Fire protection to the structural frame of the building and fire retardant coatings

Question 1

Describe the insulating materials that can be used to protect structural timber and state the
factors that affect the required thickness of the protective layer.
(4 marks)

Answer 1

structural elements, including mechanical fasteners, can be insulated from
heat by covering them with one or more layers of fire resisting insulating material, for example gypsum
plasterboard or a calcium silicate board, of a specified thickness.
The thickness of the fire protective layer will be governed by the density and makeup of the structural
element, e.g. solid timber, glulam, Laminated Veneer Lumber (LVL) etc

Question 2

a) Explain why the thickness of a steel structure needs to be considered when planning
for appropriate fire resistance.
(2 marks)
b) State and explain the “section factor” formula used when determining the length of fire
resistance.
(3 marks)

Answer 2

The thicker and heavier a steel section becomes the longer it will take to heat up, therefore the
amount of structural fire protection required to control the steel temperature to below the critical
level will be less than would be required for a thin lightweight section.

In relation to steel frame construction, the thickness of the structural fire protection, and the steel
configuration to which it will be installed, will determine the length of fire resistance period achieved
and will be calculated based on the size and weight of the steel section using a formula known as the
‘Section Factor’ (A/V) where:
* A = Surface area of steel exposed to the fire per unit of length
* V = Volume of the section per unit length
In the past A/V has also been described as Hp/A (heated perimeter of the exposed cross section
divided by the total cross-sectional area).

Question 3

Explain the difference between box, profile and solid application of fire protection to steel.
(6 marks)

Answer 3

• Profile – by directly following the shape of the structural element by applications directly to
  the perimeter surface
• Box – by application to a pre-installed metal lathing
• Solid – by applying directly to the surface of the structural element but filling in any of the
  web area

Question 4

a) State three advantages of applying intumescent coatings off-site.
(3 marks)

b) State two challenges that can arise when intumescent coatings are applied off-site.
(2 marks)

Answer 4

a) Three advantages of applying intumescent coatings off-site:

Controlled Environment: Application in a factory ensures consistent quality due to controlled temperature, humidity, and cleanliness.

Faster On-Site Installation: Coated steel can be delivered ready-to-install, reducing on-site work time.

Reduced Weather Dependency: Avoids delays due to unsuitable weather conditions at the construction site.

b) Two challenges of applying intumescent coatings off-site:

Damage During Transport/Handling: Coated steel can be chipped or scratched during delivery, requiring repair with the same materials

Limited Flexibility for Site Modifications: If design changes occur on-site, coated elements may not align or require recoating.

Question 5

Describe the process of impregnation treatments used for timber and wood-derived building
materials and state two limitations with this type of treatment.
(4 marks)

Answer 5

Dipping timber in treatment solutions alone will not impregnate sufficiently to upgrade timber to
either Class 1 surface spread of flame or to Class 0. Such performance can only be achieved via an
industrial process involving vacuum and pressure conditions to force the flame-retardant solution into
the timber or timber-based derivative.

given that timber impregnated with the
flame-retardant chemicals normally forms an envelope around an untreated zone, it is important
wherever possible that timbers should be machined to approximately their final dimensions before
the treatment is carried out.
It is therefore advisable to restrict machining operations to a minimum, as over machining may negate
the effect of treatment should all, or most, of the treated material be removed.
In addition, precautions may need to be taken to protect operators, and in the disposal of wood-waste
containing such treatment, therefore the manufacturers guidance should always be consulted before
any work is undertaken