CLASS I, GROUP C-D, DIVISION 2 gen.

[x-z]

Division 2?

[Lonely Knight]

Можно написать "категория", ибо это характеристика зоны (завязанная на режиме присутствия взырвоопасных веществ)

2. Division—The Division defines the probability of the
hazardous material being able to produce an explosive
or ignitable mixture based upon its presence.
a. Division 1 indicates that the hazardous material
has a high probability of producing an explosive or
ignitable mixture due to it being present
continuously, intermittently, or periodically or from
the equipment itself under normal operating
conditions.
b. Division 2 indicates that the hazardous material
has a low probability of producing an explosive or
ignitable mixture and is present only during
abnormal conditions for a short period of time.

[Lonely Knight]

Газпром считает так:
"441.2. К зонам класса 1 категории 1 (Class I, Division 1) относятся зоны, в которых:..."
http://www.tehlit.ru/1lib_norma_doc/46/46626/