3.3 Direct-Reading Instruments and Calibration

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

3.3 Direct-Reading Instruments and Calibration

Key Takeaways Explain This Topic AI

Photoionization Detectors (PIDs) utilize UV lamps (typically 10.6 eV) to ionize volatile organic compounds with Ionization Potentials (IP) <= lamp energy, calibrated against isobutylene.

Flame Ionization Detectors (FIDs) pyrolyze organic molecules in a hydrogen-air flame, detecting virtually all hydrocarbons including methane, but requiring hydrogen fuel gas cylinders.

Electrochemical sensors measure target gas diffusion across a membrane into an electrolyte; oxygen galvanic cells consume lead anodes and exhibit a finite 1-2 year operational lifespan.

Primary calibration standards (DryCal electronic piston meters, soap bubble meters, spirometers) measure volume and time directly from fundamental physical dimensions without referencing other instruments.

Sampling pump pre- and post-sampling calibration flow rates must agree within +/-5.0% using the complete, representative sampling train in-line.

Last updated: August 2026

2.3 Direct-Reading Instruments and Calibration

Direct-Reading Instruments (DRIs) provide real-time or near-real-time measurement of airborne gases, vapors, aerosols, and physical agents. They are indispensable for emergency response, confined space pre-entry screening, leak detection, tracking rapid exposure transients, and evaluating the immediate effectiveness of engineering controls.

However, because DRIs operate on physical and electrochemical detection mechanisms rather than compound-specific laboratory separation, industrial hygienists must understand their operating limits, selectivity, cross-sensitivities, humidity interferences , and strict calibration protocols .

Photoionization Detectors (PID)

A Photoionization Detector (PID) uses high-energy ultraviolet (UV) light emitted by a gas-discharge lamp to ionize volatile organic compound (VOC) molecules entering a detection chamber. [ High-Energy UV Discharge Lamp ]

• | (Photons: hν)
• v
• Incoming Sample Air (R) ===> [ Ionization Chamber ] ===> Exhaust
• | |
• v v
• [ Cathode (-) ] [ Anode (+) ]
• | |
• +-----[ pA ]---+ (Ionization Current Measured)
• Physical Principle of Operation

When a photon strikes an airborne molecule (R) with an energy (hν) greater than or equal to the molecule's Ionization Potential (IP) , an electron is ejected, creating a positive molecular ion: R + h ν → R + + e − ( Occurs only when I P ≤ h ν ) R + h\nu \rightarrow R^+ + e^- \quad (\text{Occurs only when } IP \le h\nu) R + h ν → R + + e − ( Occurs only when I P ≤ h ν )

The resulting positive ions and free electrons migrate under an applied electric field to opposing collector electrodes, producing an ionization current measured in picoamperes (10⁻¹² A). The current is directly proportional to the molecular concentration in the chamber.

UV Lamp Energy Levels and Selectivity

PIDs are fitted with interchangeable UV lamps containing specific excitation gases sealed behind optical crystal windows:

10.6 eV (Standard Lamp, Krypton gas / Magnesium Fluoride window) : The most widely used industrial hygiene lamp. Has a long operating life (>1–2 years) and ionizes a broad range of aromatics, chlorinated alkenes, ketones, and fuels.

9.8 eV or 10.0 eV (Low-Energy Lamp, Xenon gas) : Selective for aromatic hydrocarbons (e.g., benzene IP = 9.25 eV, toluene IP = 8.82 eV, xylene IP = 8.56 eV) while ignoring aliphatic solvents and alcohols with higher IPs.

11.7 eV (High-Energy Lamp, Argon gas / Lithium Fluoride window) : Required for short-chain chlorinated alkanes such as methylene chloride (IP = 11.32 eV), chloroform (IP = 11.37 eV), and 1,1,1-trichloroethane (IP = 11.00 eV). Limitation : The LiF crystal window is hygroscopic, degraded by atmospheric moisture and solar radiation, giving it a short working lifespan (often <2–3 months).

Common Compounds NOT Ionized by a 10.6 eV PID

Any compound with an Ionization Potential exceeding 10.6 eV will not be detected:

• Methane (IP = 12.61 eV)
• Ethane (IP = 11.52 eV)
• Propane (IP = 11.07 eV)
• Carbon Monoxide (IP = 14.01 eV)
• Carbon Dioxide (IP = 13.78 eV)
• Water Vapor (IP = 12.60 eV)
• Oxygen (IP = 12.07 eV) & Nitrogen (IP = 15.58 eV)
• Hydrogen Cyanide (IP = 13.60 eV)
• Isobutylene Calibration & Correction Factors (CF)

PIDs are universally calibrated using isobutylene gas (IP = 9.40 eV) as the reference surrogate. When monitoring a known single chemical other than isobutylene, a Correction Factor (CF / Response Factor) must be applied: True Concentration (ppm) = PID Instrument Reading (ppm isobutylene equivalent) × CF \text{True Concentration (ppm)} = \text{PID Instrument Reading (ppm isobutylene equivalent)} \times \text{CF} True Concentration (ppm) = PID Instrument Reading (ppm isobutylene equivalent) × CF

CF < 1.0 : The instrument is more sensitive to the analyte than to isobutylene (e.g., benzene CF ≈ 0.53; a reading of 10 ppm equals 5.3 ppm of benzene).

CF > 1.0 : The instrument is less sensitive to the analyte than to isobutylene (e.g., hexane CF ≈ 4.3; a reading of 10 ppm equals 43 ppm of hexane).

Warning

Humidity Quenching Interference :

At high relative humidity (RH > 70% at 25°C), water vapor molecules absorb and scatter UV photons and collide with positive analyte ions, neutralizing them before they reach collector electrodes. This quenching effect can suppress PID readings by 30% to 70%, producing hazardous false-negative indications.

Flame Ionization Detectors (FID)

A Flame Ionization Detector (FID) mixes sample air with pure hydrogen (H2) fuel and burns it in an excess of clean air inside a shielded combustion chamber. Sample Inflow + H2 Gas ===> [ High-Temp Hydrogen Flame ] ===> Pyrolysis (CH + O -> CHO+ + e-)

• |
• v
• [ Polarized Electrodes ] ===> [ Linear Amplifier / Current ]
• Detection Mechanism

Hydrocarbon molecules undergo thermal cracking and oxidation in the hydrogen flame, generating carbon-containing ionic intermediates: CH + O → CHO + + e − ( ≈ 1 ion produced per 10 6 carbon atoms burned ) \text{CH} + \text{O} \rightarrow \text{CHO}^+ + e^- \quad (\approx 1\text{ ion produced per } 10^6\text{ carbon atoms burned}) CH + O → CHO + + e − ( ≈ 1 ion produced per 1 0 6 carbon atoms burned )

An electric potential applied across the flame jet (anode) and a collector ring (cathode) collects the ions, generating an electric current proportional to the total number of carbon atoms.

PID vs. FID Detailed Comparison

Technical Feature Photoionization Detector (PID) Flame Ionization Detector (FID)

Excitation / Energy Source High-energy UV gas-discharge lamp (10.6 eV) High-temperature Hydrogen-air combustion flame

• Methane (CH4) Response Zero response (IP = 12.61 eV > 10.6 eV) Excellent response (sensitive to all C-H bonds)
• Inorganic Gas Response Zero for CO, CO2, H2O, N2, O2 Zero for CO, CO2, H2O, N2, O2
• Auxiliary Gases Required None (ambient air drawn directly) Requires compressed Hydrogen (H2) fuel cylinder
• Linear Dynamic Range 0.1 to 2,000 ppm 0.1 to 50,000+ ppm (10⁵ decade linearity)
• Moisture Sensitivity Severe quenching at high RH Minimal moisture quenching interference
• Destructive to Sample Non-destructive (exhaust sample intact) Destructive (sample completely incinerated)

Primary Field Application Handheld VOC screening, HAZMAT entry EPA Method 21 fugitive leak detection, total hydrocarbon

Non-Dispersive Infrared (NDIR) Spectrometers

NDIR spectrometers measure gas concentration based on the selective absorption of infrared radiation at discrete vibrational-rotational molecular absorption bands, governed by the Beer-Lambert Law : A = log ⁡ 10 ( I 0 I ) = ϵ ⋅ b ⋅ C A = \log_{10}\left( \frac{I_0}{I} \right) = \epsilon \cdot b \cdot C A = lo g 10 ​ ( I I 0 ​ ​ ) = ϵ ⋅ b ⋅ C

Where:

• A = Absorbance
• I0 = Incident light intensity at target wavelength
• I = Transmitted light intensity exiting the sample cell
• ε = Molar absorptivity (extinction coefficient)
• b = Optical path length of the absorption cell

C = Gas concentration [ IR Source ] ===> [ Sample Gas Cell (Path Length b) ] ===> [ Optical Filter (4.26 µm) ] ===> [ IR Detector ]

Specific Infrared Absorption Bands

Carbon Dioxide (CO2) : 4.26 µm (fundamental asymmetric stretching band; zero cross-talk from water vapor). Primary DRI for indoor environmental quality (IEQ) ventilation rate assessments.

Carbon Monoxide (CO) : 4.67 µm .

Hydrocarbons (C-H stretch) : 3.3 to 3.4 µm .

Nitrous Oxide (N2O) : 4.5 µm .

Electrochemical Sensors & Multi-Gas Confined Space Monitors

Electrochemical sensors measure target gas concentration via a chemical reduction or oxidation (redox) reaction at a catalytic sensing electrode. Target Gas Inflow ===> [ Gas-Permeable PTFE Membrane ] ===> [ Electrolyte Solution ]

• |
• +--------------------------------+-------------------------------+
• | | |
• v v v
• [ Sensing Electrode ] [ Reference Electrode ] [ Counter Electrode ]
• (Oxidation/Reduction) (Constant Potential) (Complementary Redox)
• 1. Oxygen Galvanic Sensors

Galvanic oxygen sensors operate as an electrochemical battery consisting of a gold/platinum cathode, a lead (Pb) anode, and an alkaline or acidic electrolyte:

• Cathode Reaction (Reduction) : O2 + 4H⁺ + 4e⁻ arrow 2H2O
• Anode Reaction (Oxidation) : 2Pb + 2H2O arrow 2PbO + 4H⁺ + 4e⁻

Operational Lifespan : Because the lead anode is continuously consumed during operation, galvanic oxygen sensors have a finite shelf life of 1 to 2 years , regardless of whether the instrument is turned on or stored.

Regulatory Thresholds : Normal ambient O2 = 20.9%; OSHA Oxygen Deficiency ≤ 19.5%; OSHA Oxygen Enrichment ≥ 23.5%.

2. Toxic Gas Sensors & Cross-Sensitivities

Amperometric toxic gas sensors (CO, H2S, SO2, NO2, Cl2) maintain a fixed potential between sensing and reference electrodes. Key cross-sensitivities include:

CO Sensors : Exhibit positive cross-sensitivity to Hydrogen (H2) , acetylene, and ethylene (mitigated by using CO sensors equipped with internal chemical charcoal filters).

SO2 Sensors : Strongly cross-react with Nitrogen Dioxide (NO2) and Hydrogen Sulfide (H2S).

H2S Sensors : Cross-react with methyl mercaptan and sulfur dioxide.

Calibration Standards Hierarchy: Primary vs. Secondary Standards

In industrial hygiene air sampling, calibration of personal sampling pumps and DRIs establishes traceability to fundamental physical units. +-----------------------------------------------------------------------------------------+

• | CALIBRATION STANDARDS HIERARCHY |
• +---------------------------------------------------+-------------------------------------+
• | PRIMARY CALIBRATION STANDARDS | SECONDARY CALIBRATION STANDARDS |
• | (Direct measurement of Volume & Time) | (Indirect measurement / Calibrated) |
• +---------------------------------------------------+-------------------------------------+
• | 1. Electronic Dry Piston Meter (DryCal / Defender)| 1. Precision Rotameter (Float tube) |
• | 2. Soap Bubble Flowmeter (Burette + Stopwatch) | 2. Thermal Mass Flow Meter |
• | 3. Spirometer / Bell Prover (Liquid Seal Bell) | 3. Wet Test Meter (Revolving Drum) |
• | 4. Mariotte Bottle (Water Aspiration) | |
• +---------------------------------------------------+-------------------------------------+
• Primary Standards (Direct Physical Measurement)

Primary standards determine volumetric flow rate (Q = V / t) by measuring fundamental physical dimensions (volume of a cylinder V = π r² h) and time (t) without reference to any other flow-measuring instrument:

Electronic Piston Calibrators (DryCal / Defender) : A frictionless graphite piston moves inside a precision borosilicate glass cylinder. Optical infrared sensors detect the piston passage, recording displacement time with microsecond accuracy (< 1% volumetric uncertainty).

Soap Bubble Meters : A frictionless soap film is carried up a precision-calibrated glass burette by airflow while transit time between graduation marks is timed.

Bell Provers / Spirometers : A counterweighted cylindrical bell immersed in a liquid seal moves vertically as air enters, measuring displaced volume directly.

Secondary Standards (Indirect Measurement)

Secondary standards measure flow via indirect physical phenomena (pressure drop, heat transfer, drag force) and must be calibrated periodically against a primary standard :

Rotameters : Variable-area vertical glass tubes containing a float. Flow is indicated where aerodynamic drag balances the float's gravitational weight. Limitation : Highly sensitive to ambient air density, temperature, and barometric pressure variations.

Thermal Mass Flow Meters : Measure heat dissipation from a heated sensor wire to the air stream.

Pre- and Post-Sampling Calibration Protocol & Tolerance

To ensure legally defensible exposure assessments, sampling pumps must undergo pre-calibration immediately before field deployment and post-calibration immediately following sampling. +-----------------------------------------------------------------------------------------+

• | MANDATORY CALIBRATION TRAIN CONFIGURATION |
• | |
• | +-------------------+ +--------------------+ +----------------------------+ |
• | | Primary Calibrator| ---> | Representative | ---> | Personal Air Sampling Pump | |
• | | (DryCal / Bubble) | | Sorbent / Cassette | | (Under Calibration) |
• | +-------------------+ +--------------------+ +----------------------------+ |
• +-----------------------------------------------------------------------------------------+
• Rules for Field Pump Calibration

Representative Sampling Train In-Line : Calibration must be performed with the exact representative sampling media (sorbent tube, cyclone with filter, or cassette) connected in-line between the calibrator and the pump. Omitting the media during calibration alters backpressure and invalidates flow verification.

The ± 5.0% Flow Tolerance Rule : Flow Rate Difference ( % D ) = ∣ Q post − Q pre Q pre ∣ × 100 % \text{Flow Rate Difference } (\%D) = \left| \frac{Q_{\text{post}} - Q_{\text{pre}}}{Q_{\text{pre}}} \right| \times 100\% Flow Rate Difference ( % D ) = ​ Q pre ​ Q post ​ − Q pre ​ ​ ​ × 100%

If %D ≤ 5.0% : The calibration is acceptable. The average flow rate (Qavg = (Qpre + Qpost)/2) is used to calculate total sampled air volume (V = Qavg × t).

If 5.0% < %D ≤ 10.0% : The sample is flagged with caution; reported exposures must be documented as estimates.

If %D > 10.0% : Flow instability is excessive; the sample is voided under OSHA and NIOSH quality assurance criteria.

Worked Step-by-Step Example: PID Correction & Pump Flow Calibration ========================================================================================

• WORKED EXAMPLE: PID Direct Reading & Pump Calibration Verification
• ========================================================================================
• Part A: Direct-Reading PID Isobutylene Correction

Scenario:

An industrial hygienist investigates a trichloroethylene (TCE, MW = 131.39 g/mol) vapor

degreaser using a 10.6 eV PID calibrated to 100.0 ppm isobutylene.

• Direct instrument display reading = 42.0 ppm (isobutylene equivalent)
• Manufacturer 10.6 eV Correction Factor (CF) for TCE = 0.54

Calculation:

• True Airborne TCE Concentration = PID Reading × CF
• True Concentration = 42.0 ppm × 0.54 = 22.68 ppm

• ---------------------------------------------------------------------------------------
• Part B: Pump Calibration Flow Rate Tolerance Check

Scenario:

Prior to conducting 8-hour active sorbent sampling for confirmation, the personal pump is

calibrated with a representative coconut charcoal tube in-line using a DryCal primary standard.

• Pre-sampling calibration flow rate (Q_pre) = 202.4 mL/min
• Post-sampling calibration flow rate (Q_post) = 194.1 mL/min
• Total sampling duration (t) = 450 minutes

• Step 1: Calculate Absolute Percent Flow Rate Difference
• % Difference = (|Q_post - Q_pre| / Q_pre) × 100%
• % Difference = (|194.1 - 202.4| / 202.4) × 100%
• % Difference = (8.3 / 202.4) × 100% = 4.10%

Step 2: Evaluate Flow Acceptance Criteria

Finding: 4.10% ≤ 5.0%. The calibration passes the NIOSH/OSHA quality standard.

• Step 3: Calculate Average Flow Rate (Q_avg) and Total Sampled Air Volume (V)
• Q_avg = (202.4 mL/min + 194.1 mL/min) / 2 = 198.25 mL/min = 0.19825 L/min
• Total Volume (V) = Q_avg × t = 0.19825 L/min × 450 min = 89.21 L = 0.08921 m³
• ========================================================================================