Chemical Exhaust Systems

Chemical vapours and gases can cause immediate irritation, burns, dizziness and loss of consciousness, as well as long-term damage to the lungs, nervous system, liver and kidneys. Source capture chemical exhaust removes these contaminants before they reach the breathing zone, keeping exposure within safe limits.

Acid and alkali fumes that escape into a building attack steel structures, roofing sheets, cable trays, electrical panels and machinery. Uncontrolled corrosion leads to costly repairs, electrical faults and shortened equipment life. A chemical exhaust system keeps these fumes contained and away from your assets.

Solvent vapours and hydrogen can form flammable mixtures in poorly ventilated rooms and ducts. A flammable vapor exhaust system keeps concentrations well below the lower explosive limit, while spark-resistant and flameproof equipment removes ignition sources from the airstream.

Indian occupational safety law, hazardous chemical rules and pollution control boards all expect hazardous emissions to be captured, treated and discharged responsibly. Scrubbers, carbon adsorbers and correctly designed stacks help you meet consent conditions, pass inspections and avoid complaints from neighbours.

Pickling, plating, etching, digestion and chemical processing release acid mists and fumes that rapidly corrode steel. Hydrochloric and nitric acids are highly volatile, sulphuric acid forms dense mists, and hydrofluoric acid attacks glass and silica-based materials. An acid exhaust system uses PP, PVC or specially lined FRP components with a neutralising scrubber.

Caustic soda, potassium hydroxide and other alkalis are used in cleaning, degreasing, etching and chemical manufacturing. Their mists damage aluminium, galvanised surfaces and some plastics. They are typically captured with tank hoods and treated in an acid-dosed scrubber.

Toluene, xylene, acetone, alcohols, MEK and other solvents are used in paints, coatings, inks, adhesives, pharmaceuticals and cleaning. A solvent or VOC exhaust system must handle both toxicity and flammability, often using activated carbon or oxidisers and spark-resistant fans. An exhaust fan for paint fumes, for example, must never be an ordinary ventilation fan.

Chlorine in water treatment, ammonia in refrigeration and fertilisers, and gases such as hydrogen sulphide, sulphur dioxide and phosphine in process and semiconductor plants are acutely toxic. They need reliable local exhaust, gas detection and, in many cases, an emergency scrubber to neutralise a leak.

Solvent storage rooms, dispensing areas and battery charging rooms can accumulate flammable vapours or hydrogen. Hydrogen is lighter than air and collects at ceiling level, while most solvent vapours are heavier and settle low. Exhaust points, fans and electrical equipment are designed for the specific hazard.

Hot perchloric acid digestion can deposit perchlorate salts inside hoods and ducts, which may become shock-sensitive and explosive. Perchloric acid work needs a dedicated wash-down exhaust system with no shared ductwork and regular wash cycles to keep internal surfaces clean.

Laboratory fume hoods, chemical exhaust hoods, canopy hoods, chemical slot hoods along tank edges and ventilated enclosures form the first line of defence. Chemical tank exhaust typically uses lateral slot or push-pull hoods that capture fumes across the tank surface without obstructing work.

Chemical exhaust duct systems are built from PP, PVC, CPVC, FRP, stainless steel or PVDF and PTFE-coated steel, depending on the chemicals and temperature. Joints are welded, flanged or bonded to remain leak-tight under constant chemical attack.

A chemical exhaust scrubber removes acid, alkali and water-soluble gases by contacting the airstream with a scrubbing liquid. Packed bed scrubbers are the most common chemical gas scrubber for process and laboratory exhaust, with automatic pH control and chemical dosing.

Activated carbon chemical exhaust units adsorb solvent vapours, VOCs and odours. Impregnated carbons target specific gases such as ammonia, hydrogen sulphide or mercury vapour. Carbon beds are sized for adequate contact time and replaced before breakthrough.

Chemical resistant exhaust fans are built with FRP, PP or coated casings and impellers. An FRP chemical exhaust fan or corrosion resistant exhaust fan handles acid fumes for years where a standard steel fan would fail in months. For flammable vapours, spark-resistant construction and flameproof motors are used.

PP, PVC and FRP dampers balance airflow between branches and isolate hoods when not in use. In laboratories, VAV valves and airflow controllers adjust exhaust to sash position, maintaining face velocity while saving energy.

The chemical exhaust stack discharges treated air at a safe height and velocity. Stacks include sampling ports and platforms for emission monitoring and are designed to avoid rain entry without using rain caps that push air downward.

Fixed gas detectors monitor for toxic or flammable gases in rooms and near equipment. On alarm, they can start emergency exhaust fans, trigger scrubbers, shut off gas supplies and alert staff, forming a critical part of chemical exhaust gas detection.

Laboratory fume hood exhaust systems connect one or more hoods to chemical-resistant ducts and roof-mounted fans. Laboratories are kept under negative pressure relative to corridors, so fumes cannot escape into offices or other areas.

Chemical process exhaust systems capture fumes from reactors, charging points, mixing vessels, dryers, filling lines and tank farms. They are often combined with scrubbers or carbon adsorbers to meet emission norms.

Acid fume extraction systems for pickling, plating, etching and digestion combine tank hoods, PP or FRP ductwork, a packed bed scrubber and an FRP chemical exhaust fan. These are among the most common chemical fume exhaust systems with scrubbers in Indian industry.

Solvent exhaust systems serve paint booths, coating lines, printing, pharmaceutical processing and solvent storage. They use spark-resistant fans, earthed ductwork and carbon adsorption or oxidation to control VOC emissions.

Perchloric acid hoods are connected to dedicated, straight-run ductwork with built-in water spray nozzles. Regular wash-down cycles remove perchlorate deposits from the hood, duct and fan, preventing the build-up of explosive residues.

Chemical storage rooms and ventilated safety cabinets need continuous exhaust to remove vapours released from containers. Exhaust points are placed at high or low level based on vapour density, and fans are selected for corrosive or flammable duty.

Battery charging and UPS rooms release hydrogen, which must be removed from ceiling level to prevent an explosive build-up. We design continuous or detector-triggered exhaust with spark-resistant fans and suitable electrical equipment.

Gas cabinets for toxic, corrosive or pyrophoric gases in semiconductor, electronics and research facilities are continuously exhausted. Exhaust flow is monitored, and any failure alarms and shuts off the gas supply.

Chlorine tonner rooms and ammonia plants require emergency exhaust connected to a leak absorption scrubber. When gas detectors sense a leak, the exhaust fan and scrubber start automatically to neutralise the gas before it reaches the atmosphere. A chlorine room exhaust fan is always selected for corrosive, wet-gas duty.

PP chemical exhaust ducts offer excellent resistance to most acids, alkalis and salt solutions at moderate temperatures. They are lightweight, easy to weld and cost-effective, making them the most popular choice for acid fume extraction in plating and pickling plants. Flame-retardant PP grades are available where fire performance matters.

PVC chemical exhaust ducts resist a wide range of acids, alkalis and chlorine, and are inherently self-extinguishing. They are widely used in laboratories and water treatment plants. CPVC extends the temperature range for warmer exhaust streams.

FRP chemical exhaust ducts combine chemical resistance with high structural strength, making them ideal for large-diameter ducts, outdoor runs, stacks and scrubbers. Resin and liner selection, such as vinyl ester resin with a synthetic veil, is matched to the chemical service. Acid fume exhaust systems with FRP ductwork are a proven choice for heavy industrial duty.

Stainless steel is suited to solvent vapours, many alkalis, nitric acid and high-temperature exhaust. It is non-combustible and conductive, which suits flammable vapour systems. However, it is attacked by chlorides and hydrochloric acid, so SS 316 or alternative materials are chosen where chlorides are present.

PVDF and PTFE-coated ducts are premium options for aggressive or mixed chemical streams, higher temperatures and cleanroom or semiconductor applications. They offer broad chemical resistance and, in coated steel form, the fire performance of a metal duct.

*This chart is a general guide. Final material selection depends on concentration, temperature, moisture, fire requirements and a chemical compatibility check by our engineers.*

A packed bed scrubber passes contaminated air upward through a bed of random or structured plastic packing while scrubbing liquid flows downward. The large wetted surface area gives high removal efficiency for acid gases, alkali mists and water-soluble vapours. It is the workhorse of chemical exhaust treatment.

Venturi scrubbers accelerate the gas through a narrow throat where the scrubbing liquid is atomised into fine droplets. They are effective for fine particulate, mists and sticky fumes, and are often followed by a packed section or cyclonic separator.

For acid fumes, a caustic solution neutralises the gas; for ammonia and alkaline vapours, a dilute acid is used. Automatic pH control and chemical dosing keep the scrubbing liquid at the right strength, while blowdown removes spent solution to the effluent treatment plant.

Activated carbon captures organic vapours, odours and some inorganic gases on its internal surface. It is ideal for low to moderate VOC concentrations, laboratory exhaust with mixed organics and odour control. Carbon replacement is planned based on the solvent load.

For large or concentrated VOC streams, thermal oxidisers destroy solvent vapours at high temperatures, while catalytic oxidisers do the same at lower temperatures. Regenerative designs recover heat to cut fuel consumption significantly.

Mist eliminators, such as chevron blades or mesh pads, remove entrained droplets from the air leaving a scrubber. They prevent chemical carryover into fans, ducts and the surrounding environment, and are also used to capture acid mist directly from process tanks.

The Manufacture, Storage and Import of Hazardous Chemical (MSIHC) Rules, 1989 require sites handling listed hazardous chemicals to identify major accident hazards, take preventive measures and maintain emergency plans. Occupational safety law, carried forward from the Factories Act, 1948 into the Occupational Safety, Health and Working Conditions Code, 2020 (operative since 21 November 2025), requires fumes to be removed at source and exposure kept within permissible limits. Effective chemical exhaust ventilation is a core control measure under both.

Chemical exhaust discharged to atmosphere falls under the Air (Prevention and Control of Pollution) Act, 1981. State Pollution Control Boards, such as the Maharashtra Pollution Control Board, set emission limits, stack requirements and monitoring conditions through your Consent to Establish and Consent to Operate. Scrubbers, carbon adsorbers and properly designed stacks with sampling ports help meet these conditions.

The Petroleum and Explosives Safety Organisation (PESO) licenses the storage of petroleum products and flammable liquids above specified quantities. Electrical equipment such as fan motors and controls installed in hazardous areas must be of an approved flameproof or explosion-protected type. We design solvent exhaust systems to align with these requirements.

NFPA 45 covers fire protection for laboratories using chemicals, including fume hood and laboratory exhaust requirements. NFPA 91 addresses exhaust systems for conveying vapours, gases, mists and particulates, including duct materials, construction and fire protection. These standards are widely referenced by multinational, pharmaceutical and research facilities in India.

ANSI/ASSP Z9.5 is a leading standard for laboratory ventilation. It sets requirements for fume hood performance, laboratory pressurisation, airflow monitoring, exhaust stack discharge and routine performance testing. We use it as a reference for laboratory chemical exhaust system design.

ASHRAE 110 is the recognised method for testing laboratory fume hood containment. It combines face velocity measurement, smoke visualisation and tracer gas testing to confirm that a hood contains fumes under realistic conditions.

We begin with a review of every chemical used, its quantity, concentration, temperature, vapour pressure and hazard classification using safety data sheets. This determines materials of construction, treatment needs, fire protection and whether hazardous area classification applies.

Some chemical streams must never share a duct. Acids and cyanides, oxidisers and organics, and perchloric acid and anything else can react dangerously or form explosive deposits. We group compatible streams and design dedicated systems where needed, which also simplifies treatment.

Chemical fume hood face velocity is commonly designed at around 0.4 to 0.6 m/s at the working sash opening. Chemical exhaust airflow is calculated as face velocity multiplied by open area; for example, a sash opening of 0.75 m² at 0.5 m/s needs about 1,350 m³/h. Tank and slot hoods are sized based on tank dimensions, liquid temperature and hazard level.

Chemical exhaust duct velocity is typically kept around 5 to 10 m/s for gases and vapours, balancing noise, pressure loss and duct size. Higher velocities are used where mists or particulates are present. Ducts are sized branch by branch and balanced for correct airflow at every hood.

Scrubber diameter is set by the gas velocity through the packing, while packing height is set by the required removal efficiency and the solubility of the gas. Well-designed packed bed scrubbers commonly achieve 95% to 99% removal for soluble acid gases, with recirculation rate, pH and dosing sized accordingly.

The chemical centrifugal exhaust fan is selected for total airflow and chemical exhaust static pressure, including losses through hoods, ducts, scrubbers, carbon beds, mist eliminators and the stack. Fan material, seals and motor protection are matched to the chemical and hazardous area requirements.

The chemical exhaust stack must carry treated air clear of the building wake. Common laboratory design references call for a discharge velocity of around 15 m/s and a stack height at least 3 m above the adjacent roof line, adjusted for nearby air intakes, taller buildings and wind conditions. High plume chemical exhaust fans achieve effective dispersion without very tall stacks.

Exhausted air must be replaced with conditioned make-up air. Laboratories and chemical rooms are kept at negative pressure relative to surrounding areas by supplying slightly less air than is exhausted, so fumes always flow inward. Chemical exhaust make-up air is balanced to maintain this pressure without drafts that disturb hood performance.

Humid or wet chemical exhaust, especially downstream of scrubbers, can condense inside ducts and form corrosive liquid. Ducts are sloped toward drain points at low spots, with drains connected to suitable collection or effluent systems.

For flammable vapour exhaust, fans are built with spark-resistant construction, such as non-ferrous impellers or rub rings, following recognised spark-resistance classes. Combined with flameproof motors, they remove the fan as an ignition source.

Areas where flammable atmospheres may occur are classified into zones based on how often and how long they are present. India follows the IS/IEC 60079 series for area classification and equipment protection, aligned with international ATEX and IECEx practice. Hazardous area chemical exhaust equipment is then selected to suit each zone.

Motors, starters, sensors, damper actuators and lighting in classified areas must be of certified explosion-protected types. Where practical, we locate motors and panels outside the hazardous zone or outside the airstream to simplify compliance and maintenance.

Combustible plastic ducts and solvent-laden exhaust can carry fire through a building. Depending on the risk, we use flame-retardant or non-combustible duct materials, fire-rated enclosures and, where required, sprinkler or suppression systems inside ducts and hoods.

Toxic gas cabinets, chlorine and ammonia rooms, perchloric hoods and critical laboratory exhaust must keep running during a power failure. We connect these fans and controls to DG or UPS-backed supplies, with automatic restart and alarm signals.

VAV chemical exhaust controls adjust the exhaust flow of each fume hood as the sash is raised or lowered, keeping face velocity constant. When sashes are closed, exhaust and make-up air both reduce, delivering large savings in fan and air conditioning energy.

A chemical exhaust VFD adjusts fan speed to match demand. Because the stack still needs enough discharge velocity for safe dispersion, bypass air dampers or variable-geometry nozzles maintain stack velocity even at low exhaust flow.

High-plume or induced-flow exhaust fans entrain outdoor air into the discharge and project the plume high above the roof. They improve dispersion, reduce the need for tall stacks and help prevent re-entrainment into fresh air intakes.

For rooms with toxic or flammable gas risks, gas detectors can boost exhaust from normal to emergency flow only when a leak is detected. This avoids running high airflow continuously while keeping the room safe.

Fume hood airflow monitors display face velocity and alarm when it falls below the safe level. Chemical exhaust airflow monitors and chemical exhaust differential pressure sensors on ducts, scrubbers and filters give early warning of blockages, fan problems or filter loading.

A chemical exhaust system with BMS integration brings fan status, airflow, room pressure, scrubber pH, gas alarms and energy data onto your building management or SCADA platform. Facility teams gain real-time visibility and faster response to faults.

Source capture removes toxic, corrosive and flammable fumes before they reach workers, keeping exposure within safe limits and preventing both acute incidents and long-term illness.

Chemical-compatible ducts, fans and scrubbers last many years in service where ordinary GI systems fail quickly. Fewer replacements mean lower lifecycle cost and less production downtime.

Captured, treated and properly discharged emissions support compliance with occupational safety law, hazardous chemical rules and pollution control consent conditions. Commissioning records provide documented proof for audits.

Negative pressure design keeps fumes inside controlled areas, while correctly designed stacks disperse treated exhaust away from fresh air intakes, neighbouring buildings and communities.

Keeping flammable vapours below explosive limits and using spark-resistant, flameproof equipment dramatically reduces the risk of fire or explosion in solvent and hydrogen areas.

PP, FRP, PVDF, stainless steel and chemical-resistant fans cost more than standard GI and steel. However, they last far longer in corrosive service, making them cheaper over the system's life.

Wet scrubbers consume water and neutralising chemicals and produce blowdown that must go to effluent treatment. We design dosing and blowdown systems that minimise consumption and simplify handling.

Incompatible streams, perchloric acid, hazardous areas and stack dispersion all require specialist knowledge. Generic ventilation contractors often miss these details, which is why an experienced chemical exhaust contractor matters.

Many chemical exhaust systems run continuously and exhaust conditioned air that must be replaced. VAV controls, VFDs and demand-based emergency exhaust significantly reduce this energy use.

Scrubbers, carbon beds, gas detectors, airflow monitors and fans need routine inspection and calibration. An AMC ensures these tasks are done on schedule and performance stays within design.

Chemical plant exhaust systems serve reactors, vessels, filling stations, drum handling and tank farms. They combine process hoods with scrubbers, carbon adsorbers or oxidisers to control both workplace exposure and stack emissions.

Pharmaceutical chemical exhaust handles solvent vapours from reactors, centrifuges, dryers and dispensing booths in API and formulation plants. Systems often need flameproof equipment, solvent recovery or carbon adsorption, and integration with cleanroom HVAC.

QC, R&D and testing laboratories depend on reliable fume hood exhaust, safe room pressurisation and good stack dispersion. We design laboratory chemical exhaust systems with negative pressure, VAV controls and airflow monitoring.

School, college, university and hospital laboratories need safe, simple and low-maintenance fume hood exhaust. Correctly sized systems protect students, staff and patients in adjoining areas.

Electroplating exhaust systems capture acid, alkali, cyanide and chromic acid fumes from process tanks using slot or push-pull hoods. PP or FRP ductwork, mist eliminators and packed bed scrubbers make up a complete wet process exhaust system.

Semiconductor chemical exhaust handles acid, alkali, solvent and toxic gas streams from wet benches, etching and gas cabinets. These streams are segregated and treated separately, with high reliability and continuous monitoring.

Battery plants require acid fume exhaust from formation and charging areas, as well as hydrogen ventilation. Corrosion-resistant ducts, scrubbers and spark-resistant fans are standard.

Chlorine rooms in water and sewage treatment plants need continuous ventilation, chlorine gas detection and emergency exhaust to a chlorine neutralisation scrubber. Chlorine room exhaust fans are always of corrosion-resistant construction.

Paint, ink, adhesive and solvent manufacturers need exhaust for mixing, grinding, filling and storage areas. Every exhaust fan for paint fumes or solvent vapours must be spark-resistant with a flameproof motor, with VOC treatment where emission norms require it.

Fertiliser and agrochemical plants handle ammonia, acids and pesticide intermediates. Scrubbers, corrosion-resistant ducts and gas detection protect workers and control emissions to atmosphere.

Greenheck is a US-based manufacturer of air movement and control equipment. It is well known in laboratory projects for high-plume and induced-flow laboratory exhaust fans designed for safe dispersion from roof-mounted systems.

Thermax is an Indian engineering company with a strong presence in energy and environmental solutions. Its air pollution control offerings include scrubbers and other emission control equipment for industrial process exhaust.

Nederman is a Swedish industrial air filtration company. Its range includes extraction arms and snorkels for laboratory and light chemical applications, along with filtration systems for industrial processes.

Esco is a laboratory equipment manufacturer headquartered in Singapore. It offers ducted and ductless fume hoods, along with a wide range of other laboratory safety cabinets.

India has a large base of specialist fabricators producing FRP and PP chemical exhaust fans, packed bed scrubbers, ducts and stacks. Selecting a supplier with proven resin systems, quality welding and balanced impellers is essential for long service life, and our engineers help you evaluate these options.

*Brand names are trademarks of their respective owners and are mentioned for reference only.*

Ductwork is pressure tested and inspected for leaks, especially at welded and flanged joints. Positive-pressure sections downstream of the fan receive particular attention, since any leak there would release fumes.

Fume hood face velocity is measured across a grid at the working sash height, and smoke tests confirm containment. Where specified, testing follows ASHRAE 110 methods. Tank and slot hoods are checked for capture with smoke visualisation.

Scrubber recirculation flow, pressure drop, pH control and dosing are verified. Stack emission testing can be arranged through accredited laboratories to confirm compliance with consent limits.

Airflow at every hood and branch, fan duty, static pressure and stack discharge velocity are measured and compared with design. Dampers and VAV controls are balanced and set.

Airflow alarms, gas detector responses, emergency exhaust start-up, interlocks and backup power changeover are tested in real conditions to confirm the system responds correctly.

You receive a detailed commissioning report with measured airflows, velocities, pressures, test results and control settings, together with as-built drawings and operation and maintenance manuals.

We inspect scrubber packing for fouling or damage, clean spray nozzles, check recirculation pump performance and inspect mist eliminators to maintain removal efficiency.

pH sensors are calibrated, dosing pumps checked and chemical strength verified. Blowdown and make-up water rates are adjusted to keep neutralisation effective.

Carbon beds are monitored for saturation and replaced before breakthrough. Spent carbon is handled and disposed of according to its hazard classification.

Fans are checked for vibration, impeller corrosion or build-up, bearing condition, belt tension and drain function. Motors are checked for insulation and current draw.

Ducts, joints, supports and stacks are inspected for corrosion, cracking, sagging and leaks. Early repairs prevent fume leakage and costly structural failures.

Toxic and flammable gas detectors are bump-tested and calibrated at recommended intervals so they respond reliably when it matters.

Fume hood airflow monitors and duct pressure sensors are verified against measured values and alarms are tested, ensuring users can trust what they see.

Cause: Undersized fan, leaking or corroded ducts, clogged scrubber packing, closed dampers or too many hoods added over time. Solution: Measure airflow and pressure through the system, repair leaks, clean or replace packing, rebalance dampers and upgrade the fan or add VAV control where needed.

Cause: Poor hood design, cross-drafts from doors or supply diffusers, positive room pressure or leaks in positive-pressure ducts. Solution: Improve hood design, relocate supply outlets, restore negative room pressure and ensure the fan is at the end of the system.

Cause: GI or mild steel components in corrosive service, or the wrong plastic or resin for the chemical. Solution: Replace with PP, FRP, PVC, PVDF or suitable stainless steel based on a proper compatibility review.

Cause: Excessive gas velocity, damaged mist eliminator, blocked nozzles, wrong pH or fouled packing. Solution: Correct airflow, repair or upgrade the mist eliminator, clean nozzles and packing, and recalibrate pH control and dosing.

Cause: Ducts laid flat or sagging, no drain points, or saturated air from scrubbers cooling in the duct. Solution: Re-slope and re-support ducts, add drains at low points and insulate where necessary.

Cause: Short stacks, low discharge velocity, rain caps or stacks placed close to air intakes. Solution: Raise stacks, increase discharge velocity, remove rain caps, relocate intakes or install high-plume exhaust fans.

Cause: Untreated VOC or acid emissions, saturated carbon or poor dispersion. Solution: Add or upgrade scrubbers and carbon adsorbers, replace saturated carbon and improve stack design.

Cause: Wrong fan material, impeller build-up, no casing drain or bearing damage from vapour ingress. Solution: Upgrade to an FRP or PP chemical exhaust fan, add casing drains, improve shaft seals and include the fan in regular AMC checks.

We replace corroded GI or mild steel exhaust piping and ducts with PP or FRP, often section by section during planned shutdowns to minimise downtime.

Where pollution control boards require emission reduction, we add packed bed scrubbers, mist eliminators or carbon adsorbers to existing exhaust systems, with stacks and sampling ports to match.

Converting constant-volume laboratory hoods to VAV control reduces exhaust and make-up air when sashes are closed, delivering significant energy savings while improving safety monitoring.

Replacing short-stack fans with high-plume laboratory exhaust fans improves dispersion and solves re-entrainment problems without building taller stacks.

We retrofit toxic and flammable gas detectors, emergency exhaust fans and leak scrubbers to chlorine, ammonia, solvent and battery rooms, linked to alarms and backup power.

Airflow is the biggest cost driver because it sets the size of ducts, fans, scrubbers and stacks. Each additional fume hood or tank hood adds airflow, ductwork and controls, while VAV and diversity can reduce total design airflow in laboratories with many hoods.

Ductwork is priced by size, length, wall thickness and fittings. As a general guide, PP and PVC are the most economical corrosion-resistant options, FRP costs more but offers greater strength for large sizes and outdoor runs, stainless steel is higher again, and PVDF or PTFE-coated ducts are premium choices for the most aggressive service.

Scrubber cost depends on airflow, gas load, required removal efficiency, number of stages, material and instrumentation such as pH control and automatic dosing. Carbon adsorber cost depends on the volume of carbon needed for adequate contact time and the carbon grade, with impregnated carbons costing more.

• Chemicals handled, concentration and temperature
• Number and type of hoods, tanks and enclosures
• Total airflow and static pressure
• Materials of construction for ducts, fans and stacks
• Treatment: scrubber, carbon adsorber, oxidiser or mist eliminator
• Hazardous area requirements and flameproof equipment
• Stack height, supports and sampling platforms
• Controls: VAV, VFD, gas detection, airflow monitors and BMS integration
• Make-up air and room pressure control
• AMC, consumables and chemical dosing over the system's life

A cheaper system in the wrong material usually costs far more in replacements, downtime and compliance issues. A correctly engineered chemical exhaust system delivers the lowest lifecycle cost.