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We develop a test station where we might have H2 leakage.

To prevent explosion we are considering intertisation using N2 gas (primary explosion protection).

However we also want to detect leakage events.

We are searching for a sensor, which (ideally) has the following characteristics:

  • Reliable H2 readings in Air and N2/Air mixtures
  • Temperature range -55 °C .. 80 °C
  • Range, 0 .. LEL (4% vol-N2)
  • t90 smaller 15s
  • ATEX certified
  • PL according to EN ISO 13849-1
  • less than 5000 USD
  • combination of sensors also possible First point is mandatory. In the otherpoints compromises are possible.

Sensors on the catalytic of electrochemical type seem to rely on O2. I have found sensors based on thermal conductivity, but these seem to have a bigger range and cost.

Any idea, what to use?

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    $\begingroup$ If safety is your primary concern why are you worried about cost? $\endgroup$
    – Solar Mike
    May 6 '20 at 9:35
  • $\begingroup$ Safety of course. But costly gas analyser which are designed for lab purposes are no option. Price range upto 5000 usd is OK. $\endgroup$
    – BerndGit
    May 6 '20 at 9:39
  • $\begingroup$ You should include a sketch or drawing of the station that shows the H2 gas sources, fittings, other potential leak points, and the current point where the detection will occur. Maybe you can get suggestions on a re-design that makes the detection easier. Otherwise, you need to speak directly with some vendors and get quotes on systems that will work and then convince management to pay what's needed to protect people. Lawsuits are more expensive than an H2 monitoring system. $\endgroup$
    – J. Ari
    May 6 '20 at 11:40
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    $\begingroup$ @BerndGit Recommendations on the specific type of sensor I will leave to the system vendors to recommend once you've reviewed the application with them. I'd suggest speaking with Honeywell, MSA Safety Inc, Draeger, DOD Technologies Inc. In general, monitoring in an inerted atmosphere is a challenge, so options may be limited. $\endgroup$
    – J. Ari
    May 6 '20 at 12:07
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    $\begingroup$ @Mart: Price indication is just to give a rough idea of budget. I could also state ~ 5 kEUR. But 50 kEUR are surely too high. Standard refers to reliability of sensor. It is an internation standard, but I have just found the EU version of it. Similar standards are ok. Final location of testbet is in Asia. This standard is well accepted there. $\endgroup$
    – BerndGit
    May 7 '20 at 8:20
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I think you are right to rule out catalytical and electrochemical sensors, as these likely require oxygen, though I'd confirm this with a manufacturer.

As a proxy for hydrogen, use density. As a first order approximation, a mix of 99% N2 and 1% H2 will have 0.99 x the density of N2. The first density measurement device I found (Schwing PMT, site only german it seems) is precise to 0.1% of the measured value, likely precise enough to detect H2 in the single digit percentage range, maybe smaller. Some of these devices give the value as density under standard conditions, which is what you want here.

However the moment you have a gas mix (Air/N2/H2) the accuracy is gone.

IMO, this off-label use of a density measurement could work in pure nitrogen environment, but I would not bet anyones life on it: Get an additional sensor for ex-hazard detection.

I don't know the cost but I doubt you get both sensors for <5000 USD, you also need to consider operating costs for recalibration, possibly training on the sensors etc. I would seriously question if the information you get is useful enough to justiy the effort.

(nitrogen has a density of 1.25 kg/m³ at standard conditions, hydrogen 0.08)

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  • $\begingroup$ This is an interesting suggestion, Mart. The density of Air and N2 do not differ to much just a fre percentages (basically since Air mainly consitsts of N2). So accuray of sensor signal (uncorrecdted for inertisation level) might be affected but it can still be accurate enough for detecting a treshhold value. ... The off-label use is a concern, which we need to research deeper in an FMEA. Maybe reduce risk by additional sensors. Thanks! $\endgroup$
    – BerndGit
    May 7 '20 at 8:31
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    $\begingroup$ @BerndGit This is assuming that the inerted volume has some means of being well mixed and not allowing the H2 to just separate out based on density, right? If the inertion was achieved by a constant flow of N2, that would encourage mixing, but if it is just a one time pressurization, this suggestion may not work. $\endgroup$
    – J. Ari
    May 7 '20 at 11:18
  • $\begingroup$ @J. Ari: yes this is ensured by sufficeint ventilation in the room. Thank you for that hint anyhow. $\endgroup$
    – BerndGit
    May 7 '20 at 11:21
  • $\begingroup$ Consider measuring near the top. $\endgroup$
    – mart
    May 7 '20 at 12:18
  • $\begingroup$ @BerndGit I don't exactly follow how room ventilation affects the mixing inside the inerted volume, but without a sketch of the test apparatus and the surrounding room, it will be hard to discuss. I see that you have some technologies to consider now from your answer. Best of luck! $\endgroup$
    – J. Ari
    May 7 '20 at 15:33
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Doing more research i have found a very good database on H2 sensors at (> 400 entries!!): https://netzwerke.bam.de/Netzwerke/Content/EN/Downloads/h2sense-database.pdf

It includes promising canditates for my application. Seems the prefered type of sensor is a thermal conductivy based one.

At current time more detailed evaluation of the options including supplier discussion is required. So I cannot post the final decission here, yet.

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