Fire-Rated OTE Ductwork for Riyadh Metro Line 3

ArRiyadh New Mobility Consortium (ANM) was one of three consortia appointed to deliver the Riyadh Metro project. ANM was responsible for the 41.8km Line 3, the longest of the six lines forming the city’s new 176km metro network.

Led by Italian construction group Salini Impregilo, the consortium included Larsen & Toubro, Nesma, Ansaldo STS, Bombardier, Idom and WorleyParsons.

Line 3 runs across Riyadh from an area near the Jeddah Expressway in the west to the vicinity of the Khashm El Aam National Guard Camp in the east comprising 22 stations, including the landmark Downtown and Western stations, alongside two depots and six park-and-ride facilities.

The route includes 25.8km of elevated track with ten elevated stations, 11km of underground track serving eight underground stations and a 4.8km at-grade section incorporating four shallow-underground stations.

Invicta ANARA was contracted to design and install a fire-rated over-track exhaust duct at Qasr Al-Hokm Station (3E2) on Line 3 of the Riyadh Metro. The duct formed part of the station’s smoke-extraction system and was designed to remove smoke in the event of a train or station fire, helping people evacuate the underground station safely.

The system needed to be fully tested and certified to provide 4 hours of fire protection at temperatures up to 1,000°C, and incorporated 94 fire-rated grilles as part of the extraction system.

The duct configuration varied across the station. Some sections were designed as three-sided ducts, using the existing concrete soffit as the fourth side, while other areas required conventional four-sided rectangular ductwork.

In addition to the fire-performance requirements, the completed system had to withstand an internal extract-fan pressure of 1,140 Pa and an external piston-effect pressure of ±500 Pa generated by trains passing underneath. The entire system therefore required internationally recognised fire certification alongside the structural performance needed for the operating conditions.

One of the principal installation challenges was the duct’s relationship with the existing platform screen door structure. The over-track exhaust duct had to fit within the supporting steelwork while remaining structurally independent from it.

The vertical posts and horizontal beams supporting the platform screen doors were already installed. As the duct had to be constructed on the inner side of this framework, sections could not be prefabricated at ground level and lifted into their final positions.

Instead, the complete system had to be assembled in situ from mobile scaffolding erected within the track area. Installation was restricted to night shifts so that train testing and other work could continue during the day. The scaffold system consequently had to be erected and dismantled during every shift. This ensured that the track remained unobstructed and could be energised safely for daytime testing.

The completed ductwork also needed to integrate with the station’s architectural appearance, requiring a carefully coordinated painted finish.

Invicta ANARA developed an installation sequence suited to the station’s restricted working environment. During each night shift, a mobile scaffold platform was positioned on the track to provide access to the overhead work area.

The CRC framework and independent hanger system were installed first, supporting the duct without transferring loads to the platform screen door steelwork. Durasteel sheets were then installed to form the required three-sided and four-sided duct sections.

Components were prepared and painted off-site before delivery, reducing on-site finishing work. Local touch-ups were completed after assembly to achieve a consistent finish that blended with the surrounding structure.

Chemical sleeve anchors were used at the extract shaft’s hollow-block walls as an alternative to standard mechanical anchors, while maintaining the required structural stability and integrity.

A team of eight Invicta operatives successfully installed the fully certified, fire-rated OTE duct system over a four-month period.

The completed installation provides:

• 4-hour fire integrity and 2-hour insulation
• Fire performance at temperatures up to 1,000°C
• 1,640 Pa pressure rating, incorporating fan pressure and train piston effect
• 94 fire-rated grilles integrated into the extraction system
• A duct system installed independently of the existing PSD framework
• Three-sided and four-sided duct configurations to suit the station structure
• In-situ installation within a restricted track environment
• Night-shift installation without compromising daytime train testing
• A finished appearance coordinated with the surrounding station environment

The project brought together fire performance, structural coordination and a highly controlled installation process within one of Riyadh Metro’s most constrained working environments.