Understanding Of Fire Protection Design

Fire Protection Design by M&E services are active system which complements the passive system designed by architect and structure engineer. For M&E Engineers, most of us are familar with the active fire protection system. These systems are activated during time of fire such as sprinkler system, foam system, fixed inert gas system, hosereel system, wet riser system etc.

As such the science of fire protection design active system should not be carried out independently from consideration of passive system designed by architect and structure engineer, usage of the building and consideration of fire operation of fire and rescue deparment.

For those who are not familiar yet with fire protection design, the passive system means system that does not need to activate during fire as they offer protection all the time. Examples are fire doors that prevents fire from spreading from one room to another room via the access door for a prescribed fire rating hours. Other examples are the concrete floor slabs designed by structure engineer which offers fire protection by preventing fire spread from one floor to another floor.

The importance of passive system should not be overlooked as most fire spread could be prevented if the passive system is in place during time of fire. For example, if the fire door does not perform by closing automatically or normal door is used at escape route instead of fire rated door, it could allow the spread of fire from one room to another room. The worst that can happen is if the fire spreads into the escape route designed by the architect, thus compromising the time available for escape originally. Another familiar example of failure of design/ construction lies on not using the right type of cladding for the external of high rise building, ie the material installed are not class O and can combust and promote the spread of fire easily (Famous incident is Grenfell fire in London which kills 71 people on 14th June 2017). External fire could also spread easily when the floor slab is not joined properly to the external wall allowing fire to spread from one floor to another. It must be noted that fire spread vertically within a cavity is at four times the rate than fire spread in the centre of a room.

Where passive fire protection design is compromised such as lack of escape staircases, active fire protection design can be implemented sometimes to compensate such as installation of sprinklers for automatic detection and fire fighting at early stage of fire, installation of smoke detector for early warning of fire, installation of smoke extraction or pressurisation system to ensure that smoke does not compromise the escape routes, etc. All these need to be evaluated in performance based design and the science of it is referred to as fire engineering design.

Secondly, the usage of the building and layout of building plays very important role in prescribing the required active fire protection system. Examples would be storage warehouse for paints or other flammable products may dictate a higher level of protection offered by both the passive and active fire protection system as the risk and probability of occurance of fire is very high as compared to storage area for products that do not combust easily. Consideration will also be given to type of occupants. Say if occupants are familiar with building and are capable of evacuating the building without any assistance and are awake during the occupation of the building such as office would require a less demanding fire protection system as the required time for evacuation is less compared to hospital building housing patient beds. An apartment resident would require less time to evacuate from building as compared to hotel guest as the prior is familar with the building. Thus the prescriptive code that requires hotel rooms to have emergency lighting and automatic fire detection as compared to apartment which if high rise in Malaysia only requires automatic fire detection system and no mandatory requirement for installation of emergency lights inside residential area.

The usage of the building can also dictate on the size of fire growth and thus the most important input to active fire protection design such as sprinkler and foam system.

Understanding the fire risk and also fire operation of fire and rescue department is important in order to design a system which can mitigate the fire risk and also enable safe and easy operation of the fire and rescue department during fire. For example for LPG gas storage, it is desirable to install isolation valves which are easily accessible and protected from fire, so that the gas can be shut off during fire. In some cases, we have installed valves which automatically shuts of the gas supply upon detection of gas leakage or fire. Another example is the necessity to install fire man switch to cut off power supply from each floor as the risk of electrocution is high if water is used as means to fight fire. Fireman switch is normally installed close to fireman lift or inside protected staircases as these would be the safe access routes for the fire and rescue team from where they carry out their activities.

There are mainly 2 approaches to fire protection design. The first approach is by adopting the prescriptive code. Examples of prescriptive code are uniform building by law enforced in a country, BS9999 which supersedes BS5588, etc. The prescriptive code prescribes the minimum standards to follow for an identified type of building layout and usage. It is fairly straight forward. However, if there is loop hole in the formulation of prescriptive code that is not patched up, it could spell disaster especially when the engineers and architects do not understand the science behind all the codes and how it relates to fire spread.

Second approach is performance based design which is sometimes referred to as fire engineering approach. Guidelines which can help in design is BS7974 and also some simulation software such as pyrosim (https://www.thunderheadeng.com/pyrosim) for simulation of fire and smoke spread in a building and pathfinder (https://www.thunderheadeng.com/pathfinder/) for simulation of evacuation. In software simulation, careful consideration must be given to the quality of input data by design engineer and the limitation of the software.

Thus a clear understanding in all the above matters would assist in the successful implementation of a design that is fit for purposes. Engineers and architects are thus encouraged to advance their knowledge in fire safety through reading up on fire safety, taking courses or exams such as exam offered by IFE UK which offers level 2, 3 and level 4 certification. Their website could be accessed via this link www.ife.org.uk/.

It is hoped that with this blog, more engineers and architects would venture into the field of fire safety and fire engineering in order to improve their designs in the field of fire protection.

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