- PAMS
- Partial pressure
- Particle counter
- Particle detector
- Parts Per Billion (PPB)
- Parts Per Million (PPM)
- Pascal
- Permissible Exposure Limits (PEL)
- PGVM
- Phyrophoric gas
- Physical hazard - chemical
- Physical Vapour Deposition (PVD)
- Physikalisch - Technische Bundesanstalt (PTB)
- Piston cylinder
- Poison
- Polymerization
- POU
- Pressure
- Primary Reference Material (PRM)
- Process accuracy
- Proof pressure
- PSIA
- PSIG
- Pulse Discharge Photo Ionisation Detector (PDPID)