The CLC certificate concerns liability insurance in connection with damage caused by oil pollution when carrying oil. A Certificate of Insurance or Other Financial Security in respect of Civil Liability for Oil Pollution Damage. CLC is the College Leaving Certificate. Civil Liability Certificate (CLC) · Certification Services · Civil Liability for Oil Pollution Damage, 1992,. International Convention on Civil Liability for Oil Pollution Damage (CLC). It is issued by the ship's P&I insurer to the Flag State registry and they, in turn, issue a CLC Certificate to the registered owner of the tanker.