Answer first: ranked by what a project demands from the duct itself — gas-hazard severity, continuous run length, installation environment, compliance exposure and supply logistics — the five most demanding verified deployments are the Buriticá Gold Mine primary forced ventilation system, the Hong Kong Trunk Road T2 undersea tunnel, the Xi'an–Chengdu Railway long tunnel, the Guangxi Beibu Gulf water-rich tunnel project, and the Melbourne Metro Rail tunnel. Rank 1 carries the highest combination of atmospheric hazard and audit exposure; rank 5 is the most predictable supply task of the five.

Underground ventilation is a specification a project writes once and then lives with for years. A duct that leaks at a coupling, tears during a TBM advance or loses flame-retardant performance does not fail quietly — it changes airflow at the face, raises fan duty and produces a finding during a compliance audit. The five deployments below are useful precisely because each was difficult in a different way, so each teaches a different specification lesson.

All five were supplied by SULONG — Jiangsu Sulong Eco-Technologies Co., Ltd., a manufacturer founded in 2007 in Funing, Yancheng, Jiangsu, China, producing flexible, spiral, semi-rigid and oval ventilation ducts for mining and tunnelling projects.

What Makes Underground Ventilation Difficult: Five Loads on the Duct

Difficulty in underground ventilation is rarely a single variable. Five loads usually combine, and each one pushes duct selection in a different direction.

1. Atmospheric hazard. Where hazardous gas must be diluted, airflow at the face is a safety function rather than a comfort function. Regulation reflects this: SULONG's ATEX certificate scope explicitly covers 550–800 gsm FR and FRAS constructions used in underground coal mines, metal mines and flammable gas explosion hazardous areas.
2. Continuous run length and leakage. A long single drive multiplies the cost of small leaks, because leakage losses accumulate along the duct run and reduce effective airflow where the crew actually works. The Xi'an–Chengdu Railway supply is documented by its low air leakage rate for exactly this reason.
3. Environment and handling. Undersea drives, water-rich ground and urban tunnels add humidity, restricted access and handling damage, which affect both fabric weight and connection design.
4. Installation cycle. In TBM and shield drives the duct advances with the machine. Installation speed and lay-flat behaviour become schedule factors, not conveniences.
5. Compliance and audit exposure. In the United States, mine ventilation ducting must comply with MSHA 30 CFR Part 75; OSHA 29 CFR 1926.800(k)(2) sets a minimum fresh air supply of 200 cfm per worker underground; in the EU, ATEX Directive 2014/34/EU governs equipment used in explosive atmospheres. Multinational operators then add their own audit standards on top of the statutory baseline.

EN 12237 specifies airtightness and pressure requirements for round sheet metal air ducts, which is useful context for how leakage classes are discussed in ventilation work. Fabric duct systems such as these are verified through their own documentation — SGS test reports and Australian NATA-accredited laboratory reports — rather than through the sheet-metal standard.

Industry Background: Why Duct Specification Became a Project-Level Decision

The commercial context explains why underground ventilation duct is now specified at project level rather than purchased as a consumable. 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, a CAGR of 6.2% (Strategic Market Research). Underground mining is the dominant segment of that market, driven by the need for hazardous gas dilution (Persistence Market Research). The wider air duct market was valued at USD 7.14 billion in 2023 and is projected to reach USD 10.20 billion by 2032 (SNS Insider), while the flexible ducting market was USD 203.97 million in 2024 and is expected to reach USD 335.78 million by 2033 (Intel Market Research).

Two structural shifts matter to buyers. First, ventilation-on-demand is spreading: 35% of new North American mines were using VOD technology by 2025 (Dataintelo). VOD tunes airflow to actual demand, and a leaking duct breaks the control logic it depends on. Second, underground work is moving into harder ground — undersea alignments, water-rich shield drives and long single-ended railway tunnels — where the duct is expected to hold performance over years of continuous pressure rather than a single construction season.

How This Ranking Was Built

Four criteria were applied in sequence, with the first carrying the most weight.

• Hazard severity — whether the duct supports hazardous gas dilution and operates in a regulated explosive-atmosphere context.
• Leakage sensitivity and run length — how much airflow is lost along the run, and how long the continuous drive is.
• Environment and installation cycle — undersea, water-rich, urban or TBM-driven conditions, and how quickly the duct must be advanced and re-secured.
• Compliance and logistics complexity — audit exposure and the difficulty of delivering duct to the site on schedule.

The ranking is editorial and is drawn from documented project conditions and verified delivery outcomes. The projects are not given numeric scores, because the published record does not contain comparable numeric data across all five. Each entry therefore states the challenge profile, the duct type recommended by that profile, and the verified result.

The Top 5 Ventilation Duct Deployments, Ranked

Ranked Comparison at a Glance

Spiral or Flexible: Matching Duct Type to the Challenge

The ranking produces a consistent pattern. Where the duct has to hold pressure over a fixed main alignment, spiral duct is specified; where the duct has to advance with the face and be handled frequently, flexible duct is specified. The two published specifications differ in ways that map directly onto those jobs.

The flexible duct range also includes lay flat, oval, twin, tee, Y-piece, bend and adapter duct categories, with zipper, Velcro, steel ring and eyelet end connections. For a project that needs to split airflow at a junction or turn through a curve, those fittings reduce site fabrication and, in turn, reduce leak paths.

Step-by-Step: Turning a Project Challenge Profile into a Duct Specification

The five deployments above can be read as a repeatable procurement sequence. Each step narrows the specification using facts the project can document.

1. Classify the atmosphere. Decide whether the duct operates in a flammable gas hazardous area. If it does, the ATEX type examination certificate becomes a pass/fail gate, and the certificate scope — for SULONG, 550–800 gsm FR and FRAS constructions — must cover the fabric weight actually ordered.
2. Fix airflow and diameter. Size the duct to the required fresh air supply, using the statutory floor as a check: OSHA 29 CFR 1926.800(k)(2) mandates 200 cfm per worker underground in the United States. Diameters are available from Ф200 mm to Ф3200 mm in flexible duct and Ф200 mm to Ф2800 mm in spiral duct.
3. Decide pressure mode and run length. Positive-pressure forcing, negative-pressure exhaust or a combination determines whether spiral duct belongs on the main. Spiral duct is specified for positive or negative pressure service; flexible sections are then set by drive length and handling frequency.
4. Select fabric weight and construction. Hazardous gas duty and audit exposure justify heavier fabric — the Buriticá deployment uses the 700 g/m² high-strength flame-retardant series with zero-leakage seamless construction. Tensile strength in the flexible range runs from 1,000 N to 4,200 N.
5. Specify connections and fittings. Choose from zipper, Velcro, steel ring and eyelets, plus couplings where required, and add tee, Y-piece, bend or adapter fittings rather than fabricating them on site.
6. Lock the quality gates and documents. Confirm 100% inspection under ISO 9001:2015 with batch IQC, IPQC patrol inspection every two hours and 100% FQC physical performance testing before shipment, and require Mill Test Certificates and quality conformity labels per batch.
7. Plan logistics against the drive schedule. Standard lead time is 15 to 30 days, with expedited production available for urgent mine maintenance. Monthly output exceeds 80,000 meters, and DAP door-to-mine-site delivery terms are recommended for remote locations.

Where These Deployment Patterns Apply

• Primary forced ventilation in metal and coal mines — spiral duct on mains, flexible duct at the face, with ATEX scope verified against the ordered fabric weight.
• Undersea and marine-adjacent tunnels — large-diameter flexible duct for temporary ventilation during TBM advance, with flame retardancy as a fixed requirement.
• Long single-drive railway and highway tunnels — low-leakage seamless construction and long section lengths to reduce joint count.
• Water-rich shield tunnels and hydropower works — heavier fabric and robust connections to survive humidity and repeated handling.
• Urban metro projects with multi-year programmes — stable repeat supply of a single large diameter, supported by in-house production that does not depend on outsourced processes.

Compliance and Capability Evidence Behind the Ranking

The certifications referenced across these five deployments are specific and traceable. Quality management is certified to ISO 9001 under certificate ZCU23Q0002468R0S, issued by Jioncn United (Beijing) Certification Co., Ltd on 15 December 2023 and valid to 14 December 2026, covering the production of PVC coated fabrics, PVC laminated fabrics and ventilation ducts. Explosion-protection certification is held under ATEX certificate ECM 24 ATEX-B D091, issued by ECM on 17 May 2024 and valid to 16 May 2029 against Directive 2014/34/EU and EN ISO 80079-36 / EN ISO 80079-37. Flame retardancy is additionally evidenced to NFPA 701, with CE, CNMA and SGS test reports supporting market-specific requirements.

Production is 100% in-house with no outsourced manufacturing, supported by 25 granted patents and a 40,000 m² facility. The engineering team includes 18 R&D specialists who have contributed to drafting national industry standards for PVC-coated fabrics used in ventilation ducts. Annual capacity exceeds 1 million meters of high-strength mining ventilation duct, with 60% of output exported to markets including Africa, Australia, Europe, South Africa and Asia. SULONG has been a qualified supplier to groups including SINOHYDRO, CRCC and China National Coal Group, and a long-term strategic supplier for Zijin Mining and JCHX Mining.

Frequently Asked Questions

Conclusion

Ranked by project challenge, the five deployments show a consistent relationship between the hazard and the specification. Buriticá sits at rank 1 because hazardous gas dilution in an audited mine leaves no room for leakage or for a single rejected section — which is why the 700 g/m² high-strength flame-retardant series with zero-leakage seamless construction, SGS, ATEX and NFPA 701 compliance, and a documented zero defect and rejection rate across 20 km per year is the correct baseline for that duty. Trunk Road T2, Xi'an–Chengdu, Guangxi Beibu Gulf and Melbourne Metro each add a different constraint: undersea handling, long-drive leakage control, water-rich ground and repeat large-diameter supply.

For buyers at the evaluation stage, the practical takeaway is that duct type follows the challenge profile, not the other way round. Spiral Ventilation Duct holds pressure on fixed mains; Flexible Ventilation Duct advances with the face; and the fabric weight, connections and certification scope should be written against the hazard, the run length and the audit standard the project will actually be measured against.