Ventilation 10 : For purposes of tank entry, cleaning, or repair, the introduction of air into a tank or container to maintain an atmosphere within acceptable limits and provide the required number of air changes per hour
NFPA 326 Standard for the Safeguarding of Tanks and Containers for Entry, Cleaning, or Repair, 2005 ed. https://www.nfpa.org/assets/files/AboutTheCodes/32 6/326-F2009-ROC.pdf, (Std: Safeguarding of Tnk and Cont for Entry, Cleaning, or Repr - Amer) {298 NFC}