1. areas with more rain, more humidity and heavier salt spray.
2. the working environment is humid and there is a place for water vapor.
3. the altitude does not exceed 2000m.
4. the working environment contains non-flammable dust such as sand and dust.
5. the working environment contains corrosive gases such as weak acids and weak bases.
6. applicable to petroleum, chemical, food, pharmaceutical, military, warehousing and other places.
7. used as command transmission and status monitoring.
