BS 5950 Part 5

 

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Fire Resistance of Steel Structures

Methods of Fire Protection

 

The capacity for a building to remain functional for a specified length of time during a fire is of  utmost importance for life safety and fire department access. However, all conventional construction materials begin to degrade when exposed to elevated temperatures for  prolonged periods of time. Therefore, it is often necessary to provide means of fire protection to the building’s structural elements in order for them to properly carry load during this important time period.   Building fire protection may be categorized into two main systems, active and passive. An obvious approach is to eliminate the heat source by extinguishing the fire or by generating an alert so that an extinguishing action can be initiated. Extinguishing systems such as sprinklers and smoke and heat detection devices are responses to this approach, and are classified as active fire protection systems. Active protection relies on devices requiring external activation to alert occupants of a fire and to control building fire conditions.  Automatic sprinkler systems, smoke detectors, and fire department department suppression are all examples of active systems. Alternatively, Alternatively, another approach for improving the fire safety of a steel structure is to delay the rate of temperature increase to the steel to provide time for  evacuation of the environment, to allow combustibles to be exhausted without structural consequence, and/or to increase the time for extinguishing the fire. This approach, which involves insulating the steel or providing a heat sink, is classified as a passive fire protection system. Passive protection provides fire protection by relying on in-place elements, and requires no external activation. Examples of passive protection include fire-rated ceilings, gypsum board or lath and plaster systems, spray-applied fire resistive materials (SFRM), and mastic coatings.   There are three generic types of fire protection for structural steel: cementitious products board and casing systems intumescent coatings Cementitious Products

 

Cementitious products based on gypsum or Portland cement binders are normally applied by low pressure spray techniques to the profile of the steel section to be protected. These materials contain low density aggregates and rheological aids to help the application characteristics. Fire protection is provided to the steel by these materials in two ways, the first being the ‘cooling effect’ as the trapped moisture (physically and chemically bound) evaporates as the temperature of the surrounding fire increases. Once all the moisture has turned to steam the product then behaves as a thermal insulation material. Low density mineral and synthetic aggregates are used in these products since they are efficient in allowing the steam to escape, while denser materials might impede its progress and cause the product to spall.   Board and casing systems

 

Board and casing systems use materials such as ceramic wool, mineral wool, fire resistant plasterboard, calcium silicate and vermiculite to provide fire protection to steel. These products provide fire protection in much the same way as the cementitious products and are dry fixed around the steel using clip, pin, noggin and screw systems.   https://www.nbmcw.com/tech-articles/peb-steel-structures/37224-fire-resistance-of-steel-structures.html

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6/2/2019

Fire Resistance of Steel Structures

  Intumescent coatings   Intumescent coatings derive their name from the Latin verb ‘tumescere’, which means to begin to swell. In a fire situation, these thin film products swell up to form a char which protects the steel, thanks to its insulating properties. Using various types of industrial coating equipment, these materials are applied as a thin film and are often available with a range of  topcoats in different colours so that the designer can achieve his or her aesthetic needs as well as those of fire protection on visible steel. Intumescent coatings are particularly effective for steel that requires up to 90 minutes’ fire protection.  

https://www.nbmcw.com/tech-articles/peb-steel-structures/37224-fire-resistance-of-steel-structures.html

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