Performance of Intumescent Fire Protection Coatings in Non-Standard Heating Scenarios

Non-Standard Heating Scenarios: Travelling Fires

Present fire scenarios used in structural fire design assume uniform temperature distribution throughout a compartment over the entire duration of the fire, based on data extrapolated from fire tests that are cubic in nature (Torero, 2010). Research carried out, by the University of Edinburgh, into the World Trade Center fires, revealed a previously unknown fire scenario, ‘Travelling Fire’, where fire spread is non-uniform in large, open compartments. Travelling fires do not burn simultaneously throughout a compartment Torero suggests that a range, or "family", of fires burn within a compartment. Each fire will burnout when their fuel source has depleted and the flame will spread to further fuel sources due to the heat within the overall space. In relation to the individual structural elements, this fire spread within the compartment, produces an overall compartment heat at a rate which increases dramatically when the fuel ignites near the element. The diagram below illustrates the temperature-time curve at a structural element in one area of a compartment during a travelling fire (Torero, 2010) 
Picture
Travel Guide- Temperature-time curve at a structural element in one area of a compartment during a travelling fire
where:
Tnf
   - Near field temperature
Tff
    - Far field temperature
T∞ 
    -Ambient temperature
tpre    -
The time after ignition but before the fire arrives
tb      -
The time the fire burns locally at the element being examined
tpost  -The time after the fire has travelled past the element
The above fire was modelled using a single, averaged fire temperature, where the growth and decay of the fire in the gas phase is ignored, as these as considered to be much faster and thus neglected from the curve (Torero, 2010). The far field temperature is the temperature within the compartment, characterised by the full range of fire sizes, while near field temperature, is the floor area in flames, normally 1200 °C (Torero, 2010). Current research into the performance of intumescent paints, have not been tested for a travelling fire scenario, and as such, it is important to establish whether the intumescent performs in the expected manner.