Overview
This lecture reviews essential equations, constants, and conversions relevant to the CIH (Certified Industrial Hygienist) examination, covering ventilation, noise, radiation, general sciences, and heat stress.
Ventilation Equations
- Continuity: Q₁A₁ = Q₂A₂, where Q = flow rate and A = area.
- Conservation: Q_total = Q₁ + Q₂, and 1/k_total = 1/k₁ + 1/k₂.
- Pressure-velocity: V = 4005√ΔP (US), V = √(2ΔP/ρ) (SI).
- Effective velocity: V = Q/A.
- Losses: H = Σ(velocity head × loss coefficient).
- Changes in conditions: Q₁P₁/T₁ = Q₂P₂/T₂.
- Mixing: C = (Q₁C₁ + Q₂C₂)/(Q₁ + Q₂).
- Fan laws: Q₂ = Q₁(N₂/N₁), P₂ = P₁(N₂/N₁)², HP₂ = HP₁(N₂/N₁)³.
Noise Equations
- Sound level: dB = 20 log₁₀(P/P₀), where P = sound pressure.
- Intensity: dB = 10 log₁₀(I/I₀), I = intensity.
- Adding levels: dB_total = 10 log₁₀(Σ10^(dB_i/10)).
- Dose calculation: % = 100(D₁/L₁ + D₂/L₂ + ...).
- Exchange rate: L = 10 log₁₀(%/100) + 85 or L = 16.61 log₁₀(%/100) + 90.
General Sciences & Statistics
- Gas laws: PV = nRT.
- Standard conversions: 1 atm = 760 mmHg, 1 ft³ = 28.32 L.
- Probability and statistics: Variance σ² = Σ(x-μ)²/N, Standard deviation σ = √variance.
- Confidence intervals: 95% CI uses z = 1.96, 90% uses z = 1.645.
- Weighted mean: μ = Σ(wₙxₙ)/Σwₙ.
Heat Stress Equations
- Wet Bulb Globe Temperature (WBGT): WBGT = 0.7Tnwb + 0.2Tg + 0.1Tdb (indoors); WBGT = 0.7Tnwb + 0.3Tg (outdoors).
- Metabolic rate: Heat = (Metabolic rate - External work).
Radiation Equations
- Inverse square law: I₂ = I₁(d₁/d₂)².
- Radioactive decay: N = N₀(0.5)^(t/T½).
- Decay constant: λ = 0.693/T½.
- Half-life: T½ = 0.693/λ.
- O.D. (Optical Density): O.D. = log₁₀(I₀/I).
Constants & Conversions
- Temp: F = 9/5(C) + 32, K = C + 273.15.
- Vol: 1 ft³ = 28.32 L, 1 gal = 3.785 L.
- Mass: 1 lb = 453.6 g, 1 g = 15.43 grains.
- Pressure: 1 atm = 14.7 psi = 760 mmHg.
- Energy: 1 BTU = 1054.8 J, 1 cal = 4.184 J.
- Speed of sound (20°C): 344 m/s.
- Avogadro's number: 6.024×10²³.
- Gas constant, R: 8.314 J/mol·K.
Key Terms & Definitions
- acfm — actual cubic feet per minute (airflow at actual conditions).
- scfm — standard cubic feet per minute (airflow at standard conditions).
- WBGT — Wet Bulb Globe Temperature, a heat stress index.
- dB (decibel) — a logarithmic unit to measure sound intensity.
- T½ (half-life) — time for a radioactive substance to halve its activity.
Action Items / Next Steps
- Review actual equation sheet and familiarize yourself with variable meanings.
- Reference Table 6-2 and Figure 9-a in the ACGIH Industrial Ventilation Manual as allowed during exam.
- Practice applying these formulas to sample problems.