FRP in Semiconductor Fabs: Exhaust Ducts, Scrubbers and Tanks

In short: A wafer fab sends acid fumes from wet benches and tools to a central acid exhaust and scrubber system that can move hundreds of thousands of cubic feet of air per minute. With the right resin, FRP handles diluted fab acids well, but in a fab fire rules decide more than corrosion. FM Global's semiconductor data sheet asks for noncombustible ducts or ducts approved to FM 4922 inside the fab, and for scrubbers to be kept out of the cleanroom envelope. That leaves FRP a clear role in outdoor or yard equipment: central scrubbers, fans, chemical and wastewater tanks, grating and cable trays. This guide shows where FRP fits, where it does not, and what to check with your insurer first.

How this guide fits with our others

This is the fab-specific guide, built around fire rules and acid chemistry. For corrosion in battery materials plants, from acid roast off-gas to caustic crystallizers, read FRP in lithium refineries: corrosion points step by step. For acid fume scrubbers in plating and PCB shops, see acid fume scrubbers for electroplating and PCB plants. Other sectors are on our industries page and emerging industries page.

How a fab handles acid exhaust

FM Global Data Sheet 7-7, Semiconductor Fabrication Facilities (April 2025), describes two levels of gas treatment:

• Point-of-use (POU) systems treat waste streams at the process tool, before they enter the central exhaust. FM lists wet scrubbers, oxidation units, cold bed and hot bed types, used to prevent exhaust restrictions, fires, explosions and corrosion.
• Facility (central) systems collect exhaust from many tools. FM states that the central acid exhaust usually has the largest airflow, which can be hundreds of thousands of cubic feet per minute, and that central acid scrubbers treat it before discharge. Separate central systems may handle ammonia, volatile organic compounds (VOC), general exhaust, heat and pyrophoric exhaust.

OSHA's semiconductor etchant table shows what the acid side carries: hydrofluoric acid and buffered oxide etch (HF with ammonium fluoride) for silicon dioxide, phosphoric with hydrofluoric for silicon nitride, mixtures of phosphoric, nitric, acetic and hydrochloric acids for aluminum, and aqua regia for some metals. Corrosion matters here, but so does fire: FM 7-7 lists combustible plastic construction materials (tools, ducts and scrubbers) among the main fire and explosion hazards in a fab.

What the fire rules say about ducts

This section decides most FRP questions in a fab, so read it before you choose a material.

FM 7-7 asks owners to:

1. Specify only noncombustible ducts (unlined ferrous metal) or ducts FM Approved to Standard 4922, listed for fume and/or smoke exhaust duct systems for use in cleanrooms.
2. Not use other duct categories in the FM Approval Guide for cleanroom application.
3. Avoid aluminum ducts, which can collapse early in a fire.
4. Provide low-point condensate drains where condensate may gather in FM 4922 ducts.
5. Use noncombustible or FM 4922 ducts from the outlet of a flame oxidation unit to the collector duct.

FM Global's industrial exhaust data sheet, 7-78, explains why. It states that ducts of polypropylene, PVC or FRP can readily support the spread of fire on the inside or outside, and that plastic liners alone can carry a fire through a duct. It also notes that FRP, as a thermoset, stays rigid when burning, with minimal to no dripping, unlike thermoplastics that melt and form pool fires.

What this means for buyers. A standard FRP duct is a combustible duct. Inside or connected to the cleanroom, it does not meet FM 7-7 unless it carries the FM 4922 cleanroom listing. FIBROVX does not claim FM 4922 approval for any duct. FRP fume ducts are custom / available on request for projects where the owner, the insurer and the authority having jurisdiction accept them, for example in outdoor runs to a yard scrubber with the fire protection FM 7-78 describes.

Central acid scrubbers

FM 7-7 asks owners to:

• keep scrubbers out of the cleanroom envelope and off the floors above it;
• place scrubber stacks away from cleanroom air intakes, with dispersion calculations if the separation is uncertain;
• protect scrubbers as described in Data Sheet 7-78.

Data Sheet 7-78 notes that plastics are used in ducts, hoods, fans, scrubbers, absorbers and mist eliminators because of the corrosive gases, and that PVC and FRP are often used in large fume removal systems because of rigidity, ease of handling and lower fabrication cost than corrosion-resistant alloys. For combustible systems, it sets sprinkler or water spray protection inside ducts and, where required, outside the system, at intake points, where ducts enter and leave equipment and buildings, at changes in direction of 90° or more, and at combustible equipment.

FRP is a strong candidate for the central scrubber shell, sump, packing supports, spray headers and mist eliminator housing. Our acid fume scrubbers are built to your gas flow and chemistry. See packed bed scrubber sizing and what a mist eliminator does. For the fan, see our FRP fan selection guide.

Resin choices for fab acids

Because so many etchants contain hydrofluoric acid (HF), which attacks glass, resin and veil choice comes first. A resin manufacturer's FRP Material Selection Guide gives the key points:

• HF. Premium resins have been used for HF up to 20%. Fabricators most often use synthetic surfacing veils, though C-veil has also worked where the corrosion barrier is properly built. Silica-based thixotropic agents should not be used.
• Hydrochloric acid. FRP has served up to the commercial limit of about 37%, with a cooler limit for concentrated acid than for dilute grades.
• Nitric acid. Up to 15% is readily handled; up to 50% brings significant temperature limits. Oxidizing acids need a full cure.
• Sulfuric acid. Dilute acid is handled well; above about 76% it becomes more aggressive to FRP.
• Fillers. Avoid fillers in acid service; they can increase permeation, and carbonates react with acids.

The same guide notes that ducting from cleanrooms in fabs is one of the uses where FRP has served as a corrosion-resistant material. That is a corrosion statement, not a fire approval; the duct rules above still apply.

Tell us every chemical a scrubber or tank will see, including cleaning chemicals. Our chemical resistance guide explains how we choose.

Concentrated chemicals: usually not FRP

OSHA's table lists standard supply concentrations for fab chemicals, including 49% hydrofluoric, 96% sulfuric, 67% nitric, 85% phosphoric and 36% hydrochloric acid. Compare those with the same manufacturer's limits above: 49% HF is well above the 20% that premium resins have handled, and 96% sulfuric is above the roughly 76% where sulfuric acid turns aggressive to FRP. Bulk storage and delivery of these concentrated grades normally follow the chemical supplier's and the fab's own material rules, and FRP is not our recommendation for them. FRP fits once the chemicals are diluted, spent or neutralized.

Chemical and wastewater tanks

FM 7-7 covers chemical handling in detail. It asks that:

• hazardous liquids are not stored in the cleanroom envelope, beyond limited daily supplies in approved cabinets;
• corrosive liquids in pumped distribution use stainless steel or double-contained plastic piping, drained back to the bulk system;
• bulk distribution units have double containment and drain to a bulk waste tank, disposal area or treatment plant;
• bulk storage tanks have a unique fill connection for each chemical;
• incompatible liquid waste streams have separate drainage systems, and pumped waste lines are double contained.

That points to several FRP items outside the fab building:

• Waste collection and neutralization tanks, with secondary containment set by your designer. US effluent rules for semiconductor plants (40 CFR 469) require a discharge pH between 6.0 and 9.0, so acid wastewater has to be neutralized before discharge.
• Acid waste and caustic dosing tanks in the wastewater plant.
• Scrubber recirculation tanks and blowdown tanks.

Our FRP tanks are built to your data sheet, filament-wound to ASTM D3299-26 or to a specification based on ASME RTP-1; that is a design basis, not an ASME stamp. See FRP tank standards. Ultrapure water systems have their own purity specifications; the same manufacturer's guide cites FRP case histories in deionized water up to 17–18 megohm resistivity, but your fab's water specification decides, so send it with any inquiry.

Grating, platforms and cable trays in the yard

Scrubber yards, chemical tank farms and wastewater plants need access platforms, stairs and cable routes in acid-laden air. FRP fits here:

• molded FRP grating and stair treads on scrubber and tank platforms;
• FRP handrail and ladders;
• FRP cable trays for instrument and power cables near acid equipment.

For fire performance of grating, see FRP grating fire rating and ASTM E84, and check what your insurer asks for in each area.

Honest limits of FRP in a fab

• Fire. FRP is combustible. Inside the fab, FM 7-7 points to noncombustible or FM 4922 ducts, and to FM 4910-listed plastics for some tool and cabinet construction. We hold neither listing.
• Temperature. Exhaust from heated baths and thermal abatement must be checked against resin limits; see FRP temperature limits by resin type.
• Static. FRP is non-conductive. Where the exhaust may carry flammable vapors, ask for a grounded carbon veil and confirm with your safety engineer.
• Purity. Do not assume FRP suits ultrapure water or chemical delivery to tools; those lines follow the fab's purity specification.

What to send for a quote

1. Equipment list and location: yard, roof or building.
2. Gas or liquid analysis with concentrations: HF, HCl, nitric, sulfuric, phosphoric, caustic, solvents.
3. Airflow, temperature and pressure for scrubbers and ducts.
4. Tank volume, specific gravity, nozzles and containment.
5. Insurer and code requirements, including any FM data sheet references.
6. Grating loads, spans and cable tray sizes.

Our tank data sheet checklist and grating RFQ checklist list more detail.

How we customize fab yard equipment

We build scrubbers, tanks, fans, grating and cable trays to your drawings and chemistry: resin and veil per stream, wall build, nozzles, manways, internals supports, platforms and color. Exhaust ducts, double-wall tanks and special housings are custom / available on request. Read custom FRP manufacturing for how an order runs.

We do not claim FM 4922, FM 4910, SEMI or any other approval or certificate. Tell us your requirements and we will state which tests and records we can supply.

VOC and particulate equipment for fabs

Solvent exhaust from fabs is often treated by a zeolite rotor feeding an oxidizer; acid mist after scrubbers by a wet ESP. See zeolite rotor concentrators, RTOs and wet ESPs.

Watch: Fab Exhaust in 27 Seconds

FAQ

Can FRP ducts be used in a semiconductor fab?

Inside or connected to the cleanroom, FM 7-7 asks for noncombustible ducts or ducts FM Approved to 4922 for cleanrooms. Standard FRP does not meet that. Outdoor runs may be accepted with fire protection; check with your insurer.

Is FRP suitable for HF scrubbers?

Yes, with the right build: premium vinyl ester resin, a synthetic surfacing veil and no silica thixotropes, per the same manufacturer's guide.

Where should the central scrubber go?

FM 7-7 says outside the cleanroom envelope and not on floors above it, with the stack away from air intakes.

Can FRP tanks store 49% HF or 96% sulfuric acid?

We do not recommend it. Those supply strengths are above the limits the same manufacturer's guide gives for FRP. FRP suits diluted, spent and neutralized streams.

Do you supply FM 4922 ducts?

No. We do not claim FM 4922 approval. FRP ducts are custom / available on request where the project accepts them.

What tanks does a fab need in FRP?

Mostly waste collection, neutralization, dosing and scrubber recirculation tanks outside the fab building.

Sources

• FM Global Property Loss Prevention Data Sheet 7-7, Semiconductor Fabrication Facilities, April 2025 (hazards; 2.5.8 ducts, scrubbers, liquid waste; 2.9 HPM liquids; 3.2.2 POU and central systems): https://www.fm.com/FMAApi/data/ApprovalStandardsDownload?itemId=%7B417F20B6-EFCA-463A-935C-3C52DEBEA28B%7D
• FM Global Property Loss Prevention Data Sheet 7-78, Industrial Exhaust Systems, October 2021, interim revision October 2024 (plastic ducts and fire spread; thermoset vs thermoplastic; protection locations): https://www.fm.com/FMAApi/data/ApprovalStandardsDownload?itemId=%7B9832E070-0CDF-4B1F-87F7-357F3902B707%7D
• A resin manufacturer, FRP Material Selection Guide, 2009 (HF to 20%, veils, thixotropes; HCl; nitric; sulfuric; fillers; cleanroom ducting; deionized water)
• OSHA, Semiconductors: Wet chemical etchants (Table 2), etchants and standard concentrations: https://www.osha.gov/semiconductors/tables/table2
• 40 CFR 469.14, Semiconductor subpart BPT effluent limitations (pH 6.0–9.0): https://www.law.cornell.edu/cfr/text/40/469.14
• ASTM D3299-26, Filament-Wound and Contact-Molded Glass-Fiber-Reinforced Thermoset Resin Corrosion-Resistant Tanks: https://store.astm.org/d3299-26.html