Constants & Standards

Physical constants, noise reference values, STP definitions, and standard conditions used in ASP & CSP calculations.

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Constant / Standard Value Unit Notes
Acceleration of gravity (g) 9.8 m/s² or 32.2 ft/s² m/s² or ft/s² Standard gravitational acceleration
Speed of light (c) 3.0 × 10⁸ m/s m/s Electromagnetic radiation
Planck's constant (h) 6.626 × 10⁻³⁴ J·s Quantum constant
Avogadro's number (Nₐ) 6.022 × 10²³ per gram-mole Particles per mole
Universal gas constant (R) 0.08206 L·atm/mol·K Used in PV = nRT
Molar volume at NTP (25°C, 1 atm) 24.45 L/mol Used in ppm ↔ mg/m³ conversion
Molar volume at STP (0°C, 1 atm) 22.4 L/mol Physical science STP
Constant / Standard Value Unit Notes
Density of water 1 g/cm³ = 62.4 lb/ft³ — At standard conditions
Weight density of water 62.4 lb/ft³
1 US gallon of water 8.345 lb
Air density (standard) 0.075 lb/ft³ At 70°F and 1 atm
Density of air (metric) 1.2 kg/m³ At standard conditions
Speed of sound in air 344 m/s At standard conditions
Constant / Standard Value Unit Notes
1 rad (absorbed dose) 0.01 Gray (Gy) Gy Older unit
1 rem (dose equivalent) 0.01 Sievert (Sv) Sv Older unit
1 Curie (Ci) 3.7 × 10¹⁰ Bq Bq Activity unit
1 Becquerel (Bq) 1 disintegration/second dps SI unit of activity
Constant / Standard Value Unit Notes
Velocity constant (standard air) 4005 — V = 4005√VP at 70°F, 1 atm
Ventilation STP 70°F and 1 atm — ACGIH standard for duct calcs
Constant / Standard Value Unit Notes
Reference sound pressure (p₀) 0.00002 N/m² (Pa) Threshold of hearing — dB formula
Reference acoustic power (W₀) 10⁻¹² Watts Sound power level formula
OSHA noise PEL (8-hour) 90 dB(A) Action level = 85 dB(A)
OSHA exchange rate 5 dB Halves allowable time per 5 dB
Constant / Standard Value Unit Notes
Pi (π) 3.14159 —
Natural log base (e) 2.71828 — Decay, reliability, ventilation
ln(2) 0.693 — Radioactive decay half-life
Constant / Standard Value Unit Notes
STP — Physical Science 0°C (273 K) and 1 atm — Molar volume = 22.4 L/mol
STP — Industrial Hygiene (NTP) 25°C (298 K) and 1 atm — Molar volume = 24.45 L/mol
STP — Ventilation (ACGIH) 70°F (21°C) and 1 atm — Standard for duct calculations
Constant / Standard Value Unit Notes
Base hours constant 200,000 hours

Source: Yates Safety Professional's Reference and Study Guide, 4th Ed., Appendix B