Telephone: 01420 471612 Site Map

Sign up to the ASFP mailing list. Enter Email address below:

  TYPES OF FIRE PROTECTION MATERIAL

 

 

FIRE PROTECTION - PASSIVE

Fire protection that carries out its function without requiring manual or automatic initiation of its operation in the event of fire

FIRE PROTECTION  - ACTIVE

Fire protection system which, in event of fire, can function only after its operation has been manually or automatically activated.

 

The methods used to protect steel are:

  • Fire resisting boards

  • Vermiculite cement sprays

  • Fibre sprays

  • Dry linings.

  • Mineral wool

  • Intumescent coatings

Let us consider each of these separately.

a.   FIRE RESISTING BOARDS.

These are fitted around the steel columns and beams to form a box and are usually secured by fixing "noggins" into the web of the steel with friction or adhesive and then securing the board to the noggin with screws.  They protect the steel by providing a heatproof insulation in some form and the mechanism of this varies with individual formulation of the board.  Correctly fitted boards must have noggins of the same size, placed at the same intervals, as the original test installation and should have the same number of screws and other fixings.

The boards can be made up of anything from gypsum-based plasters or calcium silicate, through fibres and specialist vermiculite containing materials.  Boards come in a wide variety of thicknesses and it is essential to ensure that the correct board thickness is chosen to give the required period of protection.

They are sometimes fixed with special, corkscrew like screws, which are used when boards are of a particularly soft pliable nature.  In modern systems some manufacturers have special spring clips to secure the bottom board, in other cases they rely on forming an almost self-supporting box.  In many cases the boards will require decoration if they are exposed to view.

Services can obviously be fitted behind these boards and it also follows that whenever these services have to be maintained the fire protection has to be removed to provide access to the services.  Afterwards the board system will need to be refitted in line with the official requirements.  Boards can be left untreated in not in public view, or can be decorated for aesthetic reasons.  Manufacturer developments will try to find alternative fixing methods and therefore careful note should be taken of  their instructions.

b.   VERMICULITE CEMENT SPRAYS.

These are probably the least expensive form of fire protection and can often be seen in places like multi-storey car parks and basement areas of buildings, where a very rough and thick coating has obviously been applied to the profile of the steel.  The material is supplied to the contractor as a dry powder made up of cement and exfoliated vermiculite.  The vermiculite contains air and protection is provided by a combination of water evaporation and insulation.

The material is mixed in a portable paddle mixer with water before application and the amount of water is critical to the application and fire performance of the coating.  It is then sprayed onto the surface using a screw feed pump usually manufactured by a company called Putzmeister.  Vermiculite sprays are widely used internally and also on petrochemical plants where special weatherproof grades are available.  In certain circumstances they require steel wire mesh support and weld pins to anchor the mesh.  A water-repellent coat is often applied to give protection against moisture.

Thickness varies from around 10/12 mm up to 50 mm and, as the material is highly alkali they require 3epoxy or other alkali resisting primers to be applied to the steel after blast cleaning.

This type of material can also be used for concrete protection, particularly common in France and certain other countries.  Tunnel lining can also be protected in this way.

c.   FIBRE SPRAYS.

These are very similar in nature to vermiculite sprays and everything I have said applies to these. The only difference is that this type of material uses mineral wool and insulates by providing a thick layer of heat resistant material onto the surface.

d.   DRY LINING SYSTEMS.

Essentially boarding as described above is dry lining but other ways of boxing in steelwork using heat resistant materials can also be undertaken. Examples are steel cladding systems, which are insulated with layers of mineral wool behind the steel cladding, and other types of boarding systems built to create a void around the steelwork.

Such systems are often pre-finished and particularly popular when the level of aesthetic finish is important.

e.   MINERAL WOOL

Cladding with mineral wool slabs or blankets which is used in ceiling voids or other areas not requiring an aesthetic finish is also common.  In many instances the mineral wool will have foil facing.  The material is fixed usually with adhesives sticking "noggins" into the web of the steel.  Once again it can easily be removed when surfaces are repaired and altered but will require refitting afterwards.  Weld pins can also be used for fixing with large washers or clips to secure the blanket.    It provides fire protection by wrapping a non-combustible layer of insulating material around the steelwork and thus slowing the rate of heat ingress into the steelwork because of the insulation.

f.   INTUMESCENT PAINT COATINGS.

These paints, or coatings, offer the most complex method of providing structural fire protection.  They work by changing their nature from a decorative paint, which has been applied to the steelwork, into an intumescent layer of carbonaceous char, which forms when the coating is subjected to heat.  This layer of char can be 50 times the thickness of the initial coat, and is formed as the paint is heated to around 200C and above.  At these higher temperatures the resin system melts and allows the release of a mineral acid, which reacts with a carbon rich element in the paint to form a carbon char.

Also released at the same time is a spumific, which provides a gas, which expands the foam to form the thicker layer. As the fire progresses and time passes this layer of char grows thicker thus increasing the insulation provided.  The outer surface of it finally becomes soft and friable rather in the same way as the charcoal on a barbecue turns into a dry white powder.

During this period energy is being absorbed by the reaction within the insulating layer being formed thus limiting the amount of heat which passes through the coating to the steel below.  The resin systems used to bind the chemicals together as paints vary and may use either a hydrocarbon solvent (usually xylene), or water as the dillulant of the resin.  These have become known in industry jargon as either 'water based' or 'solvent based' intumescents, which is not technically correct but understood.

The materials are applied at very widely varying film thicknesses from as little as 275 microns for 30-minute protection in some areas up to 6mm for 120-minute protection.  This thickness is required from the base coat, which is the active element of the system and may require application in many coats at the higher thicknesses.  They are most widely used for 30 minute and 60-minute work where one spray coat will provide the required dft.  A sealer coat is normally required and steel again should be blast cleaned and primed with a zinc phosphate primer in most cases.  Many primer types can be used according to manufacturers instructions.

There are also materials known as 'thick film intumescents', which are used mainly in the petrochemical industry.  They work in the same way but differ by using epoxy resin systems rather than the softer types used in thin film materials. The material expands at slower rate and to only 5 times the original.  The char formed is much tougher and the protection provided is capable of withstanding the high temperatures of hydrocarbon fires and jet fires.  These products are rarely used in the building industry but common for steel protection in the offshore and petrochemical industry.   They can be very successful on gas storage tanks and similar circumstances.

The use of both types of intumescent paints requires blast cleaning of the steel and suitable primers and topcoats.

Manufacturers literature will indicate any special requirements, but in general a zinc phosphate primer is used.  The primer can be alkyd based for thin film materials but must be epoxy based for the thick film types.  Primers containing metallic zinc must be thoroughly cleaned to remove any zinc salts and may not be suitable at all for water based materials.  In many cases such primers will require a sealer coat but this will be made clear in manufacturers instructions.