Case study
The ventilation system of a road tunnel, built end to end
When smoke fills a tunnel, the ventilation system is what buys people time to get out. For Vranduk II we drew the electrical design, built and certified the switchgear, installed the controllers, wrote the logic that drives them, and signalled every state and alarm back to the tunnel's control centre.
Photograph: zenicainfo.ba — Vranduk II tunnel during the rehabilitation
- Client
- BBM d.o.o. Sarajevo
- Site
- Vranduk II tunnel, M-17 Doboj–Zenica
- Sector
- Road infrastructure · life safety
- Delivered
- 2019–2021
5
Cabinets designed, assembled and factory-certified
13
Reversible fans powered and controlled
2
PLCs, master and slave, linked over fibre
30 MW
Design fire the system is sized against
The problem
A tunnel fan is not a ventilation system
Road tunnel ventilation exists for two reasons. Day to day it clears exhaust so the air stays breathable. In a fire it does something else entirely: it controls where the smoke goes, holding a survivable layer above the roadway long enough for people to walk out and for the fire service to walk in.
Those two jobs want opposite things from the same fans. Normal operation wants throughput. A fire wants controlled, directional airflow — sometimes less of it, sometimes reversed — decided from what the sensors say is happening and where. The fans are the same hardware; the difference is in the switchgear that can reverse them and in the logic that decides when to.
So the deliverable was never a program. It was the chain from the busbar to the control room: boards that can start, reverse and protect thirteen motors underground, a control system that changes behaviour the moment a zone catches fire, and a signal path that tells the operator the truth about all of it.
The work
From the drawing to the commissioned plant
Comex worked as BBM's subcontractor on the tunnel's ventilation electrical installation and on the supervision and control system for substations TS1 and TS2. Four things came out of it, and only one of them was code.
- 01
The electrical design
A separate EPLAN project per board — ROV-1, ROV-2, ROV-S, the portal command cabinets KO-1 and KO-2, the niche cabinets KO-V1 and KO-V2, the distribution boards RO-PP1 to RO-PP3 and ROR-1 and ROR-2, the reservoir instrumentation panel — drawn against the investor's design books for lighting, LV supply and electro-ventilation, and closed out as as-built documentation for TS1 and TS2.
- 02
The cabinets themselves
Five switchgear and control cabinets assembled and put through factory testing before they went underground, each with its own serial number and certificate. Comex designed and built them; TING d.o.o. of Žepče worked as our subcontractor and held the accreditation to certify them.
- 03
The control system
A master/slave pair of industrial PLCs in the niche command cabinets KO-V1 and KO-V2, linked by single-mode fibre through industrial Ethernet switches, plus the program that runs normal and fire modes. Manual control is possible from four places, each with the same authority over the whole system.
- 04
Protection and signalling
Every fan carries overload, short-circuit, thermal and vibration protection, and heats its own windings when it is stopped. Every state and alarm is signalled to all four command interfaces over 24 V DC relay circuits and onward to the tunnel's central supervisory and control system.
What we built
Five cabinets, tested before they went underground
ROV-1 sits in electrical niche EN-1 and feeds fans V1 to V4. ROV-2 sits in EN-2 and feeds V5 to V10. ROV-S sits in the widening of the first cross-passage and feeds the three service-tube fans. KO-1 and KO-2 are the command cabinets in the portal substations.
| Cabinet | Role | Rating | Enclosure |
|---|---|---|---|
| ROV-1 | Ventilation board, niche EN-1 — fans V1–V4 | 3×400 V, 240 A | 2100 × 2400 × 400 mm |
| ROV-2 | Ventilation board, niche EN-2 — fans V5–V10 | 3×400 V, 360 A | 2100 × 2400 × 400 mm |
| ROV-S | Service-tube ventilation board — fans V1–V3 | 3×415 V, 160 A | 2100 × 600 × 400 mm |
| KO-1 | Portal substation command cabinet — TS-1 | Control only, 1 A | 2100 × 600 × 400 mm |
| KO-2 | Portal substation command cabinet — TS-2 | Control only, 1 A | 2100 × 600 × 400 mm |
All five are IP54 and rated for a 10 kA short-circuit current, and all five were certified together under factory certificate 3C-4-320/20 of 26 April 2020, serials 19-6000-000007-1 through -5.
The logic
What the system has to decide
The investor's design specifies the behaviour; the signal list we issued is what turns it into something a controller can act on. Thirteen reversible fans — ten in the main tube at 34 kW each, three in the service tube at 11 kW — started through soft-starters and driven by the master/slave PLC pair, with every sensor and control circuit on a UPS while the motors and heaters run off the mains busbars.
What it reads
- 3CO and visibility meters, in-tunnel
- 3Air speed and direction meters, in-tunnel
- 2Fog detectors, ahead of the portals
Normal mode
Analogue sensor values arrive at the controller and are discretised in software, then staged against the thresholds set by the ventilation design: CO above 80 ppm or an extinction coefficient above 6×10⁻³ m⁻¹, sustained for five minutes, brings on a fan group; 150 ppm or 12×10⁻³ m⁻¹ sustained for ten closes the tunnel to traffic. Four rules make the difference between logic that works on paper and logic that survives a year in a tunnel:
- 01
Don't chase the sensor
Readings are conditioned before they drive anything, and a fan group that comes on stays on for a minimum period. Raw values would cycle the fans around a threshold — expensive in wear, and useless as ventilation.
- 02
Never pull fog inwards
When a portal fog detector trips, the airflow direction is chosen so the ventilation does not draw fog into the tunnel. Correct for air quality, wrong for visibility — the logic has to know the difference.
- 03
Command in pairs, not one fan at a time
The ten main-tube fans are commanded as five blocks — V1 and V2 through V9 and V10 — each with a left, right and stop command, while every fan still reports its own motor current, run-up state and vibration individually. Control at the group, monitoring at the unit.
- 04
Sequence the reversal
These fans run both ways, and reversing one is not a single command. The specification lists sequencing of fan reversal as a function the control system must provide in its own right, alongside motor control, the executive-level safety functions and the automatic algorithms.
Fire mode
A separate control regime, entered on linear heat detection, a manual call point, an extinguisher lifted from an SOS niche, or the operator's own call. The design requires the fan block inside the fire zone to drop out while the rest run to a directional pattern, and the signal list carries that command explicitly. The numbers it has to satisfy come from the tunnel's own fire model:
- Design fire
- One truck and two cars — 30 MW
- Smoke produced
- 120 m³/s
- Required capacity
- 120 m³/s at minimum 2 m/s airflow
- Air quality limits
- CO 100 ppm · NOx 25 ppm · extinction k = 0.007 m⁻¹
- Methodology
- Austrian RVS tunnel guidelines
The service tube is held at overpressure by two of its three fans so smoke cannot follow people into the escape route; the third only starts if one of them fails. The phase timings — evacuation, partial clearing, full clearing, return to normal — are required to be parameters in the PLC rather than values compiled into it, so an authorised person can retune them on site.
Handover
What was proven, and when
The cabinets were tested before they ever went underground. Factory certificate 3C-4-320/20, issued on 26 April 2020 under Federal Ministry of Energy, Mining and Industry authorisation, records each of the five against IEC 60439-1 and IEC 60529: enclosure protection, insulation clearances, a 2 kV dielectric test held for sixty seconds, temperature rise under load, and a function check of the switchgear inside. Each cabinet carries its own serial number.
The algorithms and the signal list were issued as a controlled, stamped, revision-numbered document in August 2021 — thirty-two pages covering both operating modes, the fan sequencing table by fire zone, and the full signal list to the central supervisory and control system. An as-built revision followed that October, after the plant was running.
Works were completed on 10 August 2021 and notified to the contractor under reference 112/21 — the design, supply and construction of the supervision and control system for substations TS1 and TS2 — with a request to convene a commission and carry out the technical inspection.
At a glance
Project specification
- Client
- BBM d.o.o. Sarajevo — Comex as subcontractor
- Investor
- JP Ceste Federacije BiH d.o.o., Sarajevo
- Main contractor
- JV Hering d.d. Široki Brijeg & BBM d.o.o. Sarajevo
- Parent project
- Reconstruction of the Vranduk II tunnel on the M-17, Topčić Polje – Lašva section
- Site
- 1,037.5 m traffic tube and a 712.5 m service tube, joined by three cross-passages
- Scope
- Electrical design, cabinet manufacture and factory testing, PLC control system, control program, and state and alarm signalling to the central supervisory and control system
- Design basis
- The investor's main design — book 5-2 (lighting, LV supply and electro-ventilation), 5-5 (tunnel control system) and 5-6 (ventilation, mechanical part)
- Ventilation plant
- 10 reversible fans at 34 kW in the traffic tube, 3 at 11 kW in the service tube, all soft-started
- Control
- Master and slave PLCs in cabinets KO-V1 and KO-V2, single-mode fibre between industrial Ethernet switches, four identical command interfaces
- Power
- Motors and heaters from the mains busbars; all control equipment and process sensors on uninterruptible supply
- Cabinet certification
- Factory certificate 3C-4-320/20 of 26 April 2020
- Completion
- Notified 10 August 2021 under reference 112/21
Have a system where the cabinet and the code have to agree?
Switchgear, controllers and the logic that drives them — designed, built and certified by the same team, with the test sheets to show for it. Tell us what you are protecting.