Common definitions and terms used for hydrogen and hydrogen systems. These are typical across Australian and international codes and standards AS, IEC, ISO
Terms and definitions for hydrogen and hydrogen systems vary across different jurisdictions, standards, industries, hydrogen applications and manufacturers. The definitions provided below have been sourced from the most commonly used standards, codes and publications. When using a definition from a code or standard it must be used for the specific application of that code or standard. For example:
Normal Temperature and Pressure (NTP) is normally referred to as 20°C (293.15 K) and 1 atm (101.325 kPa). However, the temperature has not been harmonised across all international standards relating to hydrogen and may be read as 15°C, 20°C or (25°C – scientific)
This glossary from the – A TECHNICAL INTRODUCTION TO HYDROGEN & HYDROGEN SYSTEMS course.
For full course details and module prices – https://atagateway.com.au/courses/
A
Absolute zero
Minus 273.52°C, (0 Kelvin, 0 K) It is commonly thought of as the lowest temperature possible and it is the temperature where fundamental particles of nature have minimum vibrational motion.
Absorbed
To be taken and held through the formation of bonding interactions within the bulk of the material.
Acidic
A chemical species with a pH lower than 7 that donates protons or hydrogen ions and/or accepts electrons.
Active electrode area
Also known as the effective electrode area is geometric area of the electrode where the electrochemical reaction takes place.
Active hybrid system
A hybrid system equipped with a DC/DC converter between the fuel cell and the battery, adjusting the voltage of each power source to the bus voltage and managing the power sharing between each power source.
Adiabatic
Is a type of thermodynamic process that occurs without transferring heat or mass between the thermodynamic system and its environment.
Adsorption
The process by which a solid holds molecules of a gas or liquid.
Alkaline
Refers to an aqueous solution having a pH greater than 7 that produces hydroxide ions (OH-) in a solution.
Approved
Acceptable to the authority having jurisdiction (AHJ).
AS:62282.3.300
Area-specific resistance (ASR)
The internal resistance of any component of a cell or a stack, per unit length.
Atomic Hydrogen
Single hydrogen atom (H)
Authority Having Jurisdiction (AHJ)
An organisation, office, or individual responsible for enforcing the requirements of a code or standard, or for approving equipment, materials, an installation or a procedure.
AS:62282.3.300
Auto ignition temperature
The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark.
Auxiliary load
The power consumed by auxiliary machines and equipment such as balance of plant (BOP) necessary to operate a fuel cell power system or electrolyser system.
AWE
Alkaline water electrolysis
B
Balance of Plant (BOP)
The balance of plant is the supporting and auxiliary components based on inputs and out puts or site specific requirements and integrated into a comprehensive fuel cell power system, electrolyser system, reversable fuel cell power system or Electric Energy Storage (EES) system using hydrogen.
Bar
A unit of measurement, used for pressure and is equal to 100 kPa or 1 atmosphere (10m head of water)
Battery
An electrochemical energy storage device that provides energy input to support parasitic loads and/or provides electric energy output.
Battery Energy Storage System BESS
An electrical energy storage system with an accumulation subsystem based on batteries fitted with secondary cells.
Boil off gas. (BOG)
Heat transfer to cryogenic liquid hydrogen systems can lead to boil-off, causing hydrogen to evaporate.
Boiling point
The temperature at which a substance changes state from a liquid to a vapour / gas.
Buoyancy
Vertical force exerted on a body of less dense gas by the surrounding heavier static gas, typically air
Built in Hydrogen Generator appliance
A hydrogen generator intended to be installed in a cabinet, in a prepared recess in a wall, or in a similar location.
AS:22734
Bus bar
Stack terminal is the output terminal at which electric power is supplied from a fuel cell stack.
IEC 62282.2.100
C
Capacitance
The ability of a component or circuit to collect and store energy in the form of an electrical charge.
Capacitors
Energy-storing devices available in many sizes and shapes.
Catalyst
A substance that increases a reaction rate without being consumed itself.
Cell
A single cell that is basic unit of an electrochemical device such as an electrolyser cell, a fuel cell or reversible fuel cell which consists of a negative electrode, an electrolyte, and a positive electrode.
Cell Stack
multiple single electrolyser cells or fuel cells clamped together in series to form a cell stack.
CHSS
Compressed Hydrogen Storage system for a FCEV
Cell voltage
Voltage between the terminals of an electrochemical cell
IEC 60050-111:1996
Cold state
The state of a fuel cell power system or electrolyser at ambient temperature with no power input or output.
Combustible material
An item capable of being ignited and burned.
AS:62282.3.100
Combustion
A chemical reaction between substances, usually including oxygen and usually accompanied by the generation of heat and light in the form of flame.
Commercial use
The use of hydrogen equipment by laymen in non-manufacturing business facilities such as stores, hotels, office buildings, educational institutes, filling stations, warehouses, and other non-residential locations.
AS:22734
Component
Any part of a complete item or system
Compression
The act of pressing something into a smaller space or putting pressure on it from different sides until it gets smaller.
Compression force
(Axial load) The compressive load applied to the single cell or the end plates of a planar fuel cell or electrolyser stack to ensure electric contact and/or gas tightness. The compression force is in practice expressed in Newtons (N).
Conductor
Materials that permit electrons to flow freely from particle to particle.
Confinement
Physical restriction, sufficient to influence the combustion process or to facilitate the accumulation of hydrogen
Consumer piping
The system of pipes fittings, components and equipment, which conveys gas from the outlet of the gas supply meter to the appliance inlet and may or may not include the billing meter.
Continuous operating conditions
The operating conditions within which a system is designed to operate within specified performance limits.
Cryogenic
Temperatures below -150°C.
Current
Electric current is the rate at which electric charge flows past a point on the electric circuit. Typically referred to in Amps
Current collector
An electronically conductive material in a cell/stack assembly unit that collects/conducts electrons from/to the electrodes.
Current density
The current per active area of the electrode.
D
DC -DC converters
A solid state device to convert a low DC voltage to a higher one, or vice versa. Used to connect electrical equipment to ensure compatibility whilst maximising efficient transfer of power. For example, to control voltage and current to maximise efficiency and product/process gas output in water electrolysis.
DC output current
Output current that can be continuously supplied to the load side.
DC output power
Output that can be continuously supplied to the load side. That is expressed as a product of output voltage and output current.
DC output voltage
Output voltage that can be continuously supplied to the load side.
Delivered power
For mobility purposes, the current and voltage delivery requirements of the vehicle at various intervals as necessary in order to maintain acceptable plant performance.
Design pressure
The highest pressure that may occur under any and all operating modes, including steady state and transient.
AS:62282.3.100
Detonation
Is a type of combustion involving a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it.
Diffusivity
A measure of the rate at which particles or heat or fluids can spread.
Dipole- dipole bonds
Intermolecular forces that occur between polar molecules, while hydrogen bonding is a type of attraction force between two atoms of two different molecules. All hydrogen bonds are dipole-dipole interactions. However, please note that not all dipole-dipole interactions are hydrogen bonds.
Discharge water
Water discharged from a fuel cell power system or electrolyser including waste-water and condensate.
Distribution pipeline
A system of mains and service lines that convey natural gas from the transmission pipelines at the (city gate) to the inlet of the consumer gas meter for residential dwellings and businesses. Distribution pipelines operate at a relatively low pressure, and may or may not include the billing meter.
Dynamic pressure
The pressure of fluid or liquid that has velocity or is flowing, as opposed to static pressure where the fluid or liquid is stationary.
E
EES system (Electric energy storage system)
An installation with defined electrical boundaries, comprising at least one EES, whose purpose is to extract electric energy from the electric power system, store this energy in some manner and inject electric energy into the electric power system and which includes civil engineering works, energy conversion equipment and related ancillary equipment.
62282.8.201
EES system using hydrogen
An EES system comprising at least one EES using hydrogen, whose purpose is to extract electrical energy from the electric power system, store this energy as hydrogen and inject electric energy into a power system, using hydrogen as a fuel.
62282.8.201
Electrochemical cell
An assembly of electrodes, fluid containment, flow means, and electrical current conduction means that may include product gas separation membranes and may be arranged as single unipolar cells or in bipolar cell stacks within or without a process containment vessel, for the purpose of producing hydrogen and or oxygen from water.
AS:22734
Electrode gas
The gas present at the positive or negative electrode.
Electrolyser
An electrochemical device using DC electricity to drive a chemical reaction that would not otherwise occur spontaneously. A water electrolyser splits water or steam to hydrogen and oxygen by electrolysis.
Electrolyser conditioning
A preliminary step of treatment that is required to properly operate an electrolyser and is usually realized by following a protocol specified by the manufacturer.
Electromagnetic disturbance (EMD)
An electromagnetic phenomenon that may degrade the performance of a device, equipment or system, or adversely affect living or inert matter.
AS:62282.3.100
Electromagnetic interference (EMI)
The degradation of the performance of an equipment, transmission channel or system caused by an electromagnetic disturbance.
AS:62282.3.100
Electropedia
The free dictionary of electrical and electronic terminology and equivalent terms in 14 languages from the IEC.
Embrittlement / hydrogen induced fatigue
The hydrogen caused deterioration of the mechanical properties of metallic materials and alloys.
Emergency
Unintended circumstance, bearing clear and present danger to personnel or property, which requires an immediate response.
Emergency shut down
To control system actions, based on process parameters, taken to stop the hydrogen system and all its reactions immediately to avoid damage to equipment and or persons.
AS:62282.3.100
Endothermic
A chemical reaction that absorbs heat from its environment. A substance that is undergoing an endothermic reaction feels cold when touched.
Energy density
The amount of energy stored in a given system or region of space. Energy density can be measured in energy per volume or per mass. The energy density of gases can be expressed as Higher Heating Value (HHV) or Lower Heating Value (LHV). This energy can be expressed in Watts or Joules.
Energy efficiency of an EES system
useful energy output at the primary POC divided by the requested energy input by the EES system, including all parasitic and auxiliary energy needed to run the EES system and evaluated during EES system operation with the same final state of charge as the initial state of charge.
Enriched oxygen atmosphere
A gas that contains a volume fraction of more than 23.5% oxygen with the remainder of its components being inert.
AS:22734
Exhaust
Gases removed from a hydrogen system and not reused.
AS:62282.3.300
Exhaust system
A gas conveying system for moving gases from a source to a point of discharge.
AS:62282.3.300
Exothermic
A chemical reaction that releases heat to its environment. A substance undergoing an exothermic reaction feels hot when touched.
Explosion
A rapid expansion in volume associated with an extremely vigorous outward release of energy.
F
Fire prevention
Measures directed toward avoiding the inception of fire.
AS:62282.3.300
Fire protection
Methods of providing for fire control or fire extinguishment.
AS:62282.3.300
Fire risk evaluation
A detailed engineering review of a plant’s construction features and operating processes conducted to ensure that applicable fire prevention and fire protection requirements for safe guarding life and physical property are met.
AS:62282.3.300
Flame length
Flame length is the distance measured from the average flame tip to the middle of the flaming zone at the base of the fire. It is measured on a slant when the flames are tilted due to effects of wind and slope.
Flame speed
The flame speed is the measured rate of expansion of the flame front in a combustion reaction.
Flame temperature
The temperature reached by a flame.
Flashback
Where a gas flame moves ‘upstream’ into hoses, regulators and even gas bottles and cylinders. It can result in serious injury and equipment damage.
Flash Gas
In liquefaction, flash-gas is gas produced spontaneously when the condensed liquid is subjected to boiling.
Flash point
The flashpoint is the lowest temperature, at which the fuel produces enough vapours at its surface to form a flammable mixture with air.
Flue gas vent
A passageway for conveying vent gas from the utilisation equipment or their vent connectors to the outside atmosphere.
AS:62282.3.100
Fuel cell power system
A generator system that uses one or more fuel cell modules to generate electric power or electric power and heat.
Fuel cell stack / module conditioning
A preliminary step of treatment that is required to properly operate a fuel cell stack/module and is usually realized by following a protocol specified by the manufacturer.
fuel cell system electric efficiency
The ratio of the average electric power output of a fuel cell power system at a given duration to the average fuel power fed to the same fuel cell power system at the same duration.
Fuel cell/battery hybrid system
A fuel cell power system combined with a battery, for delivering useful electric power. The fuel cell power system can deliver electric power, charge the battery, or both. The system can deliver and accept electric energy.
Fuel consumption
The volume or mass of fuel consumed by a fuel cell power system under specified operating conditions.
Fuel input
The amount of fuel supplied to the fuel cell power system.
G
Gas carrying circuit
An assembly of parts of the hydrogen system that carry or contain supply gas or process (product) gas.
AS:62282.3.100
Gauge pressure
The term gauge pressure is used when the pressure in the system is greater than the local atmospheric pressure. Gauge pressure can be measured where one side of the gauge is exposed to the pressure media that is to be measured, while the other side is exposed to the ambient atmospheric pressure.
Gravimetric Energy Density
The amount of energy that can be released by a given mass (weight) Also known as Mass Energy Density. This energy can be expressed in Watts or Joules
H
Hydrogen atom – Atomic hydrogen
H2
Molecular hydrogen in the gas phase.
H2O
Water molecule = two hydrogen atoms and one oxygen atom.
Hazard
A potential source of harm.
AS:22734
Hazardous area
An area in which an explosive atmosphere is present or may be expected to be present in quantities such as to require special precautions for the construction, installation and use of electrical apparatus. AS:22734
Hazardous zone
Any work area or space where combustible dust, ignitable fibres, or flammable, volatile liquids, gases, or mixtures are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures as defined by IEC 60079-10-1.
HHV – Higher Heating Value
The HHV of hydrogen is 141.9 MJ / kg
Also known gross calorific value or gross energy of a fuel is defined as the amount of heat released by a specified quantity (initially at 25°C) once it is combusted and the products have returned to a temperature of 25°C, which considers the latent heat of vaporization of water in the reaction products and the heat is recovered by condensing the water vapour.
Homeostasis
In biology, homeostasis is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits.
Hydride
Compound containing hydrogen and another element.
SA TR 15916:2021
Hydride canister
A single complete hydrogen storage system, including shell, metal hydride, PRD, shut-off valve and other appurtenances (e.g. for heat exchange, to prevent excessive stress on the shell walls due to hydride expansion, etc).
ISO/TS 16111:2006 This standard has been withdrawn and replaced with AS ISO 16111:2020
Hydrocarbon
An organic chemical compound that is composed exclusively of hydrogen and carbon atoms.
Hydrogen absorbing alloy
A material capable of combining directly with hydrogen gas to form a reversible metal hydride.
ISO/TS 16111:2006 This standard has been withdrawn and replaced with AS ISO 16111:2020
Hydrogen bonding
Type of attraction force between two atoms of two different molecules while dipole-dipole bonds are intermolecular forces that occur between polar molecules. All hydrogen bonds are dipole-dipole interactions. However, please note that not all dipole-dipole interactions are hydrogen bonds.
Hydrogen colour coding
A certification system used to identify the source and environmental impacts of hydrogen.
Hydrogen embrittlement
Deleterious changes in the ductility properties of a metal that exposure to hydrogen can produce
Hydrogen Evolution Reaction (HER)
Where hydrogen is formed at the cathode in water electrolysis.
Hydrogen fuel quality
Also referred to as hydrogen purity or hydrogen quality describes the presence of impurities in hydrogen when used as a fuel gas.
I
Indoor installation
A hydrogen system completely surrounded and enclosed by walls, a roof and a floor.
AS:62282.3.300
Industrial use
The use of hydrogen equipment by qualified and experienced personnel in a controlled manufacturing or processing environment.
AS:22734
Infrared
Infrared light is a type of light that feels warm but cannot be seen and has a wavelength just greater than that of the red end of the visible light spectrum but less than that of microwaves.
Installation
The location where a hydrogen system is sited as a unit or built as an assembly.
The act to install a hydrogen system.
AS:62282.3.300
Integrated fuel cell power system
A complete system of fuel cell components and parts that are incorporated into the industrial truck with the various parts of the system potentially distributed throughout the truck.
Inversion temperature
The critical temperature above which a gas that is expanded will experience a temperature increase and below the inversion temperature that gas will experience a temperature decrease. The change in temperature is referred to as the Joule Thomson Effect.
Ion transport medium
A medium that provides ionic transport within a cell. (Electrolyte)
AS:22734
J
Joule Thomson effect
When most gases are subjected to an adiabatic expansion process, where no heat is exchanged with the surroundings, it loses its temperature and feels cold to touch. This cooling effect of gas expansion is known as the ‘Joule Thomson effect’. The temperature at which cooling or heating occurs is called the inversion temperature.
K
Kelvin K
K is the same temperature as -273.15°C. The SI base unit of thermodynamic temperature, equal in magnitude to the degree Celsius.
kWh
1000 Watts, measurement of power – Volts x Amps = kWh
L
Large fuel cell power system
A fuel cell power system having a net electrical output of more than 10 kW.
AS:62282.3.300
LH2
Molecular hydrogen in the liquid phase.
LHV – Lower Heating Value
The LHV of hydrogen is 120.1 MJ / kg
Also known as net calorific value of a fuel is defined as the amount of heat released by combusting a specified quantity (initially at 25°C) and returning the temperature of the combustion products to 150°C, which assumes the latent heat of vaporization of water in the reaction products is not recovered.
Load leveling system
An electric or electronic device able to balance the power flow among fuel cell stack, secondary batteries and load. A method where during periods of high-power demand that secondary batteries can provide additional electrical power to the energy provided from the fuel cell stack to meet electrical demand. During periods of lower electrical power demand, power from the fuel cell stack can be stored in the secondary batteries.
Lower flammability limit (LFL)
Or Lower Explosive Limit (LEL) is the minimum concentration of fuel in a fuel-air mixture where a combustion can be ignited by an ignition source.
M
Mass Energy Density
The amount of energy that can be released by a given mass (weight) Also known as Gravimetric Energy Density. This energy can be expressed in Watts or Joules
Material compatibility
The ability of a material to exhibit reliable mechanical integrity and a low probability of leaks in a given hydrogen application.
Maximum allowable working pressure (MAWP)
Is the maximum pressure permissible in a vessel or system at the temperature specified for the pressure
AS:22734
Maximum developed pressure (MDP)
Is the highest gauge pressure for a hydride canister at rated capacity and equilibrated at maximum surface temperature.
ISO/TS 16111:2006 This standard has been withdrawn and replaced with AS ISO 16111:2020
Maximum operating pressure (MOP)
Is the maximum pressure that can be expected by the pressure containing components when a hydrogen system is functioning within its designed and controlled parameters, including anticipated transients.
AS:22734
Maximum voltage
The highest cell/stack assembly unit voltage specified by the manufacturer.
Mechanical ventilation
The replacement of air inside an enclosure with fresh air accomplished by a mechanical device such as a fan, to prevent or eliminate hazardous concentrations of hydrogen.
AS:22734
Melting point
The temperature at which a substance changes state from solid to liquid.
Metal Hydride
A solid material formed by reaction between hydrogen and hydrogen absorbing alloy.
ISO/TS 16111:2006 This standard has been withdrawn and replaced with AS ISO 16111:2020
Micro flame
A diffusion flame observed under a normal gravitational field; however, the form becomes small-spherical. This is because the buoyancy force due of gravity becomes negligible compared to forced convection.
researchGate abstract
Micro fuel cell power system
An alternative to batteries for use as a power source for mobile devices.
Minimum electric power output
The minimum power output, at which a fuel cell power system is able to operate continuously at a steady state.
Minimum ignition energy (MIE)
Is the lowest energy required to ignite the flammable material in air or oxygen.
Minimum voltage
The lowest cell/stack assembly unit voltage specified by the manufacturer.
N
Natural ventilation
The replacement of air inside an enclosure with fresh air accomplished exclusively by a natural draft caused, for example, by the effects of wind, temperature gradients or buoyancy effects, to prevent or eliminate hazardous concentrations of hydrogen.
AS:22734
Negative electrode – Fuel cells and electrolysers
The electrode at which fuel (reductant) gas is consumed or produced as opposed to the positive electrode at which oxygen is consumed or produced
Noise Level
The sound pressure level produced by a system measured at a specified distance in all operation modes.
Nominal Energy Storage capacity
The value of the energy capacity by which the EES system is designated and identified
Non-combustible
A substance not capable of supporting combustion in accordance with ISO1182 or an equivalent method.
AS:62282.3.300
Normal metres cubed (Nm3)
For gases in Australia, Nm3 is 1000 litres, measured at an absolute pressure of 101.325 kPa (1.013 bar or atmospheric pressure at sea level) and 293.14K (20°C) The definition of Nm3 can vary and readers should be alert to these variations.
AS TR 15916:2021
Normal operation
All operating and non-operating modes encountered during product use that are not the result of a malfunction or failure.
Normal release
limited localized volumes of hydrogen concentrations released during normal operation that may include fuel cell purge.
Normal Temperature and Pressure (NTP)
Is defined as 20°C (293.15 K) and 1 atm (101.325 kPa). However, the temperature has not been harmonised across all international standards relating to hydrogen and may be read as 15°C, 20°C or (25°C – scientific)
O
Odorant
Is an odorous substance; especially one added to a dangerous odorless substance to warn of its presence.
Ohm
The standard unit of electrical resistance in the International System of Units (SI ). – Volts ÷ Amps = Ohms
Ohms law
Ohm’s law states that the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions and temperatures remain constant. Therefore, watts (power) divided by volts (electromotive force) equals amps (current). Volts divided by amps equals resistance (Ohms).
Operating history
A record of the operating conditions of the system.
Operating mode
The condition during which the system is performing at least one application.
Operating procedure
Set of operational tasks carried out to achieve functional goals in a system.
Ortho hydrogen
When the rotation (spins) of the protons of both hydrogen atoms in a H2 molecule are in the same direction. The Ortho form of hydrogen is more stable than the para form at room temperature and under normal atmospheric conditions. In ortho hydrogen molecules there is a higher energy state than for para hydrogen.
Outside or outdoor installation
A hydrogen system installation that is not an indoor installation. When permitted by local or national regulations, an open-air structure with partial roof and or walls may be considered an outdoor installation.
AS:62282.3.300
Oxidant
Is a reactant that oxidizes or removes electrons from other reactants during a redox reaction
Oxygen Evolution Reaction (OER)
Where oxygen is formed at the anode in water electrolysis.
P
Para hydrogen
When the rotation (spins) of the protons of both atoms in a H2 molecule are in the opposite direction. With decreasing temperature, the probability of a molecule being in a para-hydrogen state increases because of its lower energy.
Passive state
State of a hydrogen system when fuel and oxidant systems have been purged with steam, air or nitrogen or per manufacturers instruction.
AS:62282.3.100
PEMWE
Proton Exchange Membrane Water Electrolysis
Phase change
When a substance changes from a solid to a liquid or from a liquid to a gas.
Point of connection for an EES System
POC The reference point on the electric power system at which an EES system is connected.
Point of connection for an EES system using hydrogen
The point where an EES system using hydrogen is connected to a supply/extraction exterior to the system.
62282.8.201
Portable fuel cell power system
A fuel cell power system that is not intended to be permanently fastened or otherwise secured in a specific location.
AS:62282.3.300
Portable hydrogen generator
A hydrogen generator that is not intended to be permanently fastened in a specific location and can be carried easily by a person.
AS:22734
Positive electrode – fuel cells and electrolysers
The electrode at which oxygen is consumed or produced as opposed to the negative electrode at which fuel (reductant) gas is consumed or produced.
Power conditioning system
An electric or electronic system able to convert generated power in the requested output conditions.
Pre generation state
State of a fuel cell power system being at sufficient operating temperature and in such an operational mode, with zero electrical output power, that the fuel cell power system is capable of being promptly switched to an operational state with substantial electrical active output power.
AS:62282.3.100
Pressure
A force exerted by the substance per unit area on another substance.
Pressure bearing component
A part subject to a positive internal pressure of 100kpa or greater.
AS:22734
Pressure relief device (PRD)
A pressure and/or temperature activated device used to prevent the pressure from rising above a predetermined maximum and thereby prevent failure of a pressurized part or system.
Properties
The qualities and characteristics of a substance that describe and identify it.
Purge
A protective operation to remove gases and or liquids, such as fuel. Hydrogen, air or water, from a hydrogen system.
AS:62282.3.100
Purge gas
A gas used to maintain protective pressurisation or to dilute flammable gas or vapour to a concentration well below the lower flammability limit.
AS:22734
Purging
The passage of sufficient volume of purge gas through a pressurised enclosure and its ducts, before the application of voltage, to the apparatus, to reduce any ignitable (flammable) gas atmosphere to a concentration well below the lower flammability limit.
AS:22734
Q
Quenching distance
The distance between two parallel plates (flat walls) that will just quench (extinguish) the flame front of a particular fuel oxidant mixture. It is smaller than the quenching diameter in cylindrical tubes.
R
Radiant heat
Also known as Thermal radiation -Heat energy transmitted by electromagnetic waves. When radiant energy impinges on a solid surface it can cause a temperature rise on that surface. (absorption).
Rated charging pressure (RCP)
The maximum pressure allowed to be applied to the hydride canister or cylinder for refilling.
Rated power
maximum continuous electric power output that a fuel cell power system is designed to achieve under normal operating conditions specified by the manufacturer.
Recovered heat
Thermal energy that has been recovered for useful purposes.
AS:62282.3.100
Reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that “donates” an electron to an electron recipient
REDOX reaction
Occurring in water electrolysis and electrochemical fuel cells, Redox is short for Reduction and Oxidation. The simplest way to understand a redox reaction is to use the term OIL RIG. OIL equals Oxidation Is Loss of electrons. RIG equals Reduction Is Gain of electrons.
Reduction reaction
Is a reaction involving the gain of electrons.
Reference environmental conditions
Physical conditions, such as ambient temperature range, pressure range, radiation range, humidity range and chemical spray range, under which a system is designed to operate continuously.
Reformer
A reactor to produce a hydrogen rich gas mixture from a raw fuel.
AS:62282.3.100
Regenerated power
For mobility purposes, the electro-dynamic power in which the energy produced by the motors is fed into the contact line or into energy storage on-board devices.
Residential use
The use of hydrogen equipment by laymen in private households (non-commercial and non-industrial).
AS:22734
Reverse Joule Thomson effect
At room temperature, all gases except hydrogen, helium, and neon cool upon expansion. At some temperatures the reverse can happen, and the gases will heat up on expansion.
Reversible cells
Produce electricity from hydrogen and oxygen and generate heat and water as by products, Reversible fuel cell systems can also use electricity to split water into oxygen and hydrogen fuel by water electrolysis.
Reversible metal hydride
A metal hydride for which there exists an equilibrium condition where hydrogen absorbing alloy, hydrogen gas and the metal hydride co-exist.
ISO/TS 16111:2006 This standard has been withdrawn and replaced with AS ISO 16111:2020
Reversible mode
(Regenerative mode) The operation mode of a reversible cell which alternates between fuel cell mode and electrolysis mode.
Risk analysis
The systematic use of available information to identify hazards and to estimate the risk.
Risk assessment
The overall process comprising a risk analysis and a risk evaluation.
Risk evaluation
The procedure based on the risk analysis to determine whether a tolerable risk has been achieved.
Roundtrip electrical efficiency
The electric energy discharged measured on the primary point of connection (POC) divided by the electric energy absorbed, measured on all the POC (primary and auxiliary), over one EES system standard charging/discharging cycle in specified operating conditions.
62282.8.201
Rupture disk
Also known as a pressure safety disc, burst disc, bursting disc, or burst diaphragm, is a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from over pressurization or potentially damaging vacuum conditions.
S
Safety control
Automatic controls and interlocks including relays, switches, sensors and other auxiliary equipment used in conjunction therewith to form a safety control system, which is intended to prevent unsafe operation of the controlled equipment.
Safety critical component
A component, device, circuit, software or similar part whose failure would affect the safety of a system.
Safety Shutdown
To control system actions, based on process parameters, taken to stop the hydrogen system and all its reactions immediately to avoid damage to equipment and or persons.
AS:62282.3.100
Safety valve
A pressure relief valve actuated by inlet static pressure and characterised by rapid opening.
Sensible heat
When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat.
Service life
The duration from a system’s commissioning test to the end of its service life. Generally, service life is expressed in years or in duty cycles.
Service pressure
The nominal working pressure, as specified by the manufacturer, at a uniform gas temperature of 15 °C and full gas content. This term may relate, for example to a hydrogen pressure vessel.
Shut down time
The time required for shutdown from the rated state to the cold state of fuel cell stack or electrolyser.
Single fault condition
A condition in which one means for protection against hazards is defective or one fault is present which could cause a hazard.
AS:22734
Slush hydrogen
Slush hydrogen is a mixture of solid and liquid molecular hydrogen at the triple point temperature 0f 13.8 k and a pressure of 7.2 kPa.
Small fuel cell power system
A fuel cell power system with a rated electrical output less than 10kW, and a maximum pressure of less than 0.1MPa (gauge) for fuel and oxidant passages.
AS:62282.3.100
Small fuel cell power system
A fuel cell power system having a net electrical output up to 10 kW.
AS:62282.3.300
Solid oxide cell (SOC)
An electrochemical cell composed of three functional elements (negative electrode, solid oxide electrolyte and positive electrode).
Solid oxide fuel cell (SOFC)
A fuel cell incorporating a solid electrolyte that conducts oxygen ions.
Specific density
The ratio of the mass vs the volume of a material. Temperature used for measuring specific density can vary and readers should be alert to these variations.
Start-up energy
The total energy input during the start-up from the cold state to the rated state.
State of charge
The available capacity in a battery pack or system expressed as a percentage of rated capacity.
Static pressure
The pressure of fluid or liquid that is stationary as opposed to the pressure of fluid or liquid that has velocity or is flowing.
Stationary
A hydrogen system permanently connected and fixed in place.
AS:62282.3.300
Supply gas circuit
An assembly of parts of the fuel cell power system that carry or contain the supply gas between the gas inlet connection and the outlet of the safety shut off valves.
AS:62282.3.100
System
Assembly of components in which hydrogen is derived, stored or used. A system can include components such as storage vessels, piping, valves, pressure relief devices, pumps, vacuum subsystems, expansion, joints and gauges.
T
Test temperature
The test temperature required in a standard for hydrogen systems. Applications for required test temperatures may vary from15°C, 20°C and 25°C.
Thermal conductivity
The rate at which heat is transferred by conduction through a unit cross-section area of a material, when a temperature gradient exits perpendicular to the area.
Thermal radiation
Electromagnetic radiation emanating from material as a consequence of its temperature. From a human perspective, this is heat radiation.
AS TR:15916
Thermally activated pressure relief device (TPRD)
A pressure relief device that is activated thermally. This is not to be confused with a Temperature and Pressure Relief Valve (TPRV).
Transmission pipeline
Pipelines used to transport natural gas to customers, for use or for further distribution, and operate at very high pressures.
Triple point
Is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance co-exist. (slush hydrogen.
Turbo-expanders
Rotating devices that convert the pressure energy of a gas or vapor stream into mechanical work as the gas or vapor expands through the turbine. Turbo-expanders can be used as energy recovery devices or as a part of a thermodynamic cycle to provide low-temperature refrigeration.
U
UEG Hydrogen Technologies Training Package
Upstream of the gas meter hydrogen work, including Water electrolysis, storage, distribution, transmission, pipeline construction and maintenance, blending and safety.
Ultraviolet
Ultraviolet light has a wavelength that is beyond the violet (light purple) end of the range of colours that can be seen by humans. Light of this type causes the skin to become darker in the sun.
Upper flammability limit (UFL)
Or Upper Explosive Limit (UEL) is maximum vapor concentration in air which a mixture will burn when an ignition source is present.
Utility EES
EES system as a component of a utility grid, and which exclusively provides services to the utility grid.
V
Vent terminal
The fitting at the end of the vent pipe that directs the flue products into the outside atmosphere.
AS:62282.3.100
Volt
Is the Standard International (SI) unit of electric potential.
Volumetric energy density
The amount of energy stored in a given space. This energy can be expressed in Watts or Joules.
For hydrogen we use the HHV or the LHV.
W
Water electrolysis
A way to produce hydrogen using electrical energy to split water molecules (H2O) into H2 and O2 molecules.
Watt
The unit of electrical power equal to one ampere under the pressure of one volt. Volts x current equals watts.
Water management system
A subsystem of hydrogen system, for controlling the water and/or steam flows in the system.
Wholesale Demand Response (WDR)
The WDR mechanism allows demand side (or consumer) participation in the wholesale electricity market at any time.