Fire Protection in Steel

Designers must follow Approved Document B advise to comply with building regulation. BS 9999, Code of practice for fire safety in the design, management and use of buildings which is known to provide safer solutions for fire than the approved document B due to extensive research.

Fire resistance requirement is stated in terms of minutes. It is not how long the structure will withstand the fire, but a standard measure for comparing the performance of different designs in a consistent manner. The requirement of different floors depended on the existence of sprinklers, building occupation, height and floor location.

All structural hot rolled steel elements have inherent fire resistance. This is a function of the size of the section, the degree of exposure to the fire and the load that the section carries. Unprotected steelwork deemed to have 15mins fire resistance. Fire protection is usually required. This is known as passive fire protection, which splits into:

  • reactive: thin-film intumescent coatings (most common). Can be applied on-site or off-site. Typically used for buildings with fire resistance requirements of 30, 60 and 90 minutes. Some products can provide 120mins. They come in water or solvent-based depends on the intended use of the structure. It can cover complex shapes and post protection service installation is relatively simple.
  • Non-reactive: boards and sprays
    • Boards are widely used for structural fire protection in the UK. There are lightweight 150-250kg/m3 which is generally cheaper and used where aesthetics are not important. Heavyweight 700-950kg/m3 boards accept decorative finishes.
    • Sprays protection is extensively used in the USA, can cover complex shape and details. Some can be used for external and hydrocarbon fire applications. The downside is not suitable for aesthetic purposes, and the application is a set trade which may impact on other site operations.
    • Flexible blanket systems are easily applied fire protection material that is a dry trade. There are limited manufacturers of these products.
  • Concrete encasement: Traditional type of fire protection to steel. Tend to be used where resistance to impact damage, abrasion and weather exposure is important. Much higher cost, thickness and weight.

Detail guidance on the installation of coatings, boards and spray protection systems is available for the Association for Specialist Fire Protection. Info on the thickness of concrete encasement for specific periods of fire resistance is published by BRE and EC2.