- Safety Data Sheet (SDS - MSDS)
- Safety Relief Valve (SRV)
- Selective Catalytic Reduction (SCR)
- Selective Non-Catalytic Reduction (SNCR)
- Self-relieving (self-venting) device
- Set pressure
- Shelf life
- Short Term Exposure Limit (STEL)
- SI system
- Single stage regulator
- Solvent
- Span gas
- Specific density, gas
- Specific gravity (SpG)
- Specific heat
- Specific heat ratio
- Specific Volume (SpV)
- Spectrometry
- Sputter deposition
- Stability - mixture
- Standard Reference Material (SRM)
- Standard Temperature and Pressure (STP)
- Standard uncertainty
- Static pressure
- Sublimination
- Supercritical Fluid Chromatography (SFC)
- Supercritical Fluid Extraction (SFE)