Option 1: Fire protection to the structural frame of the building and flame retardant coatings Flashcards
a) Describe how structural concrete behaves in fire. (2 marks)
b) Describe two methods by which additional fire protection may be applied to concrete.
(2 marks)
A
Generally, most concrete frames constructed within the built environment do not require additional
passive fire protection measures, as they are designed to achieve a specified fire resistance period.
In certain circumstances spalling of the concrete may be considered an issue (for example a road
tunnel), in which case additional passive fire protection measures may be required. Only products
intended and tested to provide the necessary protection for this type of application should be used.
Spalling is where entrapped moisture within concrete turns into steam and expands causing areas of concrete to break away. This can expose structural steel reinforcement to the effects of fire and further weakening the structure.
B
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.
One option for enhancing the fire resistance of timber is sacrificial timber. Name and describe
two other options. (6 marks)
Flame retardant treatments by impregnation or surface treatments. Impregnation takes place off site, surface treatments can be appled on or off site. Used to prevent heat release and surface spread of flame, delaying the time within a compartment for flashover to take place.
Encasement
Timber can be enclosed with fire-resistant materials such as gypsum boards, calcium silicate boards, or intumescent paints. These materials act as a barrier, delaying the exposure of timber to flames and heat. Intumescent paints, in particular, expand when exposed to fire, forming an insulating layer that protects the timber from burning.
a) Describe how steel is affected by heat in a building fire. (2 marks)
b) State the factors that affect the fire resistance of a steel frame. (3 marks)
A
Fires in buildings regularly exceed 1000°C within a relatively short period of time (30 – 60 minutes),
yet heavily loaded steel loses its design margin of safety, (about 40%) at temperatures around 550°C
regardless of the grade, and as its temperature rises further the loss ofstrength is rapid and significant.
B
Steel Section Size and Thickness – Larger and thicker steel sections take longer to heat up and lose strength compared to thinner sections, which reach critical temperatures more quickly.
Load and Stress Levels – Heavily loaded steel members fail more quickly in a fire as the loss of strength and stiffness occurs at lower temperatures.
Thermal Conductivity and Heat Transfer – Steel is a good conductor of heat, so unprotected members heat up rapidly. Surrounding materials like concrete or fire-resistant insulation can slow down heat transfer - temperature gradient
Name and describe three different types of fire protection boards. (6 marks)
- Gypsum-Based Fire Protection Boards
Made from gypsum (calcium sulfate dihydrate) with added fire-resistant materials like glass fibers and vermiculite.
Commonly used in walls, ceilings, and steel encasement to slow down heat transfer.
Can resist fire for up to 2 hours, depending on thickness and layering. - Cementitious Fire Protection Boards
Composed of cement, fibers, and fillers, making them highly durable and moisture-resistant.
Used for steel structures, walls, and ceilings, especially in high-risk areas like industrial buildings.
Offers excellent fire resistance (up to 4 hours) and can withstand harsh environments. - Calcium Silicate Fire Protection Boards
Made from calcium silicate, fibers, and fillers, providing superior fire resistance and thermal insulation.
Commonly used in fire doors, steel protection, and industrial settings where high fire resistance is required.
Can resist fire for up to 4 hours and is known for its high strength and low shrinkage when exposed to heat.
Describe how thick reactive (intumescent) paint coatings on steel sections perform in fire
conditions. (3 marks)
Thick film is mostly used in hydrocarbon risk fires as oposed to cellulosic in the built environment
Expansion and Char Formation
The coating expands up to 50 times its original thickness, forming a thick, stable, and insulating char.
This char slows down heat transfer to the steel, delaying its temperature rise.
This layer of char can be 50 times the thickness of the initial coat, and is formed as the paint and steel
substrate is heated to temperatures above 275°C.
At around 200°C the acid generator creates a mild acid, which combines with a blowing agent to form
a gas. The coating then swells to form an insulating ’char’.
In relation to materials used to enhance the structural resistance of steel, describe each of the
following methods of application:
a) Profile (2 marks)
b) Box (2 marks)
c) Solid (2 marks)
Profile - Sprayed reactive and non-reactive coat the perimeter/profile of the steel
Box - board systems (mechanically fixed) and non-reactive if lathing Mechanically fixed is used to fill gap between flanges outer edges
Solid - concrete and non-reactive web area is filled out to width of flange
