Fire

Below is an introduction to the topic Fire. You can also search for your specific topic using the Search box at the top of the page or click on any of the following keywords and phrases: Passive fire protetcion; Cementitious spray; Boarded systemsIntumescent coatings; Fire safety engineering.

Passive fire protection systems

Every form of fire protection has advantages and disadvantages. An excellent list of the pros and cons was published in Specifier magazine by Peter Fordham of Davis Landgon:

Cementitious Spray

Sprays are either mineral fibre/cement or vermiculite. The advantages are that it is relatively cheap. It can be applied to complex shapes. It assists thermal and acoustic insulation. And it provides up to four hours fire protection. Recent explosion tests, prompted by events at the World Trade Centre in 2001, have demonstrated that some modern materials have excellent stickability and can survive extreme events without significantly impairing function.

The disadvantages are that it is only likely to be suitable for non-aesthetic protection. Surrounding areas may require masking and/or sealing off – this is likely to be a particular issue in congested sites and/or tall buildings. And it is difficult to ensure uniform thickness; bonding agent may be required.

Boarded Solutions

Boarded fire protection solutions are promoted as a clean, dry process that can provide a neat finish with the required functional fire protection in one. They are generally impractical for protection to beams where holes are used for services penetrations. Boards are available in discrete thicknesses and one usually finds that the minimum board thickness provides 30 and 60 minutes fire resistance over the common section range.

Intumescent Coatings

These products consist of a thin-film coating – generally less than 1mm for most open sections for 60 minutes fire resistance but up to 6mm on hollow sections to provide higher periods of fire resistance. Intumescent coatings expand to typically 40-50 times their original film thickness, producing an insulating carbonaceous char that reduces the rate of temperature increase of the steel. In exposed situations or situations where aesthetics are important, a separate decorative sealer is applied over the intumescent basecoat that also provides moisture and abrasion resistance.

The cost of intumescent coatings has reduced in recent years as a result of improved technology and increased competition and they have made considerable inroads into the general market for fire protection to structural steelwork. They are no longer seen as a solution for decorative purposes only. Intumescent coatings can now provide protection to structural steelwork for up to 90 minutes at competitive cost. Some solvent-based coatings can provide up to 120 minutes fire resistance for a limited range of sections.

Fire resistance without passive fire protection

One of the most effective ways to fire protect a steel framed building is to design the resistance into the building without using additional protection. There are numerous ways of doing this; the best known of which is probably the Corus Slimdek system which will achieve 60 minutes fire resistance without protection. It is possible to design a building for 60 minutes fire resistance without added protection.

The idea of designing fire resistance into a building without protection has been taken a step further with the recent publication of design guidance drawn from experience of large scale testing. This guidance, inspired by the experience of tests in which unprotected beams reached temperatures of 1100ºC, allows the engineer and architect to leave much of the secondary steelwork unprotected. Some compensatory features may be necessary to strengthen the floor, for example the use of added reinforcement.

Fire safety engineering

Increasing innovation in design, construction and usage of modern buildings has created a situation where it is sometimes difficult to satisfy the functional requirements of the Building Regulations by use of the provisions outlined in publications such as Approved Document B. Recognition of this, and also increased knowledge of how real structures behave in fire, has led most authorities to acknowledge that improvements in fire safety may now be possible in many instances by adopting analytical approaches. This usually means adopting a fire safety engineering approach.

Fire safety engineering can be seen as an integrated package of measures designed to achieve the maximum benefit from the available methods for preventing, controlling or limiting the consequences of fire. It can bring real value to building design by reducing the cost burden of fire precautions. It will not do so in all buildings but its use is widespread in large, complex and multi-use buildings.

Guidance on all issues relating to structural steelwork in fire is provided free by the steel construction industry (Fire Resistance of Steel Framed Buildings, available from Corus Publications).