The Need for a Minimum Flow-rate on Interior Attack Nozzles

Paul Grimwood (author of Euro Firefighter)

The debate over what is a 'safe' minimum firefighting flow-rate has been developing in several countries over the past decade. The training concepts associated with CFBT, where firefighters enter Fire Development Simulators (FDS) (shipping containers), appears to have created some false illusions in this respect.

When firefighters adapt their training approaches in the 1.5MW (demonstrator FDS) or 2.3MW (attack FDS) units they are only experiencing a very 'mild' fire that is predominantly in the gaseous phase with very little fuel base. In reality, this 'training fire' is only representative as 50% of a fully involved room fire in terms of heat release and perhaps far less in relation to the involved fuel base (fire load). In fact, a five-roomed apartment can develop from flashover in one room to full involvement of all five rooms in less than 30 seconds, where internal doors remain open.

With the potential for fire spread to accelerate so quickly, it is essential that we equip our firefighters with a minimum safe amount of water immediately available at the first attack nozzle.

This is where there is some conflict with training in FDS units and fires in the 'real world'. In the confines of an FDS unit, experience has shown us that we can safely suppress burning layers of fire gases and control the fire's development with flow-rates as low as 40 litres/min (demonstrator) and 100 litres/min (attack). Experience has also shown us that where 'real-world' fires are rapidly escalating to involve fire gases building up in adjacent compartments; or where sudden ventilation occurs through windows breaking through heat; or where an exterior wind causes sudden fire development and possibly even 'blow-torch' conditions, the firefighter must have a practical flow-rate immediately available to counter such conditions and support an escape or temporary retreat to a location of greater comfort and tenability.

In France and the USA they have established a minimum 'safe' flow-rate for firefighters to enter fire involved compartments and this is 500 litres/min (France) and 378 litres/min (USA). There are very good reasons for this as they have been scientifically calculated against potential fire loads and heat release. In fact, in the USA it is far more common to see flow-rates of 550 litres/min or more on the first attack nozzle.

In the UK I have campaigned across a ten year period for a similar flow-rate minimum to be legislated (based on extensive empirical research and scientific calculation) and this has been compounded by the latest tragic deaths of eight firefighters in three incidents since 2004, where compartment fires were reportedly under-flowed on the initial attack nozzle.

Whilst it appears that only small amounts of water are needed to effectively cool gas-phase layers in a single compartment where droplet size is adequate and ventilation parameters are strictly controlled, we seem to have forgotten the basic need for higher flows that may be urgently needed as a fire rapidly escalates to involve additional fuels or compartments.

I do not support the use of firefighting nozzles that cannot provide minimum flows of 380 litres/min for interior firefighting. Most importantly, is the point that this minimum flow-rate must be practically achievable at the nozzle and this is dependant on friction losses and supply pressure. In the UK it has been established that 450 litres/min nozzles are being ineffectively flowed to an average 280 litres/min flow-rate due to ineffective hose and pumping arrangements. 

In the past it has been demonstrated that flow-rates as low as 200 litres/min will effectively deal with single room fires that are fully involved, having passed the flashover stage. However, the accumulation of heated fire gases in adjacent hallways and other rooms means that a fire can suddenly erupt into other areas of the building and develop faster than the 200 litres/min flow will be able to deal with. A 3MW fire can become a 15MW fire in less than 30seconds! Therefore, higher flow-rates should be immediately available. 

It is essential that firefighters train with nozzles they will use in the 'real-world', even if these are not ideally suited to the training environment of FDS units. If the nozzle has a flow control that allows small amounts of water droplets to be directed into the upper gas layers near the ceiling but also allows an immediate flow-rate of +380 litres/min where needed, then this should be used for all interior training scenarios and also in the 'real' world.

Paul Grimwood's IFE articles on fire-fighting flow-rate -

1.4MB Changing Tactics 2004

287KB Primary Attack 2005

2MB Go with the Flow 2006

Paul Grimwood -  www.euro-firefighter.com