To the average non-chemist, even rendering the nomenclature of most of the 118 elements found on the Periodic Table is nearly impossible. However, hydrogen is far from obscure. The very first element on the Periodic Table due to its sole proton and atomic number of 1, hydrogen is the most abundant element in the universe, comprises about 10 percent of the weight of living organisms, has the lowest density of any crystalline solid or liquid when in the corresponding forms, and is believed to be one of the three elements produced in the Big Bang.
Accordingly, hydrogen has many applications, including being used to make ammonia for agricultural fertilizer, serve as a protective atmosphere for making flat glass, act as a pollution-free source of energy by powering fuel cells, and, once upon a time, fire balloons and airships. However, this last application ended with the Hindenburg Disaster, and hydrogen has been utilized safely in industry practices since the mid-Twentieth Century.
Regardless of its range of uses, according to CGA G-5.3-2017: Commodity Specification For Hydrogen – 7th Edition, hydrogen can be bunched into two primary types: Type I—gaseous hydrogen, and Type 2—liquid hydrogen.
There are additional means to classify hydrogen, including total hydrogen present, quality verification levels (QVLs), and fuel cell grade. Common purity nomenclature for hydrogen can be stated with respect to the number of nines. For example, 3 nines refers to the minimum hydrogen concentration of 99.9% and an impurity limit of 1000 ppm, while 4 nines would be 99.99% and 100 ppm.
Helium normally is not considered as an impurity in hydrogen, but argon, oxygen, carbon dioxide, carbon monoxide, and nitrogen are. Therefore, it is important to determine the content of these elements and molecules through suitable procedures. Such analytical procedures, as well as sampling, quality tests, and guidelines for transportation compliance for containers, are discussed in CGA G-5.3-2017.
As stated by its scope, CGA G-5.3-2017, which was developed by the Compressed Gas Association (CGA), an ANSI-accredited standards developing organization, describes the specification guidelines for gaseous and liquid hydrogen (including hydrogen for fuel cell applications).
As the seventh edition of the standard, CGA G-5.3-2017 contains some important changes from the previous version, which was published in 2011. Key changes include the addition of lot definitions, or those for the amount of a product produced during a period of time indicated by a specific code or some other identifying characteristic, and that total hydrocarbon content (THC) as methane can be determined by a gas chromatograph.
CGA G-5.3-2017: Commodity Specification For Hydrogen – 7th Edition is available on the ANSI Webstore.