Introduction
An electroplating ventilation system is not just a scrubber with some ductwork attached — it is an integrated airflow design problem where the exhaust hood determines capture velocity, the duct layout determines whether cyanide and acid gases are safely segregated, the fan determines whether the entire system operates at its design point, and the scrubber is the final stage, not the first. Most plating shop ventilation problems originate upstream of the scrubber: an undersized hood that cannot capture the chrome mist rising from a decorative chrome tank at 1.5 m/s face velocity, a common duct manifold that combines acid and cyanide exhaust in violation of every safety code, or a fan sized for the duct friction at commissioning that is now operating against partially clogged packing. This guide covers the complete electroplating ventilation system from hood to stack: tank exhaust hood sizing for capture velocity, zoned duct layout for chemical segregation, fan selection for corrosive service, and scrubber integration for compliance. For the chemistry-specific scrubber design that handles HCl, chrome mist, H₂SO₄, and cyanide — the component that goes at the end of the duct system — see our companion article on electroplating acid scrubber design.
Key Takeaways
– The exhaust hood is the most common point of failure — an undersized hood at the tank edge fails to capture the contaminant at the source, and no downstream scrubber can recover what never entered the duct. Face velocity at the hood opening must be 0.5–1.5 m/s depending on the process and contaminant toxicity.
– Zone segregation by chemistry is a life-safety requirement, not a design preference — cyanide-bearing exhaust and acid-bearing exhaust must never share a common duct. Acid plus cyanide produces hydrogen cyanide gas inside the ductwork. NFPA and local fire codes mandate separate duct systems.
– Fan selection in corrosive service is a lifecycle decision — a standard steel fan in HCl exhaust fails within 2–3 years. PP or FRP fan construction eliminates corrosion-driven impeller failure and provides 10–15 years of service.
– Heat recovery from plating shop exhaust can offset 30–50% of makeup air heating costs — air-to-air heat exchangers on the scrubber outlet recover waste heat from the treated exhaust stream and preheat incoming makeup air, cutting the facility’s ventilation energy consumption.
Exhaust Hood Design — Capturing Contaminants at the Source
The exhaust hood is the first component in the electroplating ventilation system and the most common source of system underperformance. If the hood does not capture the contaminant — acid mist, chrome aerosol, or cyanide vapor — at the tank surface, no downstream scrubber, fan, or stack can recover it. The contaminant enters the shop air, exposes workers, and corrodes the building structure.
Hood Types by Tank Configuration
Slot hood (push-pull): A narrow slot along the tank rim, positioned on the operator side, pulls air across the tank surface. Slot hoods are the most common design for rectangular plating and pickling tanks because they capture contaminants at their source — the liquid surface — with the minimum exhaust airflow. The slot velocity is 10–15 m/s; the capture velocity at the far tank edge must be a minimum of 0.5 m/s for acid mist and 0.75 m/s for chrome mist (higher due to Cr(VI) toxicity).
Canopy hood: A suspended hood above the tank captures rising thermal plumes from heated process baths. Canopy hoods require 2–3× the airflow of slot hoods because the contaminant plume has already dispersed before reaching the hood face. They are acceptable for non-toxic, heated water vapor exhaust (rinse tanks) but inadequate for chrome plating tanks where the Cr(VI) aerosol must be captured before it disperses beyond the tank boundary.
Enclosing hood: The tank is fully enclosed with access doors or panels, and the hood exhausts from the enclosure interior. Enclosing hoods provide the highest capture efficiency at the lowest airflow but restrict operator access. Used for automated plating lines where the process is enclosed and operator access is not required during plating.
Capture Velocity by Contaminant
| Contaminant | Required Capture Velocity (m/s) | Hood Type |
|---|---|---|
| Acid mist (HCl, H₂SO₄) — heated bath | 0.5–0.75 | Slot hood |
| Chrome mist (CrO₃) — decorative chrome | 0.75–1.0 | Slot hood (preferred) or canopy |
| Chrome mist (CrO₃) — hard chrome | 1.0–1.5 | Enclosing hood or high-velocity slot |
| Cyanide vapor (HCN) — cyanide plating | 0.5–0.75 | Slot hood — fully segregated duct |
| Water vapor (rinse tanks) | 0.3–0.5 | Canopy hood |
The OSHA ventilation standard (29 CFR 1910.94) for open-surface tanks specifies minimum exhaust rates based on tank dimensions and process hazard classification. Chrome plating tanks are Class A (most hazardous) and require the highest exhaust rates per square meter of tank surface area.
Exhaust Airflow Calculation
The required exhaust airflow for a slot hood is:
Q = v_capture × A_tank × K
Where Q is exhaust airflow (m³/s), v_capture is the required capture velocity at the far tank edge (m/s), A_tank is the tank surface area (m²), and K is a dispersion factor (1.5–2.5, higher for heated baths and agitated surfaces).
A 2m × 1m decorative chrome plating tank at 55°C with 0.75 m/s capture velocity and K=2.0 requires Q = 0.75 × 2 × 2.0 = 3.0 m³/s (6,360 CFM). This is the design airflow for the duct branch serving this tank.
Zoned Duct Layout — Segregation by Chemistry
Duct layout in an electroplating ventilation system is governed by one non-negotiable safety rule: cyanide-bearing and acid-bearing exhaust must never share a common duct. If acid mist — even a small leak at a tank hood — enters a cyanide exhaust duct, the acid reacts with cyanide salts that have deposited on the duct walls, releasing hydrogen cyanide (HCN) gas inside the ventilation system. HCN has an IDLH of 50 ppm; a duct leak into an occupied area can be fatal. The NFPA 33 standard for spray application using flammable materials applies to plating shop duct segregation where various chemical hazards coexist.
Zone Assignment
| Zone | Tanks | Duct Material | Scrubber | Discharge |
|---|---|---|---|---|
| Zone A: Acid exhaust | HCl pickling, H₂SO₄ anodizing, decorative chrome | PP (round, welded) | NaOH packed bed, pH 7–9 | Common stack after scrubber |
| Zone B: Chrome exhaust | Hard chrome plating (high CrO₃ concentration) | PP (round, welded) | NaOH packed bed + high-efficiency mist eliminator, pH 8–10 | Separate stack or after mist eliminator |
| Zone C: Cyanide exhaust | Cyanide zinc, cyanide copper | PP (round, welded) — dedicated, no interconnection | NaOH packed bed, pH >10 | Separate stack — never combined with acid exhaust |
| Zone D: General ventilation | Rinse tanks, non-toxic process areas | PP or galvanized steel | None (dilution ventilation) | Direct to atmosphere |
Duct design rules:
- Round PP duct for all corrosive exhaust. Rectangular duct accumulates condensate at bottom corners and is difficult to drain.
- Welded joints throughout — flanged connections only at equipment interfaces (fan inlet/outlet, scrubber inlet, damper locations).
- Slope all horizontal duct runs 1–2% toward a drain point. Acid condensate pooling in a low section of duct attacks the duct wall from the inside.
- PP duct support spacing: 2.5–3.5 meters for diameters up to 500mm. Supports must be saddles with EPDM pads — never clamp rigidly (PP expands 0.15 mm/m·°C).
- Color-code or label each zone’s ductwork: red for acid, yellow for chrome, blue for cyanide, grey for general ventilation. Visual identification prevents cross-connection during maintenance.
For complete PP duct installation procedures including welding parameters and leak testing, see our PP duct installation guide.
Fan Selection for Corrosive Plating Shop Service
The fan in an electroplating ventilation system moves corrosive air containing acid mist, chrome aerosol, and sometimes cyanide vapor. A standard carbon steel fan in this service fails within 6–12 months — the impeller corrodes, loses balance, and either seizes or throws a blade. Fan selection is a lifecycle decision.
PP vs FRP vs Coated Steel Fans
| Fan Material | Max Temp | HCl Resistance | Chrome Mist Resistance | Relative Cost | Service Life |
|---|---|---|---|---|---|
| PP centrifugal | 80°C | Excellent — chemically inert | Excellent | 1.0× | 15+ years |
| FRP centrifugal (vinyl ester) | 120°C | Excellent | Good (resin-dependent) | 1.3–1.5× | 10–15 years |
| FRP centrifugal (polyester) | 100°C | Good | Moderate — Cr(VI) attacks resin | 1.1–1.3× | 7–10 years |
| Coated steel (epoxy, PTFE) | 200°C | Moderate — coating defects expose substrate | Moderate | 0.8–1.0× | 3–5 years |
| SS316 centrifugal | 400°C | Poor — chloride pitting within 2–3 years | Moderate | 1.5–2.0× | 3–5 years |
Fan Sizing Parameters
The fan static pressure must overcome: duct friction (0.5–2 Pa/m × total duct length), fitting losses (0.2–0.5 velocity heads per elbow, tee, or damper), scrubber pressure drop (500–1,500 Pa for packed bed), mist eliminator (100–300 Pa), and stack draft. A typical electroplating shop with 100 meters of total duct, four elbows, and a packed bed scrubber requires 1,500–3,000 Pa total static pressure at the fan. This is within the range of a single-stage PP or FRP centrifugal fan. For the fan system curve design methodology, see our FRP anti-corrosion fan selection guide.
Makeup Air and Heat Recovery — The Overlooked Half of the System
Every cubic meter of air exhausted from the plating shop must be replaced by makeup air. Without a designed makeup air system, the building operates under negative pressure, pulling unfiltered outdoor air through door gaps, loading docks, and window frames. In winter, unheated makeup air drops the shop temperature below the process minimum (typically 18–20°C for plating baths) and freezes water lines in exterior walls.
Makeup air system design:
- Supply air volume = 90–95% of exhaust volume (slight negative pressure prevents fugitive odor escape to adjacent areas).
- Supply air distribution — introduce makeup air at the operator breathing zone (behind the worker, blowing toward the tanks) and at the ceiling to create a downward displacement flow pattern.
- Filtration — MERV 8 minimum for general industrial areas; MERV 13 for areas adjacent to clean assembly or packaging operations.
Heat recovery from exhaust:
The exhaust air from an electroplating shop is typically 25–40°C (heated tanks + process heat). This heat can be recovered to preheat incoming makeup air through an air-to-air heat exchanger:
- Run-around coil system — a glycol loop with coils in both the exhaust and supply airstreams. Physically separates the corrosive exhaust from the supply air (no cross-contamination). Recovers 40–55% of the exhaust heat. PP or FRP coils are required in the exhaust airstream; copper or aluminum coils in the supply airstream.
- Heat pipe exchanger — passive two-phase (refrigerant) heat pipes transfer heat from the exhaust to the supply air. Higher efficiency (50–65% recovery) but requires the two airstreams to be adjacent, which is not always practical in retrofit installations.
- Payback period — for a shop exhausting 50,000 CFM at 30°C in a climate with 2,000 heating degree-days, heat recovery saves $15,000–30,000 per year in natural gas costs. The installed cost of the run-around coil system (approximately $40,000–60,000) pays back within 2–3 years.
Frequently Asked Questions
What capture velocity do I need for chrome plating tank exhaust?
0.75–1.0 m/s at the far tank edge for decorative chrome; 1.0–1.5 m/s for hard chrome. The higher velocity for hard chrome reflects the higher Cr(VI) concentration and toxicity. Use a slot hood positioned on the operator side of the tank. An enclosing hood with interior exhaust is preferred for automated hard chrome lines. The OSHA ventilation standard table above provides the tank classification and minimum exhaust rates.
Can I combine all plating shop exhaust into one scrubber?
No. Cyanide-bearing exhaust and acid-bearing exhaust must be ducted to separate scrubbers. Combining them produces HCN gas inside the ductwork. Even within the acid zone, chrome mist requires a separate scrubber with high-efficiency mist eliminator if the Cr(VI) concentration is high enough to require dedicated treatment (typical for hard chrome operations). The zone segregation table above provides the assignment.
How do I prevent my PP exhaust duct from sagging?
Support PP duct on saddles with EPDM pads at 2.5–3.5 meter intervals for diameters up to 500mm. Every support between the fixed point and the expansion joint must be a sliding support — never clamp rigidly. Slope horizontal runs 1–2% toward drain points to prevent acid condensate pooling. The duct installation procedures in our PP duct installation guide cover the complete support system design.
What fan material should I use for electroplating exhaust?
PP centrifugal fan for exhaust below 80°C containing HCl, chrome mist, and H₂SO₄. FRP centrifugal fan (vinyl ester resin) for exhaust between 80–120°C. Do not use coated steel or stainless steel fans in HCl or chrome service — the former fails at coating defects within 2–3 years; the latter pits from chloride attack within the same period. The fan material comparison table above provides the full analysis.
Can I recover heat from electroplating exhaust?
Yes — a run-around coil system with PP/FRP coils in the corrosive exhaust airstream and copper/aluminum coils in the supply airstream recovers 40–55% of the exhaust heat and preheats incoming makeup air. Payback is 2–3 years for facilities in heating-dominated climates. The heat recovery section above provides the design methodology.
Conclusion
An electroplating ventilation system is an integrated design from hood to stack — not a collection of independently specified components. The exhaust hood determines whether the contaminant enters the duct or the worker’s breathing zone. The duct layout determines whether the system operates safely or creates a hydrogen cyanide generation point. The fan determines whether the system overcomes its total static pressure with a corroding steel impeller or a chemically inert PP impeller. And the makeup air and heat recovery system determines whether the shop pays for the energy lost in the exhaust air or recovers it. Every component from the hood slot to the stack discharge is fabricated from PP — the only material that resists HCl, chrome mist, and H₂SO₄ simultaneously for 15+ years without corrosion. For the scrubber chemistry that goes at the end of the duct system, see our companion article on electroplating acid scrubber design. Send us your tank list, shop layout, and local emission requirements, and we will return a complete electroplating ventilation system design with hood sizing, duct layout, fan selection, and scrubber specification — at factory-direct pricing.
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Written by Corbin, a senior process engineer whose career has spanned over a decade designing ventilation systems for electroplating shops, anodizing lines, and metal finishing facilities across three continents. Every hood sizing parameter, duct segregation rule, fan material comparison, and heat recovery calculation in this article is drawn from documented outcomes of our 500+ completed installations.
