Option 1: Fire protection to the structural frame of the building and flame retardant coatings Flashcards
a) Identify three factors that affect the fire resistance of concrete frames.
(3 marks)
b) State three methods by which additional fire protection may be applied to concrete.
(3 marks)
A
1 Thickness of concrete
2 The mixture and ratios of the concrete, cement and agregate types overall density
3 The load applied to the concrete
4 The amount of concrete cover over the enacased steel reinforcement.
B by adding insulation
Intumescent Coatings – These are specially designed fire-resistant paints that expand when exposed to heat, forming an insulating char layer that protects the concrete from high temperatures.
Fireproof Cladding or Board Systems – Fire-resistant boards, such as calcium silicate or gypsum-based panels, can be installed over concrete surfaces to enhance fire protection.
Fire-Resistant Sprays and Coatings – Cementitious or fibrous fireproofing sprays can be applied to concrete to improve its thermal resistance and prevent spalling under fire conditions.
a) Explain what is meant by “sacrificial timber” and explain how this improves the stability of
timber in fire.
(4 marks)
b) Describe the process of impregnation treatments and state the limitations with this type of
treatment.
(4 marks)
A
Sacrificial Timber refers to the outer layer of timber that deliberately chars in a fire, forming a protective insulating layer that slows down the burning rate and preserves the inner structural core. This phenomenon improves the stability of timber in fire through the following mechanisms:
Char Layer Formation – When exposed to fire, the outer surface of timber chars, forming a carbonized layer. This char is a poor conductor of heat and acts as an insulating barrier, reducing the rate at which heat penetrates deeper into the timber.
Slower Burning Rate – Timber burns at a predictable rate (typically 0.6–1.0 mm per minute for softwoods), meaning structural integrity can be maintained for a certain period. The sacrificial layer ensures the core remains intact for longer.
Retained Load-Bearing Capacity – Unlike materials like steel, which weaken significantly at high temperatures, the inner core of timber maintains much of its structural integrity even as the outer layer chars away, allowing the structure to stand for longer in a fire.
Self-Extinguishing Properties – Once oxygen supply is limited by the formation of the char layer, further combustion slows down, helping to reduce the spread of fire.
This concept is used in mass timber construction, such as cross-laminated timber (CLT), to ensure fire resistance and compliance with building regulations.
B
Timber is dried
Timber is treated in a vacum to remove air content
Timber is pressure treated in a vessel forcing the retardent deeper into the surface, a secondary process may be used to fixate the retardants.
Limitations are:
has to be done off site
further machining on site may remove the impregnations.
Cost
Protecting on site workers and disposal of waste timber
In relation to structural steel protection, describe the purpose, and application, of
cladding/encasement systems made from fire-resisting boards or stone wool products.
(4 marks)
Purpose:
Cladding or encasement systems protect structural steel from fire by insulating it and preventing it from reaching critical failure temperatures (typically around 550°C). Since steel loses strength rapidly when exposed to high temperatures, these systems help maintain the integrity and load-bearing capacity of the structure during a fire.
Application:
Fire-Resisting Boards:
Made from materials such as gypsum, calcium silicate, or cement-based boards.
Mechanically fixed around steel columns and beams to form a protective barrier.
Provides passive fire protection by insulating steel and slowing heat transfer.
Stone Wool Products:
Consist of high-density mineral wool panels designed for fire insulation.
Wrapped or mechanically fixed around structural steel elements.
Offer high thermal resistance and maintain integrity even under prolonged fire exposure.
In relation to materials used to enhance the structural resistance of steel, one method of
application is “box”. Name and describe the other two methods of application.
(6 marks)
- Profile – by directly following the shape of the structural element by applications directly to
the perimeter surface. This method can be used in the application of spray applied reactive and non reactive coatings. - Box – by application to a pre-installed metal lathing for non reactive coatings. Boards can be fixed in this configuration also
- Solid – by applying directly to the surface of the structural element but filling in any of the
web area, for example, with concrete.
Describe the stages and checks to be followed when applying intumescent coatings for fire
protection of structural steelwork.
(6 marks)
- Surface preparation is completed as specified by the manufacturer.
- Surface is free of dust or other contamination.
- Air temperature, substrate temperature, relative humidity and dew point (throughout the
application process) are as specified or as manufacturer’s data sheet. - There is compliance with recommended over-coating times from manufacturer’s data
sheets. - Wet film thickness checks are carried out.
- Thicknesses at each stage should be in accordance with the specification.
- Visual appearance to ensure this is as specified or in accordance with agreed standard.
