Safety and hydrogen
The properties of hydrogen
Hydrogen is highly flammable and explosive under certain conditions. Hydrogen is colorless and odorless. The hydrogen flame can become extremely hot. The burning hydrogen flame is almost invisible during the day due to the very clean combustion. The flame only becomes visible when it comes into contact with the environment, such as due to pollution. Hydrogen is not classified as a toxic substance, but it can cause asphyxiation if the air is displaced.
Hydrogen has a relatively wide range of flammability, a lower ignition energy and a higher deflagration index when compared to conventional fuels such as gasoline and natural gas (methane). Translated into practice, this means that the risk of fire or explosion is much higher with hydrogen than with other fuels, because this substance ignites relatively much faster and also requires less energy (such as sparks) to ignite. This means that even a small leak can ignite, for example due to static electricity.
Hydrogen can ignite, explode and/or detonate in several ways:
- Deflagration: A type of fire that burns quickly and intensely, often with a loud noise.
- Detonation Explosion: A rapid, explosive combustion that occurs when a mixture of hydrogen and air is within explosive limits and a suitable energy source is available.
- Flash fire: rapidly burning fires that are often accompanied by the release of flammable liquids or gases.
- Boiling Liquid Expanding Vapor Explosions (BLEVEs: explosions that occur when a liquefied gas, such as hydrogen, is heated and there is a path to the environment.
- Jet Fire – a high temperature flame in a specific direction.
- (Unconfined) Vapor Cloud Explosion ((U)VCE): a flammable gas cloud that can ignite until the concentration of the gas cloud falls below the lower flammable limit (LFL).
This lower flammability limit is a concentration of >4% in air.
Hydrogen requires relatively little energy to ignite. Ignition can arise from various ignition sources, such as electrical equipment, lighting, pollution in the installation and natural causes (lightning strike). When compressed hydrogen leaks from a high-pressure source, it can ‘heat up’ (self-heating), where the pressure under which the gas is released already provides sufficient energy for hydrogen to ignite. This means that hydrogen leakage has a higher risk of causing a flame and a so-called thermal explosion.
Safety aspects relating to the use of hydrogen in
confined spaces
‘Is hydrogen the way forward, or will it be electricity after all?’ A frequently asked question
with regard to mobility as well as to the supply of energy to households and industry. Nobody knows the answer for sure, and it is within the context of this report also less relevant.
Whatever the future brings us (perhaps a mix of these two or even more options), it will be
necessary to evaluate the safety risks in order to ensure that a solution is developed and
implemented. That development falls largely under the responsibility of market participants,
with the government’s role being to create the necessary frameworks. Some of these
frameworks may, or perhaps must, be established by the Dutch Safety Regions. The Safety
Regions are safety advisory bodies to the competent authorities, boasting knowledge in the
field of building and environmental safety, incident development and incident management.
The safety of hydrogen in confined spaces certainly falls under this remit. Confined spaces
are spaces that are largely shielded from the environment, meaning that (a)typical
distribution patterns may occur and any hydrogen released within them may accumulate.
This study reviews the specific safety aspects associated with the release of hydrogen in
confined spaces. It provides information that advisors at the Safety Regions can use when they are consulted about projects and developments in relation to various applications of hydrogen in confined spaces. The information is structured according to the logical sequence (chronology) of a hydrogen incident scenario: release of hydrogen, its dispersion and the associated potential risks. For each of these ‘phases’ in the development of the incident scenario, measures are listed that the Safety Regions can refer to in their advisory reports.
Many organisations have a knowledge base available regarding some aspects of hydrogen safety. The beauty of this report is that it brings the various knowledge components together
in one place. I thank the experts of the network operators and Safety Regions for their contribution to this document. Click here to read the Report
Gas leakage at storage tanks
Hydrogen gas leaks are often caused at points such as couplings, gaskets and screw connections. Leaks can result in fire or explosion, which can lead to more serious consequences. Hydrogen leakage from storage tanks can occur as a result of defective equipment, inadequate maintenance of installation parts, tank ruptures, corrosion and/or release through a pressure relief valve.
During maintenance, it is also important to pay attention to correct sealing and correct compliance with all checks and procedures, such as a method for screwing procedures. Prior maintenance, extra attention should also be paid to ‘de-fuelling’ the installation, whereby correct flushing (purge) is important to remove remnants of hydrogen gas from the system before opening it. Robust procedures and training of staff in dealing with installations containing high-pressure hydrogen gas are also important here.
Design choices and equipment fail
Hydrogen can build up in systems when there are dead-end installation/pipe components, increasing the risk of ignition and explosion. Leakage at flanges can lead to jet fire scenarios. It is rare for a flammable gas cloud of hydrogen to form from storage tanks, given the rapid ignition of hydrogen gas when released under high pressure.
In addition, attention should be paid to the design material from which the installations and pipes are constructed, to ensure that there is sufficient compatibility between hydrogen and material with regard to operational conditions (such as pressure and temperature). If the correct material is not chosen, embrittlement of the installation parts can occur.
In systems where pressure differences are used, attention must also be paid to the risk of backflow between the different installations.
Intake of air must be prevented in storage tanks for hydrogen gas, as an explosive mixture of hydrogen and oxygen (from air) can be formed. This can lead to explosions.
The location of larger storage tanks for compressed hydrogen gas should be chosen carefully, with attention to risks to and from the internal and external environment of the business location.
When storing hydrogen under high pressure, there is a risk of overpressure, which can cause damage to equipment and installations. For storage tanks for hydrogen gas under high pressure, it is important to take sufficient safety measures, including pressure safety valve (to mitigate overpressure scenarios) and critical safety equipment (such as alarms and interlocks).