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Protecting Steel From Fire

The objective of fireproofing a structure is to:

  • Save lives and allow safe evacuation of personnel
  • Allow safe access for fire-fighters
  • Protect the building from structural failure

When exposed to fire, all commonly used structural materials lose some of their strength. Concrete cracks and spalls, timber depletes by charring and steel starts to lose its load bearing capacity. Steel loses about 75% of its strength at 600°C and critical temperatures are, therefore, generally accepted to be between 400°C and 600°C.

Girders, beams and other structural steel components need to be protected so as to limit the temperatures to a level where its load-bearing ability is not compromised. The human and economic costs of fire damage can be significantly reduced, if not eliminated, by the use of an appropriate protection system. Fire protection has three distinct phases: Detection, Extinguishing and Passive Fire Protection.

Required levels of protection are normally specified in terms of time, on the basis of a number of criteria. These may include statutory requirements as laid down in Building Regulations and Design Codes, design considerations and insurance implications.

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Passive Fire Protection Systems

Structural Steelwork can be protected either by the application of protective material to the substrate, or by enclosure in a protective system. The methods and materials used include boards or blankets of fibrous materials such as mineral wool and ceramic fibre, cementitious products such as concrete, gunite and other sprayed inorganic materials, composite fire resistant boards and intumescent coatings.

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Intumescent Coatings

Intumescent materials are thin film coatings that, when applied and cured on the steelwork, are typically less than 2mm in thickness.

Intumesence is a complex process in which, under heat of the fire, the solid coating is converted into a highly viscous liquid. Simultaneously, endothermic reactions take place that result in the release of inert gases with low thermal capacity. These gases are trapped inside the viscous fluid where cross-linking reactions take place between the polymer chains. The result is the expansion or foaming of the coating, to form a low density, carbonaceous or meringue-like char. This char will then solidify, having a depth of up to 50mm which restricts the build up of heat in the steel substrate, prolonging the structures load bearing capacity, and hence the stability of the structure.

Intumescent coatings have several advantages over the other forms of passive fire protection:

  • Relative ease of application and durability
  • Takes up very little space compared to other forms of passive fire protection
  • Weight of the fire protection is kept to a minimum, which in turn allows greater spans to be achieved. This is of key importance when designing large bay warehouses and sports stadia, for example
  • Off-site application enables time and cost savings to be made during construction, assisting with construction programmes
  • Ability to overcoat the intumescent layer with a decorative sealing coat
  • More ceiling void space for services
  • Advanced fire engineering allows reduction in intumescent thickness by structural analysis of the steel frame design
  • Easily repaired if damaged
  • If left damaged, the self healing nature of the intumescent char ensures only a minimum reduction in overall performance. This makes it the ideal choice for a whole life of building fire protection

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Benefits Of Off-Site Fire Protection

It is well known that most coatings are only as good as their application, and fireproofing materials are no exception. Those factors that contribute to the success of a protective coating application can be properly controlled when an off-site application is specified. Surface preparation, ambient conditions, operator skill and experience, equipment efficiency and consistency of thickness. All activities are controlled by quality assurance and control procedures. These factors all combine to ensure the maximum performance of the specified fireproofing application.

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Further benefits of off-site fire protection are:

Faster construction

  • Fire protection taken off critical path
  • Weather sensitivity reduced

Cost savings

  • Quick return on investment from faster construction
  • Reduced cost of prelims including scaffolding
  • Potential reduced cost of materials by fire engineering

An independent study shows the typical savings on a Multi-storey building outside London to be between £5 and £10 per m2, gross internal floor area. The savings relate to the overall construction height and time related preliminaries. A detailed report is available on request.

Reduction in site disruption

  • No need to seal off areas for spraying
  • Less labour on site
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Environmentally friendly

  • Elimination of overspray problems
  • Reduced solvent emissions at site
  • No airborne dust or fibres

Benefits to following trades

  • Service integration as soon as steel is erected
  • Follow-on trades start earlier

Improved safety on site

  • Fewer trades on site
  • No application in dangerous areas, e.g. edge beams

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Where To Apply Intumescent Coatings

Intumescent coatings are commonly used throughout steel frame structures in both on-site and off-site applications. The application of intumescent coatings off-site, prior to steel erection is now an accepted method of application due to its many benefits. It is particularly suited to high-rise steel framed structures in inner city locations.

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Intumescent coatings have been successfully used in:

  • Sports and Leisure Centres
  • Stadia
  • Swimming Pools
  • Industrial & Commercial Buildings
  • Multi-storey Retail
  • Office Blocks
  • Manufacturing Facilities
  • Multi-storey Industrial and Commercial
  • Cinemas
  • Airports
  • Hospitals
  • Universities

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Product Specifications

  • Leigh's Paint Firetex M782 Intumescent Coating
    A single pack thin film intumescent coating designed for shop application by airless spray, to provide fire resistance for up to 1,5 hours on structural steel.
  • Leigh's Paint Firetex M78 Intumescent Coating
    A single pack thin film intumescent coating designed for shop application by airless spray, to provide fire resistance for up to 2 hours on structural steel.
  • Leigh's Paint Firetex M95 Intumescent Coating
    An epoxy intumescent suitable for shop application. An exterior durable intumescent, which can be applied directly onto blast cleaned steel, to provide fire resistance for up to 2 hours on structural steel.
  • Leigh's Paint Firetex FB120 Intumescent Coating
    A single pack thin film intumescent coating designed for shop application by airless spray, to be used on Fabsec® products, to provide fire resistance for up to 2 hours on structural steel.

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