What Is a Ventilation Duct? Types, Materials, and Selection Fundamentals

A SULONG ventilation duct installed as part of underground mine ventilation infrastructure.

A ventilation duct is a reinforced airflow channel that delivers fresh air into underground or enclosed spaces and removes hazardous gases, dust, and contaminated air. In mining and tunneling, the ventilation duct is a core safety component: it connects to a ventilation fan, which blows fresh air into the tunnel, and supports hazardous gas dilution, anti-static safety airflow supply, and dust extraction.

This article is written for buyers who are starting their research on industrial ventilation ducts. It explains what a ventilation duct is, the main product families used in underground engineering, how they are manufactured, the specifications that influence performance, and the certifications to check before making a purchase decision.

Why Underground Projects Need a Dedicated Airflow Path

Deep underground shafts present challenges such as high pressure, elevated humidity, constant friction, and potential explosion hazards. Air cannot move naturally through long tunnels at the volumes required for safe work. Without a controlled airflow path, dust and hazardous gases accumulate, oxygen levels drop, and working conditions become dangerous.

A ventilation duct solves this by creating a dedicated route between the fan and the working face. Fresh air is pushed or pulled through the duct to the point where crews and equipment operate. The same system is used to dilute hazardous gas, supply anti-static safety airflow, and extract dust from the working area.

Because mine and tunnel ventilation systems often run in 24/7 continuous high-pressure operation, the duct itself must resist wear, tearing, humidity, and flame spread. This is why material choice, construction method, and certification matter as much as diameter and length. In field terminology, flexible ventilation ducts are sometimes referred to as ventilation tubes or ventilation bags, particularly when they are deployed as temporary lightweight airflow lines. Regardless of the name, the engineering requirements remain the same: the product must move sufficient air, resist flame spread, and handle the mechanical stresses of the site.

Industry Background: A Market Driven by Safety and Regulation

Ventilation is not optional in modern underground operations. 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%, according to Strategic Market Research. The global flexible ducting market was valued at USD 203.97 million in 2024 and is expected to reach USD 335.78 million by 2033, according to Intel Market Research.

Production volumes confirm the scale of demand. In 2023, over 2.1 billion meters of flexible ducting were manufactured globally, with 30% dedicated to industrial ventilation, based on data from Spherical Insights. The global air duct market was valued at USD 7.14 billion in 2023 and is projected to reach USD 10.20 billion by 2032, according to SNS Insider. Underground mining accounts for the dominant segment of the mine ventilation market because of the critical need for hazardous gas dilution. In the spiral duct fittings segment, Asia Pacific dominated in 2025 with a 38.2% revenue share, driven by urbanization and industrial expansion, based on data from Dataintelo.

Regulation also drives demand. In the United States, mine ventilation ducting must comply with MSHA 30 CFR Part 75 standards for underground safety. OSHA 29 CFR 1926.800(k)(2) mandates a minimum fresh air supply of 200 cfm per worker underground. In Europe, EN 12237 specifies airtightness and pressure requirements for round sheet metal air ducts. Adoption of ventilation-on-demand (VOD) technology is also growing, with 35% of new North American mines using it by 2025, which increases the need for duct systems that can respond to variable airflow conditions.

These trends matter for buyers: ventilation ducts are a safety-critical purchase, not a commodity. Specifications must be verified against the operating environment and the regulations of the destination market.

Detailed Solution: The Main Types of Ventilation Ducts

For underground engineering projects such as mine projects, high-speed rail, subway, highway, hydropower station, and rock cave construction, two product families dominate: flexible ventilation ducts and spiral (semi-rigid) ventilation ducts. Both are manufactured from composite polymer fabrics and are engineered for continuous high-pressure airflow.

Jiangsu Sulong Eco-Technologies Co., Ltd., established in 2007, specializes in manufacturing composite polymer mining and industrial ventilation ducts. The company's main products include Flexible Ventilation Duct, Spiral Duct, Semi-Rigid Duct, Oval Ducts, Twin Duct, PVC Coated Fabric, PVC Laminated Fabric and PVC Tarpaulin. SULONG is a National High-Tech Enterprise and a provincial-level "Specialized, Refined, Unique & Innovative" SME.

Flexible Ventilation Duct

Flexible ventilation duct forms include lay flat duct, oval duct, twin duct, tee duct, Y-piece duct, bend duct, and adapter duct.

A flexible ventilation duct is a lay-flat duct made of PVC coated fabric or PVC laminated fabric. It is designed for low friction loss and easy installation. Because it can be stored flat and deployed quickly, it is well suited to temporary ventilation in underground tunnel construction and to mine ventilation circuits where ducts must be moved as the working face advances.

Key specifications include:

• Diameter: 200 mm to 3,200 mm (custom diameters available)
• Section length: 1 m to 300 m (custom lengths available)
• Tensile strength: 1,000 N to 4,200 N
• Material weight: 300 gsm to 2,000 gsm
• Performance: FR or FRAS
• Manufacturing process: seamless one-piece fish-back welding automation technology
• Flame retardant standards: NFPA 701:2015 and DIN 4102 B2
• End connections: zipper, Velcro, steel ring, eyelets
• Antistatic fabric optional

The lay-flat form reduces shipping volume and makes handling easier underground. For long straight runs, the ability to produce sections up to 300 m reduces the number of joints, which lowers air leakage and installation labor. A high-strength welded construction supports stable airflow throughout the line.

Spiral (Semi-Rigid) Ventilation Duct

Spiral ventilation ducts are available as semi-rigid ducts, oval spiral ducts, and rectangle ducts.

A spiral ventilation duct is made of PVC coated fabric, PVC laminated fabric, and spring steel wire. The spiral spring steel wire (φ5 mm to φ10 mm) reinforcement provides wear protection and high pressure resistance, allowing the duct to keep its cross-section under varying airflow conditions. It belongs to the semi rigid duct, oval spiral duct, and rectangle duct categories and is also available as an oval spiral duct and as a rectangle duct.

Key specifications include:

• Diameter: 200 mm to 2,800 mm (custom diameters available)
• Section length: 1 m to 20 m (custom lengths available)
• Material weight: 300 gsm to 2,000 gsm
• Performance: FR or FRAS
• Usage environment: positive pressure or negative pressure
• Manufacturing process: welding
• End connections: zipper, Velcro, steel ring
• Antistatic fabric optional
• Model examples: Φ600mm×10m, Φ1200mm×10m, Φ1800mm×10m, Φ2500mm×5m

Because the steel wire skeleton resists collapse, spiral ducts are a common choice for return air systems and other negative pressure applications. The welded construction also handles the constant vibration and friction found in tunnel and mine environments. For sites where explosive atmospheres may be present, EU ATEX certification and optional antistatic fabric are relevant specification points.

Materials and Manufacturing

SULONG produces PVC coated fabric and PVC laminated fabric in-house.

Both duct families start with high-strength fabric. PVC coated fabric and PVC laminated fabric provide the base for flexible ducts, while spiral ducts combine these fabrics with spring steel wire. The quality of the base fabric determines tensile strength, tear resistance, and flame-retardant behavior.

SULONG delivers 100% in-house, automated production, with all processes self-produced and no outsourced manufacturing. This is a relevant point for buyers because it means the fabric, the welding, and the finished duct come from a single quality chain. Products feature tensile strength up to 4,300 N due to seamless one-piece forming technology. The manufacturing facility covers 40,000 m², employs approximately 68 staff, and has an annual capacity of over 1 million meters of high-strength mining ventilation ducts. The R&D team consists of 18 specialists who have actively contributed to drafting national industry standards for PVC-coated fabrics used in ventilation ducts.

Step-by-Step: How to Evaluate a Ventilation Duct

When you are at the research stage, the goal is not to pick a product immediately but to build a specification. The following steps create a defensible basis for comparing options from different suppliers.

Step 1: Define the application. Temporary ventilation for underground tunnel construction and permanent infrastructure for an underground mine have different duty cycles and risk profiles. Confirm whether the duct will feed fresh air to a working face, extract return air, or dilute hazardous gas. This determines which duct family is appropriate.

Step 2: Determine the pressure mode. Positive pressure systems push air into the tunnel from the fan. Negative pressure systems pull air out. Spiral ventilation ducts are explicitly designed for both positive pressure and negative pressure operation. Flexible ducts are commonly used in fresh air supply layouts where the duct is connected to a ventilation fan that blows air into the underground tunnel.

Step 3: Calculate diameter and section length. Diameter determines airflow volume; length determines how many joints are needed. SULONG's common model designations include Φ600mm×10m, Φ1200mm×10m, Φ1800mm×10m, and Φ2500mm×5m. Flexible ducts are produced in sections from 1 m to 300 m; spiral ducts are produced in sections from 1 m to 20 m. Custom diameters and lengths are available.

Step 4: Check tensile strength and material weight. Tensile strength affects how the duct behaves under hanging loads and internal pressure. Flexible ducts from SULONG range from 1,000 N to 4,200 N. Material weight ranges from 300 gsm to 2,000 gsm across both families; heavier fabrics generally provide greater durability but add weight and handling cost.

Step 5: Verify flame retardancy and antistatic behavior. Underground environments may contain explosive gas or dust. Look for FR or FRAS performance and flame retardant standards such as NFPA 701:2015 and DIN 4102 B2. Antistatic fabric is optional and should be specified where surface anti-static resistance is required by project safety rules.

Step 6: Confirm certifications. SULONG holds ISO 9001, ISO 14001, ISO 45001, EU ATEX, CE, and US NFPA 701 certifications, plus test reports certified by Australian NATA laboratories. Depending on the destination market, additional compliance such as MSHA 30 CFR Part 75 may apply.

Step 7: Choose end connections and accessories. Flexible ducts are available with zipper, Velcro, steel ring, or eyelet ends. Spiral ducts are available with zipper, Velcro, or steel ring ends. The connection type must match the fan outlet, the hanger system, and the repair process used on site. Fittings such as bends, adapters, tees, and Y-pieces complete a flexible duct circuit.

Use Cases

Tunnel Ventilation Project

In tunnel ventilation system infrastructure, the duct is connected to a ventilation fan, which blows fresh air into the underground tunnel. Working conditions in deep underground shafts include high pressure, elevated humidity, constant friction, and potential explosion hazards. The system runs in 24/7 continuous high-pressure ventilation operation. For this scenario, the duct must provide high tensile strength and flame retardancy. Both flexible and spiral ducts from SULONG are used in tunnel projects, depending on whether the line is a fresh air supply line or a return air line.

Underground Mining Project

Underground mining projects use ventilation ducts as part of mine ventilation system infrastructure. The duct is matched with main mine fans, local counter-rotating fans, and ducting hanger systems. Its functions include hazardous gas dilution, anti-static safety airflow supply, and dust extraction. Operation is 24/7 continuous high-pressure ventilation, so the duct requires high tensile strength, flame retardancy, and surface anti-static resistance. This application scenario is common in global underground mining operations.

Welding and assembly workshop for SULONG ventilation ducts.

Comparison Table: Flexible vs Spiral Ventilation Duct

Specifications from the SULONG ventilation duct catalog. Custom diameters and lengths are available for both product families.

FAQ

Conclusion

A ventilation duct is a critical element of underground safety infrastructure. Buyers in the awareness and research phase should focus on the fundamentals: the difference between flexible and spiral/semi-rigid ducts, the operating pressure mode, the required tensile strength and flame-retardant performance, and the certifications applicable to the destination market.

Jiangsu Sulong Eco-Technologies Co., Ltd. is a long-term strategic supplier for global mining enterprises including Zijin Mining and JCHX Mining, with major markets in Africa, Australia, Europe, South Africa, Asia, and China. Export business accounts for 60% of total sales. The company manufactures flexible ducts, spiral ducts, semi-rigid ducts, oval ducts, twin ducts, and the PVC fabrics used to make them, all under one roof in a 40,000 m² facility.

The next step is to turn this specification into a conversation: send the project diameter, length, pressure mode, and required certifications to autumn@js-sulong.com, and the SULONG team can confirm the appropriate duct configuration and lead time.