Hydrogen is a colourless, odourless, and tasteless gas, therefore small gaseous leaks are difficult to detect by human senses. Small leaks are common due to the small size of hydrogen molecules and usually do not present a problem since the tiny amount of mixture will not be enough to cause a flammable mixture in the air. Small amounts of leaking hydrogen will rise and diffuse quickly in air because of its low density resulting in high buoyancy (it’s 14 times less dense than air).
Hydrogen is less likely to cause a fire or explosion hazard in an open or well-ventilated space, but a problem arises when hydrogen gas is allowed to accumulate in a confined area. If this is allowed to happen, there will be a risk of a flammable mixture building up. When a large amount of accumulated hydrogen rises and mixes readily with air, it creates an ignitable mixture that can result in flames or explosions. Hydrogen is flammable in air at a volume of 4-75% by volume.
Any structure that contains hydrogen components should be ventilated adequately. Since hydrogen is lighter than air, it collects under roofs and overhangs. Most people are familiar with protecting plants from heavier than air vapours, but are unfamiliar with upward issues. There have been many reports of hydrogen leaks igniting over the decades, and several potential ignition prevention mechanisms and hydrogen leak detection systems have been proposed.
Methods for hydrogen leak detection include:
Reducing the Volumetric ratio of Hydrogen to Air
Ignition can occur at a volumetric ratio of hydrogen to air as low as 4% due to the oxygen in the air and the simplicity and chemical properties of the reaction.
The best practice to avoid accumulation is to determine where hydrogen leaks are likely to occur and how they may disperse and ventilate accordingly to manage the airflows sufficiently to keep hydrogen concentrations below the lower flammability level(LFL) during probable release scenarios. Ventilation rates should be sufficient to dilute hydrogen leaks to less than 25% of the LFL which is about 1% volume by air. The minimum ventilation rate should safely dilute hydrogen build-up in the event of leakage and the ventilation should not shut down in emergency or during periods of shut down.
It is generally safe to exhaust hydrogen into open atmosphere providing it is kept high enough that the heat does not harm anyone. Ventilation systems should not be used for the disposal of hydrogen; this should be managed by a separate system called a vent system.
IIC Fans for Potentially Explosive Environments
Hydrogen is a gas group IIC gas and belongs to the T1 temperature class making it one of the hottest, most dangerous gases. Mechanical exhaust fans should be ATEX rated to the appropriate IIB+H2 or IIC T1 ATEX certification andconstructed from the suitable permissible material pairings as noted in the current legislation surrounding equipment for explosive environments. Material pairings should specifically relate to the rotating and stationary parts that may come into contact with each other during standard or rare malfunction. This material pairing reduces the risk of ignition created from friction and the build up of static electricity to create a spark. ATEX fans are therefore often referred to as having a spark proof construction.
Our entire range of ATEX certified fans are suitable for gas group IIC or IIB + Hydrogen applications for effective hydrogen ventilation. Learn more by visiting our website.
www.axair-fans.co.uk
