Certified Industrial Hygienist (CIH) — Study Guide

Certified Industrial Hygienist (CIH) — Study Guide

Credential: Certified Industrial Hygienist (CIH) Issuing body: Board for Global EHS Credentialing (BGC) — formerly ABIH (renamed 2019) Jurisdiction: United States (global recognition) Level: Professional (the senior IH credential) Prerequisites: Bachelor's degree or higher in a science/engineering field with specific IH coursework (or approved alternatives); 4 years of professional IH experience (≥50% IH duties); two professional references; application approval before examination. (Verify current BGC eligibility specifics — coursework and experience rules are detailed and change.) Exam format: 180 multiple-choice questions (150 scored + 30 unscored pilot), 5 hours, computer-based testing. (Verified via ANSI/Workcred documentation.) The exam blueprint weights the IH functional areas: anticipation/recognition, evaluation (exposure assessment, sampling, analysis), control, and management/communication. Renewal: 5-year certification maintenance cycle with continuing education/CM points (verified via ANSI/credly sources).

Why this credential matters

The CIH is the industrial-hygiene profession's senior credential — it certifies the ability to anticipate, recognize, evaluate, and control workplace health hazards (chemical, physical, biological, ergonomic) quantitatively. Where the CSP is the safety generalist, the CIH is the exposure-science specialist: the person who designs the sampling strategy, interprets the lab data against OELs, models the ventilation, and defends the conclusions. In litigation, regulatory negotiation, and program design, the CIH is the credential that carries weight.

Knowledge domains

Domain 1 — Anticipation and recognition

Walkthrough survey methodology: process review, SDS analysis, workforce interviews, and the qualitative exposure assessment that precedes sampling. Hazard classes: gases/vapors (acute vs. chronic), aerosols (dusts, fumes, mists, fibers — and the size-selective fractions: inhalable, thoracic, respirable — with the respirable convention ~4 µm median cut), metals, solvents, particulates not otherwise specified. Physical agents: noise, vibration (hand-arm, whole-body), thermal stress (heat/cold), non-ionizing radiation (RF, lasers, UV), ionizing radiation (ALARA principles). Biological: bioaerosols, bloodborne pathogens, mold. Ergonomic: MSD risk factors.

Why recognition precedes evaluation: sampling without a qualitative model wastes resources and misses the worst-case exposure. The exam tests the survey-to-strategy sequence.

Domain 2 — Exposure assessment strategy

The AIHA exposure-assessment model: qualitative categorization → similar exposure groups (SEGs) → statistical sampling plan → data interpretation → control/reassessment. SEG formation (workers with similar exposure profiles grouped for sampling efficiency). Bayesian decision analysis (using prior professional judgment + data — the exam tests the concept, not the computation). Compliance vs. control sampling objectives. Worst-case vs. representative sampling.

Domain 3 — Air sampling and analysis

Active sampling: calibrated pumps (pre/post calibration with a primary standard — the exam tests the calibration discipline), sorbent tubes (charcoal for organics — two sections, front/back for breakthrough analysis; silica gel for inorganics), filters (PVC for gravimetric dust, MCE for metals), impingers/bubblers, direct-reading instruments (PIDs, FIDs, multi-gas meters — calibration gas, response factors, limitations: a PID calibrated to isobutylene reads other VOCs with correction factors). Passive/diffusive badges (Fick's law, uptake rates). Sampling parameters: flow rate × time = volume; volume × analytical sensitivity = detection limit feasibility. Breakthrough (>10% on back section = invalid sample — memorize). Analytical methods: NIOSH/OSHA method numbers conceptually (e.g., gravimetric 0500, metals 7300 by ICP), LOD/LOQ, blanks (field, media, lab) and their corrective roles.

Pump calibration: pre- and post-calibration must agree within ±5% (typical criterion); use the average flow for volume. Temperature/pressure corrections for rotameters (primary standards — bubble meters, DryCal — are volumetric and need T/P correction to standard conditions conceptually).

Domain 4 — Exposure limits and data interpretation

OEL families: OSHA PELs (legal, 1910.1000 Tables Z-1/Z-2/Z-3 — many dating to 1971/1989, often less protective), NIOSH RELs (health-based recommendations), ACGIH TLVs (consensus, updated annually — TWA, STEL, ceiling, excursion limits, skin/BEI notations). Action levels (typically ½ PEL — e.g., lead 30 µg/m³). Statistics: lognormal distribution of exposures, geometric mean/geometric standard deviation, the 95th percentile vs. the OEL (compliance judged on the upper tail, not the mean — the AIHA compliance statistic: 95% confidence that the 95th percentile < OEL), minimum/maximum variance, censored data (<LOD handling).

Mixtures: additive effects — Σ(C_i/OEL_i) ≤ 1 (same target organ/system); independent effects evaluated separately; potentiation/synergism conceptually.

BEIs: biological exposure indices (blood/urine metabolites — e.g., blood lead) — internal dose, complementing air monitoring.

Domain 5 — Control: ventilation and hierarchy

Dilution ventilation: Q = G×K/C (and its limits — see CSP guide). Local exhaust ventilation: capture velocity (the velocity at the contaminant release point needed to draw it in — by release condition: still air 50–100 fpm, low velocity 100–200, active generation 200–500, high-velocity release 500–2000+), hood types (exterior vs. enclosing — enclosing is always more efficient), duct design (transport velocity to prevent settling: ~2,000–4,500 fpm depending on contaminant; the exam tests the concept, not duct sizing), air cleaners (cyclones, baghouses, ESPs, scrubbers — selection by particle size and loading), and make-up air (exhausted air must be replaced — the #1 LEV commissioning failure). ACGIH Industrial Ventilation is the reference. Hierarchy of controls applied to health hazards: substitution (the IH's favorite — eliminate the solvent), isolation, engineering (ventilation), administrative, PPE/respiratory protection last.

Respiratory protection (1910.134): written program, medical evaluation, fit testing (QNFT/QLFT), APFs (half-face 10, full-face 50, PAPR 25–1000, SCBA 10,000 — memorize the anchor APFs), MUC = APF × OEL, cartridge selection and change schedules (no relying on odor breakthrough — objective data or ESLI required), voluntary-use provisions (Appendix D).

Domain 6 — Noise, thermal stress, radiation, ergonomics

Noise: 90 dBA 8-h TWA PEL (5-dB exchange), 85 dBA action level triggering the hearing-conservation program (1910.95: audiometry, training, hearing protectors); NIOSH REL 85 dBA (3-dB); engineering controls (enclosure, damping, isolation) before administrative/PPE; octave-band analysis conceptually. Heat: WBGT index, ACGIH TLV work/rest regimens, acclimatization, hydration; cold: wind chill, ACGIH TLV. Radiation: ionizing — time/distance/shielding, ALARA, 10 CFR 20 dose limits conceptually (5 rem/yr occupational); non-ionizing — laser classes, RF exposure. Ergonomics: NIOSH lifting equation (RWL and its six multipliers conceptually), HAL TLV, MSD risk factors (force, repetition, posture, vibration), controls (engineering redesign > administrative).

Domain 7 — Management, communication, ethics

IH program management, record-keeping (exposure records: 30-year retention per 1910.1020 — memorize), risk communication (explaining the 95th-percentile concept to a workforce), ethics (the ABIH/BGC code — the exam tests conflict-of-interest and data-integrity scenarios), expert-witness principles.

Key equations

• Volume = flow rate × time (consistent units; correct rotameter readings for T/P).
• TWA = Σ(C_i·T_i)/8; STEL = 15-min average; Ceiling = never-exceeded.
• Mixture: Σ(C_i/TLV_i) ≤ 1 (additive, same target organ).
• Breakthrough: back section > 10% of front = sample invalid.
• MUC = APF × OEL (maximum use concentration).
• Noise dose D = 100Σ(C/T); OSHA TWA = 16.61·log10(D/100) + 90 (5-dB); NIOSH TWA = 10·log10(D/100) + 85 (3-dB).
• Dilution Q = G·K/C.
• GM/GSD lognormal: 95th percentile = GM × GSD^1.645.

Worked examples

Example 1 — Sampling volume and feasibility. Toluene TLV 20 ppm (~75 mg/m³). Pump at 0.2 L/min for 8 h = 96 L = 0.096 m³. At ½ TLV (10 ppm ≈ 37.6 mg/m³): collected mass = 37.6 × 0.096 = 3.6 mg — well above typical LODs (~0.01 mg) → feasible. The exam tests this feasibility check: can the method detect at the level of interest?

Example 2 — Breakthrough. Charcoal tube: front 1.20 mg, back 0.18 mg. Back/front = 15% > 10% → sample invalid (breakthrough); resample at lower flow or shorter duration, or use a larger tube. At 0.08 mg (6.7%) → valid, total = 1.28 mg.

Example 3 — Mixture. Acetone 300 ppm (TLV 250), MEK 100 ppm (TLV 200), same irritant effects. Σ = 300/250 + 100/200 = 1.2 + 0.5 = 1.7 > 1 → overexposed even though each is below its TLV individually. The exam's favorite mixture trap.

Example 4 — MUC. Full-face APR, APF 50, contaminant OEL 5 ppm → MUC = 250 ppm. Measured 300 ppm → APR insufficient; upgrade to supplied-air. Also check: no IDLH (IDLH = SCBA/SAR only), no eye irritation issues (full-face covers), oxygen ≥19.5%.

Example 5 — 95th percentile. SEG data: GM 0.4×OEL, GSD 2.5. 95th %ile = 0.4 × 2.5^1.645 = 0.4 × e^(1.645×0.916) = 0.4 × e^1.507 = 0.4 × 4.51 = 1.81×OEL → non-compliant despite the mean being 40% of the OEL. This is why IH statistics matter — compliance lives in the tail.

Example 6 — Noise (NIOSH). 85 dBA for 8 h: NIOSH dose = 100% exactly (REL = 85, 3-dB) → at the recommended limit; OSHA dose = 50% (TWA ≈ 85 → below PEL, at the action level → hearing-conservation program required).

Standards/regulations cross-reference

• 29 CFR 1910.1000 / 1926.55 — PELs; substance-specific standards (lead 1910.1025, asbestos 1910.1001, silica 1910.1053, etc.).
• 1910.95 — occupational noise exposure; 1910.134 — respiratory protection; 1910.1020 — access to records (30-year retention).
• ACGIH TLVs/BEIs — annually updated consensus limits (the exam's primary OEL reference).
• NIOSH RELs / Pocket Guide — health-based recommendations and method guidance.
• AIHA exposure-assessment strategy — the SEG/statistical framework.
• ACGIH Industrial Ventilation — LEV design reference.
• ANSI/ASSP Z88.2 — respiratory protection practices.

Pitfalls

1. Mean vs. tail. Judging compliance by the arithmetic mean instead of the 95th percentile — the exam's deepest conceptual trap.
2. Breakthrough 10%. A hard validity rule, not guidance — back >10% of front invalidates the sample.
3. Additive mixtures. Each-below-TLV ≠ compliant when target organs match.
4. Exchange rates. 5-dB (OSHA) vs. 3-dB (NIOSH/ACGIH) — know which the question invokes.
5. Record retention. Exposure records 30 years; medical records duration of employment + 30 years (1910.1020) — the exam tests the numbers.
6. PEL age. Many PELs are 1970s-era and less protective than TLVs — the exam tests whether you know the PEL is the legal floor, not the health-based target.

Exam strategy

• Calculation fluency: sampling volumes, TWAs, mixtures, noise dose (both exchange rates), MUC, lognormal percentiles — drill until mechanical.
• The BGC rubric: read the current exam blueprint — evaluation (sampling + statistics) and control (ventilation + respirators) dominate.
• Reference discipline: ACGIH TLV book navigation (notations: skin, SEN, carcinogen A1–A5) — know what the notations do to your assessment.

Practice problems

1. Pump 0.15 L/min × 6 h. Volume in m³? At 2 mg/m³ dust, mass collected?
2. Xylene 80 ppm (TLV 100), ethylbenzene 60 ppm (TLV 100), same CNS effects. Mixture assessment?
3. Charcoal tube: front 0.90 mg, back 0.12 mg. Valid? Total mass?
4. Half-face APR (APF 10), OEL 2 ppm, measured 15 ppm. MUC? Adequate?
5. SEG: GM 0.3×OEL, GSD 3.0. Estimate the 95th percentile as a multiple of the OEL.
6. Explain why a PID reading of "0 ppm" does not prove the absence of a specific toxic vapor. (Short essay.)

Answers

1. 0.15 × 360 = 54 L = 0.054 m³. Mass = 2 × 0.054 = 0.108 mg.
2. 80/100 + 60/100 = 1.4 > 1 → overexposed (additive).
3. 0.12/0.90 = 13.3% > 10% → invalid; resample.
4. MUC = 10 × 2 = 20 ppm ≥ 15 → adequate on concentration (subject to all 1910.134 program elements: fit test, medical, change schedule).
5. 0.3 × 3.0^1.645 = 0.3 × e^(1.645×1.099) = 0.3 × e^1.808 = 0.3 × 6.10 = 1.83×OEL → non-compliant.
6. PIDs are non-specific (total VOC signal, isobutylene-equivalent), have compound-specific response factors (some compounds read low or not at all — e.g., methane poorly, some chlorinated compounds weakly), are affected by humidity and calibration gas, and have detection limits above some OELs. A zero reading means "no detectable PID-amenable vapor above the LOD," not "no toxic vapor present" — confirm with compound-specific sampling.

Original ETS reference writing, verified against public sources on 2026-09-30. Thin sourcing is flagged inline. Not legal advice — confirm current editions with the issuing body.