Fire Protection Systems for Structural Steel Elements

Fire Protection Systems for Structural Steel Elements The Turkish Language Association defines the term fire as "a large flame causing damage" [1]. Fire is a chemical reaction that occurs when oxygen, a heat source, and fuel components come together. This chemical reaction produces heat, flame, gas and smoke in the environment and spreads in structures through convection, heat transmission and radiant transfer. Three basic measures are taken to protect buildings from fire. These are; 1. Detection systems (Smoke detection alarms, automatic doors, etc.), 2. Active fire suppression systems (Sprinklers, portable fire extinguishers, etc.), 3. Structural fire protection systems (Fire stops, intumescent paints, etc.). The systems mentioned above are complementary and must work integrated with each other. Detection systems serve life safety by informing building users during a fire through various electrical installations. Active fire suppression systems aim to extinguish the fire during a fire with the help of various mechanical installations. Finally, structural fire protection systems keep the building standing during a fire and prevent flame, toxic smoke and heat from spreading within the building. In fire safety, statistics from fires that have occurred in the past have always guided us. In particular, published fire reports allow detailed examination of those fires and lessons to be drawn from the incidents. Many regulations and standards worldwide have been developed with additions made following major fires. Maintaining and sharing fire statistics at regular intervals in Turkey would contribute to the development of the sector. Looking at general statistics worldwide, an average of 3.8 million fires occur annually and approximately 45,000 people die in these fires [2]. While 3/4 of fire deaths are caused by smoke [3], 57% of deaths occur not at the fire source compartment but in a different compartment [4]. These statistics show that the spread of flame, smoke and heat within a building causes fatal consequences. By ensuring the fire resistance of structural elements, these fatal consequences can be reduced. In this study, the design and application principles of fire protection paints used to protect structural steels, whose use is increasing in Turkey, from fire were examined.  

2. Protection of Steel Surfaces and Fire Resistance

With the increase in the use of structural steel in projects, it is important that these elements show structural resistance during fire, do not collapse and are protected from fire for a certain period. In buildings, the surfaces of steel elements are painted or coated for protection from corrosion, protection from chemical interaction, decorative and fire protection purposes. When specifying systems, these objectives should be considered. There are three fundamental methods used in fire protection of structural steel. These are; • Cement-Based Coating Systems: Application is relatively easy, but aesthetically unattractive, especially in commercial buildings such as shops, offices or stadiums. • Board Coating Systems: Used to encase beams or columns requiring fire protection. The advantages of this method are that it can be aesthetically pleasing, but it must be done on-site and can be quite time-consuming due to the complex woodwork required to work around difficult shapes. • Intumescent Paint Systems: Have the advantage of being installable both on-site and off-site, are relatively easy to apply and take less time, and can have a colored finish. Additionally, they leave the original steel work visible, which many find attractive, and provide additional space when needed for services. Among these systems, intumescent paint coatings have come to the fore in recent years. Paints referred to as structural steel fire protection paint are intumescent in nature. The concept of intumescence means expanding and increasing volume when exposed to heat and flame. The main advantages of intumescent coating paints compared to other systems are rapid application, lightweight and dust-free material, decorative appearance suitable for indoor and outdoor environments, odorless and low VOC content, application advantage on complex steel geometries and saving space with thin application thickness. [caption id="attachment_129384" align="aligncenter"] Figure 1. Example of cement-based coating system application[/caption] [caption id="attachment_129385" align="aligncenter"] Figure 2. Example of board coating system application[/caption] [caption id="attachment_129386" align="aligncenter"] Figure 3. Example of intumescent paint coating system application[/caption]

3. Regulations, Standards and Design Principles

In our country, the "Regulation on Fire Protection of Buildings" published in the Official Gazette in 2007 and updated in 2015 contains the rules and design principles that must be followed regarding fire prevention measures [5]. In Article 5 of the Regulation, the requirement is emphasized with the statement "If projects, in addition to legal regulations, do not comply with the conditions provided for in this regulation regarding fire safety, a building permit will not be issued". When examining the Turkey Regulation on Fire Protection of Buildings specifically for structural fire protection systems, we encounter the Second Part – General Fire Safety Provisions for Buildings, Second Section – Load-Bearing System Stability. Article 23, paragraph (4) in this section states "All steel structures that do not pose a danger of fire spread to the environment and whose combustible materials will not cause a temperature increase exceeding 540°C in steel elements during fire are considered fire-resistant. Except for single-story structures with an area of less than 5,000 m², other steel structures must be properly insulated from heat. Insulation can be done by coating with fire-resistant spray mortar, painting with fire-resistant paint, wrapping around with fire-resistant materials, boxing and mass insulation." [5] Test standards for structural fire protection systems are based on international norms and three fundamental test standards are used globally.

• (TS) EN 13381-8:2013: Test method for determination of the contribution to fire resistance of structural elements - Part 8: Reactive protection applied to steel elements,
• BS 476 Part 20/21: Fire tests on building materials and structures. Methods for determination of fire resistance of load-bearing elements of buildings,
• ANSI/UL 263: Fire safety tests standard for building construction materials.

In general, EN (European Norms) is used in European Union countries, BS (British Standards) is used in United Kingdom countries and ANSI/UL (American National Standards Institute / Underwriters Laboratories) is used in countries on the American continent to conduct fire resistance tests on structural steel elements. Additionally, in our country, the Turkish Standards Institute (TSE) has adopted the EN 13381-8 standard and published it as TS EN 13381-8. Although the conditions, procedures and phases of test standards differ from each other, all 3 standards have international validity and are tests conducted by independent organizations. In the table below you can find a general comparison table of the content of test standards. The results of fire resistance tests conducted according to the test standards mentioned above appear as performance tables in independent test report approvals. In the design phase, by evaluating these performance tables, the minimum paint thicknesses required to be applied for the structural steel element to provide the necessary fire resistance are determined.

Performance tables contain the following information;

• Fire resistance duration (60 minutes, 120 minutes, etc.), • Steel element type (Column, Beam, I-section, Rectangular section, etc.), • Steel section factor; calculated with the formula Hp/A = Heated perimeter / Cross-sectional area, • Critical design temperature; the critical temperature at which steel loses its strength, determined by the designer or standard values can be used, • Required paint dry film thickness; as the output of the table, specifies the minimum thickness at which the product to be applied must be applied to the structural steel. [caption id="attachment_129388" align="aligncenter"] Table 2. Example of performance table[/caption] In conclusion, structural fire protection systems keep the building standing during a fire and prevent flame, toxic smoke and heat from spreading within the building. With the global increase in the use of steel structures, fire resistance of structural steel elements emerges as an engineering problem requiring solutions. Intumescent coating paints offer a solution with advantages over cement-based coatings and board coatings used for this application. Considering our national fire protection regulation and international test standards and approvals, the fire resistance of structural steel must be taken into account in the design phase. In this study, a general evaluation was made on fire resistance of structural steel elements, but in future studies, field control of these applications, problems encountered during the application phase and suggested solutions should be examined in detail.

References [1]TURKISH LANGUAGE ASSOCIATION, General Turkish Dictionary [2]CTIF (International Association of Fire and Rescue Service), Report n. 21 - World Fire Statistics 2016. [3]HALL, JR. JOHN R., NFPA Fire Analysis & Research, Quincy, MA. "Burns, Toxic Gases and other Hazards" [4]NFPA Fire Protection Handbook, 18th Ed. [5]Turkey Regulation on Fire Protection of Buildings, 2015

  Tolga Aycı Business Development Manager Construction Products Group (CPG) Turkey