Ventilation & Dilution of Hydrogen Leaks with Exhaust Fans
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:
Download ATEX Fans for Hydrogen Exhaust Brochure[/caption]
Case Study: Absence of Ventilation, Dilution, and Exhaust Fans
A 42 ½ foot diameter sphere made of 3/16in steel stored hydrogen in a plant. The sphere was separated into two hemispheres by a neoprene diaphragm attached around the equator. The lower half, under the diaphragm stored Hydrogen, while the upper half stored air.
An explosion proof fan was situated in the upper portion to provide a slight positive pressure on top of the diaphragm.
When the plant was shut down for a local holiday, the fan on top of the hydrogen sphere was also stopped. During plant start-up two days later, an explosion occurred in the sphere. The sphere shell was torn into many sections by the explosion, and some of the sections were propelled as far as 1,200 ft. Some of these sections struck flammable liquid storage tanks and cracked the roofs of adjacent buildings. Most of the windows in the surrounding buildings were broken by the blast wave. Fortunately, there were no serious injuries.
A loss investigation indicated that hydrogen had leaked past the diaphragm when the fan was shut down. (The diaphragm had been installed about a year before the explosion as a replacement for another leaky diaphragm.) Ignition of the resulting hydrogen-air mixture was attributed to an electrostatic discharge caused by the motion of the diaphragm when a compressor was started downstream of the sphere. However, another possible ignition source was the 'explosion-proof' fan at the top of the sphere.
*Hydrogen leaks across the diaphragm may have been due to the hydrogen permeability of neoprene. Measurements of hydrogen and oxygen diffusion through neoprene and other synthetic rubber skins have indicated this is the primary cause of a series of hydrogen-filled balloon explosions in Germany.
Case Study 2: Exhaust Fan Failure: Why Operate Fans on Run & Standby?
A routine security patrol reported a strong odour of sulphur coming from a battery charging facility. The battery charging facility is used for charging the various forklift batteries for the shipping and receiving operation. The building is approximately 450 sq. ft. and has four charging stations. Emergency response was initiated, and the incident commander responded to the scene. Initial air monitoring indicated readings above the Lower Explosive Limit (LEL) for hydrogen gas. The local fire department responded and setup for the situation. Facilities personnel responded and turned power off to the building. The building was ventilated and verified to be safe by the fire department. There were no injuries or damage.
The exhaust fan for the building failed, allowing hydrogen gas to build up. A mechanical failure in the fan caused the automatic on/off sensor to overheat and shut the fan off.
The Preliminary Hazard Assessment (PHA) did not include the hazard of hydrogen build-up in the building from an exhaust fan failure. Because of this, there was no back-up exhaust system in place to keep this from becoming a problem.
The original PHA for the battery charging facility did not address the hazard of hydrogen build-up from an exhaust fan failure. The PHA will be revised to include this new information. Some additional concerns that were addressed were the addition of a vent and cooling system, a hard-wired breaker box switch, and the posting of the forklift battery charging procedures in the building. These additional concerns did not contribute to the occurrence but were identified as improvements.
The above case study highlights the need for a run and standby configuration in Hydrogen ventilation, dilution, and exhaust systems to ensure that there is always a suitable system in place. When one fan fails, the duty can be picked up by the second fan while the first is being repaired or replaced.
Normal Leakage: Lead Acid Batteries
Hydrogen leakage from lead acid batteries is normal and the procedures in place to respond to increases concentrations of hydrogen work effectively if designed correctly to lower the concentration of hydrogen gas before it becomes a potential problem. Learn more about battery room ventilation here.
Our entire range of ATEX certified fans are suitable for gas group IIC or IIB + Hydrogen applications for effective hydrogen ventilation.
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:
- listening for high pressure gas leaking such as a loud hissing sound
- using portable hydrogen detectors
- using permanently installed hydrogen detectors linked to local facility-wise audible or visible alarms. Set ar 1% by volume (25% of LFL)
- monitoring piping pressures or flow rate changes
- locating detectors where leaking hydrogen can accumulate
- ventilation, dilution, and exhaust
Download ATEX Fans for Hydrogen Exhaust Brochure[/caption]
Case Study: Absence of Ventilation, Dilution, and Exhaust Fans
A 42 ½ foot diameter sphere made of 3/16in steel stored hydrogen in a plant. The sphere was separated into two hemispheres by a neoprene diaphragm attached around the equator. The lower half, under the diaphragm stored Hydrogen, while the upper half stored air.
An explosion proof fan was situated in the upper portion to provide a slight positive pressure on top of the diaphragm.
When the plant was shut down for a local holiday, the fan on top of the hydrogen sphere was also stopped. During plant start-up two days later, an explosion occurred in the sphere. The sphere shell was torn into many sections by the explosion, and some of the sections were propelled as far as 1,200 ft. Some of these sections struck flammable liquid storage tanks and cracked the roofs of adjacent buildings. Most of the windows in the surrounding buildings were broken by the blast wave. Fortunately, there were no serious injuries.
A loss investigation indicated that hydrogen had leaked past the diaphragm when the fan was shut down. (The diaphragm had been installed about a year before the explosion as a replacement for another leaky diaphragm.) Ignition of the resulting hydrogen-air mixture was attributed to an electrostatic discharge caused by the motion of the diaphragm when a compressor was started downstream of the sphere. However, another possible ignition source was the 'explosion-proof' fan at the top of the sphere.
*Hydrogen leaks across the diaphragm may have been due to the hydrogen permeability of neoprene. Measurements of hydrogen and oxygen diffusion through neoprene and other synthetic rubber skins have indicated this is the primary cause of a series of hydrogen-filled balloon explosions in Germany.
Case Study 2: Exhaust Fan Failure: Why Operate Fans on Run & Standby?
A routine security patrol reported a strong odour of sulphur coming from a battery charging facility. The battery charging facility is used for charging the various forklift batteries for the shipping and receiving operation. The building is approximately 450 sq. ft. and has four charging stations. Emergency response was initiated, and the incident commander responded to the scene. Initial air monitoring indicated readings above the Lower Explosive Limit (LEL) for hydrogen gas. The local fire department responded and setup for the situation. Facilities personnel responded and turned power off to the building. The building was ventilated and verified to be safe by the fire department. There were no injuries or damage.
The exhaust fan for the building failed, allowing hydrogen gas to build up. A mechanical failure in the fan caused the automatic on/off sensor to overheat and shut the fan off.
The Preliminary Hazard Assessment (PHA) did not include the hazard of hydrogen build-up in the building from an exhaust fan failure. Because of this, there was no back-up exhaust system in place to keep this from becoming a problem.
The original PHA for the battery charging facility did not address the hazard of hydrogen build-up from an exhaust fan failure. The PHA will be revised to include this new information. Some additional concerns that were addressed were the addition of a vent and cooling system, a hard-wired breaker box switch, and the posting of the forklift battery charging procedures in the building. These additional concerns did not contribute to the occurrence but were identified as improvements.
The above case study highlights the need for a run and standby configuration in Hydrogen ventilation, dilution, and exhaust systems to ensure that there is always a suitable system in place. When one fan fails, the duty can be picked up by the second fan while the first is being repaired or replaced.
Normal Leakage: Lead Acid Batteries
Hydrogen leakage from lead acid batteries is normal and the procedures in place to respond to increases concentrations of hydrogen work effectively if designed correctly to lower the concentration of hydrogen gas before it becomes a potential problem. Learn more about battery room ventilation here.
Our entire range of ATEX certified fans are suitable for gas group IIC or IIB + Hydrogen applications for effective hydrogen ventilation.