Understanding Mandatory Language in Weathering and Corrosion Testing Standards

Reading technical standards can be a challenge, especially when trying to determine which parts are strict requirements and which are just recommendations. In this blog, we give some simple guidelines for understanding the sometimes-complicated language used in testing standards.

Mandatory vs Non-Mandatory Language

Standards like those used in ASTM and ISO use specific words to indicate whether something is required or optional. Words like must, shall, or will indicate a mandatory rule. For example ASTM G154 states: “The light source shall be fluorescent UV lamps.” This means that other types of light sources are not permitted.

On the other hand, words like should, may, or can suggest recommendations or possiblities, rather than strict requirements. Additionally, expressing measurements and quantities using words like typical or about means that these measurements are not strictly required. For example, ISO 4892-1 says: “A typical length and width is about 70 mm by 40 mm.” Specimens of other sizes are therefore permitted in this test. 

Mixing Mandatory and Non-Mandatory Language in Testing Standards

Sometimes, both types of language appear in the same sentence, making interpretation even harder. For example, a popular corrosion testing standard states: “The device for salt spraying shall preferably be made of a number of flat spraying nozzles...” The phrase "shall preferably" seems contradictory. In this case, our interpretation is that the word preferably makes the requirement non-mandatory.

Important Rules in ASTM and ISO Standards

• Notes in ASTM and ISO standards are usually non-mandatory. The exception is notes that appear inside a table, which are allowed to be mandatory..
• In ASTM standards, an Annex is mandatory while an Appendix is non-mandatory. An easy way to remember this: You can live without your appendix, so an Appendix isn't required.
• In ISO standards, a Normative Annex is mandatory, while an Informative Annex is non-mandatory. Think of Informative as “for your information.”

Final Thoughts

Understanding weathering testing standards and corrosion testing standards takes practice, but knowing how to interpret their language can help. Always read the entire standard carefully to avoid misunderstandings. At Q-Lab, we study a wide range of international and OEM testing standards closely to ensure our products meet the right requirements, and we’re here to help our customers navigate them too!

Do you have a question regarding language in a specific standard? Contact our team of experts today:

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