When you think of a building structure and it being alight, what do you think of? A tall commercial building with flames leaping out the windows? A smaller house fire? Or maybe a residential apartment building? If you did you are not alone. However, how many of you thought about industrial complexes – Factories, oil pipelines and petrochemical plants? The human mind works such that we think about things we see ourselves or on TV and the truth is we see more of the former types of fire than the latter.
However, from a technical perspective, the difference in the two types of fire couldn’t be more pronounced, and how they are treated (both in terms of preventative measures and to extinguish the flames) is as a result, very different.
Classes of Fire
- Cellulosic Fire (CF) – This kind of fire occurs when the fuel source is comprised primarily of cellulose material such as timber or paper. A fire of this nature has a slow flame and spreads – by comparison – gradually.
This type of fire is most common in residential and commercial buildings. When the combustible material burns, it gets hot with temperatures reaching up to 500°C in as little as 5 minutes and can escalate to up to 1100°C. Its radiation value has been measured at 50 kW/m2 (Kilowatt/square meter).
- Hydrocarbon Fire (HF) – Hydrocarbon fires are caused by combustible liquid such as oil and gas. Carbon and hydrogen make up hydrocarbons and they do not have affinity for H2O (water). Some examples are petrol, diesel, benzene and kerosene. Within 5 minutes, a hydrocarbon fire can heat up to 1000°C and peaks to 1100 °C in a short time. By comparison to a cellulosic fire, the radiation value is 160 kW/m2.
- Others – Other fires are also hydrocarbon fires that have extremely high burning rate caused by the mixture of turbulent air or fuel such as jet fires.
How Classes of Fire Differ
The difference between Cellulosic fires and Hydrocarbon fires extends beyond the temperature and the fuel sources. Each of these fires has a unique behaviour which can be noted in duration, growth rate and peak combustion. For bench-marking, the fire protective products industry adopted standard fire curves for each type of fire. Fire protective products are then classified into two categories based on these fire curves:
A, B, and F – for products that offer protection against cellulosic fire
H or J – for products that produce hydrocarbon fire; where J represents specialised hydrocarbon fires resulting from combustion from high class fuels.
If we are to boil it down, whilst all fires can be catastrophic, fires caused by hydrocarbons are more violent than those caused by cellulosic materials.
Fire Protection Systems
Fire protection systems can be classified into two broad categories – active and passive fire rating. Active fire protectors are set in place as responses in the case of fire. Where fire or smoke is detected (and by the way, there are new technologies to detect these elements too. Check out our blog on Advances in Building technology), these systems act to supress the spread of smoke and flame and thus include smoke alarms, fire doors and fire sprinklers. Conversely, a passive fire protection system protects a structure from fire through insulation applied to structural steel (and increasingly wood) elements which delays combustion and prolongs structural adequacy. These systems are designed to allow for fire-fighters to safely enter a building and for occupants to exit the vicinity.
Both systems have a vital role in the preservation of human life and should be employed correctly. In the case of passive fire rating, understanding your requirements (in other words knowing how to interpret the NCC) and determining what to fire rate and with what products can be daunting. That is why we are here – to make it easier for you. If you need some assistance in understanding what you can and should be doing, contact one of the Permax team today.
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