For compartment fires, the transition period between a fuel and ventilation controlled fire is usually defined as ‘flashover’. An under-ventilated fire may be defined as one where fire development has been curtailed by a lack of air supply and an accumulation of highly flammable gases have formed within an enclosed fire compartment. The hazards associated with under-ventilated building fires are increasing, as fire loads incorporating an increased hydrocarbon (plastic) content, combine with modern energy efficient construction to create exceptionally dangerous working environments for firefighters. It is a fact that firefighter life losses in the UK have near doubled since 2005 as a ratio of the number of building fires and the relationship between under-ventilated fires and tactical ventilation by firefighter’s demands far greater attention, if such life losses are to be curtailed.
At every fire the default position should be to begin by immediately controlling the air flow-paths, where practical. This means that any open access doors might need to be partially closed to prevent air flowing in to feed the fire, whilst we prepare our deployment with charged hose-lines. In 1987 Paul Grimwood's Tactical Ventilation strategy was proposed as a compromise between US and UK ventilation approaches and was defined as follows:
‘Tactical ventilation is the containment or venting actions by firefighters, used to take control from the outset of a fire’s burning regime, in an effort to gain tactical advantage during interior structural firefighting operations’.
Such an approach recognised that there were clear benefits in some cases of tactically creating openings in the fire building but in many more situations there was a danger that creating such openings without an objective, without precision and timing, that the situation for building occupants may become worse. This was particularly evident where firefighters were occupying the building.
To be able to understand when, where, why and how to ventilate fire buildings demands awareness and knowledge of practical fire dynamics. It also requires on-scene intelligence of where the fire is located and where occupants/firefighters may be sited. It needs an understanding of flow-paths (previously termed 'air-tracks' in the UK).
In EuroFirefighter-1 (2008) on p78 I repeated a critical piece of guidance that has preceded flow-path research by some decades. It is a basic fire-ground rule that many seem to forget - 'Don't vent in situations that place interior crews between the fire and vent opening you are creating'. For example, if crews are fighting a basement fire, any openings you might make behind and above them to relieve smoke can literally cause the newly created flow-path to 'pull' intense flaming or hot smoke directly towards them.
A review of firefighter fatality reports in the UK and USA over the past 15 years demonstrates several incidents where firefighters lost their lives, as a result of being located between the fire and the outlet vent that was created, or on occasions - where the outlet created was at a higher point than the firefighters location (drawing the fire to them). On occasions there may have been flow-path reversals as interior pressure differentials balanced each other where outlet vents were under-sized. In other situations, the venting of fire buildings by fire commanders caused the fire to intensify to a point where conditions became untenable for firefighters, leading to heat effects on the body causing firefighters to make bad decisions when trying to exit the building, becoming lost and entrapped in the process.
In the UK there were three fatal fires where tactical venting actions occurred, placing firefighters between the fire and the outlet vent. There were other fatal incidents where tactical venting actions caused fire intensification to a point where firefighters became disoriented and entrapped.
In the USA there have been several incidents where firefighters deployed from the leeward side of the fire building, resulting in a wind driven fire trapping and killing them as windows on the other side of the building failed through heat. In other situations firefighters deployed from the front into the upper level of a split level building, causing unfavourable flow-paths to lead the fire right at their location.
In each of these cases, firefighters were caught by flow-path reversals, causing fire to head back towards their entry point and causing untenable levels through the venting actions.
In some well equipped big city fire departments, with adequate or high staffing levels, a pre-planned procedure for vertical venting of fire buildings under strict protocols may be beneficial in certain types of buildings. Roof venting of scuttles, hatches or doors may be very useful after the fire has been controlled. The strategy of making roof cuts with power saws is a high-risk operation that may increase firefighter life loss rather than prevent it and demands highly experienced firefighters and a sound knowledge of roof construction. The likelihood that older roofs have been reconfigured and redeveloped over decades means that roof operations become even more dangerous.
Horizontal ventilation is a strategy well within the reach of even the most limited of staffed fire crews but again, an awareness of practical fire dynamics and street-wise fire commanders/firefighters are essential. Before creating horizontal openings, the following considerations should be foremost in the commanders/firefighters mind:
Through a series of articles in the late 1980s Paul Grimwood presented a case for a review of ventilation tactics in the UK and this resulted in a government sponsored report by Adrian Hay (1994) looking at ventilation by firefighters. In this report the author introduced Grimwood's term 'Tactical Ventilation' but failed to define the term correctly and omitted to talk of fire isolation tactics and controlling air-flow feeding into the fire (Grimwood 1987). He then concluded that a US approach to venting fire buildings by UK firefighters may well be beneficial but this would be subject to further research. Paul Grimwood did urge caution in Adrian Hay's 1994 interview with him and this was reported in the document as follows:
Adrian Hay 1994
One life safety strategy, termed VEIS, is something that may be adapted to suit both well-staffed or limited-staffed fire departments. In situations of known, likely or confirmed occupant entrapment in a room easily reached from the exterior, a VEIS operation should encompass the following actions, even in situations prior to fire attack taking place:
If VEIS is deployed effectively, this strategy has a medium risk/high return benefit - consider fires you have attended where this strategy may have provided a better outcome for occupants.
The application of VEIS demands great care and is often seen as a 'last resort' strategy. In effect, the entry firefighter may be placing themself directly into the exit point of a dangerous flow-path. Consider all other options first.
It may be safer and more effective to deploy one of the following approaches before resorting to VEIS:
1. Attack the fire first - this may save more lives, even if working from the exterior or using water (or CAFS) off the tank supply
2. Isolate the fire on entry to the ground floor level by closing doors, or by siting a support hose-line to protect egress (at the stair) before searching beyond or above the fire compartment.
3. Coordinate search and suppression together in unison, if staffing is adequate.
Paul Grimwood 2017