Fixed firefighting systems for tunnels

Fixed firefighting systems for road tunnels

Johnny Jessen, Business Development Manager - Underground Facilities, VID Fire-Kill reports that the company has experienced an increase in interest for the TUNPROTEC® Low Pressure Watermist Solution for tunnel protection. The reason for this is believed to be a combination of different factors such as a growing focus on safety and property damage in road tunnels and the large amount of research conducted showing the effectiveness and benefits of fixed firefighting systems in tunnels.

TUNPROTEC® Fixed Fire Fighting System for tunnel protection has been developed by VID Fire-Kill, a Danish-based leading developer and supplier of low pressure water mist firefighting systems and components. Within the last couple of years, we have noticed a growing interest for our specially designed tunnel solution. This interest, we believe, is due to a combination of things. Full-scale tunnel fire tests have proven that fixed firefighting systems can even suppress large heavy goods vehicle fires, while tunnel owners are required to provide better protection of their tunnels to protect people as well as property assets and decrease the downtime or closure of a tunnel after a vehicle fire.

The most common fixed firefighting systems for tunnels are either deluge or water mist (low or high pressure). Both technologies work in deluge operation, dividing the tunnel into 20 - 30 m fire zones with open nozzles that are activated by opening a section valve. Both technologies use many of the same firefighting methods, but with variations.

Deluge/sprinkler firefighting Deluge systems operate with distribution of large droplet sizes (> 1mm) with low kinetic energy when discharged by the nozzle. Deluge systems suppress the fire by discharging large amounts of water over specified areas and thereby wetting and cooling the fuel surface.

Deluge/sprinkler systems typically use open sprinkler heads/nozzles, applying typically:

Nozzles: Min. 1.1 bar Pumps: 6 bar

Deluge/Sprinkler offers:

Robustness,

High water consumption/flow rate,

Less maintenance than high pressure water mist, Lower component costs (using typically coated steel pipes (PN16)), Can share water-main with the hydrants

Water mist firefighting Water mist employs several firefighting methods that make it equal or better than deluge/ sprinkler solutions, but with significantly less water consumption. Water mist uses a combination of wetting the surface and distributing smaller droplets which quickly can absorb more energy/heat from the fire than the larger droplets distributed by deluge systems.

Water mist (High Pressure) Operates with a relatively high pressure and uses open sprinkler heads/nozzles, applying typically:

Nozzles: 35-80 bar Pumps: 64-140 bar

High pressure water mist technology distributes water in very

small droplets and the high pressure applied (35+ bar) results in a high droplet energy/heat absorption and evaporation rate.

High pressure water mist offers:

Smaller pipe dimensions than a deluge system,

Less spatial requirements than a deluge system,

Significantly lower water consumption than a deluge system,

Require larger pumps and power than deluge and low pressure water mist

More complexity and less robust than a deluge system and low pressure water mist,

Require more maintenance service/sequences than a deluge system and low pressure water mist,

A less cost-effective system than deluge & low pressure water mist.

Water mist (low pressure) Operates with a relatively low pressure and uses open sprinkler heads/nozzles, applying typically:

Nozzles: 10 bar Pumps: 15 bar

Low pressure water mist technology can be described as a technology that utilises or bridges the best from the deluge and high pressure water mist technologies. Low pressure water mist offers:

Smaller pipe dimensions and spatial requirements similar to high pressure,

Simplicity and robustness like deluge,

Low maintenance requirements like deluge,

Low water consumption like high pressure,

Can share water-main with hydrants like deluge,

Cost efficient = can utilise standard PN 16 components and press-fit like deluge,

Japan was the first country to install a fixed firefighting system in a tunnel more than 50 years ago. Japan, together with Australia and USA, prefer deluge systems. In European tunnels, (except for Sweden) water mist is the preferred technology.

Singapore is another country that typically applies deluge systems in their road tunnels. For the major upgrade of South-East Asia’s longest urban road tunnels, the KallangPaya Lebar tunnel and Central Expressway tunnel, Land Transport Authorities (LTA) in Singapore wanted to install a fixed firefighting system in the tunnels, as Singapore authorities prohibited long vehicles from entering the road tunnels as part of the fire safety measures to minimize the risk of heavy goods vehicle fires. The tunnels were opened without fixed firefighting systems being installed. When studying the installation of a deluge system it became clear that there was a very practical problem in that the drainage capacity in the existing tunnels was unable to support the installation of a deluge system.

In 2018, Land Transport Authorities (LTA) initiated a tender for refurbishing the tunnels, including the installation of a fixed firefighting system, indicating water mist as the preferred technology in the tender due to the lower water consumption.

In spring 2018 VID Fire-Kill’s TUNPROTEC® Low Pressure Water mist Solution was selected as the preferred solution for the two tunnels in Singapore.

Our low pressure water mist solution was selected due to several advantages over a deluge solution and high pressure water mist

Our system offered significantly less consumption of water than conventional deluge systems

Our system allowed for a significantly smaller water reservoir and drainage system

Our system required significantly less space for pipes and valves

Our system reduced installation time by 35% due to the modular prefab nozzle pipes and press-fit installation, less complex valve trims and installation.

Another criterion from LTA was that the low pressure water mist solution should offer the same capabilities as a deluge system in relation to fighting a heavy goods vehicle fire, i.e. reducing the heat release rate at high ventilation velocities.

In 2018, TUNPROTEC® underwent an extensive series of full-scale tunnel fire testing in San Pedro de Anes test centre in Spain with potential fire scenarios of up to 250 MW. The tests showed that the heat release rate reduction was equal to a deluge system. Further, all tenability requirements in accordance with NFPA 502 were fulfilled and the system was approved by LTA. (KPE) & (CE) tunnel protection highlights:

The project includes more than 1,200 deluge valves 100 km of pre-fabricated nozzle pipes.

Tunnel width: varies between 15.3 and 19 m

Tunnel Height: 5.9 m

Installation Year: 2018-21

We are confident that the firefighting industry will see an increasing demand for more sustainable active tunnel firefighting solutions in the future.