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18.3 Vapor Degreasing, Pickling, Electroplating, and Cyanide Baths

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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

18.3 Vapor Degreasing, Pickling, Electroplating, and Cyanide Baths

Key Takeaways Explain This Topic AI

Chlorinated solvent vapour degreasers exploit vapour density: trichloroethylene and perchloroethylene vapours are several times heavier than air and collect in pits, sumps, and the degreaser well itself.

Freeboard ratio, chilled condensing coils, and low lip velocity control degreaser emissions; excessive lip exhaust actually increases solvent loss by dragging vapour out of the blanket.

Chromic acid electroplating generates hexavalent chromium mist, controlled by lateral or push-pull slot hoods plus fume suppressants or floating polypropylene balls.

Adding acid to a cyanide plating bath liberates hydrogen cyanide gas; cyanide and acid baths must be physically separated with independent containment and spill control.

Last updated: August 2026

Vapor Degreasing, Pickling, Electroplating, and Cyanide Baths

Chemical processing, metal finishing, electroplating, and industrial painting operations encompass an extraordinary diversity of chemical and physical hazards. Industrial hygienists must evaluate corrosive acid and alkali mists , toxic metal aerosols , carcinogenic solvent vapors , sensitizing polymers , and pyrophoric or acutely toxic hydride gases .

Controlling these operations requires applying fluid dynamics, local exhaust ventilation (LEV), chemical kinetics, and rigorous physical isolation safeguards.

1. Solvent Vapor Degreasing (SVD) Operations

Solvent vapor degreasers ( SVDs ) clean non-porous metal parts by suspending cold metal components in the hot, concentrated vapor zone of a boiling chlorinated or halogenated solvent. As the solvent vapor contacts the colder workpiece, it condenses into pure liquid solvent, dissolving oils, cutting fluids, and greases, which then drip back into the boiling sump. +-------------------------------------------------------------------------+

  • | SOLVENT VAPOR DEGREASER (SVD) SCHEMATIC |
  • +-------------------------------------------------------------------------+
  • | |
  • | | <-------------- Tank Width (W) --------------> | |
  • | +------------------------------------------------+ |
  • | | | ^ |
  • | | [ Lip Exhaust Hood / Slot LEV ] | | |
  • | | | | Free-|
  • | | ========================================== | | board|
  • | | [ Primary Condensing Water Coils (12-15°C)] | | Height|
  • | | ========================================== | | (H) |
  • | | | | |
  • | VAPOR ZONE | - - - - - - - - - - - - - - - - - - - - - - - | v |
  • | (Heavy Dense | . . . . . . . . . . . . . . . . . . . . . . . | |
  • | Solvent Gas)| . . . . [ Suspended Cold Workpiece ] . . . . | |
  • | | . . . . . . . . . . . . . . . . . . . . . . . | |
  • | |------------------------------------------------| |
  • | BOILING SUMP | ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | |
  • | (Liquid TCE/ | ~ ~ ~ ~ ~ [ Immersion Electric Heaters ] ~ ~ ~ | |
  • | PCE / DCM) +------------------------------------------------+ |
  • +-------------------------------------------------------------------------+
  • Solvents Utilized in SVDs

Trichloroethylene (TCE, C2HCl3): Highly effective degreaser; IARC Group 1 known human carcinogen (kidney renal cell carcinoma, non-Hodgkin lymphoma, liver cancer). Under EPA TSCA regulations, TCE use is subject to comprehensive workplace bans.

Perchloroethylene (PCE / Tetrachloroethylene, C2Cl4): IARC Group 2A probable human carcinogen; central nervous system depressant and hepatotoxin.

Methylene Chloride (Dichloromethane / DCM, CH2Cl2): OSHA substance-specific standard (29 CFR 1910.1052, PEL 25 ppm, STEL 125 ppm, Action Level 12.5 ppm); metabolizes in vivo to carbon monoxide (extCO) , producing carboxyhemoglobinemia (extCOHb).

Mandatory SVD Engineering Design Parameters

Freeboard Ratio (FBR): Freeboard Ratio (FBR) = Freeboard Height ( H ) Tank Width ( W ) \mathbf{\text{Freeboard Ratio (FBR)} = \frac{\text{Freeboard Height } (H)}{\text{Tank Width } (W)}} Freeboard Ratio (FBR) = Tank Width ( W ) Freeboard Height ( H ) ​

Requirement: Under EPA NESHAP (40 CFR 63 Subpart T) and ACGIH guidelines, the Freeboard Ratio must be ≥ 0.75 to 1.0 .

Physical Rationale: A high freeboard traps the heavy solvent vapor layer (vapor density > 3.0 relative to air) and prevents cross-drafts in the plant from scouring solvent vapor out into the breathing zone.

Condensing Water Coils: Peripheral cooling coils located around the interior wall above the vapor line must circulate chilled water (12°C to 15°C) to continuously condense vapors back into the liquid sump.

Automated Hoist Velocity Restrictions:

Workpiece baskets must enter and exit the vapor zone at a vertical speed ≤ 11 ft/min (3.3 m/min or 0.055 m/s) .

Physical Rationale: Excessive hoist speed creates a piston effect (aerodynamic wake) that forcefully drags the heavy vapor layer out of the tank into the workplace air.

Workpiece Drainage and Dwell Time: Parts must remain suspended in the freeboard zone above the vapor line until liquid dripping completely ceases (minimum 15--30 seconds).

Lip Exhaust LEV (Lateral Slot Hoods): Exterior slot hoods along the top perimeter must provide lateral exhaust capture without disturbing the calm interface of the vapor zone.

2. Acid Pickling and Electroplating Surface Finishing

Electroplating deposits a thin, protective or decorative metallic coating onto a substrate by passing direct electric current between an anode and the workpiece cathode submerged in an aqueous electrolyte solution. +-------------------------------------------------------------------------+

  • | ELECTROPLATING TANK DYNAMICS & MIST GENERATION |
  • +-------------------------------------------------------------------------+
  • | |
  • | Direct Current (DC Power Source) |
  • | ===> Cathode (Workpiece): Metal Ion Reduction (Cr^VI + 6e- ===> Cr^0) |
  • | AND Parasitic Water Hydrolysis (2 H+ + 2e- ===> H2 Gas) |
  • | |
  • | ===> Hydrogen Bubbles Nucleate & Rise Rapidly to Liquid Surface |
  • | ===> Violent Bubble Bursting at Surface |
  • | ===> Ejection of Submicron Liquid Aerosols (Acid Mists) |
  • | |
  • | ENGINEERING CONTROLS: |
  • | 1. Chemical Fume Suppressants / Non-PFAS Wetting Agents (Surface |
  • | Tension < 33 dynes/cm via Stalagmometer / Tensiometer) |
  • | 2. Polypropylene Floating Blankets / Hexagonal Solid Balls |
  • | 3. Push-Pull Lateral Exhaust Ventilation (Capture Velocity >= 100 fpm) |
  • | 4. Composite Mesh Pad (CMP) Mist Eliminators (EPA NESHAP standard) |
  • +-------------------------------------------------------------------------+
  • Acid Pickling Operations

Prior to electroplating, metal parts undergo acid pickling to strip oxides, scale, and rust:

Hydrochloric Acid (extHCl), Sulfuric Acid (extH2 extSO4), Nitric Acid (extHNO3), Hydrofluoric Acid (extHF): Generate dense, corrosive acid mists.

Carcinogenicity: Occupational exposure to strong inorganic sulfuric acid mists is classified by IARC as a Group 1 known human carcinogen (causing laryngeal cancer and lung cancer).

Physical Pathology: Dental erosion (dissolution of tooth enamel from chronic acid vapor inhalation), severe chemical skin burns, and pulmonary edema upon acute peak exposures.

Hard Chrome vs. Decorative Chrome Plating

  • Operational Feature Decorative Chrome Plating Hard (Industrial) Chrome Plating
  • Coating Thickness Very thin (0.25--0.5 µm) Thick (10--500+ µm) for wear/corrosion resistance
  • Current Density Low (0.5--1.5 A/in²) Very High (2.0--6.0+ A/in²)
  • Plating Duration Brief (1 to 3 minutes) Extended (2 to 24+ hours)
  • Cathodic Efficiency Low (10--15%) Extremely Low (10--15%)
  • Mist Generation Low mass per batch Massive, continuous Cr(VI) mist generation
  • Regulatory Mandate Wetting agents or composite mesh Strict EPA NESHAP Composite Mesh Pad (CMP)

Mist Generation Mechanism: Because cathode current efficiency is only 10%--15%, roughly 85% to 90% of the electrical energy goes into the electrolysis of water, generating copious volumes of hydrogen gas (extH2) at the cathode and oxygen gas at the anode. As millions of micro-bubbles rise and burst vigorously at the liquid-air interface, they atomize the chromic acid electrolyte into respirable hexavalent chromium (extCr^ extVI) mists .

Control Technologies:

Chemical Fume Suppressants: Surfactants that lower bath surface tension (< 33 dynes/cm or mN/m measured via stalagmometer). Note: Perfluorooctane sulfonate ( PFOS ) has been globally phased out due to environmental persistence; non-PFAS fluorosurfactants and synthetic hydrocarbon alternatives are now mandated.

Composite Mesh Pad (CMP) Scrubbers: Multi-stage pad systems achieve > 99.9% capture efficiency of submicron acid droplets.

3. Cyanide Plating Bath Hazards & Lethal HCN Acidification

Cyanide-based electroplating solutions are widely used for copper, zinc, cadmium, gold, silver, and brass plating because cyanide ions ((CN)⁻) act as powerful complexing ligands (e.g., [Cu(CN)2]⁻, [Cd(CN)4]²⁻), promoting uniform metal deposition and fine grain structure. +-------------------------------------------------------------------------+

  • | THE CATASTROPHIC CYANIDE ACIDIFICATION EVENT |
  • +-------------------------------------------------------------------------+
  • | |
  • | ALKALINE CYANIDE PLATING BATH (pH 11 - 13) |
  • | Contains: Free Cyanide Ions (CN-) & Metal Cyanide Complexes |
  • | |
  • | + |
  • | |
  • | ACID PICKLING SOLUTION (pH 0 - 2) |
  • | Contains: Hydrochloric (HCl), Sulfuric (H2SO4), or Nitric Acid |
  • | |
  • | ║ |
  • | ACCIDENTAL MIXING / CROSS-CONTAMINATION (pH Drops < 9) |
  • | ║ |
  • | ▼ |
  • | 2 NaCN + H2SO4 ===> Na2SO4 + 2 HCN (g) ↑ (Violent Gas Surge!) |
  • | |
  • | HYDROGEN CYANIDE (HCN) TOXICITY: |
  • | • NIOSH IDLH: 50 ppm | Rapid Inhalation Lethality: > 100 - 300 ppm |
  • | • Mechanism: Inhibits Cytochrome c Oxidase in Mitochondrial ETS |
  • | • Cellular Asphyxiation / Histotoxic Hypoxia |
  • +-------------------------------------------------------------------------+
  • The Acidification Hazard

In an alkaline solution (pH > 11), cyanide remains dissolved in the non-volatile ionic state ((CN)⁻). However, if an alkaline cyanide bath is accidentally acidified (or if cyanide-bearing rinse water mixes with acid pickling effluent in a common drain or sump) such that the pH drops below the dissociation constant (pKa = 9.21), cyanide ions instantaneously protonate to form Hydrogen Cyanide (extHCN) gas , which boils off vigorously (Tb = 25.6°C): CN − + H + ⇌ HCN ↑ ( p K a = 9.21 ) \text{CN}^- + \text{H}^+ \rightleftharpoons \text{HCN}\uparrow \quad (pK_a = 9.21) CN − + H + ⇌ HCN ↑ ( p K a ​ = 9.21 )

Mandatory Engineering & Operational Segregation Rules

Physical Spatial Isolation: Cyanide tanks and acid tanks must never be placed adjacent to one another where splashes, drips, or dropped parts could cause cross-contamination.

Dedicated Drainage & Spill Containment: Floor drains, sumps, and containment berms for cyanide lines must be completely physically isolated from acid effluent lines. Cyanide wastewater must undergo alkaline chlorination destruction ((CN)⁻ + OCl⁻ arrow CNO⁻ arrow CO2 + N2) in a separate dedicated treatment stream.

Continuous Toxic Gas Detection: Electrochemical extHCN sensors with audible/visual alarms must be installed at plating line breathing zones.

Emergency Cyanide Antidote Protocol: Facilities must stock immediate cyanide medical antidote kits:

Hydroxocobalamin (Cyanokit): Primary modern therapy; binds cyanide to form non-toxic cyanocobalamin (Vitamin extB12), excreted in urine without producing methemoglobinemia.

NITHIODOTE / Cyanide Antidote Kit: Sodium nitrite (induces methemoglobinemia to sequester cyanide from cytochrome oxidase) followed by sodium thiosulfate (substrate for hepatic rhodanese to convert cyanide into thiocyanate).