Maximising fixed fire protection systems 24 Aug 2017

When it comes to protecting critical underground infrastructure, compromises in fire safety cannot be made. Improving safety of vital underground infrastructure during the operation is a primary concern for governments and authorities having jurisdiction (AHJ). The requirements for installing a robust fire protection strategy that not only ensures life safety, but also prevents damage to the tunnel structure, is the ultimate goal.

Protecting road tunnels in the case of a fire raises challenges according to the specific design of different tunnels, increased traffic levels and a lack of uniform and consistent safety standards in tunnel design. Understanding the characteristics and behaviour of a fire in an enclosed space, where fires are typically hotter, last longer last and create extensive damage⁽¹⁾ helps to identify the key considerations when specifying and selecting a robust fire protection system.

Single-pipe, back-to-back installation of nozzles

Limited access highways, road tunnels, bridges, elevated highways, depressed highways and roadways situated beneath airtight structures are covered, in some instances, in Europe by the NFPA (National Fire Protection Association) 502 standard for fire protection and fire life safety. This standard establishes minimum requirements for each of the identified facilities, with appropriate measures also defined by the local AHJ. The European UPTUN research project for Cost-effective, Sustainable and Innovative Upgrading Methods for Fire Safety in Existing Tunnels developed the Engineering Guidance for Water-Based Fire Fighting Systems for the Protection of Tunnels and Subsurface Facilities. This sets engineering practices and principles on the design, installation and maintenance of water-based fixed fire fighting systems (FFFS) to be used in tunnels.

Fixed water-based systems offer the ability to suppress and cool a fire, prevent fire spread, protect the overall tunnel structure and its facilities, and support essential fire-fighting activities, particularly in road tunnels through which heavy goods vehicles mix with passenger cars and where evacuation of people from vehicles is required.

Fire protection for road tunnels

Designing a water-based system with these considerations in mind is vital to alleviate concerns relating to reduced visibility during evacuation, hot steam and potential deflagration once the system has discharged, and the perceived high cost of installation and maintenance. Fixed fire protection systems are tested extensively in Europe to ensure that the functional performance of the system is based on real-life fire scenarios and provide confidence to designers and operators that the selected method matches the application for safe evacuation, improved access for fire services, control to prevent fire spread, and reduced damage to the tunnel structure.

A total solutions approach

The drive for safer and more effective maintenance across a wide variety of fire protection applications has led manufacturers to invest in research and development to introduce increasingly sophisticated solutions which combine several components to form a complete protection system. Under its TYCO brand, Johnson Controls has developed proven and trusted technology for fixed water-based fire fighting systems. The company operates in more the 150 countries worldwide and focuses on product design, performance capability and service support to drive its product innovation. This, combined with technical expertise, training and knowledge, provides operators and asset owners with the reassurance of proven performance, even in the most challenging of applications.

In its extensive specialised product range, the horizontal spray nozzles, models TN-25 and TN-17, are intended for integration into a water spray/deluge fire protection system. The nozzles are UL (Underwriters Laboratories) approved and by ULs in Canada (C-UL) and have been independently tested and proven to suppress or control full-scale tunnel fires. The newest model in the range, the TN-17 sprinkler was designed specifically to meet requirements for minimized water use while maximizing coverage area (Table 1).

Both the TN-17 and TN-25 sprinklers generally require only a single pipe to help protect up to 20m (50ft) of tunnel width, with the nozzles installed with a back-to-back configuration instead of using multiple mains with branch and drop lines. With fewer installed nozzles and minimal fittings and couplings reduce costs by reducing installation time and materials. Performance testing and pipe-flush maintenance can be achieved by regular discharge in the deluge zones.

The complete fire protection system integrates TYCO DV-5 deluge valves, detection and control equipment, plus a combination of ancillary equipment, including GRINNELL grooved couplings and fittings, and metal framing and supports.

Continuous development within the fire protection industry prepares tunnel designers, engineers and operators to meet evolving challenges, legislation changes and the specific constraints and limitations of more demanding tunnel projects. Investing in proven products and total fire protection systems from an accredited manufacturer helps alleviate common design and supply chain pain points and minimise the need for extensive, complex and expensive retrofitting of active fire protection systems.