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We regularly talk to consultants and contractors about explosion protection for new hydrogen initiatives, upcoming bio-methane projects, and multiple applications that involve the presence of hydrogen gas. Our discussions quite often revolve around the potential for ignition in areas where hydrogen could be present, either through leaks, or when dispersed into atmosphere. For example, where retrofit work is being completed in a battery charging room, vented lead acid batteries will release hydrogen throughout their charging period naturally. Inadequate ventilation or dilution of hydrogen rich air could ignite if static electricity from the use of tooling, creates a spark, or an electrical arc could be initiated by the battery charging unit, or stopped-up vent caps resulting from contaminated electrolytes permit hydrogen pressure to build up to an explosive force.
Electrostatic Ignition & Electrostatic Discharge in the Presence of Leaked Hydrogen Gas:
Static electricity is generated whenever two surfaces make and then break contact or rub against each other. Electrostatic charge generation is therefore expected during many common operations and once electrostatic charge is generated it can accumulate on conductive objects. It is this accumulation charge which, if allowed to occur, can result in electrostatic discharges. Electrostatic discharges can ignite most common flammable gas or vapour atmospheres and some dust clouds. This occurs when the electrostatic discharge is greater than the minimum ignition energy (MIE) of the flammable atmosphere. The MIE is defined as the smallest electrostatic discharge capable of igniting the flammable atmosphere at its most easily ignitable concentration. The ability of a spark to ignite a flammable atmosphere depends on its energy and duration. If the sparks energy exceeds the minimum ignition energy (MIE) of a flammable mixture, the result will likely be a fire or explosion. A stoichiometric mixture of hydrogen with air has a very low minimum ignition energy of 0.017 mJ. This makes it far more sensitive to ignition than most other gaseous or vapourised flammable materials, and therefore the potential for electrostatic ignition is much greater.
There are three types of electrostatic discharge to consider:
Spark discharges: These are characterised by a single plasma channel between the high potential conductor and an earthed conductor. The discharge is completed in a very short time, and almost all the charge is transferred in a single spark. An energy of 0.164 mJ is more than sufficient to ignite the stoichiometric hydrogen-air mixture.
Brush discharges: These are characterised by a discharge between a charged insulator and a conducting earthed point. They are characterised by many separate plasma streamers, combining at the conductor, and are typical of those from insulating plastics. As the charged surface is a non-conductor, a capacitance and hence energy cannot be determined.
Corona discharges: These are silent, usually continuous discharges which are characterised by a current but no plasma channel. A corona discharge is able to ignite a hydrogen-air mixture without there being a discrete spark or single discharge event. This is a known potential ignition source, particularly from atmospheric electrical activity. Where a potential exists some distance from an earthed surface, an electric field will be present. This field will be linear between a pair of parallel plates. However, if a small point is placed on one of the plates, it will modify the field, and concentrate the lines towards the point. If the local concentrated field strength exceeds the breakdown strength of the air, then a current will pass in the form of a corona.
The most important safety feature of any industrial fan construction, to minimise ignition, is the clearance between the rotating elements and the fan casing. This is a substantial part of the design and manufacture of fans suitable for explosive environments as mentioned in BS EN 14986:2017, a British Standard that is purely dedicated to industrial fans suitable for explosive environments. The majority of the points of warning over explosive proof fan design are structured around preventing sparks from static discharge.
Award Winning IIC ATEX Fans for Hydrogen Exhaust:
In February 2023 Axair's ATEX fans were awarded the Net Innovation Award by Hazardous experts HazardEx. The significant contribution of Axair's expert industrial team, their application knowledge and technical assistance in the development of low carbon and newly emerging technologies to assist in the future of green hydrogen generation was recognised by the industry. The use of ATEX fans certified to IIC for use in hydrogen systems is an important consideration in reducing the risk of explosions.
Contact Axair's industrial team for more information on ventilation and dilution best practices for Hydrogen gas.
Talk to one of Axair's trained ATEX explosion proof fan experts about fan integration into your system, they can advise on the most effective type of industrial fan for effective hydrogen ventilation, dilution and explosion prevention.
For more information on Electrostatic Discharge in Potentially Hazardous Applications talk to Axair Fans UK Ltd