combustion, which is typically detected through CO₂ emissions, hydrogen flames are primarily identified by the presence of water vapour — a difference that appears central to this detection method. The 3IR detector focuses on the 2–4 µm region of the electromagnetic spectrum, where hydrogen’s characteristic spectral features are found. Each of the three separate IR sensors focuses on a specific region of this band: One focuses on the area where combustion signatures are strongest, and the other two provide reference channels, to help distinguish any detected hydrogen flame signature from other potential heat sources in the vicinity. By a continuous comparison of the three signals, the detector is able to filter out sources of false positives such as welding equipment or sunlight.
A variety of issues come into play when safeguarding a site that uses or stores hydrogen in any way. When conducting a risk assessment, Dräger advises on issues such as the placement and choice of gas and flame detectors, in addition to matters such as suitable storage locations for hydrogen, and working out where any gas will go if it escapes.
Safeguarding a site may also involve integrating gas and flame detectors with an internal alarm management system, and other systems that can, for example, shut down processes that might carry an explosion risk when combined with hydrogen.
Dräger provides an end-to-end service which also incorporates third-party products such as alarms, “to create a seamless safety infrastructure”.
While the landscape of risks might be unfamiliar to many at this point – or the world is in the process of getting familiar with them – a consistent message from Dräger seems to be that all the risks can be managed. With awareness of the appropriate safeguards, selection of the right technologies, and putting best-practice into action, this promising clean energy source can become as routine as any other form of fuel.
Notes
[1] “Hydrogen: How to meet the safety challenges.” Ebook available from Dräger. https://www.draeger.com/Content/Documents/Content/hydrogen-safety-challenges-ebk-11064-en-master.pdf.
[2] “Detecting the Invisible: Understanding hydrogen flames and choosing the right detector”, PDF, available from Dräger.
Hydrogen risk factors – SIDE PANEL
The universe’s lightest element presents its own unique set of risk factors, some of which are listed here.
- Explosion risk: While hydrogen is not explosive on its own, it becomes highly explosive when mixed with air in certain concentrations. It also has a relatively low ignition energy. After production, hydrogen will tend to be compressed to prepare it for storage or transport, and this adds to the explosion risk. It also produces a much bigger explosion than natural gas, with around 7x the explosion velocity.
- Leak risk: With its small molecule size, and low viscosity, hydrogen leaks more readily than other fuels such as methane. A container that is “air-tight” for methane, might not necessarily be “air-tight” for hydrogen. This also means pipelines and other structures have to be engineered to hydrogen-ready specifications, and it will be important to ensure there are regular inspections of things like joints in pipelines.
- Threat to structures: The small size of molecules also accounts for hydrogen’s ability to embrittle structures, by permeating their interior. To protect against this, storage tanks tend to be made of stainless steel or composites.
- Forms gas pockets: Its lightness is one important difference with methane, and the fact of hydrogen’s being lighter than air means leaks are not so easily detected at ground level, even when dangerous amounts might be accumulating beneath a nearby ceiling, as Dräger’s literature explains. The placement of gas detectors should reflect this.
- Odourless: Hydrogen is odourless, like methane. An odourant marker is added to the latter (most commonly a particular blend of mercaptans), to get around this nasal invisibility. Such a possibility is being investigated and trialled with hydrogen, but the results are still awaited.
