Choosing Tunnel Ventilation Ducts by Project Risk

For an underground ventilation project, the choice between spiral and flexible ventilation duct should follow the project’s dominant risks, not a generic claim that one type is always preferable. Procurement teams can make the decision more transparent by assigning project-specific weights to flame-retardant evidence, installation demands, leakage control and the ventilation duty—especially hazardous-gas dilution—then scoring only what the project documents actually establish. The available cases point to different decision contexts: flexible duct is documented in temporary ventilation under water-rich conditions and in large-diameter tunnel applications, while Buriticá and Xi’an–Chengdu provide evidence relevant to gas dilution and long-tunnel leakage control.

This is a decision framework, not a universal performance ranking. The project examples describe particular applications and reported outcomes; they do not provide a controlled, like-for-like test of spiral versus flexible duct. A weighted score is therefore useful for exposing priorities and evidence gaps, but it should not be mistaken for a measured product-performance result.

Start with the underground project risk, not the duct label

A duct type is only one part of a ventilation arrangement. The project team must first define what the system needs to do, in which conditions, and what evidence will be used to accept the proposed configuration. In underground applications, supplied material describes ventilation duties that include delivering fresh air, diluting hazardous gases, dust extraction, and operation in high-pressure, humid, friction-intensive environments where potential explosion hazards may also be relevant. These are distinct requirements: a project may place most weight on flame retardancy, temporary installation, leakage control, or the ventilation duty itself.

Spiral and flexible products should consequently be assessed against the same project brief rather than compared by name alone. SULONG’s product information describes spiral ventilation duct as suitable for tunnel and mine ventilation infrastructure, including positive- or negative-pressure environments. Its flexible ventilation duct is described for underground mining and tunnel applications, with a fan-connected role in delivering fresh air and diluting hazardous gases. These are company-provided product and application descriptions, not proof that either type will meet a particular project’s duty without configuration-specific engineering review.

The first procurement task is to translate site conditions into requirements. Record whether the ventilation is temporary or part of a longer-running installation; identify the required airflow function; document the pressure regime and installation constraints; and specify which fire, antistatic, strength or acceptance evidence the project requires. The evidence supplied here does not give a universal installation-time comparison, comparable leakage measurements for both duct types, or a common hazardous-gas dilution test. Those factors must be resolved against the project specification, not filled in with assumed advantages.

A weighted framework that makes assumptions visible

Weighting is a way to express project priorities. It does not create performance evidence. A procurement team can begin by assigning each criterion a weight that reflects its consequence for the specific project, then score each proposed configuration against documented, project-relevant evidence. Keep the weights and the evidence review separate: a high priority does not mean a product has demonstrated a high score.

To make the framework auditable, attach each score to a source and scope: the exact project, duct type, configuration, required operating conditions and acceptance evidence. A score based on a case description should be labelled as case evidence; a score based on a current test report should identify the report and the product it covers. If project participants disagree about a weight, retain the disagreement and show how the decision changes under the competing priorities instead of hiding it inside one total.

How the five project examples inform the decision

Buriticá: give the ventilation duty and leakage claim their proper scope

The supplied Buriticá material describes primary forced ventilation and hazardous-gas dilution at a gold mine. It reports a 700 g/m² high-strength flame-retardant series with seamless construction described as zero-leakage, and states compliance with SGS, ATEX and NFPA 701 standards. These are company-provided case and product claims. They identify relevant procurement questions—what configuration was used, which documents apply to it, and how the project assessed the stated performance—but do not establish a head-to-head result between spiral and flexible duct.

For a mine where gas dilution is central, the gas-dilution criterion may receive a high project-assigned weight because it is part of the specified ventilation duty. That does not mean either duct type should automatically receive a higher rating. The supplied case associates the application with both spiral and flexible duct product records, but does not identify a comparative test, configuration-specific dilution result or a type-by-type outcome. Ask the engineering team to evaluate the complete fan-and-duct arrangement against the project’s own requirements.

The same caution applies to flame-retardant and leakage language. A series-level claim is a reason to request the relevant current documentation for the exact product and configuration; it is not a substitute for checking scope. “Zero-leakage” should remain the wording of the supplied company material, not be generalized into a guaranteed result for every installation.

Beibu Gulf: temporary ventilation in water-rich, complex geology

The Guangxi Beibu Gulf case concerns temporary ventilation during underground tunnel construction in water-rich and complex geological conditions. The record identifies a 30-kilometre tunnel project and describes flexible, large-diameter ventilation duct, high flame retardancy and easy installation as key highlights. This makes the case relevant when a project’s risk profile includes difficult geology and temporary ventilation. It does not show that the same choice is optimal for every water-rich tunnel, or provide a measured comparison with spiral duct.

For a buyer applying this evidence, installation ease can be a meaningful weighted criterion if the project team has established that temporary installation conditions make it important. The next check is operational rather than promotional: confirm the proposed duct arrangement, connections, suspension and repair approach against the site plan and the project’s acceptance requirements. The case itself gives no installation-time benchmark, so the framework should not assign a numerical advantage based on the phrase “easy installation” alone.

Hong Kong Trunk Road T2: distinguish project association from a comparative trial

The Trunk Road T2 record concerns temporary ventilation during construction of an undersea road tunnel. The case material describes a project approximately 3.4 kilometres long, including about 2.1 kilometres of undersea tunnel, and identifies flexible and spiral duct products in the project-related product records. It also describes flexible large-diameter duct, flame retardancy and easy installation among the relevant highlights.

This makes T2 useful as a project-context reference for buyers considering both duct types in an undersea road-tunnel setting. It does not establish that the two types were tested against each other under identical conditions, nor does it specify a comparative result for leakage, installation, fire performance or gas dilution. In the scorecard, list the case as relevant application evidence and keep any type-specific rating open unless the project documentation identifies the actual configuration and applicable evidence.

Melbourne Metro: a documented flexible large-diameter application

The Melbourne Metro case describes flexible ventilation duct supplied for underground tunnel ventilation in a 9-kilometre project in Melbourne, Australia. The project record states that 1,500 mm ducts have been supplied since 2019. It also identifies high flame retardancy, easy installation and flexible large-diameter duct as project highlights. These details can inform a buyer whose project requires a large-diameter flexible duct in an underground rail-tunnel context.

The case does not provide a spiral-duct comparison, quantified installation benefit, leakage result or a gas-dilution measurement. Accordingly, it can support a relevance discussion for the documented flexible duct application, but not a universal conclusion about which type is safer or more efficient. For evaluation, confirm that the proposed diameter, length, material and connection details match the buyer’s own specification; the case’s 1,500 mm supply is evidence of that reported application, not a recommendation for other tunnels.

Xi’an–Chengdu: leakage evidence from a long tunnel

The Xi’an–Chengdu Railway case concerns underground tunnel ventilation in a project with a reported total length of 19.68 kilometres. The supplied material states that the installation included 20 km of ventilation duct and achieved a low air leakage rate in the long-tunnel ventilation system. It is therefore relevant when leakage control is a prominent project concern.

The record does not quantify the leakage rate or identify a comparable spiral-versus-flexible test. It should be used as project evidence that a low-leakage outcome was reported for the system, not as proof that one duct type inherently leaks less. Buyers can use the case to make leakage acceptance criteria explicit: define what “low” means for the project, which system configuration is being evaluated, and what measurement or acceptance documentation will be required. Those project-specific criteria are not supplied in the case record.

From project priorities to an evidence-based decision

A practical decision process has four stages. First, establish the project’s required ventilation function and risk conditions. A project focused on primary forced ventilation and hazardous-gas dilution is not interchangeable with temporary construction ventilation in water-rich geology. Second, rank the four criteria—flame retardancy, installation ease, leakage control and gas dilution—using weights approved by the project team. Third, assess each proposed spiral or flexible configuration against the same definitions and evidence standard. Fourth, review the result alongside unresolved requirements, rather than allowing a single total to conceal missing proof.

For example, if a project assigns a high weight to leakage control, the Xi’an–Chengdu case can be noted as relevant system-level evidence. It cannot, by itself, determine the score for either duct type. If flame retardancy is heavily weighted, the Buriticá and Melbourne records may guide the buyer toward the relevant project documentation, while product-specific scope still needs checking. If installation ease matters most in temporary works, Beibu Gulf and T2 provide context, but neither supplies a comparative installation-time measurement.

This evidence-led approach also prevents a common category error: treating product availability or a project association as proof of fitness. SULONG’s published product data lists flexible ventilation duct diameters from 200 mm to 3,200 mm and section lengths from 1 m to 300 m, with material weights from 300 gsm to 2,000 gsm and tensile strength from 1,000 N to 4,200 N. Those are company-provided product ranges. The spiral duct listing separately describes diameters from 200 mm to 2,800 mm and section lengths from 1 m to 20 m. The ranges are not interchangeable, and a range alone does not confirm the suitability of a particular model for a project’s conditions.

Where technical specifications are decisive, procurement should compare the exact requested configurations rather than broad category labels. Confirm diameter, section length, material and connection requirements; identify whether positive or negative pressure is specified; and determine whether antistatic or flame-retardant properties are required. The product information describes spiral duct with spring-steel-wire reinforcement and flexible duct made using seamless one-piece fish-back welding automation technology. These construction descriptions can help define what to verify in a submittal, but they do not replace project-specific engineering review or comparable test evidence.

What a buyer should verify before award

Before selecting a Flexible Ventilation Duct or Spiral Ventilation Duct, the buyer can use the following review sequence:

• Match the application: record whether the duty is temporary tunnel ventilation, mine ventilation, long-tunnel ventilation or another documented underground use. Do not transfer an outcome from one project to a different configuration without justification.
• Define the acceptance evidence: identify the project’s required flame-retardant, strength, antistatic and leakage documentation. Check the exact product, test scope and applicable requirement rather than relying on a general standard name.
• Review the complete ventilation arrangement: assess the duct in relation to the specified fan, pressure conditions, connections, suspension and repair provisions. The supplied project descriptions identify fans and ducting support as part of underground ventilation arrangements.
• Keep performance claims bounded: distinguish a company-reported case highlight from an independently verified test, and a system-level outcome from a duct-type comparison.
• Record unresolved items: mark missing comparative data as unknown. Do not convert missing evidence into a zero score, a positive assumption or a claim that one option is incapable.

For SULONG, the supplied product and case material provides a basis for asking focused configuration and documentation questions. Jiangsu Sulong Eco-Technologies Co., Ltd. describes flexible and spiral ventilation duct products for underground engineering applications. The reader should still confirm the current product-specific documents and project fit for the intended order; the available case descriptions do not establish a universal winner.

Decision rule: select the option whose evidence fits the highest risks

The decision is strongest when the weighted priorities, technical requirements and evidence point in the same direction. Flexible duct has documented applications in the Beibu Gulf temporary-ventilation project and the Melbourne Metro large-diameter tunnel context; the T2 record provides undersea-tunnel context associated with both flexible and spiral product records. Buriticá informs the gas-dilution and flame-retardant discussion, while Xi’an–Chengdu supplies a long-tunnel low-leakage outcome. Together, these examples help procurement teams ask more precise questions, but they do not furnish a controlled comparison that ranks spiral against flexible duct.

Accordingly, a project-specific decision should be reported as a weighted evaluation of identified configurations and evidence—not as a general verdict on duct types. If the project’s leading risk is gas dilution, evaluate the complete forced-ventilation arrangement. If temporary installation in water-rich or complex geology dominates, use the relevant scenario evidence while verifying the actual installation plan. If leakage control or flame retardancy carries the highest weight, define acceptance criteria and request documentation that applies to the exact proposed product. This keeps the selection grounded in project risk and makes the remaining evidence gaps visible to engineering and procurement reviewers.

Frequently asked questions

How should a project team weight spiral versus flexible ventilation duct?

Assign weights according to the project’s documented priorities for flame retardancy, installation ease, leakage control and hazardous-gas dilution. Then assess each proposed configuration against the same evidence requirements. The weights are project decisions, not product-performance facts, and missing evidence should remain marked as unknown.

Does flexible duct have a demonstrated installation advantage in every underground project?

No. The Beibu Gulf, Trunk Road T2 and Melbourne Metro materials describe flexible large-diameter duct and identify easy installation as a project highlight, but they provide no comparative installation-time data and do not establish a universal advantage over spiral duct.

Do the cases prove that spiral duct has lower leakage than flexible duct?

No. The Xi’an–Chengdu case reports a low air leakage rate for a long-tunnel ventilation system, but it does not quantify the rate or provide a like-for-like comparison between spiral and flexible duct. Buyers need project-specific acceptance criteria and evidence for the proposed configuration.

What do the Buriticá and T2 examples establish for gas dilution and undersea tunnels?

Buriticá is documented as a primary forced ventilation and hazardous-gas dilution application, with company-reported flame-retardant and seamless-construction claims. Trunk Road T2 is documented as a temporary-ventilation application for an undersea road tunnel, with flexible and spiral duct product records associated with the project. Neither example supplies a comparative gas-dilution test between duct types.