But “why protect steel from fire as it doesn’t burn?” is an often asked question. However structural steel does lose some of its strength and stiffness as it heats up. As temperatures in a fire can easily exceed 1000ºC, unprotected steel under load will start to lose its strength and stiffness, potentially leading to premature collapse within minutes.
In order to delay this loss, steel members need to be protected with products that will slow down and limit their temperature rise. In most cases steel will only be exposed to a cellulosic fire such as might occur in a normal commercial building. However steel used in certain industrial applications, such as Oil and Gas Facilities, the fire is likely to be far more intense. This type of fire is known as a hydrocarbon fire which presents a more onerous fire case.
National building regulations require certain elements of structure to have fire resistance. Whether or not an element requires fire resistance depends upon such things as size, height, use and occupancy of the building and the function of the element. Where structural steel members are required to have enhanced fire resistance, they can be protected by applying insulating materials. A wide range of materials is available to enhance the fire resistance of structural steel members. They can be applied in a variety of ways to meet specific site requirements.
The quantity of fire protection required by a steel member is a function of a number of different parameters including Fire resistance period required, steel dimension, section type and orientation and the utilisation of a steel members load bearing capacity.
The load bearing capacity of a steel member is often used to calculate its critical failure temperature, which is normally quoted for ease of understanding. Steel dimension is used to calculate the Section Factor (U/A or reciprocal mass factor) of a steel member. With a critical failure temperature, required fire resistance period and a section factor, the required protection thickness can be determined from a Products Certificated information.
In considering any fire protection system it is also important to distinguish between profile, box and solid methods of application. Sprayed materials would normally be applied to follow the profile of the section. Board materials would normally be used to form a box around the section and special insulating concretes can be used to form solid protection.
European fire testing standards have been published to replace the former national standards and to remove technical barriers to trade within Europe. In assessing the performance of fire protection materials for structural steel, the relevant test methods are the EN13381 series of test methods, which are then used to obtain a classification according to EN13501-2.