Fire safety in subsurface environments
Published on 6 January 2009
Fires in tunnels tend to make headline news, largely because of the potential loss of life that such an incident presents. At the turn of the new millennium three catastrophic fires in as many years ensured that tunnel protection became a real focus on the fire safety agenda.
In 1999 the Mont Blanc tunnel fire, probably the most well known of the three, resulted in 39 deaths when a Belgian transport truck caught fire, resulting in temperatures of 1,000°C and taking some five days to cool sufficiently for crews to enter the tunnel to begin three years of repairs and significant enhancements of the safety equipment and procedures.
This was followed in November 2000 by the Austrian Kaprun funicular tunnel fire which killed some 155 people as they headed for the pistes in a popular ski area some 350 kilometres to the west of Vienna.
Then, in October 2001, the St Gotthard Tunnel in Switzerland, the third longest road tunnel in the world, saw two lorries collide to create a fire that killed eleven people. Tunnel fires have, of course, occurred before and since but three such major incidents in such a short timeframe highlighted very clearly the dangers of tunnel fires and the need to recognise the specific challenges that tunnels present in terms of fire safety engineering.
When construction work is undertaken in an underground location, the project plan for safety and in particular fire safety needs to address the extra risks associated with work in an area that, by definition, will have limited means of escape. The area will inevitably be one in which ventilation will be restricted. Lighting will also be a prime consideration.
Managing an emergency successfully is a matter of planning, having the correct equipment in place and employing an effective maintenance programme to ensure that the equipment works when required. The first essential is a risk assessment undertaken by a competent person.
Particularly during the construction phase of a project, the risk assessment needs to be a dynamic working document that changes as the work progresses. The ownership and authorship of said document needs to be one of the project manager’s prime tasks. It should link to a project fire and safety strategy document that indicates how the risks identified are being managed and how the process for emergencies are to be handled.
For example, if a risk from mechanical plant operating in the underground location is identified, the strategy may require that a mechanical plant containing volatile fuel or gas be fitted with an automatic fire suppression system and that during operation a specified number and type of portable fire extinguishers be available. The strategy document may also require that persons operating the equipment undertake specific training on the use of fire extinguishers.
Fire risk and fire strategy are the tools of the trade for driving down financial loss and reducing project delay.
A fire risk assessment follows a logical pattern
Specific fire risks in construction work underground are determined on each site. However, all such work will need to consider the following when producing a proposed fire strategy:
The hazards will change as the construction progresses. The risk will increase as initial construction gives way to first and second fix. The materials used in construction are often delivered in flammable packing to prevent transit damage. A management process for safe storage and for efficient removal of packaging materials is required. The need for fire extinguishers suitable for Class A fires (those involving solid materials, such as paper wood or textiles) is apparent.
The construction programme can be part of the risk control programme. For example, the completion of enclosed stair routes before other work proceeds can help address safe escape routes. Early provision of a ventilation system will assist in control of the environment to allow escape. Control of the area by a ‘permit to work’ system and a temporary fire alarm system can assist in the risk reduction process.
All of the above underlines my assertion that the risk assessment needs to be a dynamic working document that changes as the work progresses.
The fire protection of an area can be enhanced by using heat or smoke detection. The services that a tunnel normally carries can form part of the detection. For example, fibre optic cables can form the sensor for a linear heat detection system that can provide precise location information. As with many fire situations, providing warning at the earliest possible point is the goal and identifying the source of a fire is a significant factor in this process. CCTV systems can also provide a smoke detection output as well as supplying video information.
From construction to use
Once the construction phase is complete the elements of the operation of a tunnel need to be built into the equation. The risk and the fire load - that is the amount of combustible material in the area or passing through - need to be recognised and the fire protection measures employed accordingly. The requirement for fire fighting systems and the location of portable fire extinguishers will depend on the use to which the structure will be put.
If personnel are normally located within a given area of the tunnel, the system to alert them to potential danger needs careful consideration. The variety and versatility of voice and message sounders is an important factor here, with voice-based messaging increasingly being used to provide a precise instruction for an evacuation that is not available from a purely tone-based sounder.
Rising to the challenge
Roger Wilton - Assistant Technical Manager - Fire Industry Association (FIA)
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