Hydrogen
These days there is a huge ammount of research and development in relation to hydrogen applications. Also commencially suitable systems become more and more available on the market. "Hydrogen has the future", among other developments, in relation to the global climate goals, that were stated in the Paris Agreement.
Hydrogen has sufficient benefits for further exploration in relation to the energy transition. Beside that hydrogen, has also some other, very interesting and serious safety issues.
Odourless gas
Hydrogen is an odourless gas, so one cannot smell a leakage of hydrogen gas.
Small size
Hydrogen is the smallest molecule on earth: the H2 molecule consists only of two H+ atoms. Because of this, normally enclosed systems can easily leak hydrogen; much more easy like e.g. natural gas systems.
Easy ignitable
The minimum ignition energy (MIE) needed for igniting hydrogen is very low: only 0,017 mJ. Compare this to natural gas (methane) which has a minimum ignition energy of 0,28 mJ. So the smallest spark can ignite hydrogen.
Poor visability
When hydrogen burns, the flame is almost invissible. A slightly, hard to see, blue flame can be seen in some cases, but this depends of the puruty of the hydrogen. The burning of hydrogen is the perfect burning without any formation of CO or CO2 and these substances causes the yellow/orange flames.
Dillution
Because of the size and the moleculair mass of the hydrogen atmos, the weight of a hydrogen molecule is very low: only 2 grams per mole. The molecule mass of one mole of dry ar is appr. 29, so hydrogen is appr. 15 times lighter than air. This is the reason that hydrogen molecules tends to move upwards in air. On the other hand: due to its small molecule size, hydrogen mixes rapidly with air, and therefore behaves also very quickly like air and its movements. In relation to safety this has some advantages but also some disadvantages.
Force of an explosion
Hydrogen is easy to ignite and the force of a hydrogen explosion is enormous. The pressure rise in time is much higher than a methane air mixture and therefor the effects of a hydrogen explosion are significant. When a hydrogen cloud gets ignited in open atmosphere however, there is hardly any shock waves to be detected, only a rather fast buring of the cloud with some heat radiation.
Storage at high pressure
Hydrogen is an ultra-light gas that occupies a substantial volume under standard conditions of pressure, i.e., atmospheric pressure. In order to store and transport hydrogen efficiently, this volume must be significantly reduced. This can be done by storage under high pressures upto 700 - 800 bars in a tank. This results a potential safety issues due to leaking of hydrogen at high pressures and high speeds. It is known that hydrogen leaking at high pressures leads to spontanious ignition of hydrogen.
Assessment of hydrogen
The hazardous area classification around hydrogen based systems can easily be performed with the EN-IEC 60079-10-1 standard. And of course the HAZcalc software can be used for that.
Release rate of hydrogen
For hydrogen systems the release rate of hydrogen can be calculated based on system e.g. pressure, system temperature and the size of the opening of the release area.
Ventilation and dillution
For determination of the pressence of a hazardous area, the release must be highly dilluted with air:
- For outdoor situations the wind velocity is a good marker for that.
- For indoor situations the ventilation capacity and the resulting air velocity around the source of release is a good marker for that.
Typical for hydrogen, special attention is needed for assessing the background concentration, since the background concentration is an average concentration within the whole room under consideration. Hydrogen however, is very light and will tend to move upwards within a room and a ceiling layer can be formed. This can lead to a high concentration under the ceiling and this can create hazards.
Layer formation
So the background concentration, defined under the IEC 60079-10-1 standard, is not always a good value to assess the dilution within a room. Other tools like e.g. HyRAM can be used for assessing the possibility of ceiling formation.
Conclusion
So with Hazcalc, the hazardous area and its size can be assessed and in addition to that, the formation of a ceiling layer can be assessed. These two assessments together give a good way of assessing hydrogen releases for indoor and outdoor situations which will result in a specific hazardous area.
Within the (future) hydrogen economy, specific and more detailed standards will be developed e.g. for electrolyzers and fuel cells. For more specific advice or help with hydrogen assessments, feel free to contact us.
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