Fire - stages of a fire, fire resistance of different building materials, construction to resist fire.
Fire Technology
CONTENTS
INTRODUCTION
Fire Protection
From the fire tetrahedron, we learnt that we could stop fire by obstructing the chain reaction(s), hence, by means of:
- Reduce the fuel
- Reduce the oxygen
- Reduce the heat
Is it possible?
For the sake of fire safety in building, we have implemented measures to overcome this issue, for example:
However, victims of a fire disaster are usually died of smoke inhalation.
Hence, Beside putting out the fire, it is crucial for us to evacuate people out of the premises asap at time of fire and implement some measures to control the spread of smoke, esp. for those premises with high nos of people, e.g. theatre, cinema, shopping arcade, etc.
Compartment Fire Development
Part of the process of reading the fire involves recognizing the stages of fire development and burning regime (e.g., fuel or ventilation controlled). Fire conditions can vary considerably throughout the building with one compartment containing a fully developed fire, an adjacent compartment in the growth stage, and still other compartments yet uninvolved.
Similarly, burning regime may vary from compartment to compartment. Recognizing the stages of fire development and burning regime allows firefighters to predict what is likely to happen next (if action is not taken), potential changes due to unplanned ventilation (such as failure of a window), and the likely effect of tactical action.
Compartment fire development can be described as being comprised of four stages: incipient, growth, fully developed and decay. Flashover is not a stage of development, but simply a rapid transition between the growth and fully developed stages.
Figure: Heat Release Rate (HRR) ...
This is a preview of the whole essay
Similarly, burning regime may vary from compartment to compartment. Recognizing the stages of fire development and burning regime allows firefighters to predict what is likely to happen next (if action is not taken), potential changes due to unplanned ventilation (such as failure of a window), and the likely effect of tactical action.
Compartment fire development can be described as being comprised of four stages: incipient, growth, fully developed and decay. Flashover is not a stage of development, but simply a rapid transition between the growth and fully developed stages.
Figure: Heat Release Rate (HRR) and Fire Development
Compartment fires do not always follow the simple, idealized fire development curve illustrated in the figure. The speed with which the fire develops, peak heat release rate, and duration of burning are dependent on both the characteristics of the fuel involved and ventilation profile (available oxygen).
Going back to the basics of fire behavior, ignition requires heat, fuel, and oxygen. Once combustion begins, development of an incipient fire is largely dependent on the characteristics and configuration of the fuel involved (fuel controlled fire). Air in the compartment provides adequate oxygen to continue fire development. During this initial phase of fire development, radiant heat warms adjacent fuel and continues the process of pyrolysis. A plume of hot gases and flame rises from the fire and mixes with the cooler air within the room. This transfer of energy begins to increase the overall temperature in the room. As this plume reaches the ceiling, hot gases begin to spread horizontally across the ceiling. Transition beyond the incipient stage is difficult to define in precise terms. However, as flames near the ceiling, the layer of hot gases becomes more clearly defined and increase in volume, the fire has moved beyond its incipient phase and (given adequate oxygen) will continue to grow more quickly.
Depending on the size of the compartment and ventilation profile, there may only be a limited indication (or no indication at all) from the exterior of the building that an incipient stage fire is burning within.
Hazard of Ventilation Controlled Fires
Many if not most fires that have progressed beyond the incipient stage when the fire department arrives are ventilation controlled. This means that the heat release rate (the fire’s power) is limited by the ventilation profile, in particular, the existing openings.
If ventilation is increased, either through tactical action or unplanned ventilation resulting from effects of the fire (e.g., failure of a window) or human action (e.g., exiting civilians leaving a door open), heat release rate will increase, potentially resulting in a ventilation induced flashover as illustrated in the following figure.
Figure: Ventilation Induced Flashover
Stages of Fire & Corresponding BS 476 Standards
NFPA Standard 550 - NFPA Fire Safety Concept Tree
This concept tree can be used as tools for effective communication amongst different parties.
FIRE TERMINOLOGY
Fire resistance
During a fire test of a product’s or a construction’s fire resistance the properties are determined when exposed to a certain heat exposure, normally an equivalent room fire. The fire resistance is one or several properties of the assembled construction/product and consequently not a sole property of the incorporated materials. The construction can then be classified in different .
Compartmentation
A compartment in premises is formed by the structural enclosures, e.g. reinforced wall, FRP door, fire dampers, etc. Compartmentalization in structures, such as land-based , traffic , , , or , is the fundamental basis and aim of . The idea is to subdivide a structure into "fire compartments", which may contain single or multiple rooms for the purpose of limiting the spread of fire, smoke and flue gases, in order to enable the three goals of :
- life safety
- property protection
- continuity of operations.
Fire precautions
Fire safety refers to precautions that are taken to prevent or reduce the likelihood of a that may result in death, injury, or property damage, alert those in a structure to the presence of a fire in the event one occurs, better enable those threatened by a fire to survive, or to reduce the damage caused by a fire. Fire safety measures include those that are planned during the construction of a building or implemented in structures that are already standing, and those that are taught to occupants of the building.
Fire prevention
The goal of fire prevention is to educate the public to take precautions to prevent , and be educated about surviving them. It is a proactive method of reducing and the caused by them.
Fire protection
Fire protection is the study and practice of mitigating the unwanted effects of . It involves the study of the behaviour, , suppression and investigation of and its related emergencies, as well as the research and development, production, testing and application of mitigating .
F.R.P. (Fire Resistance Period)
FRP means the period for which the element of construction is capable of resisting the action of fire. E.g., a fire resisting door is a door which, together with its frame can stand for certain hours of fire.
Fire Load
The total fuel contributed to a fire by a building’s contents, combustible materials used in its construction, and/or its finishes.
THE EFFECTS OF FIRE ON MATERIALS AND STRUCTURE
Materials are classified as combustible or non-combustible by identifying those which made little or no thermal contribution to the heat of the furnace and do not produce a flame, and by calling the remainder 'combustible'.
Combustibility and non-combustibility
BSI BS 476-4: 1970, Fire tests on building materials and structures — Part 4: Non-combustibility test for materials, this document includes definition of non-combustibility. Determines whether materials; with or without coatings; used in construction or finishing of buildings meet the definition.
Non-combustible materials
The non-combustible materials have the following characteristics:
- do not contribute to the growth of fire
- most of the structural members are of this type
- can be danger if the critical temperatures for the materials is reached; the following may happen:
- decomposition
- fusion
- deflection
- loss of strength
For example:
- steel - loss of strength, expand, bend, buckle.
- Concrete -spalling, loss of cover
THE EFFECTS OF FIRE ON MATERIALS AND STRUCTURE
Combustible materials
- contribute to growth of fire as fuel
- spread of flume
- for example : wood, paints, wall paper, petroleum, plastic etc.
GENERAL BEHAVIOUR OF MATERIALS IN FIRE
Timber
- 220 to 300 ℃
- Charring – insulation
- No significant loss in strength
Timber Product
- Ease of ignition
- Rapid spread
Concrete
- Disintegrates at 400-500 ℃
- Cover to project steel bars
- Loss of strength above 600℃
Stone
- Loss in strength at 575 ℃
Plastic
- Combustible
- Toxic smoke
- Charring at 400 ℃ and burn at 700-900 ℃
Clay Products
- Fusion above 1000 ℃
- Can resist building fire
Brick – good resistance to fire
Steel
- increase in strength up to 250 ℃,
- return to normal strength at 400 ℃ followed
- rapid loss of strength at the critical temperature 550 ℃
- High strength steels behave similar to mild steel
- for pre-stressed concrete tendons the critical temperature is 400 ℃
- high thermal expansion can be a problem eg. 10m @ 550℃ be expanded by app. 60 mm
- spread the fire on the reverse side
- unprotected solid steel - 1/2 FRP
- unprotected structural steels in an open space
Aluminium
- loss strength rapidly, critical temperature is about half of steel, melting point is about 650 ℃
- thermal expansion is about twice of steel
- a higher standard is required if aluminium is used
- aluminium cladding, common application of aluminium, does not survive for long in fires
FIRE PROTECTION OF STRUCTURE AND CONSTRUCTION
Active fire protection
the installation of fire fighting services starting, eg:
- a warning system
- fire extinguishing system such as sprinklers, high expansion foam etc.
Passive fire protection
- Fire resisting construction
- Means of escape in case of fire
- Means of access for fire fighting and rescue
FIRE RESISTING CONSTRUCTION – COMPARTMENTATION
Compartmentation
- To prevent the spread of fire within a building. It must be divided into compartments of restricted cubic capacity
- Table 3 Maximum Compartment Volume
FIRE SAFETY REQUIREMENTS OF A CONTRACTOR’S SHED
From PNRC 54 - Criteria for Contractor’s Sheds that could be certified by RGBC/RSC
- The contractor’s shed is of single storey with storey height less than 3m and with floor area less than 230 m2;
- The base of the contractor’s shed from the ground level, if stilted above ground, does not exceed 1.5m;
- The proposed shed does not pose any geotechnical concern in that
(i) The maximum gradient across the site for erection of shed is not more than 15º.
(ii) The overall gradient of an area bounded by lines 10m outside the footprint of the shed in any direction is less than 15º.
(iii) There is no slope within the area 10m outside the footprint of the shed steeper than 30º or higher than 1.5m.
(iv) There is no retaining wall or terrace wall higher than 1.5 m either within the site for erection of shed or within the area 10m outside the footprint of the shed.
- The contractor’s shed is not sited
(i) on a cantilevered structure; or
(ii) above a hoarding or covered walkway; and
- The contractor’s shed is located within the boundaries of the building site and is not readily accessible to the general public.
Fire Safety Requirements for Contractor’s Sheds
Note :
Travel distance within the shed should comply with the Code of Practice for the Provision of Means of Escape in Case of Fire 1996.
Class Work
For a contractor’s shed with the following items, please state the fire protection requirements:
- The site office is to be enclosed with corrugated GI sheets
- Openings at end & middle of the office
/
