Fire Resistance of Steel Framed Buildings – Site Applied Protection Materials

Passive Fire Protection Materials

Passive fire protection materials insulate steel structures from the effects of the high temperatures that may be generated in fire. They can be divided into two types, non-reactive, of which the most common types are boards and sprays, and reactive, of which intumescent coatings are the best example.

Boards

Board systems are the most popular type of fire protection in the UK. They are widely used both where the protection system is in full view and where it is hidden.

The principal advantages are:-

  • Appearance - rigid boards offer a clean, boxed appearance which may be pre-finished or suitable for further decoration. The specifier should be aware however that cheaper board systems are available where appearance is not important.
  • Fixing - application is dry and may not have significant effects on other trades.
  • Quality assured - boards are factory manufactured thus thicknesses can be guaranteed.
  • Surface preparation - boards can be applied on unpainted steelwork.

The principal disadvantages are:-

  • Cost - a non-decorative board system can be relatively cheap however a decorative system can significantly increase costs.
  • Application - fitting around complex details may be difficult.
  • Speed - board systems may be slower to apply than some other methods.

Sprays

Spray protection systems have decreased in popularity in the past decade, despite being the cheapest in terms of application costs.

The principal advantages are:

  • Cost - spray protection can usually be applied for less than the cost of the cheapest board. Because the cost of sprayed material is low compared to that of getting labour and equipment on site, costs do not increase in proportion to fire resistance times.
  • Application - it is easy to cover complex details.
  • Durability - some materials may be used externally.
  • Surface preparation – some materials may be applied on unpainted steelwork.

The principal disadvantages are:

  • Appearance - sprays are not visually appealing and so are usually used only where they are not visible.
  • Overspraying - masking or shielding of the application area is usually required on-site.
  • Application - is a wet trade, this can have significant knock on effects on the construction program with the result that the real cost of spray protection may be significantly higher than that assumed using the application costs only.

Thin Film Intumescent Coatings

Intumescent coatings are paint like substances which are inert at low temperatures but which provide insulation by swelling to provide a charred layer of low conductivity materials at temperatures of approximately 200-250 °C. At these temperatures the properties of steel will not be affected.

The principal advantages are:

  • Aesthetics - the thin coating allows the shape of the underlying steel to be expressed.
  • Finish - attractive, decorative finishes are possible.
  • Application - complex details are easily covered.
  • Servicing - post-protection fixing is simplified.

The principal disadvantages are:

  • Cost - typical application costs are higher than sprays and generally comparable with board systems.
  • Application - is a wet trade which requires suitable atmosphere conditions during application and precautions against overspray.
  • Limited Fire Resistance Periods - most intumescent coatings can provide 30 and 60 minutes fire resistance. A limited number can be used for longer periods, i.e. 90 and 120 minutes, however the cost increases considerably for periods over 60 minutes.

Flexible/Blanket Systems

Flexible fire protection systems have been developed as a response to the need for a cheap alternative to sprays but without the adverse effects on the construction program often associated with wet application.

The principal advantages are:

  • Low Cost - blanket systems are comparable with cheap boards.
  • Fixing - application is dry and may not have significant effects on other trades.

The principal disadvantage is:

  • Appearance - unlikely to be used where the steel is visible.

Concrete Encasement and Other Traditional Systems

Until the late 1970’s concrete was by far the most common form of fire protection for structural steelwork. However the introduction of lightweight, proprietary systems such as boards, sprays and intumescents has seen a dramatic reduction in its use. At present concrete encasement has only a small percentage of the fire protection market with other traditional methods such as blockwork encasement also used occasionally.

The principal advantage of concrete and blockwork is:-

  • Durability - these robust encasement methods tend to be used where resistance to impact damage, abrasion and weather exposure are important e.g. warehouses, underground car parks and external structures.

The principal disadvantages are:-

  • Cost - concrete encasement is normally one of the most expensive forms of fire protection.
  • Speed - time consuming on-site.
  • Space Utilisation - large protection thicknesses take up valuable space around columns.
  • Weight - building weight can increase considerably.

Source: Corus         

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