Simulation & training

- how computers & firefighers interact

Published:  01 October, 2005

It’s fascinating to talk about computers and fire safety engineering - but how do they actually interact? Fire origin, fire development, fire spread and fire decay in enclosed fires depend on several factors such as the room geometry, type and quantity of materials, number and size of openings, type of firefighting operations etc.

Fire size is always a reflection of all these factors.
While the influence of a single factor can be approximately measured, understanding the interaction between all factors is usually a very ‘tough nut’.
Experimental data from large scale fire testing facilities can help us with realistic fire development parameters and creates an environment for computer codes validation and upgraded reliability. Besides large fire tests there are some devastating and well-documented fires like the World Trade Center fire in 2001 which improved these codes as well.
Looking at models
Let me introduce the background of computer codes or models used in fire safety engineering. In general, there are two ways how computers can identify the spread of a fire using zone models and field models.
Zone models are simple computer codes dividing the volume to be simulated into uniform hot upper, and cold lower layers, solving the conservation equations of mass, energy and species for each zone. They use empirical correlations to describe characteristics such as air flow into the fire plume.
The main advantages of zone models are: they are easy to run, require little computational time, and are relatively inexpensive. The main disadvantage associated with zone models are limited scenarios where the empirical correlations are breached, such as irregular geometries, or fires, which have restricted entrainment areas; results of zone models are then likely to be imprecise.
Field models are more sophisticated. A three- dimensional grid of tiny cells is used it calculates asked parameters for every cube. The basics of every field model consist of a set of three-dimensional, time dependant, non-linear partial differential equations called the Navier-Stokes equations.
These equations express conservation of mass, momentum, and energy. The advantages of field models are that they rely minimally on empirical correlations; hence they are capable of simulating scenarios without the limitations associated with empirical correlations. Besides that, the disadvantages are that they are difficult to use, relatively expensive and depending on the characteristics of computer very slow.
Both zone and field models are in a continuous process of development and improvement. When improving computer codes scientists are trying to follow two main goals: prepare the codes in such way that they will be realistic and make them as user friendly as possible. From the standpoint of the firefighter both goals are appreciated and expected. But let us ask ourselves how can computer codes help us?
Besides doing calculations, many computer codes include so-called visualisation tools where results become visible and are presented in a very dynamic way through animations. Speaking with simple words users can transfer plain calculated numbers into animation. In knowing this we are getting closer to importance of computer codes for firefighters.
Using computer codes
Let’s try to imagine a multi-dwelling house fire scenario with very conservative assumptions. The fire origin is in a TV set, the apartment furnishings are typical and contain wood, carpets and a lot of plastic. Yes - it’s like 70% of all fires.
Can computer codes help us here? The answer is yes. Even a very small fire can lead into a flashover or backdraft, two of the most detrimental scenarios. Wouldn’t it be useful if we could predict when and where this could occur?
Recent editions of field models can be used as a good prognostic tool. Codes will help us to understand various flows into and out of compartment, hot layer height and time dependence of temperature but it can last hours or even days to get the results.
This means that sophisticated computer codes can still not be used on a fire scene though they are realistic and reliable. Can they be used at all? Hopefully, we are all aware of needs for education and training of new and experienced firefighters
Let’s now try to imagine another fire scenario where new firefighter candidates are preparing themselves for their first whiff of smoke diving into a flashover container.
On their career path to become a firefighter they have passed several courses including fire dynamics. In their heads they are now trying to use what they know about cold and hot layers, temperatures at the ceiling and all kind of spray patterns to suppress the fire. Furthermore, they are trying to imagine how a new opening in a room will effect the fire’s development - or perhaps how the sprinkler operation will change flows in a compartment?
All these parameters can nowadays be simulated very effectively with computer codes. Predefined fire scenarios can be very easily demonstrated and used during the firefighter education process. 
Amongst the greatest benefits of computer codes use is their relative flexibility and good visualisation. Since all results are in a realistic time frame it is great opportunity to train on tactics and preplan operations or standard operation procedures as we are fighting the real fires. At some stage computer models can be used to assess almost all firefighting operations at the fire scene. It means that it is possible to predict how open doors or broken window will change flows in a compartment.   y

  • Operation Florian

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