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3.1 Active and Passive Air Sampling Strategies

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CIH Certified Industrial Hygienist Exam

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1 Chapter 1: The CIH Exam and How to Use This Guide

1.1 CIH Exam Format, Scoring, and Test-Day Logistics 1.2 Eligibility, Application Windows, Fees, and Certification Maintenance 1.3 The BGC Blueprint, Subject Areas, and a Calculation-First Study Plan

2 Chapter 2: Basic Science & Calculations

2.1 Gas Laws and Vapor Calculations 2.2 Unit Conversions: ppm, mg/m³, and Standard Temperature/Pressure 2.3 Fluid Mechanics and Airflow Fundamentals

3 Chapter 3: Air Sampling & Instrumentation

3.1 Active and Passive Air Sampling Strategies 3.2 Particulate and Aerosol Sampling 3.3 Direct-Reading Instruments and Calibration

4 Chapter 4: Analytical Chemistry & Lab Methods

4.1 Gas Chromatography and Mass Spectrometry 4.2 High-Performance Liquid Chromatography and Ion Chromatography 4.3 Spectroscopy and Elemental Analysis 4.4 Gravimetric, Microscopy, and Wet Chemical Methods 4.5 Laboratory Quality Assurance, Chain of Custody, and Desorption Efficiency

5 Chapter 5: Biostatistics & Epidemiology

5.1 Lognormal Distributions and Exposure Data Statistics 5.2 Upper Confidence Limits (UCL95) and Compliance Decision Rules 5.3 Epidemiological Study Designs and Measures of Association 5.4 Sampling Strategy: Sample Size, Power, and Worker Selection

6 Chapter 6: Toxicology & Biological Monitoring

6.1 Dose-Response Relationships and Points of Departure 6.2 Toxicokinetics: Absorption, Distribution, Metabolism, and Elimination 6.3 Aerosol Deposition, Clearance, and Respiratory Tract Dosimetry 6.4 Hepatic, Renal, Neurologic, and Hematologic Target Organ Toxicity 6.5 Pulmonary Toxicology, Carcinogenicity, and Reproductive Hazards 6.6 OEL Frameworks, Classifications, and Excursion Limits 6.7 Chemical Mixtures and Extended Work-Shift OEL Adjustments 6.8 Biological Exposure Indices (BEIs) and Biomonitoring

7 Chapter 7: Biohazards & Indoor Environmental Quality

7.1 Mold, Fungi, and Microbial Contaminants 7.2 Infectious Agents, Bloodborne Pathogens, and Biosafety Levels 7.3 Indoor Environmental Quality (IEQ) Investigations 7.4 Sanitation, Potable Water, and Personal Hygiene Programs

8 Chapter 8: Community Exposure & Environmental Health

8.1 Clean Air Act Framework, NAAQS, and New Source Review 8.2 Hazardous Air Pollutants, CEMS, and EPA Reference Methods 8.3 Atmospheric Stability, Lapse Rates, and Plume Morphology 8.4 Gaussian Plume Modeling, Plume Rise, and Environmental Fate 8.5 HAZWOPER Scope, Mandates, and Training Tiers 8.6 Protection Levels, Site Zoning, Incident Command, and Decontamination 8.7 Water Pollution, Hazardous Waste, and Community Right-to-Know

9 Chapter 9: Health Risk Analysis & Hazard Communication

9.1 GHS Hazard Classification: Health and Physical Hazard Criteria 9.2 GHS Labels, Safety Data Sheets, and Trade Secret Rules 9.3 The AIHA Exposure Assessment Strategy and Similar Exposure Groups 9.4 Qualitative Exposure Profiling and the AIHA Risk Matrix 9.5 Quantitative Health Risk Characterization: HQ, HI, and ELCR 9.6 NIOSH Occupational Exposure Banding 9.7 Risk Communication and Reporting to Affected Parties

10 Chapter 10: Industrial Ventilation Principles & LEV Design

10.1 Elimination, Substitution, Isolation, Containment, and Process Change 10.2 LEV Hood Taxonomy and Capture Velocity Selection 10.3 Hood Airflow Equations, Entry Losses, and Hood Static Pressure 10.4 Particulate Transport Aerodynamics and Duct Sizing 10.5 Duct Friction, Fitting Losses, and System Balancing 10.6 Fan Categories and Pressure Dynamics Across the Fan 10.7 System Curves, the Fan Laws, and Density Corrections

11 Chapter 11: General Ventilation, Air Cleaning & Diagnostics

11.1 Dilution Ventilation Principles and Steady-State Modeling 11.2 Transient Purging and Air Distribution Geometry 11.3 Particulate Air Cleaning: Cyclones, Baghouses, Scrubbers, and ESPs 11.4 Gaseous Emission Control and Air Cleaner Selection 11.5 Ventilation System Troubleshooting and Testing

12 Chapter 12: Noise Measurement & Hearing Conservation

12.1 Acoustic Physics and Decibel Mathematics 12.2 Sound Propagation, Octave Bands, and Frequency Weighting 12.3 Noise Dose Metrics and OSHA versus ACGIH Criteria 12.4 Exchange Rates, Extended Shifts, and Dosimetry Field Protocols 12.5 Engineering Noise Controls and Hearing Protector Attenuation 12.6 Hearing Conservation Programs and Standard Threshold Shifts 12.7 Hand-Arm and Whole-Body Vibration

13 Chapter 13: Thermal Stress Assessment & Control

13.1 Wet Bulb Globe Temperature (WBGT) and Heat Stress Indices 13.2 Heat-Related Disorders, Acclimatization, and Work/Rest Regimens 13.3 Cold Stress Evaluation and Wind Chill

14 Chapter 14: Ionizing Radiation Protection

14.1 Ionizing Radiation Physics and Radioactive Decay Kinetics 14.2 Radiation Units, Radiobiology, and Health Effects 14.3 ALARA, Stay-Time, and the Inverse Square Law 14.4 Shielding Physics, Material Selection, and Gamma Constants 14.5 Radiation Detection Instruments and Spectrometry 14.6 Personnel Dosimetry, Dose Limits, and Contamination Surveys

15 Chapter 15: Non-Ionizing Radiation & Laser Safety

15.1 The Non-Ionizing Spectrum and Static/ELF Field Exposures 15.2 Radiofrequency and Microwave Exposure: SAR, Standards, and Surveys 15.3 Ultraviolet, Visible, and Infrared Radiation Hazards 15.4 Laser Safety Classifications and Optical Density Calculations 15.5 Illumination, Lighting Design, and Visual Performance

16 Chapter 16: Non-Engineering Controls & Personal Protective Equipment

16.1 Respiratory Protection Programs and Assigned Protection Factors 16.2 Maximum Use Concentration, Oxygen Deficiency, and Breathing Air 16.3 Particulate Filters, Sorbent Cartridges, and Change Schedules 16.4 Respirator Fit Testing Protocols 16.5 Chemical Protective Clothing and Dermal Exposure Control

17 Chapter 17: Ergonomics & Workstation Design

17.1 Soft-Tissue Biomechanics and WMSD Pathophysiology 17.2 Ergonomic Risk Factors and Their Interaction Effects 17.3 The Revised NIOSH Lifting Equation 17.4 RULA, REBA, the Strain Index, and the ACGIH HAL TLV 17.5 Anthropometry and Workstation Geometry 17.6 VDT Workstations, Hand Tool Design, and Administrative Ergonomics

18 Chapter 18: Work Environments & Industrial Processes

18.1 Welding Fume Emissions, Metal Fume Fever, and Cr(VI)/Manganese Toxicology 18.2 Foundry Operations and Hot Work Fire Prevention 18.3 Vapor Degreasing, Pickling, Electroplating, and Cyanide Baths 18.4 Spray Coatings, Isocyanates, and Semiconductor Manufacturing 18.5 Confined Spaces and High-Hazard Industrial Operations 18.6 Asbestos, Lead, and Silica: Regulated Substance Programs 18.7 Abrasive Blasting and Surface Preparation

19 Chapter 19: IH Program Management & Professional Ethics

19.1 The BGC Code of Ethics: Canons and Enforcement 19.2 Professional Liability, Standard of Care, and Expert Testimony 19.3 Occupational Health & Safety Management Systems (ISO 45001, ANSI Z10) 19.4 Exposure Records Access and Medical Surveillance 19.5 OSHA Injury and Illness Recordkeeping and Enforcement

3.1 Active and Passive Air Sampling Strategies

Key Takeaways Explain This Topic AI

Active sampling relies on personal sampling pumps drawing air through sorbents or filters at controlled volumetric flow rates within the worker's 30-cm breathing zone.

Standard solid sorbent tubes utilize a primary front section (typically 100 mg for charcoal) and a backup section (50 mg) separated by polyurethane foam to capture and quantify breakthrough.

Breakthrough is defined when the analyte mass on the backup section exceeds 10% of the mass on the front section (or >10% of the total collected mass), invalidating the quantitative accuracy of the sample.

Passive diffusive dosimeters operate via molecular diffusion governed by Fick's First Law (dm/dt = D*(A/L)*C), requiring a minimum face velocity of 10 to 25 ft/min (0.05-0.15 m/s) to avoid sample starvation.

Field blanks must be submitted at a minimum frequency of 10% of total samples (or at least 1-2 per batch) to detect handling, transit, and storage contamination.

Last updated: August 2026

2.1 Active and Passive Air Sampling Strategies

Air sampling for gases and vapors is a cornerstone of industrial hygiene practice. Sampling strategies generally fall into two broad methodologies: active sampling , which utilizes a mechanical air sampling pump to draw a known volume of air through a collection medium, and passive (diffusive) sampling , which relies on the spontaneous diffusion of gas molecules across a defined diffusion path onto an adsorbent substrate without the use of a pump.

Selecting the appropriate sampling strategy requires a rigorous understanding of physical chemistry, fluid dynamics, analyte-sorbent interactions, environmental interference factors, and strict quality assurance protocols.

Active Sampling Systems & Sampling Train Components

An active sampling train consists of a collection medium (such as a solid sorbent tube, filter cassette, or impinger), flexible non-reactive connective tubing (e.g., Tygon or PTFE), and a battery-powered personal sampling pump . +-------------------------------------------------------------------------+

  • | ACTIVE SAMPLING TRAIN |
  • | |
  • | +--------------------+ +----------------+ +---------------+ |
  • | | Breathing Zone | ---> | Flexible Inert | ---> | Constant-Flow | |
  • | | Sorbent / Cassette | | Tubing (Tygon) | | Personal Pump | |
  • | +--------------------+ +----------------+ +---------------+ |
  • +-------------------------------------------------------------------------+
  • Breathing Zone Definition

For personal exposure monitoring, the collection device must be mounted directly within the worker's breathing zone , defined as a hemisphere with a radius of 30 cm (approximately 1 foot) extending forward from the worker's nose and mouth. The sampler is typically secured to the lapel or collar of the outer garment, oriented downward or according to method specifications to prevent particulate or liquid droplet settling into the tube opening.

Constant-Flow Personal Sampling Pumps

Modern personal sampling pumps incorporate electronic flow sensors and internal feedback loops that adjust motor speed to maintain a constant volumetric flow rate against fluctuating pressure drops ( backpressure ). Key engineering features include:

Pulsation Dampeners : Diaphragm and piston pumps generate pulsating flow. Internal dampeners smooth these pulsations to ensure laminar or steady flow through the collection substrate.

Backpressure Compensation : As sorbent tubes or high-efficiency particulate air (HEPA) filters load, resistance increases. Constant-flow pumps maintain target flow rates within ± 5% over backpressures exceeding 40 to 50 inches of water gauge (in. H2O).

Low-Flow Controllers / Critical Orifices : For low-flow sorbent sampling (10 to 200 mL/min), pumps either use a geared low-flow mode or an external multi-port manifold equipped with precision needle valves or critical orifices.

Solid Sorbent Media Chemistry

Solid sorbent sampling tubes are glass tubes with flame-sealed ends packed with granular adsorbent media. Sorbent media capture gaseous molecules via physical adsorption (van der Waals interactions) or chemisorption (covalent chemical reaction on chemically treated media).

Sorbent Medium Surface Properties Primary Target Analytes Common Desorption Solvent / Method Representative Methods

Coconut Shell Charcoal Non-polar, high surface area (1000–1400 m²/g) Non-polar organics: aliphatic & aromatic hydrocarbons, chlorinated solvents, alcohols, esters Carbon Disulfide (CS2) NIOSH 1500 (Hydrocarbons), NIOSH 1501 (Aromatics)

Silica Gel Highly polar, hydrophilic (active silanol -Si-OH groups) Polar organics: aliphatic amines, pyridines, low-MW alcohols, phenols, inorganic acids Water, Methanol, or polar aqueous mixtures NIOSH 2002 (Amines), NIOSH 7903 (Inorganic Acids)

Porous Polymers (Tenax TA) Hydrophobic 2,6-diphenyl-p-phenylene oxide High-boiling VOCs, semi-volatiles, thermal desorption targets Thermal Desorption (TD) into GC-MS EPA TO-17, ISO 16000-6

Amberlite XAD-2 Hydrophobic styrene-divinylbenzene copolymer Semi-volatile organic compounds (SVOCs), polycyclic aromatic hydrocarbons (PAHs), pesticides Methylene chloride (CH2Cl2), Toluene NIOSH 5506 (PAHs), NIOSH 5515 (PAHs)

Carbon Molecular Sieves (Carboxen/Carbotrap) Uniform microporous graphitized carbon Highly volatile, low-molecular-weight organic compounds (vinyl chloride, chloromethane) Thermal Desorption or CS2 NIOSH 1007 (Vinyl Chloride), EPA TO-15/17

Treated / Coated Sorbents Chemically derivatized media (e.g., 2-HMP on XAD-2, DNP on silica) Reactive aldehydes, isocyanates, ethylene oxide Acetonitrile, Acidic solvent extraction with HPLC NIOSH 2016 (Formaldehyde), OSHA 42/47 (Isocyanates)

Sorbent Tube Geometry & Breakthrough Phenomena

Standard solid sorbent tubes (e.g., the standard 6-mm OD × 70-mm length coconut charcoal tube) are constructed in a two-section configuration :

Front (Primary/Sampling) Section : Contains the primary mass of sorbent (typically 100 mg in a standard charcoal tube).

Back (Backup/Secondary) Section : Contains half the sorbent mass of the front section (typically 50 mg ), separated from the front bed by a porous polyurethane foam plug.

Foam and Glass Wool Retainers : Secure the beds in place to prevent channeling or movement during transport and sampling. Air Inflow ==============================================================> To Pump

  • [ Flame-Seal Tip ] [ Flame-Seal Tip ]
  • +--------------+------------------+---------------+-------------------+
  • | Glass Wool | FRONT BED | Urethane Foam | BACKUP BED |
  • | Retainer | (100 mg) | Separator | (50 mg) |
  • +--------------+------------------+---------------+-------------------+
  • Breakthrough Volume (Vb) and the 10% Breakthrough Rule

As air passes through the front sorbent bed, gas molecules adsorb onto active surface sites, establishing an adsorption wave that moves progressively downstream. If the capacity of the front bed is exceeded, analyte molecules migrate into the backup section—a phenomenon known as breakthrough . Breakthrough Percentage ( % B ) = ( m back m front ) × 100 % \text{Breakthrough Percentage } (\%B) = \left( \frac{m_{\text{back}}}{m_{\text{front}}} \right) \times 100\% Breakthrough Percentage ( % B ) = ( m front ​ m back ​ ​ ) × 100% or % B total = ( m back m front + m back ) × 100 % \text{or} \quad \%B_{\text{total}} = \left( \frac{m_{\text{back}}}{m_{\text{front}} + m_{\text{back}}} \right) \times 100\% or % B total ​ = ( m front ​ + m back ​ m back ​ ​ ) × 100%

Important

The 10% Breakthrough Rule (NIOSH / OSHA Standard) :

If the mass recovered from the backup section exceeds 10% of the mass on the front section (i.e., mback > 0.10 × mfront), breakthrough has officially occurred. This indicates that the front bed was saturated and the backup bed may have also lost analyte to the pump exhaust. The sample is considered quantitatively compromised (invalid) and cannot be used for strict regulatory compliance demonstration without qualifying it as a minimum (underestimated) concentration.

Critical Environmental Factors Affecting Breakthrough

Relative Humidity (RH) : On non-polar sorbents like activated charcoal, water vapor at high humidity (RH > 80%) competes directly for adsorption sites and promotes capillary condensation. This can reduce the breakthrough volume (Vb) by a factor of 2 to 10.

High Ambient Temperature : Adsorption is an exothermic physical process (Δ Hads < 0). Elevated temperatures shift the equilibrium toward desorption, sharply lowering sorbent capacity.

Competitive Displacement (Chromatographic Effect) : In multi-component vapor mixtures, chemicals with higher molecular weights, higher boiling points, or higher affinities for the sorbent will actively displace lighter, lower-boiling-point volatiles previously captured on the front bed, pushing the lighter chemicals rapidly into the backup section.

Excessive Sampling Flow Rate : Increasing flow rate shortens the residence time (contact time) of the air parcel within the sorbent bed, causing premature kinetic breakthrough before the equilibrium adsorption capacity is reached.

Passive (Diffusive) Air Sampling Dosimeters

Passive samplers (diffusive badges) collect airborne gases and vapors without an active air pump. Transport of contaminant molecules from ambient air to the internal collection substrate occurs purely through molecular diffusion across a static air barrier. Ambient Air [ Concentration = Ca ]

  • ====================================================== Badge Face
  • | Static Air Layer |
  • | (Diffusion Path Length L) | Diffusion Area (A)
  • | Diffusion Flux (J) |
  • ====================================================== Sorbent Surface
  • Adsorbent Substrate [ Concentration C0 ≈ 0 ]
  • Mathematical Basis: Fick's First Law of Diffusion

The mass transfer rate through the stagnant diffusion layer inside the badge is governed by Fick's First Law of Diffusion : J = − D d C d x J = -D \frac{dC}{dx} J = − D d x d C ​

Where:

  • J = Diffusive mass flux per unit area (mg/(cm² · s))
  • D = Molecular diffusion coefficient of the analyte in air (cm²/s)
  • dC/dx = Concentration gradient across the diffusion barrier

Assuming a constant concentration in ambient air (Ca), zero concentration at the sorbent surface (C0 ≈ 0 due to instantaneous adsorption by the collection medium), a cross-sectional diffusion area A, and a diffusion path length L: d m d t = D ⋅ ( A L ) ⋅ ( C a − C 0 ) = D ⋅ ( A L ) ⋅ C a \frac{dm}{dt} = D \cdot \left( \frac{A}{L} \right) \cdot (C_a - C_0) = D \cdot \left( \frac{A}{L} \right) \cdot C_a d t d m ​ = D ⋅ ( L A ​ ) ⋅ ( C a ​ − C 0 ​ ) = D ⋅ ( L A ​ ) ⋅ C a ​

Integrating over sampling time t yields the total collected mass (m): m = D ⋅ ( A L ) ⋅ C a ⋅ t m = D \cdot \left( \frac{A}{L} \right) \cdot C_a \cdot t m = D ⋅ ( L A ​ ) ⋅ C a ​ ⋅ t

The term D · ( A/L ) represents the theoretical sampling rate (Qdiff) in units of volume per unit time (typically mL/min or cm³/min): Q diff = D ⋅ ( A L ) Q_{\text{diff}} = D \cdot \left( \frac{A}{L} \right) Q diff ​ = D ⋅ ( L A ​ ) C a = m Q diff ⋅ t C_a = \frac{m}{Q_{\text{diff}} \cdot t} C a ​ = Q diff ​ ⋅ t m ​

Environmental Limitations of Passive Samplers

Face Velocity & Starvation Effect : Passive badges require a minimum ambient air velocity across the badge face (typically 10 to 25 ft/min or 0.05 to 0.15 m/s ). In completely stagnant air, analyte molecules entering the badge deplete the concentration in the immediate boundary layer outside the face, creating a local micro-environment where Cface < Ca, resulting in a severe negative sampling bias (starvation) .

Temperature and Pressure Effects : Diffusion coefficients vary with absolute temperature (T) and atmospheric pressure (P) according to D ∝ T(1.5) / P. Consequently, the diffusive sampling rate adjusts with environmental conditions: Q ( T , P ) = Q 0 ⋅ ( T T 0 ) 0.5 ⋅ ( P 0 P ) Q(T, P) = Q_0 \cdot \left( \frac{T}{T_0} \right)^{0.5} \cdot \left( \frac{P_0}{P} \right) Q ( T , P ) = Q 0 ​ ⋅ ( T 0 ​ T ​ ) 0.5 ⋅ ( P P 0 ​ ​ ) (Note: While D varies as T(1.5), the ideal gas concentration conversion introduces an inverse temperature factor, resulting in a net (T/T0)(0.5) temperature dependence for volumetric sampling rate).

Sorbent Saturation and Reverse Diffusion : Unlike active tubes with backup sections, most passive badges do not possess a second collection stage. In extremely high vapor concentrations or long deployment times, sorbent active sites become saturated, leading to back-diffusion (loss of captured analyte) back into ambient air.

Comparison: Active vs. Passive Sampling

  • Feature Active Sorbent Sampling Passive Diffusive Badges
  • Air Mover Required Yes (calibrated personal sampling pump) No (relies purely on molecular diffusion)

Flow Rate Verification Pre- and post-calibration required (within ± 5%) Fixed geometric sampling rate (Qdiff provided by manufacturer)

Breakthrough Monitoring Yes (front and backup beds analyzed separately) Generally No (single sorbent wafer in standard badges)

Minimum Face Velocity None (internal suction pulls sample) 10–25 ft/min required to avoid starvation

Worker Interference Moderate (harness, pump weight, tubing hazards) Very low (lightweight badge pinned to lapel)

Sensitivity for Short Tasks High (can increase pump flow to collect mass) Lower (sampling rate fixed by geometry and diffusion)

Cost per Sample Higher (pump maintenance, calibration, tubing) Lower initial hardware cost; badge media unit cost

Quality Assurance: Field, Media, and Trip Blanks

Rigorous industrial hygiene data requires strict quality control blanks to verify that detected masses represent true occupational inhalation exposures rather than background contamination, media artifacts, or transit interference. +-----------------------------------------------------------------------------------------+

  • | QUALITY ASSURANCE BLANKS |
  • +-------------------+-------------------------------------+-------------------------------+
  • | Blank Type | Handling Protocol | Analytical Purpose |
  • +-------------------+-------------------------------------+-------------------------------+
  • | Field Blank | Taken to site, opened briefly, | Quantifies contamination from |
  • | (Min 10% or >=1) | sealed, never connected to pump. | field handling, storage, |
  • | | Shipped with active samples. | and analytical processing. |
  • +-------------------+-------------------------------------+-------------------------------+
  • | Media / Lot Blank | Retained in laboratory from same | Verifies manufacturing purity |
  • | | production lot without field trip. | and baseline media background.|
  • +-------------------+-------------------------------------+-------------------------------+
  • | Trip Blank | Accompanies media from lab to site | Detects diffusive permeation |
  • | | and back; never opened in field. | or cross-contamination during |
  • | | | transit and shipping. |
  • +-------------------+-------------------------------------+-------------------------------+
  • Analytical Correction: Desorption Efficiency (DE)

When the analytical laboratory desorbs the analyte from the sorbent (e.g., using CS2), not all molecules release into solution. The Desorption Efficiency (DE) represents the fraction of recovered mass: DE = Mass Measured by Instrument Actual Mass Spiked onto Sorbent \text{DE} = \frac{\text{Mass Measured by Instrument}}{\text{Actual Mass Spiked onto Sorbent}} DE = Actual Mass Spiked onto Sorbent Mass Measured by Instrument ​

The true mass collected on the sample (mcorrected) is calculated by subtracting field blank mass (mblank) and dividing by the batch DE: m corrected = ( m front + m back ) − m blank DE m_{\text{corrected}} = \frac{(m_{\text{front}} + m_{\text{back}}) - m_{\text{blank}}}{\text{DE}} m corrected ​ = DE ( m front ​ + m back ​ ) − m blank ​ ​ Airborne Concentration ( C ) = m corrected V = m corrected Q ⋅ t \text{Airborne Concentration } (C) = \frac{m_{\text{corrected}}}{V} = \frac{m_{\text{corrected}}}{Q \cdot t} Airborne Concentration ( C ) = V m corrected ​ ​ = Q ⋅ t m corrected ​ ​

Worked Step-by-Step Example: Sorbent Tube Sampling Calculation ========================================================================================

  • WORKED EXAMPLE: Toluene Exposure Assessment and Breakthrough Evaluation
  • ========================================================================================

Scenario:

An industrial hygienist samples a degreasing operator for airborne toluene (MW = 92.14 g/mol)

using a coconut shell charcoal tube (100/50 mg) connected to a pump calibrated at 0.200 L/min.

The sampling duration is 4.0 hours (240 minutes).

Laboratory Analytical Report:

  • Front section mass (m_front) = 1.420 mg (1420 µg)
  • Backup section mass (m_back) = 0.085 mg (85 µg)
  • Field blank mass (m_blank) = 0.005 mg (5 µg)
  • Desorption Efficiency (DE) = 0.95 (95%)
  • ---------------------------------------------------------------------------------------
  • Step 1: Calculate Total Air Volume Sampled (V)
  • V = Flow Rate (Q) × Sampling Duration (t)
  • V = 0.200 L/min × 240 min = 48.0 L = 0.0480 m³
  • Step 2: Evaluate Sorbent Tube Breakthrough
  • %Breakthrough = (m_back / m_front) × 100%
  • %Breakthrough = (0.085 mg / 1.420 mg) × 100% = 5.99%
  • Evaluation: 5.99% < 10.0%. The sample meets the NIOSH/OSHA breakthrough criterion

and is valid for quantitative compliance evaluation.

  • Step 3: Calculate Corrected Mass Collected (m_corrected)
  • m_net = (m_front + m_back) - m_blank
  • m_net = (1.420 mg + 0.085 mg) - 0.005 mg = 1.500 mg
  • m_corrected = m_net / DE = 1.500 mg / 0.95 = 1.579 mg (1579 µg)
  • Step 4: Calculate Airborne Concentration in mg/m³
  • C (mg/m³) = m_corrected / V
  • C = 1.579 mg / 0.0480 m³ = 32.90 mg/m³
  • Step 5: Convert Concentration to Parts per Million (ppm) at NTP (25°C, 1 atm)
  • C (ppm) = [C (mg/m³) × 24.45] / MW
  • C (ppm) = [32.90 mg/m³ × 24.45] / 92.14 g/mol
  • C (ppm) = 804.41 / 92.14 = 8.73 ppm
  • ========================================================================================