Tunnel ventilation

Tunnel ventilation is a central planning and execution topic in underground construction, in concrete demolition and special deconstruction, as well as during gutting works. It affects safety, work quality, and efficiency. Depending on the construction phase and the technology used-from rock excavation at the tunnel heading to the deconstruction of concrete cross-sections-airflow management, air volumes, and monitoring must be adapted to emissions, dust, and heat. Tools and equipment from Darda GmbH, such as concrete demolition shears or rock and concrete splitters, directly affect the emissions profile and can reduce the requirements for ventilation by causing less dust and vibration than percussive methods. Early integration of ventilation into method statements and sequencing improves compliance, reduces rework, and stabilizes productivity.

Definition: What is meant by tunnel ventilation?

Tunnel ventilation is the targeted supply of fresh air and the removal of contaminated, dust-laden, or heated air in underground structures. The aim is to ensure sufficient oxygen, low concentrations of exhaust gases (for example CO, NO₂), low dust levels, and appropriate temperatures. In construction and deconstruction phases, tunnel ventilation includes mobile and stationary ventilation systems that are dynamically adapted according to the work step, equipment, cross-section, and drive length. In the event of an incident (for example fire or heavy dust release), the ventilation must additionally limit smoke spread and support escape and rescue conditions. Typical systems comprise primary fans, ducts or hoses, air distribution elements, and sensor-based control loops with automatic shutdown and override logic for incidents.

Tasks and objectives of tunnel ventilation

The essential tasks are to ensure breathable air quality, reduce dust and aerosols, remove exhaust gases, and provide thermal relief. In addition, ventilation serves to control flow directions to supply work areas with targeted supply air and to protect adjacent areas from contamination. In deconstruction work on reinforced concrete-for example with concrete demolition shears-the focus is on dust and fiber release; in rock excavation and tunnel construction, fine dust and, where applicable, blasting fumes or vapors from cutting and separation work are added. Appropriate airflow management prevents recirculation and dead-end flows. Clear definition of target values, measurement locations, and alert thresholds supports consistent quality assurance.

Ventilation systems and flow concepts

In practice, different systems and combinations are used, tailored to tunnel geometry, construction length, and construction state:

• Longitudinal ventilation: Flow along the tunnel axis, often generated by jet fans or pressure/suction blowers; suitable for long, slender cross-sections with clear flow paths and low obstruction density.
• Transverse and semi-transverse ventilation: Supply air and exhaust air are routed via separate ducts or ventilation hoses; advantageous when emissions vary locally or several workplaces operate in parallel, or when zoning is required.
• Hose ventilation during construction: Flexible ventilation hoses (supply or exhaust) routed close to the emission source; reduces the mixing zone and improves source capture, for example directly at the deconstruction section.
• Extract ventilation: Removal of contaminated air in the work area while clean air flows in from “behind”; promotes directed flow and reduces exposure.
• Hybrid concepts and zoning: Combination of longitudinal push with local extraction and temporary bulkheads to guide flows, avoid short-circuiting, and isolate high-emission tasks.

Air quality in construction and deconstruction: emissions and dust

Air quality is determined by several factors: exhaust gases (CO, NO_x), fine dust (including respirable fractions), quartz dust during rock processing, aerosols from water misting, vapors from cutting and separation work, and heat sources. The choice of work technique is crucial. Concrete demolition shears typically generate less fine concrete dust than percussive demolition methods and reduce secondary resuspension. Rock and concrete splitters as well as rock wedge splitters can enable low-stress, low-vibration separation in rock excavation, thereby reducing dust generation and the required air exchange. When using combination shears, Multi Cutters, steel shears or a tank cutter, thermal and metallic particles and vapors may arise depending on the material; here, near-source extraction with high capture efficiency and a clear exhaust airflow is advisable. Where internal combustion engines are used, low-sulfur fuels and exhaust aftertreatment reduce pollutants; with electric drives, heat becomes the dominant residual load.

Dust reduction and local capture

• Wet methods (targeted wetting) to bind fine dust without impairing visibility or electrical systems.
• Near-source extraction at cutting and separation points, short capture hoods, and adjusted hose diameters.
• Controlled volume flows to avoid backflow; keep airflow velocities moderate near the work area so that dust is not drifted into uninvolved areas.
• Use appropriately rated filters in mobile extractors (for example H-class vacuum units) for silica-bearing dusts.
• Maintain slight negative pressure in the immediate work zone to limit fugitive emissions to adjacent areas and adits.

Dimensioning and key parameters

Dimensioning is based on emission quantities, required dilution, flow paths, and permissible concentrations. Relevant parameters are air volume flow (m³/h), pressure losses (Pa), airflow velocities (m/s), leaks, as well as temperature and humidity conditions. A pragmatic approach is to combine a base ventilation rate for background dilution with additive source capture flows per activity.

1. Identify emission sources (demolition equipment, power supply units, transport vehicles, welding and cutting processes).
2. Determine required dilution or capture volume flows per source; prefer source extraction.
3. Consider flow path, cross-section, roughness, and obstructions; calculate pressure loss.
4. Position supply/exhaust so that a directed airflow passes through the workplace and safely removes contaminated air.
5. Plan for reserve and controllability (variable volume flow for changing construction states).
6. Verify design assumptions by on-site smoke tests or CFD-backed spot checks and document outcomes.

Typical influencing factors

• Cross-section and length of the tunnel, construction progress, temporary partitions.
• Number of simultaneously operating devices and their emissions profile.
• Heat loads from drives, power units, and lighting.
• Outdoor climate (inlet temperature) and the desired temperature in the work area.
• Ventilation doors, bulkheads, and temporary coverings that alter leakage paths.
• Risk of recirculation between parallel headings or cross-passages.

Influence of equipment and power supply

Hydraulically operated tools from Darda GmbH – such as concrete demolition shears, rock and concrete splitters, combination shears, or Multi Cutters – are supplied by hydraulic power packs (i.e., hydraulic power units). The choice of energy source directly influences ventilation requirements. Electrically driven hydraulic power packs produce no local exhaust gases; with combustion engines, CO and NO_x must be diluted and removed. A clean power supply reduces the ventilation rate required for exhaust dilution; the remaining ventilation capacity can then focus more on dust reduction and heat removal. Even with electric supply, motor and hydraulic losses generate heat that must be removed to maintain suitable working conditions.

Tool selection and emissions profile

• Splitting methods (rock and concrete splitters, rock wedge splitters) and shearing methods (concrete demolition shears, steel shears) are often less dust-intensive than percussive methods; they favor a lower base load in the ventilation.
• Thermal cutting methods (tank cutter) require targeted capture of vapors and a consistent exhaust airflow.
• Select lower speed-high force settings where feasible to minimize abrasive dust generation while maintaining cut quality.

Work organization, safety, and health protection

Effective tunnel ventilation combines technology and organization: spatially separate work areas, define flow direction, stagger emission peaks over time. Personal exposure is reduced by sufficient airflow, source extraction, and low-dust methods. Exposure limits and guidelines may vary by country and application; it is sensible to define conservative project-specific target values and to monitor them continuously. Access control, signage of airflow direction, and coordinated logistics reduce turbulence and congestion in the airstream.

Monitoring and adjustment

• Continuous measurement of CO, NO₂, dust (PM fractions), and temperature at critical points.
• Alarms when thresholds are exceeded and automatic adjustment of fan output.
• Documentation of measured values for traceability and optimization.
• Calibrate sensors at defined intervals and place them at representative breathing heights and in return flows.
• Use trend analyses and simple KPIs (for example exceedance minutes per shift) to steer improvement.

Planning and monitoring over the project lifecycle

Air volumes, hose routes, and locations of power packs should be defined at the planning stage. As tunnel heading progresses or deconstruction advances, flow paths and pressure losses change; ventilation must keep pace. Mobile sensors, data recording, and regular walkdowns help identify hotspots and improve airflow management. Version-controlled ventilation drawings and change logs support safe implementation of modifications.

Hose routing and flow discipline

• Lay ventilation hoses taut and with as few bends as possible; avoid leaks.
• Do not direct supply air straight at dust sources to limit resuspension; it is better to extract contaminated air and introduce fresh air from the side or from behind.
• Position exhaust openings so that no backflow occurs into occupied areas.
• Use antistatic, flame-retardant hoses and ensure proper earthing where required.
• Inspect and maintain couplings, hangers, and suspension at regular intervals to prevent collapses and leaks.

Practical procedures for rock excavation and tunnel construction

In rock heading and enlargement of excavations, emissions and dust generation are highly location-dependent. The use of rock and concrete splitters and rock wedge splitters can reduce shock and dust peaks. During transport and loading processes, secondary dust sources arise; here, directed supply air that follows the material flow helps, while nearby extraction points secure the transfer locations. During drilling or cutting cycles, synchronize extraction with duty cycles to avoid unnecessary over-ventilation between passes.

Recommendations for the sequence

1. Cordon off the work section and define the flow direction (supply air → workplace → exhaust air).
2. Near-source extraction at splitting and cutting points; use water mist dosed as needed.
3. Apply low, uniform airflow along transport routes to improve visibility and dust binding.
4. Check measurements and adapt fan output, especially after changes in the construction state.
5. Perform a quick smoke test and confirm capture at the source before ramping up production.

Demolition of concrete structures in tunnels

In the deconstruction of linings, foundations, or cross-passages in tunnels, concrete demolition shears and shearing tools are often advantageous because they can cut reinforcement and detach components in a controlled manner. This lowers the likelihood of dust-intensive secondary breakage. A combination of source extraction, moderate supply air, and exhaust air directed at the component reduces exposure and deposits. Multi Cutters and steel shears process reinforcement and built-ins; the heat generated should be removed by directed airflows. Where silica-bearing concrete is processed, appropriate dust control and monitoring of respirable crystalline silica are required.

Strip-out and cutting

• In strip-out, preferably use shearing and splitting methods; perform cutting work with sparks separately and with its own exhaust zone.
• Set up hydraulic power packs in well-ventilated niches or outside the main work area; prefer electrical supply where possible.
• Keep work areas clean via wet sweeping or H-class vacuuming; avoid dry sweeping.

Special considerations for special operations

Special tasks – such as cutting tanks or removing contaminated installations – require particularly stable and well-controlled ventilation. When using a tank cutter, vapors and aerosols must be captured in a targeted manner; ignition sources and flow paths must be carefully planned. In areas with potentially explosive atmospheres, only suitable components and methods may be used; safety assessments must be carried out on a project-specific basis. Continuous monitoring for flammable gases or vapors, including use of LEL sensors where appropriate, and robust permit-to-work processes increase safety margins.

Energy efficiency and sustainability

Ventilation is energy-intensive. An efficient combination of low-emission work techniques, source extraction, variable-speed control, and streamlined hose routing noticeably reduces energy demand. Methods with less dust and exhaust – such as the use of concrete demolition shears or rock and concrete splitters – reduce the air volumes required for dilution. This allows the available fan capacity to be targeted to thermal loads or local hotspots. Variable-speed drives, demand-controlled ventilation based on gas and dust signals, and efficient duct layouts minimize fan energy while maintaining compliance.