The terms 'normative' and 'informative' are commonly used in IEC and other derivative standards to define applications of annexes. A normative annex is an integral part of a Standard which requires mandatory compliance, whereas an informative annex is for information and guidance only, compliance of which is optional.
A good example of this was when a third party review queried the design of a gas anaylyzer shelter. The query states that the analyzer shelter is not adequately ventilated creating a Zone 1 as per AS/NZS 60079.10.1-2009 Table ZA.1 - Ventilation Criteria Item 2.a to quote
(a) Within a structure having no more than three walls and where all walls have continuous or virtually continuous ventilation openings along their full length comprising not less than 0.4 m high effective opening at the bottom, 0.3 m high effective opening at the top of the walls and 0.3 m virtually continuous effective opening at the highest part of the roof
The designer's explanation was that Annex ZA was informative rather than normative. A more detailed analysis was performed for the shelter and have indicated that the gas release was very small creating only a low and easily diluted gas up to a negligible extend by ambient air movement. Given this scenario, it was confirmed that the shelter ventilation will be assessed as medium degree with good availability. This analysis will make the gas analyser shelter to be classified only as Zone 2.