Fig.1: Fire Protection Systems for Steel Structure
What are Common Fire Protection Systems for Steel Structures?
Following are different fire protection systems generally used for steel structures:- Boards and blanket fire protection system
- Intumescent coating steel structure fire protection system
- Sprayed cementitious or gypsum based coatings
Boards and Blanket Fire Protection System
This type of fire protection system as shown in Figure-2 is widely used due to several reasons such as, it is clean, cost effective, water resistant and can be applied to non-painted steel members.
Fig.2: Boarded Fire Protection System Used for Structural Steel
Moreover, not only it is strong and durable but also compatible with decorative finishes. Boarded fire protection system is suitable for steel columns and beams with regular shapes. The thickness of the board is dependent on the material type used for board production and specified fire rating needed. Boards can be produced from different types of materials like calcium silicate, gypsum plaster or mineral fiberboard with resin or gypsum, and may contain lightweight fillers including vermiculite. Furthermore, boarded fire protection system is divided into main types namely: heavy weight and lightweight boards. The former is appropriate for the case where aesthetic view is major concern because it is in harmony with aesthetic finishes. However, the lightweight board is suitable for the case where aesthetic appearance is not important since it is not compatible with decorative finishes. Board fire protection system is capable of resisting fire for maximum four hours. As far as blanket protection system is concerned, it is applied for a steel element that cannot be protected by board fire protection system due to irregularity in theirs shapes such as truss members.
Fig.3: Installation of Boarded Fire Protection System
Intumescent Coating Steel Structure Fire Protection System
Intumescent coating is similar to painting material that is inactive at ambient temperature but it would activate at a high temperature ranges from 200 to 250C. When intumescent painting activates, it undergoes complex chemical reactions and swell dramatically as shown in Figure-4.
Fig.4: Intumescent coating system before exposed to fire (left side), expansion of fire protection system after the steel element exposed to fire
The thickness of swollen intumescent coating could reach up to fifty times its original thickness. This increased thickness would provide fire protection and fire-resistant ratings is up to 2 hours. It should be bore in mind that steel properties at this temperature would not undergo any changes, so the fire protection system protects steel structure satisfactorily. The advantages of intumescent fire protection system are easy to apply, durable, cover complex shapes and design details easily, applied to steel element surface quickly and can be repaired and maintained easily. However, disadvantages include high cost, maintenance of good quality coating needs great attention and effort and it could be damaged if it applied offsite. This type of protection system can be applied both at construction site and off construction site. The latter is commonly considered if aesthetic appearance is not a major concern whereas the former is used to obtain aesthetic views.
Fig.5: Intumescent Application Offsite
Fig.6: Application of Intumescent Pain at Construction Site
It is considerably suitable for irregular and complex fabrications such as cellular steel beams and girders. The thickness of intumescent coating is based on the size of steel structure elements and it varies from 0.5mm to 5mm. Finally, if secondary casing is applied to the surface of steel elements, it should not prevent the expansion of intumescent coating during fire.
Fig.7: Intumescent Coating Applied for Both Regular and Cellular Steel Beams
Sprayed Cementitious or Gypsum Based Coatings
Cement based material or gypsum in combination with lightweight aggregate are materials used to produce sprayed compendious or gypsum based coatings. The cost of this fire protection system is considerably low and provides perfect fire protection rating of up to 4 hours. Added to that, not only it is reliable and efficient but also it can be applied quickly and is suitable for complex steel members and details of the structure such as bolts and connections. However, it does not have sufficient strength to withstand mechanical damages. The spray application process is wet and messy which might influence the schedule of the project and its cost. Finally, the surface of steel structure should be prepared prior to spray applications, and great effort would be needed to achieve aesthetically pleasing finishes.
Fig.8: Sprayed Cementitious Fire Protection System
Fig.9: Application of Spray Cementitious Fire Protection System
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