Pressure 11 : General. The force per unit of area. Values in this recommended practice are based on the unit of pressure derived from the International System of Units (SI), which is the pascal (Pa) or newton per square meter (N/m2)
NFPA 53 Recommended Practice on Materials, Equipment, and Systems Used in Oxygen-Enriched Atmospheres, 2004 ed. https://www.nfpa.org/assets/files/AboutTheCodes/53 /53-F2009-ROP.pdf, (Recmm Prac: on Mtrl, Equip and Sys Used in Oxy-Enriched Atm - Amer) {209 NFC}