Fire safety has been a major concern in the structural design of buildings for a very long time, and today it has become an indispensable part of all types of construction works.
Fire breakouts can be sudden and damage not only the building and valuable property, but also endanger the lives of the occupants. But with the growing awareness around fire safety, engineers and architects have managed to devise methods and designs to guarantee maximum possible safety in case of fire accidents.
In this article, we discuss some important design considerations to ensure fire safety in construction.
General approach to Fire Safety
Naturally, the very first step in fire-resistant construction is to maximize the use of non-combustible materials. Several Indian Standard (IS) codes provide the guidelines for safety protocols and the use of fire-resistant materials at construction sites. A few codes which can be referred to are: IS codes 1644:1988, 1646:1982, and 3809:1979.
A building is a combination of various integral components. To make a building fireproof or fire-resistant, it is vital to ensure that these elements stay unaffected by the impact of fire.
1. Load-bearing walls
Load-bearing walls are an integral part of any building, along with the foundation. These walls are responsible for transferring vertical loads from slabs and beams to other appropriate structural members and ultimately to the foundation. Therefore, these walls should have a specific thickness to withstand the effects of fire. They should be thicker in section to act as fire barriers for a considerable time. The exact section thickness can be obtained from IS code- 1642 (1989).
The flooring materials are often made from bricks, concrete, stones, tiles, etc. as they are considered a part of fire-resilient construction. However, if the use of such materials is not feasible, wooden flooring or other floorings that are more susceptible to fire need to be used.
For wooden floors, thicker joists should be used in the construction. Also, these joists should be placed at a greater distance apart. Alternatively, protective coverings of insulators can also be provided on the flooring. These can include materials like bricks and ceramic tiles.
3. Framed Structures
There can be two types of framed structures, reinforced concrete and steel structures. Steel structures generally tend to twist and distort under heavy fire. Therefore, they are given a protective coating of metal lath or plaster. Bricks, concrete, or tiles may also be used, and their minimum thickness should be 10 cm.
In case of reinforced concrete, frame members (beams and columns) should have a sufficient concrete cover to ensure their maximum performance under fire. This cover should be at least 5 cm thick.
4. Partition walls
Usually, Reinforced Cement Concrete (R.C.C), Reinforced Brick Concrete (R.B.C), asbestos cement board, hollow concrete, etc. are used for building fire-resistant partition walls. However, when wooden partition walls are built, they are covered with metal lath and plaster.
Asbestos cement board, metal lath, and plaster are often used in the ceiling framework to strengthen its fire-resistance. Also, the ceiling and the floor joists must be directly attached for greater stability and strength.
The doors and windows act as the escape points in case of a fire emergency, and therefore, ensuring their integrity during construction is very crucial. They must be glazed and fitted with reinforced glass panels, as they have a higher thermal resistance than normal glass panels. Using metal frames for doors is also one step towards providing fire safety.
For one-storey or two-storey buildings, windows and doors provide adequate escape routes in the event of a fire. But, in case of multistorey buildings, the location of the staircase is essential. It should be equally accessible from different points of the building. As far as the material is concerned, it is advisable to use R.C.C. for building stairs. Also, enclosure walls made up of fire-resistant materials should be built around the staircase hall for further safety.
A flat roof is always better from the fire safety point of view. This is due to the fact that fire spreads more rapidly on a sloped surface in case of unfavorable wind conditions. However, if constructing a sloped roof is required, then the ceilings should be built or coated with fire-resistant materials.
A metal lath is a meshed sheet of galvanized steel. Metal laths come in all shapes and types. Plastering is often done on the required surface after placing these lath sheets on them. This is done to provide extra strength and durability. One of the advantages of using metal laths is that they offer ductility and can turn and twist over a surface according to the requirement. Metal laths general types include: ribbed laths, wired laths, self furring laths, strip laths, etc.
Metal Lath mesh
Fire-resistant mortar is used in plastering all types of walls, such as bearing, non-bearing, and partition walls. Doing so increases the fire resistivity of any structure up to a certain degree. The main constituent imparting its property to fire-resistant mortar is calcium alumina cement. This cement is then mixed with sand, fire clay, and water in the required ratio, and hence, fire-resistant mortar is formed. Fire clay is a type of ceramic clay having resistivity to extremely high temperatures. For this reason, they are used in fire-resistant linings and mortar in buildings, furnaces, and professional kitchens.
Asbestos cement board is also known as asbestos insulating board. Asbestos occurs naturally and readily mixes with cement. Adding asbestos to cement makes it more durable and heat resistant, and this makes the asbestos cement board fireproof. Hence, it is obvious that asbestos cement boards offer a huge advantage in developing fire safety in any construction. But at the same time, it is also well known that adding asbestos to cement can be toxic and often avoided in construction.