Any material that resists fire and does not melt for a while, that is to say, it can withstand heat; so that the residents of the structure can safely leave the premises is called Fire Resistant Building Materials. It is crucial to pay attention to fire safety especially in the construction industry.
Fire retardant materials are different than fire-resistant materials. Fire retardant materials are materials that burn slowly.
Fire Resistance Rating is the duration for which the material will withstand the standard fire exposure, which is determined by the fire tests done following the standard methods of fire test as per the National Building Code (Section IV: Fire Safety).
Why Fire Safety is Important?
Architects, designers, and engineers nowadays are paying great attention to fire safety in the building. Owing to a large number of accidents, fire safety in construction started becoming more and more important.
To employ greater fire-resistant materials to a structure, attention began to be paid to the properties of the materials used. The materials started to be evaluated for their resistance to a standard fire and some standard tests were developed.
Based on the duration for which the material did not show any major damage was evaluated and the materials were classified. This classification can be accessed from NBC.
General Requirements of Fire Resistant Construction Materials
- It should be able to resist fire for such duration that occupants can safely vacant the building
- It should not lose its strength considerably
- It should have a low coefficient of thermal expansion, i.e. it should not expand when subjected to heat, preventing the generation of additional stresses in the building
- Its thermal conductivity should also be less
- It is preferable if it has self-insulation properties.
Fire Resistant Construction Materials
Following are fire resistant building materials used in construction,
- Reinforcement steel
- Cast iron
- Asbestos cement
Read More: 17+ Uses Of Concrete In Construction
Concrete is the most widely used building material in the construction industry for a long. Its worldwide usage is double that of steel, wood, plastic, aluminum took altogether.
Such a popular material worldwide, surely its fire resistance is also quite excellent. Concrete is an insulator in terms of transmission of heat, and as such offers greater fire resistance to buildings as compared to steel.
Its thermal conductivity is also poor, i.e. the structural, load-bearing ability is sustained for a longer period. Meanwhile, it also diminishes the spread of fire further.
The melting point of concrete is not defined. But, its strength decreases considerably at high temperatures. However, strength is not much affected up to 250 °C. Normally, reinforced concrete structures can resist fire for about 1 hour at 1000 °C.
Concrete also has low heat absorption power. Even if the outer temperature of concrete reaches 500, the internal temperature of inner concrete remains relatively low. Hence, the weakening of concrete structures occurs only when intense fire for long-duration takes place.
There is no fixed thermal resistance of concrete since it is made up of different materials mixed. Concrete comprises cement, aggregates, water, steel, and admixtures. Hence, the fire-resisting capacity of concrete is dependent on the properties of these materials used, their proportions, and position of steel, and so on.
When the fire takes place, concrete is dehydrated. And heat causes aggregates to expand and cement to shrink. These opposite changes cause debonding amongst the constituents of concrete. This not only causes strength to reduce but also shrinkage cracks are induced. Concrete is one of the best fire resistant materials used in building construction.
Why concrete is being preferred extensively?
- Concrete, in addition to the reduction in fire load, does not drip molten particles, as in case of steel structures.
- It has a higher resistance to fire, ceasing the fire spread.
- Not only that, but it is also easy to repair after the fire. Thus, it eases out financial concerns too.
- It does not liberate any smoke or toxic gases, thus reducing risk to the occupants of the building
- Its heat absorption process is quite slow.
2. Reinforcement Steel
Steel, in general, is a non-combustible fire resistant materials. In building structures, steel is used in beam, lintel, purlin, walls. It is also used in fixtures and fittings such as rails, stairs, etc.
Even though steel is non-combustible, it has low fire resistance value. This happens because steel softens as the temperature rises, resulting in a decreased capacity to resist tension and compression.
At 600 ° C, its yield strength is reduced to 1/3. And it starts melting at 1400 ° C
If fire extinguisher utilizing water is used, then steel tends to contract. And as the strength is already reduced due to melting, twisting and distortion also begin. Consequently, the stability of the structure is also affected.
Bricks are one of the oldest used materials since ancient civilizations. It is commonly used for the construction of walls and pavement.
In terms of fire resistant materials, bricks do not show serious damage until a very high temperature of about 1200-1300 degrees C as it is a poor conductor of heat.
Bricks can show good fire resistance if the following things are considered:
- Mortar type
- Quality workmanship
- Clay type
- Method of masonry construction
Timber has been used in construction even before history was recorded. Since ancient civilization, it has remained a major construction material.
Timber shows considerable resistance to fire owing to its self-insulating property.
When timber catches fire, it is first charred up to a certain depth. Then the outer charred layer acts as a barrier and subdues fire. This property to put out the fire on its own is characterized as the self-insulating property of concrete.
Treatment to Timber:
It is impregnated with fire-retarding chemicals viz.
- Ammonium phosphate
- Ammonium sulphate
- Borax & Boric acid
- Zinc chloride, etc.
For Moderate protection, 32-48 kg of chemical is required while High protection requires as much as 80-96 kg of the chemical.
Recently, fire resistant paint are used,
- Iron oxides
How the chemicals provide aid in fire control?
- They control the temperature rise during a fire
- Decrease rate of flame spread
It is the most unsuitable material from a fire safety point of view. Different types of stones are listed out below with their behaviour during fire:
Polished granite is used for tabletops, cladding for walls and columns, etc. Limestone and sandstone are used for wall construction.
Glass can and has proved to be good at resisting fire owing to:
- Bad conductivity of heat
- Low coefficient of thermal expansion
But, cracks are developed under high temperatures. To resolve this issue, reinforced glass panes have been developed now, which are used in glazed windows. The reinforcement in these glass panes holds the cracked pieces of glass together if the glass cracks. It is important to fire resistant materials used in building construction.
These reinforced glass panes are used in the following structural components:
- Lanterns, etc.
6. Cast Iron
It is rarely used in today’s construction industry for it flies into pieces when heated and cooled down suddenly.
If used, it is covered by 1 brick thick brick masonry or other fire resisting material like concrete.
It is employed in:
- Window frames
- Cast door handles
- Catches for windows & staircases
7. Asbestos Cement
The constituents of asbestos cement produce great fire resistance value.
Along with its non-combustible nature, it is a poor conductor of heat as well. Hence, the structural members blended with AC offer better resistance to cracking, swelling, and disintegration when exposed to fire.
It is broadly used fire resistant materials used in construction as,
- Fire resistance partitions
- Roofs, etc.
Gypsum is known as ‘wonder mineral’ as the water returns to its original form. It is mostly used for interior design.
Gypsum sheeting is put together with the structural materials to prevent fire hazards.
The most commonly used gypsum derivative in the construction stream is Gypsum Board or commonly called Dry Wall. It comprises a gypsum sheet inserted between paper sheets. Out of that, ‘Type X’ drywall is the most popular one. It is also one of the important fire-resistant materials.
Dry wall (Gypsum boards):
The dry wall has a paper layer, which burns slowly not contributing to the fire spread.
The incombustible core consists of chemically combined water with Ca2SO4 (calcium sulphate).
When a fire takes place, this water comes out in the beginning in the form of steam and hinders the heat transfer through the gypsum board. When this steam flow halts, the gypsum board continues to resist fire.
To obtain increased fire resistance, multiple layers of gypsum boards are used.
Above are all fire resistant building materials used in construction. This are also most used building construction materials around the world.
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