5.b) Explain the stages of fire development and factors affecting fire severity.
Answer:
The protection of life is of primary importance in fire situation & therefore aware of the hazards & its development, fire developed over time & the environment detritions as smoke & heat build up to endanger life.
Initially, when fuel, Oxygen and heat combine there is little or no hazard when ignition occur, fires develops slowly & the rate of hazard increases as the fire develops.
The figure shows the general effect of fire development on hazards to life safety; from the figure we can say that there is a time interval between the first detection & the critical level of fire development which represents hazards to life cycle. All actions to preserve life safety must be undertaken in this interval to time.
Stages of fire development:
Ignition: The ignition source along with the fuel first ignited will determine the initial fire development, the ignition source dependent on the fuel & presence of flammable vapors in the right mixtures.
Flames spread: Flame spreads along the surface of the original fuel which was ignited depends on the properties of the fuel & the supply of Oxygen. The moving flame heats adjacent un-burnt fuel, adding more flammable vapors & increasing the flame sites. In general flame spreads faster upwards than reduce little horizontally or downward due to heating by the combustion products flowing upwards & outwards from the fire.
Decay:
- Description: The final stage where the fire’s intensity diminishes, and it eventually burns out or is controlled. This stage can involve smoldering and the presence of residual hot spots.
- Key Factors: Reduced fuel availability, changes in weather conditions, and fire suppression efforts contribute to this stage.
Factors Affecting Fire Severity
- Fuel:
- Description: The type, amount, and arrangement of combustible materials (e.g., trees, shrubs, grass) that the fire consumes.
- Influence: High fuel loads and continuous fuels (like dense forests) can increase fire severity. Fuel moisture content also affects how easily materials ignite and burn.
- Weather:
- Temperature: Higher temperatures can increase the flammability of fuels.
- Humidity: Low humidity levels can dry out fuels, making them more susceptible to ignition and increasing fire intensity.
- Wind: Wind can spread flames and embers rapidly, increasing the fire’s spread and intensity. It can also change the direction of the fire.
- Topography:
- Slope: Fires burn faster uphill because the flames can reach more unburned fuel above them. Steeper slopes can lead to more intense fires.
- Aspect: The direction a slope faces can affect fuel dryness (south-facing slopes in the Northern Hemisphere typically receive more sunlight and are drier).
- Human Activity:
- Description: Activities such as land management practices, building construction, and recreational activities can influence fire behavior.
- Influence: Poor land management, accumulation of flammable materials, or human-caused ignitions can increase the likelihood and severity of fires.
- Natural Factors:
- Lightning: A common natural ignition source, particularly in dry conditions.
- Volcanic Eruptions: Can cause fires through lava flows or pyroclastic flows.
Understanding these stages and factors helps in both predicting and managing wildfires, aiming to reduce their severity and impact on communities and the environment.