If you comply with the requirements in this regulatory position statement (RPS) you can operate air separation units without an environmental permit.
Many installations covered by the Integrated Prevention and Pollution Control (IPPC) Directive need to use process gases – typically nitrogen for inerting/dilution, but also other inert gases, oxygen and carbon dioxide. Where demand for these gases cannot be met by bottled supplies, it may be provided by dedicated air separation units (ASUs) using pressure swing absorption, cryogenic or membrane separation units.
ASUs can be found on a variety of installations including food & drink, chemical and metal works.
You will not need to apply for an environmental permit for ASUs that are directly associated to an IPPC-listed activity if you meet the requirements set out in this guidance.