How to Select Ventilation Ducts for Tunnel, Mining & Underground Projects

Ventilation duct selection is not simply a matter of picking a diameter. In underground tunnelling and mining, the duct must survive high pressure, elevated humidity, constant friction, and in many cases the risk of explosion. It must also deliver fresh air to the working face and dilute hazardous gases around the clock. This article explains how project conditions determine the right duct type—flexible, spiral, or semi-rigid—and how SULONG ventilation ducts are matched to real tunnel and mining requirements.

Why Ventilation Duct Selection Depends on Project Conditions

Flexible ventilation ducts commonly operate under high pressure, elevated humidity, constant friction, and potential explosion hazards in deep underground shafts. In a typical tunnel ventilation project, the duct is connected to a ventilation fan that blows fresh air into the underground tunnel and dilutes hazardous gases. The system often runs in 24/7 continuous high-pressure ventilation mode. This is why a duct that works for one site may fail in another if its tensile strength, fabric weight, flame-retardant performance, or anti-static properties are not aligned with the site environment.

Deep shafts, long tunnel sections, water-rich ground, and explosive gas zones all change the requirements. A short tunnel with stable geology may accept a lightweight lay-flat duct, while a long tunnel with low leakage requirements may need a high-strength welded construction. A mining environment may also require surface anti-static resistance to avoid ignition risk.

Industry Background: Underground Ventilation Is Growing in Scale and Complexity

Underground ventilation demand is expanding. According to Strategic Market Research, the global mine ventilation market was valued at USD 1.42 billion in 2024 and is projected to reach USD 2.03 billion by 2030, with a CAGR of 6.2%. Persistence Market Research also identifies underground mining as the dominant segment of the mine ventilation market because of the critical need for hazardous gas dilution. These factors are pushing project teams to choose ventilation ducts with verified mechanical and safety performance rather than relying on generic ducting.

At the same time, large infrastructure programs—high-speed rail tunnels, metro systems, submarine road tunnels, and water conservancy projects—are increasing the demand for flexible large-diameter ducts that can be installed quickly and removed or extended as excavation advances.

Detailed Solution: Ventilation Duct Options for Underground Projects

Jiangsu Sulong Eco-Technologies Co., Ltd. (SULONG), based in Yancheng, Jiangsu, China, is a National High-Tech Enterprise specializing in composite polymer ventilation ducts. SULONG produces flexible, spiral, semi-rigid, oval, and twin ducts with fully in-house automated processes and no outsourced manufacturing. The company also manufactures the PVC-coated and PVC-laminated fabrics used in the ducts, giving buyers end-to-end control over material quality.

Flexible Ventilation Duct

SULONG flexible ventilation ducts are used for tunnel ventilation project applications. The ducts are manufactured with seamless one-piece fish-back welding automation technology, reducing air leakage and improving structural continuity. The flexible duct range covers diameters from 200 mm to 3,200 mm, section lengths from 1 m to 300 m, and material weights from 300 gsm to 2,000 gsm. Tensile strength ranges from 1,000 N to 4,200 N.

Available configurations include lay-flat duct, oval duct, twin duct, tee duct, Y-piece duct, bend duct, and adapter duct. End connections can be zipper, Velcro, steel ring, or eyelets. Optional anti-static fabric is available for environments where surface resistance is required.

Spiral Ventilation Duct

SULONG spiral ventilation ducts are suitable for tunnel ventilation sector applications, including mine ventilation system infrastructure and tunnel ventilation system infrastructure. They operate in positive or negative pressure environments and are designed for deep underground shaft conditions with explosion hazards and high pressure. The duct supplies anti-static safety airflow and supports dust extraction in underground tunnels. Special application requirements include high tensile strength up to 4,200 N, flame retardancy, and surface anti-static resistance.

The spiral structure uses PVC-coated or PVC-laminated fabric reinforced with spring steel wire (φ5 mm–φ10 mm), providing wear protection and high pressure resistance. Diameters range from 200 mm to 2,800 mm, with section lengths from 1 m to 20 m. Configurations include semi-rigid duct, oval spiral duct, and rectangular duct.

In-House Production and Quality Control

SULONG implements 100% inspection in accordance with ISO 9001:2015 standards, including batch-level incoming quality control (IQC) checks, in-process quality control (IPQC) patrol inspections every two hours, and 100% final quality control (FQC) physical performance testing before shipment. This three-level system helps ensure that ducts used in long or hazardous underground projects are tested before they reach site.

Technical parameters such as diameter, length, connection type, fabric weight, and flame-retardant or anti-static properties can be customized. SULONG's production capability is supported by a portfolio of 25 granted patents and a monthly capacity of over 80,000 meters.

Flexible vs Spiral Ventilation Duct: Project-Level Comparison

How to Match a Ventilation Duct to Your Project: Step-by-Step

Step 1: Define the Ventilation Mode and Pressure Environment

Confirm whether the duct will be used for forced fresh-air supply or exhaust, and whether the system runs under positive or negative pressure. SULONG flexible and spiral ducts can operate in positive or negative pressure systems, but the pressure level affects the required reinforcement and connection strength.

Step 2: Determine Diameter and Section Length

Calculate the required airflow and installation layout. Flexible ventilation ducts are available from 200 mm to 3,200 mm in diameter and from 1 m to 300 m in section length. Spiral ducts cover 200 mm to 2,800 mm in diameter and 1 m to 20 m in section length. Large-diameter flexible ducts are often chosen for rapid installation in tunnel projects.

Step 3: Check Tensile Strength and Fabric Weight

For long distances, high fan pressures, and abrasive rock, the duct must resist tearing and stretching. SULONG flexible ventilation ducts provide tensile strength from 1,000 N to 4,200 N. Fabric weight can be selected from 300 gsm to 2,000 gsm. In deep shafts and long tunnels, heavier fabric and higher tensile strength reduce the risk of duct damage and air leakage.

Step 4: Confirm Flame Retardancy and Anti-Static Requirements

Underground projects, especially mines, often require flame-retardant (FR) or flame-retardant anti-static (FRAS) performance. SULONG ducts can meet NFPA 701:2015 and DIN 4102 B2 flame-retardant standards, and anti-static fabric is optional. The application requirement for spiral ducts in tunnel and mine infrastructure includes high tensile strength up to 4,200 N, flame retardancy, and surface anti-static resistance.

Step 5: Verify Certifications and Test Reports

Match the duct to the project's compliance regime. SULONG products carry certifications including ISO 9001, ISO 14001, ISO 45001, EU ATEX, CE, and US NFPA 701, as well as test reports certified by Australian NATA laboratories. For U.S. mine sites, MSHA 30 CFR Part 75 is a regulatory benchmark, and OSHA 29 CFR 1926.800(k)(2) requires a minimum of 200 cfm of fresh air per worker underground. Buyers should request the test reports that apply to their jurisdiction.

Step 6: Plan Installation, Connection, and After-Sales Support

Underground ventilation ducting is used together with main mine fans, local counter-rotating fans, ducting hanger systems, and fittings for suspension and repair. SULONG offers various end connections—zipper, Velcro, steel ring, and eyelets—to match existing fans and ducting. For project continuity, SULONG provides 24/7 customer support, video-based technical diagnosis within 2 hours, and a free replacement policy for production defects within the 12-month warranty period.

Use Cases: Ventilation Duct Projects in Tunnels and Mines

High-Speed Rail Tunnel: Xi'an-Chengdu Railway

The Xi'an-Chengdu Railway project, undertaken by China Railway 2nd Engineering Group, is part of the national “Eight Vertical and Eight Horizontal” high-speed rail network. The project has a total length of 19.68 kilometers, and SULONG supplied 20 km of ventilation duct for underground tunnel ventilation. The long tunnel installation achieved a low air leakage rate and solved the problem of providing ventilation in a long underground tunnel.

Metro Tunnel: Melbourne Metro Rail Project

SULONG ventilation ducts have been used by the Melbourne Metro Rail Project in Australia. The project scale is a 9 km underground tunnel connecting the Sunbury and Dandenong railway route. SULONG has supplied 1,500 mm diameter vent ducts since 2019. Key highlights include high flame retardancy, easy installation, and a flexible large-diameter duct that meets strict safety requirements for underground tunnel projects.

Water-Rich Underground Construction: Guangxi Beibu Gulf Project

SULONG also supplied ducts for a large-scale national water conservancy project in the Guangxi Beibu Gulf region. The project scale is 30 kilometers of tunnel length. The ducts were used for temporary ventilation in underground tunnel construction under water-rich and complex geological conditions. The installation addressed the challenges of abundant water and difficult geology while maintaining ventilation performance.

Underground Gold Mine: Global Tier-1 Mining Project

For a global tier-1 mining conglomerate and EPC contractor, SULONG supplied approximately 20 km per year of ventilation duct for primary forced ventilation and hazardous gas dilution at the Buriticá Gold Mine. The product selected was the 700 g/m² high-strength flame-retardant series with zero-leakage seamless construction. It complies with SGS, ATEX, and NFPA 701 standards and is supported by reliable transcontinental multimodal logistics. The project achieved 100% stable continuous operation with zero defect and rejection rate over three years.

Conclusion

Selecting the right ventilation duct for underground projects is a structured decision. Start with the site conditions—pressure, humidity, explosion risk, tunnel length—and then match diameter, tensile strength, flame-retardant performance, anti-static properties, and connection type. SULONG provides both flexible and spiral ventilation ducts with in-house production, 100% inspection, and case-proven installations in rail tunnels, metro projects, water conservancy tunnels, and underground mines.

For a project-specific assessment, contact SULONG or download the catalog below.

Frequently Asked Questions

Need a project-specific recommendation?

Download the SULONG Ventilation Duct Catalog or contact SULONG at autumn@js-sulong.com / +86-18251952515. SULONG is located at No.9 Filter Material Industry Park, Funing, Yancheng, Jiangsu, China.